Spatial Distribution Patterns And Competition Of Main Species In Abandoned Farmland Under The Sloping Land Conservation Program

The Sloping Land Conservation Program,also known as the 'Returning Farmland to Forest Program',aims to gradually restore farmlands back to the original forested state.Information on the effects of the policy on the distribution of dominant species is important to better understand plant community structures,development dynamics,regeneration conditions,and possible underlying ecological mechanisms.In this study,we aimed to investigate the population structure of Pinus yunnanensis and Coriaria nepalensis Wall in an abandoned farmland of 2,500 m2 that was restored to forest in 2004.The results were as followings:(1)The population structure of P.yunnanensis based on tree age had an inverted J-distribution(20.1%seedlings,34.2%young trees,38.5%middle-aged trees,and 7.1%adult trees)since 2009,which was between expanding age structure and stabilized age structure.Whereas,C.nepalensis Wall showed an expanding age structure.(2)Seedlings,young trees,and middle-aged trees of P.yunnanensis showed an clustered distribution.Seedlings of P.yunnanensis had the highest aggregation degree(g(r)= 6.4),followed by young trees(g(r)= 2.3)and middle-aged trees(g(r)= 1.7).Adult trees of P.yunnanensis showed a random distribution throughout the research area.However,C.nepalensis Wall showed a random distribution in almost the whole scales.(3)The spatial relationships among seedlings,young trees,middle-aged trees,and adults of P.yunnanensis were studied and showed that the aggregation effect increased with the decreasing difference in the diameter at breast height between the tree groups.However,three diameter classes of C.nepalensis Wall has no relations with each other.(4)The correlation of canopy height and diameter at breast height decreased with the increasing competition among the individuals,indicating that seedlings and young trees growing in the same area might use less resources than needed.(5)P.yunnanensis and C.nepalensis Wall has no associations in small scales.However,with the scale increased,the degree of positive association increased gradually.With the scales increased continually,the degree of positive association between P.yunnanensis and C.nepalensis Wall decreased,until the scale of 20.3m.After that,P.yunnanensis and C.nepalensis Wall had no relationship.