Search

Continuous-cover forestry (CCF) is expected to reduce the negative environmental impacts of peatland forestry in comparison with rotation forestry (RF), but the unknown profitability of CCF on peatlands limits its application in practice. The profitability of CCF was analyzed by simulating management scenarios with a process-based ecosystem model, EFIMOD, which was complemented to describe the interplay between tree growth and water table depth, which is typical of peatland forests. A variety of harvest intervals and post-harvest basal areas for a mature Norway spruce (Picea abies (L.) Karst.) dominated stand was simulated on a nutrient-rich peatland site. Conventional RF was simulated for comparison. CCF provided a higher profit than RF. The best financial performance was obtained with a 15-year harvest interval regardless of interest rate, although the overall profitability of CCF depended on the interest rate used. Ditch network maintenance was needed to maintain the stand growth only when the post-harvest basal area was smaller than 10 m²·ha⁻¹. There were many CCF scenarios in which the difference in the net present value of harvest revenues was within 10% compared with the best CCF scenario. Hence, there are many relatively profitable CCF harvesting alternatives for forest management in boreal spruce-dominated peatland forests. Résumé Comparativement au rendement soutenu (RS), le couvert forestier permanent (CFP) devrait réduire les impacts négatifs de l’exploitation forestière des tourbières, mais le fait que la rentabilité du CFP dans les tourbières ne soit pas connue limite en pratique son application. La rentabilité du CFP a été analysée en simulant des scénarios d’aménagement avec un modèle écosystémique, EFIMOD, qui a été complété pour décrire l’interaction typique dans les tourbières boisées entre la croissance des arbres et la profondeur de la nappe phréatique. Une variété d’intervalles de récolte et de surfaces terrières résiduelles pour un peuplement mature dominé par l’épicéa commun (Picea abies (L.) Karst.) a été simulée dans une tourbière riche en nutriments. Le RS conventionnel a été simulé à des fins de comparaison. Le CFP a généré des profits plus élevés que le RS. La meilleure performance financière a été obtenue avec un intervalle de récolte de 15 ans peu importe le taux d’intérêt, même si la rentabilité globale du CFP dépendait du taux d’intérêt utilisé. L’entretien des réseaux de fossés était nécessaire pour maintenir la croissance du peuplement seulement lorsque la surface terrière résiduelle était inférieure à 10 m²·ha⁻¹. La valeur actualisée nette des revenus de la récolte de plusieurs scénarios de CFP atteignait au moins 10 % de celle du meilleur scénario de CFP. Par conséquent, il existe plusieurs choix de récolte relativement rentables dans le cas du CFP pour l’aménagement forestier dans les tourbières boréales boisées dominées par l’épicéa commun.

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 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.

The objective of this study was to evaluate the potential of different water management options to mitigate sediment and nutrient exports from ditch network maintenance (DNM) areas in boreal peatland forests. Available literature was reviewed, past data reanalyzed, effects of drainage intensity modeled, and major research gaps identified. The results indicate that excess downstream loads may be difficult to prevent. Water protection structures constructed to capture eroded matter are either inefficient (sedimentation ponds) or difficult to apply (wetland buffers). It may be more efficient to decrease erosion, either by limiting peak water velocity (dam structures) or by adjusting ditch depth and spacing to enable satisfactory drainage without exposing the mineral soil below peat. Future research should be directed towards the effects of ditch breaks and adjusted ditch depth and spacing in managing water quality in DNM areas.

Calibration-period/control-area approach was used to study nitrogen and phosphorus export from drained and productive Norway-spruce-dominated peatland forests following conventional stem-only and whole-tree harvesting. The study indicated high nitrogen and particulate phosphorus exports and lack of significant differences between the harvest treatments during the first 3-4 years after harvesting. The high extra nitrogen exports, increasing to a maximum level of about 10 kg ha(-1) during the third year after harvesting, were partly caused by the higher nitrate export than in previous studies. The study has a practical outcome that management of harvest residues (i.e. left on site or harvested) may not be an efficient means of mitigation of nitrogen and phosphorus exports. The high exports following harvesting underline the importance of using the best available water protection methods, such as sufficiently large wetland buffer areas, to decrease nutrient exports to watercourses from productive Norway spruce dominated peatland catchments.

In Finland, ditch network maintenance (DNM) is carried out annually on 60–70,000 ha of drained peatland to promote tree growth for forestry purposes. However, it is important to avoid ditching that contributes little to the stand growth and productivity, both to improve the economical profitability of forestry and to mitigate DNM-induced nutrient release to watercourses. We hypothesised that mature forest stands with substantial evapotranspiration potential do not necessarily need DNM, even if the ditch networks are in poor condition.We estimated evapotranspiration (EVT) of forest vegetation during the growing seasons (June–September) of 2007–2011 in four forested artificial peatland catchments dominated by Scots pine stands (Pinus sylvestris L.) (stand volume 93–151 m3 ha-1) located in southern, western, central and northern Finland. Precipitation (P), runoff (R) and water table level (WTL) were monitored continuously in the field. The water storage change (ΔS) was estimated on the basis of WTL measurements and peat pF curves determined from in situ peat samples. In addition, tree stand transpiration (T) was estimated in two of the catchments using the sap flow method. EVT was estimated as the residual term of the water balance equation.During the growing season, EVT (153–295 mm) was 49–161 % of the total accumulated P (155–368 mm), and decreased from south to north. Within each growing season, EVT was always largest in July or August. Tree transpiration was about 50 % of the total forest EVT in the two sites where it was measured directly. The mean WTL was at depth 36–63 cm during the growing seasons. Clear-cutting of a 100m3 ha-1 stand on one site resulted in an average rise of WTL by 18 cm.The results suggested that, in the southernmost site in particular, no drainage network management would be necessary to sustain satisfactory drainage conditions for tree growth because growing-season precipitation is transferred back to the atmosphere by forest EVT. In the northernmost site, ditch networks were considered important in controlling drainage conditions because of the low EVT potential of