| 1. |
- Isaeus, Martin, 1964-
(författare)
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Factors structuring Fucus communities at open and complex coastlines in the Baltic Sea
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with physical factors and biological interactions affecting the distribution of two fucoid species, Fucus vesiculosus and F. serratus, in the Baltic Sea. Studies have been carried out in two quite different environments: an archipelago, and an open rocky coast. The archipelago has an extremely long coastline with a heterogeneous submerged landscape of different substrate types, slopes, water qualities, and degrees of wave exposure. The factors influencing F. vesiculosus distribution, morphology and epiphyte composition were studied in the Stockholm archipelago using field surveys and spatial modelling in Geographic information systems (GIS). A GIS-method to estimate wave exposure was developed and validated by comparing the result to an index based on vertical zonation of lichens. Wave exposure was considered an important factor for predicting the distribution of F. vesiculosus by its ability to clean hard surfaces from silt, and a predictive model was constructed based on the information of wave exposure and slope of the shore. It is suggested that the lower distribution boundary of attached F. vesiculosus is set by sediment in sheltered parts of the archipelago, and by light availability in highly wave exposed parts. The morphology of F. vesiculosus was studied over a wave exposure gradient, and several characters responded in accordance with earlier studies. However, when separating effects of wave exposure from effects of other confounding water property parameters, only thallus width was significantly different. Several water property parameters were shown to be correlated with wave exposure in the Stockholm archipelago, and the mechanism responsible for the effects on F. vesiculosus morphology is discussed. The composition of epiphytes on F. vesiculosus varied over a wave exposure gradient with a positive correlation to Elachista fucicola, and a negative to Chorda filum. At an open coast the physical environment is much less heterogeneous compared to an archipelago. The distributions of F. vesiculosus, F. serratus, turf-forming algae, and the seafloor substrate, were surveyed along the open coasts of Öland and Gotland. Turf-forming algae dominated all hard substrates in the area, and Polysiphonia fucoides was most abundant. At the Gotland coast F. vesiculosus was less abundant than at the Öland coast, and F. serratus occurred only in the southern-most part. Fucus serratus was increasingly more common towards south which was interpreted as an effect mainly of the Baltic salinity gradient, or the variation of salinity that has occurred in the past. The effects of turf-forming algae and sediment on F. serratus recruitment at 7 m depth off the Öland east coast were studied in the field, and by laboratory experiments. Almost no recruits were found in the algal turf outside the F. serratus patches. More fine sediment was found in the turf than in the F. serratus patches, suggesting that the turf accumulates sediment by decreasing resuspension. Both filamentous algae and sediment decreased the attachment ability of F. serratus zygotes and survival of recruits, and sediment had the strongest effect. It is therefore suggested that F. serratus has difficulties recruiting outside its patches, and that these difficulties are enforced by the eutrophication of the Baltic Sea, which has favoured growth of filamentous algae and increased sedimentation. An overall conclusion is that Fucus distribution is affected by large-scale-factors, such as the eutrophication and salinity changes of the Baltic Sea, as well as by small-scale variation in wave exposure, substrate and slope, and by surface competition with neighbouring species.
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| 2. |
- Lindborg, Regina, 1966-
(författare)
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Land Use Change in Space and Time : implications for plant species conservation in semi-natural grasslands
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Land use change has during the last century altered the traditional rural landscape in Sweden, resulting in a major decline in species diversity. Traditional small-scale farming, with a remarkably high small-scale species richness, has changed in favour of rationalized agriculture, and many semi-natural grasslands, i.e. traditionally managed pastures and meadows, have become abandoned. In this thesis I examine how spatio-temporal processes affect plant species in Swedish semi-natural grasslands exposed to habitat degradation as well as recovery (restoration). I also discuss how to conserve plant species associated with semi-natural grasslands. In general, species responded slowly to habitat degradation, but quickly to improvement of habitat quality. Population viability analysis (PVA) of the grazing favoured herb Primula farinosa suggested, in contrast to historical records, that populations in abandoned grasslands performed better than populations in traditionally managed grasslands, a result questioning the accuracy of PVAs. Restoration of grasslands counteracted species richness decline and the number of species increased within seven years after restoration. It was possible to recruit grassland species in grazed former arable fields by artificial seed-sowing. This may help to speed up the natural recruitment, which often is low due to dispersal limitations in modern fragmented landscapes. Studies at larger regional scales showed century long time-lags in the response of plant species richness to land use change. Species richness was not related to present-day connectivity of grasslands, but positive effects appeared for grassland configuration in 1950s and 1900s. Thus, making conservation guidelines based solely on present-day data may be strongly misleading and under-estimate the actual risk of species loss. To secure long-term survival of species, it is important to focus on processes associated with larger spatial scales. This may benefit natural dynamics at longer time-scales, where abandoned and restored grasslands, together with species-rich semi-natural grasslands, could become natural parts of sustainable landscape management.
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