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Tropical forests are a major component of the global carbon cycle and home to two‐thirds of terrestrial species. Upper‐canopy trees store the majority of forest carbon and can be vulnerable to drought events and storms. Monitoring their growth and mortality is essential to understanding forest resilience to climate change, but in the context of forest carbon storage, large trees are underrepresented in traditional field surveys, so estimates are poorly constrained. Aerial photographs provide spectral and textural information to discriminate between tree crowns in diverse, complex tropical canopies, potentially opening the door to landscape monitoring of large trees. Here we describe a new deep convolutional neural network method, Detectree2, which builds on the Mask R‐CNN computer vision framework to recognize the irregular edges of individual tree crowns from airborne RGB imagery. We trained and evaluated this model with 3797 manually delineated tree crowns at three sites in Malaysian Borneo and one site in French Guiana. As an example application, we combined the delineations with repeat lidar surveys (taken between 3 and 6 years apart) of the four sites to estimate the growth and mortality of upper‐canopy trees. Detectree2 delineated 65 000 upper‐canopy trees across 14 km2 of aerial images. The skill of the automatic method in delineating unseen test trees was good (F1 score = 0.64) and for the tallest category of trees was excellent (F1 score = 0.74). As predicted from previous field studies, we found that growth rate declined with tree height and tall trees had higher mortality rates than intermediate‐size trees. Our approach demonstrates that deep learning methods can automatically segment trees in widely accessible RGB imagery. This tool (provided as an open‐source Python package) has many potential applications in forest ecology and conservation, from estimating carbon stocks to monitoring forest phenology and restoration. Python package available to install at https://github.com/PatBall1/Detectree2.

Climate change is driving widespread changes in ecological communities. Warming temperatures often shift community composition toward more heat-tolerant taxa. The factors influencing the rate of this “thermophilization” process remain unclear. Using 10-y census data from an extensive forest plot network, we show that mature tree communities of the western United States have undergone thermophilization. The mean magnitude of climate warming over the 10-y study interval was 0.32 °C, whereas the mean magnitude of thermophilization was 0.039 °C. Differential tree mortality was the strongest demographic driver of thermophilization, rather than growth or recruitment. Thermophilization rates are associated with recent changes in temperature and hydrologic variables, as well as topography and disturbance, with insect damage showing the strongest standardized effect on thermophilization rates. On average, thermophilization occurred more rapidly on cool, north-facing hillslopes. Our results demonstrate that warming temperatures are outpacing the composition of western US forest tree communities, and that climate change may erode biodiversity patterns structured by topographic variation.

During recent decades, tree mortality and dieback have been reported in forest ecosystems across global biomes. Although numerous forest species, including those of the genus Quercus, have been affected by hotter and drier conditions in the Mediterranean Basin during the last decades, there is scarce information regarding the interactive role of past management and climate across large areas of south-western Europe. Here, we examined the influence of several climatic factors (mean annual temperature, annual precipitation) over the last 3 decades, latitude, land management and site conditions on the cork oak (Quercus suber L.) population dynamics given their high ecological and economic relevance. We sampled 20 plots across contrasting environmental conditions in SW Iberian Peninsula with different land property (public vs. private) to characterize cork oak tree size, stand density, mortality ratio and regeneration. We observed widespread effects of latitude (8.9% at northern vs. 15.6% at southern plots) and land property (6.9% in private properties vs. 13.9% in public ones) on tree mortality. Tree density and basal area differed with latitude, with higher values (307.2 trees ha-1 and 38.4 m2 ha-1, respectively) at northern populations. In addition, the more intense cork-focused productive management resulted in higher tree sizes in private (mean DBH = 47.3 cm) than in public (mean DBH = 37.8 cm) plots. Tree regeneration was higher in northern forests (94.9 ± 25.2 vs. 26.0 ± 6.1 saplings ha-1 for the southern location), being this difference more pronounced in public plots. These findings highlight the importance of sustainable forest management in public and private forests for further reduction of mortality processes, as well as for enhancing the regeneration aimed to the conservation of cork oak under forecasted drier conditions of these economically invaluable Mediterranean forests.

15 páginas, 4 figuras, Dynamic resource availability leads to trade-offs among functions in plants. The growth-differentiation balance hypothesis (GDBH) predicts greater allocation of carbon to defense than growth when resources are scarce, with optimum defense production occurring at a point between the minimum and maximum growth rates. While the GDBH has been widely tested, consideration of phenotypic variation in rates for which defense is traded for growth and what this variation means for plant resistance remains rare. For defense, pines produce and store oleoresin in “resin ducts.” Retrospective comparisons of resin ducts in pines have revealed that trees with greater numbers, sizes, or areas of xylem resin ducts are more likely to avoid or survive insect attack. We used tree ring chronologies to quantify phenotypic variation in growth and resin duct defenses in pairs of living and bark beetle-killed Pinus ponderosa trees in southern New Mexico, USA, and to test the utility of the GDBH for explaining tree mortality. We also assessed the sensitivity of annual growth to climate and competitor density in years preceding mortality in each pair. Survivors had greater growth rates and total cross-sectional areas of resin ducts than trees killed by bark beetles. We did not observe a difference in climate–growth relationships among the groups; however, trees killed by bark beetles suffered negative effects of competition while survivors did not. Growth-defense trade-offs conformed to the GDBH's prediction of a quadratic relationship; however, the two groups significantly differed in the rate at which defense was traded for increasing levels of annual growth. Our results demonstrate that phenotypic variation in the trade-off between growth and defense could be used to characterize trees that were killed by or survived recent natural enemy epidemics. We hypothesize that the GDBH could be integrated with the characterization of phenotypic variation in growth-differentiation strategies—along with parsing of gene versus environment influences on phenotypes—at both local and landscape scales to increase our understanding of patterns of natural enemy impacts in plant populations.

Many studies show that mixed species stands can have higher gross growth, or so-called overyielding, compared with monocultures. However, much less is known about mortality in mixed stands. Knowledge is lacking, for example, of how much of the gross growth is retained in the standing stock and how much is lost due to mortality. Here, we addressed this knowledge gap of mixed stand dynamics by evaluating 23 middle-aged, unthinned triplets of monospecific and mixed plots of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) repeatedly surveyed over 6–8 years throughout Europe. For explanation of technical terms in this abstract see Box 1. First, mixed stands produced more gross growth (+10%) but less net growth (−28%) compared with the weighted mean growth of monospecific stands. In monospecific stands, 73% of the gross growth was accumulated in the standing stock, whereas only 48% was accumulated in mixed stands. The gross overyielding of pine (2%) was lower than that of beech (18%). However, the net overyielding of beech was still 10%, whereas low growth and dropout of pine caused a substantial reduction from gross to net growth. Second, the mortality rates, the self- and alien-thinning strength, and the stem volume dropout were higher in mixed stands than monospecific stands. The main reason was the lower survival of pine, whereas beech persisted more similarly in mixed compared with monospecific stands.Third, we found a 10% higher stand density in mixed stands compared with monospecific stands at the first survey. This superiority decreased to 5% in the second survey.Fourth, the mixing proportion of Scots pine decreased from 46% to 44% between the first and second survey. The more than doubling of the segregation index (S) calculated by Pielou index (S increased from 0.2 to 0.5), indicated a strong tendency towards demixing due to pine. Fifth, we showed that with increasing water supply the dropout fraction of the gross growth in the mixture slightly decreased for pine, strongly increased for beech, and also increased for the stand as a whole. We discuss how the reduction of inter-specific competition by thinning may enable a continuous benefit of diversity and overyielding of mixed compared with monospecific stands of Scots pine and European beech., The study received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No952314 and under the Marie Skłodowska-Curie grant agreement No 778322. The first author also wishes to thank the German ScienceFoundation (Deutsche Forschungsgemeinschaft) for funding the project “Structure and dynamics of mixed-species stands of Scots pine and European beech compared with monospecific stands; analysis along an ecological gradient through Europe” (# DFG PR 292/15-1). Felipe Bravo is grateful for Funds by the Junta de Castilla y León through the projects “CLU-2019-01 and CL-EI-2021-05 - iuFOR Institute Unit of Excellence” of the University of Valladolid and the co-financing by the European Regional Development Fund (ERDF “Europe drives our growth”). Miren del Río thanks for the support by the Spanish Ministerio de Ciencia e Innovación (# PID2021-126275OB-C21/C22). Dejan Stojanović thanks the Ministry of Education, Science and Technological Development of the Republic of Serbia for funding. Tzvetan Zlatanov thanks the Ministry of Education and Science of the Republic of Bulgaria (# DO1-405/18.12.2020 LTER-BG).

