Genetic considerations for the restoration of riparian populations

Rom

2001

S. 25-34

Bandaufführung

75800

P. nigra is a typical pioneer tree species of the riparian forest ecosystem. Therefore, the in situ gene conservation strategies and methods developed for other forest tree species are not always suitable. In fact, successful in situ conservation strategies for black poplar need to consider the current status and management of existing populations as well as the physical dynamics of the natural habitat formed by the river. Furthermore, conservation relies heavily on the potential to restore entire floodplain ecosystems, as well as the development of appropriate strategies for the management of restored sites. These factors not only determine the objectives of designated in situ conservation units, but also the methods and costs of the approach that is ultimately adopted. The flow chart in Figure 1 is intended to assist in the selection of the most appropriate type of in situ conservation strategy for each given situation. As black poplar naturally forms metapopulations rather than small, isolated stands, in situ conservation activities should not consider local sites or conservation units in isolation but should rather consider them as part of the complete network of inter-linked local populations. It is proposed that a network of natural and managed in situ conservation units be established, covering the most important genetic resources of black poplar throughout the distribution area. Black poplar is heavily dependant on the hydrological conditions of the riverside environment for its regeneration. For example, flood disturbances create ideal microsites for regeneration from seed. At the same time, the risk presented by flood disturbances, especially to the youngest cohorts, is to some extent avoided through the adoption of multiple regeneration strategies. The different regeneration strategies of the species are discussed and concrete measures are proposed to promote the survival of germinants and the balanced growth of seedlings. Knowledge of the timing and duration of seed release of a P. nigra population, for instance, will confer a distinct advantage in the successful in situ conservation at those sites where there is a lack of suitable microsites for natural regeneration. In thse situations, it is advisable to intervene and manage the riparian area in such a way as to benefit seedling establishment, just prior to the period of maximum seed release.