Tree Height Diversity Research Articles

Alpha and beta diversity of functional traits in subtropical evergreen broad-leaved secondary forest communities.

Intra-speciic variation is the main source of functional trait diversity and has similar ecological effects as inter-speciic variation. We studied 79 species and 3546 individuals from 50 ixed monitoring plots in subtropical evergreen broad - leaved secondary forests in Zhejiang Province, China. Using trait gradient analysis, we examined nine traits (speciic leaf area, leaf dry matter content, wood density, leaf area, chlorophyll content, leaf nitrogen content, leaf phosphorus content, leaf potassium content, and nitrogen-phosphorus ratio) by decomposing species functional traits into alpha (within-community) and beta (among-communities) measure the impact of environmental gradients and the presence of other species on the variation of traits. All nine functional traits showed some degree of differentiation in the forest communities, with a greater range of variation in alpha values than in beta values . Correlations were signiicantly different between the trait differences in the communities. The alpha values of each trait showed a higher correlation with other components than the beta values. The factors affecting intra-speciic trait variation were relatively complex. The alpha component had a more signiicant and stronger effect on intra-speciic trait variation compared to the beta component. Abiotic factors, such as soil nutrient content, soil nitrogen-phosphorus content, directly affected the beta component. In contrast, biotic factors, such as tree height variation, had a direct and stronger effect on the alpha component. Our results demonstrate that alpha and beta components, as independent differentiation axes among coexisting species, have different sensitivities to different environmental factors and traits in different ecological strategies and spatial scales. Trait gradient analysis can more clearly reveal the variation patterns of species traits in communities, which will help to understand the scale effects and potential mechanisms of trait relationships.

Maximum tree height in European Mountains decreases above a climate-related elevation threshold

Mountain forests face important threats from global change and spatio-temporal variation in tree height can help to monitor these effects. In this study, we used the Global Ecosystem Dynamics Investigation space-borne laser sensor to examine the relationship between maximum tree height and elevation, and the role of climate, in the main European mountain ranges. We found a piecewise relationship between elevation and maximum tree height in all mountain ranges, supporting the existence of a common breakpoint that marks the beginning of tree development limitations. Temperature and precipitation were identified as the most important drivers of tree height variation. Additionally, we predicted significant upward displacement of the breakpoint for the period 2080-2100 under climate change scenarios, potentially increasing the area without growth limitations for trees. These findings contribute to understanding the impacts of global warming on mountain forest ecosystems and provide insights for their monitoring and management.

Plant functional traits and tree size inequality improved individual tree height prediction of mid-montane humid evergreen broad-leaved forests in southwest China

Tree height and diameter at breast height (DBH) are key survey factors in forest inventory. Compared to measuring DBH, the process of measuring tree height is time-consuming, labor-intensive and costly, especially in natural mixed forests. Tree height is therefore commonly predicted using height-diameter (H-D) models. Nevertheless, developing H-D models for natural mixed forests are hampered by the large diversity of tree species and the small number of rare tree species observed. In this study, a nonlinear mixed effects H-D model was established for a mid-montane humid evergreen broad-leaved forest in southwest China. For this purpose, we classified tree species by K-means clustering according to the specific plant functional traits. Data were collected from 5, 737 trees in 100 subplots with 86 species. The results revealed that the nonlinear mixed effects model of tree height accounted for 75% of the variation in tree height without significant heteroscedasticity, and that the model parameters had biological significance. In the 10-fold cross validation, no clear fluctuation in the model evaluation metrics was observed, indicating the absence of overfitting in the model. Of the 15 stand variables, dominant height (Hd) and Margalef’s index of DBH (DMg), which contributed the most to the height-diameter model, were selected to expand the model. Our findings suggest that tree height increased with increasing values of Hd and DMg, and vice versa. This study highlights the feasibility of categorizing natural mixed forests by utilizing plant functional traits and the influential role of tree size inequality on tree height variation.

