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Abstract Increases in the frequency and severity of climate-sensitive disturbances like wildfire, drought, and insect outbreaks pose an imminent threat to Earth’s forests, including their status as a net carbon sink. Forest treatments including thinning and prescribed fire are increasingly viewed as key tools for mitigating disturbance impacts, but their efficacy in stabilizing carbon stocks and reducing mortality, especially for drought and insect outbreaks, remains uncertain. Moreover, we have limited understanding of whether the moderating effect of forest treatments provides a net benefit to vegetation carbon stocks, or if the initial carbon loss required to implement treatments outweighs potential reductions in carbon losses during subsequent disturbance. Here we conduct a systematic meta-analysis of published literature to understand how thinning, prescribed fire, and combined treatments impact survival and carbon stocks following wildfires, droughts, and insect outbreaks. We found that treatments improved survival following wildfires, but had only marginal impacts on survival following drought and insect outbreaks. While thinning had a modest positive effect on carbon stocks following wildfire, treatments generally reduced carbon stocks following drought and had no impact following insect outbreaks. Overall, our findings suggest that the benefits of forest treatments for vegetation carbon stocks are limited, especially following drought and insect disturbances. These findings have important policy implications for carbon credit programs. 

Abstract Climate change has increased the frequency and severity of drought and large wildfire events across western North America. Despite the increasing concurrence of drought and wildfire events and the importance of forests as a global carbon sink, the impacts of fire on tree drought and carbon acquisition traits are not well understood, particularly on multi‐year time‐scales.In 2022–2024, we leveraged a natural experiment at a large 2018 wildfire in southwestern Colorado, comparing leaf and xylem functional traits related to drought resistance and carbon acquisition in burned and unburned ponderosa pine, quaking aspen, subalpine fir, and Engelmann spruce trees.Relative to unburned trees of the same species, we found reduced xylem vulnerability to embolism (P₅₀) in burned ponderosa pine and subalpine fir; decreased leaf heat tolerance (T₅₀) in burned quaking aspen and ponderosa pine; and increased investment in leaf structural over photosynthetic components (leaf C:N isotopic ratio) in burned quaking aspen, subalpine fir, and Engelmann spruce.In contrast to previous studies, our results suggest that wildfire positively impacts functional traits related to drought resistance and water movement in surviving burned trees. However, generally negative impacts of wildfire were found with respect to leaf physiological and photosynthetic traits, suggesting divergent water and carbon responses to fire. Read the freePlain Language Summaryfor this article on the Journal blog. 

Abstract Climate change driven extreme droughts have major impacts on forest ecosystems, including large‐scale mortality and reduced primary production, which feedback to affect the global carbon cycle. The long‐term impacts of extreme drought events on forest mortality, ecosystem responses, and recovery/post‐drought trajectories are poorly understood. In this study, we combine annual tree ring widths of five major species occurring in the southwestern United States and data obtained from long‐term forest inventory and monitoring plots to study the effect of an extreme drought event in 2002 on subsequent tree growth. We quantified the extent to which trees that survived the drought had increased growth due to potential increases in resources from reduced stand density or reduced growth due to lingering impacts of drought stress. We found diverse patterns of post‐drought growth trajectories across species, with drastic increases in growth in some species such as trembling aspen (Populus tremuloides) and clear growth suppression in other species such as ponderosa pine (Pinus ponderosa), reflecting notable drought legacy effects. Total basal area was the best predictor of post‐drought growth responses, though the regression effect (positive or negative) varied by species; for example, ponderosa pine showed less growth than predicted in higher density stands while spruce had greater growth than expected in the higher density stands. Climatic water deficit and stand age also emerged as important drivers of post‐drought growth trajectories for multiple species. The results of this study can help to elucidate how different forest types in the southwestern United States will respond to future drought events and the ramifications for carbon cycling in this region. 

ABSTRACT Nature‐based climate solutions in Earth's forests could strengthen the land carbon sink and contribute to climate mitigation, but must adequately account for climate risks to the durability of carbon storage. Forest carbon offset protocols use a “buffer pool” to insure against disturbance risks that may compromise durability. However, the extent to which current buffer pool tools and allocations align with current scientific data or models is not well understood. Here, we use a tropical forest stand biomass model and an extensive set of long‐term tropical forest plots to test whether current buffer pool contributions are adequate to insure against observed disturbance regimes. We find that forest age and disturbance regime both influence necessary buffer pool sizes. In the majority of disturbance scenarios in a major carbon registry buffer pool tool, current buffer pools are substantially smaller than required by carbon cycle science. Buffer pool tools and estimates urgently need to be updated to accurately assess disturbance regimes and climate change impact on disturbances based on rigorous, open scientific datasets for nature‐based climate solutions to succeed. 

Summary Human‐caused climate change is predicted to bring more frequent droughts and higher temperatures in the western United States, which threaten ecologically important trembling aspen forests.We used ring‐specific vulnerability curves of aspen branches along two climate gradients to determine whether damages to pit membranes accumulate as the xylem ages.We found that rings older than 3 yr have a significant decline in hydraulic conductivity, especially at average summer water potentials for the species. These differences were not due to differences in the diameter of the vessels, but a difference in how much xylem was active between rings older than 3 yr and 1 yr, suggesting the presence of accumulated damage to pit membranes impairing water transport.Vulnerability to embolism differs across ring age and between wetter and drier populations, underscoring that damages due to drought may accumulate to lethal levels if the xylem does not acclimate to climate change in newer growth. 

