Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Clonal demography

Fragmentation in many European landscapes is accompanied by a slow deterioration of many of the remaining habitats. This deterioration is largely due to change in the landscape management, such as cessation of grazing or mowing, increased load of nutrients etc. which typically lead to increased intensity of competition from grasses and/or all tall forbs. While the rare plants are often able to survive in these deteriorated habitats for some time, competitive effects of a few tall species change their survival ability. This is particularly important for long-lived plants with vegetative reproduction, as their life cycles typically show large sensitivity to change in their survival parameters, and reproductive parameters are less important than in annual or short-lived plants.

The second major task of the WP4 thus was an assessment of changes in ramet-level demography of such long-lived perennial plants. This was done by manipulating competitive stress and observing changes in plant survival in three selected grassland perennials (Centaurea scabiosa, Hypochoeris radicata and Succisa pratensis). Target plants were sampled over 3 vegetation seasons (2001-2003) in plots that differed in habitat quality (two levels of competition that was manipulated by clipping of neighbours). To be able to make a full account of species demography (in order the importance of survival can be assessed in the context of the whole life cycle of the plant), all plant size classes were included in the measurements. Using these data it became possible to assess the role of this survival to the overall demography of the plants.

The results demonstrated a clear negative effect of habitat deterioration on population survival. Critical life cycle stages for population dynamics of these three species were identified. In species Centaurea scabiosa and Hypochoeris radicata, lower survival of vegetative and generative adults in plots with stronger competitive stress most negatively influenced population dynamics. In Succisa pratensis, there is a clear effect of competition on flowering and seed production patterns, but population dynamics of this species were only weakly affected by competitive stress.

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