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The urgent need to mitigate and adapt to climate change necessitates a comprehensive understanding of carbon cycling dynamics. Traditionally, global carbon cycle models have focused on vegetation, but recent research suggests that animals can play a significant role in carbon dynamics under some circumstances, potentially enhancing the effectiveness of nature-based solutions to mitigate climate change. However, links between animals, plants, and carbon remain unclear. We explored the complex interactions between defaunation and ecosystem carbon in Earth's most biodiverse and carbon-rich biome, tropical rainforests. Defaunation can change patterns of seed dispersal, granivory, and herbivory in ways that alter tree species composition and, therefore, forest carbon above- and belowground. Most studies we reviewed show that defaunation reduces carbon storage 0-26% in the Neo- and Afrotropics, primarily via population declines in large-seeded, animal-dispersed trees. However, Asian forests are not predicted to experience changes because their high-carbon trees are wind dispersed. Extrapolating these local effects to entire ecosystems implies losses of ∼1.6 Pg CO 2 equivalent across the Brazilian Atlantic Forest and 4-9.2 Pg across the Amazon over 100 years and of ∼14.7-26.3 Pg across the Congo basin over 250 years. In addition to being hard to quantify with precision, the effects of defaunation on ecosystem carbon are highly context dependent; outcomes varied based on the balance between antagonist and mutualist species interactions, abiotic conditions, human pressure, and numerous other factors. A combination of experiments, large-scale comparative studies, and mechanistic models could help disentangle the effects of defaunation from other anthropogenic forces in the face of the incredible complexity of tropical forest systems. Overall, our synthesis emphasizes the importance of-and inconsistent results when-integrating animal dynamics into carbon cycle models, which is crucial for developing climate change mitigation strategies and effective policies., (© 2024 Society for Conservation Biology.)

Understanding the role of climate in the assembly of rainforest tree communities is informative for predicting how future climates will impact species and communities. We surveyed rainforest tree communities across the Australian subtropics (spanning 600 to 2500 mm rainfall year -1 ) and measured functional traits on 285 (91%) of all recorded species. We used principal component analysis to create axes approximating species' hydraulic strategies, leaf economics and stature and included these as predictors in joint species distribution models, along with traits describing dispersal ability and leaf phenology. Hydraulic strategy and leaf phenology strongly modulated species' occurrence trends along the moisture availability gradient, while stature and leaf economics modulated species' responses to minimum temperature and soil variables, respectively. Overall, we quantify the occurrence trends of almost half of Australia's subtropical rainforest tree species based on their functional traits, providing a general foundation for prediction under ongoing climate change., (© 2024 John Wiley & Sons Ltd.)

Understanding the long-term impact of projected climate change on tropical rainforests is critical given their central role in the Earth's system. Palaeoecological records can provide a valuable perspective on this problem. Here, we examine the effects of past climatic changes on the dominant forest type of Southeast Asia - lowland dipterocarp forest. We use a range of proxies extracted from a 1400-yr-old lacustrine sedimentary sequence from north-eastern Philippines to determine long-term vegetation responses of lowland dipterocarp forest, including its dominant tree group dipterocarps, to changes in precipitation, fire and nutrient availability over time. Our results show a positive relationship between dipterocarp pollen accumulation rates (PARs) and leaf wax hydrogen isotope values, which suggests a negative effect of drier conditions on dipterocarp abundance. Furthermore, we find a positive relationship between dipterocarp PARs and the proxy for phosphorus availability, which suggests phosphorus controls the productivity of these keystone trees on longer time scales. Other pollen taxa show widely varying relationships with the abiotic factors, demonstrating a high diversity of plant functional responses. Our findings provide novel insights into lowland dipterocarp forest responses to changing climatic conditions in the past and highlight potential impacts of future climate change on this globally important ecosystem., (© 2023 The Authors New Phytologist © 2023 New Phytologist Foundation.)

1. Patterns of water availability are frequently implicated in local and regional tree species distributions. A major floristic and climatic transition from aseasonal to seasonal evergreen tropical forest is the Kangar–Pattani Line (KPL) in the Indo-Sundaic region of Southeast Asia. We hypothesize that differences in species’ drought tolerance will correspond with their distribution with respect to the KPL. Using a common garden study, we assess the role of differences in physiological drought tolerance traits to geographic distributions for 24 tropical tree species in relation to rainfall seasonality. 2. Inherent differences in desiccation tolerance of seedlings were quantified as water potentials and relative water contents (RWCs) below which the plant could no longer support living tissue, and plant water relation parameters were measured using pressure–volume analysis. The relationships among these traits were examined using bivariate trait relationships and a principal components analysis (PCA). The physiological traits contributing most to lethal water potential and RWC were assessed using multiple regression analysis. 3. Distribution-related differences in all desiccation tolerance and pressure–volume traits were detected both with and without phylogenetic correction. Widespread species that occurred in seasonally dry forests were able to maintain living tissue at more negative water potentials and lower RWCs than were species restricted to aseasonal forests. Likewise, widespread species demonstrated more negative water potentials at turgor loss, more negative saturated osmotic potential, lower symplastic water fraction and higher bulk modulus of elasticity values. Turgor loss point (TLP) and bulk modulus of elasticity were the best predictors of lethal water potential while symplastic water fraction and bulk modulus of elasticity were included as predictors of lethal RWC. 4. Inherent differences in physiological traits contributing to drought tolerance are associated with differences in tropical tree species distributions in relation to rainfall seasonality. These results, combined with lack of support for hypothesized historical factors, strongly implicate climate as a determinant of tree species distributions around the KPL. [ABSTRACT FROM AUTHOR]

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Introduction: Global climate change and associated stressors threaten forest ecosystems due to the rapid pace of climate change, which could exceed the natural migration rate of some tree species. In response, there is growing interest to research and implement forest assisted migration (FAM). Here, we used a species-independent indicator based on climate analogy, according to the sigma (dis)similarity (σd) index, to match planting sites across the eastern US with (future) climatically-compatible seedlots (CCS). Methods: We developed CCS for a grid composed of 1 × 1° of latitude and longitude. CCS were based on future climate analogs with ≤2σd analogy to ensure CCS were representative of future climate change. CCS were located for three time periods, 2030's, 2050's, and 2090's and three emissions scenarios (SSP2-4.5, SSP3-7.0, and SSP5-8.5) from the Coupled Model Intercomparison Project phase 6 database, using 12 climate variables. Results: CCS were identified for the majority of 1 × 1° grids based on the SSP3-7.0 scenario. Approximately 28% of 1 × 1° grid's 2090's projections included future climate novelty. The 2030's, 2050's, and 2090's CCS were located on average 222, 358, and 662 km or 1, 2, and 3 eastern seed zones away from the 1 × 1° grids, respectively. CCS were also located further south-southwest (188–197°). In addition, the average forest cover of CCS was approximately 2%, 5%, and 10% less than that of the 1 × 1° grids. Discussion: Our development and synthesis of CCS emphasized four key results: (i) average distances to 2030's and 2050's CCS were similar to seed-transfer guidelines for some tree species, but 2090's CCS exceeded current recommendations; (ii) south-southwesterly locations of CCS aligned with tree species habitat distribution dynamics; (iii) future climate novelty potentially challenges the conceptual basis of FAM if tree species are not adapted to climate change; and (iv) variation in forest cover among CCS presents potential opportunities and challenges due the presence or absence of forestland to source seed. Ultimately, our goal was to locate and synthesize CCS that could enable FAM decision support. [ABSTRACT FROM AUTHOR]

Permafrost thawing as a result of climate change has major consequences locally and globally, both for the biosphere and for human activities. The quantification of its extent and dynamics under different climate scenarios is needed to design local adaptation and mitigation measures and to better understand permafrost climate feedbacks. To this end, numerical simulation can be used to explore the response of soil thermal and hydrological regimes to changes in climatic conditions. Mechanistic approaches minimise modelling assumptions by relying on the numerical resolution of continuum mechanics equations, but they involve significant computational effort. In this work, the permaFoam solver is used, along with high-performance computing resources, to assess the impact of four climate scenarios of the Coupled Model Intercomparison Project Phase 6 (CMIP6) on permafrost dynamics within a pristine, forest-dominated watershed in the continuous-permafrost zone. Using these century-timescale simulations, changes in the soil temperature, soil moisture, active layer thickness, and water fluxes are quantified, assuming no change in the vegetation cover. The most severe scenario (SSP5-8.5) suggests a dramatic increase in both the active layer thickness and annual evapotranspiration, with the maximum values on the watershed increasing by, respectively, +65 % and +35 % by 2100 compared to current conditions. For the active layer thickness, a variable that integrates both the thermal and hydrological states of the near-surface permafrost, this projected increase would correspond to a ∼350 km southward shift in current climatic conditions. Moreover, in this scenario, the thermal equilibrium of near-surface permafrost with the new climatic conditions would not be reached in 2100, suggesting a further thawing of permafrost even in the case in which climate change is halted. [ABSTRACT FROM AUTHOR]

