The relationship between productivity and tree-ring growth in boreal coniferous forests.
Guillermo Gea Izquierdo, Yves Bergeron, Jianguo Huang, Marie-Pierre Lapointe-Garant, J. Grace, Frank Berninger.
Ecosystem productivity estimated with a model calibrated with eddy-covariance data was related to tree-ring growth of two different boreal conifers along a latitudinal gradient. The relationship between ecosystem productivity and growth changed with species and site. Greater photosynthesis in spring and summer increased annual anomalies of radial growth in both species, and the response of growth to productivity was earlier in warmer southern stands particularly for pine. Radial growth of jack pine increased in the long-term with higher productivity, whereas this relationship was more reduced in black spruce. This could express species-specific differences in carbon allocation strategies but likely it is a consequence of the limiting marginal soils where spruce is found in the south. Only tree-rings of jack pine at some sites showed certain potential as direct proxies for ecosystem productivity at the low and high-frequency responses. Introduction Climate warming and the increase in atmos-pheric-CO 2 concentrations cause changes in forest growth and ecosystem productivity. There are reports of contrasting growth responses to warming over recent decades in different types of forests. Although some boreal species show negative growth trends in response to recent climate change (Hoofgaard et al. 1999, D'Arrigo et al. 2004), net ecosystem productivity in boreal and temperate conditions is generally expected to increase with increasing temperatures (Myneni et al. 1997, Boisvenue and Running 2006). Forest growth measurements and models assume that there is a close connection between the stem