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Globe-LFMC is an extensive global database of live fuel moisture content (LFMC) measured from 1,383 sampling sites in 11 countries: Argentina, Australia, China, France, Italy, Senegal, Spain, South Africa, Tunisia, United Kingdom and the United States of America. The database contains 161,717 individual records based on in situ destructive samples used to measure LFMC, representing the amount of water in plant leaves per unit of dry matter. The primary goal of the database is to calibrate and validate remote sensing algorithms used to predict LFMC. However, this database is also relevant for the calibration and validation of dynamic global vegetation models, eco-physiological models of plant water stress as well as understanding the physiological drivers of spatiotemporal variation in LFMC at local, regional and global scales. Globe-LFMC should be useful for studying LFMC trends in response to environmental change and LFMC influence on wildfire occurrence, wildfire behavior, and overall vegetation health.

Dry lightning is a prevalent episodic natural ignition source for wildfires, particularly in remote regions where such fires can escalate into uncontrollable events, burning extensive areas. In this study, we aimed to understand the interplay of environmental, fuel, and geographical factors in evaluating the probability of fire initiation following dry lightning strikes in Tasmania, Australia. We integrated dry lightning, active fire records, and gridded data on fire weather, fuel, and topography into a binary classification framework for both fire‐initiating and non‐fire‐causing lightning strikes. Employing statistical and machine learning techniques, we quantified the likelihood of fire initiation due to dry lightning, with the resampled Random Forest model exhibiting notable performance with an ROC‐AUC value of 0.98. Our findings highlight how fuel characteristics and moisture content associated with particular vegetation types influence fire initiation and provide an objective approach for identifying susceptible regions of dry lightning ignitions, informing associated fire management responses. Plain Language Summary: Lightning strikes occurring with minimal rainfall, known as dry lightning strikes, often ignite wildfires in dry vegetation, especially in remote areas. These fires can remain undetected for hours to days and quickly grow out of control under favorable conditions, causing extensive damage and burning large areas. Our study investigated how environmental factors such as weather, terrain, and fuel variables (fuel load, fuel type, and fuel moisture) affect the probability of a fire starting after a dry lightning strike in Tasmania, Australia. We analyzed data on lightning strikes, active fires, topography, fuel (via vegetation and fire history), and weather conditions, to build advanced machine learning models to predict the chances of a fire started following a dry lightning strike. Our findings indicate a high probability of ignition in scenarios characterized by high fuel loads and low fuel moisture content, particularly in treeless vegetation types such as buttongrass sedgelands. This information can help fire authorities identify areas or times most at risk of dry lightning‐ignited wildfires, allowing for better fire prevention and response strategies. Key Points: Random Forest modeling accurately identified fires ignited by dry lightning strikes in TasmaniaWestern Tasmania exhibits heightened vulnerability to wildfires ignited by lightning strikesTreeless fuel types have higher risk than forests of dry lightning ignitions [ABSTRACT FROM AUTHOR]

Aim: Increased tree mortality linked to droughts and fires is occurring across temperate regions globally. Vegetation recovery has been widely reported; however, less is known about how disturbance may alter forests structurally and functionally across environmental gradients. We examined whether dry forests growing on low‐fertility soils were more resilient to coupled extreme drought and severe fire owing to lower tree mortality rates, higher resprouting success and persistence of juveniles relative to wetter forests on more fertile soils. Location: Fire‐tolerant eucalypt forests of temperate southeastern Australia. Time period: 2020–2023. Major taxa studied: Eucalyptus, Corymbia, Angophora. Methods: Demographic surveys of tree mortality and regeneration in all combinations of dry/wet forest, fertile/less fertile substrates exposed to extreme drought and fire were conducted. We used Bayesian regression modelling to compare tree mortality, diameter, response traits, population structure and occurrence of fire scars between substrates/forest types. Results: Overall mortality (20%–33%) and topkill (34%–41%) were within historically reported ranges for various forests and soil types. However, we observed an atypical trend of increased mortality and topkill in the largest trees, particularly when they had structural damage from past fires. Trees in wet forests on more fertile soils had the highest levels of mortality. Numbers of persistent resprouting juveniles were highest in dry forests on low‐fertility soils. Dry forests growing on low‐fertility soils appear more resilient to compound disturbances due to lower rates of mortality and higher rates of juvenile persistence. Wet forests on more fertile soils may experience greater demographic change due to higher mortality of small and large trees. Main conclusions: Mesic forests on relatively fertile soils were found to be at relatively high risk of demographic change from compound disturbances. Combined, fire and drought are likely to reduce the number of large trees in affected areas, with consequences for forest carbon cycling and storage. [ABSTRACT FROM AUTHOR]

