陕北退耕还林区植被NPP时空变化及其驱动因子

为了给陕北退耕还林区植被生产力评价及退耕还林等生态工程完成情况的评估提供科学依据，笔者应用美国蒙大拿大学提供的净初级生产力(NPP)产品 (MOD17A3)，利用ArcGIS软件进行统计分析，研究区分NPP与气候因素（年降水量、年均气温）和土地利用类型转变的关系。结果表明：陕北退耕还林区植被NPP呈现南部高北部低的明显特征，2000—2013年植被NPP均值大部分区域在150~ 300 g C/(m²·a)之间，均值为134.23 g C/(m²·a)；植被NPP年际变化除无植被覆盖区域，其他地区均为增加趋势；植被NPP与气候因子相关系数均表现为正相关与负相关并存，大部分地区NPP与降水量的相关性较强，与平均气温相关性总体没有与降水量相关性明显，且均有极小部分地区通过α＜0.05显著性检验；土地覆被的改变对该区域植被NPP的变化起着显著的推动作用。

Temporal and Spatial Variation of Vegetation Net Primary Productivity and Its Driving Factors in Reforestation Zone of Northern Shaanxi

The paper aims to scientifically evaluate the vegetation productivity and implement relevant ecological projects of reforestation in northern Shaanxi. A quantitative analysis was carried out on the temporal and spatial distribution and variation characteristics of NPP and their relationships with the climate factors and human activity in this area, based on 2000-2013 annual net primary productivity (NPP) data from MOD17A3 dataset and land use classification data and meteorological data. The results showed that: in the study area, the annual NPP ranged from 150 gC/(m²·a) to 300 gC/(m²·a) during 2000-2013, with an average of 134.23 gC/(m²·a); the average annual NPP was higher in the south and lower in the north. The overall annual NPP showed an increasing trend in the study area except that with zero vegetation coverage. The correlation of NPP with climate factors showed both positive and negative side, a majority of which was found to have a significantly positive correlation with precipitation, but the correlation with average temperature was less significant. A tiny part of NPP passed the test of significance (α＜0.05) in both correlation studies. The land cover change dramatically impacted vegetation NPP evolution, which suggested that closing hill for forestation and restoring farmland into forestland improved the vegetation.