In January 2005, the storm Gudrun hit Sweden. It has been estimated to have caused an overall economic damage of 2.4 billion euros in Swedish forestry alone. But has there been more damage to the forest than was clearly visible? A recently published study by Seidl and Blennow shows that Gudrun caused not only immediate damage corresponding to 110% of the average annual harvest in Sweden from only 16% of the country's forest area but also pervasive effects in terms of growth reduction.
In recent decades, the frequency and severity of natural disturbances by e.g., strong winds and insect outbreaks has increased considerably in many forest ecosystems around the world. Future climate change is expected to further intensify disturbance regimes, which makes addressing disturbances in ecosystem management a top priority. As a prerequisite a broader understanding of disturbance impacts and ecosystem responses is needed. With regard to the effects of strong winds -- the most detrimental disturbance agent in central and northern Europe -- monitoring and management has focused on structural damage, i.e., tree mortality from uprooting and stem breakage. Effects on the functioning of trees surviving the storm (e.g., their productivity and allocation) have been rarely accounted for to date.
Seidl and Blennow show that growth reduction following the storm was significant and pervasive in a 6.79 million hectare forest landscape. Wind-related growth reduction in Norway spruce forests surviving the storm exceeded 10% in the worst hit regions. At the landscape scale, wind-related growth reduction amounted to 3.0 million m3 in the three years following Gudrun. It thus exceeds the annual long-term average storm damage from uprooting and stem breakage in Sweden and is in the same order of magnitude as the volume damaged by spruce bark beetles after Gudrun.
Seidl and Blennow conclude that the impact of strong winds on forest ecosystems is not limited to the immediately visible area of structural damage, and call for a broader consideration of disturbance effects on ecosystem structure and functioning in the context of forest management and climate change mitigation.
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