Dispersal and life span spectra in plant communities: a key to safe site dynamics, species coexistence and conservation

Dispersal and life span of individual plant species within five plant communities were assessed to obtain a characterization of these communities in this respect. Such a characterization is important in the context of restoration and maintenance. The most frequent species of five communities were ranked in eight classes according to their level of seed dispersal capability, their seed bank formation (dispersal in time and space) and their individual life span. In the communities, all eight classes were found, but communities differed in the distribution of the species over the classes. A theoretical framework was constructed to use the level of specialization of plant species in terms of dispersal in space and time, and life span, to define the characteristics of safe site dynamics within communities. Following simple rules, the relative reliability of the occurrence of safe sites in space and time was defined. After that, the relative reliability of the habitat was linked to the best fitting combination of trait specialization level. Having defined this link, communities could be characterized in a comparative way by their level and pattern of reliability of the opportunities for recruitment in space and time. The meaning of the coexistence of a range of trait combinations in one community was discussed. It was postulated that habitat reliability can explain this by assuming that the habitat of the community is part of a larger system, or consists of several "subsystems". These insights need to be considered in nature conservation. Succession and also specializations beyond the scope of dispersal and life span may influence the occurrence of species in a seemingly unfit habitat (for instance the occurrence of semi parasitic annuals in a community of perennials, because they use the perennial root system of other species). Finally, the meaning of safe site reliability in space and time in the context of restoration of communities was discussed. The reliability in space and time may be different today from that of the past, which restricts the feasibility of restoration of communities