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Return to the wild?

What happens to a forest if it is no longer managed? Research in natural forest reserves provides some answers.

When the WSL car stops, the woman walking along the tarred road that leads through Schlierental asks sceptically “Have you got a permit?” “Yes, of course,” answers Lucien Schoch, the young zivi, as men doing their civilian service are called, getting out of the car. He is splashed with paint. The passer-by walks on. She cannot have been in this idyllic valley high above Sarnen (OW) for quite a while because the WSL car has been parked here each morning for the past three weeks.

At the end of a short path across a field, Lucien plunges into the “Seeliwald” – a natural forest reserve in one of the now rare raised bogs in Switzerland. In many places the ground consists of sphagnum moss, which is very soggy. Water squelches up from under the soles of your shoes with each step you take. The blueberry bushes between the upright mountain pines are knee-high and full of dangling berries. The pine trees with their grey trunks are mostly short and dotted across the mossy ground, sometimes loosely and sometimes in dense groups. A striking number of the trees are dead, but their roots keep them standing upright. It is not just the type of vegetation here that makes it feel like Scandinavia, but also the silence – apart from some birds calling – with the hectic of the city far away.

Natural dynamics instead of timber yields

For about 60 years, ETH Zurich has been monitoring how the forest develops in natural forest reserves like Seeliwald. These forests were once managed, but are now left alone to develop naturally under contrac­tual guarantee. This protection en­sures that the forest can go through its entire development process without being disturbed, and the trees can germinate, grow, age, die and decompose with no human interference. Such forests also provide habitats for many animal and plant species that have become rare in managed forests. Since 2007, ETH and WSL have managed the project jointly, with considerable support from the Federal Office for the Environment (FOEN), and now monitor 49 reserves. In comparison with the rest of Europe, Switzerland has a diverse network of relatively old natural forest reserves. Seeliwald, which is at about 1450 m a.s.l., is one of the larger reserves covering 80 ha. It has been protected since 1972, when ETH signed a contract with the owner of the forest, the Corporation Schwendi.

Seeliwald, like many of the other early reserves, grows on an unproductive site. Only the mountain pines can cope with the bog’s acidic, nutrient-poor and wet soil, and even they grow only very slowly. Moreover, peat bogs are difficult to drive on. The forest’s low yield potential and restricted accessibility may have helped to persuade the owners to let the forest be protected – especially as they received financial compensation in return for not using it. Finding large areas of productive forest to set aside as reserves was, and still is, much more difficult. This is one reason why the proportional area of forest reserves on the Central Plateau is the smallest in the whole of Switzerland (see the Infographic).


Monitoring trees over time

“There you are at last,” exclaims Jonas Stillhard when Lucien appears, and adds with a wink: “Did you get lost?” The 33-year-old environmental engineer and his team, consisting of another zivi, David FitzGerald, and the two field technicians, Gilbert Projer and Gallus Keller, had got to the Seeliwald earlier in the morning than Lucien. While Jonas cleans the trees with a wire brush, David picks up the stamping set: ‘73’, ‘85’, ‘95’ – all trees get a number in color as soon as they reach a diameter of at least 4 cm. The trees marked in blue grow in one of the six permanent plots roughly 1 ha in size. Each time an inventory of the permanent plots is made – this one is the fourth since the Reserve was established – the fate of the marked trees is exactly recorded. Jonas: “We measure the diameter, note the species and record any structural details like holes or cracks that can serve as important habitats for animals, fungi and plants.”

Jonas hands the wire brush to Lucien and leaves the two zivis alone to mark the trees. They move on to the sample plots, one of the innovations introduced in 2007. In the Seeliwald, altogether 99 of these 500 m2 circular plots are distributed in a fixed grid across the whole Reserve. Gilbert and Gallus have just started to tackle sample plot 56. They are holding a Transponder and Vertex – tools that are also used in land surveying to measure the distance between two points. Gallus tells Gilbert which tree to look at, and measures the diameter at breast height with so-called calipers. Gallus uses the Vertex to measure the height of the tree, assesses whether it is dead or alive, and checks the condition of its crown, recording all the data directly in the field computer. Following a set protocol, they register any young trees growing on a sub-plot and how much deadwood is lying around. If one of them is unsure about the assessment, the other will help out. They are clearly an experienced team after working together almost every day for months. Jonas also helps with the field surveys from time to time, as he has done for the past few days in Seeliwald. More often, however, he can be found in his office coordinating his colleagues’ fieldwork or focusing on the database in which all the Reserve project’s survey data is stored. At the moment he is working on transferring all of the data gathered since 1948 into a new database and correcting inconsistencies. Jonas: “Over the years so many different people have worked on the same project that some errors are inevitable.”

A new virgin forest is forming

Many research projects have come about thanks to data from the Reserve Project. According to one such study, the reserves are already beginning to show some of the characteristics of a virgin forest with, for example, more deadwood and large diameter trees than in a managed forest. If this development is to continue, however, it will be essential to protect the Reserve for much longer than the normal contract period of 50 years. And even then, it will still be different from a real virgin forest such as that which once covered the landscape before any of the wood and timber was used. Instead, it will turn into a new form of virgin forest: a so-called natural forest. Conditions today are different: the climate is warmer, large carnivores no longer roam the forests and regulate the growing populations of wild ungulates, and more nitrogen is entering the forest floor via the air.
Last year a Masters student assessed, for the first time, how much deadwood she found lying in the spruce-dominated mountain forest reserves. Such indicator values provide valuable references for making recommendations about how much deadwood is necessary in forests, including managed ones, to promote those species that depend on it. A doctoral thesis was also published last year, which used the enormous data-set to model the mortality of different tree species. These findings are also relevant for the owners of managed forests. Jonas: “Knowing, for example, that a valuable admixed tree species can thrive in natural forest reserves in large enough numbers and good enough quality without any expensive interventions could mean less pressure on forest owners’ wallets, especially with the low prices for timber today.”

After a long day in the field, Gilbert, Gallus and Jonas pack up their things. They have assessed six sample plots today. The two zivis are already waiting by the car. During the around three months it takes to do the inventory in Seeliwald, the men will examine up to 7000 trees closely. This is work which even today no modern technology can do for them. The inventory will not be repeated again for another 10 to 20 years. (Christine Huovinen, Diagonal 1/17)