Materials

Abstract

Knowledge about tree age is critical to forestry, nature conservation and ecological studies. Direct age determination of large diameter trees through increment cores is complicated by various obstacles, primarily because of rot and insufficient borer length. Here, we aim to (1) test the accuracy of various methods (tree-ring width, basal area increment, age-size relationship) for tree age estimation, (2) select the most accurate approach and (3) enable age estimation of large individuals of Quercus robur. This was done through increment cores collected in an alluvial forest in the Czech Republic. We achieved 75 age estimates for each tree, including our novel approach, which reduces the effect of decreasing tree-ring width and increasing basal area increment during tree life. The extrapolation of mean ring width to missing radius generally overestimates the number of missing rings (by up to 27.5% of actual age) and the level of overestimation increases with decreasing partial core length, while the application of basal area increment largely underestimates the age estimation (by up to 20.5%). Thus, to eliminate the over- and underestimation caused by natural tree ring width decrease and basal area increase during the tree senescence and increasing size, we averaged the number of estimated rings by these two methods. This technique obtained the most reliable age estimates, with an error up to 3.5%. Thus it is suggested here that this technique provides a relatively accurate age estimate for trees where it is impossible to directly determine the age; at least for light-demanding species. Moreover, the proposed technique does not require complicated analysis and is not time consuming. However, future research should test the applicability of this technique for tree species with various ecological strategies, i.e. shade-tolerant species. Finally, we estimate that the age of large oaks in our study area does not exceed 400 years. Due to such fast growth, it is possible to keep the continuity of these keystone structures in a given landscape and thus preserve the associated biodiversity.