The variation of vegetation productivity and its relationship to temperature and precipitation based on the GLASS-LAI of different African ecosystems from 1982 to 2013

In recent years, many studies have focused on the changes of partial or single African ecosystems and the drivers of those changes. However, focusing only on partial or single ecosystems has limited the understanding of the relationships between the vegetation and climate changes in all of the African ecosystems. In this study, the temporal trends of the satellite-derived annual mean leaf area index (GLASS-LAI) were analyzed, and the inter-annual relationships were developed between the annual mean LAI and the climate variables (precipitation and temperature) for the time period ranging from 1982 to 2013. Additionally, this study applied seasonal curves and step-wise multiple regression methods to investigate the relationships between intra-annual LAI and climate changes. It was found that the GLASS-LAI over half of Africa had shown general significant greening or browning trends during the period from 1982 to 2013. From the results of inter-annual analysis, with mean annual precipitation lower than 600 mm, the greening of the savannas and grasslands in the Sahel was found to highly correspond with the increased precipitation. In contrast, the evergreen broadleaf forests in the Gulf of Guinea and Congo Basin showed strongly positive responses to the annual temperature when the mean annual temperature was below 25 °C. In regard to the intra-annual responses, the precipitation with 1-month lags was found to be helpful for the vegetation growth, with the exception of the evergreen broadleaf. The results of this research study indicated that the different land-covers in Africa had displayed clear differences in their annual trends during the examined 32-year period and had responded differently to the inter- and intra-annual climate drivers. This difference was evident by the characteristics of the vegetation covers and the geographic distributions. Therefore, further examinations of these differences can potentially improve the understanding of the land surface-atmosphere interactions among the different African ecosystems.