汉江流域植被净初级生产力时空格局及成因

运用MOD17A3-NPP等数据,分析汉江流域植被NPP的时空格局及其形成演变机理,为区域生态环境管治提供科学理论依据。运用GIS空间分析法、线性拟合法研究流域NPP的时空格局,结合相关系数法、土地利用程度指数等方法探析成因。结果显示:(1)汉江流域植被NPP多年平均值为439 g C m~(-2)a~(-1),整体呈微小的波动上升趋势,年增长幅度为3.11 g C m~(-2)a~(-1)。植被NPP集中分布在300—600 g C m~(-2)a~(-1),占全域面积的83.65%。(2)从流域空间上看,多年平均NPP呈上游中游下游,各子流域内部差异呈上游中游下游。高值区集中分布在汉中,十堰、襄樊和荆门平均NPP呈下降趋势的所占面积最大。(3)垂直景观上植被NPP的空间分布往往受水热综合作用的影响,汉江流域降水是植被NPP累积的主要制约因素。(4)垂直方向上NPP呈规律性变化:高程上表现为"陡升-下降-缓升-陡降,坡向上为阳坡半阳坡半阴坡阴坡。(5)浅山丘陵区NPP变化主要受土地利用方式的影响,高山区NPP变化受气候变化的影响。汉江流域植被NPP稳定,中下游平原区植被NPP略有下降;气候和地形特征决定了植被NPP的空间分布特征,气候变化和人类活动对植被NPP的变化有重要影响。

Spatiotemporal pattern of net primary productivity in the Hanjiang River Basin

For the Hanjiang River Basin, we studied the spatiotemporal pattern of net primary productivity (NPP) based on MOD17A3-NPP (Modis NPP is part of the NASA Earth Observation System project) data, and the factors affecting the pattern, in order to provide a scientific basis for eco-environmental improvements and management of land. The GIS spatial analysis method, linear fitting method, and variation coefficient method were used to study the spatiotemporal pattern of NPP; the correlation coefficient method, land use degree index, and dynamic degree index of land use were used to analyze the factors affecting the spatiotemporal pattern. The results showed:(1) The multi-year average NPP in Hanjiang River Basin was 439 gC m^-2 a^-1. NPP was high in the northwest and low in the northeast, higher in the south than in the north, and slightly higher in the middle region like a armchair, opening to the southeast. In general, annual growth increased at a rate of 3.11gC m^-2 a^-1, NPP ranged from 300 to 600 gC m^-2 a^-1, and 83.65% of the total area accounted for the NPP. High NPP was recorded for Hanzhong city. (2) The multi-year average NPP was the lowest in the upstream region, followed by the middle region, and then the downstream region, whereas the reverse trend was noted for the diversity of NPP. Because the upper reaches of the basin is mainly mountainous, there were obvious vegetation differences between the different vertical zones and therefore there were more complex and diverse vegetation type, and considerable spatial differentiation of vegetation NPP for this region. Maximum NPP was noted in Hanzhong. The largest area (Shiyan, Xiangfan, and Jingmen) had a decreasing trend for average NPP. (3) Due to the nonlinear change in climatic conditions of vertical landscapes, the spatial distribution of NPP is usually affected by the reallocation of hydro-thermal combination in vertical landscapes. In the Hanjiang River Basin, precipitation is the main factor of affecting NPP. (4) Vertical variation in NPP was also observed:from the perspective of elevation, NPP is steeply rising first and then falling, then slightly rising and steeply dropping again; from the perspective of slope, NPP is sharply increasing first and then slowly decreasing, then slowly increasing and steeply decreasing again; according to the slope aspects, NPP in sunny slope is highest, NPP in shady slope is lowest and NPP in semi sunny slope is higher than semi shady slope. Topography is the main factor affecting the vertical variation in NPP. (5) NPP was evidently decreased in hilly regions and in region with slopes less than 5°,which was mainly because of land use patterns and human activity. Soil and water loss areas also had decreased NPP, which was mainly related to the terrain and the heavy precipitation in the mountainous region. In conclusion, NPP in Hanjiang River Basin is stable, NPP in the middle and lower reaches of the basin are slightly decreasing in the flat and hilly regions and NPP is decreasing in low and mid-low mountains. Climate and topographic features determines the spatial distribution of NPP, and climate changes and human activities have an important role in affecting vegetation NPP.