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Climate warming and permafrost thaw induced land cover change are well documented in much of the circumpolar north. The extensive exposure of Precambrian continental crust in Canada's Taiga Shield ecoregion could mean impacts of land cover change documented in other regions without this feature are not transferable. This study examined energy partitioning with eddy covariance measurements, vegetation water use with stable isotopes and soil water state with time domain reflectometry sensors in conifer stands in the Taiga Shield ecoregion. The goal was to determine how changes in forest density with climate warming could influence water budget response and soil water state. Paired measurements of sensible and latent heat imply evaporative processes in denser canopies are controlled more by radiative than the aerodynamic factors predominant in sparser canopies. As denser canopies become more prevalent on the landscape, this switch in relative importance of evapotranspirative processes will lead to a reduction in inter‐annual variability of evapotranspiration. The dominant tree species (black spruce, tamarack and jack pine) were all quick to draw water from shallow soils after spring thaw and rainfall. Stand structural changes resulted in older, more evaporatively enriched water prevalent in soils below dense canopies. While there is evidence for forest infilling, widespread lakes and exposed bedrock restricts extensive expansion of forested land covers. The insufficient difference between sparse and dense canopy evapotranspiration suggest a fundamental change in how water cycles in Taiga Shield catchments is unlikely, which is notably different than previously investigated landscapes in Alaska and the Canadian Taiga Plains. Key Points: Evapotranspiration becomes less sensitive to precipitation variability as canopy density increases in Taiga Shield forestsTaiga vegetation tends to draw younger less evaporatively enriched soil water, and denser forests tend to have older more evaporatively enriched water in soils by the end of the growing seasonIncreased forest cover is not expected to change catchment water cycles because open water and exposed bedrock restrict tree expansion [ABSTRACT FROM AUTHOR]

This study investigates whether an exposure to two different received sound pressure levels at equal cumulative energy affects anti-predator behaviour and auditory detection thresholds of common roach (Rutilus rutilus) and sand goby (Pomatoschistus minutus) differently. This was examined in regard to a vessel slowdown as a management strategy to decrease vessel noise impact on fishes. Using continuous broadband noise, we found significant temporary threshold shifts (TTS) in roach, with 11.9 and 13.4 dB at 250 and 1000 Hz respectively, for the louder exposure. In contrast, gobies exhibited a non-significant shift of 6.6 dB at 125 Hz. Group cohesion increased in roach exposed to an artificial predator in the control group, but not during noise exposures. Gobies showed an initial freezing reaction towards the predator stimulus remaining motionless regardless of treatment. Our results show that a reduction in vessel speed with a corresponding reduction in source level could mitigate the effects on the auditory senses of sensitive fish, but does not appear to have any mitigating effect on their noise-induced behavioural changes. Further studies should investigate the effects of multiple vessel passages, but also the ecological consequences of the described effects on hearing and behaviour at individual and population level., (© 2023 Acoustical Society of America.)

The North Sea faces intense ship traffic owing to increasing human activities at sea. As harbour seals (Phoca vitulina) are abundant top predators in the North Sea, it is hypothesised that they experience repeated, high-amplitude vessel exposures. Here, we test this hypothesis by quantifying vessel noise exposures from deployments of long-term sound and movement tags (DTAGs) on nine harbour seals from the Wadden Sea. An automated tool was developed to detect intervals of elevated noise in the sound recordings. An assessment by multiple raters was performed to classify the source as either vessels or other sounds. A total of 133 vessel passes were identified with received levels > 97 dB re 1µPa RMS in the 2 kHz decidecade band and with ambient noise > 6 dB below this detection threshold. Tagged seals spent most of their time within Marine Protected Areas (89 ± 13%, mean ± SD) and were exposed to high-amplitude vessel passes 4.3 ± 1.6 times per day. Only 32% of vessel passes were plausibly associated with an AIS-registered vessel. We conclude that seals in industrialized waters are exposed repeatedly to vessel noise, even in areas designated as protected, and that exposures are poorly predicted by AIS data., (© 2023. The Author(s).)

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.)

