地形对草甸草原植被生产力分布格局的影响

草原植被生产力在陆地生态系统碳平衡分析中扮演重要角色,而地形作为影响植被生产力(NPP)分布格局的重要环境因子在已有的草原遥感监测研究中没有被充分重视。以USGS和GLCF共享MODIS和DEM数据为数据源,选取呼伦贝尔辉河湿地保护区草甸草原核心区为研究对象,在地面光谱生物量模型构建的基础上,采用ARCGIS的空间分析功能对呼伦贝尔草甸草原2000—2012年的NPP分布格局进行了分析。研究结果表明,地形对草甸草原植被生产力分布格局有显著的影响。在海拔高度、坡度和坡向等3个地形因子中,海拔高度引起的NPP变化幅度最大,坡度次之,坡向最小。在总体特征上,海拔高度每升高10m,生产力增加4.78 g/m2;坡度每增加1°生产力增加-1.42 g/m2;N坡向植被生产力水平最高(184.8 g/m2),西南(SW)坡向最低(173.3 g/m2)。从不同地形因子的分布面积特点判断,地形对草甸草原NPP的影响尺度介于土壤环境异质性和草场类型异质性之间。不同生产力水平年份对生产力分布格局的影响趋势一致,但变化幅度不同,在中等生产力水平年份NPP变幅最大。

Impact of topography on the spatial distribution pattern of net primary productivity in a meadow

Net primary productivity (NPP) of grassland plays an important role in terrestrial ecosystems, and its spatial heterogeneous traits have significant influence upon regional carbon cycle, grazing capacity, soil erosion, and ecosystem safety assessment. How topography, one of significant environmental factors, affects grassland productivity is not well addressed in the remote sensing of grassland ecosystems. This paper selected a protected meadow of the National Natural Reserve of Huihe wetland, used USGS EOS-MODIS/Terra NDVI data and GLCF DEM data, and adopted spatial analysis function of ARCGIS to analyze the NPP distribution pattern form 2000 to 2012 in Hulunbuir meadow based on the ground spectrum biomass model, topographical controlling factors, and yearly precipitation classification. The results showed that the ground spectrum biomass model can be used to assess meadow productivity, and the most suitable model is y =15.968e^3.5434x (Sig=0.000) for predicting Hulunbuir meadow productivity in regional scale (where y and x represent productivity and NDVI, respectively). Simulated results confirmed that topography had a remarkable impact on meadow productivity distribution pattern. Consequently, among three topographical factors of altitude, slope and aspect, altitude gave rise to the most significant changes, the effect of the slope was intermediate, and the aspect played a minimal effect. Firstly, under the conditions of the slope of 0-2 degrees and aspect of NE, NPP increased 0.478 g/m² per meter rising of elevation in normal yearly precipitation level; 0.414 g/m² in lower yearly precipitation level; 0.482 g/m² in moderate yearly precipitation level; and 0.525 g/m² in higher yearly precipitation level, respectively. Secondly, under the conditions of altitude of 760-780 m and aspect of NE, the meadow productivity decreased 0.142 g/m² per degree increase of slope in the normal yearly precipitation level, and decreased 0.161 g/m² in the lower yearly precipitation level, 0.135 g/m² in the moderate yearly precipitation level, 0.133 g/m² in the higher yearly precipitation level, respectively. Thirdly, under the conditions of the altitude of 760-780 m and the slope of 0-2 degrees, the highest NPP (184.6 g/m²) occurred on the N aspect and the lowest NPP (173.3 g/m²) on the W aspect, respectively. The NPP was lower on the SW aspect in the lower yearly precipitation level and on the W aspect in the moderate yearly precipitation level. By contrast, lower NPP occupied on the SE aspect in the higher yearly precipitation level. According to NPP distribution area, the topographical factors had higher (lower) effect on NPP of the meadow than soil heterogeneity (grassland type) on spatial scale. The trend of this effect did not vary across years with various NPP but differed in effect degree, being higher in the years with intermediate NPP.