2000—2014年甘南高原植被覆盖度变化及其对气候变化的响应

Variation of vegetation coverage and its response to climate change in Gannan Plateau from 2000 to 2014

基于2000—2014年MODIS NDVI数据,分析了甘南高原植被覆盖度的时空变化格局,并结合同期气温、降水数据及物候信息,从不同时空尺度和植被类型分析了甘南高原植被覆盖度的年、月际变化及其对气候变化的响应。结果表明:甘南高原2000—2014年年均温和降水均呈波动上升趋势(0.04℃·a^(-1),4.7 mm·a^(-1)),降水由西南向东北呈递减趋势,年均温由东南向西北呈递减趋势;近15年甘南高原植被覆盖度总体呈东南高西北低的特征,平均植被覆盖度为77.5%,其中,森林覆盖度最高(77.8%),高山亚高山草地覆盖度最低(60.3%);甘南高原植被覆盖度总体呈上升趋势,增加速率为0.32%·a^(-1)。其中,坡面草地增加趋势显著,为1.04%·a^(-1),平原草地次之,为0.47%·a^(-1),高山亚高山草甸为0.19%·a^(-1),森林仅为0.10%·a^(-1),而沼泽湿地和高山亚高山草地覆盖度呈下降趋势(-0.03%·a^(-1)、-0.06%·a^(-1));从年际变化来看,植被覆盖度与气温和降水均呈不显著正相关(R=0.45,R=0.21);从不同类型植被来看,高山亚高山草甸、高山亚高山草地、平原草地、坡面草地和沼泽湿地覆盖度受气温影响较大,森林覆盖度受降水影响较大;从月际变化来看,生长季植被覆盖度对降水的滞后效应主要表现在植被生长初期和末期,对气温的滞后效应主要表现在关键生长期,且对降水的滞后效应优于气温。

MODIS NDVI data from 2000 to 2014 were adopted to extract the time series of the vegetation coverage in Gannan Plateau, and its spatial and temporal variation were analyzed. The response of vegetation coverage to climatic variations at annual and monthly time scales was analyzed by using phenological phase, temperature and precipitation time series at Gannan meteorological stations from 2000 to 2014. The results showed that the annual mean temperature increased with an annual rate of 0.04 ℃ and the annual mean precipitation increased with an annual rate of 4.7 mm in the Gannan Plateau from 2000 to 2014. Spatially, precipitation decreased from the southwest to the northeast and the annual mean temperature decreased from the southeast to the northwest. During the past 15 years, the vegetation coverage increased from the southeast to northwest in Gannan Plateau. The mean vegetation coverage was 77.5%, and exhibited apparent spatial heterogeneity, being the highest （77.8%） in forest and the lowest （60.3%） in alpine and subalpine grassland. There was a slight increase of vegetation coverage over the study period with an annual rate of 0.32%. The increase in sloping grassland area was as high as 1.04% per year and the plain grassland area increase was 0.47% per year, while the increases in coverage of alpine and subalpine meadow and forest were lower （0.19% and 0.10% per year, respectively）. On the contrary, the marsh wetlands, alpine and subalpine grassland had a slight decrease of vegetation coverage over the study period （-0.03% and -0.06% per year, respectively）. At the annual time-scale, there were no significant positive correlations between vegetation coverage and annual temperature or precipitation. However, the vegetation coverage was mainly affected by temperature in alpine and sub-alpine grassland, alpine and sub-alpine meadow, sloping grassland, plain grassland and marsh wetlands, while the vegetation coverage in forest was mainly affected by precipitation. At the monthly timescale, the time-lag response of vegetation coverage to precipitation occurred mainly in early and late growing season, while the time-lag response to temperature occurred mainly in key growth stage, and such response to precipitation was better than that to temperature.