**2. Study area**

194 Ecosystems Biodiversity

mires in the northern part of Sweden are strongly influenced or even destroyed, and 55% are weakly influenced while the rest are considered uninfluenced by human impact. Impacts are mainly from machines used for forestry and the digging of ditches. Small mires and mires in the Scandinavian Mountain Range were not covered by the VMI, however, and it may be assumed that processes such as increased tree cover or successional shifts to other vegetation types are more evident in such habitats. The main threats to the mountainous mires are tracks from all-terrain vehicles and snowmobiles, and much concern has been expressed from County Boards and the Swedish Environmental Protection Agency about

Fig. 1. A significant proportion of the arable land in Sweden has been created through drainage of wetlands. The figure (Color Infra Red aerial photo) shows an area in southern Sweden. The farm buildings are placed on the uplands in the SE corner and the wetlands have been drained and form long rectangular arable fields (light tones). Trees and shrubs (pink tones) now invade along the ditches and into the center of some fields as a result of decreasing land use intensity. The area above the drained fields shows invasion of trees and

It is generally anticipated that climate change will cause considerable impacts and changes on landscapes and ecosystems. Dale et al. (2001) provide a review of the impacts of climate change on forests, which included altering the frequency, intensity, duration, and timing of fire; drought; introduced species; insect and pathogen outbreaks; hurricanes, windstorms, ice storms; and landslides. Similar impacts may be expected in peatlands. Several reviews on predicted impacts of climate change on wetlands and peatlands have been published (Gorham, 1991; 1995; Gorham et al., 2001; Strack et al., 2004; Tarnocai, 2006; Warner &

this issue (e.g. Renman, 1989; Allard et al., 2004).

shrubs on a previously open string flark fen.

The study area is situated in the northern part of Sweden, coinciding with the two northernmost counties of Västerbotten and Norrbotten (Fig. 3). The landscape ranges from the coastal boreal areas consisting of often flat forested areas, up through the interior with a mixture of boreal forest and mires, to the mountains and birch-forested valleys of the Scandes Mountains. The study area has been classified into Natural Geographic Regions, sometimes referred to as Biogeographical Regions, according to the Nordic Council of Ministers (1977), Helmfrid (1996), and Lennartsson & Stighäll (2005). These regions were chosen as they take into account both east-west and north-south variations. As we wanted to study the distribution in the context of occurrences at different elevations as well as the climatic aspect, the regions were regrouped into five Elevation Zones which then were used as the basis for summarizing wetland and peatland data (Fig. 2).

#### **2.1 Characteristics of the elevation zones**

**Zone 1. The Arctic/Alpine zone** has steep mountains with glaciers and vegetation zones at lower altitudes. The prevailing Atlantic wind and precipitation provide strong climatic differences between westward slopes and eastward facing slopes with more continental climates. Nutrients in the bedrock and soil are varied and the soil layers are usually very thin. The zone encompasses the gradual shift from forest to treeless alpine habitats, and, hence, the alpine tree line.

Main Ecosystem Characteristics and Distribution of Wetlands

in Boreal and Alpine Landscapes in Northern Sweden Under Climate Change 197

stereo models and ii) field-based inventory of sample plots and sample transects. This chapter will deal only with the aerial photo part of the inventory. The data set consists of the first set of air photo samples collected in 2003 to 2005, and is restricted to the northern part of the country. The data used here consists of 116, 11 km squares, which contain a total of

3229 registered polygons interpreted from the Colour Infra-Red imagery (Fig. 3).

Fig. 3. The study area with five Elevation Zones, and with the distribution of the 1x1 km squares. The grid locations of the permanent NILS squares are indicated in red, the yet

The scale of aerial photos allows mapping based on vegetation structure and overall vegetation composition (e.g. Ihse, 2007; Morgan et al., 2010). A basic level of classification utilizes the fundamental division into bog (rain-nourished) or fen (mineral soil nourished). Each of the finer divisions is based on different hydrotopographic conditions slope (e.g., flat, sloping, raised), location in landscape, and distinctive vegetation patterning on the surface. At the polygon level the types are described for general dominance of main vegetation in the understory. Within polygons smaller units, such as hummocks, hollows, and flarks, can be identified. This means that one can use the structure of the vegetation and peat surface, along with several other ecological indications, to distinguish between the different main types of mires and vegetation elements inside them. On the landscape scale the different hydrotopographic types of mires can be put together as mire complexes (Rydin et al., 1999). We hypothesize that the geographic distributions and areal extents of types will vary from east to west and north to south in northern Sweden, and also when comparing

unsampled squares are not filled.

**3.1 Aerial photo interpretation** 

north with south Sweden.

**Zone 2. The Northern boreal zone** has wide heaths and forests of mountain birch or coniferous trees, mainly Norway Spruce (*Picea abies*) but also Scots Pine (*Pinus sylvestris*), mixed with mires. The relief includes scattered mountains and plateaus.

**Zone 3. The Upper middle boreal zone** has mixed coniferous forests in flat or hilly terrain and is rich in mires of mixed types, together with willow and birch swamps. The zone is predominantly above the highest post-glacial coastline and the metamorphic bedrocks are covered by till. Few and scattered human settlements of late date can be found.

**Zone 4. The Lower middle boreal zone** is vegetated by coniferous forest and swamp forest, in a hilly terrain rich in lakes. The transition from above to below the highest postglacial coastline occurs predominantly in this zone.

**Zone 5. The Coastal boreal zone** is characterised by sandy or morainal islands and coastal boreal plains, with hilly terrain and valleys dominated by marine sediments back from the coast. The vegetation ranges from the marshlands, meadows and lowland forests along the Gulf of Bothnia coast to the inhabited parts where cultivated land and towns are situated (sparsely), which brings open grassland and deciduous forest between the coniferous parts. The precipitation is somewhat higher than the inland forest zones.

Fig. 2. The five Elevation Zones from west to east: 1 Arctic/Alpine, 2 Northern boreal, 3 Upper middle boreal, 4 Lower middle boreal, and 5 Coastal boreal zone. The zones are based on the Natural Geographic Regions of Sweden (Helmfrid, 1996). The table in the figure shows the mean, minimum and maximum of elevation heights (m above sea level), and the standard deviation of the mean height.