Elevational Patterns of Tree Species Richness and Forest Biomass on Two Subtropical Mountains in China

Increasing evidence shows that both abiotic and biotic factors affect species richness and stand biomass in forests, yet the relative and interactive impacts of these factors remain debated in different forest ecosystems. We sampled 55 forest plots (600 m2 per plot) on two subtropical mountains with distinct diversity levels in China to explore the elevational patterns of tree species richness and stand biomass and examined how they were affected by climate, stand structure, and dominance of mycorrhizal types. The tree species richness of both mountains decreased with elevation, while the stand biomass exhibited unimodal or no apparent trends. On both mountains, the tree species richness was strongly shaped by climatic factors, especially the mean annual temperature, whereas the stand biomass was mainly affected by the stand structure. Specifically, on the mountain with higher species richness, both the tree height variation and maximum tree size were strongly correlated with the stand biomass. Meanwhile, on the species-poor mountain with higher elevations, only the maximum tree size correlated with the stand biomass. The dominance of ectomycorrhizal trees also had positive effects on the stand biomass of both mountains. These results suggest that climate, stand structure, and mycorrhizal dominance may jointly drive the decoupling between tree species richness and stand biomass, which should be given more attention in further research and forest management to achieve the climate change mitigation goals.

Soil morphological, physical and chemical properties affecting Eucalyptus spp. productivity on Entisols and Ultisols

Soil fertility in forestry systems has usually been constrained to soil nutrients, with little attention to soil morphological attributes and physical properties. Our hypothesis was that soil physical properties and morphological attributes are more closely related with commercial forest growth than soil chemical fertility. The objective of the study was to analyze the influence of soil properties, in different soil types, on dendrometric variables and productivity of clonal E. saligna and seminal E. dunnii, both widely employed in commercial plantations managed for pulp and lumber production in southern Brazil. On inventory plots with two Eucalyptus species, namely Eucalyptus saligna (clone 32864) and seminal E. dunnii, we evaluated morphological attributes and physical and chemical properties of 17 soils (Ultisols and Entisols), and the dendrometric variables tree height, tree dominant height (h100) and diameter at breast height (DBH), all measured in 7-years old plantations. Eucalyptus growth was variable and influenced by profile attributes and soil properties, but correlations between h100 and soil properties were weak (r < 0.7) and usually not significant. Tree height and DBH were not affected by Eucalyptus species, soil type and their interaction. Overall, DBH ranged from 77.98 to 304.30 mm, with an average value of 183.23 mm. By contrast, tree h100 was affected by Eucalyptus species and soil type, but not by their interaction. Trees of E. saligna (23.4 m) were taller than E. dunnii (22.1 m), while among soil types Ultisols had the tallest (23.4 m) and Entisols the shortest trees (22 m). Chemical properties were more variable in surface soil layers, whereas physical properties mainly differentiated subsurface soil layers. The lowest dominant height resulted from the interaction between the lowest field capacity and plant available water capacity and the smaller depth of Entisols' soil profile. Contrary to our hypothesis, most soil properties/attributes were not significantly correlated with dominant tree height. Neither soil physical, morphological properties nor soil chemical fertility are determinants to forest growth when these parameters are not at critical limits for forest growth, particularly with absence of extreme edaphoclimatic conditions such as low rainfall or high temperatures. Associations among soil morphological attributes, physical properties and edaphoclimatic variables should be validated in future studies to better understand their effect of forest productivity in subtropical environments.

Global-scale biomass estimation based on machine learning and deep learning methods

Modeling accurate aboveground biomass (AGB) is a critical aspect of remote sensing research. Besides selecting the appropriate model from significant inputs, integrating optical and microwave products can improve biomass estimation accuracy. Three models were used to estimate biomass to accomplish these goals: Convolutional Neural Network (CNN), Random Forest (RF), and Support Vector Machine for Regression (SVR). Two feature selection techniques, Support Vector Machine for Regression Feature Selection (SVRFS) and Random Forest Feature Selection (RFFS), were used to select the most significant variables to include in the AGB estimation models. Grid search with cross-validation was employed to optimize the hyperparameters for each algorithm. This research aimed to reduce the effects of Radio Frequency Interference (RFI), where RFI filtering outperformed the remaining three models (R2 values were 0.79, 0.80, and 0.82 without reducing RFI effects and were 0.85, 0.87, and 0.88 with reducing RFI effects for SVR, RF and CNN models respectively). Two feature selection techniques jointly selected the variables tree height, vegetation optical depth (VOD), and normalized difference vegetation index (NDVI). The highest Root-Mean-Square deviation (RMSE) values were obtained when CNN and RF models were used in conjunction with the SVRFS method (31.22 Mg/ha and 31.28 Mg/ha for CNN and RF models using the SVRFS model, respectively). This study investigated machine learning and deep learning algorithms’ capability to improve global-scale AGB estimation.

