Using the old-growth concept to identify old species-rich semi-natural grasslands

Abstract

The concept of ‘old growth’, originally developed for forests, was recently extended to grassland to distinguish old natural grasslands (NG) from semi-natural grassland (SNG). Comparing mesophile SNGs of different ages, we show that the concept is also able to distinguish old SNGs from young SNGs and also that assembly time plays a determining role in the ecology and evolution of SNG. As expected from the old-growth concept and like NG, old SNGs have an unique floristic composition with a higher greater proportion of long-lived species with underground storage, clonal growth organs and bud banks, higher species richness, diversity and evenness. Furthermore, they have much greater floral abundances and contain sedge species not found in younger SNGs such as Carex caryophyllea which is a reliable indicator of old unimproved species-rich grasslands. Comparison with other old grassland systems suggests that the old SNGs are probably remnants of the rich biodiversity of the grassland vegetation that was once widespread in the Atlantic biogeographic region. Given their ecological, cultural and aesthetic values and their role in essential ecosystem services, these threatened old SNGs deserve urgent protection.