PS 39-75 - Importance of large and old trees and natural disturbance to maintain tree-related microhabitats for temperate forests biodiversity

Abstract: Tree-related microhabitats (TreMs) are important features for the conservation of biodiversity in forest ecosystems. Protecting TreMs, is a cost-effective tool crucial for biodiversity conservation applicable to large forested landscapes. Standardized TreMs typologies have been developed to facilitate the assessment of resource availability for multiple forest taxa. Although the development of TreMs is relatively well studied in managed forests, comparative studies between managed and primary forests are rare. Primary forests benefit from increased habitat heterogeneity due to the presence of natural disturbances and structural features such as large and old trees, which may help diversify TreM profiles and which are often scarce in managed forest stands. Primary forests serve as an important baseline for ecological studies yet they are still being lost at an alarming rate therefore, quantifying drivers of TreMs profile is critical to help fast-track the conservation of diverse primary forest communities. Following the standardized typology, we surveyed 47 TreM types, structural and environmental characteristics across > 400 spruce forest plots. Using a tree-ring based approach, we investigated the effect of tree age and 300-year disturbance history, defined by disturbance timing, severity and frequency. This research aims to: i) compare the occurrence of TreMs in primary and managed forests, ii) analyze the effect of historical natural disturbances on contemporary patterns of TreMs occurrence, and iii) assess the effect of tree age and diameter on TreMs occurrence in primary forests. Our results indicate that trees in primary forests hosted a greater richness of all and specific types of TreMs than trees in managed forests. Natural forest dynamics, characterized by fluctuating disturbance intervals and variable severity levels, maintained a diverse and complex TreM profile. Moreover, trees in primary forests showed increased TreM richness with increasing age and diameter of the tree. Our findings underscore the fundamental role of natural processes in promoting conditions that maximize biodiversity potential. 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.