Large and old trees have critical ecological roles, such as carbon sequestration and habitat provisioning. Despite their importance, they are in a steep decline across the globe. Thus, members of a Subprogramme 7 of the EVA4.0 project decided to quantify the potential of individual trees to host biodiversity, by developing the concept of tree-related microhabitats (TreMs). TreMs can be described as distinct, well-delineated structures occurring on living or standing dead trees, that constitute a particular and essential substrate or life site for species or species communities during at least a part of their life cycle to develop, feed, shelter, or breed. These microhabitats mainly include cavities, tree injuries, exposed wood, fungal fruiting bodies, and excrescences. Although the development of TreMs is influenced by tree diameter, species, and vitality, the relationships between tree age and TreM profile remain poorly understood.
Using a tree-ring-based approach and a large data set of 8038 trees, generalized mixed-effect models were used to differentiate the relative strength of the effects of tree age, diameter, and site characteristics on TreM richness and occurrence across some of the most intact primary temperate forests in Europe, including mixed beech and spruce forests. The study area was restricted to primary forests in the western Carpathians (Slovakia) and the southern Carpathians (Romania).
As dr. Kozák clarifies “We observed an overall increase in TreM richness on old and large trees in both forest types. The occurrence of specific TreM groups was variably related to tree age and diameter, but some TreM groups (e.g., epiphytes) had a stronger positive relationship with tree species and elevation. Although many TreM groups were positively associated with tree age and diameter, only two TreM groups in spruce stands reacted exclusively to tree age (insect galleries and exposed sapwood) without responding to diameter”.
Thus, the retention of trees for conservation purposes based on tree diameter appears to be a generally feasible approach with a rather low risk of underrepresentation of TreMs. Because greater tree age and diameter positively affected TreM development, placing a greater emphasis on conserving large trees and allowing them to reach older ages, for example, through the establishment of conservation reserves, would better maintain the continuity of TreM resources and associated biodiversity. However, this approach may be difficult due to the widespread intensification of forest management and global climate change.
The full article dedicated to the research is available here.