Sustainability sets limits to the use of forest-based energy.
The gathering of logging residue has both positive and negative effects on forestry and biodiversity.
Removing logging residues from the logged area speeds up the regeneration of forest by two years at best, and decreases the cost of the seedling stand management by 20‒30 percent.
The seedlings get off to a good start because competition from ground vegetation is minor during the first summer after felling. Grasses and raspberry, for example, get a good hold of the area only in later years.
Removing logging residue has been observed to increase the soil temperature by 1‒2 degrees centigrade, which accelerates the root development of the seedlings, thus increasing their chances of survival.
Removing logging residue removes nutrients
When the branches and stumps are removed from an area, the nutrients they contain are also removed. The major part of the nutrients is, however, contained in the needles, and as the residue is dried on site before removal, the needles fall off and the nutrients stay in the forest.
The needles are not wanted in energy production, for they contain chlorophyll which causes toxic emissions when burned.
The decisive thing for the remaining trees and new seedlings is whether they get enough complementary nutrients from the organic material and minerals in the soil and from atmospheric fallout.
The greatest effects of the removal of nutrients occur in young, fast-growing forest stands. Immediately after thinning, their need for nutrients is high due to the growth increase caused by the increase of space and light available. On a regeneration felling site, the decrease in the amount of nutrients available has less effect, because seedling do not require as much of them.
Environmental guidelines are set for harvesting
MIn gathering forest energy as in all forestry, biodiversity protection and conditions of soil are taken into account. So far, few scientific long-run studies have been carried out on the effect of energy wood gathering on the environment, mainly because the practice is much more recent than other forestry work.
The Forestry Development Centre Tapio has created guidelines concerning the gathering of energy wood in cooperation with the other stakeholders. Finnish Forest centre monitors the compliance with the recommendations. The recommendations concern the selection of suitable harvesting sites, harvesting in itself, quality of work and storage, as well as nature management and respecting waterways and prehistoric relics.
According to the guidelines, dry heathlands are not harvested at all for energy wood. In addition to this, stumps are not harvested on groundwater areas. Stout, decayed wood cannot be harvested either.
30 percent of logging residue must be left
30 percent of the logging residues on the harvestintg area must be left in the forest. When lifting stumps, old and decayed ones are left, as are those with a diameter below 15 centimetres. At least 25 live stumps larger than 15 centimetres must be left per hectare, dispersed evenly over the area.
Stumps are not harvested on steep slopes and sites with natural or cultural values. Buffer zones of at least three metres must be left around waterways and ditches and retention trees.
Harvesting energy wood can increase the recreational value of an area. This is important especially near population centres.
It is easier to move about in a forest if the logging residue has been removed and the view opened up. Some feel that a “tidy” forest like this is aesthetically pleasing.
The removing of logging residue does not seem affect berry crops much. The raspberry crop might decrease but the lingonberry crop increases.
Updated on the 4th of January, 2016.