Metapopulation viability of an endangered holoparasitic plant in a dynamic landscape

Abstract

By creating transient patch mosaics, disturbance can influence the dynamics of interacting populations in many ecosystems. In European heathland, traditional land use created such dynamic systems favourable for both early and later successional species. Little empirical evidence is, however, available on the impact of current management on metapopulations occurring in such landscapes. This paper looks at the metapopulation viability of the endangered holoparasite Cuscuta epithymum, a species that typically occurs in early successional stages of recently managed heathlands. We used both observational and experimental data from a 4-yr study to parameterise a spatially explicit metapopulation model. This model explores the impact of demographic characteristics and spatiotemporal landscape patterns created by management events on metapopulation viability. Both occasional long-distance dispersal and dormant seeds are shown to be critical for the long-term survival of C. epitbymum in a dynamic heathland landscape subjected to a fixed rotational mowing of 15 yr. A relatively high management frequency (< 15 yr between two consecutive mowing events) appeared to be necessary to sustain a viable C. epithymum metapopulation. When there is a longer interval between management events, grazing can counterbalance the negative effects of vegetation succession. Our results indicate that small-scale cyclical management events combined with extensive grazing are the most appropriate management strategy to maintain viable populations of C. epithymum instead of the current large-scale management events. Our results further emphasise the importance of incorporating both spatiotemporal patch availability and key demographic characteristics, especially seed banks, for a realistic view of metapopulation dynamics in disturbed landscapes. This study clearly demonstrates the usefulness of metapopulation models to understand the impact of management events and to provide new ecological insights into processes acting at a landscape scale.