Spatial and Temporal Trends in terrestrial Ecosystems Net primary Production: A Model-Data Comparison

Abstract:

The net primary productivity (NPP) is commonly used for understanding the dynamics of terrestrial ecosystems and their role in carbon cycle. The global NPP, highly variable over space and time, cannot be directly observed; however, satellite based observations of Normalized Difference Vegetation Index (NDVI) are used as a proxy to understand and monitor the NPP dynamics. In this study, we used a combination of most recent NDVI dataset and modeled NPP (from TRENDY project) for the period 1982-2012, to study the role of terrestrial ecosystems in carbon cycle under the prevailing climate conditions. We found that 67% and 80% of the global land showed positive NDVI and NPP values, respectively, for this period. The global spatial trends of NPP and NDVI were consistent, and in general agreement; however, this consistency was more prominent regionally in Western Europe, Eurasia, Sahel region of Africa, India, and China. Generally, on temporal scale, both global NPP and NDVI showed a corresponding pattern of increase (decrease) for the duration of this study except, for few years (e.g. 1990 and 1995-98). Northern hemisphere showed higher NDVI and NPP increasing trends over time compared to Southern hemisphere. Overall, the results of this study suggest that NDVI was able to capture the broader pattern of vegetation production as estimated by the ecosystem models. This pattern was stronger in temperate and boreal regions compared to tropical and extra tropical regions.