Forest Composition Research Articles

Legacy effects control root elemental composition and stoichiometry in subtropical forests: Empirical support for the biogeochemical niche hypothesis

Legacy effects control root elemental composition and stoichiometry in subtropical forests: Empirical support for the biogeochemical niche hypothesis

Experimental summer fires do not affect fungal diversity but do shape fungal community composition in Mediterranean Pinus nigra forests

BackgroundFire regimes (in terms of frequency, severity, and intensity) in ecosystems are changing. Summer fires are occurring in Mediterranean forests more frequently and are more severe than spring or autumn fires. Soil microbial communities provide essential ecosystem services and are essential in post-fire recovery. However, to date, studies to determine the impact of summer fires on soil microbial communities have been limited. To explore how more severe fires may affect fungal diversity and community composition, we conducted an experimental summer fire in June 2019 at an experimental site that had been previously established in a pure stand of black pine (Pinus nigra Arn.) in 2016 in the Cuenca Mountains in Spain (Central-Eastern Spain).ResultsMetabarcode DNA analyses of soil samples collected in three blocks (with three plots sampled in unburned and burned areas per block) in spring 2020 revealed that total soil fungi richness and diversity were not affected by summer burning; although no significant, summer burning did have a contrary influence on the most dominant fungal trophic groups. The relative abundance of ectomycorrhizal (ECM) fungi was negatively affected by burning, whereas saprotrophic fungi were positively affected by burning. Fire also had a significant effect on the composition of the total community and when analyzed by the trophic group. Multilevel pattern analysis showed that ECM fungi were significantly correlated with unburned plots. Physicochemical analyses revealed that there were no changes in the main edaphic variables measured.ConclusionsThe application of fire under more critical summer conditions (out of typical prescribed fire weather windows in Europe) did not produce significant differences in the diversity of the fungal community, being ECM fungi more sensitive to heat than other trophic groups. However, the composition of the fungal community differed significantly between burned and unburned plots. Overall, burned plots showed an adaptation to fire with a rapid proliferation of several pyrophilous genera that are able to improve soil conditions, which would enhance post-fire regeneration of the stand.These pioneering results can inform managers in conducting controlled summer fires to surrogate low to medium surface fire in Pinus nigra stands, knowing that the fungal diversity of the ecosystem is not affected, and thus the key ecological role of these organisms is not significantly harmed.

Effects of Climate and Land Use on the Population Dynamics of the Bank Vole (Clethrionomys glareolus) in the Southernmost Part of Its Range

This study investigated the effects of habitat structure and climatic variables on populations of bank voles (Clethrionomys glareolus), a northern species with adaptations to cooler climate, at the southern end of their range in Western Europe over a 16-year period. This is the first long-term analysis of its kind in this region. The study aims to understand how these variables influence the population dynamics and occupancy of bank voles. The results suggested that warmer years and extreme precipitation events lead to a reduction in bank vole abundance. Although changes in land use were minimal in the plots studied, changes in forest composition, particularly the expansion of coniferous forests at the expense of deciduous forests, were also related to lower bank vole abundance. Occupancy models, taking into account detectability, indicated stable occupancy in all regions. Our results suggest that climate change and habitat alterations, such as changes in forest composition, could pose threats to bank vole populations in these regions.

Variation in wood density across South American tropical forests

Wood density is a critical control on tree biomass, so poor understanding of its spatial variation can lead to large and systematic errors in forest biomass estimates and carbon maps. The need to understand how and why wood density varies is especially critical in tropical America where forests have exceptional species diversity and spatial turnover in composition. As tree identity and forest composition are challenging to estimate remotely, ground surveys are essential to know the wood density of trees, whether measured directly or inferred from their identity. Here, we assemble an extensive dataset of variation in wood density across the most forested and tree-diverse continent, examine how it relates to spatial and environmental variables, and use these relationships to predict spatial variation in wood density over tropical and sub-tropical South America. Our analysis refines previously identified east-west Amazon gradients in wood density, improves them by revealing fine-scale variation, and extends predictions into Andean, dry, and Atlantic forests. The results halve biomass prediction errors compared to a naïve scenario with no knowledge of spatial variation in wood density. Our findings will help improve remote sensing-based estimates of aboveground biomass carbon stocks across tropical South America.

