Mortality of tree species around the globe is increasingly driven by hotter drought and heat waves. Tree juveniles are at risk, as well as adults, and this will have a negative effect on forest dynamics and structure under climate change. Novel management options are urgently needed to reduce this mortality and positively affect forest dynamics and structure. Potential drought-ameliorating soil amendments such as nanochitosan – a biopolymer upcycled from byproducts of the seafood industry – may provide an additional set of useful tools for reducing juvenile mortality during hotter droughts. Nanochitosan promotes water and nutrient absorption in plants but has not been tested in the context of drought and heat stress. We evaluated factors affecting mortality risk and rate for dryland Pinus edulis juveniles (2–3 years old) in a growth chamber using a factorial experiment that included ambient and +4°C warmer base temperatures, with and without a 10 day +8°C heat wave, and with and without a nanochitosan soil amendment. The nanochitosan treatment reduced the relative risk of mortality, emphasizing a protective function of this soil amendment, reducing the relative risk of mortality by 37%. Importantly, the protective effects of nanochitosan soil amendment in delaying tree mortality under hotter drought and heat waves provides a new, potentially positive management treatment for tree juveniles trying to survive in the climate of the Anthropocene.

Rising temperatures associated with climate change are impacting household energy use. Many of today’s industrial-technological-urban humans thermoregulate in the face of varying temperatures using extra-metabolic energy use for heating and cooling our indoor microclimates. Previously, household energy use as a function of temperature change over seasons and time has been described using a three-part model of thermoregulation, the Extra-Metabolic Scholander-Irving model (EMSI), where energy use is lowest in the thermal neutral zone around room temperature and increases in colder and hotter temperatures. However, the EMSI model has only been evaluated for moderately warm cities to date, covering only two parts of the three-part model and lacking evaluation of data for extremely hot temperatures. We show that household energy use in Arizona, a U.S. state that includes hot semi-arid environments, varies across topography, and increases in response to the hottest summer months–exemplifying the third part of the EMSI model. Additionally, household energy use is lowest in the spring and fall and increases in response to colder temperatures in the winter. This relationship has hysteresis related to differences in household income; service regions with lower-income households delay the onset of extra-metabolic energy use for cooling. We use this model to gain predictive insights into energy use demand due to ongoing warming in the context of the desert city of Yuma, Arizona, where a relatively small increase in mean temperatures of ~1.5°C since the Industrial Revolution produced a 20-day increase (6%) in cooling days annually. Our study expands the EMSI model of thermal regulation to the previously missing hot part of the model, thereby gaining insights into the unique challenges of sustaining extra-metabolic thermoregulation in the face of global warming.

Livestock production in drylands requires consideration of the ecological applications of ecohydrological redistribution of water. Intensive cattle trampling and the associated increase of surface runoff are common concerns for rangeland productivity and sustainability. Here, we highlight a regional livestock production system in which cattle trails and trampling surrounding an artificial impoundment are purposely managed to enhance redistribution and availability of water for cattle drinking. Based on literature synthesis and field measurements, we first describe cattle production systems and surface water redistribution in the Dry Chaco rangelands of South America, and then develop a conceptual framework to synthesize the ecohydrological impacts of livestock production on these ecosystems. Critical to this framework is the pioshere-a degraded overgrazed and overtrampled area where vegetation has difficulties growing, usually close to the water points. The Dry Chaco rangelands have three key distinctive characteristics associated with the flat sedimentary environment lacking fresh groundwater and the very extensive ranching conditions: (1) cattle drinking water is provided by artificial impoundments filled by runoff, (2) heavy trampling around the impoundment and its adjacent areas generates a piosphere that favors runoff toward the impoundment, and (3) the impoundment, piosphere, and extensive forage areas are hydrologically connected with a network of cattle trails. We propose an ecohydrological framework where cattle transit and trampling alter the natural water circulation of these ecosystems, affecting small fractions of the landscape through increased runoff (compaction in piosphere and trails), surface connectivity (convergence of trails to piosphere to impoundment), and ponding (compaction of the impoundment floor) that operate together making water harvesting and storage possible. These effects have likely generated a positive water feedback on the expansion of livestock in the region with a relatively low impact on forage production. We highlight the role of livestock transit as a geomorphological agent capable of reshaping the hydrology of flat sedimentary rangelands in ways that can be managed positively for sustainable ranching systems. We suggest that the Dry Chaco offers an alternative paradigm for rangelands in which cattle trampling may contribute to sustainable seminatural production systems with implications for other dry and flat rangelands of the world.

