生态建设对陕北植被变化的影响分析

Effects of ecological building on the vegetation change in Northern Shaanxi Province

运用趋势分析法及相关系数检验法,分析了陕北大规模生态建设工程实施以来植被NDVI变化趋势,检验了NDVI变化与降雨量、温度以及造林面积之间的关系。结果表明:陕北大部分地区植被明显转好(通过α=0.05检验),尤其是丘陵沟壑农耕区植被改善最为显著,12 a间NDVI净增0.123 3,提高24.90%,南部森林植被区,NDVI净增最低,只有0.045 0,增加率5.56%。NDVI变化格局与生态退耕格局在空间上呈现高度吻合的特征。NDVI变化与降雨量和温度没有显著的回归关系(R2<0.15),但与造林率(造林面积占县土地面积的比)回归关系显著(R2=0.560 8),说明降雨量、温度变化对陕北NDVI变化没有明显的影响,而以退耕和植树造林为主的生态建设才是导致NDVI变化的主导因素。结论认为过去12 a的生态建设明显促进了陕北植被的恢复,改善了区域环境状况。

This paper analyzed the trend of vegetation variation and its influencing factors in Northern Shaanxi Province, China since the implementation of the ecological building in 1999, based on NDVI （MODIS 13Q1 ）, me- teorological and statistical data. Correlation analysis and SLOPE approaches were used to detect the trend and to estimate amplitude of NDVI changes, and a regression method was used to analyze the relationship between NDVI change and rainfall, temperature and afforestation area. ArcGIS was used to map the spatial variation of the NDVI and its change trend. The results showed that in most parts of Northern Shaanxi, i.e. 72.58% of the total area, the vegetation was obviously improved during 2000-2011, in terms of NDVI changes at the 0.05 significance level. This improvement was most evident in the hilly and gully loess area, the key implementation area of the ecological build- ing. In 27.18% of the study area,the NDVI had no significant change during the period,which mainly included for- est vegetation in southern Ziwu and Huanglong Mountain areas, and a small part of grassland in Yulin and Dingbian. In a small area （0.24%） of the region,the NDVI showed an apparent decline trend,due to the land converted to ur- ban and mining ＆ industry land use. Among regions covered with different vegetation types, the region formerly cul- tivated for growing crops had most evident increase in the NDVI, increasing by 24.90% （0.122 3）, with the ampli- tude （SLOPE value） of 0.014 3 during 2000-2011. The area covered by grass vegetation also had an apparent in- crease,increased by 23.15% （0.101 4） in NDVI with the SLOPE value of 0.011 8. The lowest increase appeared in the area covered by forest vegetation, where the NDVI increased only 5.56% （0.045 0） and the SLOPE value was 0.005 0. In the shrub and desert regions, the NDVI increased 10.48% （0.074 5） and 14.84% （0.068 3）, re- spectively. Two representative regions were selected, i.e. Yan＇ an City with significant NDVI changes, and Dingbian County with non-significant NDVI changes, and conducted regression analyses to check possible effects of rainfall and temperature changes on the NDVI variation. It was found that the annual NDVI values were not correlated with the annual precipitation and temperature （ R2〈 0.15） during 2000-2011. But regression analyses between changes in the mean regional NDVI and afforestation area for 25 counties in the study area, revealed a significant correlation （ R2= 0.561 ）. These regression results illustrated that the ecological building typified by returning the sloping farmland to foresfland/grassland was the main factor affecting the NDVI change during 2000-2011 in north- ern Shaanxi Province, while precipitation and temperature had no or only a minor contribution to the change. In gen- eral, the spatial NDVI variation was in accordance with the distribution of the afforestation. It can be concluded that the ecological building implemented in 1999 have been an apparent positive effect on the environment, which greatly promoted the vegetation restoration in Northern Shaanxi Province.