Finnish Forest Research Institute  Metla
Press release 07.09.2006

Increased dead wood volume and restoration burning enhance biodiversity

Increasing dead wood and restoration burning are means to emulate the disturbance phenomena (storm damage, forest fires) that are part of natural forest dynamics and to enhance preservation and proliferation of forest-dwelling species. The benefits of restoration are presented in a research report of the METSO Forest Biodiversity Programme for Southern Finland; solutions to national biodiversity issues are introduced in the report.

Increasing dead wood and prescribed burning had positive effects on the structural development of forest stands as well as on changes in species composition and abundance in a restoration experiment performed in the Natura 2000 area in Evo. The study was performed in collaboration by the Finnish Forest Research Institute (Metla), the Finnish Forest and Park Service, HAMK University of Applied Sciences, the Finnish Environment Institute and the University of Helsinki. The results indicate that with a larger volume of dead wood the intensity of fire is increased and that controlling the volume of dead wood can lead to desired effects after the fire. Despite the immediate effects of restoration actions on many species groups are predominantly negative, the long-term effects are expected to be positive.

Methods of restoration could enhance the regeneration of aspen, for example. The study covered the Evo area and the Kotinen nature reserve, and problems were detected in aspens’ regeneration and population structure. Although the stands contain fairly large amounts of young aspen, the strong moose browsing during the past decades causes uncertainty as to the recruitment of young aspens into mature trees. As a rough estimate, during the next few decades a significant proportion of the mature aspens that maintain biodiversity in the conservation areas of Southern Finland will die. This will mean lower survival chances for the species sustained by aspens. Especially in areas of protected old-growth forests the regeneration of aspen seems to have become negligible, and hence the future of aspen-associated species looks gloomy.

In a collaboration study by the Finnish Environment Institute and Metla the aim was to investigate the species composition on old prescribed burning sites. According to the results, the proportion and quality of semi-natural forests amid the forest landscape largely determine the species on the sites after burning. The experimental sites studied are located in south-western Finland , central southern Finland and North-Karelia in eastern Finland . The regions were different regarding the area of semi-natural forests and the quality of the forest landscape (history of forestry, forest fires).

The number and frequencies of both threatened and near-threatened species were highest in regions with the highest number of semi-natural forests and where the history of forestry was the shortest. Therefore, restoration of forests should be performed in the vicinity of semi-natural forests in mature stands with mixed tree species. This will provide the best benefits for specialized (threatened and near-threatened) saproxylic species (species dependent on dead wood) by increasing the connectivity of semi-natural forests and gradually also the population sizes of species.

Also in this study, the positive effects of restoration were observed with a delay. The positive effect on wood-decomposing fungi was observed as late as more than five years from the rehabilitation and restoration activities.

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