Part II (continued)
A specific risk is damage during the logging process
Regarding timber production in continuous-cover forests, the study was conducted only on selective logging of spruce stands on mineral-rich soils in southern Finland. Several studies have revealed that timber production in continuous-cover forests is 15-25% lower than in clear-felling forests. Studies conducted in Sweden showed this difference to be in the range of 10-20%.
To date, no research data is available on timber yields related to small-area felling, growing large trees in pine stands, northern Finland, peatlands, or the transition period from clear-felling to continuous-cover forestry.
Trees left during the continuous-cover forestry method can be damaged during the harvesting of larger trees. Up to 10-20% of medium-sized trees are damaged. A significant number suffer broken tops, which means they will never develop into full-fledged, strong trees.
The risk of damage to saplings depends on how close forestry operations are carried out to them. Other risk factors include the distance from the harvesting machinery, the height of the sapling, and the air temperature during felling (e.g., whether it is below zero, etc.).
Logging equipment can prune branches from trees and leave them on the ground, thus reducing damage to the forest floor. However, the amount of slash left in selective logging differs significantly from the amount of slash generated during thinning in clear-felling systems.
Profitability varies in every case
The profitability of continuous-cover forestry has been studied in the case of selective logging of spruce stands. It could be more profitable than clear-felling forestry, even if a lower volume of timber is obtained.
The most important factor increasing profitability: most forestry activities may not need to be carried out. The higher the average interest rate for savings and loans, the greater the profitability of continuous-cover forestry compared to other forestry methods.
This is explained by the fact that in the clear-felling management method, the money invested to establish and tend new forest stands after clear-felling will not be recovered until the forest is harvested and the timber sold.
As long as the money invested in this forest cannot be used elsewhere, the return on investment drops, and the higher the interest rate, the greater the losses.
The fact that natural regeneration is not guaranteed reduces the profitability of continuous-cover forestry. And if natural regeneration does not occur, the forest must be regenerated using the very methods that were initially sought to be avoided.
Furthermore, it is unclear whether forest growth will be sufficient if there are not enough trees in the forest initially. If logging is too intensive, trees do not always regenerate, and it is possible that not enough saplings emerge, and of those that do, not all survive.
Risk calculations are different
The average risk of forest damage is higher in forestry based on clear-felling than in so-called continuous-cover forestry. Types of risks include fungal diseases, nutrient deficiencies, damage from the large pine weevil, and losses caused by strong winds and rodents. However, risk probability calculations differ sharply.
A significant exception is spruce root rot, which cannot be prevented without felling the trees and planting other species. Root rot spreads through the root system and most often occurs in continuous-cover forests.
Root rot infection can also spread through the air and appear if the tree surface is damaged. Infection can be avoided by treating the stump surface with a biological pesticide. However, if standing trees are damaged during felling, they are exposed to the risk of infection by root rot spores.
Spores do not move through the air during the cold period of the year, so spruce stands being managed using the continuous-cover forestry method should be logged between November and April. This is becoming increasingly difficult as the winter period shortens, whereas opportunities for seasonal timber harvesting are increasing.
If the number of selective felling sites changed, would the amount of timber obtained also change? That depends on the user of the specific method.
Some berry species like it, others do not
In peatlands, the continuous-cover forestry method could solve a number of problems. The biggest advantage: this method improves the stability of the groundwater system, whereas in the case of periodic cover or clear-felling forestry, these systems change. As a result, peat decomposition occurs, greenhouse gas emissions are generated, and a larger amount of nutrients flows into waterways.
On the other hand, successful propagation of saplings may require soil improvement, which reduces profitability; however, more research is needed on peatlands.
Speaking of berry species, continuous-cover forestry is favourable for bilberries, but less favourable for lingonberries, as well as for mushrooms.
It is believed that clear-felling negatively affects the landscape, including recreational opportunities, yet there are very few scientifically based comparisons between logging methods in this regard.
Figure 1. Root rot is a common problem in spruce stands in southern Finland; to avoid it, logging must be planned for the cold time of year. Photo by Erkki Oksanen
Figure 2. Selective logging in a pine stand. Photo by Erkki Oksanen