Fire is regarded as an essential climate variable, emitting greenhouse gases in the combustion process. Current global assessments of fire emissions traditionally rely on coarse remotely sensed burned-area data, along with biome-specific combustion completeness and emission factors (EFs). However, large uncertainties persist regarding burned areas, biomass affected, and emission factors. Recent increases in resolution have improved previous estimates of burned areas and aboveground biomass while increasing the information content used to derive emission factors, complemented by airborne sensors deployed in the tropics. To date, temperate forests, characterized by a lower fire incidence and stricter aerial surveillance restrictions near wildfires, have received less attention. In this study, we leveraged the distinctive fire season of 2022, which impacted western European temperate forests, to investigate fire emissions monitored by the atmospheric tower network. We examined the role of soil smoldering combustion responsible for higher carbon emissions, locally reported by firefighters but not accounted for in temperate fire emission budgets. We assessed the CO/CO2 ratio released by major fires in the Mediterranean, Atlantic pine, and Atlantic temperate forests of France. Our findings revealed low modified combustion efficiency (MCE) for the two Atlantic temperate regions, supporting the assumption of heavy smoldering combustion. This type of combustion was associated with specific fire characteristics, such as long-lasting thermal fire signals, and affected ecosystems encompassing needle leaf species, peatlands, and superficial lignite deposits in the soils. Thanks to high-resolution data (approximately 10 m) on burned areas, tree biomass, peatlands, and soil organic matter (SOM), we proposed a revised combustion emission framework consistent with the observed MCEs. Our estimates revealed that 6.15 Mt CO2 (±2.65) was emitted, with belowground stock accounting for 51.75 % (±16.05). Additionally, we calculated a total emission of 1.14 Mt CO (±0.61), with 84.85 % (±3.75) originating from belowground combustion. As a result, the carbon emissions from the 2022 fires in France amounted to 7.95 MtCO2-eq (±3.62). These values exceed by 2-fold the Global Fire Assimilation System (GFAS) estimates for the country, reaching 4.18 MtCO2-eq (CO and CO2). Fires represent 1.97 % (±0.89) of the country's annual carbon footprint, corresponding to a reduction of 30 % in the forest carbon sink this year. Consequently, we conclude that current European fire emission estimates should be revised to account for soil combustion in temperate forests. We also recommend the use of atmospheric mixing ratios as an effective monitoring system of prolonged soil fires that have the potential to re-ignite in the following weeks. [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]

Veteran trees are important elements in forests, as well as urban and suburban areas, and represent part of our cultural heritage. However, increasing age also brings a reduction in vitality. Information on tree physiological vitality can be gained by examining ecophysiological traits, such as photosynthesis, stomatal conductance, and leaf water potential. Here, we assess the effects of age on the photosynthesis and water status of 600-year-old pedunculate oak trees (Quercus robur L.) by comparing them with neighbouring 25-year-old trees. While gas exchange measurements indicated lowered photosynthesis in old trees, their maximum rates of Rubisco carboxylation and electron transport were similar to younger trees, suggesting that biochemical limitations to photosynthesis are not the reason behind their reduced vitality. Moreover, there was no difference in light-adapted and dark-adapted chlorophyll fluorescence between old and young trees. In contrast, stomatal conductance (under unlimited soil water availability) was lower, indicating increased stomatal limitations to photosynthesis in veteran trees. On the other hand, high water potential during mild summer drought conditions indicated better access to soil water in old trees, while stomatal conductance in old trees was higher than in young trees at night. A reduced ability to open and close stomata may be one of the reasons for the observed decline in veteran tree vitality, with a lowered ability to regulate stomatal conductance resulting in reduced carbon gain and unnecessarily high water loss. [ABSTRACT FROM AUTHOR]

An analysis of the quantitative participation of invasive alien species (IAS) in main types of natural forests in Bulgaria and artificial plantations with the participation of native and exotic species was carried out. The object of study are forest phytocoenoses in 62 permanent sample plots (PSP) on the territory of the country part of the network for large-scale monitoring ICP Forests, located at an altitude between 250 and 1800 m above sea level. The study was conducted in the period 2019-2023 and covers 4 of the regions of the monitoring network as follows: II - Sredna Stara Planina (northern slopes) (15 PSPs), IV A - Sredna Stara Planina (southern slopes) and Sredna Gora (eastern part) (10 PSPs), V - Osogovo, Kraishte, western slopes of Rila and Vitosha (19 PSPs) and VI - Mountains in Southwestern Bulgaria (18 PSPs). The results show that limiting the spread of invasive alien species in forest ecosystems is largely influenced by the degree of their autochthony, the pronounced vertical structure, the high canopy of the trees layer, good regeneration, health status and control over the anthropogenic factor. Most IAS are heliophytes and the high coverage of the trees layer prevents their penetration. Many of the native species characteristic of our forests are highly competitive with IAS with their adaptations for vegetative reproduction (via root and stem shoots) and allelopathic properties, which in natural forest ecosystems form a specific microclimate and background of biologically active substances that repel IAS. [ABSTRACT FROM AUTHOR]

The rapid warming of the Arctic-Boreal region has led to the concern that large amounts of methane may be released to the atmosphere from its carbon-rich soils, as well as subsea permafrost, amplifying climate change. In this review, we assess the various sources and sinks of methane from northern high latitudes, in particular those that may be enhanced by permafrost thaw. The largest terrestrial sources of the Arctic-Boreal region are its numerous wetlands, lakes, rivers and streams. However, fires, geological seeps and glacial margins can be locally strong emitters. In addition, dry upland soils are an important sink of atmospheric methane. We estimate that the net emission of all these landforms and point sources may be as much as 48.7 [13.3–86.9] Tg CH4 yr−1. The Arctic Ocean is also a net source of methane to the atmosphere, in particular its shallow shelves, but we assess that the marine environment emits a fraction of what is released from the terrestrial domain: 4.9 [0.4–19.4] Tg CH4 yr−1. While it appears unlikely that emissions from the ocean surface to the atmosphere are increasing, now or in the foreseeable future, evidence points towards a modest increase from terrestrial sources over the past decades, in particular wetlands and possibly lakes. The influence of permafrost thaw on future methane emissions may be strongest through associated changes in the hydrology of the landscape rather than the availability of previously frozen carbon. Although high latitude methane sources are not yet acting as a strong climate feedback, they might play an increasingly important role in the net greenhouse gas balance of the Arctic-Boreal region with continued climate change. [ABSTRACT FROM AUTHOR]