Terrestrial disturbances are increasing in frequency and severity, perturbing the hydrologic cycle by altering vegetation-mediated water use and microclimate. Here, we synthesize the literature on post-disturbance ecohydrological coupling, including the mechanistic relationship between vegetation and streamflow, under changing disturbance regimes, atmospheric CO2, and climate. Disturbance can cause decoupling between transpiration and streamflow by altering the connectivity, size, availability, and spatial distribution of their source pools. Successional trajectories influence the dynamics of source water partitioning. Changing climate and disturbance regimes can alter succession and prolong decoupling. Increasing rates, severity, and spread of disturbances along with warming could promote greater decoupling globally. From this review emerges a framework of testable hypotheses that identify the critical processes regulating ecohydrological coupling and provide a roadmap for future research. Accurate prediction of post-disturbance coupling requires understanding the degree of hydraulic connectivity between source water pools and their response to succession under changing disturbance and climate regimes.

Amazon forests are being degraded by myriad anthropogenic disturbances, altering ecosystem and climate function. We analyzed the effects of a range of land‐use and climate‐change disturbances on fine‐scale canopy structure using a large database of profiling canopy lidar collected from disturbed and mature Amazon forest plots. At most of the disturbed sites, surveys were conducted 10–30 years after disturbance, with many exhibiting signs of recovery. Structural impacts differed in magnitude more than in character among disturbance types, producing a gradient of impacts. Structural changes were highly coordinated in a manner consistent across disturbance types, indicating commonalities in regeneration pathways. At the most severely affected site – burned igapó (seasonally flooded forest) – no signs of canopy regeneration were observed, indicating a sustained alteration of microclimates and consequently greater vulnerability to transitioning to a more open‐canopy, savanna‐like state. Notably, disturbances rarely shifted forests beyond the natural background of structural variation within mature plots, highlighting the similarities between anthropogenic and natural disturbance regimes, and indicating a degree of resilience among Amazon forests. Studying diverse disturbance types within an integrated analytical framework builds capacity to predict the risk of degradation‐driven forest transitions.

Over the past four decades, annual area burned has increased significantly in California and across the western USA. This trend reflects a confluence of intersecting factors that affect wildfire regimes. It is correlated with increasing temperatures and atmospheric vapour pressure deficit. Anthropogenic climate change is the driver behind much of this change, in addition to influencing other climate-related factors, such as compression of the winter wet season. These climatic trends and associated increases in fire activity are projected to continue into the future. Additionally, factors related to the suppression of the Indigenous use of fire, aggressive fire suppression and, in some cases, changes in logging practices or fuel management intensity, collectively have produced large build-ups of vegetative fuels in some ecosystems. Human activities provide the most common ignition source for California's wildfires. Despite its human toll, fire provides a range of ecological benefits to many California ecosystems. Given the diversity of vegetation types and fire regimes found in the state, addressing California's wildfire challenges will require multi-faceted and locally targeted responses in terms of fuel management, human-caused ignitions, building regulations and restrictions, integrative urban and ecosystem planning, and collaboration with Tribes to support the reinvigoration of traditional burning regimes.

