Tree Size Diversity Research Articles

Structural characterization and pod yields of populations of the fodder legumes trees <i>Piliostigma thonningii.</i> and <i>Prosopis africana</i> along the toposequence in western Burkina Faso

Plant communities including fodder trees play an important role in livestock production in semi-arid zones of West Africa. This study was carried out at two sites of the western region of Burkina Faso and aimed to provide information on the current status of the natural savanna-woodland pastures and predict the pod production of Piliostigma thonningii and Prosopis africana, two key fodder species of these ecosystems. All woody species were systematically identified and their dbh and height were measured in plots along a toposequence. Pods were collected from 60 trees of P. thonningii and P. africana and the stem circumference at breast height and the crown diameter were also measured. To predict pod production, regression analysis was used to develop predictive allometric equations by selecting tree size variables for fitting to models. Results showed a total of 24 species belonging to 11 families and 22 genera were inventoried with clear tendency to shrub invasion of the toposequence locations. P. thonningii trees had a good regeneration status while P. Africana individuals were old. The two species had good potential for natural regeneration of the stands from seedlings. The pod production prediction equations for both species were significantly correlated to dendrometric traits (P˂0.0001). They were species-specific, and the equations developed for each species were different. It is not advised to apply the same formula to predict pod production of fodder trees species at different savanna-woodland locations throughout West Africa.Keywords: Browse species, dendrometric traits, class distribution, Fodder equation, Natural savannawoodland pastures, Toposequence, West Africa.

Interregional Crown Width Models for Individual Trees Growing in Pure and Mixed Stands in Austria

Crown width is a functional trait that is commonly used to improve the estimation of above-ground biomass of forests and is often included as a predictor variable in forest growth models. Most of the existing crown width models reflect the relationship between crown width, tree size and competition variables, but do not consider the effect of species mixture. In this study, we developed crown width models for individual-tree of the major tree species growing in Austria. Because these models should be applicable for mixed and pure stands and should also take into account the characteristics of different sites, the relationship between crown width, site variables and species composition was investigated. For that purpose, we used data from a sub-sample of the Austrian National Forest Inventory, which comprises crown width measurements of about 8900 trees from 1508 sample plots. Because of the hierarchical structure of the data set (i.e., trees nested within the plot) which destroys the independencies between observations, linear mixed-effects models were used. The species composition of the stand was included via the species-specific relative proportions of basal area. To describe the interregional variability of crown width, dummy variables were introduced, which account for region-specific differences. Site characteristics were incorporated through the altitude, slope and aspect of the site. For Norway spruce, silver fir, Scots pine, European larch, European beech, oak species and ash/maple species it was possible to develop crown width models, which reflect the effects of site characteristics and species composition of the stand. The crown widths of shade-tolerant species reacted mainly positively to admixture, whereas light-demanding species reacted with decreasing crown widths. Coniferous species were not as strongly affected by mixture as broadleaf species.

Moderate Diversity in Forest Structure and Its Low Dynamics Are Favored by Uneven-Aged Silviculture—The Lesson from Medium-Term Experiment

For several decades, there has been growing interest in highly diversified forests as a result of their management using the so-called uneven-aged silviculture. Such management and forests resulting from its application fulfil the purpose of forest ecosystem protection without significant limitation of the other forest functions and services. The usefulness of such silvicultural system depends largely on the species composition of the stand. In Poland, this system has been used primarily in silver fir (Abies alba Mill.)-dominated forests with an admixture of other shade-tolerant tree species and rather small admixture of light-demanding species. In our study, we analyzed the structure of fir-dominated uneven-aged forest consisting of a certain mix of eight tree species with different light-requirements, in which uneven-aged silviculture was performed for over two decades. The analysis of stand structure concerned three aspects of the forest structure: species diversity, spatial pattern of tree distribution, and tree size diversity. On the basis of three stand inventories, we captured the mid-term dynamics of the stand structure under moderate human pressure conditions. The results showed that the stand was characterized by high growing stock, with stable growth over the entire period. The silver fir was the dominant tree species, but the Scots pine and pedunculate oak also played an important role. However, the silver fir was abundant in the ingrowth class, whereas the pine and oak were absent or very rare in this stand strata. Noteworthy is the increasing importance of the European hornbeam, which is particularly evident in the ingrowth class; its abundance was twice that of the silver fir. The results clearly demonstrated that within 24 years, the share of light-demanding tree species in the forest clearly decreased, while that of shade-tolerant species clearly increased. Structural parameters showed a moderate tree-size diversity, despite the high species richness of the forest. This was mainly the result of selection cuttings, which clearly decreased tree-size variability after the second period of study. However, selection cuttings did not favor regeneration establishment, especially that of light-demanding tree species, whose role in the stand is assumed to be only minor in the future. The relatively high level of volume growth indicated that cutting intensity may be increased. More intense selection cuttings would also improve the stand structure by providing better light conditions for potential regeneration of different tree species, also light-adapted ones.