Improving the Accuracy of Tree Species Mapping by Sentinel-2 Images Using Auxiliary Data—A Case Study of Slyudyanskoye Forestry Area near Lake Baikal

Timely and accurate information on forest composition is crucial for ecosystem conservation and management tasks. Information regarding the distribution and extent of forested areas can be derived through the classification of satellite imagery. However, optical data alone are often insufficient to achieve the required accuracy due to the similarity in spectral characteristics among tree species, particularly in mountainous regions. One approach to improving the accuracy of forest classification is the integration of auxiliary environmental data. This paper presents the results of research conducted in the Slyudyanskoye Forestry area in the Irkutsk Region. A dataset comprising 101 variables was collected, including Sentinel-2 bands, vegetation indices, and climatic, soil, and topographic data, as well as forest canopy height. The classification was performed using the Random Forest machine learning method. The results demonstrated that auxiliary environmental data significantly improved the performance of the tree species classification model, with the overall accuracy increasing from 49.59% (using only Sentinel-2 bands) to 80.69% (combining spectral data with auxiliary variables). The most significant improvement in accuracy was achieved through the incorporation of climatic and soil features. The most important variables were the shortwave infrared band B11, forest canopy height, the length of the growing season, and the number of days with snow cover.

Naturalness and Tree Composition Determine the Abundance of Rare and Threatened Orchids in Mature and Old-Growth Abies alba Forests in the Northern Apennines (Italy)

Forest Orchidaceae are important for European temperate forests, yet their distribution and abundance have so far interested limited research. In three pure or mixed silver fir stands in the Foreste Casentinesi National Park (NP) (Northern Apennines, Italy) we analysed how structural traits in mature and old-growth forests affected orchid communities in terms of abundance of the main genera, trophic strategy and rarity in the NP. We established three 20 × 60 m plots to quantify the structure of living and dead tree community, including a set of old-growth attributes connected to large trees, deadwood, and established regeneration. In each plot, we measured the abundance of all orchid species and explored their behaviour according to the trophic strategy (autotrophy/mixotrophy, obligate mycoheterotrophy), rarity within the NP, and threatened status according to the IUCN Red List. We used multivariate ordination and classification techniques to assess plot similarities according to forest structure and Orchid Community and identify the main structural factors related to orchid features. The main structural factors were used as predictors of community traits. Forest composition (i.e., the dominance/abundance of silver fir) affected the presence of the main orchid genera: Epipactis were abundant in silver fir-dominated forests, Cephalanthera in mixed beech and fir forests. Interestingly, Cephalanthera could become limited even in beech-dominated conditions if fir regeneration was abundant and established. Old-growth attributes like the density of deadwood and large tree volume were important determinants of the presence of rare and mycoheterotrophic species. Our results provided a first quantitative description of forest reference conditions to be used in the protection and restoration of threatened and rare orchid species.

Long-term influence of prescribed burning on subsequent wildfire in an old-growth coast redwood forest

BackgroundPrescribed burning is an effective tool for reducing fuels in many forest types, yet there have been few opportunities to study forest resilience to wildfire in areas previously treated. In 2020, a large-scale high-intensity wildfire burned through an old-growth coast redwood (Sequoia sempervirens) forest with a mixed land management history, providing a rare opportunity to compare early post-wildfire data between areas with and without previous application of prescribed burning. The purpose of this study was to analyze the differences between these two treatments in terms of tree mortality, stand structure, fuel composition, and post-wildfire regeneration. Field data were collected approximately 1 year after the wildfire using a total of fifty 20 m plots in three sites previously treated with prescribed fire more than 9 years prior to the wildfire, and fifty plots in three adjacent sites without a history of prescribed fire. Data regarding the influence of prescribed burning on forest structure and composition following wildfire were assessed using generalized linear mixed effects models (GLMMs).ResultsPrescribed burning was positively associated with greater canopy cover, tree survival, counts of early post-fire coast redwood seedlings, and lower stand density, following subsequent wildfire. In addition, the mortality of individual trees was lower within areas treated with prescribed fire and negatively associated with tree height. Topkill was also lower within treated areas and was negatively correlated with tree diameter and tree height for all basal sprouting species combined and for S. sempervirens individually.ConclusionsResults suggest that prescribed fire improved coast redwood forest stand resistance and resilience to wildfire and that these benefits were maintained after a significant wildfire event in areas treated more than 9 years prior to the wildfire. Further research is recommended in areas where prescribed fire has been applied repeatedly, to better understand long-term effects and guide best practices for future prescribed fire use in coast redwood forests.

