Model-based analysis on the relationship between production and tree-ring growth in Japanese conifer-hardwood mixed forests

Abstract:

Forest productivity is a basic and important component of terrestrial material flow and its importance increases according to recent climate warming and the increase in atmospheric–CO₂ concentrations. Forest productivity study progresses through measurement by eddy-covariance data from flux tower and prediction by terrestrial ecosystem models. However, flux tower observation has spatiotemporal bias and limitation. On the other hand, tree-ring data have a close connection with forest ecosystem productivity. Compared to flux tower observation, we can collect tree-ring data from a larger number of sites and longer time scales. Comparisons between tree-ring observation and model-estimated productivity is important to reveal underlying mechanisms of forest ecosystem productivity and growth in wide spatiotemporal scale. This study aimed at revealing the relationship between temporal changes in tree-ring data and estimated forest ecosystem productivity in Japanese conifer-hardwood mixed forest. We also addressed climatic bias in the relationship by comparing between sites at different climatic conditions. Tree-ring data of Sakhalin spruce (Picea glehnii) were obtained from the International Tree Ring Data Bank. Six sites on the Hokkaido island (northern island of Japan) were selected for the present analysis. The Vegetation Integrated SImulator for Trace gasses (VISIT) model was validated by comparing with carbon flux data from Asia flux network sites. Past climatic parameters were obtained from ERA-20C reanalysis data from the European Center for Medium-range Weather Forecasts. Correlation between basal area increment and net ecosystem productivity was highest in the coldest site but this correlation weakened in warmer sites. This result implies that long-term growth trend was mainly restricted by cold stress associated with productivity reduction in colder sites but this factor is less important and other factors exert influence in warmer sites.