Competitive displacement

This is an ever-present source of plant loss in naturalistic plant communities. It results from one species being better able to capture light, water and nutrients in order to produce leaves and stems that will further diminish the capacity of neighbouring species to compete for these resources. Species doing the displacing can be either native or exotic species, sown-planted or spontaneously occurring. In some cases they are weedy native species recruited from the soil seed bank.

Competitive displacement is most problematic on highly productive sites when relatively slow growing, small statue plants (stress tolerators) are sown or planted. Under low-intensity maintenance, these sites are soon colonised by highly productive competitor and ruderal weeds, which, if not managed, will competitively displace the desired species. On highly unproductive sites, these plants still invade but because of the lack of resources for growth are less able to dominate and eliminate the sown species.

Although most obvious in the management phase, this problem needs to be addressed first at the design stage by matching plant ecology, size and growth habit to the productivity of the site soil. Rather than use small stress-tolerators on productive sites, go for wide-spreading, dense, tall and vigorous species that will have similar growth rates to weedy colonists.