Permafrost ecosystems in high‐latitudes stock a large amount of carbon and are vulnerable to wildfires under climate warming. However, major knowledge gap remains in the effects of direct carbon loss from increasing wildfire biomass burning on permafrost ecosystem carbon sink. In this study, we used observation‐derived data sets and Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations to investigate how carbon emissions from wildfire biomass burning offset permafrost ecosystem carbon sink under climate warming in the 21st century. We show that the fraction of permafrost ecosystem carbon sink offset by wildfire emissions was 14%–25% during the past two decades. The fraction is projected to be 28%–45% at the end of this century under different warming scenarios. The weakening carbon sink is caused by greater increase in wildfire emissions than net ecosystem production in permafrost regions under climate warming. The increased fraction of ecosystem carbon sink offset by wildfire carbon loss is especially pronounced in continuous permafrost region during the past two decades. Although uncertainties exist in simulations of wildfire emissions and ecosystem carbon budget, results from different models still show that wildfire emissions offset more permafrost ecosystem carbon sink in the 21st century. These findings highlight that carbon sink capacity of permafrost ecosystems is increasingly threatened by wildfires under the warming climate. Plain Language Summary: Permafrost ecosystems have been important carbon sink in Northern Hemisphere high‐latitudes. However, some regions may shift from carbon sink to source under climate warming, as the abundant carbon stored in permafrost regions are vulnerable to wildfires. Wildfire carbon emissions further enhance the global warming, and may trigger a tipping point through the positive permafrost carbon‐climate feedback. However, how wildfires affect permafrost ecosystem sink through direct carbon loss from increasing wildfire biomass burning is not clear. Our results show that wildfire emissions are expected to further weaken ecosystem carbon sink in permafrost regions during the 21st century due to a faster increase of wildfire emissions than net ecosystem production. The increased offset of wildfire emissions to ecosystem carbon sink has been observed in continuous permafrost regions during the past two decades. Although the simulations of wildfire emissions and ecosystem carbon budget are uncertain, different models still showed that wildfire emissions offset more permafrost ecosystem carbon sink in the 21st century. These results highlight that the growing wildfire emissions under warming are expected to further increase vulnerability of permafrost carbon stock, accelerate the permafrost carbon and climate feedback, weaken permafrost ecosystem carbon sink, and potentially alter the trajectory of global climate change. Key Points: Wildfire emissions are expected to further weaken ecosystem carbon sink in permafrost regions by the end of 21st centuryIncreased fraction of ecosystem carbon sink offset by wildfire has been observed in continuous permafrost in the past two decadesThe weakening carbon sink is caused by greater increase in wildfire emissions than net ecosystem production under climate warming [ABSTRACT FROM AUTHOR]

More frequent and widespread large fires are occurring in the western United States (US), yet reliable methods for predicting these fires, particularly with extended lead times and a high spatial resolution, remain challenging. In this study, we proposed an interpretable and accurate hybrid machine learning (ML) model, that explicitly represented the controls of fuel flammability, fuel availability, and human suppression effects on fires. The model demonstrated notable accuracy with a F1‐score of 0.846 ± 0.012, surpassing process‐driven fire danger indices and four commonly used ML models by up to 40% and 9%, respectively. More importantly, the ML model showed remarkably higher interpretability relative to other ML models. Specifically, by demystifying the "black box" of each ML model using the explainable AI techniques, we identified substantial structural differences across ML fire models, even among those with similar accuracy. The relationships between fires and their drivers, identified by our model, were aligned closer with established fire physical principles. The ML structural discrepancy led to diverse fire predictions and our model predictions exhibited greater consistency with actual fire occurrence. With the highly interpretable and accurate model, we revealed the strong compound effects from multiple climate variables related to evaporative demand, energy release component, temperature, and wind speed, on the dynamics of large fires and megafires in the western US. Our findings highlight the importance of assessing the structural integrity of models in addition to their accuracy. They also underscore the critical need to address the rise in compound climate extremes linked to large wildfires. Plain Language Summary: Anthropogenic climate change has caused more frequent and widespread large fires in the western United States (US). Interpretable and accurate methods that can predict large fires in advance and at a high spatial resolution are essential for more targeted fire risk mitigation strategies, but the trade‐off between accuracy and interpretability persists in current fire models. For example, machine learning (ML) fire models can be more accurate than process models but operate as "black‐boxes" with a poor understanding of fire physics. Process fire models are more physically interpretable but remain less accurate than ML models. This research offers a novel perspective on the tradeoff and quantification of model physical interpretability and accuracy for wildfire predictions in the western US. More importantly, this study proposes a more interpretable and accurate ML fire model that explicitly incorporates fire knowledge while leveraging data‐informed modeling advantages. The model predicted fire risk showed high consistency with actually occurred fire events, and revealed strong and multivariate climate controls on large fires and megafires in the western US. Our proposed fire model enables better predictions and understanding of large fires and megafires in the western US. Key Points: Substantial structural differences were identified across machine learning (ML) fire models, but existing studies mainly focus on accuracyWe proposed a fire model with higher accuracy and physical interpretability compared to commonly used ML modelsOur fire model reasonably reflected actual fire risk and revealed complex climate controls on large fires and megafires in the western US [ABSTRACT FROM AUTHOR]

Nature-based solutions (NBS), in the form of active ecosystem conservation, restoration and improved land management, represent a pathway to accelerate net-zero emissions (NZE) strategies and support biodiversity. Meaningful implementation and successful accounting depend on the ability to differentiate between anthropogenic and natural carbon fluxes on land. The United Nations Framework Convention on Climate Change (UNFCCC) land carbon accounting methods currently incorporate all CO2 fluxes on managed land in country inventories without distinguishing between anthropogenic and natural components. Meanwhile, natural land carbon sinks are modelled by earth system models but are mostly reported at global level. Here we present a simple yet novel methodology to estimate the present and future progression of natural land sinks at the country and regional level. Forests dominate the uptake of CO2 on land and as such, our analysis is based on allocating global projections of the natural land carbon flux to individual countries using a compilation of forest land areas for a historic and scenario range spanning 1960-2100. Specifically, we use MIT's carbon cycle model simulations that are set in the context of emissions pathways from the Shell Energy Security Scenarios (2023). Our natural land carbon flux estimates for individual countries and regions such as the European Union (EU) show generally good agreement with independent estimates from recent land-use harmonisation studies for 2000-2020. Hence, our approach may also provide a simple, first-order exploration of future natural land fluxes at country level--a potential that other studies do not yet offer. In turn, this enables better understanding of the anthropogenic and natural components contributing to country NZE targets under different scenarios. Nevertheless, our findings also suggest that models such as the Shell World Energy Model (WEM) would benefit from further improvements in the apportionment of land carbon sources and sinks to evaluate detailed actions to meet country targets. More importantly, uncertainties remain regarding the resilience of land ecosystems and their capacity to store increasing amounts of carbon under progressive global warming. Therefore, we recommend that the carbon cycle modelling and energy modelling research communities continue to collaborate to develop a next generation of relevant data products to distinguish anthropogenic from natural impacts at local, regional and national levels. [ABSTRACT FROM AUTHOR]

Climate change contributes to the increased frequency and intensity of wildfires globally, with significant impacts on society and the environment. However, our understanding of the global distribution of extreme fires remains skewed, primarily influenced by media coverage and regionalised research efforts. This inaugural State of Wildfires report systematically analyses fire activity worldwide, identifying extreme events from the March 2023–February 2024 fire season. We assess the causes, predictability, and attribution of these events to climate change and land use and forecast future risks under different climate scenarios. During the 2023–2024 fire season, 3.9×106 km 2 burned globally, slightly below the average of previous seasons, but fire carbon (C) emissions were 16 % above average, totalling 2.4 Pg C. Global fire C emissions were increased by record emissions in Canadian boreal forests (over 9 times the average) and reduced by low emissions from African savannahs. Notable events included record-breaking fire extent and emissions in Canada, the largest recorded wildfire in the European Union (Greece), drought-driven fires in western Amazonia and northern parts of South America, and deadly fires in Hawaii (100 deaths) and Chile (131 deaths). Over 232 000 people were evacuated in Canada alone, highlighting the severity of human impact. Our analyses revealed that multiple drivers were needed to cause areas of extreme fire activity. In Canada and Greece, a combination of high fire weather and an abundance of dry fuels increased the probability of fires, whereas burned area anomalies were weaker in regions with lower fuel loads and higher direct suppression, particularly in Canada. Fire weather prediction in Canada showed a mild anomalous signal 1 to 2 months in advance, whereas events in Greece and Amazonia had shorter predictability horizons. Attribution analyses indicated that modelled anomalies in burned area were up to 40 %, 18 %, and 50 % higher due to climate change in Canada, Greece, and western Amazonia during the 2023–2024 fire season, respectively. Meanwhile, the probability of extreme fire seasons of these magnitudes has increased significantly due to anthropogenic climate change, with a 2.9–3.6-fold increase in likelihood of high fire weather in Canada and a 20.0–28.5-fold increase in Amazonia. By the end of the century, events of similar magnitude to 2023 in Canada are projected to occur 6.3–10.8 times more frequently under a medium–high emission scenario (SSP370). This report represents our first annual effort to catalogue extreme wildfire events, explain their occurrence, and predict future risks. By consolidating state-of-the-art wildfire science and delivering key insights relevant to policymakers, disaster management services, firefighting agencies, and land managers, we aim to enhance society's resilience to wildfires and promote advances in preparedness, mitigation, and adaptation. New datasets presented in this work are available from 10.5281/zenodo.11400539 (Jones et al., 2024) and 10.5281/zenodo.11420742 (Kelley et al., 2024a). [ABSTRACT FROM AUTHOR]

Vegetation distribution and composition are expected to change in northern high latitudes under rapid warming, which regulates ecosystem functions but remains challenging to predict. Vegetation change arises from the interplay of chronic climate trends such as warming and transient demographic processes of recruitment, growth, competition, and mortality. Most predictive models overlooked the role of demographic dynamics controlled by plant traits. Here, we simulate vegetation dynamics at the Kougarok Hillslope site in Alaska under historical and future climates using the E3SM Land Model coupled to the Functionally Assembled Terrestrial Simulator (ELM‐FATES). To evaluate the roles of plant traits, we parameterize the model with 5,265 trait configurations representing diverse physiological and demographic strategies. Results show current modeled biomass, composition, and productivity are most sensitive to traits controlling photosynthetic capacity, carbon allocation, allometry, and phenology. Among all trait configurations, ∼5% reproduce in situ biomass and plant functional type (PFT) composition measured in 2016, that are indistinguishable from these two observed ecosystem states. Notably, these same trait configurations produce diverging biomass, composition, and productivity under future climate, where the uncertainty attributable to traits is twice the change attributable to climate change. The variation of projected productivity arises from emerging PFT composition under novel climate regimes, primarily explained by traits controlling cold‐induced mortality, recruitment, and allometry. Our findings highlight the importance and uncertainty of demographic dynamics and its interaction with climate change in shaping Arctic vegetation change. Improved model predictions will likely benefit from explicit consideration of vegetation demography and better constraints of critical traits. Plain Language Summary: Rapid warming in the Arctic is expected to change plant composition and the capability to sequester carbon, which remains challenging to predict accurately. The changing trajectory depends on the strategies of Arctic vegetation coping with climate change via the demographic processes of recruitment, growth, competition, and mortality. Here, we simulate these processes at an Alaskan tundra site under historical and future climates using a dynamic vegetation model, which describes the strategy of each plant type using plant traits. We find that a large set of different strategies can lead to similar plant composition and biomass as seen in the field. However, the same set of strategies produces diverging future trajectories under projected climate, with spreads twice as wide as climate‐induced changes. This uncertainty is rooted in the trade‐offs across traits and is primarily attributed to those controlling how cold tolerant each plant type is, how fast a new individual can be recruited, and how big and tall the canopy can grow at the same stem size. Better quantification of these traits will likely contribute to improved model predictions. Our findings highlight the importance and uncertainty of vegetation demography and its interaction with climate change in shaping Arctic vegetation change. Key Points: We use a dynamic vegetation model to simulate vegetation composition and productivity at an Arctic site, constrained by in situ dataDiverse trait configurations can reproduce observations but cause projection uncertainty twice the change attributable to climate changeBetter constraints of critical traits on allometry, recruitment, and mortality will likely improve projected Arctic vegetation change [ABSTRACT FROM AUTHOR]

