Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS


The survival probabilities of local populations in fragmented landscapes depend on the local demography of the species. The demography is determined by the vital rates of the plant species, i.e. the survival and growth of individuals, their reproduction and the establishment of new recruits. These vital rates vary among species. In particular we expect that survival of individuals versus seed dispersal and seed recruitment differ, and these vital rates are the main targets for study in TRANSPLANT. In addition, there may be systematic variation in demographic parameters between local populations as well as populations between different regions.

Local differences are likely to be determined by the management of the site, soil properties and the history of the site determining selection on the properties of the plants in the past. Regional differences occur at the scale of the entire range of the species within Europe and differences are especially expected between populations at the centre of the distribution and populations at the margin. The latter populations are growing at their abiotic and biotic limits and are thus expected to be more vulnerable. It is unknown, however, how this vulnerability translates into specific demographic characteristics.

These considerations have resulted into a unique European-wide monitoring scheme of plant demography. Four species have been involved. Carlina vulgaris and Succissa pratensis as species with low dispersal capacity, (seeds without adaptations for dispersal), and Hypochaeris radicata and Tragopogon pratensis as species with high dispersal capacity (seeds with pappus for wind dispersal). Carlina vulgaris and Tragopogon pratensis form short-lived monocarpic individuals that die after flowering, while Hypochaeris vulgaris and Succissa pratensis are longer-lived and polycarpic and clonal by which individuals survive after flowering.

In close collaboration with other work packages, populations have been monitored for each of these species in at least three regions within Europe (including central and marginal populations), for at least two populations per region, for at least three growing seasons. Population sizes ranged from less than 100 up to several thousands of individuals, and distances to the closest populations ranged from 100 m up to several kilometres.

Demographic field monitoring consisted of two parts. First, established plant individuals were censused in permanent quadrates within a site. In order to follow their fates over time, individuals were tagged and their coordinates within the quadrate recorded. Plant sizes were estimated by non-destructive measurement of the number of leaves and the leaf lengths. Growth, flowering and survival rates can thus be accurately determined if no less than about 100 individuals per population are censused at least once per growing season. Seed set was estimated by recording the number of capitula (flower heads) per flowering individual, accompanied by counting the number of mature seeds per flower head on individuals outside the quadrates.

The second part of the demographic field monitoring involved an independent assessment of the germination and establishment probabilities of the species in the populations. To this aim a fixed number of seeds obtained from individuals in the population were sown in separate field plots. Germination and establishment (growth and survival) of seedlings are then recorded at regular intervals in these plots. Control plots that have not received any seeds are monitored to quantify background germination levels. These levels are generally low, however, and this is the reason that a separate evaluation of these important life cycle components is necessary.

The results of the demographic measurements indicate that methods described above are appropriate for a concise assessment of the different plant life histories, both within the regional level and across the European scale. For some species (e.g. Tragopogon pratensis), our methods revealed large differences in plant sizes and reproductive schedules between nearby populations. The protocols may serve as a blueprint for many studies interested in the status of populations, either endangered or not, allowing an accurate evaluation of the effects of habitat quality, management and alike.

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Institute of Water and Wetland Research
6525 ED Nijmegen
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