青海湖流域植被盖度时空变化研究

高寒区植被变化一直是气候和生态学领域关注的热点问题。本研究基于MODIS NDVI数据计算的植被覆盖度数据和高分辨率气象数据,分析了青海湖流域2001-2017年植被覆盖度分布格局及动态变化,探讨了其对气候变化、人类活动和冻土退化的响应。结果表明：① 近十几年青海湖流域植被覆盖度整体表现为增加趋势,不同植被类型增幅存在差异性,草地增幅最大,达到6.1%/10a,其它植被类型增幅在2%~3%/10a之间;② 流域局部地区仍存在植被退化现象,研究期植被退化面积表现为先增加后减小的变化趋势。2006-2011年重度退化区集中在青海湖东岸,2011-2017年重度退化区集中在流域的西北部,这些区域是青海湖流域荒漠分布区,植被覆盖度较低,是今后生态恢复需重点关注的区域;③ 气候变化是流域植被覆盖度变化的主导因素,气候变化对青海湖流域主要植被类型覆盖度变化的贡献率为84.21%,对草原、草甸和灌丛植被覆盖度变化的贡献率分别为81.84%、87.47%和75.96%;④ 人类活动对流域主要植被类型覆盖度变化的贡献率为15.79%,对草原、草甸和灌丛植被覆盖度变化的贡献率分别为18.16%、12.53%和24.04%,环青海湖地区人类活动对植被恢复有促进效应,在青海湖流域北部部分地区人类活动的破坏力度仍大于建设力度;⑤ 冻土退化对青海湖流域草甸和灌丛植被覆盖度变化影响很小,主要影响草原植被覆盖度变化,冻土退化造成草原植被覆盖度增长速率减小了1.2%/10a。

Spatiotemporal Dynamics of the Vegetation Coverage in Qinghai Lake Basin

Alpine vegetation change has been a hot topic for climate and ecology related studies. Based on the vegetation coverage data derived from MODIS NDVI and high resolution meteorological data, the spatial pattern and temporal changes of the vegetation coverage in Qinghai Lake basin during 2001-2017 and its response to climate change, human activity and permafrost degradation were analyzed in this study. Results showed that the vegetation coverage of Qinghai Lake basin presented an increasing trend in the last decade. There were differences among different vegetation types, with the largest increase of 6.1%/10a in grassland and 2%~3% in other vegetation types, indicating that grasslands are highly vulnerable to climate change and human activities. Vegetation degradation occurred in some areas of the basin, the area of vegetation degradation increased first and then decreased during the study period. The areas of severe degradation were concentrated in the east coast of Qinghai Lake during 2006-2011, and in the northwest of the basin during 2011-2017. These are the desert areas with low vegetation coverage in Qinghai Lake basin, key for future ecological restoration. Climate change is the leading factor of vegetation coverage change in the watershed, contributing 84.21% to vegetation coverage change of main vegetation types in the Qinghai Lake basin, 81.84%, 87.47% and 75.96% to vegetation coverage change of grassland, meadow and shrub, respectively. At different altitudes, air temperature and precipitation have different influences on vegetation coverage change. Precipitation was mainly positively correlated with vegetation coverage change when the altitude is below 4000 m, but mainly negatively correlated while altitude is above 4000 m. With the increase of altitude, the areas where air temperature is positively correlated with vegetation coverage decrease, while the areas where air temperature is negatively correlated increase. The contribution rate of human activities to vegetation coverage change of major vegetation types in the watershed was 15.79%, and that of grassland, meadow and shrub was 18.16%, 12.53% and 24.04%, respectively. Human activities in the area around Qinghai Lake had a promoting effect on vegetation restoration, but in the northern part of Qinghai Lake basin, human activities were still more destructive than construction. The degradation of permafrost had little effect on the change of vegetation coverage of meadow and shrub in Qinghai Lake basin, mainly affecting the change of grassland vegetation coverage. The growth rate of grassland vegetation coverage decreased by 1.2%/10a due to the degradation of permafrost. However, the interaction mechanism between permafrost, hydrology and vegetation is complex, it is hoped that this gap will be filled later.