Crecimiento radial de especies de pino en rodales sujetos a cortas de selección en Santa María Lachixío, Oaxaca, México

Introduction: The evaluation of the effect of management activities on trees is essential to gain a better understanding of the processes occurring in the stands. Objective: To evaluate the effect of selection cutting on the growth of pine species in uneven-aged stands. Materials and methods: Thirty sampling sites were established in two mixed pine stands subjected to selection cutting in 2003. The stumps of this harvest were used as site centers and the growth of the residual trees was evaluated in a 10-m radius; tree-size variables and competition indices were calculated. Results and discussion: In the first five years after the harvest, 47 % of residual trees showed significant growth (P ≤ 0.05). Stump diameter, diameter at breast height and competition were the most important variables to explain growth. The competition area of the harvested individuals (stumps) showed influence up to a 15-m radius. The increase in basal area (IBA) was 71 % with respect to pre-harvest growth. This increase was related to the basal area sum of the residual trees and 1.3 m2 per site (41.3 m2·ha-1) was established as the threshold from which a release is nullified by residual competition. Conclusion: Selection cutting influences residual tree growth in a differentiated way; the response may be positive, negative or nil depending on size and local competition.

Ice-storm damage to trees in mixed Central European forests: damage patterns, predictors and susceptibility of tree species

AbstractIn northern temperate forests, ice storms are a common disturbance agent, though climate change may alter their occurrence patterns. Their impact on forest ecosystems is complex, as they influence both structure and processes. In 2014, an ice storm of high intensity and large spatial extent occurred in Slovenia, Central Europe, which enabled a detailed study of ice damage to individual trees across a broader spatial scale. Pre- and post-ice storm measurement data on 11 414 trees on 960 permanent plots were used to examine ice damage patterns on trees in the disturbed forest area (~8700 km2) to determine the predictors of ice damage to trees and to investigate the relative susceptibility of eight groups of tree species in mixed Central European forests. We used a novel approach to modelling ice-storm intensity across the region based on measured data on air temperature, precipitation amount and duration, precipitation intensity and wind speed. The ice storm damaged 31 percent of the analysed trees; high variability in the damage rate was observed across the disturbed area. For the tree species, a susceptibility to ice damage index (SI) ranging between 0 (no damage) and 1 (complete damage) was calculated based on terrestrial assessment of trees. Tree species differed significantly in susceptibility to ice damage: Abies alba (SI = 0.14) and Quercus sp. (SI = 0.11) were rather resistant; Picea abies, Fagus sylvatica and Acer sp. (SI = 0.23–0.28) were moderately to very susceptible; and Pinus sp. (SI = 0.62) was extremely susceptible to ice damage. Eight predictors and three interactions were included in an ordinal logistic regression model of tree damage: ice damage on trees depends mainly on ice-storm intensity, elevation and tree species, whilst tree dbh and social status, tree size and tree species diversity indices and slope were relatively less important. Our study illustrates the complexity of damage patterns on trees due to ice storms and the significance of ice-storm intensity and tree species as predictors when modelling ice damage on individual trees.