Tropical forests are a major component of the global carbon cycle and home to two-thirds of terrestrial species. Upper-canopy trees store the majority of forest carbon and can be vulnerable to drought events and storms. Monitoring their growth and mortality is essential to understanding forest resilience to climate change, but in the context of forest carbon storage, large trees are underrepresented in traditional field surveys, so estimates are poorly constrained. Aerial photographs provide spectral and textural information to discriminate between tree crowns in diverse, complex tropical canopies, potentially opening the door to landscape monitoring of large trees. Here we describe a new deep convolutional neural network method,Detectree2, which builds on the Mask R-CNN computer vision framework to recognise the irregular edges of individual tree crowns from airborne RGB imagery. We trained and evaluated this model with 3,797 manually delineated tree crowns at three sites in Malaysian Borneo and one site in French Guiana. As an example application, we combined the delineations with repeat lidar surveys (taken between 3 and 6 years apart) of the four sites to estimate the growth and mortality of upper-canopy trees.Detectree2delineated 65,000 upper-canopy trees across 14 km2of aerial images. The skill of the automatic method in delineating unseen test trees was good (F1score = 0.64) and for the tallest category of trees was excellent (F1score = 0.74). As predicted from previous field studies, we found that growth rate declined with tree height and tall trees had higher mortality rates than intermediate-size trees. Our approach demonstrates that deep learning methods can automatically segment trees in widely accessible RGB imagery. This tool (provided as an open-source Python package) has many potential applications in forest ecology and conservation, from estimating carbon stocks to monitoring forest phenology and restoration.Python package available to install athttps://github.com/PatBall1/Detectree2

Investigating the responses of plant anatomical traits of trees to drought–rewatering cycles helps us to understand their responses to climate change; however, such work has not been adequately reported. In this study, Ginkgo biloba L. saplings were subjected to moderate, severe, extreme and lethal drought conditions by withholding water according to the percentage loss of hydraulic conductivity (PLC) and rewatering on a regular basis. Samples of phloem, cambium and xylem were collected to quantify their cellular properties including cambium and phloem cell vitality, xylem growth ring width, pit aspiration rates and pit membrane thickness using light microscopy and transmission microscopy. The results showed that the mortality rate of G. biloba saplings reached 90% at approximately P88 (xylem water potential inducing 88% loss of hydraulic conductivity). The onset of cambium and phloem cell mortality might be in accordance with that of xylem embolism. Close negative correlations between xylem water potential and PLC and between xylem water potential and cambium and phloem mortality suggested that xylem hydraulic traits are coupled with anatomical traits under declining xylem water potential. Cambium and phloem cell vitality as well as xylem growth ring width decreased significantly with increasing drought conditions. However, xylem pit membrane thickness, cambial zone width and cambial cell geometry were not affected by the drought–rewatering cycles. The tracheid radial diameter, intertracheid cell wall thickness and tracheid density decreased significantly during both drought conditions and rewatering conditions. In addition to hydraulic traits, cambium and phloem cell vitality can be used as anatomical traits to evaluate the mortality of G. biloba under drought. Future work is proposed to observe the dynamics of pit aspiration rates under drought–rewatering cycles in situ to deepen our understanding of the essential role of bordered pits in the ‘air-seeding’ mechanism.

In 2010-2018 Northern Patagonia featured the longest severe drought of the last millennium. This extreme dry spell triggered widespread growth decline and forest dieback. Nonetheless, the roles played by the two major mechanisms driving dieback, hydraulic failure and carbon starvation, are still not clear and understudied in this seasonally dry region. Here, for the 1800-2017 period, we apply a retrospective analysis of radial growth, wood anatomical traits (lumen area, cell-wall thickness) and δ13 C and δ18 O stable isotopes to assess dieback causes of the iconic conifer Araucaria araucana. We selected three stands where declining (defoliated) and non-declining (not defoliated) trees coexisted along a precipitation gradient from the warm-dry Coastal Range to the cool-wet Andes. At all sites declining trees showed lower radial growth and lower theoretical hydraulic conductivity, suggesting a long-lasting process of hydraulic deterioration in their water transport system compared to non-declining, coexisting trees. Wood anatomical traits evidenced that this divergence between declining and non-declining trees started at least seven decades before canopy dieback. In the drier stands, declining trees showed higher water-use efficiency throughout the whole period, which we attributed to early stomatal closure, suggesting a greater carbon starvation risk consistent with thinner cell walls. In the wettest stand, we found the opposite pattern. Here, a reduction in water-use efficiency coupled with thicker cell walls suggested increased carbon assimilation rates and exposure to drought-induced hydraulic failure. The δ18 O values indicated different strategies of gas-exchange between sites which are likely a consequence of microsite conditions and water sources. Multi-proxy, retrospective quantifications of xylem anatomical traits and tree-ring isotopes provide a robust tool to identify and forecast which stands or trees will show dieback or, on the contrary, which will likely withstand and be more resilient to future hotter droughts.

International audience; Refugia can facilitate the persistence of species under long-term environmental change, but it is not clear if Pleistocene refugia will remain functional as anthropogenic climate change progresses. Dieback in populations restricted to refugia therefore raises concerns about their long-term persistence. Using repeat field surveys, we investigate dieback in an isolated population of Eucalyptus macrorhyncha during two droughts and discuss prospects for its continued persistence in a Pleistocene refugium. We first confirm that the Clare Valley in South Australia has constituted a long-term refugium for the species, with the population being genetically highly distinct from other conspecific populations. However, the population lost >40 % of individuals and biomass through the droughts, with mortality being just below 20 % after the Millennium Drought (2000–2009) and almost 25 % after the Big Dry (2017–2019). The best predictors of mortality differed after each drought. While north-facing aspect of a sampling location was significant positive predictor after both droughts, biomass density and slope were significant negative predictors only after the Millennium Drought, and distance to the north-west corner of the population, which intercepts hot, dry winds, was a significant positive predictor after the Big Dry only. This suggests that more marginal sites with low biomass and sites located on flat plateaus were more vulnerable initially, but that heat-stress was an important driver of dieback during the Big Dry. Therefore, the causative drivers of dieback may change during population decline. Regeneration occurred predominantly on southern and eastern aspects, which would receive the least solar radiation. While this refugial population is experiencing severe decline, some gullies with lower solar radiation appear to support relatively healthy, regenerating stands of red stringybark, providing hope for persistence in small pockets. Monitoring and managing these pockets during future droughts will be essential to ensure the persistence of this isolated and genetically unique population.

Fires, among other forms of natural and anthropogenic disturbance, play a central role in regulating the location, composition and biomass of forests. Understanding the role of fire in global forest loss is crucial in constraining land‐use change emissions and the global carbon cycle. We analysed the relationship between forest loss and fire at 500 m resolution based on satellite‐derived data for the 2003–2018 period. Satellite fire data included burned area and active fire detections, to best account for large and small fires, respectively. We found that, on average, 38 ± 9% (± range) of global forest loss was associated with fire, and this fraction remained relatively stable throughout the study period. However, the fraction of fire‐related forest loss varied substantially on a regional basis, and showed statistically significant trends in key tropical forest areas. Decreases in the fraction of fire‐related forest loss were found where deforestation peaked early in our study period, including the Amazon and Indonesia while increases were found for tropical forests in Africa. The inclusion of active fire detections accounted for 41%, on average, of the total fire‐related forest loss, with larger contributions in small clearings in interior tropical forests and human‐dominated landscapes. Comparison to higher‐resolution fire data with resolutions of 375 and 20 m indicated that commission errors due to coarse resolution fire data largely balanced out omission errors due to missed small fire detections for regional to continental‐scale estimates of fire‐related forest loss. Besides an improved understanding of forest dynamics, these findings may help to refine and separate fire‐related and non‐fire‐related land‐use change emissions in forested ecosystems., Fire is often a key process when considering the drivers of forest loss. Fire and forest loss can be directly related, such as in wildfires, but also indirectly because of slash burning after tree felling or tree mortality after fire damage. Using a novel approach for combining satellite‐derived forest loss with fire data from burned area and active fire detections, we found that 38 ± 9% of the global forest loss during 2003–2018 was fire‐related. We discuss global patterns and trends in fire‐related forest loss, and compare our results for fire data of different spatial resolutions.