As the regulator of water and nutrient changes in the active layer after permafrost degradation, root signaling substances affect the plant–soil carbon allocation mechanism under climate warming, which is a key issue in the carbon source/sink balance in permafrost regions. To explore how plant root signaling substances regulate carbon allocation in plants and soils under permafrost degradation, the changes in carbon allocation and root signaling substances in the plants and soils of peatland in different permafrost regions at the time of labeling were studied by in situ 13C labeling experiments. The results showed that the fixed 13C of Larix gemlini, Carex schumidtii, and Sphagnum leaves after photosynthesis was affected by permafrost degradation. In regions with more continuous permafrost, the trend of the L. gemlini distribution to underground 13C is more stable. Environmental stress had little effect on the 13C accumulation of Vaccinium uliginosum. Nonstructural carbohydrates, osmotic regulatory substances, hormones, and anaerobic metabolites were the main root signaling substances that regulate plant growth in the peatlands of the three permafrost regions. The allocation of carbon to the soil is more susceptible to the indirect and direct effects of climate and environmental changes, and tree roots are more susceptible to environmental changes than other plants in isolated patches of permafrost regions. The physical properties of the soil are affected by climate change, and the allocation of carbon is regulated by hormones and osmotic regulators while resisting anoxia in the sporadic regions of permafrost. Carbon allocation in discontinuous permafrost areas is mainly regulated by root substances, which are easily affected by the physical and chemical properties of the soil. In general, the community composition of peatlands in permafrost areas is highly susceptible to environmental changes in the soil, and the allocation of carbon from the plant to the soil is affected by the degradation of the permafrost. [ABSTRACT FROM AUTHOR]

In a warming climate, an intensifying fire regime and higher likelihood of extreme rain are expected to increase watershed sediment yield in many regions. Understanding regional variability in landscape response to fire and post‐fire rainfall is essential for managing water resources and infrastructure. We measured sediment yield resulting from sequential wildfire and extreme rain and flooding in the upper Carmel River watershed (116 km2), on the central California coast, USA, using changes in sediment volume mapped in a reservoir. We determined that the sediment yield after fire and post‐fire flooding was 854–1,100 t/km2/yr, a factor of 3.5–4.6 greater than the long‐term yield from this watershed and more than an order of magnitude greater than during severe drought conditions. In this first large‐scale field validation test of the WEPPcloud/wepppy framework for the Water Erosion Prediction Project (WEPP) model on a burned landscape, WEPP predicted 81%–106% of the measured sediment yield. These findings will facilitate assessing and predicting future fire effects in steep watersheds with a Mediterranean climate and indicate that the increasingly widespread use of WEPP is appropriate for evaluating post‐fire hillslope erosion even across 100‐km2 scales under conditions without debris flows. Plain Language Summary: In a warming climate, more wildfire and more extreme rain will cause more erosion, producing more sediment that will be carried downstream by rivers. Understanding how much sediment a landscape produces after fire and extreme rain is essential for managing water resources and infrastructure, because sediment fills up storage space in reservoirs and can interfere with proper functioning of water systems and roads. We measured how much sediment was produced in a watershed due to wildfire followed by extreme rain and flooding, studying the Carmel River on the central California coast, USA. We evaluated how much sediment this watershed produced by measuring the volume of sediment deposited within a reservoir that the watershed drains into. We determined that the rate of sediment exported from the study watershed due to a large fire and post‐fire floods was much greater than the long‐term rate there. Having compared our results with the amount of sediment predicted by a model called the Water Erosion Prediction Project model, we found that the model performed well and realistically predicted the amount of sediment that this landscape would shed. These findings will facilitate assessing and predicting future fire effects in steep watersheds with a Mediterranean‐type climate. Key Points: A 116‐km2 central California watershed produced sediment yield of 854–1,100 t/km2/yr in the first year after a fire and extreme rainPost‐fire sediment yield in an extremely wet year without debris flows was 3.5–4.6 times greater than the long‐term rateThe Water Erosion Prediction Project model predicted 81%–106% of the measured post‐fire sediment eroded from hillslopes [ABSTRACT FROM AUTHOR]

Macroclimate drives vegetation distributions, but fine‐scale topographic variation can generate microclimate refugia for plant persistence in unsuitable areas. However, we lack quantitative descriptions of topography‐driven microclimatic variation and how it shapes forest structure, diversity, and composition. We hypothesized that topographic variation and the presence of the forest overstory cause spatiotemporal microclimate variation affecting tree performance, causing forest structure, diversity, and composition to vary with topography and microclimate, and topography and the overstory to buffer microclimate. In a 20.2‐ha inventory plot in the North American Great Plains, we censused woody stems ≥1 cm in diameter and collected detailed topographic and microclimatic data. Across 59‐m of elevation, microclimate covaried with topography to create a sharp desiccation gradient, and topography and the overstory buffered understory microclimate. The magnitude of microclimatic variation mirrored that of regional‐scale variation: with increasing elevation, there was a decrease in soil moisture corresponding to the difference across ~2.1° of longitude along the east‐to‐west aridity gradient and an increase in air temperature corresponding to the difference across ~2.7° of latitude along the north‐to‐south gradient. More complex forest structure and higher diversity occurred in moister, less‐exposed habitats, and species occupied distinct topographic niches. Our study demonstrates how topographic and microclimatic gradients structure forests in putative climate‐change refugia, by revealing ecological processes enabling populations to be maintained during periods of unfavorable macroclimate. [ABSTRACT FROM AUTHOR]

Wood basic density (WD) plays a crucial role in estimating forest biomass; moreover, improving wood-density estimates is needed to reduce uncertainties in the estimates of tropical forest biomass and carbon stocks. Understanding variations in this density along the tree trunk and its impact on biomass estimates is underexplored in the literature. In this study, the vertical variability of WD was assessed along the stems of large trees that had a diameter at breast height (DBH) ≥ 50 cm from a dense ombrophilous forest on terra firme (unflooded uplands) in Acre, Brazil. A total of 224 trees were sampled, including 20 species, classified by wood type. The average WD along the stem was determined by the ratio of oven-dry mass to saturated volume. Five models were tested, including linear and nonlinear ones, to fit equations for WD, selecting the best model. The variation among species was notable, ranging from 0.288 g cm−3 (Ceiba pentandra, L., Gaertn) to 0.825 g cm−3 (Handroanthus serratifolius, Vahl., S. Grose), with an average of 0.560 g cm−3 (±0.164, standard deviation). Significant variation was observed among individuals, such as in Schizolobium parahyba var. amazonicum (H. ex D.), which ranged from 0.305 to 0.655 g cm−3. WD was classified as low (≤0.40 g cm−3), medium (0.41–0.60 g cm−3), and high (≥0.61 g cm−3). The variability in WD along the stem differs by wood type. In trees with low-density wood, density shows irregular variation but tends to increase along the stem, whereas it decreases in species with medium- and high-density wood. The variation in WD along the stem can lead to underestimations or overestimations, not only in individual trees and species but also in total stocks when estimating forest biomass. Not considering this systematic bias results in significant errors, especially in extrapolations to vast areas, such as the Amazon. [ABSTRACT FROM AUTHOR]

Tropical forest management has a potential role in forest conservation if it is sustainable. This study of a forest under management in Bolivian Amazonia strongly suggests that the management project is not sustainable and that no potential changes in management would be likely to make it so. In a 216.41 ha harvested area, 278 commercial trees from 10 families, 15 genera, and 15 species were measured. The density of commercial species with diameter at breast height (DBH) ≥ 50 cm was 1.28 trees ha−1, and the harvestable commercial volume was 12.40 m3 ha−1. Due to market restrictions, the actual amounts harvested were much lower: 96 trees were harvested with commercial boles totaling 2.7 m3 ha−1. Of the total impact on biomass and carbon (above- and belowground), the logs removed from the area represented only 13.4%, while 86.6% was from losses in the forest as follows: 14.5% from the stumps, crowns, and roots of harvested trees (DBH ≥ 50 cm) plus 72.1% from the trees (DBH ≥ 10 cm) in the forest lost to roads, log landings, and skid tracks and the gap openings caused by felling the harvested trees. The estimated expenses exceeded the gross revenue of the management company (USD 519.15 ha−1), a fact confirmed by the company's subsequent bankruptcy. The project's low harvest intensity reduces the environmental impact per hectare but increases the impact per cubic meter of wood harvested because producing a given volume of wood requires disturbing a larger area and because more kilometers of access roads and skid tracks have to be installed to extract a given volume of wood. Because many costs are fixed regardless of harvest intensity, small harvest volume can render such projects financially unfeasible, increasing the likelihood that they will be abandoned and not provide long-term "sustainable" forest protection. However, this does not mean that higher harvest intensity results in sustainability, as other constraints apply to high-intensity projects. We conclude that conservation alternatives to maintain the forest would be more beneficial than management for timber. [ABSTRACT FROM AUTHOR]

