Abstract:

The Pinus tabulaeformis plantation is a low and middle hill type of the zonal vegetation and is distributing in the low hill shade slope and half shade slope in Beijing mountainous areas.Due to a generally high stand density and the lag of tending,the forests could not grow well and the general quality of the stand is in poor condition.The ecological functions of the plantation therefore cannot be fulfilled.In order to investigate the dynamic variance of the undergrowth and to provide reference for reasonable thinning,in 2000 and 2004,24 sample plots in the low hill shade slope with thick soil were selected in Beijing mountainous areas and the light,medium and heavy thinning,pruning,and bushing were conducted on each sample plots respectively.In the summers of 2005 and 2006,the changes of the growth and the undergrowth diversity of the P.tabulaeformis were investigated and analyzed.The results showed:In the 2^nd year after thinning,the DBH,height,crown length,individual volume and stocking of the tending group were significantly higher than that of the control group,while no clear evidence was observed regarding the variance on growth of the P.tabulaeformis among the light thinning,medium thinning and heavy thinning groups.In the 6^th year after thinning,the growth of the P.tabulaeformis of the 3 groups were ranked in such order:heavy thinning > medium thinning > light thinning;the growth of medium and heavy thinning groups were much better than that of the light thinning group and the control group;and the heavy thinning group obtained the best growth;In the first 2 years of thinning,the species and quantity of the undergrowth,Simpson index,Shannon-Wiener index,Evenness index and the total amount of the undergrowth biomass all increased along with the enhancing of the thinning;In the 6 th year after thinning,The species,Simpson index,Shannon-Wiener index and Evenness index all depressed and the species number increased 5,10 and 12 respectively;For the Simpson index and Shannon-Wiener index,the 3 groups were ranked under the order:heavy thinning > medium thinning > light thinning.Compared with the first 2 years after thinning,the quantity of the undergrowth was decreased for every group,but the undergrowth coverage was increased as the thinning was enhancing,and the community vertical structure became much clearer for the heavy thinning group.Besides,the medium and heavy thinning increased the ratio of the highly water demanded plants,and had an effect of turning the undergrowth to meso-xerophytes and mesophytes;After the thinning,the total amounts of the undergrowth biomass were increased as the thinning was enhancing and were ranked in such order:6^th year > 2^nd year > 1^st year.In the 6^th year after thinning,the undergrowth biomass are increased by 29.1%,45.2% and 70.9% respectively for the light thinning group,medium thinning group and heavy thinning group;Thinning has a significant effect on the growth and diversity of undergrowth of the P.tabulaeformis plantation;It would improve the plantations in Beijing mountainous area turning to a sustainable development pattern.For increasing the growth and diversity of undergrowth,the heavy thinning has the best effect,and the appropriate stand density for the Pinus tabulaeformis plantations,on 35～37 a shady slope with thick soil and an original density of 3 200～3 467 tree·hm^-2,is 1 240～1 500 tree·hm^-2.

Key words: thinning, Pinus tabulaeformis plantation, plant diversity, indicator plants