Tropical rainforest fragmentation affects plant species richness, composition and abundance depending on plant-size class and life history

Abstract

Background: Tropical rain forests have been impacted by land use change, leading to major deforestation and fragmentation. Understanding how fragmentation impacts plant communities is central for tropical conservation. Questions: i) How does species richness vary across a range of fragment sizes, and does it vary with plant size-structure? ii) how are species composition and floristic similarity affected by forest fragmentation? iii) does habitat fragmentation affect the representation of species with different life-history and regeneration patterns? Studied species: We sampled overall plant communities and calculated diversity metrics of mature-forest and light-demanding species, considering plants of different size-categories (defined by diameter at breast height, DBH). Study site: This study was carried out at Los Tuxtlas, Veracruz, Mexico. An area originally dominated extensive evergreen tropical forest, but currently highly fragmented Methods: We sampled plants in five forest fragments representing (2 - 36 ha), and a large patch of continuous forest (700 ha). Within each site we established ten-50 × 2 m transects and registered all woody plants with DBH > 1 cm. Results: Species richness declined as fragment size became smaller. Such decline was significant considering all plants (DBH > 1.0 cm) but became non-significant as plant size-category increased (DBH > 2.5, or > 10 cm.). Small fragments had distinguishable assemblages compared to continuous forest and also a reduction in the representation of mature-forest species compared to light-demanding species. Conclusions: Our findings confirm that fragmentation affects tropical plant species diversity, but the effect is differential, depending on plant size-category and life history.