The effects of forest restoration activities on the species diversity of naturally establishing trees and ground flora

The framework species method of forest restoration aims to rapidly re-establish forest ecosystem structure and function. At the same time, it aims to encourage wildlife, attracted to the planted trees, and accelerate recovery of biodiversity through facilitating seed dispersal into planted sites. The objectives of this study were to determine whether forest restoration encourages recruitment of non-planted tree species into planted areas and increases the species diversity or changes the species composition of the ground flora. The study was carried out on degraded, evergreen forest land in Suthep-Pui National Park, northern Thailand. The land had been planted with 30 framework tree species in 1997 and 1988 to compare the relative performance of different framework tree species and develop suitable silvicultural treatments to maximize tree performance. Treatments included fire protection, application of fertilizer, and weeding. Two non-planted control plots were also demarcated, in which only fire protection was implemented. Vegetation surveys were carried out in replicated 10-m diameter plots, recording the presence of ground flora species and naturally established trees (> 1 m tall). They were carried out three times in 1999: in the dry season, in the middle of the rainy season and at the end of rainy season. In the first year after planting, the species richness and evenness of
the ground flora in the plot planted in 1998 increased, compared with the plot planted in 1997. This was probably due to the effects of weeding, which removed dominant perennial herbs, allowing invasion, in the 1998 planted plots, by annual herbs, especially those of the Compositae family. However, two years after tree planting, the diversity of the ground flora decreased in the 1997 planted plot. This was probably due to shade caused by closing of the forest canopy, which reduced opportunities for establishment of new ground flora species. Evenness was also lesser here as compared to the 1997 control plot since fire removed most of the dominant weed species. Weeding and fertilizer accelerated establishment of natural seedlings and further increased the tree density of naturally established trees (wildings) in the planted plots. Most of planted tree species were in good health and fast-growing. All of the planted tree species, except Nyssa javanica and Garcinia meckeaniana, were found suitable for forest restoration.