1982) and have increased the biodiversity of tree species in the area now that the lake’s immediate surroundings have been colonized by deciduous trees, mostly Betula pubescens. In a forest landscape otherwise dominated by conifers, deciduous stands offer attractive habitats for a number of species (Berg et al., 1994). Ultimately, these habitats are likely to be colonized by Picea abies, but not as long as flooding continues. Thus, damming that was originally introduced for haymaking has become long-lasting due to other needs, first of timber floaters and then of beavers, all of which has been important for promoting local and landscape biodiversity.
Other kinds of management were less beneficial for biodiversity. Actions to reclaim arable land were introduced in the late 1800s and ultimately affected 3% of the total mire area. The common procedure was to ditch and then to prepare the soil with spades and ploughs and add fertilizer (Osvald, 1937). When a mire was turned into arable land, the natural ecosystem was destroyed as opposed to when it was just modified by haymaking. In our study area, we could see that the mires selected for cultivation were in most cases mire meadows, and generally among the most productive ones. Although reclamation was only performed on a small part of the total mire area, a relatively large proportion of the productive mires habitats were thus lost.
As hay from natural meadows became less valuable, foresters increasingly tried to turn mires into productive forest land using ditches. Regarding the real effects of these ditches, our results are ambiguous, because the conversion from mire to forest does not closely follow the presence of ditches. The part of the total mire area that is now covered with forest is as large as the area located close to ditches, 106 ha, or 39%. Although the size is the same, however, the two areas do not overlap, as only 61 ha of the former mires that are today covered with forest is located within 60 m of a ditch. One reason for this mismatch could be methodological biases, due to changing definitions of mire and forest. Also, any lack of correspondence between the mire polygons defined on the 1880 map and the actual landscape would distort the results. Nevertheless, we conclude that approximately 40% of the total mire habitat area has been lost through ditching for forestry purposes. These ditches probably promoted the establishment of forests on wet sites, but it is unclear how important they continue to be in maintaining tree growth, now that high volumes of trees are keeping groundwater levels low. But, when forests are harvested and the groundwater level subsequently rises, the ditches will likely become important again to provide drier conditions for the establishment of tree seedlings. The effects are not only local, however, as drainage has been suggested to negatively affect the mire’s ability to protect downstream areas from drought and storm flooding (Menberu et al., 2016). We have no evidence of ditching after the 1980s, when drainage of new wetlands was essentially banned in Sweden. But, as long as ditches are functional, drainage will remain effective and in most cases lead to less water storage in the peat, increased annual runoff, and higher flood peaks (Holden, Chapman, and Labadz, 2004). Increased runoff also generally leads to higher levels of organic C in rivers (Asmala, Carstensen, and Räike, 2019).
Carbon (C) sequestration and storage is another important ecosystem service promoted by mires. Haymaking affected C sequestration because a major part of the plant production was removed with the hay, resulting in less litter and a slower accumulation of organic matter to form peat (Elveland, 1982). However, the most important long-term implications for climate change are connected to the C stored in peat and the conversion of mires to other land classes, especially forest, through drainage. Northern peatlands have sequestered about 270–547 Gt of C since the end of the last glacial period, which represents 20–30% of the organic C currently stored 