Tree loss is increasing rapidly due to drought- and heat-related mortality and intensifying fire activity. Consequently, the fate of many forests depends on the ability of juvenile trees to withstand heightened climate and disturbance anomalies. Extreme climatic events, such as droughts and heatwaves, are increasing in frequency and severity, and trees in mountainous regions must contend with these landscape-level climate episodes. Recent research focuses on how mortality of individual tree species may be driven by drought and heatwaves, but how juvenile mortality under these conditions would vary among species spanning an elevational gradient—given concurrent variation in climate, ecohydrology, and physiology–remains unclear. We address this knowledge gap by implementing a growth chamber study, imposing extreme drought with and without a compounding heatwave, for juveniles of five species that span a forested life zones in the Southwestern United States. Overall, the length of a progressive drought required to trigger mortality differed by up to 20 weeks among species. Inclusion of a heatwave hastened mean time to mortality for all species by about 1 week. Lower-elevation species that grow in warmer ambient conditions died earlier (Pinus ponderosa in 10 weeks, Pinus edulis in 14 weeks) than did higher-elevation species from cooler ambient conditions (Picea engelmannii and Pseudotsuga menziesii in 19 weeks, and Pinus flexilis in 30 weeks). When exposed to a heatwave in conjunction with drought, mortality advanced significantly only for species from cooler ambient conditions (Pinus flexilis: 2.7 weeks earlier; Pseudotsuga menziesii: 2.0 weeks earlier). Cooler ambient temperatures may have buffered against moisture loss during drought, resulting in longer survival of higher-elevation species despite expected drought tolerance of lower-elevation species due to tree physiology. Our study suggests that droughts will play a leading role in juvenile tree mortality and will most directly impact species at warmer climate thresholds, with heatwaves in tandem with drought potentially exacerbating mortality especially of high elevation species. These responses are relevant for assessing the potential success of both natural and managed reforestation, as differential juvenile survival following episodic extreme events will determine future landscape-scale vegetation trajectories under changing climate.

Ecologists have long sought to understand the controls of species’ geographic distributions. Two important hypotheses have been that range limits are determined 1) predominantly by climate or 2) by competition in addition to climate, with competitive interactions dominating where climate is benign. If the first hypothesis is correct, the effect of changing climate on species’ distributions should be adequately predicted by climate-only models. Here, we used demographic range models (DRMs) to evaluate the influence of climate and competition on the geographic distribution of Pinus edulis, a desert pine in the southwestern U.S. We parameterized DRMs with data on 23,426 trees in 1,941 forest inventory plots. Vital rate responses were consistent with the predictions of the second hypothesis: negative effects of warm-dry conditions at low-elevation sites and competition at cool-humid, high-elevation sites. Further, including both climate and competition in the DRM yielded a better fit of DRM-predicted population growth rate to the observed distribution than a climate-only DRM. However, at cool-humid sites, negative effects of competition were too weak to offset positive climate effects, resulting in a mismatch between predicted population growth rate and observed distribution. This result leads us to formulate a new hypothesis: climate has complex influences on species’ distributions through its effects on range-limiting processes at a variety of scales, for example, biotic and disturbance feedbacks at community, ecosystem, landscape, and macrosystem scales. The implications of this complex systems hypothesis are that range dynamics may be poorly predictable from static, climate-only models, and may be characterized by sudden changes in abundance, even distribution collapse, with climate change.

Tree die-off, driven by extreme drought and exacerbated by a warming climate, is occurring rapidly across every wooded continent—threatening carbon sinks and other ecosystem services provided by forests and woodlands. Forecasting the spatial patterns of tree die-off in response to drought is a priority for the management and conservation of forested ecosystems under projected future hotter and drier climates. Several thresholds derived from drought-metrics have been proposed to predict mortality of Pinus edulis, a model tree species in many studies of drought-induced tree die-off. To improve future capacity to forecast tree mortality, we used a severe drought as a natural experiment. We compared the ability of existing mortality thresholds derived from four drought metrics (the Forest Drought Severity Index (FDSI), the Standardized Precipitation Evapotranspiration Index, and raw values of precipitation (PPT) and vapor pressure deficit, calculated using 4 km PRISM data) to predict areas of P. edulis die-off following an extreme drought in 2018 across the southwestern US. Using aerial detection surveys of tree mortality in combination with gridded climate data, we calculated the agreement between these four proposed thresholds and the presence and absence of regional-scale tree die-off using sensitivity, specificity, and the area under the curve (AUC). Overall, existing mortality thresholds tended to over predict the spatial extent of tree die-off across the landscape, yet some retain moderate skill in discriminating between areas that experienced and did not experience tree die-off. The simple PPT threshold had the highest AUC score (71%) as well as fair sensitivity and specificity, but the FDSI had the greatest sensitivity to die-off (85.9%). We highlight that empirically derived climate thresholds may be useful forecasting tools to identify vulnerable areas to drought induced die-off, allowing for targeted responses to future droughts and improved management of at-risk areas.

