The development of landscape structures affecting biodiversity in the Hanveden and Tyresta green wedges

Sammanfattning: The green wedges of Stockholm are meant to support a high level of biodiversity as well as cultural and recreational services but evaluating the spatial development of the wedges is difficult because their delineation has changed since they were first used in a regional development plan. This study examines a part of the Hanveden and Tyresta wedges in southern Stockholm, with the goal to use robust ecological theory to evaluate the development of the wedges from 1992 until today with focus on conserving a high level of biodiversity. Using an already existing GIS-based method of identifying connectivity weaknesses in the wedges, more weaknesses were found in 2010 than in 1992 although the total area of the wedges had only declined 3.3%. The shape of the wedges had also changed, with more narrow parts in 2010 than in 1992. To more effectively compare the development of factors in the landscape that are relevant for biodiversity, this study proposes a new method using the common shrew and hazel grouse as surrogate species. The total area loss for the common shrew was 2.96% from 1991 to 2013 and 2.23% for the hazel grouse. Fragmentation increased for both species. A large part of the greenspaces relevant to the surrogate species are covered by the green wedges, meaning that important cultural and recreational values identified by the county council are also present in areas relevant to the surrogate species. Using surrogate species to delineate and monitor the green wedges could enhance the cultural and recreational qualities of the wedges, emphasize the need for connectivity planning, identify ecologically important parts of the greenspaces as well as provide a tool for following up the development of the urban greenspaces of Stockholm. However, formulating goals relevant to biodiversity is important to fully evaluate development and municipal cooperation is needed.