Changes in abundance and distribution of European forest bird populations depend on biome, ecological specialisation and traits

Forest bird abundance in Europe has remained stable overall, unlike farmland species which have declined dramatically in recent decades. However, this apparent stability may hide large variations among species and geographical regions. We aimed to determine if forest bird species with varying life histories and biome distributions show different population trends. We used functional traits and specialisation indices to study changes in abundance and distribution of European forest bird populations. For each species, we used European‐level estimates of total abundance change over the last 40 years and changes in two components of spatial distribution: range change (i.e. area shrinkage or expansion) and distribution shift (i.e. latitudinal adjustments), both over the last 30 years. We also considered specialist groups of different biomes (i.e. boreal, temperate, Mediterranean and biome generalists) separately. We showed that boreal forest species have declined in abundance and range area, while Mediterranean and temperate species have increased in abundance and range, possibly as the result of warmer temperatures and forest expansion in these regions. The decline of boreal forest species may result from changes in forest structure and composition due to forestry practices, increasing temperatures and colonisation by warm‐dwelling species. Among boreal species, mixed forest specialists (i.e. those preferring a mix of broadleaf and coniferous trees) declined the most in abundance and range and shifted northwards. In contrast, for vertebrate carnivores (i.e. birds of prey), we observed an increase in abundance among Mediterranean species and a southward expansion among all species. Our findings suggest that forest bird species in Europe may be influenced by the combined effects of land use and climate change, with these impacts varying across biomes. Our results highlight the need for maintaining and restoring key forest habitats (e.g. through increased protected areas and extensive management) and halting or limiting climate change, especially for boreal species.

Spatial and Temporal Pervasiveness of Indigenous Settlement in Oak Landscapes of Southern New England, US, During the Late Holocene

The relative influence of climate and Indigenous cultural burning on past forest composition in southern New England, US, remains debated. Employing varied analyses, this study compared data on Indigenous settlements from over 5000 years before present (YBP) with relative tree abundances estimated from pollen and land survey records. Results suggested that fire-tolerant vegetation, mainly oak (Quercus spp.), was more abundant near Indigenous settlements from 4955 to 205 YBP (i.e., 86–91% fire-tolerant trees), and significantly (p < 0.05) higher from 3205 to 205 YBP; fire-tolerant vegetation was less abundant away from settlements, where it also experienced greater fluctuations. Correlative models showed that warmer temperatures and distance to Indigenous settlement, which are both indicators of fire, were important predictors in the 17th–18th centuries of fire-tolerant tree abundance; soil variables were less important and their relationships with vegetation were unclear. A marked increase in oak abundance occurred above 8 °C mean annual temperature and within 16 km of major Indigenous settlements. Pyrophilic vegetation was most correlated with distance to Indigenous villages in areas with 7–9 °C mean annual temperature, typical of higher latitudes and elevations that usually supported northern hardwoods. Widespread burning in warmer areas potentially weakened relationships between distance and pyrophilic abundance. Indigenous land use imprinted upon warmer areas conducive to burning created patterns in fire-tolerant vegetation in southern New England, plausibly affecting most low-elevation areas. Results imply that restoration of fire-dependent species and of barrens, savannas, and woodlands of oak in southern New England benefit from cultural burning.

Local Forest Structure and Host Specificity Influence Liana Community Composition in a Moist Central African Forest.

Lianas are important components of tropical forest diversity and dynamics, yet little is known about the drivers of their community structure and composition. Combining extensive field and LiDAR data, we investigated the influence of local topography, forest structure, and tree composition on liana community structure, and their floristic and functional composition, in a moist forest in northern Republic of Congo. We inventoried all lianas ≥ 1 cm in diameter in 144 20 × 20-m quadrats located in four 9-ha permanent plots, where trees and giant herbs were inventoried. We characterized the functional strategies of selected representatives of the main liana taxa using a set of resource-use leaf and wood traits. Finally, we used complementary statistical analyses, including multivariate and randomization approaches, to test whether forest structure, topography, and tree composition influence the structure, floristic composition, and functional composition of liana communities. The structure of liana communities was strongly shaped by local forest structure, with higher abundances and total basal areas in relatively open-canopy forests, where lianas competed with giant herbs. Liana floristic composition exhibited a weak spatial structure over the study site but was marginally influenced by the local forest structure and topography. Only forest structure had a weak but significant effect on liana functional composition, with more conservative strategies-higher stem tissue density and lower PO4 leaf concentration and SLA values-in tall and dense forests. Finally, we found evidence of host specificity with significant attraction/repulsion for 19% of the tested liana and tree species associations, suggesting that the unexplained floristic variation may be partly attributed to these host-species-specific associations, although the underlying mechanisms behind remain elusive. Overall, our findings demonstrate that liana communities' structure can be much better predicted than their composition, calling for a better understanding of the implications of the large functional diversity observed in liana communities.