With climate change, heat waves are becoming increasingly frequent, intense and broader in spatial extent. However, while the lethal effects of heat waves on humans are well documented, the impacts on flora are less well understood, perhaps except for crops. We summarize recent findings related to heat wave impacts including: sublethal and lethal effects at leaf and plant scales, secondary ecosystem effects, and more complex impacts such as increased heat wave frequency across all seasons, and interactions with other disturbances. We propose generalizable practical trials to quantify the critical bounding conditions of vulnerability to heat waves. Collectively, plant vulnerabilities to heat waves appear to be underappreciated and understudied, particularly with respect to understanding heat wave driven plant die-off and ecosystem tipping points.

Biodiversity contributes to the ecological and climatic stability of the Amazon Basin 1 , 2 , but is increasingly threatened by deforestation and fire 3 , 4 . Here we quantify these impacts over the past two decades using remote-sensing estimates of fire and deforestation and comprehensive range estimates of 11,514 plant species and 3,079 vertebrate species in the Amazon. Deforestation has led to large amounts of habitat loss, and fires further exacerbate this already substantial impact on Amazonian biodiversity. Since 2001, 103,079–189,755 km 2 of Amazon rainforest has been impacted by fires, potentially impacting the ranges of 77.3–85.2% of species that are listed as threatened in this region 5 . The impacts of fire on the ranges of species in Amazonia could be as high as 64%, and greater impacts are typically associated with species that have restricted ranges. We find close associations between forest policy, fire-impacted forest area and their potential impacts on biodiversity. In Brazil, forest policies that were initiated in the mid-2000s corresponded to reduced rates of burning. However, relaxed enforcement of these policies in 2019 has seemingly begun to reverse this trend: approximately 4,253–10,343 km 2 of forest has been impacted by fire, leading to some of the most severe potential impacts on biodiversity since 2009. These results highlight the critical role of policy enforcement in the preservation of biodiversity in the Amazon.

Analysis of past change puts risks of plant carbon management in a long-term context

Earth’s forests face grave challenges in the Anthropocene, including hotter droughts increasingly associated with widespread forest die-off. But despite the vital importance of forests—especially historical forests—to global ecosystem services, their fates in a warming world remain highly uncertain. Critically missing is quantitative determination of hotter-drought climatic drivers at globally-distributed, ground-based, tree-mortality sites. We established a precisely geo-referenced global database documenting climate-induced mortality events spanning all tree-supporting biomes from 154 studies since 1970. Here we quantify a lethal global hotter-drought fingerprint from these tree-mortality sites across 675 locations encompassing 1,303 database plots. Frequency of these lethal climate conditions accelerates under projected warming, up 140% by +4℃. Our database, soon available at tree-mortality.net, provides initial footing for further community development of quantitative, ground-based monitoring of global tree mortality (e.g., still including peer-reviewed observations, but importantly also those from forestry professionals, land managers, and citizen scientists). Furthermore, our database immediately enables critical predictive model validation and improved remote sensing of mortality. While our initial database enabled empirical quantification of a global climate signal for hotter-drought triggered tree mortality, ongoing and online contributions to the database (with efforts to be more spatially representative) will enable myriad future analyses and progress toward understanding the role of hotter-drought in the mechanistically complex process of tree mortality. Our global fingerprint of lethal hotter-drought confirms many of Earth’s forests are increasingly imperiled by further warming.

