Deforestation and associated forest fragmentation are main drivers of species loss across the tropics. In the past 30 years, studies in forest fragments focused mostly on impacts of patch size, isolation and edge effects on forest structure, species diversity and composition. Little attention has been paid to the impact of the distribution of the fragments itself on the preservation of local species pools. However, the distribution of the fragments itself will, for a large part, determine the type and diversity of taxa preserved across the landscape.
Dr. LIU Jiajia and his teacher Ferry Slik of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to test the importance of the spatial distribution of remaining forest fragments, relative to other fragmentation effects, on tree species diversity, composition and rarity patterns within a tropical landscape converted to rubber plantations in Xishuangbanna, China.
They hypothesized that rapid expansion of rubber plantations was spatially non-random and would result in remaining forest fragments being located on less accessible, steeper, higher and shady slopes. Due to the relatively recent start of forest fragmentation in the study area compared to the long lifespan of trees and the embedding of the fragments within an ‘artificial’ forest landscape, they hypothesized that tree diversity, rarity and composition patterns in forest fragments would be more related to fragment location than to forest degradation related to fragment size and edge effects.
They found that forest fragments were spatially and environmentally non-randomly distributed. The environment explained most patterns in fragment tree diversity and composition. Fragment edge, size, shape and isolation affected tree maintenance minimally. Fragment location was the main driver of tree species maintenance within landscapes. Small fragments were important as they generally represented over-exploited habitats.
Their results showed that during the initial stages of land use change, the protection of forest areas along the entire environmental gradient should be a prime focus for conservation efforts as it was at the stage that most tree species can be preserved in the landscape. They also stressed that even small forest fragments were critical for tree species conservation, especially as such small fragments were usually located in sites with the highest deforestation rates.