Seasonal, medium-term and daily patterns of tree diameter growth in response to climate

Abstract Tree growth is expected to be responsive to climatic drivers across a spectrum of temporal scales, ranging from yearly growth to daily water use and photosynthesis. Automatic dendrometers offer the potential to provide continuous high-resolution measurements of tree radius changes. The signal recorded contains three components: (1) a long-term seasonal growth component, (2) a mid-term component representing swelling after rainfall and subsequent drying and (3) daily cycles of water-uptake related to tree transpiration. For 91 trees at 4 sites (Picea abies: 58, Pinus cembra: 17, Fagus sylvatica: 14, Pinus sylvestris: 2) monitored in Austria between 2012 and 2015, we simultaneously modelled these three processes using a hierarchical nonlinear mixed-effects model represented by two logistic growth curves. The focus was on the mid-term and daily component, and therefore long-term growth that is typically modelled by including tree size, competition or site variables was represented by random effects only. Both mid-term and short-term components were species-specific. In general, P. cembra and F. sylvatica were less sensitive to climate variables than P. abies. For all species, the mid-term component was best represented using a 14-day moving average difference between rainfall and potential evapotranspiration, a 24-h moving average of precipitation and its 1–3 days lags, a 24-h moving average temperature and its 1–3 days lags. The daily cycles of water uptake were best related to hourly humidity and its 3-h lag, and interactions with the 14-day moving average difference between rainfall and potential evapotranspiration accounted for attenuating cycles after rainy events and increasing cycles in dry periods.

Development of allometric relationships for estimate above ground biomass of trees in the tropical abandoned land

Abstract. Karyati, Widiati KY, Karmini, Mulyadi R. 2019. Development of allometric relationships for estimate above ground biomass of trees in the tropical abandoned lands. Biodiversitas 20: 3508-3516. The abandoned lands have important role in the ecological function as well as carbon sequestration. The allometric equations to estimate above ground biomass in abandoned land are still limited available. This study objective was to develop allometric relationships between tree size variables (diameter at breast height (DBH) and tree height) and leaf, branch, trunk, and total above ground biomass (TAGB) in abandoned land in East Kalimantan, Indonesia. The correlation coefficients between stem DBH and tree height to leaf and branch indicating a relatively weak relationship. The moderately strong relationships were showed by DBH and tree height to trunk and TAGB. The specific allometric equation of above ground biomass for different land use and land type is needed to estimate the accurate TAGB in the site.

Estimation of Structural Diversity in Urban Forests Based on Spectral and Textural Properties Derived from Digital Aerial Images

Urban forests generally have a heterogeneous structure consisting of small vegetation patches. High spatial resolution digital aerial images are still a primary data source for urban forest inventories. In the present study, the estimation possibilities of the structural diversity of urban forests were evaluated using image properties extracted from digital aerial images. Firstly, relationships between structural diversity indices and image properties were determined using the correlation analysis. It was found out that structural diversity indices were significantly correlated with spectral and textural properties. The strongest relationship was calculated between the normalized difference vegetation index and species-based Shannon–Wiener diversity index$$\left( {H_{\text{s}}^{\prime } } \right)$$ (r = 0.599, p < 0.01). The relationship between textural properties and structural diversity indices was slightly lower compared to spectral properties. The strongest relationship between textural properties and structural diversity indices was calculated between the Entropy values derived from DVI and $$H_{\text{s}}^{\prime }$$ (r = 0.478, p < 0.01). Afterward, each used diversity index was modeled as a function of the textural and spectral properties of digital aerial images. Univariate and multivariate linear regression models were used for this purpose. While the adjusted coefficient of determination $$\left( {R_{\text{adj}}^{2} } \right)$$ of univariate regression models varies between 0.07 and 0.37, the $$R_{\text{adj}}^{2}$$ values of a multivariate model vary between 0.13 and 0.57. Among the developed models, only the estimation models of tree size diversity $$\left( {H_{\text{h}}^{\prime } } \right)$$ and tree species diversity $$\left( {H_{\text{s}}^{\prime } } \right)$$ provided an estimation accuracy that could be used in practice.

