Intraspecific variability in the context of ecological restoration projects

Population differentiation within species is a common phenomenon. The question raised in this review is whether such variability should be recognized while making a choice for populations as sources for the (re)introduction of species into former or novel environments. To estimate the ecological importance of population differentiation in the context of restoration projects, I reviewed literature in which the results from (reciprocal) sowing and transplant experiments are reported. This survey reveals that survival of the transplants (one of the earliest recognizable fitness components) is almost entirely site-dependent, while the fitness of surviving plants (measured in terms of growth and fecundity) is frequently higher for native plant populations as compared to alien populations of a species. Phenological timing is sensitive to selection and rather difficult to recover in an adequate way. As far as fitness reduction is concerned, it can be stated that this is a minor effect in comparison to the complete lack of a species from the restoration site; however, the credits and debits of quantity vs. quality of the members of a population cannot yet be estimated scientifically. Comparative experiments in restoration projects would help in solving this problem. The suitability of environmental conditions for the species and the accessibility of the dispersal units to the restoration site are actually thought to be the major constraints.