Abstract
Questions: How do the microecological conditions and the composition of the plant communities change in relation to the canopy projection of solitary trees? Do the microenvironmental conditions beneath the canopies of solitary trees alter taxonomic and functional diversities by favouring species with trait values related to shade-tolerant strategies? Do these microenvironmental conditions specifically promote the establishment and abundance of woody species beneath solitary tree canopies?
Location: Southern Transylvania, Romania.
Methods: We conducted a stratified random sampling at 30 sites in Transylvania, involving 90 plots along a microgradient of tree canopy projection—from under to outside—as a proxy for varying shadow conditions. We collected structural data on solitary trees, species cover, functional traits (plant height, specific leaf area, seed mass, and growth form) and ecological variables. We examined the effects of solitary trees' canopy projection on variation of taxonomic composition using nonmetric multidimensional scaling, analysis of similarities and indicator species analysis. We applied linear mixed effect models to test the change in taxonomic and functional diversities and the relative proportion of woody species along solitary trees' canopy projection.
Results: We found distinct shifts in taxonomic composition along a microgradient from under the canopy to outside areas, primarily due to changes in light availability and nutrient conditions. Decreasing light availability reduces species and functional diversities in line with the filtering effect of canopy cover. The woody species seedling establishment under the canopy projection suggested a reduction in competition with grassland species and a facilitation process exerted by adult trees.
Conclusions: Solitary trees are an important element of wood-pastures, creating microhabitats for shade-tolerant and woody species. Our findings underscore the importance of solitary trees in promoting different plant communities at the microscale. We suggest the application of patchy management of wood-pastures with scattered maintenance of woody species and simultaneous cutting of shrubs in places to prevent succession in case of management cessation.