Response of tree diversity and community composition to forest use intensity along a tropical elevational gradient


Question: Land-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.
Location: Eastern slopes of the Cofre de Perote mountain, state of Veracruz, Mexico.
Methods: We 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.
Results: Our 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.
Conclusion: Our 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.

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