Climate change impact on the forest
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Climate change impact on the forest

Trees generally adapt quite well to changes in the climate, but the ability to adapt varies from species to species and also depends on the change in question.

The individual tree must be able to cope with climate variation and climate extremes over periods spanning hundreds of years. However, if we consider the individual species, some show relatively limited ability to adapt, while others are characterised by great genetic variation and ability to adapt. 

Thus, many species will be able to benefit from the expected increase in temperature. Since most indigenous species in Denmark grow in their most northern distribution range, and simply cannot grow further north in particular because it is too cold, a slight temperature increase of 2°-4°C should not be a problem for them.

In general, conifers are the most vulnerable tree species in Denmark. For Norway spruce, which is the most widespread species covering 19% of forest land in Denmark (2006), increases in temperature are critical. 

Less summer rain will render most tree species more vulnerable
With less than 400mm of precipitation in the growing season, water is generally a minimum requisite for tree growth most places in Denmark, especially in areas with sandy soils that have a low ability to retain water. 

Even an 8-15% drop in the volume of summer rain and the likelihood of longer dry spells in particular, will generally render all tree species more vulnerable. However, the coniferous species, and especially those with a relatively superficial root system, will be most vulnerable. 

Conifers especially vulnerable to storms
In relation to forestry's climate change adaptation strategies, the risk of an increase in the frequency and strength of storms must be taken very seriously. Since most storms appear during winter when deciduous trees have shed their leaves, conifers are especially vulnerable to storms. 

Trees will become more vulnerable to pests
Changes to climatic conditions will also have a possible effect on the equilibrium between trees and their pests. If trees are physically weakened due to changes in the climate, they will generally be less resistant to pests. 

Pests are quicker to adapt to changes in climate due to their far quicker reproductive cycle. In particular climate-sensitive coniferous species such as Norway spruce and Sitka spruce must be considered as especially vulnerable.

Possibilities for adapting
The condition of Danish forests as a whole is not alarming. Considering conifers alone, however, it is clear that action is needed. Norway spruce and Sitka spruce should be reduced considerably in future, in favour of a number of native deciduous species including, in particular, oak, beech, ash and Sycamore maple.  This entails a major conversion of forestry during the next 50 to 80 years.

Mixed forests and close-to-nature forest management constitute the most important possibilities for adapting to climate change. Forest development is characterised by long time horizons. Since we cannot accurately predict the climate, we must focus on establishing forest ecosystems with a high ability to adapt.  There are a number of ways in which we can achieve this.

Mixed forest stands best suited for an uncertain climate
A mixed forest stand consisting of two or several different tree species with differing ecological requirements and ability to adapt to expected changes in temperature, precipitation, storm frequency and pests, will make it possible to carry out continuous adjustments in step with climate developments. The aim is to:

 

  • maintaining a permanent forest climate by avoiding clearcutting, i.e. felling large areas all at once;
  • ensuring stability and risk diversification by establishing uneven-aged mixed stands of tree species adapted to the local environment;
  • employing active forest stand management in the form of frequent and selective felling; as well as
  • ensuring the natural equilibrium between the forest's biological organisms, including pests, so as to create greater biodiversity and avoid the use of pesticides.

 

With the current conversion rate, 50% of the state-owned forests will have been converted by around 2050. The conversion will be reassessed within the next ten years, e.g. in the light of new knowledge on climate developments and how the tree species are thriving.

Senest redigeret: 07-12-2022