Boreal fire regimes are intensifying because of climate change, and the northern parts of boreal forests are underlain by permafrost. Boreal fires combust vegetation and organic soils, which insulate permafrost, and as such deepen the seasonally thawed active layer and can lead to further carbon emissions to the atmosphere. Current understanding of the environmental drivers of post-fire thaw depth is limited but of critical importance. In addition, mapping thaw depth over fire scars may enable a better understanding of the spatial variability in post-fire responses of permafrost soils. We assessed the environmental drivers of post-fire thaw depth using field data from a fire scar in a larch-dominated forest in the continuous permafrost zone in eastern Siberia. Particularly, summer thaw depth was deeper in burned (mean=127.3 cm, standard deviation (SD) = 27.7 cm) than in unburned (98.1 cm, SD=26.9 cm) landscapes 1 year after the fire, yet the effect of fire was modulated by landscape and vegetation characteristics. We found deeper thaw in well-drained upland, in open and mature larch forest often intermixed with Scots pine, and in high-severity burns. The environmental drivers basal area, vegetation density, and burn depth explained 73.3 % of the measured thaw depth variability at the study sites. In addition, we evaluated the relationships between field-measured thaw depth and several remote sensing proxies. Albedo, the differenced normalized burn ratio (dNBR), and the pre-fire normalized difference vegetation index (NDVI) derived from Landsat 8 imagery together explained 66.3 % of the variability in field-measured thaw depth. Moreover, land surface temperature (LST) displayed particularly strong correlations with post-fire thaw depth (r=0.65 , p<0.01). Based on these remote sensing proxies and multiple linear regression analysis, we estimated thaw depth over the entire fire scar. Our study reveals some of the governing processes of post-fire thaw depth development and shows the capability of Landsat imagery to estimate post-fire thaw depth at a landscape scale. [ABSTRACT FROM AUTHOR]

Under a warming climate, the occurrence of wildfires has been becoming increasingly more frequent in boreal forests and Arctic tundra over the last few decades. Wildfires can cause radical changes in forest ecosystems and the permafrost environment, such as the irreversible degradation of permafrost, succession of boreal forests, rapid and massive losses of soil carbon stock, and increased periglacial geohazards. Since 2016, we have gradually and more systematically established a network for studying soil nutrients and monitoring the hydrothermal state of the active layer and near-surface permafrost in the northern Da Xing'anling Mountains in Northeast China. Soil moisture content (depth of 0–9.4 m), soil organic carbon content (0–3.6 m), total nitrogen content (0–3.6 m), and total phosphorus and potassium content (0–3.6 m) datasets were obtained in 2016 via field sampling and subsequent laboratory tests. Ground temperature (0–20 m) and active layer thickness (2017–2022) datasets were obtained using thermistor cables that were permanently installed in boreholes or interpolated with these temperatures. The present data can be used to simulate changes in permafrost features under a changing climate and wildfire disturbances and to explore the changing interactive mechanisms of the fire–permafrost–carbon system in hemiboreal forests. Furthermore, they can provide baseline data for studies and action plans to support the carbon neutralization initiative and assessment of the ecological safety and management of the permafrost environment. These datasets can be easily accessed via the National Tibetan Plateau/Third Pole Environment Data Center (10.11888/Cryos.tpdc.300933, Li and Jin, 2024). [ABSTRACT FROM AUTHOR]

Terrestrial biomes and their biogeographic patterns have been derived from a large variety of variables including species distributions and bioclimate or remote sensing products. However, classifying the biosphere into biomes from a functional perspective using biophysical traits has rarely been tested. Such a trait-based biome classification has been limited by data availability. Here, we aimed to exploit crowd-sourced plant observations and trait databases to systematically assess which traits are most suitable for biome classification. We derived global patterns of 33 biophysical traits covering around 50 % of the land surface by combining crowd-sourced species distribution data from the Global Biodiversity Information Facility (GBIF) and trait observations from the TRY database. Using these trait maps as predictors for supervised cluster analyses, we tested to what extent we can reconstruct 31 published biome maps. A sensitivity analysis with randomly sampled combinations of traits was performed to identify the traits that are most appropriate for biome classification. Performance was quantified by comparing modeled biome maps and the respective observation-based biome maps. Finally, spatial gaps in the resulting biome maps were filled using species distribution models to obtain continuous global biome maps. We showed that traits can be used for biome classification and that the most appropriate traits are conduit density; rooting depth; height; and different leaf traits, including specific leaf area and leaf nitrogen content. The best performance of the biome classification was obtained for biome maps based on biogeographic zonation and species distributions, in contrast to biome maps derived from optical reflectance. The availability of crowd-sourced plant observations is heterogeneous, and, despite its exponential growth, large data gaps are prevalent. Nonetheless, it was possible to derive biome classification schemes from these data to predict global biome patterns with good agreement. Therefore, our analysis is a valuable approach towards understanding biome patterns based on biophysical traits and associated ecological strategies. [ABSTRACT FROM AUTHOR]

