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In forests, damage is caused by various organisms, such as mammals, insects, and fungi. Forest damage is also caused by various natural phenomena such as wind, snow, and fires.  

Climate change-induced temperature rise and the occurrence of extreme natural events are predicted to increase the likelihood of forest damage. 

In forest damage situations, the Forest Damages Prevention Act obliges forest owners and forest professionals to take certain measures. For example, a forest use notification must be filed on fellings induced by forest damage. The Finnish Forest Centre monitors the extent of the damage on the basis of these notifications.

Damage by insects

Bark beetles  

Bark beetles are small beetles just a few millimeters long with short, mallet-tipped horns. The larvae of bark beetles are white and legless. In terrain, they are most easily identified by the eating patterns that can be seen on the bark. Bark beetles flock in spring and early summer when they find suitable breeding sites. There are several dozen bark beetle species in Finland, and among them are also the insects causing the most significant forest damage – eight-dentated bark beetles and Tomicus beetles. 

The spread of bark beetles is prevented by transporting felled timber and windthrown trees away from forests in a timely manner. In Southern Finland, pine timber with bark must be transported away from forests by the end of June and spruce timber in early July. In Northern Finland, the corresponding dates are two weeks later.

Eight-dentated bark beetles 

The eight-dentated bark beetle is a dark brown bark beetle about 5 millimeters long and living in spruce. Beetles reproduce mainly in windthrown trees, spruce stacks, and poorly maintained standing trees. When in abundance, eight-dentated bark beetles can also attack living trees. The damage caused by the beetles is detected by the inlet holes in the bark, which are surrounded by brown wood wool. The beetles eat the phloem layer of the spruce and cut off the fluid flows running through the tree trunk, causing the spruce to dry up quickly. 

Mature spruce forests in areas with a high beetle population and in the vicinity of storm damage or previous eight-dentated bark beetle damage are prone to damage by eight-dentated bark beetles. The beetles are also attracted to spruce on the edge of open and sunny areas. 

Pine shoot beetles

Of the bark beetles, the Tomicus, the common pine shoot beetle and the lesser pine shoot beetle, are the worst pine pests in Finland. They cause growth losses by cutting off the leading shoots of the pines. The tops of the trees drop their needles and can dry out completely as the damage continues from year to year. The lesser pine shoot beetle also spreads blue stain fungi on the timber. 

Pine sawflies

There are several species of pine sawflies, but the actual pests are the European pine sawfly and the common pine sawfly. Pine sawflies are characterized by strong population fluctuations, and during mass occurrences the damaged areas can be tens, even hundreds of thousands of hectares. Nuclear polyhedrosis virus is available as a biological control tool for the control of the European pine sawfly. The virus, in addition to the reproduction of parasites, usually naturally collapses the sawfly population without any actual control measures. Felling and tending of seedling stand in the affected areas should only be done after the end of the mass occurrence.  

Due to the prevalence and breadth of the mass occurrences, the European pine sawfly is considered the most significant pine pest in Finland. Damage has occurred every 5-6 years and massive damage in provinces every 20-30 years. In June, the larvae eat pine needles of the previous year and older needles. Eating needles causes growth losses, but trees usually recover well. 

The mass occurrences of the common pine sawfly usually last from 1 to 3 years and are hundreds, less often thousands of hectares, in size. From late June to mid-September, the larvae eat all the pine needles and the damage is severe, especially if the eating has occurred for two years in a row. In this case, a large number of trees can die. 

Pine weevils 

The pine weevil is a dark, long-stemmed beetle, over a centimeter long, with transverse yellowish streaks on the cover wing. The beetles gnaw at the bark of young conifers leaving vaguely shaped blotches and revealing wood. Extending the damage around the tree trunk causes the tree to die. The species is found all the way up to Northern Finland. Damage can be controlled by chemical or mechanical pesticide treatment in seedling stands and by planting the seedlings in mineral soil exposed by soil preparation measures. 

Mycosis

Of the fungi, rot fungi, especially Annosum root rot, cause the most significant forest damage. The annual losses caused by Annosum root rot in Finland are at least tens of millions of euros. Resin top disease, many species of rust fungi and blight, among others, also cause damage of varying degrees each year. 

