SPATIAL AND TEMPORAL VARIATION IN AUSTROCEDRUS GROWTH ALONG THE FOREST-STEPPE ECOTONE IN NORTHERN PATAGONIA

Twenty new tree-ring chronologies of the conifer Austrocedrus chilensi s (D. Don) Endl. were developed to examine spatial variations in tree growth and climate near the forest-steppe ecotone in northern Patagoni a, Argentina, over the past 300 years. Correlation function analyses s howed that the growth of Austrocedrus is strongly positively correlate d with spring and early summer precipitation and negatively correlated with temperature during the current growing season. Although correlat ion and principal component analyses of the tree-ring chronologies fro m all sites indicate that the entire region shares a common climatic s ignal and tree-growth response, spatial patterns of tree growth and cl imatic variation also indicate significant intraregional differences. Comparison of annual maps of tree growth and climatic variation reveal s a complex pattern of tree-growth response to climatic variation that reflects the roles of seasonal versus annual climatic variation and s ingle versus multiple years of climatic variation. The most common pat tern consists of spatial tree-growth variations resembling seasonal pr ecipitation variations during the current growing season. For some yea rs, spatial patterns in tree growth are more related to spatial variat ions in annual than in seasonal precipitation. Additional patterns of spatial relationships between Austrocedrus growth and climate appear t o result from climatic prc conditioning during the previous year. Spat ial representation of tree growth for the long-term droughts (>5 years ) shows reduced growth throughout the entire region, but there are imp ortant geographical differences in the magnitude of the growth reducti on.