The presence of shade-intolerant conifers facilitates the regeneration of Quercus petraea in mixed stands

Abstract

Positive productivity-diversity relationships, pest-effect mitigation and increased resilience and stability maintain an ongoing interest for mixed stands in forestry. However, how mixing species affects forest regeneration is yet to be further explored.We used data from the French National Forest Inventory (from 2006 to 2016) to model Quercus petraea (Matt.) Liebl regeneration cover in pure and mixed Quercus petraea stands; we included the effects of abiotic and biotic factors as well as mixture. We hypothesized that the characteristics of the companion species would prevent or facilitate the regeneration of oak.Quercus petraea regeneration cover in this study responded negatively to total canopy cover and herbivory pressure. Mean July potential evapotranspiration (PET), mean December maximal temperature and soil pH are variables whose spatial variations over a given territory structure regeneration cover; all three of these variables have optimum values. Quercus petraea regeneration cover is linked to the proportion of Quercus petraea in the canopy layer in all mixed stands, except when the oak is mixed with shade-intolerant conifers: in this case, Quercus petraea regeneration is enhanced. The shade tolerance of admixed broadleaved species did not affect the Quercus petraea regeneration. This suggests that oak regeneration was facilitated with a shade-intolerant coniferous companion species due to better light transmittance through the crown or the competitive advantage of Quercus petraea over coniferous shade-intolerant species.These results are of interest for oak mixtures since Quercus petraea regeneration cover benefits from mixtures with shade-intolerant conifers and is at least equal to that of pure stands.