Browsing by Author "Stimm, B."

For several reasons the conversion of mono-species into mixed-species forests is presently a major concern of forest management and policy in Central Europe. Although it is possible to show a clear trend in favour of mixed-species forests, private forest owners and some forest economists have often not favoured mixed forests, assuming that they are less profitable. The trend towards mixed forests seems mainly for ecological reasons, while sound economic analysis of mixed forests is still rare. Based on this background the objective of the study is to answer the following four questions: (1) Does the yield of mixed-species forests differ from that of pure forests? (2) Does the mixing of tree species influence the ecological stability of forests? (3) Is the economic value of a mixed forest less than that of a monoculture? (4) How do forest economic models integrate the findings on yield and ecological stability of mixed forests? To answer these questions a literature review was conducted on the possible impacts of mixed-species forests. In comparison to pure stands a greater yield is not necessarily given in mixed stands. Yet, mixed-species stands are better able to compensate disturbances than monocultures. Moreover, there is substantial evidence that mixed-species stands are more resistant against biotic and abiotic disturbances. Applying an extended forest economic model, it was possible to demonstrate that mixing large blocks of native broadleaf species into pure conifer forests may lead to a significant reduction of financial risk. From a risk-averse perspective the economic value of a mixed-species forest may thus be greater than that of a mono-species forest. Yet, it became clear that forest economists do not often integrate the research findings on yield and ecological stability of mixed stands in modelling, but rather apply simple bioeconomic modelling. Moreover, in the context of mixed forests economists also largely ignore even classical financial approaches, which consider risk and risk preferences. We concluded that forest economics has to close substantial research gaps. Firstly, the knowledge of how to integrate biophysical properties of mixed forests in bioeconomic modelling is still an open question. Secondly, forest economists have to adopt the modern approaches of financial theory and management science to value mixed forests.

To stimulate an economically oriented discussion on mixed forest management, this paper considers economic implications of mixed investments of pure stands of the Norway spruce (Picea abies (L.) Karst.) and the European beech (Fagus sylvatica L.) on a methodological basis. It is well known that the classical economic calculus leads to an overwhelming financial superiority of single species coniferous forest management in Central Europe, especially for growing monocultures of spruce. This explains why, since the early 19th century, the range of these forest types extends far beyond their natural limits. The change in the natural vegetation cover bore severe environmental problems as it was accompanied by a loss of biodiversity and a severe reduction in the resistance against storm, snow, ice, drought and insect damage of the forest stands. In contrast to this development as early as 1886, the Bavarian silviculturist Karl Gayer claimed that the forest condition must be able to deal with the uncertainty of future development. While pointing out that this condition could only be provided by “mixed forests” he, as a pioneer, formed an ecological concept for forest management. Unfortunately, forest managers have not broadly accepted his concept up to now. In order to support the ecological idea of “mixed forests”, it seems crucial to demonstrate that mixed diverse forests also possess economic advantages. Through using the portfolio theory founded by Markowitz and Sharpe, this paper evaluates mixed forest management and compares it to single species forest management. Its focus is on mixtures of Norway spruce and European beech. The Monte Carlo simulation method was used to simulate expected financial returns and their dispersion under risk. Mixed forests reduce the profitability but also show diversification effects due to only weak positive or even slightly negative correlated timber markets and diversified time structure of the timber harvests. Risk-averse decision-makers should therefore establish ecologically desired mixed forests with beech proportions between 10% and 50%, even if the profitability for mixed forests decreases. They will however benefit largely due to a significant risk attenuation. Although, effects of small-scale mixtures in stands comprising of many species were not considered we are sure that the findings of this study will in part also apply to mixtures on the forest stand level. While analysing an ecological concept from an economic viewpoint, which is transferable to the general idea of natural diversity, we intend to arouse interest in the ecologically oriented reader to evoke intensified future cooperation.

We used height growth data from a 7-year field experiment with European beech (Fagus sylvatica L.) seedlings to test the hypothesis that the effects of above- and belowground resources on height growth depend on seedling size and age. Photosynthetically active radiation (PAR) was determined by hemispheric photography, and estimates of fine root biomass of the overstory trees were used as an inverse proportional surrogate for belowground resource availability. For recently germinated seedlings growing under the canopy of Picea abies (L.) Karst., belowground resource availability affected height growth more than light. During subsequent stages of seedling development, apart from initial seedling size, PAR increasingly determined seedling growth. Besides initial size, seedling age determined the effects of above- and belowground resources on seedling height growth. In seedlings identical in initial size but differing in age, the increase in height growth with increasing PAR was greater in older seedlings than in younger seedlings. The ranking of seedling height by year showed that small differences in size at the end of the first growing season resulted in continuously increasing differences during the following years. Mortality data indicated that the chances of a seedling surviving intraspecific competition was strongly determined by its dominance ranking within the first 5 years after establishment.