Vessel tapering is conserved along a precipitation gradient in tropical trees of the genus Cedrela

Key messageThe rate of vessel tapering is highly conserved across a precipitation gradient in tropical trees, pointing to a limit on tree height determined by a maximum basal vessel diameter.Maximum tree height in the tropics decreases strongly with decreasing precipitation. The role of hydraulic architecture in controlling this variation in tree height remains unclear. The widening of conducting xylem vessels from the apex to the base of trees, also known as tapering, is important for maintaining the hydraulic conductivity along the tree stem. If in contrast vessel diameter were constant, then resistance would increase with path length constraining flow rates as tree height increases. Whilst previous research has shown that vessel diameter scales with tree height at a similar rate (similar power law exponent) across biomes and taxa, knowledge on these relationships across precipitation gradients within a single species is incomplete, especially for the tropics. Here we report how vessel density and diameter at the tree base differ for two tropical Cedrela species across four sites varying in precipitation from 1014 to 2585 mm year−1. We find that maximum tree height decreases with decreasing precipitation across sites from 42 to 13 m. Despite the strong differences between sites in maximum tree height and water availability, tapering is indeed remarkably conserved and close to published scaling with height based on multi-species analyses. Thus, for a given tree height, basal vessel diameter does not vary between sites, whilst the maximum basal vessel size is two times smaller at the drier site (with the shortest trees) compared to the wettest site (with the tallest trees). This suggests a possible limitation of tree height determined by a maximum basal vessel diameter that can be sustained, given increasing embolism risk with increasing dryness. Our results show no hydraulic adaptation across this wetness gradient and reveal a clear relationship between maximum tree height and maximum basal vessel size.

Tropical forest strata shifts in plant structural diversity-aboveground carbon relationships along altitudinal gradients.

Aboveground carbon storage in forests can be influenced by both structural and compositional diversity of plant communities. However, the relative and interactive effects of structural and compositional diversity on multilevel aboveground carbon storage across forest strata and how these relationships vary with altitude and soil nutrients remain unclear. Using data obtained from 34 tropical forest plots (total area 8.5 ha) in Hainan Island, China, we analyzed the relationships between aboveground carbon at four levels (litter, understory, overstory, and whole-community) with structural diversity (diameter and height diversity) and compositional diversity (species diversity and evenness) in the understory and overstory. The direct and indirect effects of altitude, soil nutrients (total N and total P and N/P ratio), structural diversity, and compositional diversity on aboveground carbon were explored via Bayesian structural equation modeling. The results showed that structural diversity, rather than compositional diversity, in overstory stratum determined aboveground carbon. Specifically, overstory structural diversity was negatively associated with understory carbon, while positively associated with overstory and whole-community carbon. Furthermore, diversity‑carbon relationships were slightly affected by soil nutrients but strongly by altitude. Specifically, the relationship between overstory and whole-community carbon content with overstory tree height diversity weakened with altitude, while their relationship with overstory diameter diversity strengthened. Altitude directly and indirectly affected overstory tree height and diameter diversity through overstory species diversity, thereby reducing understory and increasing overstory and whole-community carbon. Altitude directly promoted litter carbon. We provide evidence that the effects of plant diversity on aboveground carbon storage are forest strata- and altitude-dependent. As overstory structural diversity plays a crucial role in storing aboveground carbon at all altitudes, we proposed that focusing on overstory structural diversity would be promising for predicting trends in how plant diversity affects aboveground carbon in response to climate change.

Branch xylem vascular adjustments in European beech in response to decreasing water availability across a precipitation gradient.