Understanding the Evolution of Tree Size Diversity within the Multivariate Nonsymmetrical Diffusion Process and Information Measures

This study focuses on the stochastic differential calculus of Itô, as an effective tool for the analysis of noise in forest growth and yield modeling. Idea of modeling state (tree size) variable in terms of univariate stochastic differential equation is exposed to a multivariate stochastic differential equation. The new developed multivariate probability density function and its marginal univariate, bivariate and trivariate distributions, and conditional univariate, bivariate and trivariate probability density functions can be applied for the modeling of tree size variables and various stand attributes such as the mean diameter, height, crown base height, crown width, volume, basal area, slenderness ratio, increments, and much more. This study introduces generalized multivariate interaction information measures based on the differential entropy to capture multivariate dependencies between state variables. The present study experimentally confirms the effectiveness of using multivariate interaction information measures to reconstruct multivariate relationships of state variables using measurements obtained from a real-world data set.

Regeneration and Early Tending of Black Locust (Robinia pseudoacacia L.) Stands in the North-West of Romania

Background and Purpose: The aim of this study is to highlight the importance of black locust (Robinia pseudoacacia L.), a North American-originating tree species of major importance in Romania, in extreme site conditions such as sand dunes. In this respect, a Research and Development (R&amp;amp;D) project has been carried out in Carei-Valea lui Mihai Plain (north-west of Romania) since 2016. Materials and Methods: Three sub-compartments were selected in IV Valea lui Mihai Working Circle, Săcueni Forest District: two pure natural regenerations by root suckers of black locust at different ages (sub-compartments 3B and 52A%) and a mixed black locust - black cherry stand (sub-compartment 23D). Biometrical measurements and analyses as well as biomass estimations were performed. A thorough statistical analysis using the data on initial, extracted and residual trees/stands was also performed. Results: The main outputs of the project are as follows: (1) Black locust was established naturally by root suckers and the stocking of newly established stands can be as high as 50,000 suckers·ha-1; (2) The initial growth of black locust regeneration is quick and the young regeneration can close the canopy in 1-2 years, resulting in an appropriate dune fixation and wind erosion control; (3) The young pure or mixed black locust-dominated stands are left untended until the first cleaning-respacing (mean diameter 5-6 cm), when the stand shows high stocking/density and a wide variation in tree size. This intervention is from below, heavy (intensity over 25% by number of trees or basal area) and of negative selection type, removing mostly low Kraft’s class, dead or dying, and defective trees. Conclusions: This R&amp;amp;D project has shown the high potential of black locust to establish naturally by root suckers after a low coppice cut and stump removal, as well as the fast initial growth of regenerated black locust. The quick canopy closure of young regeneration results in an appropriate dune fixation and wind erosion control.

Investigating the Feasibility of Multi-Scan Terrestrial Laser Scanning to Characterize Tree Communities in Southern Boreal Forests

Terrestrial laser scanning (TLS) has proven to accurately represent individual trees, while the use of TLS for plot-level forest characterization has been studied less. We used 91 sample plots to assess the feasibility of TLS in estimating plot-level forest inventory attributes, namely the stem number (N), basal area (G), and volume (V) as well as the basal area weighed mean diameter (Dg) and height (Hg). The effect of the sample plot size was investigated by using different-sized sample plots with a fixed scan set-up to also observe possible differences in the quality of point clouds. The Gini coefficient was used to measure the variation in tree size distribution at the plot-level to investigate the relationship between stand heterogeneity and the performance of the TLS-based method. Higher performances in tree detection and forest attribute estimation were recorded for sample plots with a low degree of tree size variation. The TLS-based approach captured 95% of the variation in Hg and V, 85% of the variation in Dg and G, and 67% of the variation in N. By increasing the sample plot size, the tree detection rate was decreased, and the accuracy of the estimates, especially G and N, decreased. This study emphasizes the feasibility of TLS-based approaches in plot-level forest inventories in varying southern boreal forest conditions.

