1982—2012年中国植被覆盖时空变化特征

Spatiotemporal changes in vegetation coverage in China during 1982—2012

利用GIMMS NDVI、MODIS NDVI和气象数据,辅以趋势分析、分段回归以及相关分析等方法,分析了1982—2012年我国植被NDVI时空变化特征及其驱动因素。结果表明:(1)近30年我国植被NDVI呈缓慢增加趋势,增速为0.2%/10a;植被覆盖变化阶段性特征明显:即1982—1997年和1997—2012年植被覆盖均呈显著增加趋势,增速分别为1.2%/10a和0.6%/10a,均通过显著水平0.05的检验。(2)空间上,我国陕北黄土高原、西藏中西部以及新疆准格尔盆地等地区植被NDVI呈显著增加趋势;而东北地区的大、小兴安岭和长白山、新疆北部的天山和阿尔泰山以及黄河源和秦巴山区等地区植被NDVI呈显著下降趋势,其中东北地区和新疆北部山区下降尤为显著,说明近年来我国中高纬度山区植被活动呈下降趋势。(3)不同区域植被对气温和降水的响应存在差异,我国北方地区植被对气温具有较长的响应持续时间;而除云南外,南方地区植被对降水的响应时间存在1—3个月的响应时间,且随着滞后时间的延长,相关性逐渐增大。(4)我国植被覆盖增加是气候变化和人类活动共同驱动的结果,尤其是1999年之后人类活动影响逐渐加强。而我国东北地区和新疆北部山区植被覆盖的下降可能是由于该区降水减少所致,东南沿海地区植被退化则受城市化影响显著。

Vegetation, the main component of terrestrial ecosystems, is not only a sensitive indicator of global climate change, but also regulates the climate through energy, water, and carbon exchange between the terrestrial environment and the atmosphere. Understanding the mechanisms of growth responses of vegetation to climate change is of great significance for projecting future vegetation change and its implications. Using the satellite-derived normalized difference vegetation index （NDVI） and climate data of the period between 1982 and 2012, we investigated changes in the growing season NDVI and its response to climate change in China based on trend analysis, piecewise regression model, and correlation analysis. Our results indicate that （ 1 ） In the past thirty years, the NDVI of the study area increased, with the linear tendency being 0.2%/10a. There exists two distinct periods with different increasing trends, with the linear tendency being 1.2%/10a and 0.6%/10a during 1982--1997 and 1997--2012, respectively, the two periods of which all through the inspection by a significant level of 0.05. （2） In spatial, the areas with increased vegetation NDVI are mainly distributed in the Loess Plateau of Shanxi, the middle and western regions of Xizang, and the Junggar basin, whereas the regions with decreased vegetation NDVI are mainly distributed in the Da Hinggan Mountain, Xiao Hinggan Mountain, and Changbai Mountain inthe northeast of China, the Altai mountain and the Tianshan Mountain in the north of Xinjiang Province, the Yellow River source region, and the Qinba Mountain, of which, the magnitude of decrease in the northeast of China, the Tianshan Mountain, the Altai Mountains is particularly remarkable. This phenomenon indicates that vegetation activities in mid-and high latitude mountain regions declined. （3） Spatial differences occur in response to temperature and precipitation from vegetation in different regions. Longer response duration of vegetation to temperature was detected in the north of China, whereas vegetation in the south of China showed not more than one month time lag. In contrast, vegetation in the north of China showed not more than one month time lag, but in the south of China, except for Yunnan Province, more than one month time lag was observed, and the correlation increased with the extension of time lag. （4） The increased vegetation coverage is mainly attributed to climate change and the implementation of the ecological protection project, the latter especially strengthened the impact of human activities on the vegetation increase after 1999. Of which, the decrease in vegetation in the northeast of China, the Tianshan Mountain, and the Altai Mountains can be attributed to the decline in precipitation, whereas the deterioration in the southeast of China may be more related to urbanization. Over the last decade, the project on the conversion of degraded farm land into forests and grass land in China has achieved encouraging results. However, the most drastic climate change also occurred during the same period. Although climate change probably played a key role in the trends of vegetation growth on a long time scale, human activities are also an important factor driving vegetation change. However, the exact influences of climate change and human activities on vegetation growth remain unclear; further studies are necessary to obtain accurate conclusions.