还林还草工程后榆林市NDVI时空变化趋势

NDVI spatiotemporal variation in Yulin after grain for green project

还林还草工程实施以来,黄土高原植被得到了有效恢复。为了研究黄土高原地区的植被变化特征和未来发展趋势,利用趋势分析、标准差分析、Hurst指数等方法对榆林市2000—2017年MODIS NDVI(Normalized Difference Vegetation Index)进行了分析。结果表明:18年来榆林市NDVI累计增长88.56%,年均增长率为4.92%;耕地、林地、草地和沙化土地上的NDVI均明显增加;随着时间的推移,不同高程和坡度下的NDVI增长迅速;NDVI和降水表现出显著正向相关;农产品在产量、牛羊存栏数、还林还草总面积与NDVI呈显著正相关,表明农业生产转型升级后,生态环境治理和农村经济达到了协调发展。Hurst指数预测结果表明,该地区目前还林还草工程已接近其承载潜力,但NDVI还有约10%的增长潜力,在未来极度干旱的年份,植被有干旱致死的威胁,NDVI存在减少的风险,主要集中在目前NDVI恢复较好的丘陵沟壑地区。在后退耕还林时代,水土资源的合理配置与植被建设相协调是实现该地区生态建设的重要任务。

Since the start of returning cropland to forest and grassland project,vegetation in the Loess Plateau has grown rapidly.To clarify the vegetation variation and change trends in this region,trend analysis,standard deviation analysis,and Hurst index were applied to analyze the MODIS 250 m resolution NDVI in Yulin from 2000 to 2017.The NDVI was increased by 88.56%from 2000 to 2017,with an annual rate of 4.92%.The NDVI of cultivated land,woodland,grassland and unused land were all obviously increased.The NDVI in different elevations and slope ranges also increased significantly.NDVI was positively correlated with rainfall but not with temperature.Increased grain yield,the total number of domestic animals,and the total area of returning cropland to forest and grassland had a significant correlation with NDVI,suggesting that after the transformation and upgrading of agricultural production,ecological environment governance and rural economy had achieved coordinated development.According to the forecast results of Hurst index,the returning cropland to forest and grassland project in this area was close to its carrying potential,but NDVI index had about 10%growth potential.In the extreme drought years of future,vegetation would experience the threat of drought-induced death and the risk of NDVI index reduction,mainly concentrated in the hilly and gully areas with better NDVI recovery.In the period of after returning cropland to forest and grassland,it is an important task to coordinate the rational allocation of soil and water resources for realizing ecological construction in this area.