Abstract
BackgroundAbandoned human-modified forests are refuges for remnant biodiversity. However, there are very few studies on the biodiversity and regeneration of native species in human-modified forests which are rich in exotic trees. Our research aim is to evaluate the regeneration status and biodiversity of two adjacent human-modified forests. The two forests have distinct overstorey exotic species richness prior to abandonment: one is an exotic tree plantation low in species richness, and the other is an exotic arboretum high in species richness. The original management practices of the two forests have been neglected for more than 20 years. A primary forest was selected as a reference forest to compare their diversity and regeneration status. We asked: (1) Is there a structural difference among the three forests? (2) What are the proportions of native saplings in the human-modified forests? (3) Are the introduced exotic species able to naturalize?ResultsWe recorded 1316 individuals from 88 species, belonging to 69 genera and 34 families in the three forests [each sampled 16 quadrats (10 m × 5 m)]. Both human-modified forests were similar in their height structure, diameter structure, and sapling density, but differed in species diversity (characterized by rarefaction curves) and floristic composition (indicated by a quantitative similarity index). In the arboretum, only 50% of the sapling individuals were native. Surprisingly, when sampling efforts were standardized, the arboretum had higher native sapling species richness than the exotic species-poor plantation. Moreover, both human-modified forests had conserved a few rare and endemic species. Nevertheless, some exotic species in the arboretum had escaped to the nearby plantation.ConclusionsAfter 20 years of abandonment, the two human-modified forests had converged in structure, but not in diversity patterns of native saplings. This could be due to that the diversity of exotic overstorey composition can influence the natural regeneration of understorey plants. Our study also raised concerns about conserving native species and managing naturalized exotic species in these human-modified forests.
Highlights
Abandoned human-modified forests are refuges for remnant biodiversity
Do native species have a chance to come inside a forest rich in exotic species when available habitats might have been occupied by those non-native ones? the tens-rule of introduced species predicted that 10% of the introduced species would be a casual alien, 1% of the introduced species would be naturalized, and 0.1% of the introduced species would become invasive (Williamson et al 1986; Richardson and Pyšek 2006)
The results demonstrated the potential for Shuanghsi Tropical Botanical Garden (STBG) to harbor more native species than Yellow Butterfly Valley (YBV)
Summary
There are very few studies on the biodiversity and regeneration of native species in human-modified forests which are rich in exotic trees. Conserving tropical biodiversity cannot neglect the ecological impacts of human-modified forests (Chazdon et al 2009), due to its ever-increasing areas (Turner and Corlett 1996). Not many have monitored human-modified forests rich in exotic tree diversity (Bhagwat et al 2008). It is not clear how the initial overstorey exotic composition may alter the forest regeneration trajectory. A plantation rich in exotic species has some potential to introduce invasive species when human management practices are absent
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