Small does not mean young: Age estimation of severely browsed trees in anthropogenic Mediterranean landscapes

The knowledge of the age of individual trees and of population age structure is of great importance for conservation purposes. In Mediterranean areas, however, trees are rarely used for dendroecological studies as ring growth is strongly perturbed by browsing and other disturbances. This study focused on the Tertiary relict tree species Zelkova abelicea (Ulmaceae) endemic to the mountains of Crete (Greece) and searched for new approaches to estimate the age of threatened trees in severely browsed populations. Our results demonstrate that dwarfed Z. abelicea trees can attain ages >500 yr and that such individuals often surpass normally growing trees of the same population in number and age. These findings significantly change the perception of population age structure in forest remnants of Mediterranean landscapes. Additionally, we show that tree age is well correlated (64%) with trunk circumference, for severely browsed dwarfed trees, however not so much (11%) for normally developed, large trees. Thus, our results can be used directly for age estimations of severely dwarfed Z. abelicea individuals in the field and the new approach can be easily reproduced for other threatened tree species affected by strong browsing pressure. Future conservation efforts and management strategies should, therefore, take into account not only normally developed trees but also severely browsed individuals and their populations.