Canopy openness, proportion of deciduous trees and topsoil C/N ratio drive the yield, but their effect on the polyphenol content of medicinal plants is species-specific

Forests and woodlands are the major source of wild medicinal plants worldwide. In our study, we aimed to identify the factors influencing the yield and polyphenol content of Aegopodium podagraria L., Galium aparine L., Rubus fruticosus L., Rubus idaeus L., Stachys sylvatica L. and Urtica dioica L., the common and abundant medicinal plant species in the study areas. We showed that European temperate forests are potentially an important source of the medicinal resources. Light availability, controlled by canopy cover, proportion of deciduous trees and stand basal area were the most important factors positively influencing both abundance and quality of medicinal plants. The C/N ratio and pH of the topsoil were the most important factors positively influencing the content of phenolic compounds. The phenolic content was highly species-specific and varied according to local environmental conditions. A high proportion of deciduous species and a high canopy openness increased the yield and quality of medicinal plants by ensuring high light availability. Plants with high total polyphenol content should also be sought on biologically active (non-acidic) soils with a high C/N ratio. Our results can be used to guide forest management in areas where harvesting of understory medicinal plants is an important provisioning ecosystem service. In many cases a forest management scenario friendly to medicinal plants may require only a minor changes in forest management intensity, as cultivation or enhanced growth of MD plants can take place in intensively thinned forests and cleared forest patches, without competing with timber production.