Crucial for the climate adaptation of trees is a xylem anatomical structure capable of adjusting to changing water regimes. Although species comparisons across climate zones have demonstrated anatomical change in response to altered water availability and tree height, less is known about the adaptability of tree vascular systems to increasing water deficits at the intraspecific level. Information on the between-population and within-population variability of xylem traits helps assessing a species' ability to cope with climate change. We investigated the variability of wood anatomical and related hydraulic traits in terminal branches of European beech (Fagus sylvatica L.) trees across a precipitation gradient (520-890mmyear-1) and examined the influence of climatic water balance (CWB), soil water capacity (AWC), neighborhood competition (CI), tree height and branch age on these traits. Furthermore, the relationship between xylem anatomical traits and embolism resistance (P50) was tested. Within-population trait variation was larger than between-population variation. Vessel diameter, lumen-to-sapwood area ratio and potential conductivity of terminal branches decreased with decreasing CWB, but these traits were not affected by AWC, whereas vessel density increased with an AWC decrease. In contrast, none of the studied anatomical traits were influenced by variation in tree height (21-34m) or CI. Branch age was highly variable (2-22years) despite equal diameter and position in the flow path, suggesting different growth trajectories in the past. Vessel diameter decreased, and vessel density increased, with increasing branch age, reflecting negative annual radial growth trends. Although vessel diameter was not related to P50, vessel grouping index and lumen-to-sapwood area ratio showed a weak, though highly significant, positive relationship to P50. We conclude that the xylem anatomy of terminal tree-top branches in European beech is modified in response to increasing climatic aridity and/or decreasing soil water availability, independent of a tree height effect.

Heritable and Climatic Sources of Variation in Juvenile Tree Growth in an Austrian Common Garden Experiment of Central European Norway Spruce Populations

We leveraged publicly available data on juvenile tree height of 299 Central European Norway spruce populations grown in a common garden experiment across 24 diverse trial locations in Austria and weather data from the trial locations and population provenances to parse the heritable and climatic components of juvenile tree height variation. Principal component analysis of geospatial and weather variables demonstrated high interannual variation among trial environments, largely driven by differences in precipitation, and separation of population provenances based on altitude, temperature, and snowfall. Tree height was highly heritable and modeling the covariance between populations and trial environments based on climatic data led to more stable estimation of heritability and population × environment variance. Climatic similarity among population provenances was highly predictive of population × environment estimates for tree height.

Testing the Height Variation Hypothesis with the R rasterdiv Package for Tree Species Diversity Estimation

Forest biodiversity is a key element to support ecosystem functions. Measuring biodiversity is a necessary step to identify critical issues and to choose interventions to be applied in order to protect it. Remote sensing provides consistent quality and standardized data, which can be used to estimate different aspects of biodiversity. The Height Variation Hypothesis (HVH) represents an indirect method for estimating species diversity in forest ecosystems from the LiDAR data, and it assumes that the higher the variation in tree height (height heterogeneity, HH), calculated through the ’Canopy Height Model’ (CHM) metric, the more complex the overall structure of the forest and the higher the tree species diversity. To date, the HVH has been tested exclusively with CHM data, assessing the HH only with a single heterogeneity index (the Rao’s Q index) without making use of any moving windows (MW) approach. In this study, the HVH has been tested in an alpine coniferous forest situated in the municipality of San Genesio/Jenesien (eastern Italian Alps) at 1100 m, characterized by the presence of 11 different tree species (mainly Pinus sylvestris, Larix decidua, Picea abies followed by Betula alba and Corylus avellana). The HH has been estimated through different heterogeneity measures described in the new R rasterdiv package using, besides the CHM, also other LiDAR metrics (as the percentile or the standard deviation of the height distribution) at various spatial resolutions and MWs (ALS LiDAR data with mean point cloud density of 2.9 point/m2). For each combination of parameters, and for all the considered plots, linear regressions between the Shannon’s H′ (used as tree species diversity index based on field data) and the HH have been derived. The results showed that the Rao’s Q index (singularly and through a multidimensional approach) performed generally better than the other heterogeneity indices in the assessment of the HH. The CHM and the LiDAR metrics related to the upper quantile point cloud distribution at fine resolution (2.5 m, 5 m) have shown the most important results for the assessment of the HH. The size of the used MW did not influence the general outcomes but instead, it increased when compared to the results found in the literature, where the HVH was tested without MW approach. The outcomes of this study underline that the HVH, calculated with certain heterogeneity indices and LiDAR data, can be considered a useful tool for assessing tree species diversity in considered forest ecosystems. The general results highlight the strength and importance of LiDAR data in assessing the height heterogeneity and the related biodiversity in forest ecosystems.

