Spatial and temporal variations of forest LAI in China during 2000-2010

Forests are crucial terrestrial ecosystems. Their leaf area index (LAI) is a key parameter determining the exchange of matter and energy between the atmosphere and the ground surface. In this study, MOD 09A1 and MCD 43A1 data were input into an inversion model based on the 4-scale geometric optical model to retrieve 8-d 500 m LAI products in China during the period 2000 to 2010. The resulting LAI product was validated using LAI measured in 6 typical areas. The spatial and temporal variations of forest LAI and its relationships with temperature and precipitation were analyzed. The results show that the accuracy of the 500 m LAI product was above 70% in the 6 typical areas, indicating the reliability of this product. From 2000 to 2010, forest LAI in northeast, north, and south central China showed increasing trends. However, forest LAI in southeast and parts of southwest China showed downward trends, mainly because of the significant decrease observed during the period 2008 to 2010. Annual mean forest LAI positively correlated with annual mean temperature (AMT) in northeastern China and negatively correlated with AMT in southwest China. It had positive correlations with annual total precipitation in central south and north China. The abnormal climate conditions in 2001 and 2009 caused forest LAI to be obviously lower than normal in regions south of the Qinling Mountains and Huaihe River. Annual mean LAI decreased by more than 1.0 in some areas.