Abstract: Studies on the impacts of extreme drought on karst plant communities are the basis for the management of degraded karst ecosystem. In order to underst
and the impacts of extreme drought event happened in Southwest China in spring 2010 on the karst vegetations, an investigation by the method of counting individual numbers of each plant species was conducted in May 2010 to analyze the structure of three natural karst plant communities (Cyclobalanopsis glaucoides forest, Quercus variabilis forest, and karst shrubs) and five artificially restored plant communities (Pinus yunnanensis forest, Alnus nepalensis forest on natural soil, A. nepalensis forest on covered new soil, Acacia dealbata forest, and Cupressus lusitanica forest) in the Shilin karst region of Yunnan. The feature of the extreme drought event was analyzed by the deviation indices of meteorological elements; the drought-suffered degree of the karst plant communities and species was analyzed by drought-suffering rate and mortality; and the impacts of the extreme drought on the karst plant cmmunities were evaluated by the biodiversity indices calculated with the dead and withered species number and individuals number, alive species number and individuals number, and alive but suffered species number and individuals number. This extreme drought event began in autumn 2009 and ended in June 2010, with the characteristics of long-lasting and deep level. The average mortality rate and drougt-suffering rate of the eight plant communities were 25.1% and 30.6%, respectively, and differed greatly with the plant communities. After the extreme drought, the naturally-restored plant communities still maintained their original species structure in regenerated layers, while the artificially restored plant communities had greater differences. The P. yunnanensis forest and the A. nepalensis forest on natural soil were less affected, the A. nepalensis forest on covered new soil and the A. dealbata forest basically lost their original species strucutre and size classs structure, and the C. lusitanica forest nearly had the original species strucutre and size classs structure, though half plants were dead. The extreme drought changed the stucutre and biodiversity of the plant communities to certain extent, and the drought-tolerance of artificially restored plant communities was weaker than that of natural plant communities. Therefore, appropriate plant species and restoration approaches should be chosen to restore the vegetations of degraded karst ecosystem.

Key words: Castanopsis carlesii forest, Scales of human disturbance, Restoration ecology