Northern fens, that host unique biota and form a remarkable carbon stock, are sensitive to changes in the moisture balance and, therefore, may be strongly affected by climatic fluctuations. However, long‐term monitoring and palaeoecological studies of fens are relatively rare and, as a result, their responses to past and current climatic fluctuations are poorly known. In this study, we examined the recent vegetation change as well as changes in testate amoeba communities in the mire margin of a subarctic fen in Finnish Lapland with four peat profiles. Testate amoebae were used as indicators of past fluctuations in water table depth. The vegetation showed a drastic shift from sedge‐dominated fen to Sphagnum‐dominated communities during the late 20th and the early 21st centuries. This shift was accompanied by a turnover in the testate amoeba community. Testate amoeba‐based water table reconstructions indicated recent drying. This may be due to the lowering of the water table either from accelerated Sphagnum increment or enhanced evaporation. The observed hummock establishment concurs with the documented hemisphere‐wide expansion trend of hummock communities in fens. This change may strengthen the carbon sink and storage capacity of these peatlands, which could be viewed as a welcome negative feedback process to the ongoing climate warming. However, the change also poses a threat to biodiversity since fens are not only species‐rich habitats but are also endangered ecosystems. [ABSTRACT FROM AUTHOR]

Primary forests are spatially diverse terrestrial ecosystems with unique characteristics, being naturally regenerative and heterogeneous, which supports the stability of their carbon storage through the accumulation of live and dead biomass. Yet, little is known about the interactions between biomass stocks, tree genus diversity and structure across a temperate montane primary forest. Here, we investigated the relationship between tree structure (variability in basal area and tree size), genus-level diversity (abundance, tree diversity) and biomass stocks in temperate primary mountain forests across Central and Eastern Europe. We used inventory data from 726 permanent sample plots from mixed beech and spruce across the Carpathian Mountains. We used nonlinear regression to analyse the spatial variability in forest biomass, structure, and genus-level diversity and how they interact with plot-level tree age, disturbances, temperature and altitude. We found that the combined effects of genus and structural indices were important for addressing the variability in biomass across different spatial scales. Local processes in disturbance regimes and uneven tree age support forest heterogeneity and the accumulation of live and dead biomass through the natural regeneration, growth and decay of the forest ecosystem. Structural complexities in basal area index, supported by genus-level abundance, positively influence total biomass stocks, which was modulated by tree age and disturbances. Spruce forests showed higher tree density and basal area than mixed beech forests, though mixed beech still contributes significantly to biomass across landscapes. Forest heterogeneity was strongly influenced by complexities in forest composition (tree genus diversity, structure). We addressed the importance of primary forests as stable carbon stores, achieved through structure and diversity. Safeguarding such ecosystems is critical for ensuring the stability of the primary forest, carbon store and biodiversity into the future. [ABSTRACT FROM AUTHOR]

Biodiversity, large trees, and environmental conditions such as climate and soil have important effects on forest carbon stocks. However, recent studies in temperate forests suggest that the relative importance of these factors depends on tree mycorrhizal associations, whereby large-tree effects may be driven by ectomycorrhizal (EM) trees, diversity effects may be driven by arbuscular mycorrhizal (AM) trees, and environment effects may depend on differential climate and soil preferences of AM and EM trees. To test this hypothesis, we used forest-inventory data consisting of over 80,000 trees from 631 temperate-forest plots (30 m x 30 m) across Northeast China to examine how biodiversity (species diversity and ecological uniqueness), large trees (top 1% of tree diameters), and environmental factors (climate and soil nutrients) differently regulate aboveground carbon stocks of AM trees, EM trees, and AM and EM trees combined (i.e. total aboveground carbon stock). We found that large trees had a positive effect on both AM and EM tree carbon stocks. However, biodiversity and environmental factors had opposite effects on AM vs. EM tree carbon stocks. Specifically, the two components of biodiversity had positive effects on AM tree carbon stocks, but negative effects on EM tree carbon stocks. Environmental heterogeneity (mean annual temperature and soil nutrients) also exhibited contrasting effects on AM and EM tree carbon stocks. Consequently, for the total carbon stock, the positive large-tree effect far surpasses the diversity and environment effect. This is mainly because when integrating AM and EM tree carbon stock into total carbon stock, the opposite diversity-effect (also environment-effect) on AM vs. EM tree carbon stock counteracts each other while the consistent positive large-tree effect on AM and EM tree carbon stock is amplified. In summary, this study emphasized a mycorrhizal viewpoint to better understand the determinants of overarching aboveground carbon profile across regional forests. [ABSTRACT FROM AUTHOR]

Characterizing foliar trait variation in sun and shade leaves can provide insights into inter- and intra-species resource use strategies and plant response to environmental change. However, datasets with records of multiple foliar traits from the same individual and including shade leaves are sparse, which limits our ability to investigate trait-trait, trait-environment relationships and trait coordination in both sun and shade leaves. We presented a comprehensive dataset of 15 foliar traits from sun and shade leaves sampled with leaf spectroscopy, including 424 individuals of 110 plant species from 19 sites across eastern North America. We investigated trait variation, covariation, scaling relationships with leaf mass, and the effects of environment, canopy position, and taxonomy on trait expression. Generally, sun leaves had higher leaf mass per area, nonstructural carbohydrates and total phenolics, lower mass-based chlorophyll a + b, carotenoids, phosphorus, and potassium, but exhibited species-specific characteristics. Covariation between sun and shade leaf traits, and trait-environment relationships were overall consistent across species. The main dimensions of foliar trait variation in seed plants were revealed including leaf economics traits, photosynthetic pigments, defense, and structural traits. Taxonomy and canopy position collectively explained most of the foliar trait variation. This study highlights the importance of including intra-individual and intra-specific trait variation to improve our understanding of ecosystem functions. Our findings have implications for efficient field sampling, and trait mapping with remote sensing. [ABSTRACT FROM AUTHOR]

Forests undergoing ecological succession following abandonment from agricultural use (i.e., old fields) are ubiquitous in temperate regions of the U.S. and Europe. Ecological succession in old fields involves changes in vegetation composition influenced by factors such as land-use history, soil conditions, and dispersal limitations. Species' behavioral, morphological, physiological and life-history attributes influence the outcomes of environmental and biotic filters on distribution and abundance. However, many studies have focused on aboveground attributes, while less attention has been placed on belowground species characteristics that influence community assembly and function. In this study, we used a trait-based approach to examine how aboveground plant composition and distribution vary with plant root functional traits (e.g., mycorrhizal association) that mediate access for nutrients such as nitrogen (N) and phosphorous (P). We inventoried every tree stem (n = 11,551) in a 10-ha forested area containing old-field and historical forests and matched every species with root functional traits (n = 33) from established databases. We found that land-use history influences community composition and distribution in old-field forests, which also varied with belowground root functional traits. Community composition in old-field forests, which were dominated by Acer saccharum and non-native species, were largely associated with arbuscular mycorrhizae (AM) and higher root nutrient concentrations. On the other hand, community composition in historical forests -- largely dominated by Tsuga canadensis -- were associated with ectomycorrhiza (EcM) and more variation of root length and depth. These results suggest that changes in aboveground communities have implications for belowground ecosystem services (e.g., nutrient cycling) which are important to forest ecosystem development. Trait-based approaches can elucidate mechanisms of community assembly, and understanding how traits influence species coexistence and interactions can inform management decisions related to biodiversity conservation and restoration efforts in disturbed or altered forests. [ABSTRACT FROM AUTHOR]

Given the high-level physiological functions and nutrient concentrations of bark that cover the entire trunks of huge trees, research into bark nutrient traits and the development of models that estimate the bark biomass of tropical trees is essential when it is sought to understand forest nutrient cycling and tree ecological traits. This study investigated the concentrations of six bark nutrients (nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)) by individual tree size and the soil nutrient concentrations for two major pioneer species (Macaranga gigantea and M. hosei) of Malaysia. To estimate bark biomass, allometric equations using tree diameter, height, and crown diameter were developed by combining previous data from adjacent forests with the present data. We found no significant relationship between tree size and most bark nutrient concentrations, though all nutrient concentrations of the two pioneer trees were significantly higher than those of primary forest tree species. Surprisingly, no relationship was found between the soil and bark nutrient concentrations for either species. All the size parameters used in the allometric equations accurately estimated bark biomass. There were no differences in equations between the two species when diameter served as an explanatory variable, but differences were apparent when height and crown diameter were so used. A comparison of allometric equations that yielded the bark biomasses of different types of forest showed that the bark biomass of the tropical secondary forest trees was less than half of that of tropical dry forest trees of the same diameter. Thus, the use of inappropriate equations and nutrient concentrations increases the possibility of serious errors in estimating bark biomass and forest nutrient cycles. [ABSTRACT FROM AUTHOR]

Understanding the spatial variation, temporal changes, and their underlying driving forces of carbon sequestration in various forests is of great importance for understanding the carbon cycle and carbon management options. How carbon density and sequestration in various Cunninghamia lanceolata forests, extensively cultivated for timber production in subtropical China, vary with biodiversity, forest structure, environment, and cultural factors remain poorly explored, presenting a critical knowledge gap for realizing carbon sequestration supply potential through management. Based on a large-scale database of 449 permanent forest inventory plots, we quantified the spatial-temporal heterogeneity of aboveground carbon densities and carbon accumulation rates in Cunninghamia lanceolate forests in Hunan Province, China, and attributed the contributions of stand structure, environmental, and management factors to the heterogeneity using quantile age-sequence analysis, partial least squares path modeling (PLS-PM), and hot-spot analysis. The results showed lower values of carbon density and sequestration on average, in comparison with other forests in the same climate zone (i.e., subtropics), with pronounced spatial and temporal variability. Specifically, quantile regression analysis using carbon accumulation rates along an age sequence showed large differences in carbon sequestration rates among underperformed and outperformed forests (0.50 and 1.80 Mg•ha-1•yr-1). PLS-PM demonstrated that maximum DBH and stand density were the main crucial drivers of aboveground carbon density from young to mature forests. Furthermore, species diversity and geotopographic factors were the significant factors causing the large discrepancy in aboveground carbon density change between low- and high-carbon-bearing forests. Hotspot analysis revealed the importance of culture attributes in shaping the geospatial patterns of carbon sequestration. Our work highlighted that retaining largesized DBH trees and increasing shade-tolerant tree species were important to enhance carbon sequestration in C. lanceolate forests. [ABSTRACT FROM AUTHOR]

