Spatial identification and scenario simulation of the ecological transition zones under the climate change in China

Explicitly identifying the spatial distribution of ecological transition zones (ETZs) and simulating their response to climate scenarios is of significance in understanding the response and feedback of ecosystems to global climate change.In this study,a quantitative spatial identification method was developed to assess ETZ distribution in terms of the improved Holdridge life zone (iHLZ) model.Based on climate observations collected from 782 weather stations in China in the T0 (1981-2010) period,and the Intergovernmental Panel on Climate Change Coupled Model Intercomparison Project (IPCC CMIP5) RCP2.6,RCP4.5,and RCP8.5 climate scenario data in the T1 (2011-2040),T2 (2041-2070),and T3 (2071-2100) periods,the spatial distribution of ETZs and their response to climate scenarios in China were simulated in the four periods of T0,T1,T2,and T3.Additionally,a spatial shift of mean center model was developed to quantitatively calculate the shift direction and distance of each ETZ type during the periods from T0 to T3.The simulated results revealed 41 ETZ types in China,accounting for 18％ of the whole land area.Cold temperate grassland/humid forest and warm temperate arid forest (564,238.5 km2),cold temperate humid forest and warm temperate arid/humid forest (566,549.75 km2),and north humid/humid forest and cold temperate humid forest (525,750.25 km2) were the main ETZ types,accounting for 35％ of the total ETZ area in China.Between 2010 and 2100,the area of cold temperate desert shrub and warm temperate desert shrub/thorn steppe ETZs were projected to increase at a rate of 4％ per decade,which represented an increase of 3604.2,10063.1,and 17,242 km2 per decade under the RCP2.6,RCP4.5,and RCP8.5 scenarios,respectively.The cold ETZ was projected to transform to the warm humid ETZ in the future.The average shift distance of the mean center in the north wet forest and cold temperate desert shrub/thorn grassland ETZs was generally larger than that of other ETZs,with the mean center moving to the northeast and the shift distance being more than 150 km during the periods from T0 to T3.In addition,with a gradual increase of temperature and precipitation,the ETZs in northern China displayed a shifting northward trend,while the area of ETZs in southern China decreased gradually,and their mean center moved to high-altitude areas.The effects of climate change on ETZs presented an increasing trend in China,especially in the Qinghai-Tibet Plateau.