Climate change and tree-ring relationships of Nothofagus menziesii tree-line forests

To assess the sensitivity of New Zealand tree lines to climate warming, we compared the tree-ring growth characteristics and temperature relationships of silver beech (Nothofagus menziesii (Hook. f.) Oerst) at two elevations, ca. 1200 m (tree line) and ca. 1100 m. Modelled relationships between clim ate series and tree rings indicated that the main climatic control on tree growth was current summer temperatures. Nevertheless, temperatures during e arlier seasons can influence tree growth, pointing to a complex relationshi p between radial growth and climate at tree line. Overall, the similarity i n the growth-temperature relationships for trees at both elevations indicat ed that high-altitude N. menziesii forests should be useful for examining t he impact of climate warming on tree growth. However, the level of common g rowth variation was greater in the below tree line chronologies, suggesting that other factors, including natural disturbance, may affect or compete w ith the influence of temperature on tree-ring growth at tree line. Despite the importance of summer temperatures for tree growth at or near tree line and the reported increase in summer temperatures since 1950 in New Zealand, ring widths have not increased in recent decades. We conclude, therefore, that in these N. menziesii tree-line forests there has been no detectable t ree-ring growth response to climate warming.