Dating uprooted trees: comparison and application of eight methods in a boreal forest

Abstract

Eight different methods for dating the fall of uprooted trees were used in a boreal spruce forest in northern Sweden: (i) cross dating, (ii) growth release, (iii) initial growth, (iv) tree regeneration on the fallen log, (v) tree regeneration in the pit, (vi) fell scar, (vii) reaction wood, and (viii) stage of decay. First, we calibrated the cross-dating method on tree falls of known age. Then, to evaluate the limitations of the remaining methods, all methods were used on 23 tree falls of unknown age where the results of cross dating were known to be reliable. Finally, 12 tree falls of unknown age, where cross dating was hard to conduct, were dated using all methods. Most methods gave only the minimum possible age. Cross dating and growth release were the only methods that gave exact-year results (i.e., the calendar year when the tree fall supposedly occurred). All methods contributed to the dating in at least some cases. Fewer methods gave valuable information in each old (> 50 years) uprooting than in each recent (< 50 years) one. For recent uprootings, cross dating always gave best obtainable results, but for older tree falls, no method was generally superior. The simultaneous use of several methods is recommended, especially for older tree falls.