Effects Of Tree Diversity Research Articles

Carabid activity‐density increases with forest vegetation diversity at different spatial scales

Abstract More diverse forests are generally more resistant to insect herbivores. This might be due to positive effects of tree diversity on predation. Although the enemies hypothesis has received conflicting evidence in forest ecosystems. Carabids were sampled by pitfall trapping in a tree diversity experiment, at the centre of plots ranging from one to five tree species mixtures. The composition and vertical structure of the vegetation was assessed at three scales, in the understorey, in the canopy of the experimental plots, and in the surrounding area of each plot. None of the tested vegetation variables had an effect on the species richness of carabids. In contrast, the vegetation compositional diversity at the understorey, canopy and surrounding scales had additive and positive effects on the activity‐density of the carabids. Our findings indicate that more diverse forests can host a higher activity‐density of predatory carabids, as a result of the combined effect of horizontal and vertical vegetation diversity, which might increase both habitat quality and the amount of feeding resources. This highlights the relevance of manipulative tree diversity experiments to identify the ecological filters shaping local carabid communities.

Modeling tree diversity, stand structure and productivity of northern temperate coniferous forests of Mexico.

There is increasing evidence complex forest structure and tree diversity correlates positively with the productivity of forest ecosystems. However, there is little quantitative information regarding the effect of these factors on stand productivity of northern temperate coniferous forests of Mexico. This study aimed to test the hypothesis tree diversity and canopy structure positively associates with forest productivity. Parameterization of tree diversity, stand structure and productivity were carried out on dasometric data from 36 permanent sampling plots re-measured in 1982, 1993, and 2004. Statistical analysis of stand parameters tested the null hypothesis. Statistical relationships revealed well-balanced canopy strata and imbalanced diameter structures positively correlated with stand productivity. Tree diversity was also positively linked with stand productivity, but the effect appeared to be most important in the early to intermediate stages of succession. Further research is required to understand the long-term effects of tree diversity and canopy structure on stand productivity. These preliminary observations stress the importance of prescribing silvicultural practices that maintain the three-dimensional structure of stands and diversity of forest canopies that aim to preserve ecosystem function, diversity, and productivity.

The effect of tree diversity on the resistance and recovery of forest stands in the French Alps may depend on species differences in hydraulic features

As climate change should lead to an increase in the vulnerability and the sensitivity of forests to extreme climatic events, quantifying and predicting their response to more severe droughts remains a key task for foresters. Furthermore, recent works have suggested that tree diversity may affect forest ecosystem functioning, including their response to extreme events. In this study we aimed at testing whether the growth response of forest stands to stressful climatic events varied between mixed and monospecific stands, under various environmental conditions. We focused on beech-fir forests (Fagus sylvatica [L.] and Abies alba [L.]) and beech-oak forests (F. sylvatica [L.] and Quercus pubescent [L.]) in the French Alps. We used a dendrochronological dataset sampled in forest plots organized by triplets (one mixture and two monospecific stands) distributed in six sites along a latitudinal gradient. We tested (1) whether stand diversity (two-species stands vs monospecific stands) modulates the stands’ response to drought events in terms of productivity, (2) whether species identity may drive the diversity effect on resistance and recovery, and (3) whether this can be explained by interspecific interactions. We found that (1) interspecific differences in response to extreme drought events (possibly due to interspecific differences in hydraulic characteristics) can induce a mixture effect on stand growth, although it appeared (2) to be strongly depending on species identity (positive effect only found for beech-fir mixed stands), while (3) there were no significant non-additive effects of diversity on stand resistance and recovery, except for some specific cases. Overall, our study shows that promoting selected mixed stands management may buffer extreme drought effect on stand productivity.

