Increment and yield in mixed stands with Norway spruce in southern SwedenLindén, Magnus
The productivity of mixed stands with Norway spruce is a matter of increasing importance in Swedish forestry. Non-wood factors, such as biodiversity issues, and the vast abundance of mixed stands, demonstrate a need for silvicultural methods that incorporate several tree species at the stand scale in the long-term. Until recently, such methods have been little studied, due to the predominant use of monospecific stand types in practical forestry as well as in research. The work underlying this thesis was designed to contribute to our knowledge of mixed stands. Through both experimental and modelling approaches, increment and yield in mixtures with Norway spruce and Scots pine or birch or oak were studied. It was found that wood decay in Norway spruce caused by butt rot can be reduced using certain types of mixed stands, and that such stands usually have similar volume increment to the more productive monocultures on sites similar to those in this thesis. An experiment with long-term mixtures using spontaneously regenerated birch in spruce regeneration areas has been initiated and the mixtures appear to be easy to manage according to a first evaluation. Productivity and economic performance of oak stands using spruce admixtures were evaluated, and indications of some beneficial effects (especially economic) were detected. The practice of retaining large deciduous trees in spruce stands for enhancing biodiversity was analysed. The results suggest that to minimise growth reductions in the spruce crop, retained green trees should be clustered rather than spread out. Mixtures consisting of two tree species are suggested to generally display a compensatory growth pattern between tree species, in which one is usually favoured at the expense of the other. Growth in the individual tree species may be very different from its corresponding growth in monoculture, whereas total productivity appears to be more similar to the mean yield of the two corresponding monocultures. Variability in stem size in mixed stands, which can be explained by differences in the growth parameters of the associated tree species, tended to increase for parameters such as height distribution and diameter distribution in the total population, whereas for the individual tree species, a more clustered distribution was noted in some of the studied mixtures.
Keywordspicea abies; pinus sylvestris; betula; quercus robur; mixed forests; diameter increment; volume; yields; plant competition; forest health; fungal diseases; heterobasidion annosum; stems; root rots
Published inActa Universitatis Agriculturae Sueciae. Silvestria
2003, number: 260
Publisher: Department of Southern Swedish Forest Research Centre, Swedish Univiversity of Agricultural Sciences
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