尼洋河流域植被特征时空变化及其对水热的响应

Spatiotemporal Variation of Vegetation Characteristics and Its Response to Hydrothermal Factor in the Niyang River Basin

尼洋河作为工布江达县的“母亲河”,探究流域植被变化特征及其与水热的关系对生态建设具有重要意义。本研究以尼洋河流域为研究区,采用了广义回归神经网络(General regression neural network,GRNN)计算模型来反演叶面积指数(Leaf area index,LAI)和植被覆盖度(Fractional vegetation cover,FVC)数据集,分析LAI和FVC的时空变化特征及其对水热因子的响应。结果表明:2001—2019年以来,尼洋河流域植被总体呈现轻微改善趋势,植被集中生长于河流两岸并以常绿针叶林为主,远离河流的高海拔区域植被生长状况不佳,随海拔高度的升高LAI和FVC均趋近零值;流域植被覆盖类型分为极低、低、中和高覆盖四种,且覆盖类型以中、极低覆盖为主,中覆盖类型主要分布在河流周围,极低覆盖类型集中于远离河流的高海拔区域,且覆盖面积逐年呈现下降趋势,相反河流两岸的高覆盖类型区域面积出现扩张;相对于气温而言,流域内植被对降水的响应更为敏感,过多的降水对植被生长存在一定抑制作用。

As the mother river of Kongpo Gyamda,exploring the characteristics of vegetation change in the watershed and its relationship with water and heat is of great significance to ecological construction.This study took the Niyang River Basin as the research area,the general regression neural network(GRNN)calculation model was used to invert the leaf area index(LAI)and the fractional vegetation cover(FVC)data set,analyzed the temporal and spatial characteristics of LAI and FVC and their response to hydrothermal factors.The results showed that from 2000 to 2019,the vegetation in the Niyang River Basin had been slightly improved.The vegetation mainly grew on both sides of the river and was dominated by evergreen coniferous forest.The vegetation growth in the high-altitude area far away from the river was poor.With the increase in altitude,both LAI and FVC approached zero;There were four types of watershed vegetation coverage:very low,low,medium and high coverage,and the coverage type wwas mainly medium and very low coverage.The medium coverage type was mainly distributed around the river.The very low coverage type was concentrated in the high-altitude area far away from the river,and the coverage area showed a downward trend year by year,on the contrary,the area of high coverage type on both sides of the river expanded.The vegetation in the watershed is more sensitive to precipitation than to temperature.Excessive precipitation had a certain inhibitory effect on vegetation growth.