Seasonal structural stability promoted by forest diversity and composition explains overyielding.

The stability of forest productivity is a widely studied phenomenon often associated with tree species diversity. Yet, drivers of stability in forest structure and its consequences for forest productivity remain poorly understood. Using a large (10 ha) young tree diversity experiment, we evaluated how forest structure and multiple dimensions of diversity and composition are related to remotely sensed structural metrics and their stability through the growing season. We then examined whether structural stability (SS) across the growing season (April-October) could explain overyielding (i.e., the net biodiversity effect, NBE) in annual wood productivity. Using Uncrewed Aerial Vehicle-Light Detecting and Ranging (UAV-LiDAR), we surveyed experimental tree communities eight times at regular intervals from before bud break to after leaf senescence to derive metrics associated with canopy height heterogeneity, fractional plant cover, and forest structural complexity (based on fractal geometry). The inverse coefficients of variation for each of these three metrics through the season were used as measures of SS. These metrics were then coupled with annual tree inventories to evaluate their relationships with the NBE. Our findings indicate that wood volume and, to some extent, multiple dimensions of diversity and composition (i.e., taxonomic, phylogenetic, and functional) explain remotely sensed metrics of forest structure and their SS. Increases in wood volume as well as functional and phylogenetic diversity and variability (a measure of diversity independent of species richness) were linked to higher SS of forest complexity and canopy height heterogeneity. We further found that higher SS of forest complexity and fractional plant cover were associated with increased overyielding, which was mostly attributable to the complementarity effect. Structural equation models indicate that the stability of structural complexity explains more variation in NBE among plots than dimensions of diversity or variability, highlighting its value as an informative metric that likely integrates multiple drivers associated with overyielding. This study highlights the potential to integrate remote sensing and ecology to disentangle the role of forest SS in shaping ecological processes.

Ecological Relationships Between Woody Species Diversity and Propagation Strategies of Aulonemia queko.

This study explores how floristic composition, diversity, and woody vegetation structure vary across floristic zones in Andean montane forests under the dominance of Aulonemia queko Goudot (Poaceae, Bambusoideae) dominance. As a culturally and ecologically significant non-timber forest product, A. queko plays a key role in shaping plant communities and requires effective propagation strategies for sustainable management. Significant differences in floristic composition were observed among zones, with indicator species identified in the lower and upper zones. However, despite environmental variability, species richness and structural attributes remained stable across the elevation gradient, suggesting resilience in woody plant communities. A. queko density was highest in the upper zone, while its basal area peaked in the lower and middle zones, probably shaping floristic composition through competitive interactions and habitat modification. Propagation experiments revealed that shoots with rhizomes exhibited higher survival and growth, particularly in mulch substrates with 1000 ppm indole-3-butyric acid (IBA), highlighting the importance of shoot type, substrate, and hormone dose. These findings suggest that A. queko is a structuring species and a potential restoration target. However, its dominance may alter forest composition, requiring adaptive management strategies that balance its ecological role with conservation and sustainable use, ensuring biodiversity and ecosystem resilience.

Assessing trends and density of bird species in bottomland hardwood forests and riparian forests using simulation and sample size optimization for surveys

The decline of neotropical migratory birds in North America is closely tied to habitat loss, including the degradation of bottomland hardwood and riparian forests, which provide essential habitats for numerous species. To address this, the U.S. Fish and Wildlife Service conducts bird surveys to monitor restoration efforts and evaluate conservation outcomes. This study assessed avian surveys from three National Wildlife Refuges in Texas and Oklahoma, using simulations, field data, and literature to evaluate current sampling protocols. Our findings revealed that achieving acceptable precision in bird density estimates (coefficient of variation: 0.15, 0.25) often requires more than 200 bird point counts, depending on the species and study area. While data aggregation across sites and years improved precision, it masked local trends critical for refuge-specific management. Imprecise results, particularly for rare species, underscored the need for improved protocols, such as repeat visits within a year, targeted sampling for priority species, and adaptive designs incorporating forest composition and structure data. These adjustments would enhance the precision of multispecies surveys, making them more effective for detecting changes in habitat quality. This study provides actionable recommendations to support service-wide efforts in strategic, data-driven monitoring and long-term conservation planning for neotropical migratory birds.