By logging in the past, humans can determine current tree population structures, but fast stump decomposition makes difficult to falsify that for Amazonian Rainforests. We reconstructed land-use histories and surveyed trees ≥ 10 cm diameter at breast height on three 1-ha plots (K1, K2, and K6) in Kühbergl, South Tyrolean Alps as we did for four plots in Atacapi, Ecuador (plots A, B, C, and D). Storm Vaia (October 27 –November 1, 2018) stroke Kübergl providing dated evidence of mass tree-mortality on plot K6. We used K6 as control for comparing its pre- and post-storm population structures with the ones of four Amazonian, and three Alpine species where Vaia did not kill trees (Kolmogorov-Smirnov tests). When compared with K6’s Picea abies, the following species had size distributions similar to post-storm, but not to pre-storm situation. Amazonian: Piptocoma discolor, Vochysia bracelineae (plots B and D), Miconia decurrens (plots B and C), and Pseudobombax sp (plot C). Alpine: Larix decidua (plot K1) and Picea abies (plot K2). Storms do not occur in Atacapi, where logging is a common practice. That makes plausible that discrete events of compulsive logging during secondary succession made Amazonian population structures to look similar to K6’s P. abies. Logging is forbidden in Kühbergl, but storms are common there. Thus, the current population structures of Larix decidua (plot K1) and Picea abies (plot K2) should be legacies of storms before Vaia. Looking into tree populations’ history can impulse research for answering some basic questions of Ecology: what alters population structures, and which population structuring processes are more influential than others.

International audience; Extreme wind blowdown events can significantly modify the structure and composition of forests, and the predicted shift in tropical cyclone regimes due to climate change could strongly impact forests across the tropics. In this study, we coupled an individual-based and spatially-explicit forest dynamics model (TROLL) with a mechanistic model estimating wind damage as a function of tree size, traits, and allometry (ForestGALES). We assimilated floristic trait data and climate data from a subtropical forest site in Taiwan to explore the effect of wind regimes on forest properties. We found that the average canopy height and biomass stocks decreased as wind disturbance strength increased, but biomass stocks showed a nonlinear response. Above a wind intensity threshold, both canopy height and biomass drastically decreased to near-zero, exhibiting a transition to a non-forest state. Wind intensity strongly regulated wind impact, but varying wind frequency did not cause discernible effects. The implementation of within-stand topographic heterogeneity led to weak effects on within-stand forest structure heterogeneity at the study site. In conclusion, the intensity of wind disturbances can potentially greatly impact forest structure by modifying mortality. Individual-based modeling provides a framework in which to investigate the impact of wind regimes on mortality, other factors influencing wind-induced tree mortality, as well as interaction between wind and other forms of forest disturbance and human land use legacy.

Drought-induced tree mortality frequently occurs in patches with different spatial and temporal distributions, which is only partly explained by inter- and intraspecific variation in drought tolerance. We investigated whether bedrock properties, with special reference to rock water storage capacity, affects tree water status and drought response in a rock-dominated landscape. We measured primary porosity and available water content of breccia (B) and dolostone (D) rocks. Saplings of Fraxinus ornus were grown in pots filled with soil or soil mixed with B and D rocks, and subjected to an experimental drought. Finally, we measured seasonal changes in water status of trees in field sites overlying B or D bedrock. B rocks were more porous and stored more available water than D rocks. Potted saplings grown with D rocks had less biomass and suffered more severe water stress than those with B rocks. Trees in sites with B bedrock had more favourable water status than those on D bedrock which also suffered drought-induced canopy dieback. Bedrock represents an important water source for plants under drought. Different bedrock features translate into contrasting below-ground water availability, leading to landscape-level heterogeneity of the impact of drought on tree water status and dieback.

European coniferous forests are currently threatened by bark beetles (e.g. Ips typographus) because of an increasing incidence of triggering factors, such as drought and windstorms. Furthermore, such natural disturbances are expected to increase in terms of magnitude and frequency due to climate change, and thus interacting with each other. Here, we present a particular case study in the Southern Italian Alps (Gares, Canale d’Agordo, Belluno), in which wind disturbance interacts with an ongoing outbreak of I. typographus, probably associated with an extended drought in the previous three years. By combining remote sensing and field surveys, we spatially reconstructed the bark beetle attack in the period 2015-2021, which includes the Vaia windstorm in October 2018. Although the windstorm occurred in an expanding phase of the bark beetle outbreak, attacks on standing trees did not occur during the first year after the windstorm but were observed two years later. Our findings suggest that an overlap of a large availability of wind felled trees with an incipient outbreak of I. typographus resulted in an immediate decrease of standing trees mortality in the year following the storm. However, the fallen trees worked as a hidden sink for the beetle population, which in the following years massively attacked the standing trees that survived the storm.

During the particularly severe hot summer drought in 2018, widespread premature leaf senescence was observed in several broadleaved tree species in Central Europe, particularly in European beech (Fagus sylvatica L.). For beech, it is yet unknown whether the drought evoked a decline towards tree mortality or whether trees can recover in the longer term. In this study, we monitored crown dieback, tree mortality and secondary drought damage symptoms in 963 initially live beech trees that exhibited either premature or normal leaf senescence in 2018 in three regions in northern Switzerland from 2018 to 2021. We related the observed damage to multiple climate- and stand-related parameters. Cumulative tree mortality continuously increased up to 7.2% and 1.3% in 2021 for trees with premature and normal leaf senescence in 2018, respectively. Mean crown dieback in surviving trees peaked at 29.2% in 2020 and 8.1% in 2019 for trees with premature and normal leaf senescence, respectively. Thereafter, trees showed first signs of recovery. Crown damage was more pronounced and recovery was slower for trees that showed premature leaf senescence in 2018, for trees growing on drier sites, and for larger trees. The presence of bleeding cankers peaked at 24.6% in 2019 and 10.7% in 2020 for trees with premature and normal leaf senescence, respectively. The presence of bark beetle holes peaked at 22.8% and 14.8% in 2021 for trees with premature and normal leaf senescence, respectively. Both secondary damage symptoms occurred more frequently in trees that had higher proportions of crown dieback and/or showed premature senescence in 2018. Our findings demonstrate context-specific differences in beech mortality and recovery reflecting the importance of regional and local climate and soil conditions. Adapting management to increase forest resilience is gaining importance, given the expected further beech decline on dry sites in northern Switzerland., Plant Biology, 24 (7), ISSN:1435-8603, ISSN:1438-8677

This study utilizes forest inventory and climate attributes as the basis for estimating models of wildfire risk and associated biomass loss (tree mortality) and then demonstrates how they can be applied in calculating CO2 emissions related to the incidence of wildfires from U.S. forests. First, we use the full set of over 150,000 FIA plots of national forest inventory and climatic parameters to estimate models of the annual probability of wildfire occurrence and loss of live tree biomass. Then, maps of the spatial allocation of both the model-derived probability of wildfire occurrences and tree mortality are presented at the national level. The probability of wildfire occurrences and tree mortality were defined by a complex non-linear association of climatic conditions and forest ownerships, available aboveground biomass, and the age of the stand. Then, we provide an example of how these models can estimate potential CO2 emissions from wildfires by using FIA inventory data. We estimated 6.10, 16.65, 22.75, and 31.01 million metric tons of annual CO2 emissions with low, medium, high, and catastrophic combustion rates, respectively, from forests due to wildfire in the continental U.S. The wildfire risk and biomass loss due to tree mortality maps can be used by landowners, managers, public agencies, and other stakeholders in identifying high-risk wildfire zones and the potential CO2 emissions. These equations can also help estimate fire risk and associated CO2 emissions for future climate conditions to provide insight into climate change-related wildfire occurrences.

Where competition suppresses tree growth, mortality of adjacent trees can release the surviving individuals, leading to a growth increase. However, primary forests are complicated systems, where trees interact in both competitive and facilitative ways mediated by their size, species, and the broad ecological context in which they grow. Thus, the magnitude and even direction of growth responses to the mortality of nearby trees may vary, which has implications for our understanding of community- and ecosystem-level dynamics following mortality events. Unfortunately, although many studies focus on the impacts of light availability and general crowding on tree growth, we know relatively little about the effects of naturally occurring mortality events on the growth of neighboring trees. To address this issue, we used 40 years of data from 15 permanent forest-monitoring plots in Mt Rainier old-growth forests, comparing observed to expected radial growth of individual trees following the death of their nearest neighbor. Although we found evidence of a general growth-release response, this was not universal among all trees, with small trees in particular exhibiting growth suppression (rather than release) following neighboring tree mortality. In addition to small size, growth-suppression was more likely if the dead neighbor was the same species, consistent with facilitative effects as mediated through belowground networks. At the stand level, the average growth release after nearest neighbor mortality was greatest in low-density stands with large trees, with elevation and community composition also playing a role. Decades more monitoring could reveal how long growth release (or suppression) is sustained by individual trees following neighboring mortality events, as well as potential response lags and the role of species identity in determining whether interactions with neighbors are competitive or facilitative. Nonetheless, our results suggest that although mature trees have competitive effects on their larger neighbors, they also have an important role in supporting the ingrowth of small trees. More broadly, we demonstrate that the nature of interactions between individual neighboring trees is highly context dependent., Forest Ecology and Management, 529, ISSN:0378-1127, ISSN:1872-7042

