Satellite measures indicate an overall greening of northern forest ecosystems between the early 1980s and the late 1990s. This greening, which indicates higher rates of tree growth, is consistent with rising temperatures, which may be caused by atmospheric increases in greenhouse gases. To validate these findings, this research project will compare satellite-based estimates of increasing growth and greening to tree-ring records from selected sites across the circumpolar zone of northern forests. Satellite data will be summarized using a standard measure of greenness in vegetation: the Normalized-Difference Vegetation Index (NDVI). The following questions will be investigated: 1. How are tree rings related to NDVI? 2. Can tree rings be used to validate intra and interannual variability in NDVI? 3. Can tree rings be used to validate trends in NDVI? 4. Do tree-ring and NDVI indices provide distinct information which, when combined, improve our understanding of biospheric activity? 5. Is there any evidence that increases in the atmospheric concentration of carbon dioxide have directly enhanced the growth of forests north of 40oN? This project will increase understanding of the complex links between global change and ecosystem function and process. Satellite and other observations of the earth system are accumulating rapidly, but the interrelations are exceedingly complex and it is essential that their interpretation include a ground data perspective. The validation of NDVI estimates of forest biomass sinks using ground measurements from tree rings can eventually aid nations concerned with meeting commitments for the Kyoto Protocol. This project will be multidisciplinary in that it will bring together members of the ecosystems/paleoclimate community, involved in ground measurement analysis of vegetation, and the remote sensing community, involved in the processing and interpretation of satellite measurements. It is anticipated that the synergy of this integrated approach will significantly improve understanding of terrestrial biospheric activity for northern latitudes and for the globe.
