 with a note of ‘former arable land’, and then used GIS to clip the areas which overlapped with the total mire area as defined from the map from 1880. We could then calculate the total area of reclaimed mires and thus the proportion of the total mire area that had become arable land.
The existing data set on ditches, obtained from the DTM, was classified according to purpose (road ditches were excluded). Ditches included in plans aimed at the creation of arable land or at frost prevention, or concerning areas appearing as present or former arable land on the aerial photographs from 1963, were classified as having been dug for agricultural purposes. The rest were classified as ditches aimed at the enhancement of forest production.
The ditch data set was then clipped with the polygons representing the total mire area, using GIS. The length of ditches was summed according to purpose. The same data set was used to analyze how much of the total mire area may still be influenced by ditches. Previously, Marcotte et al. (2008) showed significant impacts on groundwater levels on organic soils up to 60 m from ditches; therefore we used GIS to create a 60 m buffer around all ditches in the data set, representing the area potentially affected. We then clipped the affected area with the polygons representing the total mire area to see what parts of the mires were likely to be affected. Finally, we used the grading from the 1880 map tables to calculate what proportion of mires of different grades were included in the areas likely to be affected by ditching.
Unlike the ditches made to reclaim mires for agricultural purposes, no plans have been found for the ditches made for the purpose of increasing tree growth. However, most of the silvicultural ditches in the study area are located on land that was acquired by the forest company Sandviks Ångsågs AB. Therefore, the company’s forestry maps from 1941, which typically show existing ditches, were used as a means to approximately date those ditches.
The existing data set on land cover in 2013, obtained from aerial photos (Figure 2h), was used to estimate the proportion of the total mire area that today is arable land or forest. We selected all polygons classified as ‘arable and pasture land’ or ‘forest land’ and then used the GIS software to clip the areas which coincided with the total mire area from 1880. In this way, we assessed the proportion of the total mire area that has undergone long-term land-class change.
The original total mire area, defined as the sum of all polygons classified as ‘mire’, ‘mire meadow’, or ‘peat pit’ on the enclosure map of Abborrtjärn village from 1880, was 273 ha or 15% of the study area. Mire meadows covered 60 ha (22% of the total mire area), and the peat pit 3.3 ha (about 1%), while the rest (77%) is labeled as unused mire in this paper.
According to the map from 1702, the farmers of Degerfors were using a number of nearby mire meadows but had not yet extended their impact into our study area. In 1785, the impact had become more widespread and included a mire partly located in the study area (Vorrmyran) (Figures 1 and 2). About 40% of Vorrmyran was used as a meadow in 1785 (Figure 2a), but because the managed part belonged to Degerfors, it was excluded from the village territory of Abborrtjärn when it was defined in 1880 (Figure 2c) and is therefore also excluded from our study area. In other words, we have no indications that any part of the mires in the study area was used for a particular purpose during the 1700s, although human activities were clearly increasing in the surroundings.
In 1805, the village of Abborrtjärn used mire meadows covering about 30 ha, of which 27 ha were inside our study area. Of the latter, a little more than 3 ha was classified as ‘land to be cleared’ (sw. ‘röjningsland’) and about 2.5 ha partly so, which means that they were not yet managed as meadows. However, as all of these areas were included in the evaluation on which taxes were based, we assume that they were prepared soon after 1805, and we have included them in the mi