Abstract
Drainage of forested wetlands for increased timber production has profoundly altered the hydrology and water quality of their downstream waterways. Some ditches need network maintenance (DNM), but potential positive effects on tree productivity must be balanced against environmental impacts. Currently, no clear guidelines exist for DNM that strike this balance. Our study helps begin to prioritise DNM by: (1) quantifying ditches by soil type in the 68 km2 Krycklan Catchment Study in northern Sweden and (2) using upslope catchment area algorithms on new high-resolution digital elevation models to determine their likelihood to drain water. Ditches nearly doubled the size of the stream network (178–327 km) and 17% of ditches occurred on well-draining sedimentary soils, presumably making DNM unwarranted. Modelling results suggest that 25–50% of ditches may never support flow. With new laser scanning technology, simple mapping and modelling methods can locate ditches and model their function, facilitating efforts to balance DNM with environmental impacts.
Highlights
Artificial drainage of forested wetlands and peatlands that increase forest production has profoundly altered the hydrology of North-European landscapes during the twentieth century (Rydin and Jeglum 2009)
We evaluated two methods that use upslope catchment area (CA) algorithms, the CA-method and the SNOmethod for determining if ditches are inactive across the whole Krycklan Catchment Study (KCS), regardless of soil type
There were no published guidelines for ditches need network maintenance (DNM) oriented toward striking a balance between forest growth and environmental quality
Summary
Artificial drainage of forested wetlands and peatlands that increase forest production has profoundly altered the hydrology of North-European landscapes during the twentieth century (Rydin and Jeglum 2009). Near-surface water saturation of soils reduces gas exchange with the atmosphere and soil oxygen availability, which in turn impairs the function of plant roots of many species (Sikstrom and Hokka 2016). Ditching lowers the ground water level (GWL), increases the depth of the unsaturated zone, and makes conditions more favourable for tree roots. Ditching can increase tree growth if other factors are not limiting, e.g. nutrients (Sikstrom and Hokka 2016). Drainage for forestry has been most intense in Europe, affecting at least 20% of peatland areas (Rydin and Jeglum 2009). The greatest drained areas used for forestry have been in Russia and the Baltic States where over 13.5 million hectares of wetlands have been ditched (Paavilainen and Paivanen 1995); in Canada, similar approaches are being considered (Lavoie et al 2005)
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