The intraspecific variation of functional traits modulates drought resilience of European beech and pubescent oak

Abstract A higher frequency and intensity of droughts will impair forest productivity. Therefore, improving our understanding of which factors enhance tree growth resilience against drought has become a crucial issue, but we lack information at the intraspecific level. In this study, we investigate the role played by climatic conditions and tree characteristics in the growth response to severe droughts in two deciduous Fagaceae species near their southern distribution limit: the temperate European beech Fagus sylvatica and the Mediterranean pubescent oak Quercus pubescens. The study area is located in Catalonia, NE Spain, where 149 trees were cored covering the water availability gradient of the species in the region. In addition, tree size (diameter and height) and an ensemble of stem, leaf and hydraulic traits were collected for each tree. Growth responses to extreme droughts during the period 1980–2015 were assessed using resilience indicators based on residual basal area increment series predicted by a model including growing season water balance. Although resistance was unrelated to drought intensity, higher water availability improved recovery and reduced drought legacy effects. Taller trees showed higher resilience against drought, which could be explained by the relationship between the variation in tree height and functional traits, such as leaf nitrogen concentration, leaf turgor loss point and resistance to xylem embolism. For both species, trees with lower cavitation resistance, higher leaf nitrogen concentration and tighter stomatal regulation (suggested by less negative turgor loss point and carbon isotope composition) displayed better performance during and after severe droughts. Both species showed a progressive decrease in resilience and increase in legacy effects. Synthesis. This study highlights the relevance of analysing intraspecific variation of functional traits involved in tree water and carbon balance to improve our understanding of the resilience and variability of growth responses to drought within species.

Clarifying the factors affecting Larix gmelinii forest regeneration based on structural equation model

Based on data from 49 plots of natural Larix gmelinii forests in Cuigang Forest Farm of Xinlin Forestry Bureau, Daxing'anling Mountains, China, we used 37 measurable variables that mainly focused on stand non-spatial structure, stand spatial structure, species diversity, soil condition, and site condition to construct the structural equation model of natural regeneration densities and size diversities (i.e., height and ground-diameter). The direct, indirect, and total influence coefficients of each path were quantified to extract the critical and controllable factors that influence regeneration density and diversity of natural L. gmelinii forests, which would help implement sustainable forest management. The results showed that the effects of various latent variables on rege-neration density were following an order as: stand non-spatial structure (-0.410) > species diversity (0.380) > soil condition (0.250) > site condition (0.249) > stand spatial structure (0.197), while the order were changed as: soil condition (0.778) > site condition (0.748) > stand spatial structure (0.684) > stand non-spatial structure (0.287) > forest diversity (0.105), when evaluated on the regeneration diversity. Generally, the critical and controllable factors affecting rege-neration quantity and diversity were soil pH, total potassium concentration, species diversity, tree height diversity, uniform angle index and stand volume per hectare. In the management, suitable thinning treatments or replanting broadleaved trees were recommended for optimizing and adjusting species composition, species diversity, soil pH and nutrition, which would promote natural regene-ration.

Species compositional, structural and functional diversity exerts different effects on soil erosion caused by increased rainfall intensity in Chinese tropical forests

High-diversity communities may mitigate the impact of environmental changes on soil erosion owing to the compositional, structural, and functional diversity of their species. In this field study, we explored the relative contributions of these biodiversity components to soil erosion and the mitigating effects of each index under environmental changes (e.g., rainfall intensity). We investigated the compositional (species diversity and evenness), structural (tree diameter and height diversity), and functional diversity (functional richness, evenness, and divergence) of 12 plant communities on Hainan Island, where biodiversity loss is severe. We measured soil erosion in each community using erosion plots under different rainfall intensities. The direction and relative contribution of biodiversity indices to soil erosion were analyzed. Except for the functional evenness, high values of biodiversity indices were associated with significantly reduced soil erosion regardless of rainfall intensity, and the relative contribution of tree height diversity was greater than that of other biodiversity indices. In addition, multiple biodiversity factors alleviated the adverse effects of increased rainfall intensity on soil erosion, but plant structural diversity had a greater positive effect than compositional and functional diversity, predominantly because of tree height diversity. The results confirmed that the consideration of multiple biodiversity components provides an improved understanding of the relationship between biodiversity loss and soil erosion. We emphasize that protection of tree height diversity may not only effectively reduce current soil erosion, but also resist the adverse impact of increased rainfall intensity on soil erosion in the future.

Genetic relationships between terminal shoot length, number of flushes and height in a 4-year-old progeny test of Pinus brutia Ten.