Análisis espacial de las variables fenotípicas en un huerto clonal de Pinus arizonica Engelm. en el norte de México

Introduction: Seed orchards provide germplasm genetically suitable for use in forest restoration. Knowledge of the spatial distribution of attributes is crucial for their management. Objective: To model cone production and tree size variables in a clonal orchard of Pinus arizonica Engelm. from a geospatial perspective in order to determine their behavior and distribution. Materials and methods: The spatial pattern of tree size variables and cone production of 126 ramets were determined through a geospatial analysis, using the Getis-Ord G statistic. A Pearson correlation analysis (P ≤ 0.05) determined the variables best associated with cone production and these were examined with stepwise regression. In terms of cone production, the best combination was modeled through a geographically weighted regression. Results and discussion: Statistically significant (P Conclusion: Tree size variables and cone production presented a tendency towards clustering. The use of a geospatial perspective allowed a better understanding of the spatial dynamics of tree size variables.

Relationships between tree survival, stand structure and age in trembling aspen dominated stands

Canopy openings resulting from tree death provide opportunities for shade intolerant species such as aspen to establish and grow in the understory leading to development of aspen stands with multiple canopy layers and multiple cohorts. Stand structure is likely to influence survival probability since it will lead to differences in competition intensity and in resource utilization. We examined relationships among stand age (years after stand establishment), age structure (age diversity), and tree size diversity (i.e., diversity of diameter classes), using cores collected from 531 aspen trees in 18 stands distributed across the province of Alberta, Canada. Results show positive relationships between stand age, age diversity, and tree size diversity. Logistic mixed effects survival probability models were developed using data from 199 remeasured permanent sample plots. Results show an inverted U-shaped relationship between survival probability and tree diameter. Survival probability trends varied between young (≤60), mature (>60 and ≤ 100), and old (>100) age groups in relation to differences in competition intensity and stand structure. Intraspecific competition (deciduous basal area larger) was negatively related to tree survival and the magnitude of the negative impact was stronger in the young age group. Negative effects of structural diversity (tree size diversity) on survival probability were strongest in the mature age group. We suggest that effects of tree size diversity relate to environmental stresses and competition at the stand level while the influence of deciduous basal area larger serves as a measure of competition experienced by individual trees. The significance of mean annual temperature in our models indicates that, under warmer conditions, competition variables (e.g., deciduous basal area larger and tree size diversity) had stronger effects on tree mortality with the magnitude of effects varying between age groups.

Patterns of tree diameter distributions in managed and unmanaged Abies alba Mill. and Fagus sylvatica L. forest patches

Temperate forests with shade-tolerant canopy tree species can develop vertical structures of varying complexity. Forests with Abies alba Mill. and Fagus sylvatica L. can be composed of one-, two-, and multi-storied patches and selection patches. A dominant view in forest ecology is that unmanaged forests tend to have greater structural heterogeneity than managed stands. Structural integrity, however, may differ among forest developmental stages. The main objective of this study was to compare the tree diameter complexity in managed and unmanaged patches during the early developmental stage.Data were collected between 2016 and 2018 in the Świętokrzyskie Mountains in Central Europe. The investigated tree communities were dominated by A. alba and F. sylvatica. Sample plots representing the growing-up developmental stage were randomly selected; of these, 30 plots were in managed stands, and 30 plots were in unmanaged forests. The diameter at breast height (DBH) distribution patterns were determined using hierarchical cluster analysis (HCA), clustering indices, and finite mixture models.Three main DBH distribution patterns were identified for the managed stands (K-A, K-B, and K-C). These patterns consisted of three or two sub-populations. The patterns represented structurally diversified patches composed of trees of all ages with multi-, three- or two-layered canopies and with intensive natural processes of regeneration. Two main DBH distribution patterns were identified for the unmanaged forests (S-A, and S-B). These patterns consisted of two clearly separated sub-populations. They are typical in patches with two-layered canopies, and the trees from the upper layer had a large share (40–60%). The distinguished DBH distribution patterns indicated there was greater tree size diversity in the managed stands than in the unmanaged forests. When comparing managed versus unmanaged patches, it is important to consider the developmental stage.

