Contributions Of Climate Change And Human Activities To Vegetation Dynamics Of Loess Plateau

Vegetation is an important component of terrestrial ecosystem, vegetation cover indicates the quality of ecosystem structure and function. The factors affecting vegetation growth are quite complex, climate and human activity are the most major factors. Loess Plateau’s ecological environment is fragile, soil has been seriously eroded, exploring the changes in vegetation cover and the driving mechanism is great significant for guiding the vegetation restoration project in the future. Based on NOAA/AVHRR-NDVI time series data and climate data(precipitation, temperature) set from1982to2006, this study analyzed the trends and spatial variation of changes in vegetation cover, precipitation and temperature in the Loess Plateau, explored the relationship between vegetation cover and climatic, then made up the defect that underestimate the impact of human activities of the RESTREND that is a mainstream approach used to distinguish the effect of climatic factor and human activity on vegetation cover in arid and semi arid areas, established the vegetation response to climate change model, then got the improved RESTREND, used this method to assess the contribution rate of climatic and human factors in the Loess Plateau vegetation cover change The main conclusions as follow:(1) Loess Plateau vegetation NDVI value had increasing trend from1982to2006, meanwhile showed great spatial heterogeneity from north to south, from west to east.(2) Vegetation of the Loess Plateau had weakly overall upward trend of vegetation cover had been restored and improved from1982to2006. Trend of NDVI was not the same in different periods.(3) Loess Plateau1982-2006total precipitation has decreased every year overall, but its trend was not significant, precipitation from southeast to northwest, southeast and rainy northwest arid, mountainous precipitation greater than the plains. Loess Plateau vegetation cover were positively correlated with overall rainfall in some areas of negative correlation.(4) Loess Plateau warming trend evident1982-2006, heat up significantly, there were differences in the rate of warming space. Temperatures with no obvious correlation of NDVI values, the overall negative correlation, indicated that the temperature was not limiting vegetation growth factor.(5) Vegetation response to climate change models created with trend analysis based on improved residuals derived vegetation cover change was the main driving factors of human activity, its contribution was86%, the dominant climate factors was weak. Overall vegetation cover in the Loess Plateau showed an increasing trend, indicating a positive effect of returning farmland to forest restoration project was gradually rendering. (6) Improved residual trend method residuals trend method compared to human activities have a stronger ability to identify trends make up the RESTREND to underestimate the contribution of human activity, climatic factors overestimate the contribution rate of defects. Using high-resolution affect the same area at different times,can effectively improve the residual trend method validation results, and thus illustrate the trend to improve the residual method has higher reliability and applicability.