An international team of researchers, including some from the Autonoma University of Barcelona (CREAF-UAB), has carried out the first long-term study into the demographic dynamics of naturally-occurring and artificially-introduced plants of the same species. By using simultaneous monitoring, the scientists have identified biological and demographic features of the plants that could help to optimise conservation strategies.
The researchers carried out a programme between 1994 and 2004 to intensively monitor the germination, growth and reproduction of natural and introduced plants of the species Centaurea corymbosa, in order to evaluate the success of strategies to introduce the species, and to identify reasons why these fail.
“Very few long-term studies have analysed the success of such strategies, or looked at the critical demographic factors that could help improve them,” Miquel Riba, a researcher at the Centre for Ecological Research and Forestry Applications (CREAF) at the UAB and one of the authors of the study, told SINC.
The comparative analysis of six natural populations and two artificially-introduced ones of the same endemic species, Centaurea corymbosa, allowed the researchers to compare the demographic dynamics of each population type. The study, which has been published recently in the Journal of Applied Ecology, shows the usefulness of comparative demographic studies for establishing the viability of conservation strategies.
According to the researchers, “this monitoring programme has allowed us to observe the fate of almost all the introduced individuals from germination to death over the past ten years, and to analyse their growth rates throughout their entire life cycle”. The investigation has also shown that the plant’s colonisation capacity may reduce its distribution, even at local level.
One of the study’s main conclusions was that it is easier to introduce natural and unique Mediterranean species by means of artificial seed dispersion rather than by restoring degraded habitat. For this reason, the researchers believe a programme to re-introduce many endemic plant species with a limited geographical range due to their poor colonisation capacity could be successful.
Differences between reintroduced and natural plants
Natural and introduced populations displayed differences in the basic demographic parameters studied. Riba says that “individuals from the natural populations had the highest levels of fertility, while the artificially-created populations showed greater ability to survive”.
The high survival rate of the introduced species compensated for their lower fertility, and did not result in any significant difference in the plants’ growth rates. In this sense, the number of seeds produced by each plant was “probably” lower in the introduced populations than the naturally-occurring ones. In addition, the most important plant pollinators were more attracted to the natural ones.
The viability of the population observed by the scientists from the UAB, the National Natural History Museum from Paris, France, and the University of Montpellier, France, provides key knowledge to help ensure the continuance of this species and to increase the number of individuals.
- Colas, Bruno; Kirchner, Florian; Riba, Miquel; Olivieri, Isabelle; Mignot, Agnes; Imbert, Eric; Beltrame, Coralie; Carbonell, David; Freville, Helene. Restoration demography: a 10-year demographic comparison between introduced and natural populations of endemic Centaurea corymbosa (Asteraceae). Journal of Applied Ecology, 2008; 45 (5): 1468-1476
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