To explore how climatic factors influence tree growth within the context of global climate changes, we used a dendroclimatological analysis to understand the response of Larix gmelinii to climatic variations along a broad latitudinal gradient from 47.27° to 52.66° N in the Greater Khingan Mountains of Northeastern China. The growth-limiting climate factors and a detailed association between radial growth and climate were identified along the gradient using redundancy analysis (RDA) and standard correlation function analysis over the period 1960–2013. The results showed that temperatures during current June to July represented the most important factor affecting tree radial growth in the study area. Across all studied latitudes, Larix gmelinii growth might be decreasing in radial growth due to higher monthly maximum temperature (Tmax) and monthly mean temperatures (Tm) in the current June, especially for the stands at low and middle latitudes. With continued warming, Larix gmelinii radial growth at high latitudes (e.g., Mangui (MG) and Mohe (MH)) might be reduced by warmer temperatures in July. In addition, Larix gmelinii might be decreasing in radial growth from decreasing precipitation. Our results show that there is a decreasing trend in Larix gmelinii radial growth under the observed general increase of temperatures in the Greater Khingan Mountains in recent years.

Climate, topography, and tree structure have different effects on plant diversity that vary with spatial scale. In this study, we assessed the contribution of these drivers and how they affect the vascular plant richness of different functional groups in a temperate forest ecosystem in Northeast China. We investigated about 0.986 million plants from 3160 sites to quantify the impact of annual mean temperature, sunshine duration, annual precipitation, standard deviation of diameter at breast height, and forest type on richness of vascular plants (total species, tree, treelet, shrub, and herb, separately) using the gradient boosting model. The results show that annual mean temperature had the strongest impact on plant richness. The tree richness peaked at intermediate annual mean temperature and sunshine duration and increased with annual precipitation. The Shannon diversity index and Simpson dominance index increased with annual precipitation and standard deviation of diameter at breast height, decreased with sunshine duration, and peaked at intermediate annual mean temperature and forest type. The total richness and understory richness increased with annual mean temperature and standard deviation of diameter at breast height and peaked at intermediate sunshine duration and annual precipitation. A comprehensive mechanism was found to regulate the plant diversity in forest ecosystems. The relationship between tree richness and annual mean temperature with latitudinal effect could be affected by the differences in number and size of tree individuals, indicating that plant diversity varies with the utilization of energy. The force driving plant richness varied with the functional group due to the different environmental resource requirements and the life history strategies of plants layers.

Species diversity has been shown to be influenced by environmental factors, but the mechanism underlying their relationship remains unclear across spatial scales. Based on field investigation data collected from 3077 sample plots in temperate forest ecosystems, we compared tree species richness, evenness and dominance at 10 km × 10 km, 30 km × 30 km and 90 km × 90 km spatial scales. Then, we detected the scale dependence of changes in tree species composition on climate, topography and forest structure using variation partitioning and quantified their contribution to tree diversity with gradient–boosted models (GBMs) and fitted their relationships. The magnitude of tree richness, evenness and dominance significantly increased with spatial scale. Ecological factors jointly accounted for 24.3%, 26.5% and 38.5% of the variation in tree species composition at the three spatial scales, respectively. The annual mean temperature had a strong impact on tree richness, evenness and dominance and peaked at an intermediate scale. Tree evenness and dominance increased with the variation of temperature but had upper and lower limits. Tree richness obviously increased with annual precipitation on multiple scales and decreased with annual sunshine duration at large spatial scales. Tree richness, evenness and dominance obviously increased with the variation in elevation and diameter at breast height at large scales and small scales, respectively. Tree dominance decreased with tree height at a small scale. The dependence of tree diversity on ecological factors increased with spatial scales. Furthermore, different factors exert various controls on tree diversity at different spatial scales, representing a comprehensive mechanism regulating tree diversity.