Earth’s forests face grave challenges in the Anthropocene, including hotter droughts increasingly associated with widespread forest die-off. But despite the vital importance of forests—especially historical forests—to global ecosystem services, their fates in a warming world remain highly uncertain. Critically missing is quantitative determination of hotter-drought climatic drivers at globally-distributed, ground-based, tree-mortality sites. We established a precisely geo-referenced global database documenting climate-induced mortality events spanning all tree-supporting biomes from 154 studies since 1970. Here we quantify a lethal global hotter-drought fingerprint from these tree-mortality sites across 675 locations encompassing 1,303 database plots. Frequency of these lethal climate conditions accelerates under projected warming, up 140% by +4℃. Our database, soon available at tree-mortality.net, provides initial footing for further community development of quantitative, ground-based monitoring of global tree mortality (e.g., still including peer-reviewed observations, but importantly also those from forestry professionals, land managers, and citizen scientists). Furthermore, our database immediately enables critical predictive model validation and improved remote sensing of mortality. While our initial database enabled empirical quantification of a global climate signal for hotter-drought triggered tree mortality, ongoing and online contributions to the database (with efforts to be more spatially representative) will enable myriad future analyses and progress toward understanding the role of hotter-drought in the mechanistically complex process of tree mortality. Our global fingerprint of lethal hotter-drought confirms many of Earth’s forests are increasingly imperiled by further warming.

Macrosystems are integrated human–natural systems, in recognition of the fact that virtually every natural system on Earth influences and is influenced by human activities, even over long distances. It is therefore crucial to incorporate inherent properties of broad‐scale systems, such as human–nature connectivity and feedbacks at multi‐scales, into macrosystems biology studies. Here, we propose the “metacoupling” framework as a macrosystems biology approach. This framework incorporates the study of ecological and socioeconomic dimensions and their interactions within, between, and among adjacent and distant locations. We present examples highlighting that (1) human activities are increasing multi‐scale interactions; (2) the increase in frequency and intensity of distant interactions reduces the importance of proximity as a dominant factor connecting systems; and (3) metacoupling generates both ecological and socioeconomic feedbacks, with profound impacts. The metacoupling framework discussed here can advance macrosystems biology, create opportunities for innovative scientific discoveries, and address global challenges.

We outline the multiple, cross-scale, and complex consequences of terrestrial and marine ecosystem heatwaves in two regions on opposite sides of the planet: the southwestern USA and southwestern Australia, both encompassing Global Biodiversity Hotspots, and where ecosystem collapses or features of it have occurred in the past two decades. We highlight ecosystem shifts that have clearly demonstrated a substantial change from a baseline state over time, although not necessarily across their entire distribution, with evidence of collapse at local scales. Responses to temperature extremes, such as heatwaves, encompass processes at all scales, including population level (e.g. altered demography such as survival, recruitment, and fecundity, together resulting in structural changes), community level (e.g. species compositional shifts), and ecosystem level (e.g. carbon loss), as well as physical properties altered by vegetation loss (e.g. microclimate, fire behaviour on land). These changes impact all trophic levels with foundational species losses (such as seagrasses, kelp, and trees), flowing through to vertebrates (such as sea turtles, penguins, and cockatoos). Where extensive collapse has occurred, shifts in microclimate could affect important biosphere-to-atmosphere feedbacks including fluxes of energy, carbon, and water. Such extensive changes usually do not occur in isolation and frequently interact with other disturbance processes such as fire, storms, pathogen and pest outbreaks, and anthropogenic stressors. Interactions may alter the likelihood, extent, or severity of subsequent disturbances (linked disturbances) as well as condition the ecological response and recovery (compound disturbances). In addition, if ecosystem collapse is extensive enough (e.g. tree die-off), those changes also can impact climate and ecosystems elsewhere via ecoclimate teleconnections. Increasing rates of climatic extremes will drive a host of direct and indirect feedbacks certain to produce large-scale shifts in ecological functioning at unprecedented rates. Understanding how, why, and where these shifts will occur will be critical for effective ecosystem management and climate change mitigation.

This collection contains the subsets of FIA (https://apps.fs.usda.gov/fia/datamart/datamart.html) and PRISM (http://prism.oregonstate.edu/) data used in "Climate-driven, but dynamic and complex? A reconciliation of competing hypotheses for species' distributions".The two datasets contain demographic data (survival and growth in SurvivalData.csv and recruitment in RecruitData.csv) and climate data used to fit vital rate models estimating the effects of climate and competition on Pinus edulis in the southwestern US.