There has been a long-standing interest in understanding how interactions between fire and herbivory influence woody vegetation dynamics in savanna ecosystems. However, controlled, replicated experiments examining how different fire regimes interact with different herbivore groups are rare. We tested the effects of single and repeated burns, crossed with six replicated herbivore treatments, on the mortality and growth of woody vegetation in the Kenya Long-term Exclosure Experiment plots located in a semi-arid savanna system in central Kenya. Burned plots experienced higher tree mortality overall, but differences between burns and non-burns were only significant in plots excluding all wild herbivores and in plots accessible to megaherbivores. Cattle ameliorated the negative effects of repeat burns on tree mortality, perhaps by suppressing fuel load accumulation. Across all herbivore treatments, trees experienced a significant reduction in height within the first two years after fire (top-kill), which was followed by a gradual recovery. Saplings and coppices subjected to repeated burns regrew faster than those that were burned once, except in the presence of megaherbivores. This study highlights strong context-dependent interactions between fire and different herbivore groups, and extends previous approaches to understanding fire–herbivory interactions, which have tended to lump the effects of different herbivore groups, or study them separately.

Climate change‐driven droughts and insect outbreaks are becoming more frequent and widespread, increasing forest vulnerability to mortality. By addressing the impacts of climate and insects on tree growth preceding death, we can better understand tree mortality risk under a changing climate. Here, we used tree stature and interannual growth (basal area increment; BAI) to assess processes leading to trembling aspen (Populus tremuloides) survival or mortality during an unprecedented leaf miner (Phyllocnistis populiella) outbreak in boreal North America. We identified eight sites (22 plots) in the longest running forest monitoring network in Alaska, spanning ~350 km of latitude, that experienced ≥0.25 Mg·ha−1·yr−1 aspen mortality during the outbreak. We compared the size and canopy position, growth patterns, and sensitivity to climate and leaf mining of aspen that survived (living; n = 84) vs. died (dying; n = 76) and linked the normalized difference vegetation index (NDVI) to plot‐level aspen growth and stand biomass recruitment, growth, and mortality. Dying aspen were in the subcanopy, smaller in diameter, and after a drought in 1957 had lower growth than living aspen until death. Before the outbreak, growth of all trees was positively influenced by moisture and negatively by temperature, but only living trees maintained this climate response during the outbreak. Leaf mining reduced growth of both groups, exerting at least a twofold greater impact than climate. The NDVI captured plot‐level tree growth and stand biomass growth and mortality, yet it was nearly two times more strongly associated with living than dying tree growth and 12 times more strongly associated with biomass growth than mortality. These differences suggest that NDVI may inadequately detect insect‐driven dieback and dispersed mortality of aspen across the boreal biome. Our findings reveal that a historic drought triggered a multi‐decadal growth decline that predisposed aspen to mortality during the leaf miner outbreak and that while aspen growth is influenced by moisture and temperature, it is more strongly affected by P. populiella. We conclude that as the climate warms and insect outbreaks increase in frequency and magnitude at high latitudes, we should expect to see persistent and greater declines in aspen growth and increases in mortality.

Drought has promoted large-scale, insect-induced tree mortality in recent years, with severe consequences for ecosystem function, atmospheric processes, sustainable resources and global biogeochemical cycles. However, the physiological linkages among drought, tree defences, and insect outbreaks are still uncertain, hindering our ability to accurately predict tree mortality under on-going climate change. Here we propose an interdisciplinary research agenda for addressing these crucial knowledge gaps. Our framework includes field manipulations, laboratory experiments, and modelling of insect and vegetation dynamics, and focuses on how drought affects interactions between conifer trees and bark beetles. We build upon existing theory and examine several key assumptions: (1) there is a trade-off in tree carbon investment between primary and secondary metabolites (e.g. growth vs defence); (2) secondary metabolites are one of the main component of tree defence against bark beetles and associated microbes; and (3) implementing conifer-bark beetle interactions in current models improves predictions of forest disturbance in a changing climate. Our framework provides guidance for addressing a major shortcoming in current implementations of large-scale vegetation models, the under-representation of insect-induced tree mortality.

Anthropogenic activities such as uncontrolled deforestation and increasing greenhouse gas emissions are responsible for triggering a series of environmental imbalances that affect the Earth's complex climate dynamics. As a consequence of these changes, several climate models forecast an intensification of extreme weather events over the upcoming decades, including heat waves and increasingly severe drought and flood episodes. The occurrence of such extreme weather will prompt profound changes in several plant communities, resulting in massive forest dieback events that can trigger a massive loss of biodiversity in several biomes worldwide. Despite the gravity of the situation, our knowledge regarding how extreme weather events can undermine the performance, survival, and distribution of forest species remains very fragmented. Therefore, the present review aimed to provide a broad and integrated perspective of the main biochemical, physiological, and morpho‐anatomical disorders that may compromise the performance and survival of forest species exposed to climate change factors, particularly drought, flooding, and global warming. In addition, we also discuss the controversial effects of high CO2 concentrations in enhancing plant growth and reducing the deleterious effects of some extreme climatic events. We conclude with a discussion about the possible effects that the factors associated with the climate change might have on species distribution and forest composition., The occurrence of extreme weather events will prompt profound changes in several plant communities, resulting in massive forest dieback events that can trigger a massive loss of biodiversity in several biomes worldwide. Despite the gravity of the situation, our knowledge regarding how extreme weather events can undermine the performance, survival, and distribution of forest species remains very fragmented. Therefore, the present review aimed to provide a broad and integrated perspective of the main biochemical, physiological, and morpho‐anatomical disorders that may compromise the performance and survival of forest species exposed to climate change factors, particularly drought, flooding, and global warming.

The aim of research was to evaluate the variability and relations with forest health condition its main parameters (defoliation, dieback and epicormic shoots occurrence) in seven tree species: Norway maple (Acer platanoides L.), black alder (Alnus glutinosa L.), silver birch (Betula pendula Roth.), European ash (Fraxinus excelsior L.), English oak (Quercus robur L.), small-leaved lime (Tilia cordata Mill.), and white elm (Ulmus laevis Pall). Research was carried out in 2018 in Trostyanetske Forest Enterprise (Left-bank Forest Steppe; Sumy region). Diameter (DBH), Kraft class, and category of health condition were assessed for each tree. Defoliation, dieback and epicormic shoots occurrence were evaluated as proportion of trees with respective symptoms. Severity of each parameter of tree health condition was estimated using respective scores. No tree species is defoliated over 50%. A birch is characterized by the lowest health condition index (1.6) for living trees, dieback (10%), epicormic shoots occurrence (15.9%) and recently died trees proportion (0.7%), but high proportion of trees died over year ago (10.7%). An oak is characterized by the highest health condition index (2.1), proportion of trees with dieback (45.4%) and epicormic shoots (21.7%). Proportion of trees with dieback is 21.5 to 25% for alder, lime and maple, a bit higher for elm and ash (30.9 and 31.3% respectively). DBH, Kraft class, and health condition index significantly correlate with health condition parameters of analyzed tree species, but the most of correlations are very slight and slight. Correlation between health condition index and defoliation score is significant, positive and high for all tree species (from 0.78 for alder to 0.9 for birch). Correlation between health condition index and dieback score is positive and significant for all tree species, is slight for ash, birch, lime, and alder, and moderate for maple, oak and elm. Correlation between health condition index and epicormic shoots occurrence is significant and positive for all tree species except birch, but is very slight in all cases except elm, where it is slight.

