Causes of decline in rare plants of calcareous grasslands and recommendations for their management

Calcareous grasslands are among the most species-rich habitats of Europe. Their occurrence has declined since the beginning of the green revolution as many of them were transformed into intensively farmed meadows or fields. The region of northwestern Switzerland has still a remarkable number of remnants, though census data collected since the 1950s document the decline or local extinction in a number of flowering plants in them, especially in the more fragmented remnants. This trend suggests that despite the currently high protection status calcareous grasslands have and management efforts to maintain species diversity, many plants do not benefit from these conservation measures.

Overall objectives. The goal of the study is to assess the change in the vegetation of the remnants over time and understand the important drivers, including eutrophication, climate change, and management schemes. Furthermore, the project will assess why some outcrossing, insect-pollinated plants have continued declining. For some of them, the project will evaluate the contribution of mate limitation versus pollinator limitation. Outcrossing in plants is often determined by the genetic factor of self-incompatibility that leads to the avoidance both of self-pollination and pollination between close relatives. If plants of a species are rare, there may not be enough unrelated compatible mates. Another potential problem may be that terrestrial insects, many of which are important pollinators, have declined in the past decades, and those that remain may not provide sufficient pollination services.

Specific aims. The proposed research will focus on over 50 grassland remnants in the greater region of Basel that have been surveyed intensively over the last 70 years. The specific aims are:

  (1) To add to the time-serious of surveying the 50 remnants and analyse the change in plant composition in more detail. So far, the time serious includes 1950, 1985, 1996 and 2016. By repeating the census in 2024, we will be able to assess change in plant composition, link it to eutrophication and climate change, and pinpoint the management efforts that have had a positive effect on rare specialist plants.

  (2) Based on 5 selected plant species that have declined strongly over the past 70 years, we will assess the contribution of mate and pollinator limitation. We will test whether reproductive success is lower because of incompatible mates and/or a low abundance of effective pollinators.

Impact. Taken as a whole, this research should pinpoint the causes of the decline of rare plants in protected calcareous grasslands and provide guidelines for managing them adequately, to assure the promotion and long-term survival of plant diversity specialized to this type of habitat.