Restoration of the populations of a declining plant: The importance of gaps, plant stage, and plant origin

In Europe, many plants of nutrient-poor grasslands have strongly declined due to fertilisation of their habitats. Recently, extensification schemes have been introduced that may allow to restore populations of these species. We studied the effect of experimental gaps and environmental conditions on the establishment of the rare long-lived plant Scorzonera humilis (Asteraceae) from seeds, and tested the importance of provenance for the establishment of plants that had been grown for five weeks in the laboratory. After seven years, plants from sown seeds had established and survived much better at nutrient-poor than at nutrient-rich sites. Gaps had a negative effect on survival at nutrient-poor sites, but at nutrient-rich sites only plants in gaps survived at all. Survival was limited to sites with extant populations. In contrast, multiplicative fitness of transplants of S. humilis after three years was not higher at sites with an extant population and was not influenced by soil moisture or nutrient status. Both the population of origin and the specific site at which transplants were grown influenced their performance. However, there was no evidence for local adaptation, because the fitness of plants was not higher at their home site than at other sites. After three years of growth in the field, the transplanted individuals had the same number of leaves as plants derived from seeds sown into the field after seven years, and a similar proportion of them flowered as in the sowing experiment after six years. The mortality of transplanted individuals was less than half that of plants derived from sown seeds. The results indicate that transplanting young plants of S. humilis is far more succesful than sowing seeds and that the source of plant material is very important. With improving site conditions, recruitment from seeds could eventually become possible where it is not yet feasible.