Made available in DSpace on 2019-10-04T12:34:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-15 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Anglo American Arauco Arborgen ArcelorMittal Cenibra CMPC Comigo Copener Duratex Eldorado Fazenda Campo Born Fibria Florestal Itaquari Forestal Oriental Gerdau GMR International Paper Jani Klabin Lwarcel Montes del Plata Plantar Rigesa Suzano Vallourec Veracel University of Sao Paulo Sao Paulo State University Federal University of Lavras Federal University of Rio Grande do Norte Colorado State University North Carolina State University USDA Forest Service Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Several approaches for modeling whole-stand survival or mortality have been reported in the literature, although this component is often times neglected for clonal eucalypt stands in Brazil. In addition, the traditional form for projecting whole-stand survival appears incomplete for clonal eucalypt stands, since this tree species is highly sensitive to lack of water in the environment. Consequently, this study aimed to define the best approach to estimate whole-stand survival in clonal eucalypt stands and to develop a new approach for modeling whole-stand survival as a function of cumulative soil water deficit. Remeasurement of sixteen research sites composed the database used in this study. At each research site, the same eleven eucalypt clones were planted in single block plots, which results in a total of 176 plots distributed across Brazil. Two traditional approaches (two-step approach and direct estimation) were tested for modeling whole-stand survival. Additionally a new approach that replaces the age term by cumulative soil water deficit (cumulative SWD) was compared to the best selected traditional approach to estimate whole-stand survival in clonal eucalypt stands. The direct projection approach of whole-stand survival displayed better results when compared to the two-step approach. In addition, the replacement of age by cumulative SWD in the direct estimation approach allowed for an increase in the explanatory ability of the developed difference model. The newly developed difference model employing the direct estimation approach constrained by cumulative SWD ensures that the environmental stress effect is reflected on the survival of clonal eucalypt stands over time, and it is more biologically sound for extrapolation purposes. North Carolina State Univ, Dept Forestry & Environm Resources, 2820 Faucette Dr,Campus Box 8001, Raleigh, NC 27695 USA Virginia Polytech Inst & State Univ, Dept Forest Resources & Environm Conservat, 310 W Campus Dr,Campus Box 169, Blacksburg, VA 24061 USA Forestry Sci & Res Inst, Via Comendador Pedro Morganti, BR-13415000 Sao Paulo, Brazil State Univ Sao Paulo, Dept Forest Sci, Ave Univ,3780, BR-18610034 Botucatu, SP, Brazil Univ Sao Paulo, Dept Forest Sci, Ave Padua Dias,11, BR-13418900 Sao Paulo, Brazil State Univ Sao Paulo, Dept Forest Sci, Ave Univ,3780, BR-18610034 Botucatu, SP, Brazil CNPq: 249979/2013-6

International audience; Xylem hydraulic failure has been recognized as a pervasive factor in the triggering of drought-induced tree mortality. However, foundational evidence of the mechanistic link connecting hydraulic failure with living cell damage and tree death has not been identified yet, compromising our ability to predict mortality events. Meristematic cells are involved in the recovery of trees from drought, and focusing on their vitality and functionality after a drought event could provide novel information on the mechanistic link between hydraulic failure and drought-induced tree mortality. In this Opinion, we focus on the cell's critical hydration status for tree recovery from drought and how it links with the membrane integrity of the meristems.

Tree mortality rates are increasing within tropical rainforests as a result of global environmental change. When trees die, gaps are created in forest canopies and carbon is transferred from the living to deadwood pools. However, little is known about the effect of tree-fall canopy gaps on the activity of decomposer communities and the rate of deadwood decay in forests. This means that the accuracy of regional and global carbon budgets is uncertain, especially given ongoing changes to the structure of rainforest ecosystems. Therefore, to determine the effect of canopy openings on wood decay rates and regional carbon flux, we carried out the first assessment of deadwood mass loss within canopy gaps in old-growth rainforest. We used replicated canopy gaps paired with closed canopy sites in combination with macroinvertebrate accessible and inaccessible woodblocks to experimentally partition the relative contribution of microbes vs. termites to decomposition within contrasting understorey conditions. We show that over a 12month period, wood mass loss increased by 63% in canopy gaps compared with closed canopy sites and that this increase was driven by termites. Using LiDAR data to quantify the proportion of canopy openings in the study region, we modelled the effect of observed changes in decomposition within gaps on regional carbon flux. Overall, we estimate that this accelerated decomposition increases regional wood decay rate by up to 18.2%, corresponding to a flux increase of 0.27MgCha-1 year-1 that is not currently accounted for in regional carbon budgets. These results provide the first insights into how small-scale disturbances in rainforests can generate hotspots for decomposer activity and carbon fluxes. In doing so, we show that including canopy gap dynamics and their impacts on wood decomposition in forest ecosystems can help improve the predictive accuracy of the carbon cycle in land surface models.

The global rise in temperature and associated changes in climate have led to decline of forests around the globe, across multiple species and ecosystems. Yellow‐cedar (Callitropsis nootkatensis) decline is one of the most severe in North America. We found abundant evidence of tree decline and mortality on Haida Gwaii across multiple watersheds and over a range of elevations. This decline on Haida Gwaii parallels the broader yellow‐cedar decline in terms of spatial distribution, symptoms, magnitude, and timing. However, Haida Gwaii has a more temperate climate and ephemeral snowpack than declining yellow‐cedar forests in Alaska where the link to climate was first uncovered. Given these important differences, we investigated several possible drivers both at the local and at the regional scale, using population demography, dendrochronology, and daily weather data. We explored stand dynamics as a driver and tested the known link to climate. Our results are inconsistent with stand dynamics as a driver of elevated decline and mortality. Neither increased competition nor aging of a cohort explains the decline. Alternatively, the magnitude and timing of the decline are consistent with well‐documented long‐term directional trends in regional climate. Onset of basal area increment decline and mortality have been accumulating over time, with increased rates since the 1980s. Our sites were located at the edge of the expected range of mortality, and we found only four thaw–freeze events over the past ~80 yrs. However, superposed epoch analysis using daily weather data revealed that mortality and onset of decline events were associated with warmer winter conditions, consistent with the drivers from Alaska. Rather than isolated extreme thaw–freeze events, warmer winter temperatures on Haida Gwaii may mean less cold hardening throughout the winter, which exposes yellow‐cedar’s fine roots to varying degrees of freezing damage over multiple winter thaw–freeze cycles, causing physiological stress, tree decline, and eventual death.

International audience; Context In the framework of climate change, decreased tree growth and enhanced mortality induced by hot and dry conditions are increasing in many forests around the world, and particularly in Mediterranean forests.• Aims Our aim was to estimate tree growth and mortality in a Mediterranean holm oak forest, using remote sensing data from MODIS.• Methods We monitored annual increases of aboveground biomass by measuring tree basal area, and we determined tree mortality by counting dead stems. We analyzed the relationships between forest growth and mortality with mean annual values of some MODIS products and meteorological data.• Results Mortality and increases of aboveground biomass correlated well with precipitation, September standardized precipitation/evapotranspiration indices (SPEI), and some MODIS products such as NDVI and enhanced vegetation index EVI. Other MODIS products such as gross primary production (GPP) and net photosynthesis, however, showed no clear relationship with tree mortality or measured increases of biomass.• Conclusion The MODIS products as proxies of ecosystemic productivity (gross primary productivity, net photosynthesis) were weakly correlated with biomass increase, and did not reflect the mortality following the drought of autumn 2011. Nevertheless, NDVI and EVI were efficient indicators of forest productivity and dieback

Tree mortality drives changes in forest structure and dynamics, community composition, and carbon and nutrient cycles. Since tropical forests store a large fraction of terrestrial biomass and tree diversity, improved understanding of changing tree mortality and biomass loss rates is critical. Tropical tree mortality rates have been challenging to estimate due to low background rates of tree death, and high spatial and temporal heterogeneity. Furthermore, the causes of mortality remain unclear because many factors may be involved in individual tree death, and the rapid decomposition of wood in the tropics obscures evidence of possible causes of tree mortality. We present a field protocol to assess tree mortality in tropical forests. The protocol focuses on the rapid, repeatable and inexpensive assessment of individual tree death and damage. The protocol has been successfully tested with annual assessments of >62,000 stems in total in several ForestGEO plots in Asia and the Neotropics. Standardized methods for the assessment of tree death and biomass loss will advance understanding of the underlying causes and consequences of tree mortality.Tree mortality drives forest dynamics, community composition, and carbon and nutrient cycles. We present a field protocol to assess tree mortality in tropical forests. The protocol focuses on the rapid, repeatable and inexpensive assessment of individual tree death and damage. Standardized methods for the assessment of tree death and biomass loss will advance understanding of tree mortality.

Vegetation tolerance to drought depends on an array of site-specific environmental and plant physiological factors. This tolerance is poorly understood for many forest types despite its importance for predicting and managing vegetation stress. We analyzed the relationships between precipitation variability and forest die-off in California's Sierra Nevada and introduce a new measure of drought tolerance that emphasizes plant access to subsurface moisture buffers. We applied this metric to California's severe 2012-2015 drought, and show that it predicted the patterns of tree mortality. We then examined future climate scenarios, and found that the probability of droughts that lead to widespread die-off increases threefold by the end of the 21st century. Our analysis shows that tree mortality in the Sierra Nevada will likely accelerate in the coming decades and that forests in the Central and Northern Sierra Nevada that largely escaped mortality in 2012-2015 are vulnerable to die-off.

