Project

biodiversity; climate change; extreme drought; meadow; propagule pressure; resilience; resistance; seed bank; seed rain; seedling establishment; soil moisture; exotic species; drought; productivity; seed addition experiment

Lead
Lay summary
Ecological processes resulting from global change, such as more frequent extreme summer drought or increased propagule pressure of exotic species, often affect plant communities gradually at time scales of years or decades and may therefore not often be distinctly recognized. The effects of potential interactions of such processes are largely unknown. Interactions may partly compensate single effects and contribute to constancy of communities and ecosystems. However, ecologists are increasingly concerned about potentially adverse interactions that may stimulate cascades of species extinctions.Over the last decade sowing experiments have found reliable evidence for seed-availability related effects on the local occurrence of species, the size of populations and the richness and productivity of communities. This implies that processes influencing the production and dispersal of seeds and/or the establishment of seedlings are important for the functioning of ecosystems.Although major cases of adverse invasions have not occurred so far, we suspect that species-rich meadows that show a high seedling turnover are potentially susceptible to invasion. Current invasibility theory predicts increased invasion during temporary resource pulses that could be associated with increased variability of rainfall. Successful invasion may primarily depend on the propagule pressures of local resident and potential invader species. A new multi-factorial seed-addition experiment will investigate hypotheses concerning the main and interactive effects of productivity, summer drought, origin of species, and propagule pressure. The experiment will be started in 2010 in meadows covering a wide productivity gradient in different Swiss regions. The knowledge gained from this experiment will be used to predict grassland invasibility in Switzerland.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

Ecological processes resulting from global change, such as more frequent extreme summer drought or increased propagule pressure of exotic species, often affect plant communities gradually at time scales of years or decades and may therefore not often be distinctly recognised. The effects of potential interactions of such processes are largely unknown. Interactions may partly compensate single effects and contribute to constancy of communities and ecosystems. However, ecologists are increasingly concerned about potentially adverse interactions that may stimulate cascades of species extinctions.Over the last decade sowing experiments have found reliable evidence for seed-availability related effects on the local occurrence of species, the size of populations and the richness and productivity of communities. This implies that processes influencing the production and dispersal of seeds and/or the establishment of seedlings are important for the functioning of ecosystems. However, most of these experiments have applied seed additions at one single level of density. With such an approach, the degree of seed limitation cannot be quantified and the relationship between seed rain (propagule pressure) and number of successfully establishing species has remained obscure. Yet, the natural seed rain as also the production of seeds (community fecundity) have not been measured in the context of seed-addition studies and we still lack the information on how many species and/or individuals may be added to a saturation of the community and how many propagules are needed to reach species saturation of the community.Although major cases of adverse invasions have not occurred at our study sites so far, we suspect that species-rich meadows that show a high seedling turnover are potentially susceptible to invasion. Current invasibility theory predicts increased invasion during temporary resource pulses that could be associated with increased variability of rainfall. Successful invasion may primarily depend on the propagule pressures of local resident and potential invader species. Building up on our experience of vegetation dynamics based on experimentation and long-term monitoring in semi-natural grassland communities we propose a new multi-factorial experiment to investigate hypotheses concerning the main and interactive effects of productivity, summer drought, origin of species, and propagule pressure. A seed-addition experiment will be performed at 20 localities covering hay meadows over a wide productivity gradient in each of five regions of Switzerland. Seed-additions treatments that result from the combination of the factor propagule pressure (levels of augmented seed density) and the factor seed origin (two inocula representing indigenous grassland species or exotic species) will be arranged within plots that will receive normal or strongly reduced summer rain. Propagule pressure will be augmented to create communities close to species saturation. This will provide a measure of community invasibility. The ambient seed availability will be determined using representative topsoil samples at each site for reference. Seed-addition experiments will be started in 2010 and run over a period of 2 years. We intend to include many sites within recently listed meadows of Swiss “national importance”.This field experiments in natural grassland bridges the gap between current progress in theory and shortcomings of recent seed-additions experiments. Our aim is to further elucidate the relationship between community invasibility and productivity and to fundamentally advance our understanding of vegetation dynamics. Based on the results of this experiment we wish to develop a robust framework for the prediction of grassland invasibility in Switzerland and to make an important step forward in the prediction of global-change effects on herbaceous vegetation.