In this study, genetic variation in polycyclic growth was investigated in a young Pinus brutia Ten. study in Turkey. The number of flushes was partially under additive genetic control and was moderately correlated with the tree height at age 4. Pinus brutia is the most economically important tree species in Turkey. Previous limited studies suggested that its cyclic shoot elongation pattern can be useful for selecting seed sources for breeding and conservation of genetic resources. Understand the degree of genetic control of terminal shoot growth, number of flushes, and total tree height at early ages and assess the genetic relationships between the traits to guide decisions for breeding and gene conservation. Open-pollinated progenies of 188 trees from eight different seed sources were tested in three locations in the Aegean region of Turkey. Variance components, heritability and additive genetic correlations were estimated for tree height, terminal shoot length, and number of flushes. Traits were moderately under genetic control at the family. Terminal shoot length explained 76% of the variation in tree height. A strong genetic correlation (0.96) was found between tree height and terminal shoot length, while the number of flushes had a moderate genetic correlation with height (0.59). Northern seed sources tended to display less height growth, partially due to fewer flushes and lower shoot length. Shoot elongation in the species is partially under additive genetic control and could be useful to select for early height in breeding programs.

Stand density of co‐existing species regulates above‐ground biomass along a local‐scale elevational gradient in tropical forests

AbstractQuestions(1) Do stand density, species diversity and individual tree size variation jointly increase above‐ground biomass (AGB) along an elevational gradient? (2) How does the local‐scale elevational gradient explain the variation in AGB directly and indirectly via stand density, species diversity facet and individual tree size variation? (3) What are the main ecological mechanisms explaining variation in AGB through joint effects of stand density, species diversity and individual tree size variation along an elevational gradient in tropical forests? We hypothesized that higher stand packing, and diverse and complex stand structure drive higher AGB along a local‐scale elevational gradient in tropical forests.LocationWestern Nepal.MethodsWe analyzed biophysical tree data from 101 tropical forest plots along an elevational gradient ranging from 218 to 1,850 m above sea level. Structural equation models were applied to test the relationships among elevation, stand density, species diversity facet (either species richness, evenness, Shannon diversity or Simpson’s dominance), tree diameter and height variation, and AGB.ResultsStand density increased but species diversity declined AGB, whereas tree diameter and height variation did not strongly influence AGB. The indirect effects of stand density, species diversity facet, and tree diameter and height variation on AGB via each other were non‐significant. Elevation reduced stand density, species richness and AGB but increased tree height variation, and hence, the indirect effects of elevation on AGB were variable. These results suggest that competitive exclusion or selection or environmental filtering effects are shaping the species diversity, structural complexity and AGB of the studied tropical forests.ConclusionsWe argue that compact stand density, rather than diversity and individual tree size variation, of co‐existing species is important for higher AGB but higher species diversity and stand structural complexity may need to be considered in the context of biodiversity conservation and forest management.

Vegetation structure and temporality influence the dominance, diversity, and composition of forest acoustic communities

Bioacoustic methods analyze sounds to monitor wildlife in forests, providing novel perspectives to understand the relationship between forest vegetation structure and wildlife species. Bioacoustic studies differ from traditional field surveys that are often more visual and require work in the daytime. A sampling of acoustic signals is possible to explore the diurnal variation of the forest ecosystem. Normalized difference soundscape index (NDSI), acoustic diversity index (ADI), and power spectral density (PSD) were chosen as acoustic indices to quantify the dominance, diversity, and composition of the biophony of forest settings. Biophony was recorded in ten south subtropical evergreen broad-leaved forest sites in Shenzhen, China. Composition structure (species richness), horizontal structure (vegetation density and canopy cover), and vertical structure (tree height diversity and each layer height) were used to evaluate the structure of vegetation. Linear Mixed Models (LMMs) were applied to examine the effects of different vegetation structures on biophony between day and night. The relationships between various biophonic frequency bands and vegetation structural variables during day and night were estimated by redundancy analysis (RDA). Results showed that different sound frequencies and vocalization behavior of vocalizing species determine the variance between the forest sound environment during day and night. Forest canopy and understory have a significant influence on biophonic diversity and dominance separately. The vocalizing species' preferences for different habitats were affected by the same vegetation structure variables across diurnal variation. Canopy cover and understory species richness had a significant positive effect on low-frequency biophony, and tree height diversity was found to have a significant positive impact on high-frequency biophony. Finally, tree height diversity was the core variable in the forest acoustic environment, and higher tree height diversity resulted in a more dominant and diverse biophony. This study shows the potential of bioacoustic methods to reveal the day-night dynamics of vocalizing species, using easily measured acoustic variables that can help with the timely evaluation of potential impacts of vegetation structure on forest animal communities.

