Alien, invasive species are an increasing threat to biodiversity. In their paper “Competitive outcomes between two exotic invaders are modified by direct and indirect effects of a native conifer”, Kerry Metlen and co-workers has studied what two invasive species – a grass and a herb – and how they are affected by a native pine. Here, Kerry gives a short background to their study:
This research was inspired by a very striking pattern observable at undisturbed sites in the intermountain grasslands of western Montana, USA; Centaurea stoebe is supremely dominant in open prairie but virtually absent under the canopies of large ponderosa pines growing in the grassland. At disturbed sites, any component of the native vegetation has been removed, C. stoebe appears to then move in aggressively, suggesting that some complex interaction among species drives this very simple pattern.
Extensive field observations confirmed the pattern that had seemed so obvious, as at this site just east of Hamilton, Montana, USA. Germination experiments and extensive litter manipulation – in the field and in the greenhouse gradually allowed us to tease apart these complex interactions. This fantastic adventure, lead us to discover that direct effects between species were insufficient to explain patterns of invasion of C. stoebe and Bromus tectorum and that shifting interactions among species gave a more complete picture of this dynamic plant community.