The hydrological cycle of sub-arctic areas is dominated by the snowmelt event. An understanding of the mechanisms that control water fluxes during high-volume infiltration events in sub-arctic till soils is needed to assess how future changes in the timing and magnitude of snowmelt can affect soil water storage dynamics. We conducted a tracer experiment in which deuterated water was used to irrigate a plot on a forested hilltop in Lapland, tracked water fluxes of different mobility and monitored how the later snowmelt modifies the labelled soil water storage. We used lysimeters and destructive soil coring for soil water sampling and monitored and sampled the groundwater. Large spatiotemporal variability between the waters of different mobility was observed in the subsurface, while surface water flow during the tracer experiment was largely controlled by a fill-and-spill mechanism. Extensive soil saturation induced the flow of labelled water into the roots of nearby trees. We found that labelled water remained in deeper soil layers over the winter, but the snowmelt event gradually displaced all deuterated water and fully homogenized all water fluxes at the soil–vegetation interface. The conditions required for the full displacement of the old soil water occur only during a snowmelt with a persistently high groundwater table. We propose a conceptual model where infiltration into the soil and eventual soil water replenishment occur in three stages. First, unsaturated macropore flow is initiated via the surface microtopography and is directed towards the groundwater storage. The second stage is characterized by groundwater rise through the macropore network, subsequent pore water saturation and increased horizontal connectivity of macropores. Shallow subsurface lateral fluxes develop in more permeable shallow soil layers. In the third stage, which materializes during a long period with a high groundwater table and high hydrological connectivity within the soil, the soil water is replenished via enhanced matrix flow and pore water exchange with the macropore network. [ABSTRACT FROM AUTHOR]

Biological nitrogen fixation (BNF) by symbiotic and free-living bacteria is an important source of plant-available nitrogen (N) in terrestrial ecosystems supporting carbon (C) sequestration and food production worldwide. Dynamic global vegetation models (DGVMs) are frequently used to assess the N and C cycles under dynamic land use and climate. BNF plays an important role in the components of both these cycles, making a robust representation of the processes and variables that BNF depends on important to reduce uncertainty within the C and N cycles and improve the ability of DGVMs to project future ecosystem productivity, vegetation patterns or the land C sink. Still, BNF is often modelled as a function of net primary productivity or evapotranspiration, and the actual drivers are neglected. We implemented plant-functional-type-specific limitations for BNF dependent on soil temperature and soil water content, as well as a cost of BNF, in the Lund–Potsdam–Jena managed Land (LPJmL) DGVM and compared the new ("C-costly") against the previous ("Original") approach and data from the scientific literature. For our comparison, we simulated a potential natural vegetation scenario and one including anthropogenic land use for the period from 1901 to 2016 for which we evaluate BNF and legume crop yields. Our results show stronger agreement with BNF observations for the C-costly than the Original approach for natural vegetation and agricultural areas. The C-costly approach reduced the overestimation of BNF, especially in hot spots of legume crop production. Despite the reduced BNF in the C-costly approach, yields of legume crops were similar to the Original approach. While the net C and N balances were similar between the two approaches, the reduced BNF in the C-costly approach results in a slight underestimation of N losses from leaching, emissions and harvest compared to the values in the literature, supporting further investigation of the underlying reasons, such as processes represented in DGVMs and scenario assumptions. While we see the potential for further model development, for example, to separate symbiotic and free-living BNF, the C-costly approach is a major improvement over the simple Original approach because of the separate representation of important drivers and limiting factors of BNF, and the C-costly approach also improves the ability of LPJmL to project future C and N cycle dynamics. [ABSTRACT FROM AUTHOR]

Retrogressive thaw slumps (RTSs) are spectacular landforms that occur due to the thawing of ice-rich permafrost or melting of massive ground ice, often in hillslope terrain. RTSs occur in the Arctic, the subarctic, and high mountain (Qinghai–Tibet Plateau) permafrost regions and are observed to expand in size and number due to climate warming. As the observation of RTSs is receiving more and more attention due to their important role in permafrost thaw; impacts on topography; mobilization of sediment, carbon, nutrients, and contaminants; and their effects on downstream hydrology and water quality, the thematic breadth of studies increases and scientists from different scientific backgrounds and perspectives contribute to new RTS research. At this point, a wide range of terminologies originating from different scientific schools is used, and we identified the need to provide an overview of variable characteristics of RTSs to clarify terminologies and ease the understanding of the literature related to RTS processes, dynamics, and feedbacks. We review the theoretical geomorphological background of RTS formation and landform characteristics to provide an up-to-date understanding of the current views on terminology and underlying processes. The presented overview can be used not only by the international permafrost community but also by scientists working on ecological, hydrological, and biogeochemical consequences of RTS occurrence and by remote-sensing specialists developing automated methods for mapping RTS dynamics. The review will foster a better understanding of the nature and diversity of RTS phenomena and provide a useful base for experts in the field but also ease the introduction to the topic of RTSs for scientists who are new to it. [ABSTRACT FROM AUTHOR]

