Questions: What vegetational changes does a boreal rich fen (alkaline fen) undergo during a time period of 24 years after drainage? How is plant species richness affected, and what are the changes in composition of ecological groups of species? Is it possible to recover parts of the original flora by rewetting the rich fen? Which are the initial vegetation changes in the flora after rewetting? What are the major challenges for restoration of rich fen flora after rewetting? Location: Eastern central Sweden, southern boreal vegetational zone. Previously rich fen site, drained for forestry purposes during 1978–1979. The site was hydrologically restored (rewetted) in 2002. Method: Annual vegetation survey in permanent plots during a period of 28 years. Results: There were three successional stages in the vegetational changes. In the first stage there was a rapid (< 5 years) loss of rich fen bryophytes. The second step was an increase of sedges and early successional bryophytes, which was followed by an increase of a few emerging dominants, such as Molinia caerulea, Betula pubescens and Sphagnum spp. After rewetting, there are indications of vegetation recovery, albeit at slow rates. Depending on, for instance, initial species composition different routes of vegetation change were observed in the flora after drainage, although after 24 years, species composition became more homogenous and dominated by a few species with high cover. Conclusion: Major changes have occurred after changes in the hydrology (drainage and rewetting) with a severe impact on the biodiversity among vascular plants and bryophytes. Several rich fen bryophytes respond quickly to the changes in water level (in contrast to vascular plants). The recovery after rewetting towards the original rich fen vegetation is slow, as delayed by substrate degradation, dispersal limitation and presence of dominant species.
When surrounded by growing Sphagnum the rhizomes of Scirpus cespitosus grow vertically upwards in pace with the Sphagnum. It was found that there is a considerable variation in rhizome growth between years and it is assumed that this variation is determined by variation in Sphagnum growth. The latter variation is assumed to be dependent on the weather. Simple and multiple regression analysis of rhizome growth on various weather variables gave the following results: (1) Moisture conditions are decisive for the growth. (2) The distribution in time of the moisture is more important than mean values from a certain period. (3) Although moisture in June and August of the current year was important, the moisture conditions of August of the previous year explained ca 60% of the variation. (4) A combination of the two variables Birot's wetness index in August of the previous year and the same index in current June gave r2= 0.80.
Abstract. A review is presented on the literature about the distribution of savannas in humid climates in Africa and Asia and their vegetation dynamics. Sections are devoted to African lowland and montane savannas (the latter divided into southern, eastern, western and northern African), Madagascar, Indian subcontinent, SE Asia and New Guinea. It is concluded that the extension of savannas under humid climatic conditions and the relation to the distribution of forests is a function of cultivation, grazing by domestic and wild animals, present and previous climate, geomorphology and soil characteristics. Once established, savannas are often maintained by fires, both natural and man‐made. Montane savannas are generally brought about by man's clearing, cultivation and burning. Fire is a stochastic variable; it creates an ecotone sensu stricto (an environmentally stochastic stress zone) at the forest/savanna border. On the other hand, if geomorphology and soil are the determinants, the transition between forest and savanna would have the character of an ecocline (a gradient zone) with fundamentally different conditions. In humid African lowland climates forests expand into savannas if the latter are not maintained by man. Whether forests also expand in less humid climates is disputed. In montane areas forest expansion may be delayed on degraded soils and when diaspores are lacking.
Abstract. Composition of hill slope vegetation was studied in a semi‐arid part of upland Tanzania where all grazing had been banned for 12 yr. The hills had been severely overgrazed previously and suffered from heavy gully and sheet erosion. Eight vegetation types are described. Floristic gradients revealed by numerical ordination techniques were found to be related mainly to degree of erosion, soil type and succession. The more or less bare soil that prevailed after grazing had ceased is now covered by grassland, woodland and immature secondary forest. The grasslands are still characterized by early successional species and they will probably remain open grassland as long as frequent burning continues. Brachystegia woodlands may have developed during earlier periods when the field layer was sparse due to grazing. The grazing had reduced the frequency of fire which in turn promoted the establishment of Brachystegia spp. Secondary forests are believed to have developed mainly where fires were not frequent, particularly at higher altitudes.
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