Boreal forests and atmosphere–biosphere exchange of carbon dioxide

Abstract

The response of vegetation growth to fluctuations in climate or anthropogenic influences is an important consideration in the evaluation of the contribution of land biota to atmospheric CO₂ variations. Here we present two approaches to investigate the role of boreal forests in the global carbon cycle. First, a tracer transport model wihich incorporates the normalized-difference vegetation index (NDVI) obtained from advanced very high resolution radiometer (AVHRR) radiances was used to simulate the annual cycle of CO₂ in the atmosphere. Results indicate that the seasonal growth of the combined boreal forests of North America and Eurasia accounts for about 50% of the mean seasonal CO₂ amplitude recorded at Pt Barrow, Alaska (71^° N, 157^° W) and about 30% of the more globally representative CO₂ signal at Mauna Loa, Hawaii (20^° N, 156^° W). Second, tree-ring width data from four boreal treeline sites in northern Canada were positively correlated with Pt Barrow CO₂ drawdown (that is, maximum–minimum CO₂ concentration) for the period 1971–1982. These results suggest that large-scale changes in the growth of boreal forests may be contributing to the observed increasing trend in CO₂ amplitude. They further suggest that tree-ring data may be applicable as indices for CO₂ uptake and remote sensing estimates of photosynthetic activity.