冻土退化过程中植被覆盖度的变化研究

在全球气候变暖的背景下,青藏高原的多年冻土出现了不断退化的现象.退化的多年冻土隔水作用减弱或消失,并导致依赖于冻结层上水的植被变化.在模拟高原多年冻土分布的基础上,分析了冻土的退化过程植被覆盖度的变化,结果表明,冻土的变化可分为3个阶段:冻土稳定段(80年代)、冻土快速退化段(90年代)和冻土缓慢退化段(最近十几年).同时,采用GIMMS(global inventory modeling and mapping studies)第3代NDVI数据(1982—2012年)分析青藏高原植被覆盖度的斜率变化特征,结果显示:在近31a来,青藏高原的植被覆盖度斜率整体上呈微弱增加趋势;植被覆盖在冻土退化的3个时段内的变化特征为:从20世纪80年代冻土相对稳定期到90年代的冻土退化期,比退化面积增大11%;近十几年来,冻土退化逐步减缓,植被退化的增幅减弱,面积比90年代增大了3%,但退化的区域更为集中.冻土退化与植被的变化机制复杂,本文的分析与发现对理解冻土对生态的影响有一定的意义.

Vegetation responses to permafrost degradation in the Qinghai-Tibetan Plateau

Due to global warming,permafrost in the Qinghai-Tibetan Plateau degenerates continuously. Permafrost degradation has weakened or even taken away the impermeable effect,leading to changes in plants on suprapermafrost water.The distribution of permafrost in the Qinghai-Tibetan Plateau was simulated,and changes in vegetation coverage during permafrost degradation were analyzed.Permafrost changes could be divided into three phases:stabilization (1980s),fast degradation (1990s),slow degradation (last decade). Variation in slope coefficient of vegetation coverage in the Qinghai-Tibetan Plateau was analyzed with 3rd NDVI data (1982—2012)of GIMMS (global inventory monitoring and modeling studies).Slope coefficient of vegetation coverage in the Qinghai-Tibetan Plateau was found to increase slightly in the last 31 years.The area with increased coverage occupies 57% of the entire region,except for the degradation trend in southeast or in Qaida basin.Variation in vegetation coverage in 3 phases of permafrost degradation is as follows.In the 1980s, permafrost was relatively steady,only 30% of vegetation was in degraded state.Forty one percent (41%)of vegetation coverage (11% more than that in the 1980s)is in degraded state,when temperature increased universally and permafrost depredated in large scale in the 1990s.In the recent decade,permafrost degradation has gradually slowed down.The spread of vegetation degradation has also weakened,with an area of 3% more than in the 1990s,the areas have also become more concentrated.The mechanism of change in permafrost and vegetation degradation is complicated.Analysis and discovery in this study are significance for understanding permafrost impact on ecological system.