Annosum root rot

There are two species of Annosum root rot in Finland: the Heterobasidion parviporum, which causes spruce decay, and the Heterobasidion annosum, which mainly decomposes pine roots. However, these root rots also infect other tree species. In addition to spruce, the Heterobasidion parviporum also decays larch. The Heterobasidion annosum specifically affects pines, causing pine annosus root-rot, but it may also be a major rot agent in spruce and larch forests. The Annosum root rot spreads in two different ways: as spores entrained by air currents and as a fungal mycelium growing in wood. In summer fellings, the majority of Annosum root spore infections can be controlled by treating the felling surfaces of the stumps with a pesticide at the time of felling. The Forest Damages Prevention Act makes the control of root rot mandatory in fellings carried out in coniferous forests in Southern and Central Finland between the beginning of May and the end of November.

Scleroderris canker 

Scleroderris canker caused by the Gremmeniella abietina is mainly a pine disease, but it is also found in spruce and several other coniferous species. In cold and humid sites favourable to the fungus, the disease can occur from year to year. Epidemics are set off during cold and rainy growing seasons. During epidemic years, Scleroderris canker can cause large growth losses, low forest productivity and, at worst, the destruction of entire forests. Prevention is essential in the fight against the disease. Seedlings of local origins should be used in silviculture and thinning of pine trees should be done in time to maintain the airiness of the tree crowns. 

Resin top disease

Resin top disease is one of the most common pine diseases in Finland and can be found all over the country. The disease causes extensive, elongated, dark, resinous calluses in the trunk and branches of pines of all ages and reduces the quantity and quality of timber. Often the fungus kills the treetop above the callus and sometimes the entire tree if the callus occurs at the thick end of the tree.  

Trees infected by resin top disease should not be left as seed trees, as susceptibility to the disease is inherited. The origin of the seeds and seedlings should be known so that no susceptible material is used for regeneration. To prevent spreading of the disease, infected trees should be removed during tending of seedling stands and thinnings. Infected trees can spread the disease further. 

Mammal damage

Cervids

Cervids living in Finland include moose, white-tailed deer, roe deer, Finnish forest reindeer and reindeer, of which moose cause the most significant damage to forests. Moose cause forest damage mainly by cutting the leading shoots of tree seedlings, but also by eating branches and tearing off the bark of the mature trees. The most typical moose damage target is a 1–3 m long seedling stand with pine as the dominant tree species. Birch and aspen are also good for moose. Roe deer and white-tailed deer usually damage smaller seedlings than moose. They can damage pine, spruce and deciduous trees. 

The most important measures in preventing damage are the regulation of cervid populations by hunting, timely tending of seedling stands, and control of animal grazing, for example, by providing salt blocks, and by the use of barriers and deterrents. 

If the extent of cervid damage exceeds the compensation threshold of 170 euros, a damage report can be filed with the Finnish Forest Centre and applying for compensation is possible. As the compensation comes from cervid shooting license fees, no compensation will be paid for the damage caused by unlicensed roe deer. 

Voles

Voles cause massive damage to seedling stands during the peak years of population variation. In seedlings, the eating spot reveals the vole species: the top part with buds is eaten by the bank vole, the base part by the field vole and the root system by the water vole. The growth of vole populations can be prevented locally by favouring vole enemies, such as owls, and by placing bird boxes on the outskirts of seedling stands. In special areas, such as afforested fields, it is possible to use seedling protectors that prevent field vole damage. 

Other pests  

Of the other animals, minor local damage is caused by hares and wild fowl, among others. Especially in the seedling stage, trees are also susceptible to many fungal diseases. With global warming, new potential pests may also appear in our forests. Black-arched moth, Asian long-horned beetle and red band needle blight are the examples of invasive and alien species causing damage that have already been found in our country.

Wind and storm damage

In Finland, the worst wind damage has caused millions of cubic meters of wood to fall. For example, in 2001, the Pyry and Janika storms felled 7.3 million cubic meters of wood, and the 2010 series of storms Asta, Lahja and Veera felled about 8.1 million cubic meters of wood.  

With climate change, the snow-free and frost-free winters are predicted to become longer and more widespread, increasing the risk of trees falling from the winds. Old pure spruce forests are most susceptible to wind damage. 

