Mountain forests don’t need humans – but we need them

Should we, for example, plant genetically-modified tree species that are particularly resistant to drought, to ensure that mountain forests thrive in the future? This is no joke, but one of the many ideas on how mountain forests should be managed in future, hotly debated at the latest ETH Sustainability Summer School (see box). Thirty-two students from 17 countries and 14 disciplines took an in-depth look at suggestions such as these, which may seem absurd at first glance.

All that mountain forests provide  

Mountain forests are more than just a random collection of trees growing on steep slopes. Humans benefit from their many ecosystem services. On a global scale, mountain forests regulate the climate by storing CO₂ and water. At the local level, forests protect the surrounding area from natural hazards such as avalanches, landslides and rockfall. In addition, they are important for biodiversity, they provide timber for building and bioenergy, and they supply food such as game, mushrooms and herbs. Forests also enhance the landscape aesthetically, which is invaluable for tourism. Lastly but significantly, mountain forests shape the lowlands: erosion and flooding originate in mountain regions, but they have devastating effect mainly on the low-lying regions.

Most exposed to climate change

The human-induced rise in temperature is twice as high in the mountains as in the lowlands. And, as the reasons for this relate to physics, the trend will likely be the same in future. Hence, mountain regions are particularly affected by climate change; what then are the implications?

The simplest scenario is that a rise in temperature of 4 to 5 degrees Celsius by the year 2100 will shift the vegetation zones by 800 to 1000 metres in elevation. Trees such as beech, cherry or lime, which today thrive at 500 metres above sea level in Zurich, for example, will in future flourish in Davos at 1500 metres. And those species, such as Norway spruce, which today grow well in Davos, will find optimal conditions at 2500 metres, far above the current treeline.

Managing the mountain forests

Mountain forests will doubtless adapt over the long-term to such a drastically different climate. However, going by what we know at present, they will take centuries to do so. In the short-term, many mountain forests will suffer: current tree species will disappear due to extreme circumstances such as drought, insect infestation or windthrow; new species may not migrate quickly enough. Yet, in a hundred or two hundred years¡¯ time, new forests will have replaced the existing ones. So mountain forests can certainly survive without our help!

If, in a place such as Davos, we want to ensure continuing protection of human infrastructure from rockfall or other natural hazards, then we need persistent, healthy mountain forests. So, how should we manage these? This was one of the key themes at the summer school.

It is noticeable that in many mountain forests there are already a few, mostly young specimens of tree species normally found at lower levels. We should systematically promote these individuals to ensure that there are enough seed trees in a couple of decades. We should also consider planting tree species from lower areas at higher elevations. But when is the right time to do so? And should we introduce new species from other continents? Or even work with genetically modified tree species (GMOs)?

Teaching and research play their part

Many questions remain unanswered. So we need highly-qualified forest scientists to work on innovative solutions. And there is demand too for forest science research ¨C on the suitability of ¡®exotic¡¯ tree species e.g. from southerly, dry regions, or on genetically modified trees, ones which are particularly resistant to drought, for example. In other countries, GMOs are being intensively researched and also used to a certain extent in commercial forestry; in Switzerland, however, we still don¡¯t permit ourselves to even think about them.

This was not the case at the summer school! Events like this, where bright, young minds from many disciplines come together, may not immediately solve the problem at hand, but they certainly motivate both participants and organisers to step outside of trusted ways of thinking, and question conventional paradigms.   

It¡¯s not that I¡¯m unequivocally in favour of GMOs or the introduction of exotic tree species to Switzerland. But one should at least consider them seriously. An out-of-the-ordinary challenge like climate change may demand out-of-the-ordinary solutions!

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