Countryside biogeography of neotropical herbaceous and shrubby plants

摘要

As human impacts on the environment intensify, the future of plant and animal biodiversity will depend increasingly on the floras surviving in human-dominated "countryside" habitats. To begin to characterize these floras for the Neotropics, we investigated the richness and composition of herbaceous and shrubby plant communities in six forested and deforested habitats, in three replicated study areas (7.5-km in diameter), of southern Costa Rica. We chose habitat types that are common throughout the tropics, to begin building a general understanding of both the habitats of origin and the diversity of countryside floras. Focal forest habitats were understory, 1- to 2-year-old tree-fall gaps, and riverbanks, all in primary forest. Focal deforested habitats were ungrazed road verges, grazed pasture, and riverbanks in grazed pasture. Non-riverbank habitats were sampled both near and far from. forest edge. In total, we sampled 772 species from 79 families, similar to 40% of the non-tree plant diversity of the region. Only 6% of identified species are known to be exotic. In each study area, understory and pasture plots were consistently species poor, while tree-fall gaps and road verges near forest were consistently the most species-rich habitats. In each study area, we found the same proportion of species restricted to forested habitats (similar to 45%) and deforested habitats (similar to 37%), and the same proportion of "countryside-habitat generalists" ( similar to 18%) occurring in both forested and deforested habitats. However, different forested habitats supported different proportions of country side-habitat generalists in each study area, although understory plots consistently 'supported the fewest generalists. Among forested habitats, riverbanks were the most similar floristically to deforested habitats. Pasture riverbanks and road verges near forest supported plant communities most similar to those in forested habitats. The uniqueness and richness of each habitat suggests that countrysides with diverse land uses can support many native herbaceous and shrubby plant species. As it becomes increasingly difficult to protect large tracts of undisturbed tropical forest, we suggest that conservation goals expand to encompass maintenance of heterogeneity in countryside landscapes.