Forest management measures cannot completely prevent wind damage. However, the risk of wind damage in the forest can be reduced by carrying out tending of seedling stands and thinning in a timely manner. Forests that have been overgrown for a long time are particularly susceptible to damage after thinnings. A mixture of pine and birch in spruce forests reduces the risk of wind damage. The forming of stands marked for harvesting can also affect the occurrence of wind damage. The edge areas of clear cuttings are prone to wind damage. In strip fellings, strips can be formed perpendicular to the prevailing winds. 

If extensive damage occurs, tree harvesting should begin immediately. If fallen trees are not harvested in time, blue-stain fungi will ruin the timber. Consequently, severe insect damage can occur in nearby forests in the coming years.  

When you notice the signs of damage, evaluate the extent of the damage on your own. Contact a forest professional if there are trees in your forest that were recently felled or damaged by a storm.  

It is not always advisable to harvest individual windthrow, as the harvesting costs often outweigh the benefits. Fallen trees are also valuable for forest biodiversity. When there are more damaged trees, the risk of consequential damage increases. 

The Forest Damages Prevention Act obliges the forest owner to remove from the forest such conifers damaged by storms or other natural disasters, from which insects causing forest damage may spread. The obligation arises when there are more than 10 damaged spruce trees or when there are more than 20 solid cubic meters of damaged pines per hectare in the forest. In this case, the number of damaged trees exceeding the limit values must be removed by the deadlines provided by the law.

Harvesting storm-damaged forests is one of the most dangerous forestry measures. The trees felled by the storm should be harvested with a harvester, as the use of the machine significantly reduces the risk of accidents. Working with a chainsaw requires professional skills from the feller, and even experienced professionals must sharpen their attention and consider the most suitable way of felling. It is essential to keep occupational safety in mind and to adapt the pace of work to the hazards.

Harvesting storm-damaged trees from over the power lines is commissioned by the line owner, most often a local electricity company. If the feller is otherwise uncertain about felling trees safely next to the line, it is advisable to ask the line owner for instructions or assistance. Usually contacting your local electrical or telephone company will help. Whenever there is a risk of trees falling on the power line, contact the electricity company.

If the storm has felled quite many trees and harvesting them would incur unreasonable costs, it is worth exploring the area’s nature protection potential. Among other things, forests with abundant rotting trees are included in the METSO program.  

If you have insured your forest against storm damage, it is advisable to contact your own insurance company as soon as the damage is detected. 

Snow damage

Snowfall and alternation of frosts and thaw increase the snow load on the trees. Heavy wet snow bends trees, cuts treetops and, at worst, fells entire trees.  

Overcrowded freshly thinned stands are more prone to snow damage. Heavily attenuating sparsely grown trees withstand the weight of snow better than technically more advantageous less attenuating trees. 

Snow can damage all tree species. Freshly thinned pine forests that have long grown amidst overcrowding are most susceptible to snow damage. Thanks to its hanging branches, spruce is more resistant to the weight of snow than pine. For older trees, snow causes top ruptures and breaks in branches and trunks. Young thin trees can bend to the ground when pressed by snow. In areas prone to snow damage, tending of seedling stands and thinnings should be done in good time to prevent the trees from attenuating. 

  • If you detect snow damage in your forest, first determine the extent of the damage on your own. If the damage is extensive, the trees should be harvested as soon as possible. Then the damaged trees can still be utilized. Snow-breaks also predispose trees to fungal and insect damage. The forest owner's obligation to harvest damaged stands must be taken into account if the amount of the damaged stands exceeds the threshold value of the Forest Damages Prevention Act.

Forest fires

In Finland, forest fires have been small-scale in recent years. The most common cause of wildfires is the careless handling of open fires by humans. 

Special care must be taken in forestry work when forest fire and grass fire warnings are in effect. A spark from a brush saw or an ax hitting a stone can ignite a fire. The risk is the same in mechanical forestry. Sparks can be generated when using excavator buckets or machine roller wheels and chains. 

The fire risk can be predicted and reduced by good planning and by avoiding certain actions in flammable areas.

Among the habitat types, fire sensitivity is highest in forests of different stages of development of semi-dry, dry and barren heathlands. In other habitats, fire sensitivity is affected by tree species and forest composition. A large amount of forest residue increases the risk of fire. In addition, grassed areas always have a higher fire risk than low-grassed areas. 

The forest fire index (in Finnish) produced by the Finnish Meteorological Institute provides up-to-date information on the risk of forest fires caused by drought in the terrain. 