Dryland (arid and semiarid) ecosystems are extensive, home to a third of the human population, and a major contributor to terrestrial net primary productivity and associated biogeochemical cycles. Many dryland systems are undergoing woody plant encroachment, which can substantially alter landscape‐scale soil nutrient dynamics via long‐recognized “islands of fertility” mechanisms. To effectively constrain soil biogeochemistry responses to woody plant encroachment, predictions are needed for microbial biomass and especially microbial activity in addition to existing predictions for soil nutrients—referred to collectively hereafter as “collective soil functioning.” Here we evaluated whether collective soil functioning could be predicted from a suite of metrics including plant cover, precipitation, soil physiochemical characteristics, and topographic variables across complex landscapes undergoing woody plant encroachment by mesquite (Prosopis velutina). Plant cover alone predicted nearly half of the variability (R2 = 48.5%) in collective soil functioning and had a significant effect on each component of this index (soil nutrients, microbial biomass, and microbial activity). Prediction strength for collective soil functioning increased to 55.4%, and the error term decreased by 13.4% when precipitation, soil physiochemical characteristics, and topographic metrics were also included in models (plant and environment model). Besides the expected effects of plant cover, other significant predictors of collective soil functioning included state factors such as topography, precipitation, and parent material along with soil age and bulk density. These results illustrate that mesquites influence many components of soil functionality but the strength of this effect depends on which component is analyzed and which environmental variables are considered.

Abstract Tropical ecosystems are undergoing unprecedented rates of degradation from deforestation, fire, and drought disturbances. The collective effects of these disturbances threaten to shift large portions of tropical ecosystems such as Amazon forests into savanna‐like structure via tree loss, functional changes, and the emergence of fire (savannization). Changes from forest states to a more open savanna‐like structure can affect local microclimates, surface energy fluxes, and biosphere–atmosphere interactions. A predominant type of ecosystem state change is the loss of tree cover and structural complexity in disturbed forest. Although important advances have been made contrasting energy fluxes between historically distinct old‐growth forest and savanna systems, the emergence of secondary forests and savanna‐like ecosystems necessitates a reframing to consider gradients of tree structure that span forest to savanna‐like states at multiple scales. In this Innovative Viewpoint, we draw from the literature on forest–grassland continua to develop a framework to assess the consequences of tropical forest degradation on surface energy fluxes and canopy structure. We illustrate this framework for forest sites with contrasting canopy structure that ranges from simple, open, and savanna‐like to complex and closed, representative of tropical wet forest, within two climatically distinct regions in the Amazon. Using a recently developed rapid field assessment approach, we quantify differences in cover, leaf area vertical profiles, surface roughness, albedo, and energy balance partitioning between adjacent sites and compare canopy structure with adjacent old‐growth forest; more structurally simple forests displayed lower net radiation. To address forest–atmosphere feedback, we also consider the effects of canopy structure change on susceptibility to additional future disturbance. We illustrate a converse transition—recovery in structure following disturbance—measuring forest canopy structure 10 yr after the imposition of a 5‐yr drought in the ground‐breaking Seca Floresta experiment. Our approach strategically enables rapid characterization of surface properties relevant to vegetation models following degradation, and advances links between surface properties and canopy structure variables, increasingly available from remote sensing. Concluding, we hypothesize that understanding surface energy balance and microclimate change across degraded tropical forest states not only reveals critical atmospheric forcing, but also critical local‐scale feedbacks from forest sensitivity to additional climate‐linked disturbance.

Predictions of warmer droughts causing increasing forest mortality are becoming abundant, yet few studies have investigated the mechanisms of forest persistence. To examine the resistance of forests to warmer droughts, we used a five-year precipitation reduction (similar to 45% removal), heat (+4 degrees C above ambient) and combined drought and heat experiment in an isolated stand of mature Pinus edulis-Juniperus monosperma. Despite severe experimental drought and heating, no trees died, and we observed only minor evidence of hydraulic failure or carbon starvation. Two mechanisms promoting survival were supported. First, access to bedrock water, or 'hydraulic refugia' aided trees in their resistance to the experimental conditions. Second, the isolation of this stand amongst a landscape of dead trees precluded ingress by Ips confusus, frequently the ultimate biotic mortality agent of pinon. These combined abiotic and biotic landscape-scale processes can moderate the impacts of future droughts on tree mortality by enabling tree avoidance of hydraulic failure, carbon starvation, and exposure to attacking abiotic agents.