Tree mortality rates and the modes of tree death have recently been extensively investigated in the Amazon. However, efforts to describe these processes have not been well distributed across the basin. No study has yet investigated in depth tree mortality process in the unique low, open, bamboo-dominated forests of southwestern Amazonia, a region with a distinct climate and the epicenter of recent severe drought events. Here, we investigated the leading ways that trees die in the terra-firme forests of the southwestern Brazilian Amazon, to understand whether the dynamics of mortality differ from those recorded in other parts of the basin. Using data from six permanent plots located in southwestern Amazonia, we calculated the mortality rate for three main modes of tree death: standing, broken and uprooted. We thus identified the predominant mode of death over a 14 year period (2002–2016). We found that trees in the southwestern Amazon died mainly standing (325 trees, 0.8% year−1) and broken (362 trees, 0.8% year−1); significantly fewer trees died uprooted (156 trees, 0.4% year−1, equivalent to less than one in five of all trees dying). During the study period, the tree mode of death with the greatest proportion in the region alternated between standing and broken trees. Forest characteristics of the southwestern Amazon, like presence and high density of bamboo culms, and the fact that the region was subject to severe droughts in 2005 and 2010, may be affecting how trees die in southwestern Amazon. The presence of these factors makes the forest dynamics of the southwestern Amazon different from other regions of the Amazon basin.

Global forests are experiencing widespread climate-induced mortality. Predicting this phenomenon has proven difficult, despite recent advances in understanding physiological mechanisms of mortality in individual trees along with environmental drivers of mortality at broad scales. With heat and drought as primary climatic drivers, and convergence on hydraulic failure as a primary physiological mechanism, new models are needed to improve our predictions of Earth’s forests under future climate conditions. While much of ecology focuses on equilibrium states, transitions from one stable state to another are often described with alternative stable state theory (ASST), where systems can settle to more than one stable condition. Recent studies have identified threshold responses of hydraulic failure during tree mortality, indicating that alternative stable states may be present. Here, I demonstrate that the xylem of trees has characteristics indicative of alternative stable states. Through empirical evidence, I identify a catastrophic shift during hydraulic failure which prevents trees from returning to pre-droughted physiological states after environmental stressors (e.g., drought, heat) are relieved. Thus, the legacy of climate-induced hydraulic failure likely contributes to reduced resilience of forests under future climate. I discuss the implications and future directions for including ASST in models of tree mortality.

Coauthored with PhD student and undergraduate student Yes, abstract only (Peer reviewed?)

Windstorm is one of the destructive natural disturbances, but the scale-link extent to which recurrent windstorms influenced forests ecosystems is poorly understood in a changing climate across regions. We reviewed the synergistic impacts of windstorms on forests and assessed research trends and methodological approaches from peer-reviewed articles published from 2000 to 2020 in tropical (TRF), subtropical (SUF), and temperate (TEF) forests/zones, based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Overall, the majority of the reviewed studies were conducted in TRF (i.e., 40%), intermediate in SUF (i.e., 34%), and the lowest in TEF (i.e., 26%). Among the four levels of biological organization, the species-population and community-ecosystem levels had the highest number of study cases, while the molecular-cellular-individual and landscape levels had the lowest study cases in all forest types. Most of the articles reviewed dealt largely on tree mortality/survival and regeneration/succession for TRF, tree mortality/survival and species composition/richness/diversity for SUF, and stem density, gap dynamics, and regeneration/succession for TEF. However, research on the effects of windstorms on mycorrhizal symbioses, population genetics, and physiological adaptation, element fluxes via litterfall, litter decomposition, belowground processes, biological invasion, and tree health are less common in all forest types. Further, most of the studies were conducted in permanent plots but these studies mostly used observational design, while controlled studies are obviously limited. Consequently, more observational and controlled studies are needed on the topic reviewed, particularly studies at the molecular-cellular-individual and landscape levels, to help inform forest management decision-making about developing sustainable and resilient forests amid climate change.

Amazonia lost 947 million tons of carbon induced by forest edge effect between 2001 and 2015, about 30% of deforestation losses., Deforestation is the primary driver of carbon losses in tropical forests, but it does not operate alone. Forest fragmentation, a resulting feature of the deforestation process, promotes indirect carbon losses induced by edge effect. This process is not implicitly considered by policies for reducing carbon emissions in the tropics. Here, we used a remote sensing approach to estimate carbon losses driven by edge effect in Amazonia over the 2001 to 2015 period. We found that carbon losses associated with edge effect (947 Tg C) corresponded to one-third of losses from deforestation (2592 Tg C). Despite a notable negative trend of 7 Tg C year−1 in carbon losses from deforestation, the carbon losses from edge effect remained unchanged, with an average of 63 ± 8 Tg C year−1. Carbon losses caused by edge effect is thus an additional unquantified flux that can counteract carbon emissions avoided by reducing deforestation, compromising the Paris Agreement’s bold targets.

Elevated atmospheric carbon dioxide (eCO2 ) is predicted to increase growth rates of forest trees. The extent to which increased growth translates to changes in biomass is dependent on the turnover time of the carbon, and thus tree mortality rates. Size- or age-dependent mortality combined with increased growth rates could result in either decreased carbon turnover from a speeding up of tree life cycles, or increased biomass from trees reaching larger sizes, respectively. However, most vegetation models currently lack any representation of size- or age-dependent mortality and the effect of eCO2 on changes in biomass and carbon turnover times is thus a major source of uncertainty in predictions of future vegetation dynamics. Using a reduced-complexity form of the vegetation demographic model the Functionally Assembled Terrestrial Ecosystem Simulator to simulate an idealised tropical forest, we find increases in biomass despite reductions in carbon turnover time in both size- and age-dependent mortality scenarios in response to a hypothetical eCO2 -driven 25% increase in woody net primary productivity (wNPP). Carbon turnover times decreased by 9.6% in size-dependent mortality scenarios due to a speeding up of tree life cycles, but also by 2.0% when mortality was age-dependent, as larger crowns led to increased light competition. Increases in aboveground biomass (AGB) were much larger when mortality was age-dependent (24.3%) compared with size-dependent (13.4%) as trees reached larger sizes before death. In simulations with a constant background mortality rate, carbon turnover time decreased by 2.1% and AGB increased by 24.0%, however, absolute values of AGB and carbon turnover were higher than in either size- or age-dependent mortality scenario. The extent to which AGB increases and carbon turnover decreases will thus depend on the mechanisms of large tree mortality: if increased size itself results in elevated mortality rates, then this could reduce by about half the increase in AGB relative to the increase in wNPP.

Author(s): McMahon, Devon; Axelson, Jodi; Kocher, Susie | Abstract: Tree mortality is changing California’s landscape and affecting the amount and type of fuel available for wildland fires. Since the extraordinary drought of 2012 through 2015, millions of trees have died in California, particularly in the Sierra Nevada. Fire risk depends on multiple factors, including weather and ignition sources, which are not affected by tree mortality. However, in areas that have experienced mass tree mortality, the amount and distribution of dead wood that can act as fuel has changed, altering the risk posed by fires.This publication discusses examples of mass tree mortality and assesses the impact on fuels—so that landowners and managers can understand fire risk on their own property and develop strategies to reduce it.

The increase in abiotic and biotic stress driven by global change threatens forest ecosystems and challenges understanding of mechanisms producing mortality. Phytophthora spp. like P. cinnamomi (PHYCI) are among the most lethal pathogens for many woody species including Quercus spp. Dynamics of biotic agents and their hosts are complex and influenced by climatic conditions. We analysed radial growth trends of dead and live adult Quercus ilex trees from agrosilvopastoral open woodlands under intense land-use. A pronounced warming trend since the 1980s has coincided in these woodlands with high oak mortality rates generally attributed to PHYCI. Yet, tree mortality and latency of the pathogen could be expressed at variable time spans, whereas, like in many other forests worldwide, tree death could also be explained by other factors like drought. PHYCI was isolated from roots of all dead oaks from one region. Trees were younger than generally believed and ages of dead trees ranged between 38 and 230 years. Growth of dead trees reached a tipping point in 1980 and 1990 coincident with two-year extraordinary droughts. These dates set the start of growth declines up to 30 years before tree death. Live trees did not exhibit any recent growth decline. Tree growth was highly sensitive to climatic variability associated with water stress and climate-growth relationships suggested phenological changes since the 1980s. Live and dead trees showed differences in their sensitivity to moisture availability and temperature. The sensitivity of growth to climate was partially related to site environmental conditions. Simulated gross and net primary productivity were higher in live sites with less atmospheric demand for water. Tree death was not sudden but a slow multiannual process as expressed by radial growth declines likely triggered by drought. Regardless of the causal agent or mechanism, the observed mortality affected trees exhibiting negative drought and land-use legacies., This work was funded by projects AGL2014-61175-JIN and PID2019-110273RB-I00 by the Spanish Ministry of Economy and Competitiveness. GGI was partly funded by RyC-2014-15864. It is also a contribution to REMEDINAL TE-CM-S2018/EMT-4338. We gratefully thank Pedro Antolín and Victoria Calvo for sample collection and processing, respectively.