Wildfires strongly influence forest ecosystem processes, including carbon and nutrient cycling, and vegetation dynamics. As fire activity increases under changing climate conditions, the ecological and biogeochemical resilience of many forest ecosystems remains unknown.To investigate the resilience of forest ecosystems to changing climate and wildfire activity over decades to millennia, we developed a 4800‐year high‐resolution lake‐sediment record from Silver Lake, Montana, USA (47.360° N, 115.566° W). Charcoal particles, pollen grains, element concentrations and stable isotopes of C and N serve as proxies of past changes in fire, vegetation and ecosystem processes such as nitrogen cycling and soil erosion, within a small subalpine forest watershed. A published lake‐level history from Silver Lake provides a local record of palaeohydrology.A trend towards increased effective moisture over the late Holocene coincided with a distinct shift in the pollen assemblage c. 1900 yr BP, resulting from increased subalpine conifer abundance. Fire activity, inferred from peaks in macroscopic charcoal, decreased significantly after 1900 yr BP, from one fire event every 126 yr (83–184 yr, 95% CI) from 4800 to 1900 yr BP, to one event every 223 yr (175–280 yr) from 1900 yr BP to present.Across the record, individual fire events were followed by two distinct decadal‐scale biogeochemical responses, reflecting differences in ecosystem impacts of fires on watershed processes. These distinct biogeochemical responses were interpreted as reflecting fire severity, highlighting (i) erosion, likely from large or high‐severity fires, and (ii) nutrient transfers and enhanced within‐lake productivity, likely from lower severity or patchier fires. Biogeochemical and vegetation proxies returned to pre‐fire values within decades regardless of the nature of fire effects.Synthesis. Palaeorecords of fire and ecosystem responses provide a novel view revealing past variability in fire effects, analogous to spatial variability in fire severity observed within contemporary wildfires. Overall, the palaeorecord highlights ecosystem resilience to fire across long‐term variability in climate and fire activity. Higher fire frequencies in past millennia relative to the 20th and 21st century suggest that northern Rocky Mountain subalpine ecosystems could remain resilient to future increases in fire activity, provided continued ecosystem recovery within decades. [ABSTRACT FROM AUTHOR]

Successful restoration of human‐disturbed landscapes and ecosystems will be increasingly compromised by the impacts of climate warming. Assisted migration and climate‐informed restoration, in which populations and species adapted to future climates are selected for restoration planting, have emerged as management tools to mitigate climate change effects. However, it is unclear whether climate‐informed restoration could offset the negative effects of climate change and enable successful restoration. We used a forest landscape model to evaluate the potential for reclamation activities to restore western Canadian boreal forest landscapes severely degraded by oil sands mining. We parametrized tree populations adapted to growing in warmer climates and then simulated the planting of local or southern tree populations under different climate change, mining, and wildfire disturbance scenarios. We found that planting trees better adapted to a warmer climate mitigated climate‐change and wildfire‐caused decreases in biomass across the landscape, but only under moderate climate change scenarios. The compensatory effect of planting populations adapted to warmer southern climates disappeared under a more severe climate change scenario. The advantage of planting southern populations also disappeared under wildfire scenarios, generally doubling the biomass loss compared with scenarios without wildfire. With wildfire and strong climate change effects, forest cover disappeared from much of the landscape, regardless of the planting scenario, causing it to change markedly from present‐day continuous boreal forest cover. We argue that such conditions would have large ecological and economic consequences. Scenario modeling with forest landscape models could be used as a tool to identify the long‐term success of restoration actions and to understand possible consequences of climate‐informed restoration. [ABSTRACT FROM AUTHOR]

Warming and changing precipitation can alter the performance of native grasses that are essential to grassland ecosystems. Native grasses may respond to changing climate by phenotypic plasticity or lose their current ranges. Establishing plant species from southern, warmer provenances may reduce the likelihood of biodiversity loss and improve restoration success in cool, northern locations that are undergoing warming. We conducted competition trials for Pseudoroegneria spicata (bluebunch wheatgrass), a native grass commonly found in western North American grasslands, to understand the impact of temperature and moisture on plant–plant interactions. We obtained seeds from three locations along a latitudinal gradient in North America, two in British Columbia (BC), Canada, and one in California, USA. We compared the effects of warming, changing water inputs, and competitor provenance on pairwise competitive interactions among Pseudoroegneria spicata plants grown from seeds obtained from the three locations. We quantified interactions using the relative interaction intensity, which has values from −1 (complete competition) to +1 (complete facilitation). Target plants from northern British Columbia, the location with the coldest summer temperature, were generally more competitively suppressed when competing with plants from California, which had the warmest summer temperature and lowest summer precipitation. Competitive suppression of target plants from northern British Columbia and southern British Columbia was more intense when competitor provenance was more geographically distant from target plant provenance. Finally, plants from northern British Columbia and southern British Columbia were more suppressed at higher temperatures, indicating some local adaptation, while plants from California were not affected by competitors, temperature, or water input. Plants grown from seeds obtained from warm and dry locations appear to be more tolerant to competition at higher temperatures, compared to plants from cooler regions. Native plant diversity and restoration success in grasslands subjected to climate change may be preserved or improved by assisted migration of seeds from warm to cooler but warming locations. [ABSTRACT FROM AUTHOR]

Climate, disturbance, vegetation response and their interaction are key factors in predicting the distribution and function of ecosystems across landscapes. A range of factors, operating through different pathways, are amplifying the feedbacks in this three‐way interaction.In the western USA, the relative strength of the influence of climate versus vegetation on fire activity varies spatially, realizing a diversity of fire regimes and fire‐selected species traits under historical conditions of climate–fire–vegetation interactions.Human intervention, via land use and fire‐exclusion, has homogenized frequent‐fire‐adapted forests in terms of structure and composition. Climate change is reinforcing the homogenization directly via increasing temperatures and drought and indirectly through climate‐driven tree mortality. The net effect will be forming novel climate–fire–vegetation interactions that act to homogenize fire regimes and catalyse large‐scale forest loss.While long‐term persistence of tree species in a given location may not be possible due to directional change of climate, slowing the rate of wildfire‐driven forest cover loss and maximizing the in‐situ persistence of a diversity of species will allow forest ecosystems to respond more incrementally to changing climate and provide an opportunity for ecosystem reassembly to occur from a large pool of species.As climate continues to change, management to resist wildfire‐driven forest cover loss may hinge on reducing forest density and creating a higher level of heterogeneity to reach the resistance and resilience exhibited by pre‐fire‐exclusion forests. Management operations should better leverage disturbance while strategically deploying silvicultural treatments to increase managed and prescribed fire.Further research is needed to improve our capacity for quantifying key mechanisms and system responses involved in the climate–fire–vegetation interactions and predicting how best to allocate resources to manage for functional forests. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Root‐associated fungi play a critical role in plant ecophysiology, growth and subsequent responses to disturbances, so they are thought to be particularly instrumental in shaping vegetation dynamics after fire in the boreal forest. Despite increasing data on the distribution of fungal taxonomic diversity through space and time in boreal ecosystems, there are knowledge gaps with respect to linking these patterns to ecosystem function and process.Here we explore what is currently known about postfire root‐associated fungi in the boreal forest. We focus on wildfire impacts on mycorrhizal fungi and the relationships between plant–fungal interactions and forest recovery in an effort to explore whether postfire mycorrhizal dynamics underlie plant–soil feedbacks that may influence fire‐facilitated vegetation shifts.We characterize the mechanisms by which wildfire influences root‐associated fungal community assembly. We identify scenarios of postfire plant–fungal interactions that represent putative positive and negative plant–soil feedbacks that may impact successional trajectories. We highlight the need for empirical field observations and experiments to inform our ability to translate patterns of postfire root‐associated fungal diversity to ecological function and application in models.We suggest that understanding postfire interactions between root‐associated fungi and plants is critical to predict fire effects on vegetation patterns, ecosystem function, future landscape flammability and feedbacks to climate. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Protecting the climate system requires urgently reducing carbon emissions to the atmosphere and increasing cumulative carbon stocks in natural systems. Recent studies confirm that large trees accumulate and store a disproportionate share of aboveground forest carbon. In the temperate forests of the western United States, a century of intensive logging drastically reduced large‐trees and older forest, but some large trees remain. However, recent changes to large tree management policy on National Forest lands east of the Cascade Mountains crest in Oregon and southeastern Washington allows increased harvesting of large‐diameter trees (≥53 cm or 21 inches) that account for just 3% of all stems, but hold 42% of total aboveground carbon. In this article, we describe synergies with protecting large trees for climate mitigation, biodiversity, and forest resilience goals to shift species composition, reduce fuel loads and stem density, and adapt to climatically driven increases in fire activity in eastern Oregon. [ABSTRACT FROM AUTHOR]

Conservation strategies for imperiled species are frequently based on identifying and addressing the probable causes of population decline, an approach known as the declining population paradigm. Causes, however, are frequently linked to demographic outcomes by multiple mechanisms, and failing to target the primary mechanisms can reduce the effectiveness and efficiency of conservation actions. Increasingly, conservation strategies also need to consider emerging threats, such as climate change. Here, we use boreal caribou (Rangifer tarandus caribou), a threatened ecotype of woodland caribou, as a case study to illustrate how landscape disturbance and climate change can each exert negative demographic effects on caribou through multiple and complex mechanisms. We reviewed the extensive literature focused on woodland caribou to identify and assess the relative importance of each putative mechanism. While disturbance‐mediated apparent competition, the expansion of novel predators, and altered predator behavior appear to be primary mechanisms dictating past and current declines of caribou, climate change has increasing potential to exert strong direct and indirect effects now and in the future. Predicted climate effects may prevent some populations from regaining self‐sustaining status, despite local conservation actions. Our review revealed several knowledge gaps, notably a lack of clarity on the spatial extent of undisturbed habitat required for caribou populations to be stable. We used outcomes from our review to demonstrate how a mechanistic understanding of population decline can inform habitat‐based conservation strategies for caribou. For populations residing within highly disturbed ranges, habitat restoration is a key recommendation of current conservation strategies, yet the large spatial extent of disturbances will require prioritization of areas for restoration. Maximizing the conservation return‐on‐investment for caribou will require a mechanistically informed prioritization process that targets conservation actions toward the primary mechanisms underlying population decline. [ABSTRACT FROM AUTHOR]

