Short-term changes in plant functional traits and understory functional diversity after logging of different intensities: a temperate fir-beech forest experiment

The concept of plant functional traits has been demonstrated to be very effective in unravelling the ecological mechanisms governing plant community response to disturbance, especially when research is focused on short-term post-disturbance vegetation dynamics. In this study, we established an experiment to quantify how logging intensity affects the trait composition and functional diversity of understory communities in fir-beech forests in the Dinaric Mountains in Slovenia. Three different silvicultural treatments were implemented: control (no logging), 50% of the growing stock removed and 100% of the growing stock removed. Vegetation surveys of vascular plants were made before (in 2012) and two years after (in 2014) logging. Changes in species traits, C-S-R plant strategies (sensu Grime) and community-level functional diversity were analysed. The importance of traits such as small and light diaspores, short life span and anemochory increased with logging intensity. Moreover, species with the ability of both sexual and vegetative reproduction, longer flowering duration and overwintering green leaves increased in abundance after logging. C-S-R strategies mainly shifted from stress-tolerators in pre-logging conditions towards a more ruderal component in post-logging stands. Logging in the short term increased functional diversity, mainly due to newly colonized species being functionally dissimilar from persistent residents. Results suggest that logging intensity strongly influences the magnitude of change in both functional composition and diversity, which also has important implications for biodiversity conservation. At the landscape scale, increasing spatial heterogeneity by creating a mosaic of forest stands subjected to different logging intensities will likely contribute to the enhancement of plant functional diversity.