Effects of long-term and large-scale ecology projects on forest dynamics in Yangtze River Basin, China

To mitigate the ecological degradation in the Yangtze River Basin (YRB), a series of large-scale and long-standing ecology projects have been implemented. However, the long-term effects of the ecology projects on forest dynamics remain unclear. Here we investigated the spatiotemporal dynamics of forest growth and forest landscape in the YRB from 1982 to 2015. Effects of the ecology projects on the forest dynamics were analyzed by a two-step methodology. Firstly, two types of forest, Type I (affected by the ecology projects only) and Type II (by both climate change and the ecology projects), were distinguished by the correlation analysis between the Normalized Difference Vegetation Index (NDVI) and climate factors during 1982-1999. To calculate effects of the ecology projects on forest growth, regression analysis and residual trends method were then applied to test the effects of the growing-season NDVI (GSN) on growth of Type I and Type II forests, respectively. We found that during 1982-2015 the GSN increased significantly with an annual change rate of 0.001. The effects of ecology projects on forest growth dynamics exhibited high spatial heterogeneity. On one hand, the ecology projects induced forest restoration areas, which accounted for 34.57% and were mainly distributed in the middle and lower reaches of YRB. On the other hand, 12.07% of forest areas degenerated, which mainly located in the high mountains of YRB. The degraded forests might relate to the cascading effect of ecology projects rather than their implementations. Therefore, we suggest that such cascading effects should not be ignored and should be further investigated. Finally, since that the ecology projects were positive in increasing forest area but not in decreasing forest fragmentation, we concluded that the ecology projects may not profoundly change the forest landscape dynamics. Our findings are of potential in adjusting ecological conservation policies and achieving better ecological effectiveness.