Until well into the 20th century, protecting against natural hazards and maximising timber production were the main aims of forest management. In the last 30-40 years, however, many forests have become increasingly dense and dark, meaning that valuable structures for biodiversity have been lost. Forests have ceased providing a suitable habitat for many animal and plant species with distinct needs, in particular those requiring plenty of light. This has led to a decline in biodiversity, i.e. diversity of habitats, species and genes.
Over the past two decades, specific forest structures such as old trees offering special habitats, dead wood and shade-intolerant tree species have been increasingly encouraged. This is because numerous studies from all over the world show that forests need to be as diverse as possible in order to withstand the effects of external influences such as storms, diseases or insect infestation and to cope with climate change. According to Steffi Heinrichs from the University of Göttingen, speaking at the “Forum für Wissen”, this can primarily be achieved by combining different silvicultural methods on a large scale, thereby promoting biodiversity at the landscape level. It is about thinking in terms of wider landscapes that, taken as a whole, offer a habitat for viable populations.
Dead wood vital for rare insects, birds and fungi
Unmanaged, protected forests enrich the biodiversity in a landscape. However, such areas account for just 1.9% of forest in Germany, compared with 3.4% in Switzerland, according to Veronika Braunisch of the Forest Research Institute of Baden-Württemberg (FVA) and the University of Bern. "That is why the active promotion of forest structures is of particular importance in nature conservation, in areas such as the Black Forest and the Alps, where we want to improve the habitat of the capercaillie and help the species to survive." Unfortunately, she said, forest habitats particularly rich in biodiversity are scarce in Central Europe: most forests have too little light, too few gaps between trees and hardly any clearings, and only a few ancient, primeval forests survive.
The same problem affects insects, as WSL's Martin Gossner has discovered in a number of studies. "What is needed is targeted spatial and temporal planning of small and larger reserves," he said. On average, Swiss forests contain just 24 m3/ha of dead wood, whereas some rare insect species require 50 m3/ha or more. Specialist bird species such as the white-backed woodpecker can need in excess of 100 m3/ha of dead wood in some parts of their territories, added Alex Grendelmeier from the Swiss Ornithological Institute in Sempach.
Areas with a lot of dead wood can be created by storms or fires, for example. Research conducted by WSL's Thomas Wohlgemuth shows that such disturbances would significantly enhance biodiversity. "If more windthrow areas were left uncleared after major events, 10% of the forest area across Switzerland could be designated as reserves," the forest ecologist explained. Moreover, a landscape with such areas also contains many surviving individual trees and new thickets. These connect up different landscape elements, which has a positive impact on the distribution of many species, according to Reinhard Schnidrig from the Swiss Federal Office for the Environment (FOEN). The federal government has already invested CHF 340 million in forest nature conservation over the past 12 years, he noted, and in the future the aim is to bolster the importance of forests as large-scale habitats within the landscape.
Using molecular methods and remote sensing to record biodiversity
In the concluding panel discussion chaired by Kurt Bollmann (WSL), the panellists agreed that forest management had already made great strides towards increasing biodiversity. However, Regina Wollenmann of the Swiss Forestry Society stressed that a lot more work was needed to create more open forests and to better link them together. For Florian Altermatt of the Swiss Biodiversity Forum, it is important simply to recognise that diversity within forests is key to their long-term development. Often, he said, it is actually small microorganisms and the numerous species of insects that keep the metabolism of forest ecosystems going. Thanks to modern molecular methods as well as technical advances in remote sensing, the diversity of organisms can be measured much more easily and cost-effectively than just a few decades ago.
"If we want more biodiversity, we absolutely have to think about financial incentives too," said Jacqueline Bütikofer from forest owners' association WaldSchweiz, adding that forest owners could not be expected to pay for biodiversity enhancement measures out of their own pockets: since society as a whole had caused the decline in diversity, it should also bear the costs of measures to promote it. Florian Altermatt did not see why increased public funding would pose any major problems. Hitherto, approximately CHF 1 thousand millions has been spent each year on measures to promote greater natural diversity across all sectors in Switzerland, with around CHF 30 million of this going to forest biodiversity. According to a WSL study, numerous subsidies in various sectors amounting to CHF 40 billion per year are harming biodiversity. From an ecological point of view, a targeted redirection of many subsidies is needed.