The Response Of Carbon Pools And Plant Communities To Climate Change In A Mid-subtropical Forest

Climate change will affect forest community composition,species distribution and biodiversity,bring many uncertainties to forest productivity and carbon sequestration potential,and pose challenges for sustainable forest management.Subtropical forests in China are currently undergoing rapid recovery and growth,and are expected to play an important role in mitigating regional and global climate change.A systematic assessment of how subtropical forests respond to future climate change will contribute to the formulation of forest management measures to address climate change and is of great significance to the sustainable and healthy development of forests.This study used a forest landscape dynamic model,LANDIS-II,to simulate species and carbon dynamics during a 300-year succession in a subtropical mountainous forest in the Sangzhi County in central China,under two climate change scenarios(RCP4.5 and RCP8.5)and current climate scenario.According to the simulation results and analyses,five forest management measures were proposed to cope with future climate change.A systematic assessment of how the five management measures can mitigate the impacts of future climate change on forests was conducted then.The main results of this study are as follows:(1)Future climate change showed significantly effects on forest community composition in the Sangzhi County,which is mainly reflected in the impacts on species biomass.Climate change showed little effects on the biomass of the dominant species in the community,but greater impacts on the species with low dominance.The responses of forest communities at different elevations to climate change vary greatly.The low-elevation forest showed the most sensitive to the severe climate change,and the community composition tends to be simple.Climate change showed significantly effects on the distribution abundance of most plant species.Climate change forced the distribution range of plant species to shrink,with the distribution center moving toward the middle and high-elevation regions,along with loss of biomass.Mainly because climate change influenced environmental conditions,leading to the changes of habitat suitability at different elevations,and subsequently changing the interspecific competitive relationship among species.Climate change lowered the establish probability of plant species in the low-elevations,and increased the establish probability of plant species in the high-elevations.However,warm species such as Betula luminifera,Litsea elongata,and Toxicodendron succedaneum showed great adaptability to future climate change,expanding their distribution in low-elevation regions that were sensitive to climate change.(2)In the first 70 years of the simulated succession,forest net primary productivity(NPP)in the Sangzhi County increased rapidly to 6 Mg C ha-1 yr-1,and the plant carbon pool increased at a rate of 1.91 Mg C ha-1 yr-1,showing the strong plant carbon sequestration capacity.Net ecosystem carbon exchange(NEE)increased to a maximum of 3 Mg C ha-1 yr-1,showing the powerful subtropical forest carbon sink.In the early stage of succession,the rapid growth of NPP and NEE were mainly influenced by succession and natural growth of plants,and the influence of climate change began to appear in the middle and late stage of the succession.Climate change showed significant impacts on forest plant carbon pools,soil carbon pools,detrital carbon pools,and the total ecosystem carbon storage.Moderate climate change increased the soil carbon pool and the detrital carbon pool,but lowered the plant carbon pool,and eventually increased the total ecosystem carbon storage.Severe climate change reduced the plant carbon pool,the detrital carbon pool and the soil carbon pool,and eventually remarkably reduced the total ecosystem carbon storage.The effects of climate change on plant carbon pools showed an elevational gradient law:climate change significantly reduced the plant carbon pool at low-elevations;the negative effects of climate change on plant carbon pools gradually turns to positive effects as the elevation increases,promoting plant carbon sequestration at high-elevations.The detrital carbon pools and soil carbon pools of high-elevation forests were more sensitive to severe climate change than those of low-elevations.(3)The management measures which simply reduced cutting area and intensity could not effectively mitigate the impacts of climate change on forest.Apart from retaining more aboveground biomass(AGB)by reducing deforestation,these measures had minor impacts on improving forest aboveground net primary productivity(ANPP),soil carbon pools,detrital carbon pools,and the total ecosystem carbon storage,as well as species richness and forest complexity.They aggravated the aging of the forest and impeded forest regeneration.The management measures that simply increased cutting area and intensity reduced the plant carbon pool,the soil carbon pool,the detrital carbon pool,and the total ecosystem carbon storage.Although these measures showed beneficial to forest regeneration,the improvement in forest ANPP is not obvious.Planting warm tree species in low-elevations could better mitigate the impacts of severe climate change on forest ANPP,soil carbon pools and total ecosystem carbon storage.The planting measures improved species richness and forest complexity to some extent.The thinning measures at medium-and high-elevational protected forests had little impacts on species composition and age structure,but increased the amount of harvested biomass at the cost of slightly reducing AGB.The combination of increasing cutting area at low-elevational plantations and thinning at medium-and high-elevational protected forests could effectively mitigate the impact of climate change on forests and increase the amount of harvested biomass.The findings indicate that the effects of climate change on forest ecosystems varied with elevational gradient.The establishment of most species at low-elevations was restricted by climate change,which is the main reason for the decrease of forest biomass at lower elevations.However,warm species such as Betula luminifera could better adapt to the environment at low-elevations under climate change scenarios.Based on these findings,different management plans can be prepared according to management purposes.Assessment of the different management plans showed that the climate adapted management measures considering elevational pattern and species dynamics can effectively mitigate the adverse effects of climate change.