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High species diversity through protection and use

Forest reserves provide habitats for threatened animal and plant species. But species diversity can still be high in commercial forests. A conversation with Kurt Bollmann, WSL, and Ulrich Mergner, Bavarian State Forestry Enterprise.


“Intensive use can, under certain conditions, lead to high
species richness.”

In forest reserves the forest is con­tractually protected. The aim is for such reserves to make up 10 per cent of the forest area in Switzerland by 2030. What do you think about this as a goal?

UM: From the point of view of species diversity, it makes no difference whether five, eight or ten per cent is protected. Much more important is whether habitat structures like tree hollows, cracked bark or dead branches are present to provide habitats for many different species. I don’t think it makes much sense to stop using an ordinary forest just to make up the percentage. In our forest enterprise, Steigerwald, we have set aside areas where there are clusters of trees with habitat structures. With its forest reserves, 200 ‘stepping-stone’ areas, and 10 habitat trees per hectare, altogether 12 per cent of the forest area is left unused.

KB: The percentage is a political decision and is not based on scientific findings. Initially there was too much discussion about numbers and too little about content. To maintain species diversity, not only are habitat structures and diverse management types necessary, but so too are natural processes like storms, forest fires or floods. These create new habitats and can wake up certain ‘sleeping beauty’ species. The sage-leaved rock rose in Ticino, for example, may suddenly reappear after a fire. In a managed landscape, mandatorily protected areas are therefore necessary to allow natural processes to shape the habitats. If the living conditions there are optimal, strong populations may develop in the protected areas and then spread from there to other areas.

How natural are natural forest reserves really?

UM: In this part of Bavaria, every square meter of forest, regardless of whether it is managed forest or a natural forest reserve, will have been clear cut at some point during past centuries. You cannot find any virgin forest here or almost anywhere in Germany. But natural forest reserves may harbour up to 60 to 70 per cent of the species inventory found in a virgin forest, and thus serve as a kind of life insurance. They, or at least their structures and processes, can develop to become more like the virgin forests I have seen in Romania and Iran.

Is species richness greater in untouched forests than in managed forests?

KB: To create a coppice-with-standards forest, for example, the forest must be used very intensively. Of the older trees, however, only oaks are occasionally used, whereas the young growth is cut down every 10 to 20 years. Nature conservationists like this kind of forest management because it provides temporary habitats for species requiring light and warmth. This example shows that, under certain conditions, intensive use can lead to a high level of species richness.

When should management interventions be made in a natural forest reserve?

UM: We do not intervene in our natural forest reserves. Sometimes storms create gaps, which are then mostly filled by beech. These are overwhelmingly dominant in comparison with oaks, which means we will probably lose the oak. The resulting discussion is confusing for conservationists. Hardliners say “Nature is nature! Then the oak will just have to go.” Others say “But you can’t let the oak disappear.” This last group wants to intervene in natural forest reserves. But we don’t do that. We can protect the oak in commercial forests and keep single oak trees. Maybe something will happen sometime, perhaps due to climate warming, which will change everything.

KB: We used to have a much clearer idea about which species occurred naturally in particular locations and in which proportions. Recent forest and climate research has shown us that we must adapt to changes. The example of the oak and the dominant beech indicates that natural forest reserves are not the broadband solution for all nature conservation issues. We need special forest reserves and an ecologically oriented forest management.

Why is it that most research takes place in reserves?

KB: In ecological research the natural environment was studied for long periods in places where people are not constantly interfering, i.e. in national parks and reserves. This has reinforced the notion that only in such areas can ‘real nature’ be found. Used landscapes have not been considered as much, which has made forest ecology research a bit biased. This is where I see a need for action.

UM: For us research in natural forest reserves has been and still is very important. Knowing, for example, which species occur in reserves means we can make comparisons with commercial forests. We would like to see all these species growing in commercial forests – not in the same density, but in the same numbers. I completely agree with Kurt Bollmann that too little research has been done in commercial forests, but research in reserves is also useful as we still need to be able to make comparisons.

In special forest reserves, interventions are made to promote particular species. How do you decide which species, e.g. the capercaillie, to concentrate on?

UM: It is a question of taste. There is no rational reason why, say, the capercaillie should be promoted. The bird has always impressed hunters. It was considered a great skill to be able to stalk the cock. Today great efforts are made with all kinds of measures to help the capercaillie survive even though the habitat has changed. In some regions we participate in these programmes because they are required for nature conservation. Personally though I consider it rather nonsensical to concentrate on just one species in species conservation and tacitly accept that other species may then have to disappear.

KB: There is no scientific reason for favouring the capercaillie over a saproxylic beetle. This example demonstrates how nature conservation is influenced by human values, norms and priorities. These often have to do with a species’ aura, kept alive through literature, hunting, songs and folk art. In Switzerland we are a little less emotional about it than our neighbours. Before the national promotion program for the capercaillie started in 2008, facts were required. WSL was able to show that other rare species could, under the umbrella of the capercaillie, also benefit from the thinning of closed and dark mountain forest stands.

UM: I have some sympathy for the idea of an umbrella species representing a large number of other species. When considering the conservation of forest species, however, the focus should be on near-natural habitats with many habitat trees and large quantities of deadwood. (Lisa Bose, Diagonal 1/17)