中亚高海拔梯度山盆系统草地净初级生产力时空演变格局及其驱动机制分析

Analysis of the Spatial-Temporal Evolution Patterns of Grassland Net Primary Productivity and Its Driving Mechanisms in the High-altitude Gradient Mountain-Basin System of Central Asia

山盆系统是中亚地区独特而复杂的地貌结构,其较大的海拔梯度差导致了草地净初级生产力(NPP,net primary productivity)的空间异质性和对气候变化与人类活动的不同响应。定量评价气候变化和人为活动对中亚山地盆地系统草地的相对影响,对草地管理和草地可持续利用具有重要意义。选择NPP作为反映草地动态过程的指标,基于MODIS NDVI数据和气候数据等,运用CASA模型、Thornthwaite Memoria模型和HANPP模型分别对2001—2015年间NPP进行模拟,采用情景分析方法研究气候变化和人类活动对2001—2015年中亚山地盆地系统高海拔梯度差下草地NPP变化的相对影响。结果表明:15年间,草地NPP呈上升趋势的区域(35.88%)所占的面积小于下降趋势的区域(64.12%)所占面积。人类活动、气候变化以及两者共同促进NPP增加的贡献率分别为6.19%、81.30%和12.51%。人类活动促进草地NPP增加的区域主要集中在夏牧场最北部的山地;人类活动导致NPP减少的面积占退化总面积的98.21%,且主要发生在中低海拔的春秋牧场和冬牧场。2001—2015年期间,降水量的增加是促进研究区草地NPP增加的主导因素。在温度较高的中低海拔地区(460—2460 m),草地NPP与降水呈正相关,植被NPP对降水更为敏感;而在降水较充沛的高海拔地区(2460 m以上),草地NPP与气温呈正相关,且植被NPP对气温更为敏感。研究结果表明,人类活动是导致草地退化的主要原因,建议当地政府应采取相关措施降低放牧压力,并沿额尔齐斯河和乌伦古尔河沿岸建植人工草地,以缓解春秋牧场和冬牧场的放牧压力。该研究结果可为中亚干旱地区山盆系统的草地管理和草地退化防治提供可靠依据。

Mountain basin systems(MBS)are unique and complex geomorphic structure in Central Asia,wherein their elevation gradients lead to high spatial heterogeneity in grassland net primary productivity(NPP,net primary productivity)and its response to human activities and climate change.An accurate assessment of the effects of these two factors on grasslands are significant for grassland regulation and sustainability in the MBS in Central Asia.Based on the MODIS NDVI(remotely sensed normalized difference vegetation index),climatic data and livestock numbers,etc.,we have chosen net primary productivity(NPP)an index to reveal the change of grassland NPP,and the CASA model,Thornthwaite Memorial model and HANPP model were used to simulate NPP from 2001-2015,respectively.Scenario analysis was used to study the relative influence of climate change and human activities on grassland NPP change under the high-altitude gradient in the MBS in Central Asian from 2001 to 2015.The results indicated that grassland NPP showing an increasing trend(35.88%)that was smaller than that of the decreasing trend(64.12%).The respective contributions of human activity,climate change and the two together to the increase in NPP were 6.19%,81.30% and 12.51%,respectively.The areas where human activity contributed to the increase in grassland NPP mainly concentrated in the northernmost mountains of summer pasture.Human activity was largely responsible for the decrease in grassland NPP,with the area experiencing human-induced decreases accounting for 98.21% of the total area,which mainly occurred in spring/autumn pasture and winter pasture at middle and low altitudes.From 2001 to 2015,the increase of precipitation was the leading factor to promote the increase of grassland NPP.In the middle and low altitude areas with high temperature(460-2460 m),grassland NPP was positively correlated with precipitation,and more sensitive to precipitation.In the high-altitude areas with abundant precipitation(above 2460 m),NPP was positively correlated with temperature,and more sensitive to temperature.Human activities were the main reason for the grassland degradation,and the findings of the current research indicate that the artificial grasslands can be built along the rivers(Irtysh River and the Ulungur River)to relieve grazing pressure on spring/autumn pastures and winter pastures.The results of this study can provide a reliable basis for grassland management and grassland degradation control in the MBS in Central Asia.