Environmental and economic performance of forestry on drained peatlands was reviewed to consider whether continuous cover forestry (CCF) could be a feasible alternative to even-aged management (EM). CCF was regarded feasible particularly because continuously maintaining a tree stand with significant transpiration and interception capacity would decrease the need for ditch network maintenance. Managing CCF forests in such a way that the ground water levels are lower than in clear-cut EM forests but higher than in mature EM forests could decrease greenhouse gas emissions and negative water quality impacts caused both by anoxic redox reactions and oxidation and mineralization of deep peat layers. Regeneration studies indicated potential for satisfactory natural regeneration under CCF on drained peatlands. An economic advantage in CCF over EM is that fewer investments are needed to establish the forest stand and sustain its growth. Thus, even if the growth of trees in CCF forests were lower than in EM forests, CCF could at least 2 in some peatland sites turn out to be a more profitable forest management regime. An advantage of CCF from the viewpoint of socially optimal forest management is that it plausibly reduces the negative externalities of management compared to EM. We propose that future research in drained peatland forests should focus on assessing the economic and environmental feasibility of CCF.

An imbalanced nutrient status in Scots pine stands on drained mires is primarily a consequence of excess nitrogen (N) in relation to mineral nutrients such as phosphorus (P) and potassium (K). In this study, the variation of foliar N, P, and K concentrations relative to some site and environmental characteristics was examined. Foliar nutrient concentrations were determined on needle samples collected from mires representing different drainage ages, site types, geographical locations and annual weather conditions. In the overall data (n = 971 samples in 333 stands) the foliar N concentration varied between 6.7 and 24.2 mg g -1 , the P concentration between 0.83 and 2.32 mg g -1 , and the K concentration between 2.22 and 6.23 mg g -1 . The original (pre-drainage) mire site type proved to be an important factor in explaining the nutrient status of the trees: on originally forested sites, the nutrient balance (N versus K; N versus P) was mostly adequate, whereas on sparsely forested and treeless sites, K deficiency was common. N deficiency was the most common in forested 'nitrogen-poor' sites, while P and K deficiencies were more common in originally treeless or sparsely forested 'nitrogen rich' sites, where the nutrient imbalance was also the greatest. Over the whole data, 29% of the cases were diagnosed to be N-deficient, 51% P-deficient, and 25% K-deficient. The foliar N concentration increased with increasing temperature sum. The foliar K concentration decreased with increasing depth of the peat layer. On former treeless or sparsely forested sites, foliar K decreased slightly with increasing drainage age. In contrast, on thin-peated sites the foliar P concentration increased with increasing drainage age. The climate conditions (location), the original site type of the mire and peat thickness should be taken into account when planning silvicultural measures on mires drained for forestry.

Continuous cover management on peatland forests has gained interest in recent years, in part because the tree biomass with significant evapotranspiration capacity retained in selection cuttings could be used as a tool to optimize the site water table level (WTL) from both tree growth and environmental perspectives. This study reports WTL responses from six field trials established on fertile Norway spruce-dominated drained peatland forests across Finland. At each site, replicates of different intensity selection cuttings (removing 17-74% of the stand basal area) or clear-cut in parallel with intact control stands were established and monitored for the WTL for 2-5 postharvest years. The observed WTL rose after selection cuttings, and the response increased with harvest intensity and depended on the reference WTL; that is, larger responses were found during dry summers or in more southern location. Selection cuttings removing about 50% of the stand basal area raised the WTL typically by 15-40%. Using a process-based ecohydrological model, tested against data from the field trials, we show that the role of tree stand in controlling the WTL clearly decreases along the latitudinal climate gradient in Finland. This suggests that the potential of controlling WTL using selection cuttings is more prominent in southern than in northern Finland. Predictions with future climate (2070-2099) further indicated a general decrease of the WTL and that the importance of the tree stand in controlling the WTL will increase, especially in northern Finland. The results overall thus suggest that selection cuttings can be used as a tool to control the WTL in boreal drained peatland forests, and the potential is likely to increase in future climate.

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