Precision and accuracy of tree-ring-based death dates of mountain pines in the Swiss National Park.

摘要

The time of tree death is commonly reconstructed by dating the outermost ring of tree-ring series. However, due to the occurrence of partial cambial mortality, the date of the outermost tree ring may vary between different locations on the tree stem. Furthermore, a tree may continue to live following the formation of the most recent tree ring. In this study, we quantified precision and accuracy of tree-ring-based death dates from 229 dead mountain pines (Pinus montana) from a 28 km2 study area in the Swiss National Park. For almost two-thirds of the trees, a maximum difference of just 0-4 years between the dates of cambial mortality from three increment cores was observed, however, for a few trees the difference reached 30-65 years. Higher maximum differences between the dates of cambial mortality are expected for trees on steep slopes, for old trees or for trees that died a long time ago. For 84% of dead mountain pines, which were sampled in a permanent sample plot with 2-year remeasurement intervals, the difference between the date of observed crown mortality and the death date determined from three cores was 0-5 years. Sampling two or just one core per tree decreases the accuracy of tree-ring-based death dates. Based on the findings of our study, we recommend a prior assessment of the precision and accuracy of tree-ring-based death dates for any dendroecological study dealing with the reconstruction of tree mortality.