Sustainable forest management in peatlands

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.
• Remember: if drainage is too effective, it does not increase forest growth.

Ditch network maintenance only when needed

Ditch network maintenance means opening old overgrown ditches. 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.

Opt for continuous cover forestry

Growing trees evaporate water. In lush peatlands, the transpiration of trees keeps the water level stable, and new seedlings emerge naturally in open patches. Continuous cover forestry is a good option for this type of peatland. It involves methods such as regeneration cutting, selection cutting and group selection. When only some of the trees are harvested at a time, enough water will continue to evaporate from the remaining trees to make ditch network maintenance unnecessary.

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 helps maintain the balance of the water level and control nutrient emissions.

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.

Passive restoration nurtures nature values

Passive 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. Restoration is worth considering, especially if the area borders on land areas in a natural state.

TIPS FOR FOREST PASSIVE RESTORATION

• Is the bog so barren that no viable trees grow there despite drainage?
• If the area is surrounded by other similar ones, you can form larger and more uniform nature sites from them.
• Active restoration, in which ditches are blocked to raise the water level, is an option for lush and very moist sites.
• Further information is available in the Ministry of Agriculture and Forestry’s Metso programme, and the Ministry of the Environment’s Helmi programme.

Plan carefully

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.

TIPS FOR PEATLAND FOREST MANAGEMENT

• Any ditch network maintenance must always be carried out based on careful consideration and only if necessary, paying attention to the water and nutrient balance of the entire forest area.
• In nutrient-poor areas, ash fertilisation can result in a better dewatering impact than ditch network maintenance.
• Utilise any viable undergrowth, but also use cultivation if required. It is essential to get trees growing well as quickly as possible and to minimise the treeless phase.
• In lush peatlands, you can also use the white birch, which spreads naturally in the area and is often accompanied by spruce seedlings.
• With continuous cover forestry, transpiration may be sufficient to maintain an appropriate water level.