In Laos, there are extensive shifting cultivation areas and regrowth forests spontaneously established on fallow lands. The aims of the study were to conduct a comparative study of old-growth and regrowth forests in terms of structure, woody species diversity and composition as well as to investigate the potential role of regrowth forests in the conservation and restoration of degraded forest lands in Laos and the tropics in general. Systematic plot sampling was used to survey the floristic diversity, species composition and structure of oldgrowth and regrowth forests. Concentric circular plots with an area of 200 m 2 and 500 m 2 were laid on line transects. A total of 24 plots were sampled from two sites. In comparison to regrowth forests, old-growth forests had higher structural heterogeneity because of higher canopy height variations, vertical stratification, and tree sizes and their variations. Species richness and diversity indices values were similar, but abundance and species composition were significantly different between old-growth and regrowth forests. It appears that species richness recovers first followed by forest structure and species composition. Regrowth forests are important for in situ conservation of tropical biodiversity and they can also serve as a conduit for the restoration of degraded lands and forests. Regrowth forests provide habitats, serve as buffer zones around the fragmented old-growth forests, function as source of propagules, and enhance landscape connectivity. Utilization of regrowth forests for restoration purposes is comparatively inexpensive. Regrowth forests should be given the due considerations in the national forest conservation and restoration policy of Laos.
Abstract:The rehabilitation of exhausted quarries through nurse plants-led afforestation is widespread and growing in importance in many parts of the Tropics. The long-term recovery of native plant species and soil organic properties under the approach has, however, not well understood. The number of studies so far to examine soil and vegetation change in restored quarries have been mostly constrained to land mined of coal or bauxite, and post-restoration treatment time not more than 25 years. This short timeframe can only capture the colonization span of pioneer species and not those of intermediate and late successional trees and shrubs. The purpose of the study is to determine how three commonly utilized nurse-tree species (Albizia lebbek, Casuarina equisetifolia and Eucalyptus camadulensis) associate with late succession native species, estimate aboveground biomass accumulation under their respective stands, and to examine soil organic properties development under their pure plantations. The study will be conducted in limestone mining areas of coastal Kenya where quarry rehabilitation has been on-going for a continuous period of 46 years. The split plot design will be used to demarcate study plots in the area according to nurse-tree used and age of restoration planting. One month after the bimodal rainfall seasons (July 2016 & January 2017) in Kenya, independent field samplings will be conducted to determine native species richness and relative abundance in each plot type. A different set of field studies will be carried out in to investigate how the diversity of native plant communities, the soil seed bank and organic matters change with time since restoration treatment (5 -45 yrs) under the different nurse-tree species. Soil seed bank determination will be carried out through glasshouse seedling germination method and tetrazolium separation test. Soil organic matter determination will be done through hydrogen peroxide digestion experiment. Net primary production in the experimental plots will be calculated using the Forest-BCG model, while the Pipe model will be employed to estimate growth allocation to the aboveground state variables.
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