Forest pathogens are important drivers of tree mortality across the globe, but it is exceptionally challenging to gather and build unbiased quantitative models of their impacts. Here we harness the rare data set matching the spatial scale of pathogen invasion, host, and disease heterogeneity to estimate infection and mortality for the four most susceptible host species of Phytophthora ramorum, an invasive pathogen that drives the most important biological cause of tree mortality in a broad geographic region of coastal California and southwest Oregon. As of 2012, the most current field survey year, we estimate 17.5 (±4.6, 95% CI [confidence interval]) million tanoak (Notholithocarpus densiflorus) stems were pathogen killed with an additional 71 (±21.5) million infected. We estimated 9.0 million (±2.2) coast live oak (Quercus agrifolia) and 1.7 million (±0.5) California black oak (Quercus kelloggii) stems are disease impacted (mortality and infection combined). Lastly, our estimates suggest infection in 95.2 million (±8.6) California bay laurel (Umbellularia californica), which does not suffer mortality from infection and represents a critical source of continued spread. Prevalent infection as of 2012 suggests the cumulative number of disease‐killed stems likely increased from 20.8 to 42.8 million between 2012 and 2019 for all species. While these impacts are substantial, most host populations occur in a yet to be invaded region of northern California indicating that the disease will intensify in the coming decades.

Wildland fires have a multitude of ecological effects in forests, woodlands, and savannas across the globe. A major focus of past research has been on tree mortality from fire, as trees provide a vast range of biological services. We assembled a database of individual-tree records from prescribed fires and wildfires in the United States. The Fire and Tree Mortality (FTM) database includes records from 164,293 individual trees with records of fire injury (crown scorch, bole char, etc.), tree diameter, and either mortality or top-kill up to ten years post-fire. Data span 142 species and 62 genera, from 409 fires occurring from 1981-2016. Additional variables such as insect attack are included when available. The FTM database can be used to evaluate individual fire-caused mortality models for pre-fire planning and post-fire decision support, to develop improved models, and to explore general patterns of individual fire-induced tree death. The database can also be used to identify knowledge gaps that could be addressed in future research.

Reforestation following timber harvests and natural disturbances is an essential component of sustainable forest management. As disturbances such as drought-induced mortality and wildland fires spread across many forests of the western United States, a better understanding of the influences of stand structure on seedling physiology can foster more effective reforestation efforts. Moreover, as climate throughout the West is projected to become hotter and drier, it is important to investigate regeneration under xeric conditions, particularly for species restricted to mesic habitats. To study the influences of stand structure and climate on regeneration success, we monitored physiology [water potential (Ψ) and stomatal conductance (gs)], growth (change in basal diameter and biomass accumulation), and mortality rate of planted Douglas-fir (Pseudotsuga menziesii) and coast redwood (Sequoia sempervirens) seedlings for two growing seasons after partial harvesting in inland northern California. Compared to seedlings in the no-cut and moderate-retention treatments, seedlings in the gap (100% cut) treatment had the highest Ψ and gs, greatest growth, and lowest mortality. We also found that compared to Douglas-fir, redwood had higher Ψ and gs, greater growth, and lower mortality. Overall, our study indicates that low-retention silvicultural treatments can minimize water stress and maximize gas exchange, growth, and survival in regenerating seedlings. Our results also demonstrate that redwood, a species generally restricted to mesic coastal habitats, can successfully establish in xeric inland sites when planted after partial harvesting, even during drought conditions.

Exotic forest insects and pathogens (EFIP) have become regular features of temperate forest ecosystems, yet we lack a long-term perspective on their net impacts on tree mortality, carbon sequestration, and tree-species diversity. Here, we analyze three decades (1987-2019) of forest monitoring data from the Blue Ridge Mountains ecoregion in eastern North America, including 67 plots totaling 29.4 ha, along with a historical survey from 1939. Over the past century, EFIP substantially affected at least eight tree genera. Tree host taxa had anomalously high mortality rates (≥6% yr-1 from 2008-2019, versus 1.4% yr-1 for less-impacted taxa). Following the arrival of EFIP, affected taxa declined in abundance (-25 to -100%) and live aboveground biomass (AGB; -13 to -100%) within our monitoring plots. We estimate that EFIP were responsible for 21-29% of ecosystem AGB loss through mortality (-87 g m-2 yr-1) from 1991-2013 across 66 sites. Over a century, net AGB loss among affected species totaled roughly 6.6-10 kg m-2. The affected host taxa accounted for 23-29% of genera losses at the plot-scale, with mixed net effects on α-diversity. Several taxa were lost from our monitoring plots but not completely extirpated from the region. Despite these losses, both total AGB and α-diversity were largely recovered through increases of sympatric genera. These results indicate that EFIP have been an important force shaping forest composition, carbon cycling, and diversity. At the same time, less-affected taxa in these relatively diverse temperate forests have conferred substantial resilience with regards to biomass and α-diversity., Files were extracted from a private GitHub repository that supported this analysis (https://github.com/EcoClimLab/Shenandoah). They were modified to remove some extraneous information. Most importantly, we removed raw data files (along with scripts for processing them) containing some sensitive information (Shenandoah plot coordinates, information on sensitive species). The GitHub repository can never be made public because it contains this information. However, upon reasonable request, the authors are open to granting access to the GitHub repository (contact: Kristina Anderson-Teixeira, Smithsonian; teixeirak@si.edu) and to sharing additional information and data about the Shenandoah census (contact: Wendy Cass, Shenandoah National Park; Wendy_Cass@nps.gov)., {"references":["Anderson-Teixeira, K. J., V. Herrmann*, W. B. Cass, A. B. Williams, S. J. Paull, R. Helcoski, E. B. Gonzalez-Akre, A. J. Tepley, N. A. Bourg, C. T. Cosma, A. E. Ferson, C. Kittle, V. Meakem*, I. R. McGregor, M. N. Prestipino, M. K. Scott, A. R. Terrell, A. Alonso, F. Dallmeier, W. J. McShea (2020). Long-term impacts of invasive insects and pathogens on composition, biomass, and diversity of forests in Virginia's Blue Ridge Mountains. Ecosystems."]}

International audience; In the context of climate change, determining the physiological mechanisms of drought-induced mortality in woody plants and identifying thresholds of drought survivorship will improve forecasts of forest and agroecosystem die-off. Here, we tested whether continuous measurements of branch diameter variation can be used to identify thresholds of hydraulic failure and physiological recoverability in lavender (Lavandula angustifoliaandLavandulaxintermedia) plants exposed to severe drought. Two parameters of branch diameter variation were tested: the percentage loss of diameter and the percentage loss of rehydration capacity. In two greenhouse experiments with different growth conditions, we monitored variation in branch diameter in the two lavender species exposed to a series of drought/rewatering cycles that varied in drought-stress intensity. Water potential, stomatal conductance, loss of xylem hydraulic conductance, and electrolyte leakage were also measured. We observed that plants were not able to recover when percentage loss of diameter reached maximum values of 21.3% +/- 0.6% during drought, regardless of species and growth conditions. A percentage loss of rehydration capacity of 100% was defined as the point of no recovery, and was observed with high levels of cellular damage as estimated by electrolyte leakage measured at 75.4% +/- 9.3% and occurred beyond 88% loss of xylem hydraulic conductance. Our study demonstrates that lavender plants are not able to recover from severe drought when they have used up their elastic water storage. Additionally, drought-induced mortality in these species was not linked to xylem hydraulic failure but rather to high levels of cell damage. Under extreme drought, death of lavender plants occurs when the water storage of the elastic compartment of the branch is exhausted.

To understand the influence of competition indices and post-thinning effects in predicting individual tree mortality, we developed two models, one without the effect of thinning and another, with the effect of thinning for naturally occurring even-aged natural shortleaf pine (Pinus echinata Mill.) stands in the Ozark and Ouachita National Forests in Oklahoma and Arkansas, USA. Over the period of 25 years, six re-measurements of an individual tree from each plot were collected between 1985 and 2014. The logistic function was used to model the probability of mortality for which the binary response variable was, ‘0’ for living and ‘1’ for dead trees, using iteratively weighted regression and mixed-effects model. Stand-age derived competition indices such as, the ratio of stand basal area to stand age (SBAG), ratio of individual diameter to stand age (DAG), and the quadratic mean diameter (QMD), were found significant in predicting the probability of mortality. These variables were also found to be effective in the thinning effect model. However, excluding the thinning variable resulted in better performance with the chi-square test based on mortality within mid-diameter classes. Thus, the mortality model suggests that over time, individual tree mortality is influenced more greatly by competition modified by stand age rather than by a post-thinning effect in even-aged naturally occurring shortleaf pine trees.

