Metla Bulletin 1/2011 - Monitoring methods are being developed to counter storm damages in Finland

June 15, 2011

	Monitoring methods are being developed to counter storm damages in Finland

Last year saw extreme weather phenomena in Finland, with a very cold winter and a summer that set temperature records of over 37 ° Celsius, followed by exceptionally strong storms in July and August. Storms Asta, Veera, Lahja, and Sylvia caused significant damage in Finland’s forests. More than eight million cubic metres of wood, equivalent to 15 per cent of Finland's annual cuttings, were thrown by the high winds that swept over southern Finland.

The wind throw estimates are based on storm-measuring field plots maintained by the Finnish National Forest Inventory (NFI).

‘After a large storm, there is urgent need to get a quick estimate of the extent and severity of the damage,’ says Dr Kari T. Korhonen from Metla for NFI. He continues: ‘Information gained on NFI storm field plots provided the framework for a more detailed assessment of the 2010 wind-throw damage and helped to put the storms in a real context and establish their scale.’

Forest-owners and the forest administration benefit from accurate information on the extent of the destruction caused by a storm for two principal reasons: to ensure rapid and effective organisation of processing of the wind-felled trees and to enable planning of future forest management measures (e.g., planting in the storm-affected areas).

‘If the storm hits in the autumn, as strong winds frequently do, there is often not enough time to harvest the damaged timber before the snow comes. Then the quality of the timber declines because of associated insect and fungus damage.’ says Korhonen.

Wind-throw trees provide a favourable breeding ground for several insect species. Typical insects seen in a wind-throw area in boreal pine forests are the common pine shoot beetle (Tomicus piniperda) and the stripped ambrosia beetle, Trypodendron lineatum. In spruce forests, the spruce bark beetle, Ips typographus, is found.

‘According to the law on prevention of forest insect and fungal damage in forests, Scots pines should be harvested by the 1st of July and Norway spruce by 1st August,’ says Dr Heli Viiri, an entomologist with Metla.

‘Scots pine needs to be transported away from a storm-damaged forest, to avoid further damage from feeding on shoots as the pine shoot beetles start swarming in early spring. The risk of spruce bark beetles attacking fallen trunks and also surrounding healthy standing trees in this spring 2011 is high. Furthermore, blue-stain fungi, which effectively spoil the quality of timber about two weeks after a wind throw, are a threat,’ she says.

In the past 20 years, high wind speeds and storms, such as Lothar in 1999 and Kyrill in 2007, have occasionally caused significant economic loss in Central and Northern Europe, but not to the same extent in Finland.

Now, however, according to Metla’s study Finland’s Forests in a Changing Climate (pdf), forest damage caused by high wind speeds is predicted to become more prevalent.

The occurrence of strong winds is not expected to increase, but forests will be more vulnerable to the storms of autumn and early spring because of the shorter period of ground frost, which reduces trees’ resilience against winds.

Therefore, are further developing the existing monitoring system is needed in order to obtain more accurate information, more quickly, on the actual extent of the destruction, in order to avoid large-scale forest damage due to invasive insect species after big storms.

Currently, forest-owners in Finland receive general information on the extent of storm damage through the media and from forest centres and forest-owners’ associations.

‘I hope that we will be able to produce online maps of damaged areas and distribute them via the Internet in the near future. This will make it a lot easier for a forest-owner to check whether his lot has been affected by a storm. Metla's role will be to consider different methods for this task, working with local forestry centres, to outline an action plan that could be followed after extensive storm damage occurs.’ says Korhonen.

Further information:

Dr Kari T. Korhonen, tel. +358 29 532 3030, e-mail: kari.t.korhonen @ metla.fi
Finnish National Forest Inventory (NFI)
Finland’s Forests in a Changing Climate (pdf)

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