Annastina Saari, Marjo Palviainen, Mikko T. Niemi, Annamari Laurén. (2025). Impacts of reduced ditch network maintenance and ditch shallowing on ecosystem services of peatland forests in Finland. Silva Fennica vol. 59 no. 3 article id 25032. https://doi.org/10.14214/sf.25032

Keywords: stand growth; drainage; carbon balance; water table; ecosystem modelling; nutrient export load

Highlights: Effects of ditch shallowing on ecosystem services depend on latitude, site type and tree species; Ditch shallowing increased ecosystem carbon sinks; If the initial ditch depth was 0.6 m and deeper, stand volume growth mainly increased in Southern Finland; Ditch shallowing had the largest benefits for all studied ecosystem services when the initial ditch depth was 0.9 m.

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According to the 13th Finnish National Forest Inventory, 0.8 Mha of drained peatland forests require ditch network maintenance (DNM). The annual DNM area has decreased radically during the past ten years, leading to gradual shallowing of ditches and rise of water table (WT) in peatland forests. To study the impacts of ditch shallowing on ecosystem services, we applied Peatland Simulator SUSI for 20 average peatland forests representing four different geographical regions in Finland. The simulation period was 20 years and the initial ditch depths were set to 0.3 m, 0.6 m and 0.9 m. The study included drained peatland forest site types from nutrient rich to nutrient poor, with main species as Scots pine (Pinus sylvestris L.) or Norway spruce (Picea abies (L.) Karst.). We studied how ditch shallowing affected stand volume growth, ecosystem and soil carbon (C) balances, and nitrogen (N) and phosphorus (P) export loads to water courses in different peatland sites. The results showed that due to ditch shallowing, the ecosystem C sinks increased in most sites when the initial ditch depth was 0.6 m or 0.9 m. Ditch shallowing generally increased stand volume growth in Southern Finland when the initial ditch depth was 0.6 m or 0.9 m. Regardless of the location and initial ditch depth, ditch shallowing decreased N and P exports, and soil C emissions. The study calls for new water management guidelines for drained forested peatlands in Finland.

Saari, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland https://orcid.org/0009-0001-5931-4210 E-mail: annastina.saari@helsinki.fi
Palviainen, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland https://orcid.org/0000-0001-9963-4748 E-mail: marjo.palviainen@helsinki.fi
Niemi, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland https://orcid.org/0000-0003-0461-3667 E-mail: mikko.t.niemi@helsinki.fi
Laurén, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland; Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland https://orcid.org/0000-0002-6835-9568 E-mail: annamari.lauren@helsinki.fi

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