Management of urban woodlands - effects on bird communities and recreational values

摘要

The ongoing urbanisation increases the pressure on urban nature. Urban woodlandsare receiving growing attention as they provide valuable ecosystem services to urbancitizens, mainly by providing areas for recreation but also through improving airquality and reducing noise. There is an increasing demand for knowledge of howurban woodlands should be managed to combine several functions, such asrecreational values and biodiversity conservation. There are, however, few fieldexperiments that evaluate the effects of forest management.The work in this thesis is based on the results of large-scale, replicated fieldexperiments in urban woodlands in southern Sweden. Management by clearance ofwoody understory (bushes and small trees) was conducted at five sites in oakdominatedforest stands on the fringe of three midsize cities. Two different types ofclearance were applied: 90% removal of understory and 50% removal in regular50x50 meter patches. Control plots of equal size were left unmanaged. Birdcommunities were surveyed before and after management, and the impact of birdpredation on arthropods in bush and tree canopies were evaluated with exclosureexperiments. Bird communities were affected by understory clearance and a decreasein bird abundance was observed in the stands with 90% removal of understory. Patchyclearance had no negative effects on bird abundance. Bird predation had strong effectson arthropods in the understory, which suggests that an important food resource forbirds is removed when the understory is cleared. Arthropods were affected by birdpredation in the tree canopies too, but the effects of bird predation were weaker in themanaged areas, which further stresses the negative impact on birds by extensiveclearance of understory.The recreational values in relation to understory density were evaluated in a photosurvey where pictures from the managed areas were shown to panels of students.Open forests were considered most attractive for recreation but 75% of therespondents claimed that they preferred a mix of open and closed forest. In a fieldstudy, the participants used cameras to take photos of liked and disliked places alonga forest trail in an urban forest. The analysis of photo contents showed that both openand dense forest landscapes were appreciated while visible human impact was usuallyperceived negatively. Implications for management are that clearance of understorycan enhance recreational values but should be conducted in a small scale pattern topromote visual variation and minimise the negative effects on birds. Visible impactfrom recreational facilities and forest management should be minimised as far aspossible. Openness is often affected by management and was found to be useful as akey-variable to analyse management trade-offs between social and ecological values.