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Experimental design

One approach for management of second-growth temperate stands with conservation values is to favour legacy trees that contain red-listed or otherwise valuable associated species. Old hollow oaks (Quercus spp.), threatened by other invading trees, is one example. Oak regeneration also requires that enough light reaches the oak seedlings and saplings, and conservation-oriented partial cutting (conservation thinning) is one alternative for closed-canopy oak-rich forests. This is tested in the Swedish Oak Project, a BACI (Before-After-Control-Impact) field experiment that began in 2000 and is planned to be long-term. Because the forests contain many valuable trees and structures other than oaks, active management is not self-evident. Instead, we test non-traditional management (conservation thinning) versus minimal intervention – the latter alternative should not be neglected in research and management, and is sometimes called passive restoration.

Our 25 study sites are small nature reserves and woodland key habitats with large oaks and many other trees, essentially closed canopies, and basal areas of 20-38 square metres/hectare. About 60 years ago, canopy openness (% visible sky from the ground) was on average 50% and the sites have a history of agriculture (small fields and pasture woodland). The sites are spread over a large area and landscape factors are also analysed. At each site, we use one plot (1 hectare) for partial cutting, and one plot (1 hectare) nearby for minimal intervention, studying these both before and after cutting in the winter 2002/2003. We examine responses in vascular plants (herbs, shrubs and trees), bryophytes, lichens, saproxylic fungi, saproxylic and herbivorous beetles, fungus gnats (Mycetophilidae; Diptera and related families) and snails and slugs (terrestrial molluscs).

These taxa were chosen to represent both light-demanding and shade-tolerant or dessication-sensitive organisms. We do not study birds and mammals, which are generally well-known in Sweden, and would have required large study sites. The region and landscape is a mosaic of many small scattered conservation forests. We cut about 25-30% of the basal area at each site, harvesting mainly smaller, intermediate and some larger trees to create more open conditions, especially around larger oaks. Tops, branches, and two dead oaks were left in each plot, the rest was harvested (the project was funded for tests of careful biofuel cutting for biodiversity).

Experimental design

Page Manager: Sven Toresson|Last update: 5/9/2016

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