Comparison of distinguish ability on seven tree size diversity indices

Comparison of distinguish ability on seven tree size diversity indices

Larger plants promote a greater diversity of symbiotic nitrogen‐fixing soil bacteria associated with an Australian endemic legume

Abstract A major goal in microbial ecology is to understand the factors that structure bacterial communities across space and time. For microbes that are plant symbionts, community assembly processes can lead to either a positive or negative relationship between plant size or age and soil microbe diversity. Here, we evaluated the extent to which such relationships exist within a single legume species (Acacia acuminata) and their naturally occurring symbiotic nitrogen‐fixing bacteria (rhizobia). We quantified the diversity of rhizobia that associate with A. acuminata trees of variable size spanning a large environmental gradient in southwest Australia (72 trees in 24 sites spread across ~300,000 km2), using metabarcoding. We modelled rhizobia diversity using 16S exact genetic variants, in a binomial multivariate statistical framework that controlled for climate and local soil characteristics. We identified two major phylogenetic clades of rhizobia that associate with A. acuminata. Soil sampled at the base of larger Acacia trees contained a higher richness of rhizobia genetic variants. Each major clade responds differently to environmental factors (climate and soil characteristics), but the positive association between tree size and rhizobia genetic diversity was mainly driven by responses from one of the two clades. Overall tree size explained more variation than any other factor, resulting in a ~3‐fold increase in total richness and clade diversity from the smallest to the largest trees. Synthesis. Previous studies have shown that plant host species is important in structuring microbial soil communities in the rhizosphere. Our results show that host size or age within a single plant species can also structure diversity of at least one group of soil microbes. A positive relationship between plant host size and rhizobia diversity suggests that hosts may modify the niche space of their surrounding soil (niche construction hypothesis) enabling a higher richness of microbial taxa. That different rhizobial groups responded differently to host size and other ecological factors suggests that rhizobia is not an ecologically uniform group, and that entirely neutral explanations for our results are unlikely. Host plants may be analogous to “islands,” where larger plant hosts may accumulate diversity over time, through migration opportunities.

Effects of structural heterogeneity on the diurnal temperature range in temperate forest ecosystems

The microclimate in forest ecosystems can be altered by modifications of stand structure due to forest management or natural forest development. Current forest management practices in Central Europe and North America aim to promote structural heterogeneity and maintain forest canopy cover, which is known to be a major driver of forest microclimate. Here, we investigated the impacts of forest management and structural heterogeneity on the diurnal temperature range (DTR) in 128 managed forest stands in three climatically different locations (Swabian Alb, Hainich-Dün and Schorfheide-Chorin) in Central Europe. Increasing structural heterogeneity by promoting tree size diversity and differentiation increased vertical stratification and resulted in an impaired DTR during the vegetation period. Linear regression models with geographic location, elevation above sea level, canopy openness and measures of structural heterogeneity as explanatory variables explained 79.4–80.9% of variance in DTR. However, the overall effect of structural heterogeneity on DTR was small. Differences in DTR between plots of different main tree species could be attributed to differences in canopy openness and light transmission, whereas tree species diversity had no significant effect on DTR. Unmanaged forests were characterized by a significantly lower DTR than managed, even-aged forests. DTR in uneven-aged stands managed under single tree selection was comparable to unmanaged stands. Terrestrial laser scanning (TLS) derived measures of canopy openness and vertical structure allowed to explain 79.4% of variance in DTR considering geographic location and elevation, which can also be assessed by TLS with integrated GPS and an altimeter. We conclude that structural characteristics of forest stands other than canopy openness contribute marginally to variation in forest microclimate. However, the analyses of structure-microclimate analyses indicate that effects of stand structure on DTR might be more pronounced in regions with low precipitation during the vegetation period.