The capacity for terrestrial ecosystems to sequester additional carbon (C) with rising CO2 concentrations depends on soil nutrient availability1,2. Previous evidence suggested that mature forests growing on phosphorus (P)-deprived soils had limited capacity to sequester extra biomass under elevated CO2 (refs. 3–6), but uncertainty about ecosystem P cycling and its CO2 response represents a crucial bottleneck for mechanistic prediction of the land C sink under climate change7. Here, by compiling the first comprehensive P budget for a P-limited mature forest exposed to elevated CO2, we show a high likelihood that P captured by soil microorganisms constrains ecosystem P recycling and availability for plant uptake. Trees used P efficiently, but microbial pre-emption of mineralized soil P seemed to limit the capacity of trees for increased P uptake and assimilation under elevated CO2 and, therefore, their capacity to sequester extra C. Plant strategies to stimulate microbial P cycling and plant P uptake, such as increasing rhizosphere C release to soil, will probably be necessary for P-limited forests to increase C capture into new biomass. Our results identify the key mechanisms by which P availability limits CO2 fertilization of tree growth and will guide the development of Earth system models to predict future long-term C storage.Microbial pre-emption of mineralized soil P limits the capacity of trees for increased P uptake and assimilation under elevated CO2 and therefore restricts their capacity to sequester extra C. [ABSTRACT FROM AUTHOR]

Understanding the biophysical limitations on forest carbon across diverse ecological regions is crucial for accurately assessing and managing forest carbon stocks. This study investigates the role of climate and disturbance on the spatial variation of two key forest carbon pools: aboveground carbon (AGC) and soil organic carbon (SOC). Using plot‐level carbon pool estimates from Nepal's national forest inventory and structural equation modelling, we explore the relationship of forest carbon stocks to broad‐scale climatic water and energy availability and fine‐scale terrain and disturbance. The forest AGC and SOC models explained 25% and 59% of the observed spatial variation in forest AGC and SOC, respectively. Among the evaluated variables, disturbance exhibited the strongest negative correlation with AGC, while the availability of climatic energy demonstrated the strongest negative correlation with SOC. Disturbances such as selective logging and firewood collection result in immediate forest carbon loss, while soil carbon changes take longer to respond. The lower decomposition rates in the high‐elevation region, due to lower temperatures, preserve organic matter and contribute to the high SOC stocks observed there. These results highlight the critical role of climate and disturbance regimes in shaping landscape patterns of forest carbon stocks. Understanding the underlying drivers of these patterns is crucial for forest carbon management and conservation across diverse ecological zones including the Central Himalayas. [ABSTRACT FROM AUTHOR]

Background: The moisture content of litter and woody debris is a key determinant of fire potential and fire behaviour. Obtaining reliable estimates of the moisture content of dead fine fuels (i.e. 1-h and 10-h fuels) is therefore a critical requirement for effective fire management. Aims: We evaluated and compared the performance of five simple models for fuel moisture content. The models belong to two separate classes: (1) exponential functions of the vapour pressure deficit; and (2) affine functions of the (weighted) difference between air temperature and relative humidity. Methods: Model performance is assessed using error and correlation statistics, calculated using cross validation, over four empirical datasets. Key results: Overall, the best performing models were the relaxed and generalised models based on the weighted difference between temperature and relative humidity. Conclusions: Simple functions of the difference between air temperature and relative humidity can perform as well as, if not better than exponential functions of vapour pressure deficit. However, it is important to note the limitations of all these models when applied to fuels with moisture contents <10%. Implications: The moisture content of fine dead fuels and woody debris can be reliably estimated using simple models that are amenable to easy application. Five models for the moisture content of fine dead fuels were evaluated using empirical datasets. Simple functions of the difference between air temperature and relative humidity were shown to perform as well as, if not better than exponential models based on vapour pressure deficit. [ABSTRACT FROM AUTHOR]

