青藏高原高寒草地净初级生产力(NPP)时空分异

基于1982-2009 年间的遥感数据和野外台站生态实测数据,利用遥感生产力模型(CASA模型) 估算青藏高原高寒草地植被净初级生产力(NPP),分别从地带属性(自然地带、海拔高程、经纬度)、流域、行政区域(县级) 等方面对其时空变化过程进行分析,阐述了1982 年以来青藏高原高寒草地植被NPP的时空格局与变化特征。结果表明:① 青藏高原高寒草地NPP多年均值的空间分布表现为由东南向西北逐渐递减;1982-2009 年间,青藏高原高寒草地的年均总NPP为177.2×10¹² gC·yr^-1,单位面积年均植被NPP为120.8 gC·m^-2yr^-1;② 研究时段内,青藏高原高寒草地年均NPP 在112.6~129.9 gC·m^-2yr^-1 间,呈波动上升的趋势,增幅为13.3%;NPP 增加的草地占草地总面积的32.56%、减少的占5.55%;③ 青藏高原多数自然地带内的NPP呈增加趋势,仅阿里山地半荒漠、荒漠地带NPP呈轻微减低趋势,其中高寒灌丛草甸地带和草原地带的NPP增长幅度明显大于高寒荒漠地带;年均NPP增加面积比随着海拔升高呈现"升高—稳定—降低"的特点,而降低面积比则呈现"降低—稳定—升高"的特征;④ 各主要流域草地年均植被NPP均呈现增长趋势,其中黄河流域增长趋势显著且增幅最大。植被NPP和盖度及生长季时空变化显示,青藏高原高寒草地生态系统健康状况总体改善局部恶化。

Spatial and temporal variability in the net primary production (NPP) of alpine grassland on Tibetan Plateau from 1982 to 2009

Using NOAA AVHRR NDVI data (8 km spatial resolution) from 1982-2000, as well as SPOT VGT data (1 km spatial resolution) and observation data from 1998-2009, the CASA model was applied to analyze the spatial-temporal characteristics of alpine grassland NPP change on the Tibetan Plateau (TP). This study will help to evaluate the health status of the alpine grassland ecosystem and is of great importance to studies on sustainable development of pasture on the plateau, as well as to research on the national ecological security shelter function of the Tibetan Plateau. Spatial statistical analysis is carried out based on physio-geographical zonality (natural zone, altitude, latitude and longitude), river basin, and administrative areas at a county level. Data processing was completed on an ENVI 4.8 platform while spatial analysis and mapping were completed on an ArcGIS 9.3 and ANUSPLINE platform. The analysis of the spatial-temporal pattern and change in characteristics of alpine grassland NPP showed that: (1) the alpine grassland NPP gradually decreased from southeast to northwest on the TP, which corresponded with the gradients of precipitation and temperature. The average annual total NPP in alpine grassland on the TP is 177.2×10¹² gC·yr^-1, and the average annual NPP is 120.8 gC·m^-2yr^-1, from 1982 to 2009. (2) The annual alpine grassland NPP on the TP has a fluctuating and increasing tendency, ranging from 114.7 gC·m^-2yr^-1 in 1982, to 129.9 gC·m^-2yr^-1 in 2009, with a 13.3% increase; the alpine grassland showing a significantly increasing tendency of NPP is above 32% of the total, while the alpine grassland that shows a remarkably decreased tendency of NPP is 5.55%. (3) A notable change of annual NPP existed in alpine grassland: (a) NPP increased in most of the natural zones on the TP, and showed a slightly decreasing trend, except for the Ngari montane desert-steppe and desert zone, where the increasing tendency of NPP was stronger in a high-cold shrub-meadow zone, high-cold meadow steppe zone and high-cold steppe zone, than that in the high-cold desert zone; (b) The vertical variations in annual NPP are significantly different, including an "increasing-steady-decreasing" trend in area percentage with a significant increase and a "decreasing-steady-increasing" trend with a significant decrease, as altitude rises; (c) The variations of annual NPP in latitude and longitude have a relationship with the vegetation distribution. The variations in annual NPP in basins present a growing tendency, with the Yellow River Basin being the most remarkable. The relationship between NPP and vegetation coverage suggests that there was a benign trend in the quality of alpine meadow ecosystem and significant regional differences on the TP.