Local neighbourhood tree species composition effects in young forest stands: Impact of stress, species identity and multitrophic interactions

In this PhD research it was assessed how and why differences in tree species composition can influence the functioning of forest ecosystems. In addition, an attempt was made to test how this influence can change if conditions of stress occur for the trees. First, biomass and other growth characteristics were measured in a Belgian Short Rotation Coppice site, where different highly productive Swedish willow clones were mixed. The measurements were performed after two and four growing seasons since planting, before the first harvest. Second, during three growing seasons the influence of young oak saplings was assessed in two Belgian young forest stands, which are part of the FORBIO project. Here, growth as well as above- and belowground biomass were studied. Furthermore, these tree characteristics were linked to shading by neighbouring trees and infections by oak powdery mildew, an important leaf fungus. Also looked at was potential biological control of this fungus by the 22-spot ladybird, as well in the field as under better controlled lab conditions. The influence of water stress was simulated by an experimental treatment where a portion of summer precipitation was intercepted from the saplings.