The mediatory roles of species diversity and tree height diversity: Linking the impact of land‐use intensity to soil erosion

AbstractLand‐use intensification has increased soil erosion through biodiversity loss, which affects ecosystem properties and services owing to changes in species compositional and structural diversity. However, information is limited on how land‐use intensity (LUI) affects soil erosion through species compositional diversity, structural diversity and ecosystem properties. In this study we monitored soil erosion in 15 plots over 12 consecutive months on tropical Hainan Island, where land‐use changes and biodiversity loss have been severe. We quantified the direct and indirect effects of LUI, species compositional diversity (plant species diversity and evenness) and structural diversity (tree diameter and height diversity), and ecosystem properties on soil erosion using Bayesian structural equation models (BSEM). The optimal BSEM accounted for 69% of the variation in soil erosion. The LUI did not affect soil erosion directly but showed indirect impacts via species diversity, tree height diversity, and ecosystem properties. Both high species diversity and tree height diversity reduced soil erosion directly and indirectly by promoting root length density (an ecosystem property), but tree height diversity mediated the more important indirect effect of LUI on soil erosion than species diversity and ecosystem properties. We provide evidence for loss of species diversity and tree height diversity as a result of LUI leading to aggravated soil erosion, but the impact of the latter was more serious. Therefore, we emphasize that maintenance of tree height diversity through management practices may be an effective approach to control soil erosion in the context of drastic land‐use changes in tropical areas.

The conversion into high forest of Turkey oak coppice stands: methods, silviculture and perspectives

The goal of this study is to assess the impact of different thinning approaches for coppice conversion into high forest of Turkey oak stands in Italy. The stand structure and the tree/shrub diversity were analyzed in 27 long-term monitoring plots from 7 experimental trials in the Colline Metallifere district (Tuscany, Central Italy) to verify the consistency of the original cultivation goals with the current stand structures. Three different approaches were applied from 1969 onwards: thinning from below, selective thinning, and no-management. Three indexes of specific diversity (Specific Richness, Shannon index and Importance Value) and two indexes of vertical diversity (Vertical Evenness and Coefficient of variation of tree height) were used to analyze and compare the outcome of management practices. The results showed a significantly higher dimensional variability and basal area, and a more complex vertical diversity in control plots and in the plots subject to selective thinning, as compared with plots subject to thinning from below. Tree species richness was high in all plots, independently of the thinning type applied. Based on our results, we suggest Turkey oak-dominated transitory stands to be initially managed by thinning from below, which is easy to be implemented and economically feasible. Selective thinning may be applied later with the aim of promoting sporadic but valuable tree species and increasing tree species diversity.

The legacy of climate variability over the last century on populations' phenotypic variation in tree height

Phenotypic plasticity and local adaptation are the two main processes underlying trait variability. Under rapid environmental change, phenotypic plasticity, if adaptive, could increase the odds for organisms to persist. However, little is known on how environmental variation has shaped plasticity across species ranges over time. Here, we assess whether the portion of phenotypic variation of tree populations linked to the environment is related to the inter-annual climate variability of the last century and how it varies among populations across species ranges and age. To this aim, we used 372,647 individual tree height measurements of three pine species found in low elevation forests in Europe: Pinus nigra Arnold, P. pinaster Aiton and P. pinea L. Measurements were taken in a network of 38 common gardens established in Europe and North Africa with 315 populations covering the distribution range of the species. We fitted linear mixed-effect models of tree height as a function of age, population, climate and competition effects. Models allowed us to estimate tree height response curves at the population level and indexes of populations' phenotypic variation, as a proxy of phenotypic plasticity, at 4, 8 and 16 years old, and relate these indexes to the inter-annual climate variability of the last century. We found that phenotypic variation in tree height was higher in young trees than in older ones. We also found that P. pinea showed the highest phenotypic variation in tree height compared with P. pinaster and P. nigra. Finally, phenotypic variation in tree height may be partly adaptive, and differently across species, as climate variability during the last century at the origin of the populations explained between 51 and 69% of the current phenotypic variation of P. nigra and P. pinea, almost twice of the levels of P. pinaster. Main conclusionsPopulations' phenotypic variation in tree height is largely explained by the climate variability that the populations experienced during the last century, which we attribute to the genetic diversity among populations.