Changes Of Forest Ecosystem Vulnerability With Succession And Climate In Southwest China

Based on the issue of ecosystem vulnerability to climate change,it is necessary to establish a scientific vulnerability assessment system.This research is based on the identification of criteria for vulnerability ratings.It can provide some reference for the establishment of an indicator system of vulnerability to climate change of typical ecosystems and it is of great significance to the ecosystem vulnerability in southwest China.We have built 62 forest and shrub sample plots in typical forest ecosystem in southwest China so as to focus on these following problems:1)effects of clinate and community structure on forest ecosystem biomass,net primary productivity(NPP),species diversity;2)factors affecting biomass,net primary productivity,species diversity and species composition;3)establishment of comprehensive indicators of ecosystem vulnerability based on biomass,productivity,diversity and species composition;4)impacts and relative impacts of succession,climate and community structure on ecosystem vulnerability.The main results were summarized as follows1)Successional trends of biomass,NPP,species diversity and species composition in forest ecosystem differed from research sites.Biomass increased with successional stages significantly in three sites.The growth of NPP was obvious in shrub stage and early successional period,while it slowed down in middle and late successional period.The effects of succession on species diversity varied from location to location.2)NPP had an obvious latitude,altitude gradient pattern.NPP in low latitudes and low elevations were relatively higher.NPP was significantly affected by climate factors.Actually,latitude,altitude and climate factors all played the role of water and heat.NPP increased with the increase of water and heat conditions.In addition,NPP was also related to stand factors and it increased with the increase of diameter at breast height(DBH)and tree height.The biomass of conifer and broad-leaved mixed forest and evergreen broad-leaf forest was relatively high.Biomass was significantly related to many comnunity structure factors and the productivity of evergreen broad-leaf forest was relatively higher.Species diversity also had a certain geographical pattern.It was also the role of heat and water.Species diversity will increase with the increase of water and heat conditions,while exorbitant stand density may make it lower.3)The changes of biomass,NPP,species diversity and species composition in forest ecosystem varied with succession.We established an ecosystem health index based on these ecosystem traits,which can comprehensively reflect the changes of ecosystem function in different aspects.Our study showed that the ecosystem vulnerability of the samples in the shrub stage and early succession was relatively higher,while the ecosystem vulnerability was relatively lower in the middle and late succession in southwest China.4)Ecosystem vulnerability was influenced both by climate and stand factors.Ecosystem vulnerability had a significant pattern of geographical and elevation gradient,and it was significantly related to climate factors that characterize water and heat.In fact,both are the effects of heat and water,indicating that water is sufficient.Our study showed that the ecological vulnerability is relatively lower,when the temperature is suitable.The ecosystem vulnerability was significantly related to the average tree height and the average DBH,and it decreased with the increase of the tree height and DBH5)We used stepwise regression analysis of ecosystem health index with climatic factors and stand conditions,and then analyzed the relationship between ecosystem health index and these factors.The results showed that water was the key factor resulting in ecosystem vulnerability in southwest China.And the average DBH also had an influence that ecosystem vulnerability decreased with the increase of DBH.Other climatic factors and stand eonditions did not show significant effects in this study,Reducing ecosystem vulnerability is of great significance to the protection of forest ecosystem.On the one hand,protection of old-growth forests and adopting the measures of raising to promote the restoration succession of the secondary forests can be considered because ecosystem vulnerability is low in the middle and Iate stage of succession.On the other hand,based on the response of ecosystem vulnerability to water,it can be considered to take forest management measures like thinning to reduce the competition for water.