Is underplanting European beech (Fagus sylvatica L.) and small-leaved lime (Tilia cordata Mill.) effective to control black cherry (Prunus serotina Ehrh.)?
Underplanting shade tolerant, native tree species seems to be a promising method to control black cherry (Prunus serotina). This control method is discussed in literature, but reliable scientific evidence is scarce. Therefore, we planted seedlings of European beech (Fagus sylvatica) and Small-leaved lime (Tilia cordata) in pure pine stands (Pinus sylvestris; Abb. 1) with established P. serotina in the understory on 100 m2 plots. The Allg. Forst- u. J.-Ztg., 191. Jg., 9/10 193 plots were fenced to exclude deer browsing (Abb. 2b). Additionally, the invasive P. serotina was either felled or girdled to promote seedling growth (Abb. 2a). The treatment resulted in higher light availabilities. After the two growing seasons 2017 and 2018, mortality, shoot growth and radial growth (exemplary on harvested individuals; Abb. 3) of seedlings was assessed to in order to evaluate the suitability of the two tree species for underplanting and to identify optimized conditions for seedling growth. The mortality of F. sylvatica was nine times higher than of T. cordata after two consecutive drought years despite a treatment with hydrogel to improve the water storage ability of the seedlings (Abb. 4). While mortality of beech seedlings was negatively correlated with higher light availability, light showed no effect on mortality of T. cordata (Abb. 5). The different treatments applied to P. serotina had no effect on the mortality of seedlings (Abb. 6). Shoot growth did not differ between T. cordata and F. sylvatica, but both underplanted species had twelve and elven times lower growth compared to the sprouts of P. serotina (Abb. 7). Shoot growth did not differ between the two underplanted species under differently treated P. serotina trees and was not affected by light availability (Abb. 8). Radial growth could only be measuredfor F. sylvatica-seedlings and was marginal in both years, 2017 and 2018 (Abb. 9, Tab. 1). Following these results, T. cordata can be recommended for underplanting since this species is tolerant to shade and drought, which can result in high survival rates and ongoing growth, even under expanding P. serotina and on nutrient poor soils susceptible to drought. Fencing is recommended since browsing damage is to be avoided and also features seedlings vitality for the strong competitor P. serotina.