Effect of grazing intensity on understory vegetation in a Village Land Forest Reserve in Northern Tanzania.

Effect of grazing intensity on understory vegetation in a Village Land Forest Reserve in Northern Tanzania.

Regional Forest Carbon Stock Estimation Based on Multi-Source Data and Machine Learning Algorithms

Accurately assessing forest carbon stock (FCS) is essential for analyzing its spatial distribution and gauging the capacity of forests to sequester carbon. This research introduces a novel approach for estimating FCS by integrating multiple data sources, such as Sentinel-1 (S1) radar imagery, optical images from Sentinel-2 (S2) and Landsat 8 (L8), digital elevation modeling (DEM), and inventory data used in forest management and planning (FMP). Additionally, the estimation of FCS incorporates four key ecological features, including forest composition, primary tree species, humus thickness, and slope direction, to improve the accuracy of the estimation. Subsequently, insignificant features were eliminated using Lasso and recursive feature elimination (RFE) feature selection techniques. Three machine learning (ML) models were employed to estimate FCS: XGBoost, random forest (RF), and LightGBM. The results show that the inclusion of ecological information features improves the performance of the models. Among the models, LightGBM achieved superior performance (R² = 0.78, mean squared error (MSE) = 0.85, root mean squared error (RMSE) = 0.92, mean absolute error (MAE) = 0.58, relative RMSE (rRMSE) = 41.37%, and mean absolute percentage error (MAPE) = 30.72%), outperforming RF (R² = 0.76, MSE = 0.93, RMSE = 0.97, MAE = 0.60, rRMSE = 43.42%, and MAPE = 30.85%) and XGBoost (R² = 0.77, MSE = 0.90, RMSE = 0.95, MAE = 0.61, rRMSE = 42.66%, and MAPE = 34.61%).

Tree rings, forest composition, and LiDAR reveal historical forests and past agricultural land use at George Washington’s Mount Vernon

Tree-ring records of tree growth and age, current forest composition, and LiDAR bare earth elevation models each enable reconstructions of forest and land-use histories. Combining these complementary methods, we investigate the mansion house farm, the remaining portion of George Washington’s Mount Vernon agricultural plantation (Virginia, USA) for environmental legacies that persist from the eighteenth century. Across Mount Vernon, enslaved labor grew tobacco, wheat, and other produce; however, Washington also described the farm as an English landscape design with forests and scattered trees. These methods reveal a remnant landscape of forests and agricultural fields in the mansion house farm that supports historical documents and maps extending back to Washington’s lifetime. Trees dating to the eighteenth century remain on this landscape and are found near steeper slopes. Ordination of present-day forests show a distinct forest composition in locations Washington depicted as forests on a 1793 map. These forests are also associated with older ages from tree-ring samples. A comparison of tree-ring sampling at two spatial scales (1-ha vs 400 m2) shows that selecting trees across a larger scale is more likely to include old trees when considering external, morphological characteristics of tree age. LiDAR terrain elevations show evidence of cross-plowing, an agricultural method frequently used by Washington with ridges and furrows at approximately right angles, in areas that are now forested. The preserved record of past land-use apparent in tree-ring ages, forest landscape composition, and LiDAR bare earth elevations consistently highlights the long duration and pervasive extent of land-use legacies from historical plantation agriculture.

Vertical canopy gradients of respiration drive plant carbon budgets and leaf area index.