Abstract Cyclonic storms, or hurricanes, are expected to intensify as ocean heat energy rises due to climate change. Ecological theory suggests that tropical forest resistance to hurricanes should increase with forest age and wood density. However, most data on hurricane effects on tropical forests come from a limited number of well‐studied long‐term monitoring sites, restricting our capacity to evaluate the resistance of tropical forests to hurricanes across broad environmental gradients.In this study, we assessed whether forest age and aridity mediate the effects of hurricanes Irma and Maria in Puerto Rico, Vieques and Culebra islands. We leveraged functional trait data for 410 tree species, remotely sensed measurements of canopy height and cover, along with data on forest stand characteristics of 180 of 338 forest monitoring plots, each covering an area of 0.067 ha. The plots represent a broad mean annual precipitation (MAP) gradient from 701 to 4598 mm and a complex mosaic of forest age from 5 to around 85 years since deforestation.Hurricanes resulted in a 25% increase in basal area mortality rates, a 45% decrease in canopy height and a 21% reduction in canopy cover. These effects intensified with forest age, even after considering proximity to the hurricane path. The links between forest age and hurricane disturbances were likely due the prevalence of tall canopies.Tall forest canopies were strongly linked with low community‐weighted wood density (WD). These characteristics were on average more common in moist and wet forests (MAP >1250 mm). Conversely, dry forests were dominated by short species with high wood density (WD > 0.6 g cm⁻³) and did not show significant increases in basal area mortality rates after the hurricanes.Synthesis. Our findings show that selection towards drought‐tolerant traits across aridity gradients, such as short stature and dense wood, enhances resistance to hurricanes. However, forest age modulated responses to hurricanes, with older forests being less resistant across the islands. This evidence highlights the importance of considering the intricate links between ecological succession and plant function when forecasting tropical forests’ responses to increasingly strong hurricanes. 

Abstract Metrics to quantify regulation of plant water status at the daily as opposed to the seasonal scale do not presently exist. This gap is significant since plants are hypothesised to regulate their water potential not only with respect to slowly changing soil drought but also with respect to faster changes in air vapour pressure deficit (VPD), a variable whose importance for plant physiology is expected to grow because of higher temperatures in the coming decades. We present a metric, the stringency of water potential regulation, that can be employed at the daily scale and quantifies the effects exerted on plants by the separate and combined effect of soil and atmospheric drought. We test our theory using datasets from two experiments where air temperature and VPD were experimentally manipulated. In contrast to existing metrics based on soil drought that can only be applied at the seasonal scale, our metric successfully detects the impact of atmospheric warming on the regulation of plant water status. We show that the thermodynamic effect of VPD on plant water status can be isolated and compared against that exerted by soil drought and the covariation between VPD and soil drought. Furthermore, in three of three cases, VPD accounted for more than 5 MPa of potential effect on leaf water potential. We explore the significance of our findings in the context of potential future applications of this metric from plant to ecosystem scale. 

Abstract Anthropogenic climate change is projected to drive increases in climate extremes and climate-sensitive ecosystem disturbances such as wildfire with enormous economic impacts. Understanding spatial and temporal patterns of risk to property values from climate-sensitive disturbances at national and regional scales and from multiple disturbances is urgently needed to inform risk management and policy efforts. Here, we combine models for three major climate-sensitive disturbances (i.e., wildfire, climate stress-driven tree mortality, and insect-driven tree mortality), future climate projections of these disturbances, and high-resolution property values data to quantify the spatiotemporal exposure of property values to disturbance across the contiguous United States (US). We find that property values exposed to these climate-sensitive disturbances increase sharply in future climate scenarios, particularly in existing high-risk regions of the western US, and that novel exposure risks emerge in some currently lower-risk regions such as the southeast and Great Lakes regions. Climate policy that drives emissions towards low-to-moderate climate futures avoids large increases in disturbance risk exposure compared to high emissions scenarios. Our results provide an important large-scale assessment of climate-sensitive disturbance risk to property values to help inform land management and climate adaptation efforts. 

Structural overshoots, where biomass is overallocated to tree leaf area compared to sapwood area, could result in lethal stress during droughts. Climate change may alter climatic cues that drive leaf area production, such as temperature and precipitation, as well as seasonal dynamics that underlie summer rainfall due to the North American Monsoon (NAM). Combined, this could lead to temporal mismatches between leaf area‐driven water demand and availability, and increased drought‐induced mortality events.We used leaf area to sapwood area ratios to investigate the prevalence of overshoots and whether overshoots increase drought‐induced mortality. We measured populations of aspen spanning the northern transition zone of the NAM during and following severe droughts.We observed increased overshoots and drought‐induced mortality in southern latitude populations that rely more on summer monsoon rainfall. Changes in convective activity from low snowpack the preceding winter may be a climatic driver of heightened summer monsoon rainfall in the region and therefore may also trigger increased production of leaf area during wetter summers.Our results suggest that an overshoot of leaf area to sapwood area (A_L:A_S) ratios is associated with drought‐induced tree mortality and highlight that climate‐change driven alterations to the NAM could have major consequences for tree species' acclimation to environmental change. Read the freePlain Language Summaryfor this article on the Journal blog.