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.
Watering up typically ensues after clearcutting forestry-drained peatland forests. Thus, the effectiveness of maintenance drainage and soil preparation procedures becomes paramount for establishing a new generation of commercial forest. Mounding is the primary method of soil preparation applied in regeneration sites lying on deep peat. As raised planting spots, mounds are resistant to waterlogging and assumed to be beneficial for organic matter (OM) decomposition via, e.g., increased soil aeration and temperature, which would also enhance seedling growth. In recent years, however, less intensive and cheaper alternatives like scalping have been sought with some reported cases of success. Our case study investigated the survival and growth of Scots pine outplants in mounds, scalps, and unprepared microsites along a moisture gradient. After three growing seasons, mounding accelerated neither seedling growth nor OM decomposition relative to the unprepared treatment. Survival in mounds was nonetheless superior overall. Scalps behaved as water collecting depressions leading to a catastrophic regeneration result. Based on our findings, water table level (WTL) overrides other growth-controlling factors in excess moisture conditions. To combat watering up coupled with greater than normal rainfall, we recommend reforestation strategies which provide elevated, prepared planting spots (i.e., mounds) or utilize unprepared, higher microforms.
Artificial and natural seeding of Scots pine in old drainage areas-Unique features of forest regeneration on peatlands The aim of this dissertation was to investigate site characteristics unique to nutrient-poor, forestry-drained peatlands from the standpoint of establishing the second post-drainage generation of forest. Specifically, the effects of ground vegetation succession, surface peat structure and composition, water table level, and peat water retention capacity on the regeneration success of Scots pine after articial and natural seeding were examined. As Sphagnum moss cover declines and moss species typical of upland soils increase in abundance, seedbed receptivity of forestry-drained sites gradually becomes weaker. Thus, in order for natural regeneration to succeed in old drainage areas, some means of soil preparation is necessary, at the very least scarification. Depending on the progression of vegetation succession, a raw humus layer originating from plant litter may also have developed in the forestry-drained area. Following the disappearance of Sphagnum cover, the presence of raw humus most notably reduces seedbed receptivity in old drainage areas. After final felling, changes in the ground layer of vegetation often occur quite slowly especially on dwarf shrub and Vaccinium vitis-idaea drained peatland site types, provided that the water table level does not rise too high. The total coverage of vegetation in scalps decreased and succession markedly slowed when the water table level corresponded to that of a well drained site. Maintenance drainage carried out concurrently with soil preparation in the regeneration area is thus an effective measure when attempting to retard the invasion of vegetation onto scalped surfaces. In mounded areas, relatively large, over 25 cm high mounds remained free of vegetation for a long time, particularly when they had been created from deeply dug, highly decomposed peat. Due to the inherent variation in the water table level (in scalps and rotavated furrows) and sensitivity of the peat to desiccation (in mounds), forest regeneration via artificial or natural seeding is highly susceptible to weather conditions. In a growing season characterized by average rainfall and temperature, the regeneration result tends to be better in mounded than scalped regeneration areas. Such is the case particularly in years when the fluctuating water table level in a scalped regeneration area rises too high during late summer. From the seedling regeneration aspect, this problematic variation in the water level of scalps is a more probable scenario than excessive desiccation of the surface peat in mounds during an average growing season. Scalps, on the contrary, are ideal seedbeds during dry and warm growing seasons when excess drying of mounds is most likely to occur.
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