Microclimate variation and recovery time in managed and old-growth temperate forests

Abstract

Microclimate is a key driver of forest dynamics and shapes the response of forest organisms to global warming. The spatial and temporal variability of microclimate is strongly affected by forest management, so it is important to know how microclimate varies along successional gradients of managed forests, and how microclimatic dynamics in managed forests differ from those in old-growth forests.We measured forest understorey microclimate along successional gradients in regularly harvested forests and old-growth beech forests affected only by natural disturbances in the Western Carpathians (Central Europe) over a period of three years. We analysed how temperature and vapour pressure deficit (VPD) depended on forest structure and stand age, and how microclimate of managed stands differed from natural old-growth forests.Across forest landscapes we found that microclimatic conditions in managed forests were much more variable than in old-growth forests. Threshold analysis indicated that it takes approximately 54 years after clearing for microclimate to recover to conditions typical of old-growth and mature managed stands.Current forest management cycles create a microclimate landscape that is more dynamic in both space and time than the conditions to which many forest organisms are adapted in old-growth temperate forests in Europe. Adopting a harvesting approach inspired by temporal dynamics of old-growth forests, such as small-scale clearings with remnant trees providing microclimate refugia, is a suitable strategy for climate smart forestry to maintain microclimate buffering in managed forests. By increasing thermal habitat continuity, such options may help integrate biodiversity conservation targets into forest management programmes under climate change.