Functional response of plant communities to clearcutting: management impacts differ between forest vegetation zones

Functional Diversity Changes after Selective Thinning in a Tropical Mountain Forest in Southern Ecuador

Background: The impact of selective thinning on forest diversity has been extensively studied in temperate and boreal regions. However, in the tropics, knowledge is still poor regarding the impacts of this silvicultural treatment on functional diversity, especially in tropical mountain forests, which are considered to be highly biodiverse ecosystems and also endangered by human activities. By evaluating the changes on functional diversity by using different indicators, hypothesizing that selective thinning significantly affects (directly or indirectly) tropical mountain forests, this work promotes sustainable ecosystem use. Methods: A total of 52 permanent plots of 2500 m2 each were installed in a primary mountain forest in the San Francisco Biological Reserve to assess the impact of this silvicultural treatment. Selective thinning can be defined as a controlled process, in which trees that compete with ecologically and/or valuable timber species are progressively removed to stimulate the development of profitable ones, called potential crop trees (PCT). In doing so, the best specimens remain in the forest stand until their final harvest. After PCT selection, 30 plots were chosen for the intervention, while 22 plots served as control plots. The thinning intensity fluctuated between 4 and 56 trees ha−1 (average 18.8 ± 12.1 stems ha−1). Functional Diversity (FD) indices, including the community weighted mean (CWM), were determined based on six traits using the FD package implemented in R software. The difference between initial and final conditions of functional richness (FRic), functional divergence (FDiv), functional evenness (FEve), functional dispersion (FDis), and Rao quadratic entropy (RaoQ) was modeled using linear mixed models (LMM). As fixed factors, we used all the predictors inherent to structural and ecological forest conditions before and after the selective thinning and as a random variable, we used the membership to nested sampling units. Results: Functional Richness (FRic) showed significant changes after selective thinning, the other indexes (FEve, FDis, FDiv, RaoQ) were only influenced by predictors related to ecological conditions and characteristics of the community.

Integrating multiple sources of ecological data to unveil macroscale species abundance

The pattern of species abundance, represented by the number of individuals per species within an ecological community, is one of the fundamental characteristics of biodiversity. However, despite their obvious significance in ecology and biogeography, there is still no clear understanding of these patterns at large spatial scales. Here, we develop a hierarchical modelling approach to estimate macroscale patterns of species abundance. Using this approach, estimates of absolute abundance of 1248 woody plant species at a 10-km-grid-square resolution over East Asian islands across subtropical to temperate biomes are obtained. We provide two examples of the basic and applied use of the estimated species abundance for (1) inference of macroevolutionary processes underpinning regional biodiversity patterns and (2) quantitative community-wide assessment of a national red list. These results highlight the potential of the elucidation of macroscale species abundance that has thus far been an inaccessible but critical property of biodiversity.

Measurement of species abundance is fundamental in ecology, yet challenging at large spatial scales. Here, the authors show estimates of abundance of 1248 woody plant species over the East Asian islands that highlight macroevolutionary processes of biodiversity and the status of the national red listing.

Understanding the recruitment response of juvenile Neotropical trees to logging intensity using functional traits

Selective logging remains a widespread practice in tropical forests, yet the long-term effects of timber harvest on juvenile tree (i.e., sapling) recruitment across the hundreds of species occurring in most tropical forests remain difficult to predict. This uncertainty could potentially exacerbate threats to some of the thousands of timber-valuable tree species in the Amazon. Our objective was to determine to what extent long-term responses of tree species regeneration in logged forests can be explained by their functional traits. We integrate functional trait data for 13 leaf, stem, and seed traits from 25 canopy tree species with a range of life histories, such as the pioneer Goupia glabra and the shade-tolerant Iryanthera hostmannii, together with over 30 yr of sapling monitoring in permanent plots spanning a gradient of harvest intensity at the Paracou Forest Disturbance Experiment (PFDE), French Guiana. We anticipated that more intensive logging would increase recruitment of pioneer species with higher specific leaf area, lower wood densities, and smaller seeds, due to the removal of canopy trees. We define a recruitment response metric to compare sapling regeneration to timber harvest intensity across species. Although not statistically significant, sapling recruitment decreased with logging intensity for eight of 23 species and these species tended to have large seeds and dense wood. A generalized linear mixed model fit using specific leaf area, seed mass, and twig density data explained about 45% of the variability in sapling dynamics. Effects of specific leaf area outweighed those of seed mass and wood density in explaining recruitment dynamics of the sapling community in response to increasing logging intensity. The most intense treatment at the PFDE, which includes stand thinning of non-timber-valuable adult trees and poison-girdling for competitive release, showed evidence of shifting community composition in sapling regeneration at the 30-yr mark, toward species with less dense wood, lighter seeds, and higher specific leaf area. Our results indicate that high-intensity logging can have lasting effects on stand regeneration dynamics and that functional traits can help simplify general trends of sapling recruitment for highly diverse logged tropical forests.