FW-R-3: Conversion of endangered spruce stands

The picture shows an autumnal spruce forest with numerous young beech trees growing up on the ground.Click to enlarge
In forest conversion, the particularly high-risk pure spruce stands must have priority.
Source: Photograph: © AVTG / stock.adobe.com

2019 Monitoring Report on the German Strategy for Adaptation to Climate Change

Table of Contents

 

FW-R-3: Conversion of endangered spruce stands

The forest conversion of pure spruce stands is progressing. However, between 2002 and 2012, conversion measures were not focused systematically on areas with particularly warm/dry climate conditions where the cultivation risk is now distinctly high or very high.

The risk categories illustrated are as follows:

  • very low risk = spruce tree viable as main tree species
  • low risk = viable as main tree species subject to adequate mix with other tree species
  • discernible risk = viable as mixed forest component in high proportions
  • moderately high risk = viable as mixed forest component in medium proportions
  • clearly increased risk = viable as mixed forest component in modest proportions
  • high risk = viable as mixed forest component in low proportions
  • very high risk = viable as mixed forest component in very low proportions
The bar chart shows the percentage decrease in spruce area in seven risk groups (from very high risk to very low risk) in the period 2002 to 2012. The lowest decrease is in the very low risk category with 3.5 percent, the highest in the fourth category medium-high risk with 12.7 percent and the third category significantly increased risk with 12.2 percent.
FW-R-3: Conversion of endangered spruce stands

The bar chart shows the percentage decrease in spruce area in seven risk groups (from very high risk to very low risk) in the period 2002 to 2012. The lowest decrease is in the very low risk category with 3.5 percent, the highest in the fourth category medium-high risk with 12.7 percent and the third category significantly increased risk with 12.2 percent.

Source: Thünen-Institut für Waldökosysteme; Bayerische Landesanstalt für Wald und Forstwirtschaft (modeling based on the National Forest Inventory)
 

Targeted conversion of endangered spruce stands

The focus of forest conversion is on pure coniferous stands, in particular, when they are located in areas where they are out of place even now, or where they will in future, be out of place owing to climate change. In central and southern Germany and at higher altitudes, pure spruce stands were planted frequently. There are problems with unsuitable spruce stands from both forestry and ecological angles, especially on warm/dry sites. Forest conversion should therefore concentrate, as its first priority, on those locations which are categorised as critical and where, in view of the projected climate change outcomes, the situation is likely to become even more critical.

A differentiated analysis of the evolution of spruce forest areas between 2002 and 2012 shows that during that period, no systematic actions were taken on a nationwide basis which targeted forest conversion in high-risk areas of spruce cultivation. Compared to the moderate climatic situation prevailing in the period from 1961 to 1990, at the end of which targeted forest conversion was started, it is possible to see that in 2002 approximately 6.6 % of the spruce forest area would come under the category of high or very high spruce cultivation risk. This risk category now includes areas with an annual average temperature of more than 8 °C and an average total annual precipitation level of less than 800 mm. In view of the objective of sustainable forest management, spruce trees should be tolerated in those stands only as a mixed forest species in moderate to low proportions. In fact, in German forests spruce trees were still the main tree species in 2002 on approximately 196,700 hectares of those comparatively warm/dry areas, i.e. the species covered more than 90 % of the total cultivation area. By 2012 this area was reduced only slightly to approximately 186,100 hectares while amounting to 6.7 % of the total spruce cultivation area. The causes for this decline might have been either targeted forest conversion measures or destruction of stands by calamities such as infestation with bark beetles. The modest decline in those ten years might be due on one hand to the possibility that many stands in these risk categories had not reached maturity and that for commercial reasons a targeted forest conversion had been postponed. On the other hand, it is conceivable that the trunk diameter of the trees used for underplanting – in line with forest conversion measures – was still too small to register in terms of the inventory.

Looking at this issue from a nationwide angle, it is not evident from the period of 2002 to 2012, that for areas with distinctly high to very high spruce cultivation risk, any particularly strenuous efforts were made to replace spruce trees by site-adapted and less vulnerable species. By comparison it is interesting to note that the highest absolute reduction of spruce forest area took place in almost 108,100 hectares of areas in very low risk categories, where site conditions would have been conducive to the continued cultivation of spruce trees as the main tree species. It must be said, however, that this risk category is by far the largest in terms of surface area. It is reasonable to assume that storm risks not covered by this risk indicator may have played an important role in conversion decisions.

In discussions on climate-optimised forest conversion, the focus for forestry management is on site-appropriate spruce stands. It is conceivable that by the time the next inventory takes place, the regeneration of other tree species used for underplanting spruce stands will have grown to a sufficient height for figuring in the main stand thus reflecting a different situation in 2022.

 

Interfaces

FW-I-2: Endangered spruce stands

FW-R-1: Mixed stands

 

Objectives

Forest owners should advance the conversion of forests with pure stands to mixed forests of site-appropriate trees which are categorised as low-risk. […] When selecting tree species [...] care must be taken that they are site-appropriate and able to adapt to future developments. (DAS, ch. 3.2.7)

Cultivation of native and mostly autochthonous tree species with high resilience and growth performance (Waldstrategie 2020, p. 23)