Thinning Effects On Carbon Density And Plant Diversity Of Two Topical Natural Secondary Forest On The Southern Slope Of The Qinling Mountains

Thinning effects on carbon density and plant diversity of Pinus tabulaeformis and Quercus aliena var. acuteserrata natural secondary forest were investigated by sample-plot survey and laboratory tests. In this study, 24 sample-plots of Pinus tabulaeformis and Quercus aliena var. acuteserrata natural secondary forest were set respectively on different slope aspect and thinning intensity. Stand growth, carbon density of different pools and plant diversity and composition of underground vegetation were analyzed. The results are concluded as:1.The growth of stand mean DBH(diameter at breast height)were increased in stand of different thinning intensity. The growth of stand mean DBH of Pinus tabulaeformis stand both peaked in 15% intensity on sunny and shady slope. The growth of stand mean DBH ofQuercus aliena var. acuteserrata stand increased with thinning intensity. 15% intensity significantly improved the growth of stand mean DBH of Quercus aliena var. acuteserrata stand on shady slope.2.15% and 25% intensity significantly improved net primary productivity(NPP) of Pinus tabulaeformis stand on sunny slope. 15% intensity significantly improved net primary productivity(NPP) of Pinus tabulaeformis stand on shady slope. 15% and 25% intensity significantly improved net primary productivity(NPP) ofQuercus aliena var. acuteserrata stand on sunny slope.5% intensity significantly improved net primary productivity(NPP) ofQuercus aliena var. acuteserrata stand on shady slope.3. Carbon density of tree layer Accounted more than 40% of Pinus tabulaeformisstand and 50% of Quercus aliena var. acuteserratastandrespectively. The carbon density of tree layer and it’s proportion in the forest ecosystem decreased with thinning intensity.4.The tree layer carbon density increase ofPinus tabulaeformis and Quercus aliena var. acuteserratastand with different thinning intensity were improved to a certain extent. Pinus tabulaeformisstand with thinning intensity of 15%, 25% on sunny slope and 15% on shady slope were higher than control stand;Quercus aliena var. acuteserrata stand with thinning intensity of 5%, 15% on sunny slope and 5% on shady slope were higher than control stand;5. The carbon density of underground vegetation increased with thinning intensity bothinPinus tabulaeformis and Quercus aliena var. acuteserrata stand on different slope aspect. Thinning intensity had no significant influence onletter and soil carbon density.6.The species of shrub and herb increased after thinning both in Pinus tabulaeformis and Quercus aliena var. acuteserrata stand on different slope aspect. Abundance index and diversity index increased with thinning intensity. Evenness indexof shrubs and herb plants inPinus tabulaeformis and Quercus aliena var. acuteserrata forest with different thinning intensity on different slope aspect(Pielou index and Alatalo index) were had no obvious regulation with thinning intensity. Pielou index based on shannon-wiener index increased to different certain extent in thinned stand on different slope aspect.