The Black Sea is a semi‐enclosed inland sea with an unevenly distributed extensive coastal shelf area and anoxic deep waters. It is inhabited by common and bottlenose dolphins, as well as harbour porpoises, all represented by local subspecies. Between September 2020 and October 2022, 19 F‐PODs deployed by research teams from Bulgaria, Georgia, Romania, Türkiye and Ukraine collected data on acoustic activity of Black Sea harbour porpoises. Strong seasonal and diel patterns were found, which varied in three regions. In the south‐eastern part of the Black Sea, harbour porpoise acoustic activity was higher from January to May, with a peak in April. This pattern agrees with the seasonal anchovy migration from the winter spawning grounds in warmer waters in the south‐eastern region to feeding grounds on the productive shallow north‐west shelf. The diel pattern showed strong nocturnal acoustic activity, which is consistent with anchovy vertical migration. Porpoises on the western side of the Black Sea exhibited a bimodal seasonal pattern in acoustic activity, with a larger peak in April and a smaller one in October. Diel activity was primarily nocturnal. On the north‐west shelf, harbour porpoise acoustic activity was mostly recorded during the warm period from April to October. The diel pattern showed activity mainly during daylight with two peaks: a smaller one approximately at dawn and a larger one at dusk. This pattern is similar to the vertical migrations of sprat. Overall, the results of the study were consistent with the prey being an important driver of seasonal and diel dynamics of harbour porpoise acoustic activity. [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]

Introduction: To investigate the differences in the response of radial growth of larch (Larix gmelinii) at varying altitude gradients to climatic factors, this study established tree-ring width chronologies of Larix gmelinii at altitudes of 900 m, 1,120 m and 1,300 m based dendroclimatology. Methods: We also employed R packages including "dplR," "static" and "moving" to determine the correlation between larch at different altitudes and climatic factors and to explore the sensitivity and stability between radial growth and the climate of larch at different altitudes in the northern part of the Greater Khingan Mountains Range in Northeast China. Results: The results revealed the radial growth of larch in high altitude areas to exhibit a downward trend due to climate warming, while the growth of trees in intermediate and low altitude areas showed an upward trend. The growth-- climate relationship exhibited a significant negative correlation between radial growth in low altitude larch (900 m) and temperatures in the current winter (February and March) and growing season (July, October of the current year, and October of the previous year) (p < 0.05). Moreover, high altitude larch (1,300 m) showed a significant negative correlation with temperature in January, March, and October of the current year (p < 0.05). However, in intermediate altitude areas (1,120 m), the radial growth of trees was significantly positively correlated with the temperature of the growing season (May, June and August). Precipitation in April was observed to promote the radial growth of low-altitude larch. Moving correlation analysis revealed that the inhibitory effect of low temperatures in winter and high temperatures in the growing season on the radial growth of larch at three altitudes gradually strengthened, transitioning from significant negative/positive correlations to significant positive/negative correlations along the altitudinal gradient. Discussion: Larch trees in high and low altitudes exhibited an increased sensitivity to winter and spring precipitation, while in the intermediate region, the inhibitory effect of growing season precipitation on larch radial growth continued to intensify. The results of the study have an important reference value for the indepth understanding of the growth dynamics of Larix gmelinii natural forests in the northern part of the Greater Khingan Mountains under climate change. [ABSTRACT FROM AUTHOR]

Sap flow measurements are fundamental to understanding water use in trees and could aid in predicting climate change effects on forest function. Deriving knowledge from such measurements requires empirical calibrations and upscaling methods to translate thermometric recordings to tree water use. Here, we developed a user‐friendly open‐source application, the Sap Flow Analyzer (SFA), which estimates sap flow rates and tree water use from the heat field deformation (HFD) instruments.The SFA incorporates four key features to ensure maximum accuracy and reproducibility of sap flow estimates: diagnosis diagrams to assess data patterns visually, regression models implemented to increase accuracy when estimating K (the main HFD parameter), three approaches to upscale sap flow rates to whole‐tree water use and visualization of the input parameters' uncertainty. Thirteen participants were given three raw datasets and assigned data processing tasks using the SFA user guide, from estimating sapwood depth to scaling sap flow rates to whole‐tree water use to assess the reproducibility and applicability of the SFA.Participants' results were reasonably consistent and independent of their background in using the SFA, R, or HFD method. The results showed lower variability for high flow rates (SD: mean 1% vs. 10%). K estimates and sapwood depth differentiation were the primary sources of variability, which in turn was mainly caused by the user's chosen scaling method.The SFA provides an easy way to visualize and process sap flow and tree water use data from HFD measurements. It is the first free and open software tool for HFD users. The ability to trace analysis steps ensures reproducibility, increasing transparency and consistency in data processing. Developing tools such as the SFA and masked trials are essential for more precise workflows and improved quality and comparability of HFD sap flow datasets. [ABSTRACT FROM AUTHOR]

