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Colonization capacity of herb woodland species in fertile, recent alder woods adjacent to ancient forest sites

Orczewska A.

Polish Journal of Ecology

2010

Vol. 58, nr 2

297-310

The herb layer recovery in post-agricultural woods adjacent to ancient forests has not yet been studied for the wettest European woodlands, like those with black alders (Alnus glutinosa L. (Gaertn.)). Therefore, the studies aimed at: I. checking which herbs from the Polish list of ancient woodland species that are present in the alder woods show an association with these woods (AAWS=Ancient Alder Woodland Species); II. presenting their ecological profile (spectra of life forms, life strategies, dispersal modes, phytosociological affinity, and Ellenberg indicator values), and III. comparing the dispersal potential and other traits of species recorded more often in ancient woods (AAWS) vs the Polish ancient woodland indicators frequently present in ancient and recent alder woods (OAWS = Other Ancient Woodland Species). The survey was carried out in Alnus glutinosadominated woodlands, located in south-western Poland. The study sites are located within large forest complexes, where they occupy either periodically waterlogged sites or other places with a high level of groundwater. In the case of ancient woods, wet types of an oak-hornbeam community (Tilio-Carpinetum Tracz. 1962 or Galio-Carpinetum Oberd. 1957) (11 sites), alder-ash carrs (Fraxino-Alnetum W. Mat. 1952) (12 sites) and typical wet alder woods (Ribeso nigri-Alnetum Sol.-Górn. (1975) 1987) (10 sites) were investigated. The ancient woodland sites varied in size from 0.73 ha to 15.54 ha. Recent woods, adjacent to these sites, included black alder stands planted on former meadows. The area of their patches ranged from 0.72 ha to 8.6 ha. Post-agricultural woods represented the following age classes: up to 10 years, 11-20, 21-30, 31-40, and 41-50 years. The process of colonization of recent woods by woodland flora was investigated in 33 transects, approximately 80 m in length by 4 m in width, consisting of 10-12 quadrates, 16 m2 each, laid out at intervals of 4 m, perpendicularly across the ancient-recent border. In total 131 quadrates in the ancient wood, 198 in the recent woodland, and 34 in the ecotone zone were investigated. The migration rates (m yr[^-1]) based on the occurrence of the farthest individuals, were calculated for over 50 woodland species. The original lists of species obtained from the transects were completed after detailed inspections of the whole area of adjacent forest sectors where the studies on the colonization process were undertaken. Then, the frequency of herb layer species in ancient and recent woods was compared (Fisher exact probability test). The mean migration rates of species from the AAWS and OAWS groups were calculated. Although 62 herbs from the group of ancient woodland indicators for Poland were recorded in the course of the studies, only 21 of them occurred significantly more often in alder woods. The mean migration rate for herbs from AAWS was significantly lower (0.68 m yr[^-1]) than in the case of the OAWS group (1.54 m yr[^-1]). This indicates that true woodland herbs differ distinctively in their dispersal potential. Species from those two sets also showed some differences in their ecological requirements. Such results allow a conclusion to be reached that in wet and fertile recent forests adjacent to ancient source woods, recolonization of the herbaceous layer by typical woodland flora proceeds faster than in other, less fertile and drier habitats. This in turn explains why many true woodland species do not occur in ancient woodland sites exclusively. They are often recorded in recent woods, as they are able to colonize such sites reasonably fast.