Cambial dieback in declining Austrocedrus chilensis forests in northern Patagonia

AMOROSO, MARIANO; DANIELS, LORI

Vancouver, British Columbia, Canadá

Conferencia; First American Dendrochronology Conference – AmeriDendro; 2008

Tree-Ring Lab, UBC - Tree-ring Society

Field observations and previous studies in declining Austrocedrus chilensis forests have reported the existence of an asymmetrical radial growth pattern in symptomatic trees. We studied the incidence of cambial dieback in these forests. With this purpose, we sampled twelve stands presenting symptoms of ‘Mal del Cipres’ (cypress sickness). All mature living individuals were cored and given a crown height class and a sanitary condition (healthy or symptomatic). Tree cores were cross-dated using the program COFECHA and the outer-most ring date was determined. Cambial dieback date was identified when the date of the outer-most ring date was different from the year of sampling. Out of the 811 cores sampled from trees that were living in 2005, 307 cores (38%) had an outer-most ring date prior to 2005, and the maximum value of cambial dieback corresponded to 39 years. Out of these cores, 18, 49 and 70 % of them had a cambial dieback of 1, 5 and 10 years respectively. Cambial dieback was present in both healthy and symptomatic trees. Of all trees sampled, 5.5, 13.0, 16.9 and 64.5 % of the trees corresponded to the dominant, codomimant, intermediate and suppressed height classes, respectively. For each tree, we estimated the pith date and tree age assuming (a) the outer-ring of all live trees was 2005 (e.g. ring counts) and (b) using the outer-ring determined by crossdating. Comparison of age distributions derived from (a) counted versus (b) cross-dated ring-width series resulted in modal age classes that differed by up to 30 years.  The results of this study confirm the existence of partial cambial dieback in cypress trees and reiterate the importance of crossdating when determining tree ages and reconstructing stand dynamics. On the other hand, it raises questions regarding precision when cross-dating to estimate year of death in this species.