Light interception in experimental forests affected by tree diversity and structural complexity of dominant canopy

Biodiversity affects ecosystem functioning in forests by, for example, enhancing growth and altering the forest structure towards greater complexity with cascading effects on other processes and trophic levels. Complexity in forest canopy could enhance light interception and form a link between diversity and productivity in polyculture forests, but the effect of canopy structure on light interception is rarely directly measured.We modelled the canopy surface structure of a tree diversity experiment by photographing it using unmanned aerial vehicle (UAV) and combining the photos into a digital elevation model with photogrammetry tools. We analysed the effects of tree diversity and functional diversity on canopy structural complexity and light interception with a structural equation model.Our results show that: a) increased structural complexity of the canopy reduces light interception, whereas b) tree diversity increases the structural complexity of the canopy, and has a dual impact on light interception. Tree diversity decreased light interception through the structural complexity of the canopy but increased it probably through canopy packing and crown complementarity. However, the effects of both tree diversity and structural complexity of canopy were smaller than the effect of the functional identities of the tree species, especially the differences between deciduous and evergreen trees.We conclude that more complexity in canopy structure can be gained through increased tree diversity, but complex canopy structure does not increase light interception in young forests.

Forest edges, tree diversity and tree identity change leaf miner diversity in a temperate forest

Abstract In forests, besides tree diversity, tree identity can determine herbivore species diversity. Herbivore species diversity can also depend on spatial factors, such as edge effects; however, empirical evidence for this remains scarce. Furthermore, patterns in herbivore diversity may differ between forest stand level and responses at individual tree species. It is therefore important to disentangle stand‐level patterns from associational responses specific to certain host species. We studied the effects of edge distance, tree diversity and tree species composition on leaf miner abundance, richness and diversity in temperate forests. We disentangled leaf miners’ responses at stand level from those of miners associated with each of three individual tree species: Quercus robur L., Quercus rubra L. and Fagus sylvatica L. We found that tree diversity increased stand‐level leaf miner richness and diversity. Fagus sylvatica and stand‐level leaf miner abundance increased closer to edges. This was suppressed at stand level in more diverse mixtures. Underlying tree diversity effects, stand‐level leaf miner metrics are strongly associated with tree species composition, due to many unique species found on F. sylvatica and Q. robur. Additionally, F. sylvatica experienced associational susceptibility to abundance in mixtures with Q. robur. Quercus robur experienced association susceptibility to miner richness in the mixture with Q. rubra. Studying the herbivore community at different spatial scales is a first step towards better understanding tree identity effects underlying tree diversity effects. Our findings emphasise context dependency of positive diversity effects on herbivores in terms of edge effects and tree species composition.

Early positive effects of tree species richness on soil organic carbon accumulation in a large-scale forest biodiversity experiment

Abstract Aims Tree species richness has been reported to have positive effects on aboveground biomass and productivity, but little is known about its effects on soil organic carbon (SOC) accumulation. Methods To close this gap, we made use of a large biodiversity–ecosystem functioning experiment in subtropical China (BEF-China) and tested whether tree species richness enhanced SOC accumulation. In 2010 and 2015, vertically layered soil samples were taken to a depth of 30 cm from 57 plots ranging in tree species richness from one to eight species. Least squares-based linear models and analysis of variance were used to investigate tree diversity effects. Structural equation modeling was used to explore hypothesized indirect relationships between tree species richness, leaf-litter biomass, leaf-litter carbon content, fine-root biomass and SOC accumulation. Important Findings Overall, SOC content decreased by 5.7 and 1.1 g C kg−1 in the top 0–5 and 5–10 cm soil depth, respectively, but increased by 1.0 and 1.5 g C kg−1 in the deeper 10–20 and 20–30 cm soil depth, respectively. Converting SOC content to SOC stocks using measures of soil bulk density showed that tree species richness did enhance SOC accumulation in the different soil depths. These effects could only to some extent be explained by leaf-litter biomass and not by fine-root biomass. Our findings suggest that carbon storage in new forests in China could be increased by planting more diverse stands, with the potential to contribute to mitigation of climate warming.

