meadows relative to each other. For 1880, the ranking was produced directly from the relative grades. We then compared the two rankings and identified the meadows that had raised at least 10 rank positions between 1805 and 1880, assuming that such a large change might be an indication of increased productivity due to active management.
As artificial irrigation through flooding was a common way of increasing the productivity of mire meadows, the archives of the Timber Floating Association were searched for information on dams used for this purpose. We also looked for records or signs of catchwork irrigation systems in all available sources.
We searched available literature for information on the reclamation of mires, including the reports from the Swedish Roads and Waters Agency (Väg- och vattenbyggnadsstyrelsen, 1872–1910). In those reports, we found data concerning Abborrtjärn village in the reports from 1898–1903. Also, among the historical maps available from Abborrtjärn village (Lantmäteriet, 2020a) we found a cadastral map from 1912 (Figure 2d), established for the division of a property, which showed a portion of a mire that had been reclaimed as arable land. Furthermore, we searched the archives of the County Administrative Board of Västerbotten for ditching maps and plans, created for state-subsidized ditching projects for agricultural purposes, and evaluated the ones concerning mires in the study area, dating from 1915–1933 (Figure 2e).
As we did not know if the archival sources covered all reclaimed mires, we assessed what proportion of the total mire area had been converted to arable land using the existing data set on land cover in 1963 obtained from aerial photos (Figure 2f). Because the abandonment of arable land in the municipality began in the early 1950s (Bunte, Borgegård, and Gaunitz, 1982: 300), the land that was no longer used could be expected to be distinguishable on these aerial photographs. We selected all polygons classified as ‘arable and pasture land’, or found in another land class but 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 co