The aim of this study was to develop methods for constructing a simple model describing tree mortality caused by Ips typographus L. using a minimum number of variables. We developed a model for areas spanning natural mountain forests in the Tatra National Park (Slovakia) and the Šumava National Park (Czech Republic), and in managed Czech forests located in four areas varying in environmental conditions. The model describes the time series of tree mortality dynamics caused by I.typographus using two submodels: a long-term dynamics submodel, and a short-term dynamics autoregressive distributed lag(ADL) model incorporating a two year delay and temperature variable averaged over the April-May period. The quality of fit for our models (R2 value) ranged from 0.87 to 0.91. The model was formulated to capture the average monthly temperature effect, a key weather factor. We found that for high-elevation stands located at least 1000 ma.s.l., forest damage was predominantly influenced by May temperatures. For lower-elevation managed forests with warmer climates, the weather effect was insignificant.

Natural tree mortality in Central Europe: a comparison of mortality rates and patterns Mortality is one of the key processes of forest dynamics. Yet, its investigation is challenging since trees can reach high ages, and tree death is the result of several interacting drivers. Long-term monitoring data from unmanaged forests are of great importance for studying mortality. Such data from strict forest reserves in Switzerland and Germany were used in this study to 1) derive mortality rates for 18 wooden species, and 2) build species-specific mortality models. Estimated mortality rates were highly variable among the reserves, and were particularly high in stands with many young trees and a high share of short-living pioneer species. For the calculation of accurate and comparable mortality rates, adjustments towards the same caliper threshold and mortality period are necessary. Models that predict the mortality probability of individual trees can be built based on stem diameter and basal area growth. Such models revealed that small and slow growing trees had the highest mortality risk. In addition, mortality patterns featured species-specific differences. Short-living species experienced high overall mortality probability. Shade-intolerant species showed a more pronounced mortality risk at small diameter and slow growth than shade-tolerant species. Competition as well as drought and frost were identified as the dominant drivers of tree mortality in the Swiss and German reserves. Pronounced age-related mortality due to senescence was not present, in contrast to a primeval beech forest in Ukraine. In the reserves, mortality rates and patterns should become more and more similar to those of primeval forests; however, it will require several decades or centuries of undisturbed forest development to reach identical successional stage.

Five Prunus cerasifera (Myrobalan) based rootstocks, three already released (Adara, Ademir, and Myrobalan B) and two under selection (Miral 3278 AD, Myrobalan 713 AD), budded with two European plums (‘Reine Claude of Bavay’ and ‘Reine Claude Tardive of Chambourcy’) were assessed over sixteenth years at the Aula Dei Experimental Station under heavy and calcareous soil conditions. The adaptation variability of these rootstocks was expressed in tree survival, yield performance, leaf mineral concentration, fruit size and fruit quality traits. Myrobalan 713 AD and Myrobalan B rootstocks presented the highest tree mortality on both plum cultivars, whereas all trees budded on the rest of the rootstocks survived well exhibiting homogenous growth. For both plum cultivars, the less vigorous rootstock was Miral 3278 AD, having also the best agronomical performance (higher cumulative yield, yield efficiency and fruit size). Similar trend in terms of fruit production was also observed for the intermediate semi-vigorous rootstock Adara. Fruit quality traits such as flesh firmness, soluble solids content and titratable acidity were, in general, not significantly affected by rootstock. Independently of the cultivar, at the fifth year of planting all rootstocks induced optimum values of N, P, Ca, Mg, and Mn according to reference values, but lower Fe and higher K values than the optimum. However, at the sixteenth year of the study a different trend was observed, probably influenced by age and crop load of the trees. For both cultivars, rootstocks had optimum Mg, lower than the optimum N and Mn concentrations, while P was, in general, slightly higher than the optimum or close to the upper limit value in the optimum range. The results obtained in the present work showed the hybrid Miral 3278 AD as a good alternative to Myrobalan rootstocks based on its best long-term tree survival and good agronomical performance. Further work should be done with Miral 3278 AD using more intensive orchard plum systems., Financial support was provided by the Spanish grants AGL 2005-05533, AGL 2008-00283 and AGL 2011-24576 cofunded by FEDER and the Regional Government of Aragon (grant A44).

Made available in DSpace on 2022-04-29T08:36:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-12-01 Fundação de Apoio à Pesquisa do Distrito Federal Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Plant invasion can primarily affect the structure and functioning of terrestrial and aquatic ecosystems. Although there is evidence that plant invasion can modify organic matter dynamics in mangroves, it is uncertain whether and to which extent these changes can affect carbon (C) and nitrogen (N) dynamics in the sediment-plant system. Here, we measured: (i) the structure of native vegetation and C and N in the sediment-plant system in subtropical mangroves subjected to aquatic macrophytes invasion in southeastern Brazil. We answered the following questions: i) Do invaded mangroves differ in aboveground biomass compared to non-invaded mangroves?; ii) Are there C4 macrophytes in these sites? iii) What are the C and N stocks in sediment of invaded mangroves? We quantified C and N concentrations and the isotopic signature of such elements (δ13C and δ15N) in the sediment-plant system, the C and N stocks in the sediment (0–20 cm depth), and mangrove aboveground biomass. Mangrove aboveground biomass was lower at invaded compared to non-invaded sites reflecting the species displacement in invaded sites. The sediment at invaded mangroves did not significantly contribute to C4 sources because of the large predominance of both mangrove and invasive C3 plants. While sediment C stocks were similar among study sites (∼47 Mg ha−1), N stocks were lower at invaded (2.7 Mg ha−1) comparing to non-invaded (3.2 Mg ha−1) mangroves. The lower N stocks at invaded sites can reflect the higher leaf N concentrations and lower C:N ratios of invasive plants compared to mangroves. Thus, the effects of macrophytes invasion in subtropical mangroves are more apparent for vegetation structure and N stocks. C stocks alteration is expected the be detectable in the future. Núcleo de Estudos e Pesquisas Ambientais e Limnológicas – Programa de Pós-Graduação Em Ciências Ambientais Área Universitária 1 Vila Nossa Senhora de Fátima Campus de Planaltina Universidade de Brasília, Distrito Federal Programa de Pós-Graduação Em Ecologia Instituto de Ciências Biológicas Campus Darcy Ribeiro Universidade de Brasília, 70910-900, Distrito Federal Campus Experimental de Registro Universidade Estadual Paulista Campus Experimental de Registro Universidade Estadual Paulista Fundação de Apoio à Pesquisa do Distrito Federal: 0193.000344/2017 CAPES: 1422671

The purpose of this study was to investigate the role of strong winds and aging in the death and/or decline in the growth of Korean fir on Mt. Halla in Korea. Bangeoreum (BA-S), Jindalrebat (JD-E), and Youngsil (YS-W) on the southern, eastern, and western slopes of Mt. Halla (ca. 1600 and 1700 m a.s.l.) were selected for the study. The site chronologies were established using more than 10 living Korean firs at each site. Additionally, to date the years and seasons of death of standing/fallen dead Korean firs, 15/15, 14/15, and 10/10 trees were selected at BA-S, JD-E, and YS-W, respectively. After adjusting the age with the period of growth up to the sampling point, the oldest Korean fir found among the living trees was 114 years old at JD-E and the oldest fir among the dead trees was 131 years old at JD-E. Besides this, most of the trees at BA-S and JD-E were found to have died between 2008 and 2015, and at irregular intervals between 1976 and 2013 at YS-W. Also, the maximum number of trees, that is, 62.7% died between spring and summer, followed by 20.9% between summer and autumn, and 16.4% between autumn of the current year and spring of the following year. Abrupt growth reductions occurred at BA-S and JD-E, and have become more significant in recent years, whereas at YS-W, the abrupt growth reduction and recovery occur in a cyclic order. The intensity and frequency of the typhoons increased from 2012, and this trend was in-line with the increased number of abrupt growth reductions at BA-S and JD-E. Therefore, the typhoons of 2012 are considered as the most likely influencing factor in death and/or growth reduction in Korean firs. In contrast, the decline in the growth of the Korean firs located on the windward slope (YS-W) showed a relationship with winds stronger than 25–33 m/s.