Forest Fragmentation Modulates Effects of Tree Species Richness and Composition on Ecosystem Multifunctionality

In this synthesis paper, we aimed at analyzing the influence of habitat fragmentation, tree species richness, and tree composition on multiple forest ecosystem functions. The data were gathered in 53 plots situated in mature forest with no recent management activities and composed of every potential combination of common beech (Fagus sylvatica), pedunculate oak (Quercus robur), and red oak (Quercus rubra). We found a wide range of response to fragmentation, tree richness, and tree composition between the measured functions. Aggregating these functional responses revealed that tree diversity effects were stronger in smaller and more isolated fragments than in larger and well-connected ones. Photo credit: Irene M. van Schrojenstein Lantman. These photographs illustrate the article “Forest fragmentation modulates effects of tree species richness and composition on ecosystem multifunctionality” by Lionel R. Hertzog, Roschong Boonyarittichaikij, Daan Dekeukeleire, Stefanie R. E. de Groote, Irene M. van Schrojenstein Lantman, Bram K. Sercu, Hannah Keely Smith, Eduardo de la Peña, Martijn L. Vandegehuchte, Dries Bonte, An Martel, Kris Verheyen, Luc Lens, and Lander Baeten published in Ecology. https://doi.org/10.1002/ecy.2653

Forest fragmentation and tree species composition jointly shape breeding performance of two avian insectivores

Habitat fragmentation and forestry practices affect forest structure and composition, and hence, their intrinsic value for biodiversity conservation. While higher tree species diversity is commonly proposed to result in habitat of higher quality for forest species, how these tree diversity and tree composition effects interact with forest fragmentation in terms of critical resources and demographic effects on forest birds remains poorly understood. We investigated here possible synergistic effects of forest fragmentation and tree species composition on the breeding performance of two common, insectivorous forest birds in a human-dominated landscape in northern Belgium. We monitored the breeding performance of Great Tits and Blue Tits in 53 plots across independent gradients of tree species composition and forest fragmentation. In addition, data on the biomass of the main food source of these two species (i.e. caterpillars) was collected during the breeding season. Both tree composition and habitat fragmentation impacted the breeding performance of Great and Blue Tits. Effects of tree species composition were mainly driven by tree species identity, rather than by tree species diversity, and the highest breeding performance was obtained in monocultures of Pedunculate Oaks. Fragmentation effects were only observed in resource-poor Beech monocultures with breeding performance declining with reduction in forest area. Structural Equation Modelling revealed diverse and species-specific pathways: for Great Tits tree composition effects on breeding performance were driven by resource availability while for Blue Tits these effects were driven by variation in clutch size. Thus, forestry practices aiming at promoting forest-dependent birds could benefit from including tree species that support high arthropod numbers and by maintaining forest patches of larger sizes.

Understanding the controls over forest carbon use efficiency on small spatial scales: Effects of forest disturbance and tree diversity

Tropical forests are characterized by their high photosynthetic activity. Results from pantropical studies show that on average only 30% of the products from photosynthesis are allocated to new biomass compared to on average 50% in temperate forest systems. Why those forests have a low carbon use efficiency (CUE) remains unknown. We present a synthesis of studies from two tropical sites with a similar methodological setup allowing the evaluation of the ecophysiological responses of tree communities to diversity effects and forest disturbance. Here we use xylem sap flux derived gross primary productivity (GPP) that was modeled with eddy covariance data for a seven-year-old planted forest with plots of varying tree species diversity in Panama and an old-growth forest with a distinct disturbance gradient in an Amazonian moist lowland forest. Additionally, net primary productivity (NPP) was calculated from inventory data. We found evidence that GPP is relatively stable with forest disturbance but GPP increases with tree species richness. Lowest CUE with only 35% of GPP allocated to growth was present in undisturbed forest patches. Light forest disturbance had a positive effect on CUE and 62% of GPP was allocated to grow new biomass. Monospecific stands had a higher CUE than diverse tree stands. We conclude that two factors are controlling CUE in tropical forests leading to low CUE. First, forest disturbance leads to a higher allocation of carbon towards growth. Second, a great fraction of GPP is used for processes dedicated to species complementarity. This improves the overall performance of diverse forest stands compared to monocultures.

