Influence of forest management on microclimate and understorey vegetation in a mixed oak forest

Forests play an essential role in the mitigation of climate change effects, by limiting temperature extremes and creating microclimatic refuges that can contrast the thermophilization of the biotic communities that live under the tree canopies. Based on recent evidence, forest microclimatic effects are especially pronounced in regions with warm macroclimate, such as the Mediterranean one. Microclimate buffering also depends on forest structure and density, both of which are, in turn, often determined by the type of silvicultural management. Recent findings also supported that the microclimatic alterations caused by wood extraction can determine, in turn, adaptive adjustments in some functional traits of understorey plants, thus also influencing ecosystem functions. Although some of the effects induced by the main forms of silvicultural management on understorey diversity and productivity in some types of broadleaf forests have been already described, their influence on the intraspecific variability of functional traits associated with microclimate changes is still not clear. We therefore started an investigation of these effects in a deciduous mixed oak forest with Quercus cerris and Q. petraea located in the valley of Mugello, in north Tuscany (Bosco ai Frati). Thanks to its homogeneous site conditions, this semi-planitial forest area represents a suitable model system to compare the effects of two contrasting management types on understory diversity, productivity and leaf functional traits of herbaceous species. To this purpose, in 2021 we installed air and soil temperature dataloggers in three high forest sites and three close coppice-with-standards sites. Forest structural variables and light availability (photosynthetic active radiation, PAR) were determined before surveying understory vegetation in four 5 x 5 m randomly selected quadrats in each of the six sites (24 quadrats). Understory aboveground productivity (dry weight of herbaceous and woody biomass) was determined in 48 0.5 x 0.5 m plots (two per quadrat). Finally, three locally abundant understorey forest specialist herbs (Physospermum cornubiense, Anemone nemorosa, Viola reichenbachiana) and two more generalist species (Lonicera caprifolium, Cruciata glabra) were selected and sampled following standard protocols to determine variation in major leaf functional traits (Leaf Area, Specific Leaf Area, Leaf Dry Matter Content). Preliminary results showed that, in the high forest plots, extreme values of temperatures were strongly mitigated, especially their maximum during the hottest period of the year (max T in August was 6°C higher in coppice stands). The coppice understory had a higher productivity, associated with higher light availability, while diversity did not show a clear trend. Species composition in the high forest plots revealed a more shade-tolerant and neutrophilic character, as well as a greater abundance of geophytes and a reduction of the small woody species, compared with the coppice stands, which were instead characterized by more numerous generalist species. Effects on leaf traits were clear, including a significant LA reduction in A. nemorosa and P. cornubiense in the coppice stands. Moreover, increasing PAR induced a decrease in the SLA of generalists, but an increase in the specialists. Building Grime triangles based on leaf traits (using the Stratefy software) we found that forest specialists and generalists were differently affected by management. In fact, forest specialists acquired a more ruderal character in the coppice stands, while generalists were less affected. Present results are still preliminary but seem to support that the coppice-with-standard management, though not reducing overall diversity and increasing understorey productivity, is less effective in buffering macroclimate warming and maintaining microclimatic refuges for forest specialist plants of mixed oak forests. If confirmed, this might help to adopt management strategies that can help to preserve the species composition, ecological profile and optimal functionality of understory communities of our increasingly threatened forests.