Successful management requires information on pressures that threaten a species and areas where conservation actions are needed. The Baltic Proper harbour porpoise population was first listed as Critically Endangered by the International Union for the Conservation of Nature in 2008. Now, 16 years later, there is no change in conservation status despite ample conservation policy calling for its protection and an urgent need for management action to protect this population. Here, we provide an overview of the current status of the population, highlight knowledge gaps on the impact of pressures, and make recommendations for management of anthropogenic activities. Based on an exceeded limit for anthropogenic mortality, the high concentrations of contaminants in the Baltic Sea, combined with reductions in prey availability and increases in underwater noise, it is inferred that this population is likely still decreasing in size and conservation action becomes more urgent. As bycatch and unprotected underwater explosions result in direct mortality, they must be reduced to zero. Inputs of contaminants, waste, and existing and emerging noise sources should be minimised and regulated. Additionally, ecosystem‐based sustainable management of fisheries is paramount in order to ensure prey availability, and maintain a healthy Baltic Sea. Stranding networks to routinely assess individuals for genetic population assignment and health need to be expanded, to identify rare samples from this population. Knowledge is still scarce on the population‐level impact of each threat, along with the cumulative impact of multiple pressures on the population. However, the current knowledge and management instruments are sufficient to apply effective protection for the population now. While bycatch is the main pressure impacting this population, urgent conservation action is needed across all anthropogenic activities. Extinction of the Baltic Proper harbour porpoise population is a choice: decision‐makers have the fate of this genetically and biologically distinct marine mammal population in their hands. [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., (© 2023 His Majesty the King in Right of Canada and The Authors. Ecological Applications published by Wiley Periodicals LLC on behalf of The Ecological Society of America. Reproduced with the permission of the Minister of Natural Resources.)

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]

Altered fire regimes, combined with a warmer and drier climate, have been eroding the resilience of temperate rainforests and peatlands worldwide and leading to alternative post-fire vegetation communities. Chronic anthropogenic burning of temperate rainforests at the forest-peatland ecotone in western Patagonia appears to have shifted vegetation communities in poorly-drained sites from forests dominated by the threatened conifer, Pilgerodendron uviferum, to peat-accumulating wetlands covered by Sphagnum mosses. We collected and modeled post-reburn field data using ordinations and hierarchical Bayesian regressions to examine mechanisms through which P. uviferum forests may recover following fire or become locked into alternative development pathways by comparing biophysical factors of a reburned ecotone to those of an unburned (control) ecotone. We found that, (1) the significantly higher densities of P. uviferum trees and seedlings in the forested patches at both the reburned and control sites were associated with significantly lower seasonal water tables, lower cover of Sphagnum mosses and higher cover of other mosses (i.e., not in the Sphagnum or Dicranaloma genera); (2) despite abrupt boundaries in vegetation at both sites, successive fires homogenized the environment at the reburned site; and (3) the distinct life forms and individual species that characterized the understory plant communities across the ecotones affected seedling abundance by shaping microtopography and the substrates available for establishment. Together, our results suggest that fire can push edaphically wet P. uviferum-dominated sites towards a non-forested state by reducing the diversity of microsite structure and composition, thereby placing P. uviferum seedlings in direct competition with Sphagnum mosses and potentially limiting the availability of microsites that are protected from both seasonal inundation and seasonal drought. If wildfires continue under increasingly warmer and drier conditions, the forestpeatland ecotone of western Patagonia may be susceptible to large-scale transformation towards a non-forested state. [ABSTRACT FROM AUTHOR]

The moist Afromontane forest of Ethiopia plays a crucial role in carbon storage and mitigating greenhouse gas (GHG) emissions. To guide effective conservation policies, it is essential to understand the relationship between species diversity and carbon storage in this unique ecosystem. Therefore, this study aimed to evaluate the response of aboveground carbon (AGC) to species and functional diversity and their effects on AGC in the Yayu Coffee Forest Biosphere Reserve (YCFBR). Using different plot sizes, we collected vegetation data from the core, buffer, and transitional zones of the reserve. We selected traits related to plant‐life strategy, competition ability, response to disturbances, and climate change. Structural equation models (SEMs) were employed to assess the effects of species diversity, functional diversity, and functional dominance on AGC. Data analysis was conducted using R software. Our results revealed that the effects of species richness on AGC were mediated through functional diversity and functional dominance, as demonstrated by both the full mediation and partial mediation models. This suggests that the selection effects and niche complementarity are mutually exclusive yet equally important for predicting AGC. The findings further indicate that functional diversity and functional dominance together accounted for significant predictors of the AGC by 21% in the YCFBR. From a practical standpoint, findings highlight the importance of conserving species diversity as a means to maintain higher AGC in the tropical moist Afromontane forests. In conclusion, this research significantly contributes to the scientific literature by providing valuable insights into the complex relationship between species diversity and carbon storage. The results emphasize the crucial role of functional diversity and dominance in predicting AGC, underscoring the importance of biodiversity conservation for climate mitigation efforts. These findings have practical implications for the development of effective conservation policies tailored to protect and sustain the carbon storage potential of this unique ecosystem. [ABSTRACT FROM AUTHOR]