Regulating Ecosystem Services and Green Infrastructure: assessment of Urban Heat Island effect mitigation in the municipality of Rome, Italy

The Urban Heat Island (UHI) effect is one of the main environmental impacts of urbanization, affecting directly human health and well-being of the city dwellers, and also contributing to worsen environmental quality. As a key strategy to address sustainable urban development, the EU has advocated the development of Nature-Based solutions, such as the implementation of Green Infrastructure (GI), which can deliver a wide range of Regulating Ecosystem Services (ES). In this article, the ES of climate regulation provided by GI has been analyzed in the Municipality of Rome, Italy, characterized by a complex territory and by a Mediterranean climate. The methodological approach allowed to characterize the UHI and to analyze its features in a spatially explicit way and on a seasonal basis, through the Land Surface Temperature (LST) derived from Landsat-8 data. The cooling capacity of different GI elements (peri-urban forest, urban forest, street trees), as well as the effect of vegetation cover and tree diversity on the provision of this regulating ES were assessed. The results show that GI significantly mitigates the hot urban climate during summer, with an effect that is dependent on the GI element and the environmental constrains to which it is exposed. NDVI and tree cover resulted the main indicators of the provision of the ES of climate regulation, highlighting that GI elements such as urban and peri-urban forests have the highest potential to provide this ES in a Mediterranean city. In the context of the Mapping and Assessment of Ecosystems and their Services (MAES) process, our results lend support to claims that GI is important for an ecosystem-based climate adaptation strategy in urban environments, contributing to the definition of knowledge based criteria and indicators, relevant for decision-making in Mediterranean cities.

Tree diversity effects on leaf insect damage on pedunculate oak: The role of landscape context and forest stratum

Tree diversity has long been recognized as a major driver of insect herbivory in forest ecosystems. However, predicting the strength and direction of tree diversity effects in real-world situations has proven elusive. One likely reason is that most studies have focused on within-stand dynamics and insufficiently captured other ecological drivers of insect herbivory that can act at broader (i.e., landscape) and finer (i.e., individual trees) scales. We measured herbivory as leaf area consumed by insect herbivores in pedunculate oaks (Quercus robur) growing in mixed and pure forest stands in southwestern France. We assessed the effects of oak spatial isolation within the landscape, tree stand diversity, forest canopy stratification as well as the influence of leaf traits on insect herbivory. Insect herbivory increased with stand isolation regardless of tree diversity. Diversity effects were contingent upon the canopy stratum as insect herbivory in mixed stands exceeded that of pure stands only in the upper stratum. Leaf traits varied between pure and mixed stands and among canopy strata. Insect herbivory was negatively correlated with LDMC and positively with SLA. However, the observed effects of tree diversity, canopy stratum and stand isolation on insect herbivory were only partially driven by variability in oak leaf traits. Our findings illustrate that, in real-world contexts, insect herbivory can be driven by a complex interplay of multiple, scale-dependent drivers. They help step forward towards a more profound understanding of the complex forces drive insect herbivory in managed forest ecosystems.

Tropical tree diversity mediates foraging and predatory effects of insectivorous birds.

Biodiversity affects the structure of ecological communities, but little is known about the interactive effects of diversity across multiple trophic levels. We used a large-scale forest diversity experiment to investigate the effects of tropical tree species richness on insectivorous birds, and the subsequent indirect effect on predation rates by birds. Diverse plots (four tree species) had higher bird abundance (61%), phylogenetic diversity (61%), and functional diversity (55%) than predicted based on single-species monocultures, which corresponded to higher attack rates on artificial caterpillars (65%). Tree diversity effects on attack rate were driven by complementarity among tree species, with increases in attack rate observed on all tree species in polycultures. Attack rates on artificial caterpillars were higher in plots with higher bird abundance and diversity, but the indirect effect of tree species richness was mediated by bird diversity, providing evidence that diversity can interact across trophic levels with consequences tied to ecosystem services and function.

Experimental Evidence of Functional Group-Dependent Effects of Tree Diversity on Soil Fungi in Subtropical Forests.

Deconvoluting the relative contributions made by specific biotic and abiotic drivers to soil fungal community compositions facilitates predictions about the functional responses of ecosystems to environmental changes, such as losses of plant diversity, but it is hindered by the complex interactions involved. Experimental assembly of tree species allows separation of the respective effects of plant community composition (biotic components) and soil properties (abiotic components), enabling much greater statistical power than can be achieved in observational studies. We therefore analyzed these contributions by assessing, via pyrotag sequencing of the internal transcribed spacer (ITS2) rDNA region, fungal communities in young subtropical forest plots included in a large experiment on the effects of tree species richness. Spatial variables and soil properties were the main drivers of soil fungal alpha and beta-diversity, implying strong early-stage environmental filtering and dispersal limitation. Tree related variables, such as tree community composition, significantly affected arbuscular mycorrhizal and pathogen fungal community structure, while differences in tree host species and host abundance affected ectomycorrhizal fungal community composition. At this early stage of the experiment, only a limited amount of carbon inputs (rhizodeposits and leaf litter) was being provided to the ecosystem due to the size of the tree saplings, and persisting legacy effects were observed. We thus expect to find increasing tree related effects on fungal community composition as forest development proceeds.