After a forest fire, it is good to check the condition of the forest and ensure that there is enough even-aged tree stands within the meaning of the Forest Act. If there is an even distribution of even-aged trees in the area equal to or more than the minimum amount indicated in the Forest Act, the damage does not require regeneration. If timber is harvested in the damaged area and as a result an open area of more than 0.3 hectares is created, or the minimum basal area limit after the felling is not achieved, the obligation to regenerate the forest also follows from the felling. 

 After a forest fire, the forest owner can offer the site for voluntary protection. The forest fire area provides a habitat for organisms dependent on burnt and charred wood, such as fungi and beetles. The amount of burnt wood has decreased in commercial forests, so burnt trunks and stumps should be preserved when forestry activities are carried out. A single burnt stump can provide a habitat for a threatened fire-dependent species for years. 

Forest damage preparedness

Good forest management  

Forest management measures cannot eliminate the risk of damage, but they can affect the probability and extent of damage. Favouring mixed-species forests, the use of the tree species best suited to each site, timely tending of seedling stands, thinnings, and regeneration reduce all risks of damage. Stump treatment is an effective way to prevent Annosum root rot from spreading during early fellings when the ground thaws. In the case of wind damage, the risk of damage can be reduced by appropriate intensity and timing of thinnings. In regeneration fellings, the choice of method and the shape of the felling pattern have an influence on the risk of damage. 

Insurance

Forest insurance is a risk management tool worth considering for a forestry operator. Insurance can help to be prepared for sudden and unpredictable natural events such as storms and forest fires. The insurance does not provide coverage for the spread of Annosum root rot. The insurance does not cover the damages that have occurred or started before the insurance came into force either. The most common causes of damage are storms. In the event of damages, the value of the forest and the timber harvested from it is reduced or completely lost.  

Forest insurance usually covers damage to trees, felled timber, planted seedlings and seedling stands. On the other hand, sawn or otherwise further processed timber is not covered by forest insurance. 

There is a lower limit for damage compensations. Check the terms and conditions in advance with the insurance company or in your insurance. The amount of destroyed stands must normally be at least 15 cubic meters or at least 0.5 hectares of the uniform area to be afforested. If the limit is exceeded, the insurance will cover the damage in full. However, the personal liability agreed in the insurance is deducted from the sum of compensation.  

Normally, damage caused by cervids other than roe deer is not covered by forest insurance, even if it provides coverage against damage caused by animals. However, moose and white-tailed deer damage can be compensated from state funds. 

According to the Rescue Act, the forest owner is responsible for the forest fire-related clearing and security measures. If the forest owner does not take care of the clearing and security measures, the fire chief leading the rescue operation has the right to have the clearing and security measures undertaken at the forest owner's expense. The insurance also reimburses such costs when it has insurance coverage against forest fires.  

The forest insurance premium can be deducted in forest taxation. Correspondingly, forest insurance payments are forestry income subject to withholding tax. 

Contingency plans

The statutory tasks of the Finnish Forest Centre include preparing for large-scale forest damage, such as forest fires, storm, and snow damage, as well as insect and fungal damage. Preparedness concerns large-scale damage of regional or national significance.  

The Finnish Forest Centre's contingency manager is responsible for preparing for damage in co-operation with the region's rescue authorities and forest industry actors, as well as representatives of electricity companies. The operating instructions are described in the contingency plan. 

The contingency plan describes sending of notices to the storm preparedness group, raising preparedness as well as the tasks and operating instructions of the Finnish Forest Centre's preparedness group. The plan covers timber harvesting, electricity distribution, damage mapping and information measures. Operational readiness is maintained through practices.

The Ministry of Agriculture and Forestry also has a contingency plan for forest damage. The Finnish Forest Centre also assists the Finnish Food Authority in preparing for and combating the invasive species threatening forests. Such a species is, for example, the pine wood nematode.

Observation and recording of forest damage

Reporting forest damage observations is possible via the Finnish Forest Centre’s map service. The unofficial notification does not directly lead to measures at the Finnish Forest Centre, but the recording of damage observations provides additional information to supplement the official damage statistics. For example, recording a moose damage observation is not a request for an official moose damage assessment. Recording the finding does not eliminate the need to report the damage with a forest use notification in accordance with the Forest Act in connection with felling.  

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