Effects Of Gaps On The Plants Regeneration And Species Diversity In Tiantong Evergreen Broad-leaved Forest

As a kind of frequent small-scale disturbances in forest community,forest gap plays an important role in community ecology.Due to the gap formation,the former environment will be changed in local community.These changes would influence the regeneration of trees in different life forms,such as evergreen and deciduous.Consequently,gap would be a major mechanism for species coexistence in community.For this purpose,we investigated 149 canopy gaps and the corresponding non-gaps in the 20-ha stem-mapped dynamic plot in Tiantong National Forest Park,Zhejiang province in 2010 and 2015.We calculated the net recruit rates,growth rates,Jaccard index and species diversity index of gaps and non-gaps in different life forms(evergreen and deciduous).In addition,in order to remove the influence of different densities of gap and non-gap,we used the random sampling method to calculate species diversity index.Finally,we hope to explore how gap influence the species coexistence and maintain the species diversity in the community.The main results of this study are as follows:(1)The abundance and important value of deciduous tree species in gaps are increased during five years,and the deciduous species richness is increased more rapidly than evergreen species richness.While the variation of abundance,important value,richness of evergreen species and deciduous species in non-gaps is little.What's more,the Jaccard indexs between the same gaps in 2010 and 2015 are smaller than its in non-gaps.And the Jaccard indexs within gaps in 2010 and 2015 are smaller than its in non-gaps.It means that the variation of species composition in gaps is greater than it in non-gaps.These results indicate that the gaps would change the species composition in local area,increase the proportion of deciduous tree species and promote the evergreen and deciduous tree species coexisting in community.(2)The net recruit rates of evergreen and deciduous tree species in gaps are more than in non-gap significantly(p<0.05).The net recruit rates of deciduous tree species in medium gaps and large gaps are 205.80%and 269.15%respectively,which are more than evergreen tree species significantly(75.64%,p<0.05 and 82.26%,p<0.05 respectively).While there is no significant difference between the recruit rates of evergreen and deciduous tree species in non-gaps.This result indicates that gaps would promote the regeneration.This promotion on deciduous tree species is stronger than evergreen tree species.The growth rates of evergreen and deciduous tree species in gaps are 33.69%and 144.34%respectively,which are more than in non-gaps significantly(18.96%p<0.05 and 20.36%p<0.05 respectively).Furthermore,the growth rates of deciduous tree species is more than evergreen tree species in gaps(p<0.01).This result indicates that gap would promote the growth of plants,especially the growth of deciduous tree species.(3)There is no significant difference between the species diversity in gaps and non-gaps in 2010.And the individuals in gaps were less than it in non-gaps.This result indicates that the gaps may be initial when we investigated in 2010.In addition,the species diversity index(Inverse Simpson index,Exp(H')and species richness)in gaps in 2015 are more than in 2010 significantly(p<0.05).While there are no significant difference between the species diversity index in non-gaps in 2010 and 2015.This result indicates that the species diversity in initial gaps would be increased with age of gaps.In 2015,the Inverse Simpson index and Exp(H')in large gaps are more than in non-gaps significantly(p<0.05).This result indicates that the species diversity in large gaps is higher than in corresponding non-gaps after gap formation for several years.Synthesis.The recruit rates and growth rates of deciduous tree species in gaps would be increased more rapidly than in non-gaps.This phenomenon could increase the proportion of deciduous tree species in gaps and species diversity in subtropical evergreen broad-leaved forest.Consequently,gap would maintain the species coexistence in community.