Increased litter decomposition rates of exotic invasive species Hieracium pilosella (Asteraceae) in Southern Patagonia, Argentina

Abstract

Plant invasions can affect key ecosystem processes regulating carbon and nutrient balances, i.e., litter decomposition. Exotic herb Hieracium pilosella (hawkweed, Asteraceae) recently invaded steppes of Tierra del Fuego island, Southern Patagonia, Argentina, where plant communities exhibit different vulnerabilities to invasion. To investigate H. pilosella invasion’s effects on litter decomposition, we conducted a field experiment in two plant communities, a tussock grassland and a grazing lawn, having contrasting environmental conditions and different vulnerabilities of being invaded by H. pilosella. At each community, we decomposed litter of dominant native species and of the exotic herb during 24 months. In addition, we characterized the litter qualities of the different species, and the microclimates of the communities. Exotic litter decomposition was remarkably faster and showed a higher association to microenvironmental variability compared to native litter decomposition. H. pilosella decomposed three-times faster than native litter in the moister, and more susceptible to invasion by H. pilosella plant community, the tussock grassland. By contrast, decomposition of native litter was not associated to the contrasting environmental conditions of the studied communities. Results suggest that introduced species may exhibit different ecosystem process rates and controls compared to resident species, affecting ecosystem nutrient and carbon cycles.