基于NDVI的三江源地区植被生长对气候变化和人类活动的响应研究

Response of vegetation to climate change and human activity based on NDVI in the Three-River Headwaters region

采用Spot VEGETATION逐旬NDVI数据、1∶100万植被类型图和气象站资料,在掌握近10a三江源地区植被变化趋势基础上,分不同植被类型探讨植被生长对气候变化的响应机制,并通过分离气候要素与人类活动对NDVI的贡献,定量评估生态保护与建设工程的实施效果。结果表明,区域尺度上,三江源地区2001—2010年植被生长呈好转趋势,植被增长从东南向西北递减;在10a时间尺度上,气候变化是影响植被生长的决定性因素,但人类活动可在短期内加快植被变化速率,气候要素和人类活动对植被生长的贡献分别为79.32%和20.68%;降水和气温对植被生长的影响程度相当,其中受春季和秋季的降水和气温影响最大,尤其是植被生长季前后一个月(4月份和10月份)的气候条件;与林地和灌丛相比,高寒草地受气候条件的抑制作用更为明显,其中高寒草甸受气候变化的影响最大,NDVI与降水和气温均具有较高相关性,高寒草原受气温的影响比较大,而高山植被受降水的抑制作用更为明显;在气候条件利于植被生长的趋势下,2001—2010年三江源地区的人类活动对生态环境表现出正影响,实测NDVImax与模拟NDVImax之间的残差为0.0863,表明生态保护与建设行动取得初步成效,其中黄河源区东部和长江源区通天河两侧的生态恢复效益最为明显,而在唐古拉山、昆仑山、布青山、阿尼玛卿山等山脉的周边地区,人类活动对生态环境仍表现为负影响;时间尺度上人类活动对植被的正影响呈现出下降趋势,2001—2010年NDVImax残差的回归斜率为-0.0039,表明生态项目实施的短期行为严重,生态建设的效果缺乏长效性。

Vegetation change trends and the response of different types of vegetation to climate change were analyzed using spot vegetation Normalized Difference Vegetation Index（NDVI） data from 1998 to 2010,vegetation maps at a scale of 1∶1000000 and climate data obtained from 16 weather stations in or near to the Three-River Headwaters region.The effectiveness of ecological conservation and construction was also assessed by separating the contribution of human activity from climate factors to vegetation growth.Results show that vegetation in the study area increased in density between 2001 to 2010 at a regional scale and vegetation growth decreased from the southeast to the northwest of the study area.The contribution of climate change and human activity to vegetation growth was calculated at 79.32% and 20.68%,respectively,indicating that change in vegetation is mostly influenced by climate change and enhanced by human activity.Precipitation as well as temperature has a great impact on vegetation change at the study site.Precipitation and temperature during spring and autumn,especially in April and October,are the most important to vegetation growth in the alpine area.The impact of climate change on NDVI differs between vegetation types,with the greatest impact observed in alpine grassland areas over forest and shrub areas.The NDVI of alpine meadow areas correlates strongly with both precipitation and temperature.In alpine steppe areas temperature has more influence on NDVI,while precipitation has a stronger relationship with NDVI in areas of mountain vegetation.Under a changing climate between 2001 to 2010,which promoted vegetation growth because of the increase in precipitation and temperature,human activity was found to have a positive effect on vegetation growth as shown from the calculation of a residual value of 0.0863 between real NDVI and simulated NDVI.This provides evidence that ecological conservation and construction programs have achieved initial success.The most obvious effects occur in the east of the Yellow River source region and the two sides of Tongtian River of Yangtze River source region.In mountain areas such as Tanggula Mountain,Kunlun Mountain and Buqing Mountain,human activity is still found to have negative effects on vegetation growth.The positive effects of human activity on vegetation decreased between 2001 to 2010,as shown from the negative slope of-0.0039.This indicates that most ecological projects are implemented with a short-term design and a lack of long-term planning.