The Swedish population is highly urbanized with 84% of the total population living in urban landscapes (SCB 2002). This process of increasing urbanization in Sweden follows the general global trend, but unlike the explosive growth of urban landscapes seen in some areas of the world, urban growth in Sweden is taking place at a moderate rate. The increased urbanization is also increasing the degree of fragmentation and isolation of green spaces. As a response, the Swedish Government has commissioned the regional city authorities in Sweden’s three largest cities to coordinate regional programs for urban nature conservation. One of the three is theGreater Stockholm Metropolitan Area (GSMA, Fig. 1), which is the biggest population center in Sweden, with 1.2 million inhabitants (SCB 2002). The population of Stockholm County totals 1.8 million people and is estimated to grow by approximately 20 000 new inhabitants each year, mainly on the outskirts of the GSMA (RTF 2001). The population density in the GSMA is approximately 2500 inhabitants/km2, compared with 14 inhabitants/km2 in the rural parts of the Stockholm County (SCB 2002), and a total average population density in Sweden of 22 inhabitants/km2. In Stockholm County, 7–8% of green spaces have been developed over the last decades of the 20th century (SCB 1993). In recognizing this decline, the recent urban nature conservation program proposes 71 new nature reserves by 2013 in or close to the GSMA (Länsstyrelsen i Stockholms län 2003).
The GSMA is situated in a landscape of rolling hills and valleys that, to a large extent, is shaped by the last glaciation period 10 000 years ago, and the subsequent isostatic rebound that has raised the land from the sea. This has increased the land available for human use, and this, coupled with a steady increase in population, has increased human land uses since that time (Bratt 1998). The hills are partly covered with shallow moraine/glacial till, vegetated mainly by Scots pine (Pinus sylvestris) and weedy shrubs (e.g., heather (Calluna vulgaris) and lingonberry (Vaccinium vitis-idaea)); on the lower slopes, the sediments are deeper and spruce (Picea abies) trees dominate; the valley bottoms are covered with lush vegetation of deciduous tree species, communities dominated by, e.g., birch (Betula spp.), aspen (Populus tremula), maple (Acer platanoides), ash (Fraxinus excelsior), linden (Tilia cordata), and oak (Quercus robur).