Radial growth decline in Austrocedrus chilensis forests in northern Patagonia

AMOROSO, MARIANO; DANIELS, LORI; LARSON, BRUCE

Vancouver, British Columbia, Canadá

Conferencia; First American Dendrochronology Conference – AmeriDendro; 2008

Tree-Ring Lab, UBC - Tree-ring Society

The forests of Austrocedrus chilensis in northern Patagonia, Argentina suffer mortality from what is locally known as ‘‘Mal del Cipres”. The process has been referred by several authors as a type of forest decline. Symptoms of the decline at the tree level include loss of foliage and vigour followed by death and, often, a decline in radial growth.  This study is one of the first to quantify the decline in radial growth due to Mal de Cipres. We used dendrochronological techniques to study the radial growth to test the hypothesis that symptomatic living and dead trees exhibit a decline in radial growth relative to healthy trees growing in the same stand. To test this hypothesis, we sampled twelve stands where all mature trees were cored and classified as healthy, symptomatic, or dead based on their crown condition. Tree cores were statistically cross-dated using the program COFECHA and divided in two groups: 1) cores from healthy trees, and 2) cores from symptomatic and dead trees, which we used to build two master ring-width chronologies for each site. Results from six stands showed that the two chronologies had statistically significant divergent trends. Chronologies for three stands exhibited significant differences through time but converged and were not different at the end of the studied period. At three sites, differences between the chronologies were not statistically significant. At the scale of individual trees, the majority of the dead and symptomatic trees exhibited radial growth decline.  Interestingly, there were trees classified as healthy that also exhibited radial growth decline. This suggests that decrease in radial growth precedes crown dieback in some trees. Our results largely support initial studies of radial growth decline in Austrocedrus chilensis forests and clearly indicate the usefulness of dendrochronological analyses to study forest decline in northern Patagonia.