Changes in fire regime of boreal forests in response to climate warming are expected to impact postfire recovery. However, quantitative data on how managed forests sustain and recover from recent fire disturbance are limited.Two years after a large wildfire in managed even‐aged boreal forests in Sweden, we investigated how recovery of aboveground and belowground communities, that is, understory vegetation and soil microbial and faunal communities, responded to variation in the severity of soil (i.e., consumption of soil organic matter) and canopy fires (i.e., tree mortality).While fire overall enhanced diversity of understory vegetation through colonization of fire adapted plant species, it reduced the abundance and diversity of soil biota. We observed contrasting effects of tree‐ and soil‐related fire severity on survival and recovery of understory vegetation and soil biological communities. Severe fires that killed overstory Pinus sylvestris promoted a successional stage dominated by the mosses Ceratodon purpureus and Polytrichum juniperinum, but reduced regeneration of tree seedlings and disfavored the ericaceous dwarf‐shrub Vaccinium vitis‐idaea and the grass Deschampsia flexuosa. Moreover, high tree mortality from fire reduced fungal biomass and changed fungal community composition, in particular that of ectomycorrhizal fungi, and reduced the fungivorous soil Oribatida. In contrast, soil‐related fire severity had little impact on vegetation composition, fungal communities, and soil animals. Bacterial communities responded to both tree‐ and soil‐related fire severity.Synthesis: Our results 2 years postfire suggest that a change in fire regime from a historically low‐severity ground fire regime, with fires that mainly burns into the soil organic layer, to a stand‐replacing fire regime with a high degree of tree mortality, as may be expected with climate change, is likely to impact the short‐term recovery of stand structure and above‐ and belowground species composition of even‐aged P. sylvestris boreal forests. [ABSTRACT FROM AUTHOR]

Most research on boreal populations of woodland caribou (Rangifer tarandus caribou) has been conducted in areas of high anthropogenic disturbance. However, a large portion of the species' range overlaps relatively pristine areas primarily affected by natural disturbances, such as wildfire. Climate‐driven habitat change is a key concern for the conservation of boreal‐dependent species, where management decisions have yet to consider knowledge from multiple ecological domains integrated into a cohesive and spatially explicit forecast of species‐specific habitat and demography. We used a novel ecological forecasting framework to provide climate‐sensitive projections of habitat and demography for five boreal caribou monitoring areas within the Northwest Territories (NWT), Canada, over 90 years. Importantly, we quantify uncertainty around forecasted mean values. Our results suggest habitat suitability may increase in central and southwest regions of the NWT's Taiga Plains ecozone but decrease in southern and northwestern regions driven by conversion of coniferous to deciduous forests. We do not project that boreal caribou population growth rates will change despite forecasted changes to habitat suitability. Our results emphasize the importance of efforts to protect and restore northern boreal caribou habitat despite climate uncertainty while highlighting expected spatial variations that are important considerations for local people who rely on them. An ability to reproduce previous work, and critical thought when incorporating sources of uncertainty, will be important to refine forecasts, derive management decisions, and improve conservation efficacy for northern species at risk. [ABSTRACT FROM AUTHOR]

Harnessing natural solutions to mitigate climate change requires an understanding of carbon fixation, flux, and sequestration across ocean habitats. Recent studies have suggested that exported seaweed particulate organic carbon is stored within soft‐sediment systems. However, very little is known about how seaweed detritus disperses from coastlines, or where it may enter seabed carbon stores, where it could become the target of conservation efforts. Here, focusing on regionally dominant seaweed species, we surveyed environmental DNA (eDNA) from natural coastal sediments, and studied their connectivity to seaweed habitats using a particle tracking model parameterized to reproduce seaweed detritus dispersal behavior based on laboratory observations of seaweed fragment degradation and sinking. Experiments showed that seaweed detritus density changed over time, differently across species. This, in turn, modified distances traveled by released fragments until they reached the seabed for the first time, during model simulations. Dispersal pathways connected detritus from the shore to the open ocean but, importantly, also to coastal sediments, and this was reflected by field eDNA evidence. Dispersion pathways were also affected by hydrodynamic conditions, varying in space and time. Both the properties and timing of released detritus, individual to each macroalgal population, and short‐term near‐seabed and medium‐term water‐column transport pathways, are thus seemingly important in determining the connectivity between seaweed habitats and potential sedimentary sinks. Studies such as this one, supported by further field verification of sedimentary carbon sequestration rates and source partitioning, are still needed to help quantify the role of seaweed in the ocean carbon cycle. Such studies will provide vital evidence to inform on the potential need to develop blue carbon conservation mechanisms, beyond wetlands. [ABSTRACT FROM AUTHOR]

Tropical mountain forests are relatively less disturbed and store a large amount of carbon in tree biomass. A high level of species diversity compared to the boreal and temperate forests is also maintained and indicates a positive relationship with tree biomass on a small scale or at plot level. This study aimed to estimate above-ground biomass stocks (AGB) and disentangle the influence of forest structure and attributes on AGB in a small mountain forest. Forty 400 m² plots were randomly established in Takokak Nature Reserve (TNR), a 60-ha protected area at an elevation between 1150-1560 m a.s.l., located in West Java, Indonesia. All trees within the plot were identified, and their respective diameter at breast height (DBH) was measured. AGB was calculated using a global allometric model. Five independent variables, i.e., stem density, stem density of large trees (DBH >50 cm), community weighted mean wood density, rarefied species richness, and Fisher's alpha index, were analysed using a linear model. Our results showed that AGB in TNR was comparable to other forest types in Indonesia and acted as carbon storage in the mountain regions. AGB in the TNR reached 486 Mg ha-1, of which 75% was contributed by large trees (DBH >50 cm). Three species, i.e., Liquidambar excelsa (Altingiaceae), Schima wallichii (Theaceae), and Lithocarpus sp. (Fagaceae), represent at least 70% of the total biomass in the study site. We also found that forest structures and traits, i.e., stem density, stem density of large trees, and community weighted mean wood density, drive AGB variations but not tree diversity indices. However, although diversity indices were not correlated to AGB, we found that TNR is home for endemic and threatened species on the IUCN Red List. Therefore, we suggest that the management strategies of the tropical forests should include both the conservation of the carbon stock and biodiversity. [ABSTRACT FROM AUTHOR]

Aim: Climate change is affecting the distribution of species and subsequent biotic interactions, including hybridization potential. The imperiled Golden‐winged Warbler (GWWA) competes and hybridizes with the Blue‐winged Warbler (BWWA), which may threaten the persistence of GWWA due to introgression. We examined how climate change is likely to alter the breeding distributions and potential for hybridization between GWWA and BWWA. Location: North America. Methods: We used GWWA and BWWA occurrence data to model climatically suitable conditions under historical and future climate scenarios. Models were parameterized with 13 bioclimatic variables and 3 topographic variables. Using ensemble modeling, we estimated historical and modern distributions, as well as a projected distribution under six future climate scenarios. We quantified breeding distribution area, the position of and amount of overlap between GWWA and BWWA distributions under each climate scenario. We summarized the top explanatory variables in our model to predict environmental parameters of the distributions under future climate scenarios relative to historical climate. Results: GWWA and BWWA distributions are projected to substantially change under future climate scenarios. GWWA are projected to undergo the greatest change; the area of climatically suitable breeding season conditions is expected to shift north to northwest; and range contraction is predicted in five out of six future climate scenarios. Climatically suitable conditions for BWWA decreased in four of the six future climate scenarios, while the distribution is projected to shift east. A reduction in overlapping distributions for GWWA and BWWA is projected under all six future climate scenarios. Main Conclusions: Climate change is expected to substantially alter the area of climatically suitable conditions for GWWA and BWWA, with the southern portion of the current breeding ranges likely to become climatically unsuitable. However, interactions between BWWA and GWWA are expected to decline with the decrease in overlapping habitat, which may reduce the risk of genetic introgression. [ABSTRACT FROM AUTHOR]

Whether current hypotheses for geographic patterns of species richness (SR) have a strong explanatory power for the Tibetan Plateau (TP) with extreme climatic conditions remains unclear. In comparison with the classic 'water–energy dynamics hypothesis', the unique climate factors (e.g. extreme low temperature and low oxygen partial pressure) on the TP likely significantly affect the spatial variation of SR. Here, we investigate geographic patterns and determinants of SR on the TP through a systematic field investigation. We systematically analyzed a total of 2013 plant communities covering 11 different vegetation types on the TP. To compare this SR with that of other sites across the globe, we compiled a global database containing information on 87 forest and 3660 grassland plots. The SR per 400 m2 in the forests and shrubs and that per 1 m2 in alpine grasslands and deserts was 62.76 (± 1.80 SE), 44.53 (± 7.57 SE), 16.84 (± 0.39 SE) and 3.62 (± 0.55 SE), respectively. The SR of forests and shrubs decreased with latitude and altitude, whereas that of alpine grasslands and deserts showed a unimodal pattern along the altitudinal gradient. Unique climate factors, such as extreme low temperature, mean diurnal temperature and oxygen partial pressure, act synergistically with water–energy dynamics and influence the spatial pattern of SR on the TP. Furthermore, the tree SR on the TP was lower than that of global tropical and subtropical broadleaf forests but higher than that of temperate conifer forests. Alpine meadows had a higher SR than other sites; however, the SR in alpine desert grasslands and alpine deserts was lower. Our findings provide novel insights into the mechanisms underlying the spatial variation in plant diversity, especially on plateaus and in high‐latitude regions. Our findings and the SR map with 1 km resolution provide important benchmarks for biodiversity conservation and may help to improve predictions of the effect of climate change on biodiversity. [ABSTRACT FROM AUTHOR]

