Sustainable forest management in peatlands

Around a quarter of Finnish forests grow on peatland, which means that peatland forests have an important role as a source of income for forest owners and a source of wood for industry. This page offers a collection of key tips on peatland forest management.

Felling income from peatlands is often smaller than that from heath forests, while forest management costs are higher. In addition, the risk of greenhouse gas emissions and emissions into waterways is higher than in heath forests.

Measures carried out in peatlands must be carefully planned, taking different perspectives into account, so that the forest owner can choose the measures based on their own goals. At Metsä Group, we develop peatland forest management to ensure profitable forestry operations and minimise any damage to the climate and waterbodies from operations.

Aiming for an appropriate water level

An appropriate water level is important for tree growth and for reduced emissions. Trees are satisfied as long as most of their roots are above the water level. If the water level rises, tree growth suffers, the wet peat releases climate-warming methane, and the humus starts moving. If the water level drops, the peat dries up and decomposes, releasing carbon dioxide, which warms the atmosphere.

A suitable water level is 30–40 centimetres from the peat surface. This ensures that the tree roots are mainly above water, and that their growth is not hampered by water.

TIPS FOR MAINTAINING AN APPROPRIATE WATER LEVEL

  • A functioning ditch can contain water. Check the water level of old ditches in the late summer, not during the peak floods in the spring.
  • The ditch network works as it should if the water level is at a depth of 30–40 centimetres from the peat surface in the late summer.
  • Keep in mind: if drainage is too effective, it does not increase forest growth but instead increases carbon dioxide emissions as the peat decomposes.
A stable and appropriate water level is important in peatlands.

Ditch network maintenance only when needed

Ditch network maintenance means opening old overgrown ditches. We do not make new ditches in bogs with natural or near-natural water resources. Ditch network maintenance should not be performed simply out of habit. Instead, it should be carefully considered whether a water level that is too high could instead be corrected through fertilisation or continuous cover forestry, for example.

Repairs are needed if the water remains standing in the ditches, close to the peat surface, during the driest time in the late summer. In regeneration felling, which results in the removal of most of the transpiring trees, at least partial ditch network maintenance is often required.

TIPS FOR DICTH NETWORK MAINTENANCE

  • Evaluate whether tree growth has waned. Is this caused by a lack of nutrients or a water level that is too high? How about repairs? Will ash fertilisation do, or is ditch network maintenance required?
  • If ditch network maintenance​ is required, ditches usually do not need to be deeper than 60 to 80 centimetres. This ensures that the water level remains at a depth of 30 to 40 centimetres from ground level, which is optimal for tree growth.
  • It is often enough to repair only part of the ditch network.
Drainage repair is carried out only if necessary.

A fertilised forest grows and evaporates water

While peatlands by nature often contain large amounts of nitrogen, trees are unable to use it due to the lack of phosphorus and potassium. These can be added to the soil with ash fertilisation.

Fertilisation spurs forest growth. Since a forest that is in good condition and grows well evaporates more water and maintains the balance of the soil moisture, ditch network maintenance is not always necessary. This further reduces the flow of nutrients into ditches, the environment and waterways.

Ash fertilisation was also used to spur the growth of the pines in this picture, which grow in a lingonberry-dominated thick peatland. Large amounts of water evaporate from the trees, so there is no need for ditch network maintenance.

TIPS FOR FERTILISATION

  • Thick peatlands often suffer from a lack of phosphorus and potassium. If the pine needles turn yellow, this may indicate a lack of potassium.
  • Wood ashes that contain phosphorus and potassium provide an added boost to growth that can last for decades. Rapidly growing trees ensure adequate evaporation in the forest without drainage.

Opt for continuous cover forestry

In peatlands, growing trees evaporate water. When only some of the trees are harvested at a time, enough water will continue to evaporate from the remaining trees to make drainage repair unnecessary. In addition, the water level remains stable, reducing greenhouse gas emissions and impacts on waterbodies.

Continuous cover forestry methods include strip felling, selection cutting and group selection. The one-off felling income from continuous cover forestry is smaller than that earned from regeneration felling, but then again, you save in planting and young stand management costs.

Crown thinning is another option for peatlands. It lengthens the forest cycle. In crown thinning, you recover sturdy trees from the forest and make as much use of the forest’s own undergrowth, as indicated in the image above. 

TIPS FOR CONTINUOUS COVER FORESTRY

  • Continuous cover forestry focuses on the profitability of peatland forestry, as well as the impacts on the climate and waterways. Attention is also paid to the biodiversity of forest nature and the mitigation of landscape impacts.
  • Continuous cover forestry is suitable especially for lush peatlands. It helps maintain the balance of the water level and control nutrient emissions.
  • Learn more about the wood trade-specific Metsä Group Plus management model. Metsä Group’s owner-members can get an additional bonus per hectare for felling on lush, drained, spruce-dominated peatlands if continuous cover methods – group selection or selection cutting – are used instead of clear cutting, and drainage ditches are not repaired in connection with felling.

Low-yield peatlands excluded from forestry

Restoration, which means leaving the forest in a natural state, is an option in forests of stunted growth that remain watery even after drainage. In practice, the forest is left to become swampy again and gradually return to its original state. The passive restoration process can be accelerated by collecting all or some of the sturdy trees.

It is worth considering excluding an area from forestry especially if the area borders on land areas in a natural state. Active restoration, in which ditches are blocked to raise the water level, is an option for lush and very moist sites.

TIPS FOR POORLY GROWING PEATLANDS

  • Is the bog so barren that no viable trees grow there despite drainage? Consider excluding it from forestry and leaving it to restore naturally
  • If the area is surrounded by other similar ones, you can form larger and more uniform nature sites from them. On lush sites, active restoration is also an option
  • Further information about peatland protection is available in the Ministry of Agriculture and Forestry’s METSO programme, and the Ministry of the Environment’s Helmi programme.