Vindskador vid stickväg i 1:a och 2:a gallring i Boxholm, Östergötland

Wind damage is something we are all familiar with since the storms Gudrun (2005) and Per (2007). Research about strip roads and wind damage is very limited. It is commonly known that the trees next to the strip roads more often fall whit heavy winds, and the purpose of this thesis was to verify this statement. Data was collected from first- and second thinnings at Boxholms Skogar AB, Ostergotland. In first thinnings data was collected from both spruce and pine stands and second thinnings only data from spruce stands was collected. The stands were thinned after the storm Gudrun but before the storm Per. There are different factors that increase the risk of wind damage and they can be divided into three categories. The first one is exposure, which include topography. Depending on how the terrain looks like, it can increase or decrease the wind velocity. Exposure also includes thinning that opens up the stand and the surrounding terrain with clear-cuts. The second factor is stand characteristics. The risk of wind damage to a tree is higher with increasing height and also indirect with high h/d-quotient. It is also important that the stand has had the right management in the past, e.g. pre-commercial thinning. The third factor is the ground on which the spruce and pine grow. This because both species are dominant on different type of ground and their roots develop differently. The spruce often has a limited root system and therefore becomes less storm resistant than pine. The paragraph that regulates strip roads was taken out of the Swedish forestry act in 1994. This means that any strip road pattern can be applied. In the first thinnings where data was collected, the average strip road width was 4,3 meters and the average strip road distance was 18,4 meters. In second thinning the numbers were 4,6 and 20,6 meters. The numbers are in line with what is used in today's modern forestry. The results show that in first thinning with spruce the wind damage was evenly distributed. In first thinning with pine the risk of wind damage was higher right next to the strip road and decreased with distance. In second thinning the wind damage was evenly distributed in the spruce stands. In first thinning the spruce shows a weak tendency that wind damage occurs more on thinner tress than on bigger. This has not been seen in second thinnings. In the pine stands, first thinnings, the results showed that the bigger trees have more wind damage than the small ones in spruce stands and the reverse in pine stands. As in the storm Gudrun the type of wind damage that occurred the most was uprooted trees, in both first and second thinnings and in pine and spruce stands. The conclusion is that wind damage in first thinning spruce stands is hard to reduce through management compared to pine. With less strip roads, which mean longer strip road distance, the number of wind-damaged trees can be reduced. In both first and second thinning the strip road width dose not affect the risk of wind damage. Therefore, the strip roads should be wide enough from the beginning for more thinnings in the future.