FW-I-2: Endangered spruce stands

The picture shows a slope densely covered with conifers. About a third of the spruces have died. Click to enlarge
The drought years of 2018 and 2019 have affected spruce trees quite badly.
Source: Photograph: © K | Photography / stock.adobe.com

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

Table of Contents

 

FW-I-2: Endangered spruce stands

As climatic circumstances change, spruce trees will be challenged by increasingly unfavourable growth conditions. The risk situation did not yet change drastically in Germany during the period between the two National Forest Inventories of 2002 and 2012. Spruce tree cultivation on high-risk sites has not declined to any relevant extent. Overall, the expanse of spruce forest area has declined.

Two stacking columns represent the proportion of spruce stands with the share of seven graded risk groups in the total spruce stand in the old federal states for the years 2002 and 2012. In addition, the total spruce area is indicated by a graph with two points for 2002 and 2012.
FW-I-2: Endangered spruce stands

Two stacking columns represent the proportion of spruce stands with the share of seven graded risk groups in the total spruce stand in the old federal states for the years 2002 and 2012. In addition, the total spruce area is indicated by a graph with two points for 2002 and 2012. The spruce area has decreased from about 3 million hectares in 2002 to 2.8 million hectares in 2012. The shares of the very low risk and low risk groups have increased slightly. They accounted for slightly more than half of the stocked area in 2012. The shares of the very high, high and significantly increased risk groups have only slightly decreased. The decline is most pronounced in the medium-high risk group.

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

Spruce trees under increasing pressure

The targeted extension of spruce plantations in German forests began more than 200 years ago. In those days many forests were badly fragmented, because they had been opened up for the purpose of forest pasture and intensive use of timber. Owing to their undemanding nature, sturdiness, and easy propagation, spruce trees suggested themselves as the ideal tree species for rapid reforestation of large areas. The useful and versatile timber was considered suitable to overcome an impending timber shortage. It is true to say, however, that spruce trees, owing to their mostly shallow root system are vulnerable to storms and droughts. As a result of this massive extension of spruce cultivation, these trees were also planted on sites which do not meet the species‘ requirements for rather cool and moist climatic conditions. In view of prevailing climate change scenarios the conditions at those sites can only get warmer and drier.

There were early indications that pure stands of spruce trees were fraught with high cultivation risks. From the late 19th century onwards, there were already repeated incidents of pest infestation or storm events which destroyed localised stands. However, the true extent of vulnerability of this species did not come to light until vast areas of spruce plantations were affected by damaging events in the course of the past two decades. Severe hurricanes such as Vivian or Wiebke, Lothar and Cyril resulted in large volumes of damaged timber.

Even a moderate increase in temperature by less than 2 °C will heighten the spruce cultivation risk considerably as many more cultivation areas will exceed the temperature and drought thresholds for spruce trees. Problems such as above-average pest infestations and poor growth potential, currently occurring only in marginal zones of spruce cultivation areas, will in future extend to areas which have so far been regarded as productive and controllable cultivation areas.

The National Forest Inventory carries out a regular spot-check survey of forest conditions and production potentials. When the second inventory took place in 2002, the survey was for the first time extended to the whole of Germany. The third inventory took place in 2012. When superimposing the spruce cultivation area captured in the second and third National Forest Inventory on the climatic risk areas for spruce trees as defined for the 1981- 2010 Standard Climate Reference Period, it becomes clear that there have been hardly any changes during that period. In 2002 12.7 % of all spruce trees stood in locations where they were exposed to a high or very high risk, also in terms of their climate threshold, i.e. where the climatic conditions were already then quite unfavourable in view of low precipitation totals and comparatively high annual average temperature levels. In 2012 this proportion was still 12.5 %. On the other hand, the share of spruce trees (with at least 90 % of spruce trees per stand) in areas with low or very low risk has increased by 1.2 % between 2002 and 2012. These rather negligible changes suggest the inference that the situation regarding risks of drought damage for the period of 2002 to 2012 has not changed to any relevant extent. The outcomes of the next National Forest Inventory which will incorporate any impacts from recent very dry and warm years, will become available in 2022.

Overall, the spruce cultivation area was by 215,000 hectares smaller in 2012 compared to 2002. Consequently, the proportion of spruce cultivation area compared to the entire forest area in Germany has decreased from 28.4 % to 25.4 %. This development is largely due to spruce wind-blow and to the objective of converting pure spruce forest stands to deciduous and mixed forests in order to increase the amount of forests appropriate to their location. Previously, any specific adaptation of drought-sensitive spruce stands had been given secondary consideration in forestry management decisions.

In principle, the determination of cultivation risks or potentials of important species is central to forestry planning. If the risks of failure can be assessed at the point of cultivation, forestry managers can, notwithstanding any uncertainties and knowledge gaps, adapt their operational decisions on the choice of tree species accordingly.

 

Interfaces

FW-I-5: Extent of timber infested by spruce bark beetle

FW-R-3: Conversion of endangered spruce stands

 

Objectives

Driving forward the conversion of pure (single-species) stands to mixed stands consisting of site-appropriate trees which are low-risk (DAS, ch. 3.2.7)

Maintaining the overall forest area in Germany and increasing the stability and diversity of forests. Cultivation of site-appropriate tree species with high resilience, adaptability and growth performance (Waldstrategie 2020, p. 23)

Continuous reduction of the proportion of non-native tree species (NBS, ch. B 1.2.1)

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 adaptation to climate change  KomPass  monitoring report  spruce  stocked forest area  wood utilisation  warmth and dryness limit