Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Seed production measurements

In the fragmented landscapes of Europe today plants occur more and more in small and isolated populations. The survival of endangered species in this landscape configuration depends on the persistence of the local populations and the ability to colonise vacant habitat patches. Much research attention over the past years has been devoted to dispersal and colonisation and on the issue of how to define a vacant site. Much less time and effort has been spent on the seed source strength, the number of seeds that remaining populations produce. Insight in the factors that determine local seed production will improve our understanding of the functioning of metapopulation processes for plants.

We do know that local populations may begin to deteriorate if local conditions change due to succession, climate change or external impacts such as eutrophication. Malfunctioning begins when local seed recruitment comes to a halt because vegetations get higher and denser and small-scale disturbances no longer open the vegetation. This generally reduces population viability because seed germination of many species is light dependent. However, mature perennial individuals may persist for a long time under these conditions. Unknown until now is whether these individuals remain flowering and set seed and thus remain serving as a significant seed source within the metapopulation structure.

Based on the measurements described under “demography” we have made seed production measurements of the populations that we studied. The calculations are based on detailed monitoring of numbers of flowers per plant and the seed set. One of our species, Tragopogon pratensis, may serve as an example. Germination experiments indicated that seeds of this species are unable to germinate under light conditions that simulate canopy shading. In more productive habitats with very few open patches, seedling recruitment will therefore be negligible. Mature plants of Tragopogon, however, may grow and flower profusely and have an abundant seed set in such environments. Indeed, we have monitored relatively small populations that produce tens of thousands of seeds per year, albeit with very little chances for local recruitment. We conclude that there is a high potential for small populations as a seed source in the landscape, even when local conditions reduce population viability due to reduced establishment of sexual offspring.

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Institute of Water and Wetland Research
6525 ED Nijmegen
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