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

The picture shows a dense spruce forest. Several trees are dead, in the foreground dry scrub lies on the ground. Click to enlarge
Rapid clearance of beetle wood is a major challenge. Only quickly harvested wood is usable.
Source: Photograph: © Andreas Bolte / Thünen-Institut

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

Table of Contents

 

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

The spruce bark beetle benefits from dry and hot weather and prefers to infest trees that are already damaged or weakened in some way. Infestation data from eight Federal States demonstrate that hot and dry years and also storm events entail a volume of damaged timber that is distinctly higher than the long-term mean.

The graph shows data points for the individual years and the individual federal states. However, the federal states are not differentiated. The graph shows the deviations of the number of book printers from the period average 1998 to 2012 as a percentage. The values scatter more or less strongly between negative and positive values in the years. While the negative deviations vary by up to minus one hundred percent, the positive deviations vary much more strongly in some years, up to almost 300 percent.
FW-I-5: Extent of timber infested by spruce bark beetle – case study

The graph shows data points for the individual years and the individual federal states. However, the federal states are not differentiated. The graph shows the deviations of the number of book printers from the period average 1998 to 2012 as a percentage. The values scatter more or less strongly between negative and positive values in the years. While the negative deviations vary by up to minus one hundred percent, the positive deviations vary much more strongly in some years, up to almost 300 percent.

Source: Journal AFZ - DerWald (overview of the federal states on forest protection)
 

Bark beetle – a major problem for spruce trees

Many trees suffer from diminished vitality caused – as projected – by climate-related changes, especially during summer droughts. Thermophilic insects and pathogens, however, can benefit from such conditions. As far as coniferous trees are concerned, increasing damage – caused by bark beetles such as spruce bark (or typographer) beetle and six-dentated bark beetle, which breed in the bark of spruce trees – is thought to be associated with changed weather patterns. In the course of the past ten years this type of damage reached supraregional importance in Germany.

Even if climate change is not the only cause of increased pest infestation, it is assumed – at least with regard to the spruce bark beetle – that higher temperatures cause this species to swarm earlier in the year thus enabling an additional generation to develop.

Infested timber has to be removed from commercial stands in order to prevent this type of beetle from further extending its range unhindered. Beetle-infested timber is basically still usable but has to be removed quickly from affected stands. If this infested timber is left standing, eventually losing its bark, its usefulness becomes limited, i.e. only as firewood.

Data on the volume of timber damaged by pest infestation are not available in a harmonised form nationwide. However, the data series on the volume of timber damaged by spruce bark beetle collated by eight Federal Länder make it possible to estimate the development.

These data clearly show that beetle infestation caused as a result of the heat and drought year 2003 increased rapidly in nearly all the Federal Länder examined. The after-effects continued for some subsequent years, reinforced by another very warm and dry summer in 2006. In 2007 the rather rainy month of May and a cold September, the bark beetle population was not able to reproduce quite as successfully. This did not occur until 2010 when the volume of damaged timber again reached the level experienced in the heat summer of 2003. However, since the warm summer of 2015, volumes of damaged timber have been increasing again. It is also possible to discern the consequences of extreme storm years which typically entail increased beetle infestations of damaged or thrown trees. Such years account for the above-average volume of damaged timber in one of the Federal Länder in 2001 (after storm Lothar had passed through in December 1999) and in several Länder in 2008 (the aftermath of storm Cyril). In view of the succession of winter storms in 2018 (Friederike, Burglind) and the extremely hot and dry summers of 2018 and 2019 it is to be expected that the volume of damaged timber will increase considerably. According to records provided by all Federal Länder approximately 32.4 million cubic metres of damaged timber accrued in 2018, and even bigger volumes are expected to have been recorded for 2019.

The spruce bark beetle is representative of other pests which enjoy improved reproduction thanks to changes in the weather pattern. Apart from bark beetles, coniferous trees are increasingly damaged also by silver-fir adelges and by fungi as a result of climate change. As far as deciduous trees are concerned, pests include the common European cockchafer, the oak processionary moth, gipsy moth, the oak-boring beetle, the leaf-mining moth on horse chestnuts, the small beech bark beetle and the beech jewel beetle on beech trees. The increasing incidence of these species is thought to be associated with warm and dry summer weather.

 

Interfaces

FW-I-4: Damaged timber – extent of random use

 

Objectives

Aiming for particularly stable mixed stands with increased resistance to widespread misadventures caused e.g. by storms and bark beetle infestations (DAS, ch. 3.2.7)

Cultivation of site-appropriate tree species with high resilience and growth performance (Waldstrategie 2020, p. 23)