Tree diversity improves forest productivity

Forest Ecology Experimental studies in grasslands have shown that the loss of species has negative consequences for ecosystem functioning. Is the same true for forests? Huang et al. report the first results from a large biodiversity experiment in a subtropical forest in China. The study combines many replicates, realistic tree densities, and large plot sizes with a wide range of species richness levels. After 8 years of the experiment, the findings suggest strong positive effects of tree diversity on forest productivity and carbon accumulation. Thus, changing from monocultures to more mixed forests could benefit both restoration of biodiversity and mitigation of climate change. Science , this issue p. [80][1] [1]: /lookup/doi/10.1126/science.aat6405

Impacts of species richness on productivity in a large-scale subtropical forest experiment.

Biodiversity experiments have shown that species loss reduces ecosystem functioning in grassland. To test whether this result can be extrapolated to forests, the main contributors to terrestrial primary productivity, requires large-scale experiments. We manipulated tree species richness by planting more than 150,000 trees in plots with 1 to 16 species. Simulating multiple extinction scenarios, we found that richness strongly increased stand-level productivity. After 8 years, 16-species mixtures had accumulated over twice the amount of carbon found in average monocultures and similar amounts as those of two commercial monocultures. Species richness effects were strongly associated with functional and phylogenetic diversity. A shrub addition treatment reduced tree productivity, but this reduction was smaller at high shrub species richness. Our results encourage multispecies afforestation strategies to restore biodiversity and mitigate climate change.

Mixed forests to mitigate risk of insect outbreaks

ABSTRACTThe majority of agricultural and forest production systems are typically simplified systems and therefore thought to be sensitive to disturbance. Ecosystems might be less sensitive to disturbance if complexity increases. The resource concentration hypothesis predicts that complexity makes it more difficult for herbivores to find and exploit their food. The natural enemy hypothesis predicts less damage in diverse environments because enemy abundance and diversity remain higher and more stable in environments providing more alternative food sources. We explore the effect of tree diversity in two types of pine stands differing in tree diversity. We ask whether European pine sawfly (Neodiprion sertifer) larval group distribution and larval mortality, imposed by specialist natural enemies, is affected by tree diversity. We find fewer larval groups on pine trees surrounded by non-host trees, indicating that fewer egg-batches were laid. Mortality rates by specialist enemies are not affected by tree diversity but parasitism rates are likely to be higher in larger trees. Herbivores are inhibited by increased tree diversity and density, whereas natural enemies seem to be unaffected, partly increasing the resistance of more diverse forest stands against insect damage. Thus, managing for more mixed forests could mitigate risk of herbivore damage.

A high-resolution approach for the spatiotemporal analysis of forest canopy space using terrestrial laser scanning data.

Forest canopies and tree crown structures are of high ecological importance. Measuring canopies and crowns by direct inventory methods is time‐consuming and of limited accuracy. High‐resolution inventory tools, in particular terrestrial laser scanning (TLS), is able to overcome these limitations and obtain three‐dimensional (3D) structural information about the canopy with a very high level of detail. The main objective of this study was to introduce a novel method to analyze spatiotemporal dynamics in canopy occupancy at the individual tree and local neighborhood level using high‐resolution 3D TLS data. For the analyses, a voxel grid approach was applied. The tree crowns were modeled through the combination of two approaches: the encasement of all crown points with a 3D α‐shape, which was then converted into a voxel grid, and the direct voxelization of the crown points. We show that canopy occupancy at individual tree level can be quantified as the crown volume occupied only by the respective tree or shared with neighboring trees. At the local neighborhood level, our method enables the precise determination of the extent of canopy space filling, the identification of tree–tree interactions, and the analysis of complementary space use. Using multitemporal TLS data recordings, this method allows the precise detection and quantification of changes in canopy occupancy through time. The method is applicable to a wide range of investigations in forest ecology research, including the study of tree diversity effects on forest productivity or growing space analyses for optimal tree growth. Due to the high accuracy of this novel method, it facilitates the precise analyses even of highly plastic individual tree crowns and, thus, the realistic representation of forest canopies. Moreover, our voxel grid framework is flexible enough to allow for the inclusion of further biotic and abiotic variables relevant to complex analyses of forest canopy dynamics.