Species diversity has been shown to be influenced by environmental factors, but the mechanism underlying their relationship remains unclear across spatial scales. Based on field investigation data collected from 3,077 sample plots in temperate forest ecosystems, we compared tree species richness, evenness and dominance at 10 km × 10 km, 30 km × 30 km and 90 km × 90 km spatial scales. Then, we detected the scale dependence of changes in tree species composition on climate, topography and forest structure using variation partitioning and quantified their contribution to tree diversity with gradient boosted models (GBMs) and fitted their relationships. The magnitude of tree richness, evenness and dominance significantly increased with spatial scale. Ecological factors jointly accounted for 24.3%, 26.5% and 38.5% of the variation in tree species composition at the three spatial scales, respectively. Annual mean temperature had a strong impact on tree richness, evenness and dominance and peaked at an intermediate scale. Tree evenness and dominance increased with the variation of temperature but had upper and lower limits. Tree richness obviously increased with annual precipitation on multiple scales and decreased with annual sunshine duration at large spatial scale. Tree richness, evenness and dominance obviously increased with the variation elevation and diameter at breast height at large scales and small scales, respectively. Tree dominance decreased with tree height in a hump at small scale. The dependence of tree diversity on ecological factors increased with spatial scales. Furthermore, different factors exert various controls on tree diversity at different spatial scales, representing a comprehensive mechanism regulating tree diversity.

Aim: Uncertainty remains in revealing the determinants of plant diversity over regional and larger scales. Both plant diversity and the effects of environmental factors on it are scale dependent. This study aims to integrate and analyse the variations in the ecological mechanisms by which environmental factors drive plant diversity. Location: Montane forests, Northeast China Taxon: Tree Methods: In this study, we used field survey data from 3,078 sample plots in temperate forest ecosystems. First, we partitioned the species–area curve into different area scales with segmented models to explain changes in the dominant factors affecting tree richness. Then, we quantified the contribution of environmental factors to tree richness with gradient boosted model (GBM) and fitted their correlations at different spatial scales. Finally, we partitioned the contribution of climate, topography and both to tree richness with redundancy analysis (RDA) and analysed how the driving mechanisms varied with spatial scale. Results: Two area scales (small scale A ₁ and large scale A ₂ ) were segmented in regional temperate forests. The correlations between environmental contributions and spatial scale at the A ₂ scale were better than those at the A ₁ scale. The effects of environmental factors driving tree richness varied spatially nonlinearly. Tree richness at the A ₁ scale was determined by both climate and topography and climate alone, while it was determined by climate alone at the A ₂ scale. Main conclusion: Spatial heterogeneity affected the effects of environmental factors on tree diversity, especially at the A ₁ scale. Environmental factors exerted a dominant control at different spatial scales. Environmental filtering determined tree diversity at the A ₁ scale, and dispersal limitation determined tree diversity at the A ₂ scale for temperate forests. The spatial heterogeneity and collinearity of climate and topography prevented us from drawing consistent conclusions.

The functional diversity of forests, a critical determinant of ecosystem stability and services, is being reconfigured by global climate change through shifts in the traits of tree species. While the positive relationship between species richness and functional diversity is well-established, uncertainty persists regarding the relative influence and joint interactions of phylogeny, stand structural complexity, and community functional identity across extensive regional environmental gradients. Focusing on the largest temperate forest in Asia (3110 plots) and various dimensions of diversity, this study reveals that phylogenetic diversity (PD) is the paramount predictor of functional diversity indices (richness, evenness, and dispersion). Stand structural complexity and acquisitive strategies (functional identity) jointly enhance functional diversity, whereas climatic fluctuations and soil pH primarily suppress functional diversity via indirect filtering effects on components of tree diversity. Our findings underscore the potential of management hierarchy: conserving PD is fundamental, followed by promoting structural complexity and leveraging functional identity, to maximize functional diversity and resilience, particularly in high-latitude forests facing environmental change. These steps are crucial for sustainable forest management and conserving biodiversity.