Ongoing climate changes have a direct impact on forest growth; they also affect natural fire regimes, with further implications for forest composition. Understanding of how these will affect forests on decadal-to-centennial timescales is limited. Here we use reconstructions of past vegetation, fire regimes and climate during the Holocene to examine the relative importance of changes in climate and fire regimes for the abundance of key tree species in northeastern China. We reconstructed vegetation changes and fire regimes based on pollen and charcoal records from Gushantun peatland. We then used generalized linear modelling to investigate the impact of reconstructed changes in summer temperature, annual precipitation, background levels of fire, fire frequency and fire magnitude to identify the drivers of decadal-to-centennial changes in forest openness and composition. Changes in climate and fire regimes have independent impacts on the abundance of the key tree taxa. Climate variables are generally more important than fire variables in determining the abundance of individual taxa. Precipitation is the only determinant of forest openness, but summer temperature is more important than precipitation for individual tree taxa with warmer summers causing a decrease in cold-tolerant conifers and an increase in warmth-demanding broadleaved trees. Both background level and fire frequency have negative relationships with the abundance of most tree taxa; only Pinus increases as fire frequency increases. The magnitude of individual fires does not have a significant impact on species abundance on this timescale. Both climate and fire regime characteristics must be considered to understand changes in forest composition on the decadal-to-centennial timescale. There are differences, both in sign and magnitude, in the response of individual tree species to individual drivers. [ABSTRACT FROM AUTHOR]

Boreal forest and tundra ecosystems are undergoing rapid climatic and environmental changes with consequences for ecosystem structure, function, and services. Although riparian zones occupy a small footprint within subarctic landscapes, they have disproportionately high value as foci of hydrological processes, biogeochemical cycling, ecological disturbance, biodiversity, and wildlife activity. Recent observations of increased winter discharge, reduced peak flows, and increased connectivity between catchments, streams, and groundwater in subarctic riparian zones have prompted predictions of altered riverine disturbance regimes, increased channelization, and a decline in the extent of active floodplains. However, few observational data exist concerning the spatiotemporal dynamics of subarctic floodplain vegetation, which can serve as a bioindicator to corroborate such predictions. We analyzed the distribution and extent of riparian ecotypes across a network of streams in 12 Interior Alaska watersheds using high‐resolution image pairs from circa 1981–2010. All stream reaches encompassed pronounced elevational gradients and included elevational forest–tundra ecotones. We classified riparian ecotypes using an image‐based point‐intercept sampling approach, calculated the probability of ecotype transitions, and evaluated relationships between ecotype transitions and environmental covariates. Our results reveal widespread increases in the stature, density, and extent of riparian vegetation spanning gradients of elevation, floodplain morphology, and climate. Ecotype transitions occurred at >20% of sample points, and there was a strong imbalance toward forward successional transitions (16.5%) versus backward transitions (4.0%). That is, we observed a strong tendency toward increasing cover, stature, and density of vegetation communities across our extensive sampling domain across our approximately 30‐year sample period. This relatively rapid riparian "greening" signal tended to be most pronounced in our glaciated watersheds. Although the streams we studied displayed high local variability in ecotype transitions, our results support hypotheses of increasing channelization and reduced extent of unvegetated surfaces on subarctic floodplains. They also likely reflect a trend toward more rapid and extensive plant recruitment and growth due to processes associated with conspicuous warming in northern ecosystems, consistent with greening documented in other subarctic landscape segments along gradients of elevation and latitude. [ABSTRACT FROM AUTHOR]

Actions to protect against biodiversity loss and climate change will require a framework that addresses synergies between these interrelated issues. In this study, we present methods for identifying areas important for the implementation of nature‐based climate solutions and biodiversity conservation by intersecting high‐resolution spatial data for carbon storage and landscape connectivity. We explored the spatial congruence of carbon and connectivity in Ontario, Canada and examined effectiveness of current protected areas coverage. We found a weak positive relationship between carbon stocks and landscape connectivity; however, our maps revealed large hotspots, with high values of both indices, throughout the boreal forest and northern peatlands and smaller, isolated hotspots, in the settled landscapes of the south. Location of hotspots varied depending on whether we considered forest or soil carbon. Further, our results show that current protected and conserved areas in Ontario only cover 13% of landscapes with the highest values for both carbon storage and connectivity. Protection or restoration of areas that maximize the co‐benefits of carbon storage and connectivity would make significant contributions toward ambitious national targets to reduce greenhouse gas emissions and conserve biodiversity. [ABSTRACT FROM AUTHOR]

Mountain seasonal snow cover is undergoing major changes due to global climate change. Assessments of future snow cover usually rely on physically based models, and often include post-processed meteorology. Alternatively, we here propose a direct statistical adjustment of snow cover fraction from regional climate models by using long-term remote-sensing observations. We compared different bias-adjustment routines (delta change, quantile mapping, and quantile delta mapping) and explored a downscaling based on historical observations for the Greater Alpine Region in Europe. All bias-adjustment methods account for systematic biases, for example due to topographic smoothing, and reduce model spread in future projections. The trend-preserving methods delta change and quantile delta mapping were found to be more suitable for snow cover fraction than quantile mapping. Averaged over the study region and whole year, snow cover fraction decreases from 12.5 % in 2001–2020 to 10.4 % (8.9 %, 11.5 %; model spread) in 2071–2100 under RCP2.6 (representative concentration pathway), and to 6.4 % (4.1 %, 7.8 %) under RCP8.5 (bias-adjusted estimates from quantile delta mapping). In addition, changes strongly depended on season and elevation. The comparison of the statistical downscaling to a high-resolution physically based model yields similar results for the elevation range covered by the climate models, but different elevation gradients of change above and below. Downscaling showed overall potential but requires further research. Since climate model and remote-sensing observations are available globally, the proposed methods are potentially widely applicable but are limited to snow cover fraction. [ABSTRACT FROM AUTHOR]

Background: 'Megafire' is an emerging concept commonly used to describe fires that are extreme in terms of size, behaviour, and/or impacts, but the term's meaning remains ambiguous. Approach: We sought to resolve ambiguity surrounding the meaning of 'megafire' by conducting a structured review of the use and definition of the term in several languages in the peer‐reviewed scientific literature. We collated definitions and descriptions of megafire and identified criteria frequently invoked to define megafire. We recorded the size and location of megafires and mapped them to reveal global variation in the size of fires described as megafires. Results: We identified 109 studies that define the term 'megafire' or identify a megafire, with the term first appearing in the peer‐reviewed literature in 2005. Seventy‐one (~65%) of these studies attempted to describe or define the term. There was considerable variability in the criteria used to define megafire, although definitions of megafire based on fire size were most common. Megafire size thresholds varied geographically from > 100–100,000 ha, with fires > 10,000 ha the most common size threshold (41%, 18/44 studies). Definitions of megafire were most common from studies led by authors from North America (52%, 37/71). We recorded 137 instances from 84 studies where fires were reported as megafires, the vast majority (94%, 129/137) of which exceed 10,000 ha in size. Megafires occurred in a range of biomes, but were most frequently described in forested biomes (112/137, 82%), and usually described single ignition fires (59% 81/137). Conclusion: As Earth's climate and ecosystems change, it is important that scientists can communicate trends in the occurrence of larger and more extreme fires with clarity. To overcome ambiguity, we suggest a definition of megafire as fires > 10,000 ha arising from single or multiple related ignition events. We introduce two additional terms – gigafire (> 100,000 ha) and terafire (> 1,000,000 ha) – for fires of an even larger scale than megafires. [ABSTRACT FROM AUTHOR]

Identifying key traits that can serve as proxies for species drought resistance is crucial for predicting and mitigating the effects of climate change in diverse plant communities. Turgor loss point (πtlp) is a recently emerged trait that has been linked to species distributions across gradients of water availability. However, a direct relationship between πtlp and species ability to survive drought has yet to be established for woody species. Using a manipulative field experiment to quantify species drought resistance (i.e., their survival response to drought), combined with measurements of πtlp for 16 tree species, we show a negative relationship between πtlp and seedling drought resistance. Using long‐term forest plot data, we also show that πtlp predicts seedling survival responses to a severe El Niño‐related drought, although additional factors are clearly also important. Our study demonstrates that species with lower πtlp exhibit higher survival under both experimental and natural drought. These results provide a missing cornerstone in the assessment of the traits underlying drought resistance in woody species and strengthen πtlp as a proxy for evaluating which species will lose or win under projections of exacerbating drought regimes. [ABSTRACT FROM AUTHOR]

Climate change refugia are areas that are relatively buffered from contemporary climate change and may be important safe havens for wildlife and plants under anthropogenic climate change. Topographic variation is an important driver of thermal heterogeneity, but it is limited in relatively flat landscapes, such as the boreal plain and prairie regions of western Canada. Topographic variation within this region is mostly restricted to river valleys and hill systems, and their effects on local climates are not well documented. We sought to quantify thermal heterogeneity as a function of topography and vegetation cover within major valleys and hill systems across the boreal–grassland transition zone. Using iButton data loggers, we monitored local temperature at four hills and 12 river valley systems that comprised a wide range of habitats and ecosystems in Alberta, Canada (N = 240), between 2014 and 2020. We then modeled monthly temperature by season as a function of topography and different vegetation cover types using general linear mixed effect models. Summer maximum temperatures (Tmax) varied nearly 6°C across the elevation gradient sampled. Local summer mean (Tmean) and maximum (Tmax) temperatures on steep, north‐facing slopes (i.e., low levels of potential solar radiation) were up to 0.70°C and 2.90°C cooler than highly exposed areas, respectively. Tmax in incised valleys was between 0.26 and 0.28°C cooler than other landforms, whereas areas with greater terrain roughness experienced maximum temperatures that were up to 1.62°C cooler. We also found that forest cover buffered temperatures locally, with coniferous and mixedwood forests decreasing summer Tmean from 0.23 to 0.72°C and increasing winter Tmin by up to 2°C, relative to non‐forested areas. Spatial predictions of temperatures from iButton data loggers were similar to a gridded climate product (ClimateNA), but the difference between them increased with potential solar radiation, vegetation cover, and terrain roughness. Species that can track their climate niche may be able to compensate for regional climate warming through local migrations to cooler microsites. Topographic and vegetation characteristics that are related to cooler local climates should be considered in the evaluation of future climate change impacts and to identify potential refugia from climate change. [ABSTRACT FROM AUTHOR]