The forest–atmosphere exchange of carbon and water is regulated by meteorological conditions as well as canopy properties such as leaf area index (LAI, m2 m−2), photosynthetic capacity (PC μmol m−2 s−1), or surface conductance in optimal conditions (Gs,opt, mmol m−2 s−1), which can vary seasonally and inter-annually. This variability is well understood for deciduous species but is poorly characterized in evergreen forests. Here, we quantify the seasonal dynamics of a temperate evergreen eucalypt forest with estimates of LAI, litterfall, carbon and water fluxes, and meteorological conditions from measurements and model simulations. We merged MODIS Enhanced Vegetation Index (EVI) values with site-based LAI measurements to establish a 17-year sequence of monthly LAI. We ran the Community Atmosphere Biosphere Land Exchange model (CABLE-POP (version r5046)) with constant and varying LAI for our site to quantify the influence of seasonal canopy dynamics on carbon and water fluxes. We observed that the peak of LAI occurred in late summer–early autumn, with a higher and earlier peak occurring in years when summer rainfall was greater. Seasonality in litterfall and allocation of net primary productivity (FNPP) to leaf growth (af, 0–1) drove this pattern, suggesting a complete renewal of the canopy before the timing of peak LAI. Litterfall peaked in spring, followed by a high af in summer, at the end of which LAI peaked, and PC and Gs,opt reached their maximum values in autumn, resulting from a combination of high LAI and efficient mature leaves. These canopy dynamics helped explain observations of maximum gross ecosystem production (FGEP) in spring and autumn and net ecosystem carbon loss in summer at our site. Inter-annual variability in LAI was positively correlated with Net Ecosystem Production (FNEP). It would be valuable to apply a similar approach to other temperate evergreen forests to identify broad patterns of seasonality in leaf growth and turnover. Because incorporating dynamic LAI was insufficient to fully capture the dynamics of FGEP, observations of seasonal variation in photosynthetic capacity, such as from solar-induced fluorescence, should be incorporated in land surface models to improve ecosystem flux estimates in evergreen forests. [ABSTRACT FROM AUTHOR]

Spatially explicit predictions of fuel moisture content are crucial for quantifying fire danger indices and as inputs to fire behaviour models. Remotely sensed predictions of fuel moisture have typically focused on live fuels; but regional estimates of dead fuel moisture have been less common. Here we develop and test the spatial application of a recently developed dead fuel moisture model, which is based on the exponential decline of fine fuel moisture with increasing vapour pressure deficit (D). We first compare the performance of two existing approaches to predict D from satellite observations. We then use remotely sensed D, as well as D estimated from gridded daily weather observations, to predict dead fuel moisture. We calibrate and test the model at a woodland site in South East Australia, and then test the model at a range of sites in South East Australia and Southern California that vary in vegetation type, mean annual precipitation (129-1404mmyear-1) and leaf area index (0.1-5.7). We found that D modelled from remotely sensed land surface temperature performed slightly better than a model which also included total precipitable water (MAE

Atmospheric carbon dioxide enrichment (eCO.sub.2) can enhance plant carbon uptake and growth.sup.1-5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO.sub.2 concentration.sup.6. Although evidence gathered from young aggrading forests has generally indicated a strong CO.sub.2 fertilization effect on biomass growth.sup.3-5, it is unclear whether mature forests respond to eCO.sub.2 in a similar way. In mature trees and forest stands.sup.7-10, photosynthetic uptake has been found to increase under eCO.sub.2 without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO.sub.2 unclear.sup.4,5,7-11. Here using data from the first ecosystem-scale Free-Air CO.sub.2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO.sub.2 exposure. We show that, although the eCO.sub.2 treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO.sub.2, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO.sub.2 fertilization as a driver of increased carbon sinks in global forests. Carbon dioxide enrichment of a mature forest resulted in the emission of the excess carbon back into the atmosphere via enhanced ecosystem respiration, suggesting that mature forests may be limited in their capacity to mitigate climate change., Author(s): Mingkai Jiang [sup.1] , Belinda E. Medlyn [sup.1] , John E. Drake [sup.1] [sup.2] , Remko A. Duursma [sup.1] , Ian C. Anderson [sup.1] , Craig V. M. Barton [...]

