FW-I-5: Damaged timber – extent of random use
Click to enlargeSource: Alexander / stock.adobe.com
2023 Monitoring Report on the German Strategy for Adaptation to Climate Change
Click to enlargeSource: Alexander / stock.adobe.com
FW-I-5: Damaged timber – extent of random use
Random use owing to wind-blown, wind-broken and infested timber is detrimental to forestry in many ways. The proportion of random use compared to the logging total has been rising significantly in the run-up to 2021. The causes of this development vary from year to year. Major winter storms which occurred in 1990, 1999, 2007, 2010 and 2015 resulted in considerable volumes of damaged timber. However, in the years of 2019 to 2021 insect-related damage predominated.
The illustration FW-I-5 ’Damaged timber – extent of random use’ contains a biaxial chart. The chart shows the proportion of random use compared to the logging total in per cent as a line, and the proportion of damage causes compared to the total of random use in per cent in terms of stacked columns. A differentiation is made between causes such as wind/storm, insects and other causes. The proportion of random use decreased steadily until the turn of the century, amounting to roughly 10 per cent in 1999. In 2000 and 2007 short-term outliers characterise the progress of the time series. In those years, the proportion amounted to between 45 and 55 per cent. As of 2016, the proportion latterly increased significantly reaching 60 per cent in 2021. The causes of this damage vary from year to year. The amount of damaged timber that accrued for instance in 1991, 2000 and 2007 was storm-related. During the past three years, most of the damage was caused by insects. In 2021, the proportion of total random use amounted to roughly 80 per cent.
High volume of damaged timber hinders planned management
Poor forest condition and high dieback rates (cf. Indicators FW-I-2, and FW-I-4) lead to an increase in damaged timber in woodlands and forests. Wind-blown and wind-broken timber after storms as well as beetle-infested timber lead to unscheduled or so-called random use. Damaged timber can have negative effects on the safety of other production operations. If – especially in spruce stands – newly dead trees still covered in bark are left in the forest, they can provide perfect breeding sites for pest organisms, thus strongly favouring their reproduction, unless appropriate action is taken. In cases where there are extensive areas of damaged timber, this will put extra pressure on other production operations in forests and woodlands, thus giving rise to safety risks for recreational woodland users or for people who work in these areas. This is why forestry organisations – at least regionally – endeavour to remove damaged timber from forest stands as rapidly as possible. Taking prompt action is also important regarding beetle-infested timber – left standing or lying, thus losing its bark – as it is usually of limited practical use. On the other hand, leaving some dead timber in the forest is desirable with a view to enhancing biodiversity and increasing soil humidity in the forest. Deadwood provides essential habitats for fungi, insects and birds and can have beneficial effects on the interior climate of a forest or woodland.
Random use – especially after major damage events on a regional scale – is apt to tie up considerable capacity in forestry management. In such cases, the diverted capacity is consequently not available for implementing targeted cultivation measures which are, after all, of vital importance in achieving the required adaptation of forests to climate change. As a rule it takes several years until the consequences of calamities have all been dealt with enabling forestry organisations to return to planning and managing ‘normal’ utilisation and cultivation activities.
For the forest proprietor – no matter whether it is the state, the local municipality or a private forest proprietor – major volumes of damaged timber are associated with considerable revenue shortfalls. In fact, the restoration costs in damaged stands are distinctly higher and the timber qualities often inferior. At the same time – especially in the aftermath of major damage events – timber prices decline distinctly. Besides, timber will have to be stored longer and this causes added expense. Furthermore, the legal obligation to achieve reforestation of damaged forest areas can entail financial burdens faced by forestry enterprises, owing to various extra cost factors in terms of timely planting and conservation operations on ground where normally natural forest regeneration might have been a cost-effective, near-natural option. Where reforestation is delayed, this would also result in delayed harvest operations thus entailing commercial losses.
The proportion of random use resulting from damaged timber in terms of the logging total in German commercial forests has increased significantly over the past 30 years. The average proportion during this period amounted to roughly 26 % compared to the average for the period of 2019 to 2021 amounting to 67.6 % which is more than double. The record value reached in 2020 amounting to just under 75 %, exceeded the value of 66.4 % after hurricanes Vivian and Wiebke in the late winter of 1990. The volume of calamity timber recorded for the period of 2018 to September 2022 amounted to 245 million cubic metres solid. In recent years professionals in forestry circles have gained the impression that phases free from relevant impacts caused by random use are becoming ever shorter.
Up until 2018, the extremely high proportions of random use compared to the logging total were essentially caused by wind-blown and wind-broken timber in the aftermath of storms. As mentioned above, in the late winter of 1990 for example, hurricanes Vivian and Wiebke resulted in extensive restoration work required in the subsequent year of 1991, and this applied to major parts of Germany. In December 1999 ‘Lothar’ devastated extensive parts of south-west Germany. In January 2007 cyclone Cyril destroyed forests particularly in North-Rhine Westphalia with a focus on Sauerland. In late March 2015 hurricane Niklas wrought havoc in Bavaria but left behind smaller amounts of damaged timber than comparable hurricanes. The autumn tempest Xavier in October 2017 caused damage in deciduous woodlands in Brandenburg, as trees were still in full leaf, whilst the low-pressure related storm Burglind, right on the cusp between 2017 and 2018, as well as Friederike in mid-January, broke trees in the western and southern woodlands of Germany. These events led to an increase in the damaged timber statistics for 2018.
As of 2019, the situation changed insofar, as pest insects accounted for the major part of the enforced use of damaged timber. Subsequently to the extreme year of 2003 (based on the mean value for the period of 2004 to 2006), insects caused 63 % of all random use; after 2018 this value amounted to 74 % (based on the mean of the period from 2019 to 2021). It is therefore necessary to assess the importance of biotic pest organisms differently in the overall damage scenario nowadays (cf. Indicators FW-I-6 and FW-I-7).
When interpreting the data on wind-blown, wind-broken and infested timber, it is important to remember that, as a rule, these data do not provide a comprehensive overview of the actual damage caused to timber. Not all Federal Länder record and provide data on private and corporate forests in addition to data on state-owned forests. Besides, the focus of data collection has so far been on winter storms. Apart from impacts caused by climate change, there can also be other trends exerting strong influences on the time series. As far as the age structure of German forests is concerned, stands tend to contain a lot of the older range of the age spectrum. It is important to note that older and thus taller trees are more vulnerable to wind-blow than younger ones, and the greater the timber reserve, the greater the volume of damaged timber. The latter can also mean that depending on where the calamity is located, the damage caused can vary in terms of volumes. For example, storms in regions with fairly open stands of pine forest – which are widespread on the sandy soils of Brandenburg or Mecklenburg-Western Pomerania – will cause smaller volumes of damaged timber than storms or pest infestations in the timber-rich forests of the uplands, or the foothills of the Alps.
