Brunbjerg, A.K., Bladt, J., Fløjgaard, C. & Ejrnæs, R. 2023. Prioritering af biodiversitet ved udtagning og genopretning af kulstofrige lavbundsjorder. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi,44 s. - Videnskabelig rapport nr. 544. http://dce2.au.dk/pub/SR544.pdf
Summary
The Danish area of carbon-rich low-lying soil covers approx. 291,000 ha, of which 84 % is roughly equally distributed between open, protected nature types (primarily meadows and bogs) and agricultural areas with different land use. Approximately half of the remaining 16% is forest, and the rest is smaller areas, e.g. lake shores, urban areas etc.
Today, much of the Danish low-lying soil is drained and cultivated, which results in the release of greenhouse gases because the carbon in the soil is broken down by microorganisms and soil fauna after oxygenation. Although the carbon-rich low-lying soil makes up only 7 % of the total agricultural area (including bogs and meadows) in Denmark, it accounts for more than half of the total emission of greenhouse gases when the land is cultivated, and the climate effect of wetting and restoring these areas is therefore significant. The political decision to withdraw 100,000 ha of carbon-rich low-lying soil was therefore made with climate considerations in mind. Since the area of low-lying soil in Denmark is almost three times larger than that expected to be withdrawn, prioritisation is required. In this project, we investigate how to prioritise the withdrawal in order to maximise the potential for biodiversity and nature in the withdrawn areas and thereby achieve a synergy between climate and biodiversity effects.
We propose that the 100,000 ha for withdrawal should be selected based on their current and potential value for biodiversity as well as their spatial connection with nature in the surrounding landscape. Based on this, we have classified the areas with low-lying soils into 12 categories according to their expected positive effect on biodiversity by withdrawal and possible wetting. Category 1 has the highest expected positive effect on biodiversity whereas category 12 has the lowest expected positive effect on biodiversity.
The potential nature value of the individual areas is estimated using the bioscore from the national biodiversity map. The bioscore combines knowledge on observations and habitats of redlisted species of plants, animals and fungi, and maps representing the environmental conditions that indicate valuable habitats for redlisted species. Not surprisingly, the vast majority of fields have a very low nature value calculated using the bioscore, and 96% of fields and field blocks end up in category 9-11 (see table 2.1). Although the nature value is generally higher for meadows and fens, still, a considerable proportion is assigned to categories 9-11 (63 % of meadows and 40 % of fens). You can reach 100,000 ha by only including low-lying areas from category 1-9. Our prioritisation exclusively concerns carbon-rich low-lying soil, but in practice it is possible to prioritise the withdrawal of additional valuable nature areas on high-lying soil as it is only a requirement that 60 % of the area selected for withdrawal must be carbon-rich low-lying soil.
The climate effect of withdrawing carbon-rich low-lying soil from cultivation appears almost immediately. However, the biodiversity effect of withdrawing cultivated fields may not happen for a long time to come, especially without a targeted restoration effort. Restoring natural processes (natural hydrology, natural grazing, natural overgrowth) as well as measures to restore naturally low nutrient levels are obvious restoration goals to ensure the realisation of the biodiversity potential after the withdrawal of low-lying soil.