The stabilization and application of expansive geomaterials are critical in geotechnical engineering. These naturally expansive materials exhibit complex hydro-chemo-mechanical properties because they undergo volumetric changes in response to variations in moisture content and/or temperature. The characteristic shrink-swell behavior of these materials makes their use problematic and plays a substantial role in influencing the stability of geo-infrastructure applications. However, there is a lack of comprehensive knowledge of the mechanisms and factors impacting their behavior to ensure mechanical integrity in natural and built infrastructure and geo-engineering projects. This work provides a comprehensive review of the intrinsic and extrinsic factors contributing to the shrink-swell behavior and expansion mechanisms of frost-heaving and natural-expansive geomaterials, such as expansive clays and sulfate minerals. We reviewed and synthesized peer-reviewed published works in various databases and academic repositories in the last 100 years. The influence of shrink-swell behavior of these geomaterials and the critical role they play in engineering infrastructure were highlighted, explicitly focusing on their involvement in geotechnical-related hazards, such as the freeze-thaw cycle, and the damage and sulfate-attack of geo-infrastructure. We analyzed the interactions between clay minerals, especially how bentonite enhances grout stability and acts as a buffer material in high-level nuclear waste repositories. The findings indicate that water interaction with geomaterials and concrete can cause about a 10% volume expansion when frozen. Also, the exposure of fractured rocks to low (<0°C) and high (>0°C) temperatures can greatly change rock deformation and strength. Finally, gypsum interacting with water can theoretically increase in volume by 62% to form ice crystals. This forward-leading review presents the advantages, disadvantages, and unresolved issues of expansive natural geotechnical materials that improve the resiliency and sustainability of geological infrastructure. [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]

Terrestrial biosphere models are a key tool in investigating the role played by land surface in the global climate system. However, few models simulate the geographic distribution of biomes dynamically, opting instead to prescribe them using remote sensing products. While prescribing land cover still allows for the simulation of the impacts of climate change on vegetation growth and the impacts of land use change, it prevents the simulation of climate-change-driven biome shifts, with implications for the projection of future terrestrial carbon sink. Here, we isolate the impacts of prescribed vs. dynamic land cover implementations in a terrestrial biosphere model. We first introduce a new framework for evaluating dynamic land cover (i.e., the spatial distribution of plant functional types across the land surface), which can be applied across terrestrial biosphere models alongside standard benchmarking of energy, water, and carbon cycle variables in model intercomparison projects. After validating simulated land cover, we then show that the simulated terrestrial carbon sink differs significantly between simulations with dynamic vs. prescribed land cover for a high-CO 2 future scenario. This is because of important range shifts that are only simulated when dynamic land cover is implemented: tree expansion into the Arctic and Amazonian transition from forest to grassland. In particular, the projected change in net land–atmosphere CO 2 flux at the end of the 21st century is twice as large in simulations with dynamic land cover than in simulations with prescribed land cover. Our results illustrate the importance of climate-change-driven biome shifts for projecting future terrestrial carbon sink. [ABSTRACT FROM AUTHOR]

Relating forest productivity to local variations in forest structure has been a long-standing challenge. Previous studies often focused on the connection between forest structure and stand-level photosynthesis (gross primary production – GPP). However, biomass production (net primary production – NPP) and net ecosystem exchange (NEE) are also subject to respiration and other carbon losses, which vary with local conditions and life history traits. Here, we use a simulation approach to study how these losses impact forest productivity and reveal themselves in forest structure. We fit the process-based forest model FORMIND to a 25 ha inventory of an old-growth temperate forest in China and classify trees as "mature" (fully grown) or "immature" based on their intrinsic carbon use efficiency. Our results reveal a strong negative connection between the stand-level carbon use efficiency and the prevalence of mature trees: gross primary production (GPP) increases with the total basal area, whereas net primary production (NPP) and NEE are driven by the basal area of immature trees. Accordingly, the basal area entropy, a structural proxy for the prevalence of immature trees, correlated well with NPP and NEE and had a higher predictive power than other structural characteristics, such as the Shannon diversity and height standard deviation. Our results were robust across spatial scales (0.04–1 ha) and yield promising hypotheses for field studies and new theoretical work. [ABSTRACT FROM AUTHOR]

