Inter-annual variation in vegetation index and analysis of factors affecting it in Daxing’an Mountains.

The normalized difference vegetation index (NDVI) could accurately reflect the growing status of vegetation, and it could facilitate the long-term monitoring of vegetation at regional scale. In this study we monitored and analyzed the inter-annual changes of the NDVI based on the monthly MODIS/NDVI data of Daxing’an Mountains region from 2000 to 2009. And we used trend analysis, hypothesis testing and correlation analysis to investigate the effects of various factors on the changes of the NDVI values. The results showed that the annual NDVI ranged from 0.455 4-0.509 3, with the average NDVI of 0.477 3 from 2000 to 2009. No regular trend was observed for the annual variations. In addition, the effects of the forest fire, temperature and precipitation on the NDVI were analyzed. It was found that the general forest fires had no significant impact on the variation of NDVI value, while the serious forest fires and the major forest fires with the burned area smaller than 10 000 ha promoted the growth of the NDVI value; the major forest fires with the burned area larger than 10 000 ha forest fires significantly reduced the NDVI value. The temperature between 10 and 25 ℃ promoted the NDVI value, and no significant impact on the NDVI changes was observed when the temperature was below 5 ℃. The monthly precipitation less than 75 mm promoted the NDVI value, and no obvious impacts on the NDVI changes were found when the monthly precipitation was more than 100 mm.