Automatgenererad bild.

28 February 2013

More forest tree species can benefit ecosystem services

Mixed forests can contribute positively to many ecosystem services. Results from new research can indicate new ways of working for sustainable forestry in the Future Forests programme.

Most of Sweden’s forests are dominated by spruce or pine plantations. This has been seen as the most rational approach to timber production. Meanwhile, the value of having multiple tree species in the forest, partly for the sake of biodiversity, has been discussed.

‘But although this issue has long been discussed and involves many stakeholders, few studies of whether more species benefit various ecosystem services have been carried out,’ says Jan Bengtsson of the Swedish University of Agricultural Sciences.

Bengtsson has now headed a study of how tree species richness correlates with tree growth, soil carbon storage, berry production, food for wildlife, the presence of dead wood and biodiversity in ground vegetation. The survey, based on analyses of data from the Swedish National Forest Inventory and the Swedish Survey of Forest Soils and Vegetation , was funded partly by Future Forests, the Mistra research programme. Bengtsson collaborated with some 15 researchers who were experts on everything from data processing to ecosystem services.

‘What we see is that having more tree species in the forest has had beneficial effects on all ecosystem services. It surprised us that the effects are so large.’

Interconnections among ecosystem services

Certain tree species are more clearly connected with particular ecosystem services, which in turn are interrelated: one service can decrease when another increases. If the trees grow faster, for example, quantities of berries, dead wood and food for wildlife decline.

Jan Bengtsson explains that the study has nevertheless not looked at possible mechanisms underlying these effects. Examples would be ways in which ecosystem services are affected by different species, or by whether mixed forests are thinned in a particular way. A next stage would therefore be experimental studies in different types of forest.

The findings, published in the scientific journal Nature Communications, have attracted a great deal of attention. This is partly because some previous research, in contrast, has found similar or greater tree growth in monocultures, i.e. forests composed of one tree species only.

‘The great response we’ve had is tremendously pleasing, and shows that we need to carry on to find out more about this. It would also be extremely interesting to find ways of studying how recreation and outdoor activities, which are also ecosystem services, are affected by multiple tree species. That’s something we weren’t able to do in this study,’ Bengtsson says.

Discussion on how to proceed

Today, 25–70 per cent of Swedish forests (depending on how one chooses to define the term) are ‘mixed’. How they and all the forested areas dominated by single species affect different ecosystem services is interesting for Future Forests, which seeks to foster sustainable forestry.

‘The new knowledge paves the way for a discussion of how forest ecosystems work and how to apply it to forest planning and management, says Jon Moen of Umeå University, who took part in the study and works in Future Forests.

This research programme is to organise a round-table conference about these results and why other research arrives at different conclusions. Researchers and representatives of forest industry, public agencies and non-profit organisations will be invited to attend the conference, which the programme is to hold jointly with the Royal Swedish Academy of Agriculture and Forestry at the end of May.

‘The aim is to consider various approaches and discuss what lessons can be learnt, what knowledge gaps there are and how we can best study several ecosystem services at the same time, rather than looking at them one by one as we do today,’ says Jon Moen.

Text: Andreas Nilsson, Vetenskapsjournalisterna

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