Evapotranspiration and favorable growing degree-days are key to tree height growth and ecosystem functioning: Meta-analyses of Pacific Northwest historical data

While temperature and precipitation comprise important ecological filtering for native ranges of forest trees and are predisposing factors underlying forest ecosystem dynamics, the extent and severity of drought raises reasonable concerns for carbon storage and species diversity. Based on historical data from common garden experiments across the Pacific Northwest region, we developed non-linear niche models for height-growth trajectories of conifer trees at the sapling stage using annual or seasonal climatic variables. The correlations between virtual tree height for each locality and ecosystem functions were respectively assessed. Best-fitted models were composed of two distinct components: evapotranspiration and the degree-days disparity for temperature regimes between 5 °C and 18 °C (effective temperature sum and growth temperature, respectively). Tree height prediction for adaptive generalists (e.g., Pinus monticola, Thuja plicata) had smaller residuals than for specialists (e.g., Pinus contorta, Pseudotsuga menziesii), albeit a potential confounding factor – tree age. Discernably, there were linearly positive patterns between tree height growth and ecosystem functions (productivity, biomass and species diversity). Additionally, there was a minor effect of tree diversity on height growth in coniferous forests. This study uncovers the implication of key ecological filtering and increases our integrated understanding of how environmental cues affect tree stand growth, species dominance and ecosystem functions.

Leaf herbivory is more impacted by forest composition than by tree diversity or edge effects

Links between biodiversity and ecosystem functioning are well established. Beyond biodiversity per se, community composition can have strong effects on ecosystem functioning. Furthermore, spatial processes including edge effects, can impact the diversity-functioning relationship. These spatial processes are especially relevant within a food web context, such as the transfer of plant biomass across the food chain through herbivory. The relative importance of diversity, community composition and spatial context on herbivory pressure at the community and the species level is, however, poorly understood.To fill this gap in our understanding, we studied to what degree herbivory in temperate forest plots varies according to edge distance, tree diversity and forest composition. In contrast to the prevailing view of tree herbivory increasing at forest edges, we found that the effects of forest edge and tree diversity on leaf herbivory were masked by effects of forest composition, i.e. the specific contributions of the tree species. The strongest composition effect found was increased herbivory on Quercus robur in the presence of Fagus sylvatica.Our findings highlight that neither edge distance, tree diversity, nor the interaction affected one ecosystem function, namely herbivory, whilst tree community composition did. This warrants consideration of identity and composition effects in future studies if we are to deepen our understanding of the determinants of ecosystem functions across systems.

Linking forest diversity and tree health: preliminary insights from a large-scale survey in Italy

Forest health is currently assessed in Europe (ICP Forests monitoring program). Crown defoliation and dieback, tree mortality, and pathogenic damage are the main aspects considered in tree health assessment. The worsening of environmental conditions (i.e., increase of temperature and drought events) may cause large-spatial scale tree mortality and forest decline. However, the role of stand features, including tree species assemblage and diversity as factors that modify environmental impacts, is poorly considered. The present contribution reanalyses the historical dataset of crown conditions in Italian forests from 1997 to 2014 to identify ecological and structural factors that influence tree crown defoliation, highlighting in a special manner the role of tree diversity. The effects of tree diversity were explored using the entire data set through multivariate cluster analyses and on individual trees, analysing the influence of the neighbouring tree diversity and identity at the local (neighbour) level. Preliminary results suggest that each tree species shows a specific behaviour in relation to crown defoliation, and the distribution of crown defoliation across Italian forests reflects the distribution of the main forest types and their ecological equilibrium with the environment. The potentiality and the problems connected to the possible extension of this analysis at a more general level (European and North American) were discussed.