The local environment of a tree strongly determine its productivity, meaning that tree individuals growing in a species-rich neighbourhood produce more wood than those surrounded by neighbours of the same species. "Particularly impressive is the finding that the interrelations of a tree with its immediate neighbours induce higher productivity of the entire tree community (i.e. the forest stand), and that such local neighbourhood interactions explain more than 50% of the total forest stand productivity," says forest ecologist Dr. Andreas Fichtner. The importance of local neighbourhood interactions in regulating forest stand productivity increases as forest stands were richer in tree species. These findings show that the coexistence of neighbouring trees and their small-scale interactions are substantial in explaining the productivity of species-rich mixed forests.
The scientists were also able to identify mechanisms explaining why species-rich neighbourhoods promote tree productivity. Their findings show that competition is less prevalent in species-rich neighbourhoods and that species-rich neighbourhoods can even lead to facilitation by e.g. an improvement of the microclimatic conditions or by positive interactions with soil fungi.