Despite its importance for determining global carbon fluxes, leaf respiration remains poorly constrained in land surface models (LSMs). We tested the sensitivity of the Energy Exascale Earth System Model Land Model - Functionally Assembled Terrestrial Ecosystem Simulator (ELM-FATES) to variation in the canopy gradients of leaf maintenance respiration (Rdark). We ran global and point simulations varying the canopy gradient of Rdark to explore the impacts on forest structure, composition, and carbon cycling. In global simulations, steeper canopy gradients of Rdark lead to increased understory survival and leaf biomass. Leaf area index (LAI) increased up to 77% in tropical regions compared with the default parameterization, improving alignment with remotely sensed benchmarks. Global vegetation carbon varied from 308 Pg C to 449 Pg C across the ensemble. In tropical forest simulations, steeper gradients of Rdark had a large impact on successional dynamics. Results show the importance of canopy gradients in leaf traits and fluxes for determining plant carbon budgets and emergent ecosystem properties such as competitive dynamics, LAI, and vegetation carbon. The high-model sensitivity to canopy gradients in Rdark highlights the need for more observations of how leaf traits and fluxes vary along light micro-environments to inform critical dynamics in LSMs.

Investigation of the vegetation structure, diversity and composition in the tropical semi-evergreen forests of Northeast India

The Himalayan forests are highly threatened due to anthropogenic pressures ranging from agriculture intensification, deforestation, hydropower development, etc. The present study attempts to document the floristic diversity, composition and structure of vegetation communities in the tropical semi-evergreen forest of North Cachar Hills in Assam. A one-time assessment was made during the peak growing season in a 4000 m2 forest area to make an inventory of vegetation structure by using the nested quadrat method. A total of 445 individuals belonging to 52 tree species were recorded from the overstorey, while 161120 individuals belonging to 72 species were recorded from the understorey vegetation. The forest stand structure exhibited a reverse J-shaped population curve, and most tree species showed no regeneration (57%), while others showed either good (23%) or poor (17%) regeneration. This study highlights that the understorey vegetation is as important as the overstorey vegetation with respect to species diversity. This study can serve as a baseline for assessing the impacts of different natural and anthropogenic threats on biodiversity in the study area. Additionally, this study highlights the need to conserve the natural forests of Northeast India and protect them from different threats.

Does habitat or climate change drive species range shifts?

A primary prediction of climate change ecology is that species will track their climate niche poleward and upslope. However, studies have shown species responding in surprising ways. In this study, we aim to understand the impact of global change on species ranges by considering both climate and habitat changes. Using occupancy analysis of acoustic survey data in the mountains of the northeastern United States, we tested specific predictions of range responses to warming (shifting upslope), precipitation change (shifting downslope), and forest composition change (shifting downslope). We found that American red squirrels Tamiasciurus hudsonicus, key nodes in northern North American food webs, are not tracking increasing temperatures upslope, despite substantial warming in recent decades. Structural equation modeling indicates that red squirrel abundance is primarily influenced by red‐spruce forest cover, which has shifted downslope with recovery from historical logging and acid deposition. Accounting for the multiple dimensions of global change will enable better predictions and more effective conservation strategies.

Effects of Nitrogen Addition and Drought on Soil Microbial Diversity and Community Composition in a Young Tree Community

Soil microorganisms are well known to play a crucial role in carbon and nutrient cycling within terrestrial ecosystems. Numerous research efforts have demonstrated that nitrogen deposition can change forest soil microbial diversity and community composition; however, it is still unclear how nitrogen deposition will affect the soil microbial diversity and community composition in subtropical forests under the background of increasing drought. Consequently, over a period of 2.5 years, we carried out an experiment using two N addition regimes and three soil water treatment levels to reveal the effects of nitrogen, drought, and the influence of their interaction on the diversity and community composition of soil microorganisms. Overall, we found that both N addition and drought decreased the bacterial Shannon and Simpson indices yet had no significant effect on fungal diversity. In the well-watered treatments, nitrogen addition did not significantly reduce bacterial diversity, while in the moderate drought and severe drought treatments, N addition significantly decreased bacterial diversity, reducing the Shannon and Simpson indices by 27.05% and 0.13%, respectively, in the severe drought treatment. Drought significantly altered the community composition of bacteria regardless of N addition. N addition significantly changed the community composition of bacteria under moderate drought treatments, while both N addition and drought had less significant effects on the fungal community composition. The soil water content, fine root biomass, and soil pH were significantly correlated with bacterial community composition, which explained 53.3%, 11.1%, and 8.7% of the changes in soil bacterial community composition, respectively. These results suggest that drought may intensify the inhibitory effect of nitrogen on bacterial diversity and change the magnitude and direction of the impact of nitrogen on the composition of the bacterial community.