Forestation can contribute to climate change mitigation. However, increasing frequency and intensity of climate extremes are posed to have profound impact on forests and consequently on the mitigation potential of forestation efforts. In this perspective, we critically assess forestation-reliant climate mitigation scenarios from five different integrated assessment models (IAMs) by showcasing the spatially explicit exposure of forests to fire weather and the simulated increase in global annual burned area. We provide a detailed description of the feedback from climate change to forest carbon uptake in IAMs. Few IAMs are currently accounting for feedback mechanisms like loss from fire disturbance. Consequently, many forestation areas proposed by IAM scenarios will be exposed to fire-promoting weather conditions and without costly prevention measures might be object to frequent burning. We conclude that the actual climate mitigation portfolio in IAM scenarios is subject to substantial uncertainty and that the risk of overly optimistic estimates of negative emission potential of forestation should be avoided. As a way forward we propose how to integrate more detailed climate information when modeling climate mitigation pathways heavily relying on forestation. [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]

Moose (Alces alces) in the boreal forest habitats of Alaska are unlike other northern ungulates because they tolerate high densities of flies (Diptera) even though flies cause wounds and infections during the warm summer months. Moose move to find food and to find relief from overheating (hyperthermia) but do they avoid flies? We used GPS collars to measure the rate of movement (m⋅h−1) and the time spent (min⋅day−1) by enclosed moose in four habitats: wetlands, black spruce, early seral boreal forest, and late seral boreal forest. Fly traps were used in each habitat to quantify spatio‐temporal abundance. Average daily air temperatures increased into July when peak biomass of forage for moose was greatest in early seral boreal forest habitats (424.46 vs. 25.15 kg⋅ha−1 on average in the other habitats). Average daily air temperatures were 1.7°C cooler in black spruce than other habitats, but fly abundance was greatest in black spruce (approximately 4‐fold greater on average than the other habitats). Moose increased their movement rate with counts of biting flies (mosquitoes, black flies, horse and deer flies), but not non‐biting flies (coprophagous flies). However, as air temperature increased (above 14.7°C) moose spent more time in fly‐abundant black spruce, than early seral boreal forest, showing great tolerance for mosquitoes. Warm summer temperatures appear to cause moose to trade‐off foraging in fly‐sparse habitats for resting and dissipating heat in shady, wet habitats with abundant flies that adversely affect the fitness of moose. [ABSTRACT FROM AUTHOR]

Ground ice maps at small scales offer generalized depictions of abundance across broad circumpolar regions. In this paper, the effect of surficial geology mapping scale on modelled ground ice abundance is examined in the Slave Geological Province of the Canadian Shield, a region where the geological and glacial legacy has produced a landscape with significant variation in surface cover. Existing model routines from the Ground ice map of Canada (GIMC) were used with a 1:125000 -scale regional surficial geology compilation and compared to the national outputs, which are based on surficial geology at a 1:5000000 scale. Overall, the regional-scale modelling predicts much more ground ice than the GIMC due to greater representation of unconsolidated sediments in the region. Improved modelling accuracy is indicated by comparison of the outputs to empirical datasets due to improved representation of the inherent regional heterogeneity in surficial geology. The results demonstrate that the GIMC significantly underestimates the abundance and distribution of ground ice over Canadian Shield terrain. In areas with limited information on ground ice, regional-scale modelling may provide useful reconnaissance-level information to help guide the field-based investigations required for planning infrastructure development. The use of current small-scale ground ice mapping in risk or cost assessments related to permafrost thaw may significantly influence the accuracy of outputs in areas like the Canadian Shield, where surficial materials range from bedrock to frost-susceptible deposits over relatively short distances. [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]

The ecosystem of the water level fluctuation (WLF) zone of the Three Gorges Reservoir (TGR) is highly vulnerable and sensitive due to its unique cyclical flooding and drought conditions. The ecological impact of biological invasion in this area is particularly severe, making it crucial to study the differences in resource utilization strategies between invasive plants (IPs) and native plants (NPs) using functional traits to explore the mechanisms of invasion. We selected the WLF zone of Pengxi River in the TGR area and conducted a multi-scale study along the elevation gradient. The results reveal that at the regional scale, IPs have a larger height and specific leaf area, smaller leaf tissue density, and specific root length compared to NPs, showing a preference for enhancing aboveground resource acquisition over leaf defense capabilities. They allocate more tissue construction resources to their roots to withstand environmental pressures, which may be the key to their successful intrusion, highlighting the role of niche differentiation. On the community scale, the H and SLA of IPs and NPs are positively correlated with elevation, while the LTD of IPs shows a negative correlation. At elevations of 175 m and below, IP and NP exhibit functional convergence, while above 175 m, functional divergence was observed. This indicates that although the different resource utilization strategies are crucial for successful IP invasion, the environmental filtering from periodic floods and drought pressures play a significant role in community assembly in the WLF zone, allowing IP to integrate into habitats with similar functional characteristics already inhabited by NP and establish their own communities. [ABSTRACT FROM AUTHOR]