1977—2020年额济纳胡杨林植被变化特征及其影响因子分析

Vegetation Change Characteristics and Influencing Factors of Ejina Populus Euphratica Forest from 1977 to 2020

基于1977—2020年Landsat影像,采用监督分类和归一化植被指数(NDVI),并结合气象、水文数据,对近44年额济纳绿洲胡杨林面积时空动态、植被状况,以及对其有影响的主要环境因素进行综合分析。结果表明:(1)2020年胡杨林面积为2.99万hm~2,较1977年增长了1.62倍,东河西岸三角洲恢复面积较大。研究期内,胡杨林经历了衰落期和恢复期,最小面积为1990年的1.03万hm~2。(2)2001年实施生态调水后,研究区NDVI值增速达0.027/10 a(P<0.01),是研究时段NDVI值增速的2倍、调水前NDVI值增速的45倍。(3)虽然月NDVI值与月均温相关系数为0.463(P<0.01),但年NDVI值与气候因素相关性并不明显,而与正义峡径流量显著正相关(相关系数为0.437,P<0.05),并且实施黑河调水与胡杨林景观生态功能改善的时间段同步。生态调水后,研究区NDVI值升高了0.011,裸地面积减少0.17万hm~2。

Based on Landsat imagery from 1977 to 2020 and combined with meteorological and hydrological data,supervision classification and normalized difference vegetation index(NDVI)were used to comprehensively analyze the spatiotemporal dynamics,vegetation status,and main environmental factors affecting the Ejina oasis Populus eugensis forest during 1977-2020.Results show that:(1)The area of the P.eugensis forest in the study area was 2.99 ×10~4hm~2 in 2020,1.62 times the size of 1977,and the restoration area of the delta on the west bank of the Ejina River is relatively larger.During the study period,the P.eugensis forest experienced a decline and recovery period,with a minimum area of 1.03×10~4hm~2 in 1990.(2)After the implementation of ecological water transfer in 2001,the NDVI growth rate in the study area reached 0.027/10 a(P0.01),which was twice the growth rate of NDVI values during the study period and 45 times the growth rate before the water transfer.(3)Although the correlation coefficient between the monthly NDVI value and the monthly average temperature was 0.463(P0.01),the annual NDVI value was not significant related to climate factors,but was significantly positively related to the runoff of the Zhengyixia River(correlation coefficient was 0.437,P0.05),and the implementation of the Heihe River diversion was synchronous with the improvement of the landscape ecological function of the P.euphratica forest.After ecological water transfer,The study area of the NDVI increased by 0.011,where the bare land area decreased by 0.17×10~4hm~2.