Competition, tree age and size drive the productivity of mixed forests of pedunculate oak, beech and red oak

In order to understand the relationship between tree diversity and forest productivity, it is crucial to understand what is going on at the level of individual trees, since each tree responds to the prevailing environmental conditions and interacts with his neighbours. We explored tree interactions in 53 forest plots in northern Belgium (TREEWEB platform) containing all possible combinations of pedunculate oak, beech and red oak. We cored 307 trees and determined the average annual basal area increment for the last 10 years for each sampled tree. We investigated the importance of neighbourhood competition, tree age an size for tree-level growth and then scaled up the species-specific tree growth to stand-level productivity. By exploring how competition, tree age and size varied along the studied gradient of tree species richness, we were able to explain the observed species-specific tree level and stand-level growth along the tree species richness gradient. We found no relationship between tree species richness and forest productivity, due to contrasting growth patterns of the three species along the richness gradient: the growth of pedunculate oak decreased, growth of beech was constant and growth of red oak increased along the tree species richness gradient. Increased heterospecific competition was the main reason for the observed lower growth of pedunculate oak in mixtures, whereas variation in tree age and size along the studied tree species richness gradient were the main drivers for the observed growth patterns of beech and red oak. Species-specific age differences along the tree species richness gradient could be linked with the species composition. We observed a multi-aged stand structure with the light-demanding pedunculate oak being older than the more shade-tolerant beech and red oak, probably a consequence of management interventions needed to enable long-term coexistence of light-demanding and shade-tolerant species. Our study highlights that the management history of mature forests may influence diversity-productivity relationships and should therefore be taken into account during the analysis.

Climatic water availability is the main limiting factor of biotic attributes across large-scale elevational gradients in tropical forests

Climatic water availability is a key spatial driver of species distribution patterns in natural forests. Yet, we do not fully understand the importance of climatic water availability relative to temperature, and climate relative to edaphic factors for multiple biotic attributes across large-scale elevational gradients in natural forests. Here, we modelled multiple abiotic factors (elevation, climate, and edaphic factors) with each of the taxonomic-related (Shannon's species diversity, species richness, species evenness, and Simpson's dominance) and tree size or biomass-related (individual tree size variation, functional dominance and divergence, and aboveground biomass) biotic attributes through boosted regression trees (BRT) models, using biophysical data from 247,691 trees across 907 plots in tropical forests in Hainan Island of Southern China. The tested multiple abiotic factors explained simultaneously 43, 50, 36, 45, 37, 50, 17 and 46%, respectively, of the variations in Shannon's species diversity, species richness, species evenness, Simpson's dominance, individual tree size variation, functional dominance, functional divergence and aboveground biomass. After the large influences of elevation (i.e. 30.43 to 62.83%), climatic water availability accounted for most (i.e. 15.52 to 25.30%) of the variations in all biotic attributes. Beside the increasing trend with elevational gradients, taxonomic diversity increased strongly with climatic water availability whereas tree size or biomass-related biotic attributes showed strong decreasing and increasing trends. Tree size or biomass-related rather than taxonomic-related biotic attributes also decreased apparently with mean annual temperature. Most of the biotic attributes monotonically increased with soil fertility but decreased with soil pH, whereas soil textural properties had mostly negligible influences. This study strongly reveals that future climate change (i.e. a decrease in climatic water availability with an increase in mean annual temperature) is thus likely to have a substantial influence on the biotic attributes in the studied tropical forests across large-scale elevational gradients.

Equilibrium forest demography explains the distribution of tree sizes across North America

The distribution of tree sizes within a forest strongly influences how it will respond to disturbances and environmental changes such as future climate change and increases in atmospheric CO2. This means that global vegetation models must include variation in tree size to accurately represent carbon sinks, such as that seen in North America. Here we use an analytical model of large-scale forest demography which assumes tree growth varies as a power of tree diameter whilst tree mortality is independent of size. The equilibrium solutions of this model are able to accurately reproduce the tree-size distributions, for 61 species and four plant functional types, measured across North America, using just a single species-specific fitting parameter, μ, which determines the ratio of mortality to growth. The predictions of metabolic scaling theory for tree-size distributions are also tested and found to deviate significantly from observations and that maybe explained by the assumptions made about how individual trees fill the available space. We show that equilibrium forest demography implies a single curve that relates mean tree diameter to μ, and that this can be used to make reasonable estimates of the whole dataset mean trunk diameter by fitting only to the larger trees. Our analysis suggests that analytical solutions such as those in this paper may have a role in aiding the understanding and development of next-generation Dynamic Global Vegetation Models based on ecosystem demography.