Admixing broadleaved to coniferous tree species: a review on yield, ecological stability and economics

Abstract

For several reasons the conversion of monospecies 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.

Silvicultural strategies for adapting planted forests to climate change: from theory to practice

“…Mason 2006). This may reflect the fact that many species used in British forestry are light demanding or intermediate in shade tolerance (Malcolm et al 2001) whereas mixtures often discussed in the European literature such as Norway spruce and beech (Fagus sylvatica L.) (Knoke et al 2008) are generally composed of at least one shade tolerant species so that competition for light is less intense.…”

Climate change adaptation and sustainable regional development: a case study for the Federal State of Brandenburg, Germany

“…Thus, the large-scale, monospecific, and mostly coniferous forests in Germany were and shall be gradually converted into mixed broadleaved/coniferous stands. The greater resilience and stability of site-adapted, species-rich and structured forests has been proven several times (see the review by Knoke et al 2008). Furthermore, inter-specific competition in mixed forests may to a certain degree shelter some species (e.g.…”

“…planting trees to 'remove carbon from the atmosphere') seldom consider adaptation to climate change in their management plans ) despite their necessarily longer-term outlook. This lack of documentation is striking, particularly since many possible climate change adaptation actions can be justified for other reasons than climate change (Adger et al 2007;Dovers 2009): Related to forest adaptation, this could be a diversification of forest species and structures to improve stability, biodiversity, and attractiveness for visitors (Knoke et al 2008). …”

Neighbor identity and competition influence tree growth in Scots pine, Siberian larch, and silver birch

“…However, the practical value of this information has often been underrated, due to the commercial demands favoring monocultures (Kelty, 2006;Nichols et al, 2006). Requirements for sustainable management have increased the preference for species mixtures and there is a growing need for studies covering different aspects of tree cultivation and competition in mixed stands (Knoke et al, 2008).…”