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- Mörtberg, Ulla, 1960-
(författare)
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Landscape Ecological Analysis and Assessment in an Urbanising Environment - forest birds as biodiversity indicators
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To achieve a sustainable development, impacts onbiodiversity of urbanisation, infrastructure, land use changesand other developments must be considered on a landscape andregional scale. Landscape ecology can provide a conceptualframework for the assessment of consequences of long-termdevelopment processes like urbanisation on biodiversity on alandscape scale, and for evaluating the impacts of alternativeplanning scenarios. The aim of this study was to explore theeffects of habitat quality, quantity and connectivity on forestbird diversity in an urban-rural gradient. The purpose of theanalyses was to develop knowledge and methods for integratingbiodiversity issues in planning and assessments in anurbanising environment, on landscape and regional scales. The study area was situated in and around Stockholm, thecapital of Sweden, covering the city centre, suburbs andperi-urban areas. Data on breeding forest birds were collectedthrough bird censuses in an urban-suburban gradient. In orderto embrace also the peri-urban areas for a more completeurban-rural gradient, data on two fragmentation-sensitiveforest grouse species were obtained through a questionnaire tohunters in the whole study area. Response variables in theanalyses were forest bird species richness and diversity,relative species richness and occurrence of single sensitivespecies like selected sedentary forest birds, including theforest grouse species, and red list species. Habitat quality,quantity and connectivity were analysed using available data onabiotic conditions, including urban disturbances, andvegetation in geographical information systems. In addition, afield study on vegetation structure and composition wasperformed in a subset of the smaller sample sites.Relationships between the response variables and habitatquality, quantity and connectivity were explored usingstatistical methods like multivariate statistics and regressionmodelling. Further, for some models, spatial dependencies werequantified and accounted for. When habitat models wereretrieved, they were used for spatial predictions of habitatsuitability. They were also applied on future planningscenarios in order to predict and assess the impacts onsensitive species. In the urban-rural gradient, the foreststructure and composition changed, so that in more urban areas,coniferous forest on rich soils, wet forests and wetlandsbecame less abundant and more scattered. Sensitive birdspecies, tied to these habitat types, were shown to besensitive to habitat fragmentation caused by urbanisation.Large, well-connected habitat patches and aggregations ofsuitable habitat in the landscape had a higher probability ofoccupancy when compared to other patches. For the forest grousespecies, effects of car traffic added to the explanation oftheir distribution. By contrast, deciduous forest was stillquite common in predominantly urban areas, due to both latechanges in land use and a history of human preferences. Certainred listed bird species tied to deciduous forest did not seemto be affected by isolation, and also occurred in suitablehabitats in some highly urbanised areas. Furthermore, relativespecies richness in the urban-suburban gradient was related tomulti-layered deciduous forest habitats with a large amount ofdead wood. Such habitats were associated with natural shorelineand with old pastures and parks. From the derived statisticalmodels, describing the relationships between sensitive speciesand environmental variables, predictive habitat maps could becreated for the present situation and for planning scenarios.The predictions of the impacts on habitats of sensitive speciesmade it possible to quantify, integrate and visualise theeffects of urbanisation scenarios on aspects of biodiversity ona landscape scale.
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- Mörtberg, Ulla M., et al.
(författare)
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Red-listed forest bird species in an urban environment - Assessment of green space corridors
- 2000
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Ingår i: Landscape and Urban Planning. - 0169-2046 .- 1872-6062. ; 50:4, s. 215-226
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to investigate if the forest remnants of the city and the system of green space corridors could support target species for conservation, in the form of red-listed forest bird species, to show through the presence of the target species what habitat qualities are still possible near cities, and to reveal those features and properties of the landscape structure that were important in this sense. The findings could be used for developing guidelines for design of urban green space corridors. A spatial analysis was performed, covering the landscape in the study area and 67 sample sites with natural vegetation, within and outside of the green space corridors. Breeding forest birds were recorded and breeding of target species in the sample sites as functions of landscape descriptors was tested using logistic regression. Seven red-listed forest bird species were found breeding in the sample sites. Considering them as indicators of habitat qualities, the results would imply that the qualities of the urban and suburban forests were due to a vast range of deciduous forest, especially broad-leaved, and possibly also to a lower intensity of forestry than in rural areas, resulting in a sufficient number of mature and decaying trees. The logistic regression models showed that important properties of remnants of natural vegetation were large areas of forest on rich soils, together with connectivity in the form of amounts of this habitat in the landscape. These properties were associated with the green space corridors. Implications for the design of urban green space corridors would be to treat mature and decaying trees and patches of moist deciduous forest as a resource for vulnerable species, and to conserve large areas of natural vegetation together with a network of important habitats in the whole landscape, in this case forest on rich soils, also in built-up areas.
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- Mörtberg, Ulla M.
(författare)
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Resident bird species in urban forest remnants : Landscape and habitat perspectives
- 2001
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Ingår i: Landscape Ecology. - 0921-2973 .- 1572-9761. ; 16:3, s. 193-203
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate the effects of habitat loss, fragmentation and habitat quality on sedentary forest birds in an urban and suburban environment. The study area was situated in Stockholm, the capital of Sweden, embracing the city centre, suburbs and parts of the rural surroundings. Breeding forest birds were surveyed in 51 forested sample sites (2-700 ha) and five species of resident birds were selected for further studies: willow tit (Parus montanus), crested tit (P. cristatus) and coal tit (P. ater) representing coniferous forest and marsh tit (P. palustris) and nuthatch (Sitta europaea) representing deciduous forest. A spatial landscape analysis was made using a geographical information system (GIS). In 21 of the smaller sites (2-200 ha), a field study was conducted to examine habitat quality parameters like vegetation age, structure and composition, and human-induced disturbance. The probability of occurrence (breeding) of bird species as functions of landscape and habitat descriptors was tested using logistic regression. All investigated species of the Parus guild showed high probabilities of occurrence only in forest patches larger than 200-400 ha, and was not present in patches smaller than 10-30 ha. This meant that patches of presumably suitable habitat (coniferous vs. moist deciduous forest) were left unoccupied. The amount of standing dead and decaying trees provided additional explanation for the distribution of the willow tit. Large areas of urban open land, industrial land use and large bodies of water had a negative influence on the probability of occurrence of several species, which indicate that they were sensitive to isolation. The probability of occurrence of the marsh tit was also influenced by distance to other sample sites with marsh tits. Unlike the Parus species, the nuthatch was breeding in most of the parks and forest remnants. This species prefers mature deciduous forest, mainly oak, which habitat was common in the urban environment. The nuthatch was only absent in some of the smallest (a few ha) forest fragments, with a mean distance between forest patches in the surroundings of over 100 m. The study showed that large forest areas and a high amount of forest in the landscape are important for the investigated resident birds that are not adapted to the urban environment. Vast areas without tree-cover seemed to be poor habitat and/or restrict dispersal. Strips of high-quality habitats, including standing trees with nest-holes, were not entirely absent in the urban and suburban environment.
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