Growth of nitrogen-fixing Alnus incana and Lupinus spp. for restoration of degenerated forest soil in northern Sweden
Huss-Danell, Kerstin; Lundmark, Jan-Erik
In the interior of northern Sweden, more than 100.000 ha of previously productive forest land have degenerated soils. The presently thin humus layer and the resulting lack of mineralizable nitrogen and organic material results from strongly reduced litter production on the now almost tree-less areas. Intense forest fires in the past. as well as unfavourable forestry practices, are likely to have caused this situation. Cultivation of nitrogen-fixing plants, the native grey alder, Alnus incana ( L.) Moench. and introduced lupins. especially Lupinus nootkatensis Donn, was tried in the present study as a means of soil restoration. After 7 to 9 years. mesic sites with a temperature sum of 9800 daydegrees during the growing season gave higher survival and better growth of A. incana than did drier or cooler sites. At the northernmost, coolest site, L. nootkatensis performed very well while A. incana did not. Liming and, to some extent. soil scarification improved establishment of L. nootkatensis. Various amounts of alder leaves were repeatedly deposited every year to the soil in small experimental plots and the effects on soil properties were evaluated after 6 years. Nearly 1000 kg dry mass leaf litter per hectare was considered to be a realistic yearly production from dense A. incana stands. Such amounts gave a thicker humus layer with a comparably higher pH, a higher degree of base saturation. and a higher content of N,,,, and mineralizable N. Aspects of the biology and the handling of A, incana and L. nootkatensis are discussed. to serve as a guide in a choice between the two species for soil restoration purposes.
Alnus; degenerated soil; humus layer; leaf litter; Lupinus; mineralization; nitrogen fixation; organic material; soil restoration; Sweden
Studia Forestalia Suecica
Publisher: Faculty of Forestry, Swedish University of Agricultural Sciences
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