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New Danish project studies forest adaptation to climate change

Date: 2018.08.28

After the warm and dry summer in the Scandinavian countries, the concern for the effects of climate change has risen among the general public. But within forestry, where planning has to look 60-100 years head, the issue of climate change has been well addressed for quite some time now. In the future, new species and provenances may become important.

It’s not an easy task to foresee what will happen with the climate in the future and how these changes will affect forestry. But it is a reality the foresters of today must relate to. Forestry is a long-term operation. Foresters actually seldom sees the seedlings planted being felled as a tree might grow for 60-100 years before it’s ready to be harvested. Therefore, one of the biggest challenges today is to choose seeds, provenances and species that can thrive in the expected future climate.

Tree border might change

Denmark is close to the northern border of the natural distribution for many of its native tree species. With global warming, the natural distribution of species is likely to change, and this can create a new situation where Denmark become more central in the species distribution range. And species not considered native to the country today may thrive well in the future Danish forests. On the other hand, species and provenances presently used in the forests may perform poorer, if they are no longer well adapted. A new project in Denmark aims at testing new species and provenances in this perspective. It is a collaboration between the Nature Agency and IGN at the University of Copenhagen. The project has received funding from 15. Juni Fonden.

“The problem is that we don’t know exactly how the climate will change and how it in return will affect our maintenance of the forests. Climate models predict a prolonged growing period in Denmark, but also that we will experience more dry summers. Additionally, we must expect new and more aggressive pests”, said Erik Dahl Kjær, Professor at the Section for Forest, Nature and Biomass at University of Copenhagen, as he joined a NordGen working group meeting this week.

Assisted migration

Along with his colleagues Jon K Hansen and Albin Lobo, Kjær study how well native trees are adapted to their present climate. And especially, if the native species and provenances are likely to respond sufficiently fast to stay adapted during a rapidly changing future climate. If not, it will be important to import seeds from trees growing further south in Europe and plant them in Denmark.

“It is a problem that trees for the future climate has to start their life in the present climate. At first, we must therefore plant southern origins at places in Denmark where the temperatures are mild and see if they can survive there”, Jon K Hansen, senior researcher at University of Copenhagen said.

“A change of species and genetic composition will probably take place even if foresters do not interfere, because the tree species will expand to the North by themselves when the climate becomes milder. But this could take a very long time, and many factors in the fragmented European landscape can slow down the process. When foresters import seed, they speed up the process”, said Erik Dahl Kjær.

Different views in the Nordic countries

Denmark has a long tradition of using exotic species and non-local provenances. North American species such as Sitka spruce, Douglas fir, Grand fir and red oak are already common in Danish forests. Along with Larch, Norway spruce and other exotic species, they have become an important part of Danish silviculture. Their presence it is not a very controversial matter. In Norway the situation is quite different. The country wants to keep the Norwegian domestic flora and not risk import of invasive species.

“According to the Norwegian law, foresters are not allowed to plant any trees, which are not indigenous to Norway” said Ellen Finne, Senior Advisor at Fylkesmannen in Vestfold.

Finland also has a stricter policy with regard to which species you are encouraged to plant. Iceland, however, are experimenting finding trees of different origins that can thrive on the island.

Important with genetic diversity

No matter which views we have on importing tree species, it’s apparent that forestry faces great challenges when it comes to tackling climate change. Presence of genetic diversity can be crucial when new pests and pathogens emerge, but also in order to be able to respond to higher frequency of long periods with drought.

“When we seek seed sources from other countries, we want material that can adapt to continued climate change. Therefore, it’s very important with a high genetic diversity. That’s why one of the criteria for future seed sources should be areas with high genetic diversity” said Jon K Hansen.

Climate as in southern France

If the average global temperature should increase with 1-2 degrees, Denmark would experience a climate comparable to the one in northern France today. If it increases more, the climate is more likely to resemble what we today see in parts of southern France. Forest species and seed sources used in these regions will therefore be tested in Denmark. There is a long international tradition for such provenance tests. The new thing is that the tests are designed to test different climate zones defined by minimum temperatures and degree of continentality based on an expected fit to the future Danish climate.

“There are theoretical reasons to believe that our European flora actually lack some of the warm tolerant species that survived the glaciations in North America and Asia, and several tree species from North America are already important in Danish forestry. However, in this project we only work with species that are native to the European continent and that are already widely planted in Denmark. If you introduce new species on a large scale, it is always important to consider the risk of creating invasive species. The trees should grow well here, but not too well. It’s a difficult balancing act” Erik Kjær said.