雅鲁藏布江源区高寒草地退化光谱响应变化研究

Spectral Characteristics of Alpine Grassland During Degradation Process in the Source Region of Yarlung Zangbo

雅鲁藏布江源区的草地退化监测研究对于揭示全球变化影响下的区域生态系统响应特征、探讨其驱动因子及评价西藏高寒生态环境质量具有重要意义。基于高寒草甸、高寒草原和荒漠等不同类型和不同退化程度草地的地面实测数据,对雅鲁藏布江源区高寒草地的典型植物光谱特征和草地退化过程中的光谱响应变化进行了分析。结果表明作为高寒沼泽草甸、高寒草甸、高寒草原和高寒灌丛等类型的典型优势种藏北嵩草、小嵩草、紫花针茅和金露梅具有明显的光谱特征差异,主要体现在红边位置、红边形状、红谷和纤维素吸收波段处,与植物的生长形态和枯叶鞘固有特性密切相关。在草地退化过程中,光谱反射率整体上持续降低,叶绿素吸收造成的"红谷"特征弱化,近红外水分吸收谷变弱,土壤背景光谱特征渐渐凸显。通过对比常见的植被指数,发现那些能够充分描述植物红边或者叶绿素吸收特征的指数具有更高的可分性,表明可能对草地退化具有更好的表征能力,为西藏高寒草地退化遥感监测提供了参考依据。

Alpine ecosystem of source region of Yarlung Zangbo plays a vital role in maintaining ecological security of its middle and lower reaches with great population. The econvironmental quality deteriorated evidently in recent years. The present paper explored speetral characteristics of grassland features, plant community and the corresponding spectral pattern of vegetation succession during the process of degradation. The result showed that the difference in spectral features of Kobresia littledalei, Stipa purpurea, Kobresia pygrnaea and Potentilla fruticosa, as main vegetation types of alpine meadow, alpine steppe and brush- wood, mainly occurred in the position and shape of red edge, chlorophyll absorption feature and cellulose absorption features. During the proeess of degradation, reflectance values decreased gradually and spectral features of soil background appeared with deterioration of chlorophyll absorption and water absorption features. Vegetation indices capturing features of Chlorophyll absorption and red edge ean be used to monitor grassland degradation.