Wildfire is a highly variable natural phenomenon, yet despite this, climate change is already making wildfire conditions measurably worse around the world; however, detailed knowledge about Aotearoa New Zealand's wildfire climate is currently limited. This study blends weather observations with regional climate model projections to assess Aotearoa New Zealand's 21st‐century wildfire climate. We find that in the 21st‐century, the emergence of a new—more severe wildfire climate will occur. Detailed analysis of observed and simulated wildfire weather finds that "very‐extreme" wildfire weather conditions matching the levels observed in Australia's 2019/2020 "Black Summer" bushfires are possible in regions formerly unaffected. While the extent of emergence is dependent on future emissions, the frequency of very‐extreme conditions for the areas affected can occur at any time and is independent of projected 21st‐century climate changes. Our findings have significant implications for many rural fire authorities, forest managers and investors, and climate mitigation and afforestation programs. Plain Language Summary: Combining highly detailed climate simulations with daily observations of weather and wildfire conditions, we simulate Aotearoa New Zealand's current and future wildfire weather conditions. We find that wildfire weather conditions will increase on average, both in wildfire season length and in the intensity of fires that may take hold, with the most severe wildfire dangers in the central‐south inland areas of the South Island. We find that the wildfire weather conditions will become noticeably worse for many regions than current conditions. For the first time, we find that very‐extreme conditions that led to the devastating 2019–2020 "Black‐Summer" fires in Australia can occur in Aotearoa every 3–20 year for areas of the South Island (Mackenzie Country, Upper Otago, and Marlborough). Our findings have important implications for communities near pine forests, the Government's tree planting plan to tackle climate change, and financial investment stored in plantation forests. Key Points: In the 21st‐century, the emergence of a new—more severe wildfire climate will occurWe discover that "very‐extreme" wildfire weather conditions are possible in regions formerly unaffectedWhile the extent of emergence is dependent on future emissions, the frequency of very‐extreme conditions is independent [ABSTRACT FROM AUTHOR]

Wetlands are highly productive ecosystems that host unique biota and provide vital ecosystem services. Despite their critical importance, we still lack a fundamental understanding of factors controlling species suitability and climate change impacts in wetlands essential to conserving these imperiled ecosystems in the face of anthropogenic threats. Here, we applied ecological niche models (ENMs) inferred from a massive nationwide data set including field surveys and herbarium specimens representing 101 dominant plant species of China's inland wetlands, to explore the potential climate‐driven shifts in these ecosystems. Our optimal models applying machine learning and integrating key aspects of climate, soil, topographic hydrology, and anthropogenic disturbance, identified that (a) species of different types (e.g., woody/nonwoody) showed significant differences in their sensitivity to extracted key environmental factors (e.g., isothermality, water table depth) in wetlands; (b) native wetland species likely face habitat shrinkage under climate change, especially in Northeast China, as well as potential encroachment of xeric and nonnative species; (c) only less than 20% of projected conservation hotspots are currently protected. We propose four protection gaps that need to be addressed urgently in China's current wetland protection framework. This study clarifies the conservation priorities of China's inland wetlands and provides practical guidelines for the improvement of wetland conservation efforts. Plain Language Summary: Wetlands are among the most productive ecosystems on Earth and provide multiple key ecosystem services for wildlife and human societies. However, global wetlands have been experiencing extensive degradation and loss under anthropogenic threats, and anthropogenic climate change poses new challenges and uncertainties to wetland conservation efforts. Thus, there is a pressing need to assess climatic risks in wetlands, to identify potential climate‐change hotspots and develop climate‐smart conservation strategies. This study compiled a massive wetland data set and applied machine learning tools to perform the first nationwide climatic risk assessment in China's inland wetlands. The results revealed that native wetland species would face habitat shrinkage, especially woody species, whereas nonwetland and nonnative species would benefit from climate change and expand their distributions. Northeast China is a hotspot with its native wetland species under high climatic risk, while in the Tibetan Plateau, the habitats for native wetland species and nonwetland species are both likely to expand in the future. This study highlights the conservation priorities in China's inland wetlands and offers guidelines for filling the current wetland protection gaps. Key Points: Different species types vary in their sensitivity to the key environmental factors in inland wetlandsNative wetland species will overall face habitat loss, especially in Northeast China, as well as invasion of xeric and alien speciesLess than 20% of projected conservation hotspots are currently protected [ABSTRACT FROM AUTHOR]

Plant competition may intensify with climate warming, but whether this will occur equally for conspecific and heterospecific competition remains unknown. Competitive shifts have the potential to instigate community change because the relative strengths of conspecific and heterospecific negative density dependence mediate the stabilizing mechanisms underpinning species coexistence. We examined a mature temperate forest to assess both direct and indirect climate effects at multiple scales: individual species, interspecies relationships, and community stability mechanisms. Our coupled approach (1) quantified tree mortality risk dependence on the interactive effects of competition, climatic water deficit, snowpack, and soil moisture for 28,913 trees over 8 years (3149 mortalities), then (2) used a climate‐projection ensemble to forecast changes in conspecific and heterospecific competition from 2020 to 2100. We predict that projected climate warming will destabilize the foundational forest community by increasing the strength of heterospecific competition at a greater rate and to a greater degree than conspecific competition for four of five abundant tree species, particularly on dry microsites. Modeling showed that these findings were most pronounced after the year 2038, at which point snowpacks were projected to be too small to ameliorate the effects of drought on competitive interactions. Our finding that heterospecific competition is more sensitive than conspecific competition to climate warming may indicate the impending loss of ecosystem functioning. We join the growing body of work showing a predominance of indirect drought effects, yet coupled climate models still fail to consider how changing community dynamics may impact forest cover and, in turn, disrupt forest–climate carbon feedbacks. Ecosystems sharing characteristics with our example forest—those with low species richness and therefore a limited biodiversity insurance effect—may be similarly vulnerable to climate‐mediated destabilization. In such communities, increased heterospecific competition among even a small number of species can more easily destabilize communities without recourse from redundant species. This study of an overlooked but vital mechanism of community change can be adapted by research in a range of ecosystems to improve the understanding of climate change consequences. [ABSTRACT FROM AUTHOR]

Contrasts of differences within plant species and ecotypes are often best examined in ecology, evolution and genetics through provenance and biogeographical comparisons. Climate adaptation studies in plants are no exception and benefit from experiments that use these sets of factors.Reciprocal common gardens are a tool used to test for local adaptation in species to different contexts including climate.A synthesis of common gardens and intraspecific tests for climate adaptation was used to compile over 200 studies that explored the relative efficacy of this tool and the ecology of change. Exclusion criteria were applied to review this literature and to compile specific tests that explicitly examined climate, plants and reciprocity in gardens for a total of 70 independent instances.A meta‐analysis was used to test for consistency and significance of detecting ecotypes for the different categories of traits tested and by the transplanting of seeds or seedlings.This meta‐analysis provides clear evidence for plant adaptation to climate change because all significant effect size estimates were positive, relatively large, and both seed and seedling transplants demonstrated consistent evidence for local adaptation. Emergence and germination responses from seed transplant experiments and relative growth and biomass differences from seedling transplants provided particularly strong support.Synthesis. Reciprocal common gardens were a highly effective experimental design to test for ecotypic differentiation and for climate adaptation. Nonetheless, we propose that future studies clearly define whether ecotypes are being explicitly tested in common garden experiments to enable evidence syntheses and discovery, and we highlight the need for reciprocal climatic gardens to clearly test for continued capacity for local adaptation in response to divergent climate selection processes in many plant species. [ABSTRACT FROM AUTHOR]

The boreal forest landscape covers approximately 10 % of the earth's land area and accounts for almost 30 % of the global annual terrestrial sink of carbon (C). Increased emissions due to climate-change-amplified fire frequency, size, and intensity threaten to remove elements such as C and nitrogen (N) from forest soil and vegetation at rates faster than they accumulate. This may result in large areas within the region becoming a net source of greenhouse gases, creating a positive feedback loop with a changing climate. Meter-scale estimates of area-normalized fire emissions are limited in Eurasian boreal forests, and knowledge of their relation to climate and ecosystem properties is sparse. This study sampled 50 separate Swedish wildfires, which occurred during an extreme fire season in 2018, providing quantitative estimates of C and N loss due to fire along a climate gradient. Mean annual precipitation had strong positive effects on total fuel, which was the strongest driver for increasing C and N losses. Mean annual temperature (MAT) influenced both pre- and postfire organic layer soil bulk density and C : N ratio, which had mixed effects on C and N losses. Significant fire-induced loss of C estimated in the 50 plots was comparable to estimates in similar Eurasian forests but approximately a quarter of those found in typically more intense North American boreal wildfires. N loss was insignificant, though a large amount of fire-affected fuel was converted to a low C : N surface layer of char in proportion to increased MAT. These results reveal large quantitative differences in C and N losses between global regions and their linkage to the broad range of climate conditions within Fennoscandia. A need exists to better incorporate these factors into models to improve estimates of global emissions of C and N due to fire in future climate scenarios. Additionally, this study demonstrated a linkage between climate and the extent of charring of soil fuel and discusses its potential for altering C and N dynamics in postfire recovery. [ABSTRACT FROM AUTHOR]

Aim: Climate change is occurring at accelerated rates in high latitude regions such as Alaska, causing alterations in woody plant growth and associated ecosystem patterns and processes. Our aim is to assess the magnitude and speed that climate‐induced changes in woody plant distribution and volume may be reduced and/or slowed by relatively static landscape features like physical characteristics (e.g. depth to gravel, mineral cover percent and slope degree) and/or edaphic properties (e.g. soil organic matter, soil pH and site wetness rating) that resist climate‐vegetation responses. Location: We leveraged a large field data set collected across a network of Alaskan national parks, which allows for comprehensive spatial data analysis over a uniquely large spatial extent. Methods: To learn about the conditions that may either impede or accelerate vegetation changes in northern Alaska, we used a Bayesian hierarchical model to identify which landscape features may decelerate change or offer refuge for plant species. Our model quantifies the contribution of fast ('dynamic') versus slow ('static') changing variables to predict plant volume and categorize landscape types into either robust or nonrobust to climate changes. Results: We found that two landscape features, low soil wetness and low soil organic matter comprising 63.1% of sites in the data set, were the most likely landscape features to inhibit vegetation expansion. We also found that fewer numbers of sites have the potential to offer refuge to existing plant species (5.43% on average) because few sites had high soil wetness as a landscape feature. Main conclusions: Our analyses highlight the importance of incorporating static covariates representing landscape resistance to vegetation change for improving realism in forecasts of vegetation change in Alaska. [ABSTRACT FROM AUTHOR]