高山草地植被盖度对气候变暖和人类活动的响应

Responses of green fractional vegetation cover of alpine grassland to climate warming and human activities

高寒草地对气候变化和人类活动的干扰响应敏感,高寒草地植被盖度估算是了解高寒草地植被状况和评估退化草地修复效果的一个重要方法。目前,地面盖度估算的主要方法是数码照相法,其中基于多光谱照片的盖度提取是比较准确和高效的方法。本研究采用多光谱相机对疏勒河上游不同演替阶段高寒草地、围栏封育和翻耕补播草甸生长季内的植被盖度进行了观测,研究了气候变暖和人类活动干扰下高寒草地植被盖度的变化,同时对估算多光谱照片盖度的阈值法做了改进。结果表明,1)新阈值法的估算结果与真实值之间无显著差异(P=0.219),而旧阈值法与真实值之间差异极显著(P=0.001);2)处于不同演替阶段的草地类型具有不同的植被盖度,沼泽草甸最高,各草地类型盖度均在7月达到最大;3)在生产力较低的多年冻土区,围栏封育对高寒草地修复效果在短期内不明显,翻耕补播甚至会导致植被盖度进一步降低。

The alpine grassland ecosystem is sensitive to climate warming and human activities.Estimation of green fractional vegetation cover（GFVC） is important for acquiring the growing condition of vegetation and assessing the effects of restoration of degraded grassland.At present,the most popular method for estimating GFVC on the ground is to acquire it from digital pictures.This method estimates GFVC from multispectral pictures and it is relatively accurate and effective.In this study,we used the Agricultural Digital Camera（ADC） to estimate GFVC of alpine grassland on different succession stages and in those graze-banning and tillage zones over the growing season of the source region of Shule River.We improved the threshold-method for estimating GFVC by using different thresholds in different plots.Main results are as follows： 1） There is no significant difference between the results estimated from the new threshold method and real values（P=0.219）,while the results processed by the old threshold method are significantly different from real values（P=0.001）.2） Different types of grassland in different succession stages has different GFVC,and the GFVC of swamp meadow is higher than others.However,all of them reach the highest value in July.3） In the permafrost regions,where the productivity of grassland is low,effects of graze-banning is not obvious in a short term,and tillage can even further reduce the GFVC of alpine grassland.