The invasive potential of introduced exotic trees: what do arboreta tell us ?

An increasing number of woody species are being listed as invasive in Europe. Forestry is the second largest pathway of invasive tree introductions and it is likely that climate change will encourage forest managers to plant exotic tree species to maintain wood production. In the early 1900’s, several arboreta were established in Southern Belgium to assess the wood production potential of prospective exotic trees. However, they also offer the unique opportunity to assess the potential invasiveness of exotic tree species.

A systematic sampling method was used to conduct surveys in eight arboreta and a buffer zone surrounding them. Regeneration of all exotic trees was recorded as well as biotic (herbaceous competition, composition of the tree stand) and environmental variables (soil type, pH, thickness of litter, canopy closure and climate). A descriptive approach allowed as to identify species showing an abundant regeneration. Linear regressions were implemented to assess whether the patterns in the regeneration of these exotic trees could be explained by their functional traits, dispersal modes, and environmental tolerances.

Results revealed that several coniferous species from the North-American West coast exhibit rapid regeneration and/or dispersal, including Tsuga heterophylla, Abies grandis, Chamaecyparis lawsoniana, Pseudotsuga menziesii and Thuya plicata. We therefore recommend to exercise caution when planting these species in future forestry trials given their potentially invasive characteristics.