Abstract
AbstractQuestionLand‐use change and intensification are currently the most pervasive threats to tropical biodiversity. Yet, their effects on biodiversity change with elevation are unknown. Here, we examine how tree diversity and community composition vary with elevation and how the effects of forest use intensity on tree diversity and community composition change within elevations.LocationEastern slopes of the Cofre de Perote mountain, state of Veracruz, Mexico.MethodsWe assessed tree diversity and composition using a sampling design in which elevation was crossed with three levels of forest use intensity: old‐growth, degraded, and secondary forests. We established 120 20 m × 20 m forest plots, located at eight sites between 0 m and 3,545 m. At each site, five replicate plots were inventoried for each level of forest use intensity.ResultsOur analyses revealed an interactive effect between elevation and forest use intensity affecting tree diversity and community composition along the elevational gradient. Contrasting effects of forest use intensity within elevation resulted in tree diversity following a low‐plateau pattern for old‐growth and a bimodal pattern for degraded and secondary forests. Along the entire elevational gradient, there were 217 tree species distributed within 154 genera and 80 families. Species accumulation curves revealed that forests at 0 m and 1,500 m elevation showed differences in species richness among forest use intensities. In contrast, species richness did not differ between old‐growth forest and the other forest use intensities in five of the eight studied elevations. In terms of community composition, secondary forests differed from old‐growth and degraded forests.ConclusionOur results suggest that the interactive effects of elevation and forest use intensity change tree diversity patterns and community composition along a tropical elevational gradient. Degraded forests were similar to old‐growth forests in terms of species diversity and composition, suggesting that they may act as a safeguard of tree diversity in human‐dominated tropical landscapes.
Highlights
Tropical mountains are characterized by steep gradients in climate and other environmental conditions that lead to rapid changes in diversity and species composition with elevation
We asked: (a) how do tree diversity and community composition vary with elevation;and (b) how do the effects of forest use intensity on tree diversity and community composition change within elevational sites? We hypothesized that tree diversity monotonically decreases with increasing elevation (Aiba & Kitayama, 1999; Homeier et al, 2010; Slik et al, 2019; Toledo-Garibaldi & Williams-Linera, 2005), that high forest use intensity at lower elevations may shift species richness from monotonic to a hump-shaped pattern (McCain & Grytnes, 2010) and expected a consistently negative effect of forest use intensity on tree diversity and associated shifts in tree species composition (Gibson et al, 2011; Newbold et al, 2015)
We examined the effect of forest use intensity at each elevation on species richness and Shannon and Simpson diversities by a nested analysis of variance (ANOVA) using the R function aov, where forest use intensity and elevation were treated as categorical variables
Summary
Tropical mountains are characterized by steep gradients in climate and other environmental conditions that lead to rapid changes in diversity and species composition with elevation. Floristic composition — and to a lesser extent species richness — of young secondary and degraded forests usually differs markedly from that of old-growth tropical forests (Gossner et al, 2013; Rozendaal et al, 2019) How such changes in species composition are mediated by climatic changes along elevational gradients is largely unknown (but see Peters et al, 2019). We hypothesized that tree diversity monotonically decreases with increasing elevation (Aiba & Kitayama, 1999; Homeier et al, 2010; Slik et al, 2019; Toledo-Garibaldi & Williams-Linera, 2005), that high forest use intensity at lower elevations may shift species richness from monotonic to a hump-shaped pattern (McCain & Grytnes, 2010) and expected a consistently negative effect of forest use intensity on tree diversity and associated shifts in tree species composition (Gibson et al, 2011; Newbold et al, 2015) We asked: (a) how do tree diversity and community composition vary with elevation;and (b) how do the effects of forest use intensity on tree diversity and community composition change within elevational sites? We hypothesized that tree diversity monotonically decreases with increasing elevation (Aiba & Kitayama, 1999; Homeier et al, 2010; Slik et al, 2019; Toledo-Garibaldi & Williams-Linera, 2005), that high forest use intensity at lower elevations may shift species richness from monotonic to a hump-shaped pattern (McCain & Grytnes, 2010) and expected a consistently negative effect of forest use intensity on tree diversity and associated shifts in tree species composition (Gibson et al, 2011; Newbold et al, 2015)
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