The moisture content of vegetation and litter (fuel moisture) is an important determinant of fire risk, and predictions of dead fine fuel moisture content (fuel with a diameter

The role of the circadian clock in controlling the metabolism of entire trees has seldom been considered. We tested whether the clock influences nocturnal whole-tree water use. Whole-tree chambers allowed the control of environmental variables (temperature, relative humidity). Night-time stomatal conductance (gs ) and sap flow (Q) were monitored in 6- to 8-m-tall Eucalyptus globulus trees during nights when environmental variables were kept constant, and also when conditions varied with time. Artificial neural networks were used to quantify the relative importance of circadian regulation of gs and Q. Under a constant environment, gs and Q declined from 0 to 6 h after dusk, but increased from 6 to 12 h after dusk. While the initial decline could be attributed to multiple processes, the subsequent increase is most consistent with circadian regulation of gs and Q. We conclude that endogenous regulation of gs is an important driver of night-time Q under natural environmental variability. The proportion of nocturnal Q variation associated with circadian regulation (23-56%) was comparable to that attributed to vapor pressure deficit variation (25-58%). This study contributes to our understanding of the linkages between molecular and cellular processes related to circadian regulation, and whole-tree processes related to ecosystem gas exchange in the field.

Context: Accurate and precise monitoring practises are key for effective wildlife conservation management; providing reliable estimates of spatiotemporal changes in species abundance on which sound decision-making can be based. Advancements in drone and satellite technology are providing new standards for survey accuracy and precision and have great potential for enhancing population monitoring of numerous difficult to survey species. Flying-foxes (Pteropus spp.) are large bats that roost in groups of a few hundred to many thousands in the canopies of trees, where they are difficult to census accurately and precisely by human observers. Globally, 35 of the 64 flying-fox species are listed as threatened under the IUCN Red List of Threatened Species, and reliable monitoring methods are needed for the effective management of this ecologically important group. Aims: Recently, we showed that drone-acquired thermal imagery can be used to count flying-foxes in their roost with high accuracy and precision. In the present study, we aimed to assess the accuracy and precision of whole colony counts derived from ground-based counting methods against reference counts derived from drone-acquired thermal imagery. Methods: We evaluated the relationship between ground-based counts by two groups of human observers to highly accurate and precise counts derived from drone-acquired thermal orthomosaics for 25 counts conducted across seven flying-fox roosts throughout the Greater Sydney region, Australia. Key results: We found that ground-based counts by human observers were positively correlated with those obtained from concurrent drone-acquired thermal imagery. However, drone-acquired estimates of colony size were 2.05 and 1.92 times higher than ground-based counts by the experimenter and Australian government counters respectively. When compared against drone-acquired reference counts, the precision (coefficient of variation) of ground-based counts was 26.3% when conducted by a single counter and 55.1% when conducted by multiple counters. Conclusions: Our research indicates that ground-based counting methods underestimate true population sizes by substantial margins and have limited precision. Drone-based monitoring provides highly accurate and precise population estimates, and thus is expected to yield more reliable information on flying-fox abundance and allow for trends to be established over shorter timescales. Implications: Using ground counting methods alone, population trends can only be established with significance after protracted periods of monitoring. Incorporating the use of thermal drones into current monitoring practises would enhance the capacity to detect population trends earlier and more accurately, so that conservation management can more effectively respond. Reliable monitoring of trends in flying-fox populations is essential for flying-fox conservation. By comparing ground-based counting methods with reference counts derived from drone-acquired thermal imagery, we found that ground-based methods severely underestimate the true number of flying-foxes in roosts and had very limited precision. Drone-based monitoring of flying-foxes can facilitate more effective conservation management of these ecologically important species. Photographs by Justin A. Welbergen (left) and Eliane D. McCarthy (right). [ABSTRACT FROM AUTHOR]