VAXJO, Sweden, Nov. 5, 2015 (Press Release) -Södra has learned many valuable lessons from the severe storms in recent years. This experience and knowledge has now been harnessed in new management instructions to reduce future storm damage to forests. Thinning at lower heights and earlier final harvesting for spruce-dominated stands are two of the important changes.
Carefully designed measures aimed at creating stability in the forest will reduce the risk of storm damage. Pre-commercial thinning at the right time, for example, is key to promoting moderate stand density. The timing of the first thinning operation is also crucial to a stand's future stability and storm resistance.
"If thinning in a spruce-dominated stand starts when trees are 12-14 metres high, ends when they measure 20-22 metres and does not remove more than 30-35 percent of the surface area, the risk of future storm damage to the stand will be reduced," says Göran Örlander, Head of the Silviculture Department at Södra.
"Immediately after thinning, the stability of the remaining trees will deteriorate, but eventually improve. Södra's view is that thinning is necessary to increase forest value, and a measure that can be implemented without any major risk of storm damage. However, mature high forest should not be thinned, as this will increase the risk of storm damage, and older forests takes longer to stabilise than young forests."
Exposed areas are at greatest risk of storm damage, such as west-facing slopes and sites adjacent to lakes and fields. Great care should therefore be taken when thinning buffer zones, and they should never be thinned when the trees have grown high. Several stands should never be thinned at the same time.
Since most storms arrive after defoliation, most storm damage occurs in softwood forests that are mature and high. Although summer storms are relatively rare, they can also cause severe damage in hardwood forests.
"To reduce the extent of storm damage, we now recommend that spruce-dominated stands be harvested 10-15 years earlier than our recommendations prior to Cyclone Gudrun, i.e. when trees have reached a maximum height of 26-28 metres."
In an effort to reduce storm damage to forests, Södra continuously garners new knowledge, and develops new methods and techniques in a range of areas.
"We work to develop forest management, for example, by preventing the spread of root rot and reducing soil damage. Combined with the development of new reproductive material, which makes root systems more symmetrical, for example, this will improve the storm-resistance of trees in the future," says Göran Örlander.