C Fairgrieve, Scottish Wildlife Trust
| Erasmus+ Archnetwork exchange | 29/08/2019-05/09/2019
Include a range of insect species (Coleoptera, Lepidoptera and Hymenoptera) as well as several fungal pathogens and bacteria affecting a range of tree species (Stokmane, M., Smits, A., and Zalkans, O. 2018). Prior to the year of plant protection in Europe (2020) these pests and diseases pose a considerable threat to production forestry as well as national forest conservation. In Latvia as elsewhere in Europe, at a time of great uncertainty caused by climate change, increased mobility of plant pathogens, and corresponding increasing vulnerability, it is vital that an effective control strategy be part of a package of solutions to minimize losses. With specific reference to Latvia, this translates into identifying and protecting good stands of trees which are under threat rather than complete elimination of threat, and monitoring and control are conducted in the complex setting of ownership status of both managed and conservation forests. In addition, conflicts of interest between private, state sector and nature conservation forests complicate control strategies and the practicalities and logistics of control pose considerable challenges to owners, researchers and forest workers. Some of these conflicts may be reduced by change to legislative processes and frameworks in future but the forest sector must take some actions to mitigate damage losses and control further spread.
SPRUCE BARK BEETLE (IPS TYPOGRAPHUS) DAMAGE, CONFLICT AND SOLUTIONS
One such forest pest that constitutes a significant risk to mature stands of Norway Spruce both in Latvia and throughout central Europe is the eight-toothed spruce bark beetle, Ips typographus. With a widespread European distribution this beetle causes damage to mature (>50 yr old or >20cm diameter) spruce trees in stands rather than in single trees and has the potential to spread rapidly with beetles dispersing between 0.5 km up to 40km.
Although the beetle is natural to spruce forests, and may have a role in their ecosystem, it can spread devastatingly through single species spruce forests planted in the last two centuries (Lopatka 2018). Damage results from males drilling holes in mature Norway spruce to attract females who then make breeding ‘galleries’ where larvae subsequently infest and cause extensive damage. Infestations then occur when subsequent generations of beetles are reproduced and spread throughout vulnerable stands. Smaller and younger trees do not sustain large populations of beetles or larvae as trees are killed before infestation at high density occurs. Data from Latvia indicate heavy infestations in mature stands of Norway spruce can reach over 40,000 beetles per cubic metre (A. Smits pers. comm.) and although presence in the UK does not yet reach significant levels, threat is perceived high enough to warrant annual Protected Zone monitoring (B. Fairgrieve pers. comm).
Throughout central Europe, in countries including Czech Republic, Austria, Slovakia, Germany and Poland, there have been recent incidences and outbreaks ranging in extent, particularly exacerbated in recent years by drought induced effects of climate change (Lopatka, J. 2018). For example, in the Czech Republic, during a very dry spring, with large areas of the country experiencing drought and trees accordingly weakened defensively, conditions for the beetle to spread were also favorable, and the results were devastating. An estimated 18 million cubic metres of spruce (more than 10 times usual infestation rate) were affected at a potential total financial loss to the timber economy of up to £671.5 million. These losses were incurred not just in terms of damaged timber production but also lowering timber prices, premature felling of trees, and logistical costs, and were predicted to rise further this year (Lopatka 2018). These figures probably do not take into account additional losses of natural capital/ecosystem services such as water conservation, carbon capture, flood prevention, soil protection, nature conservation and amenity value.
We were told in during this study tour in the Latvia context, subsequent to heavy storm damage in Latvia during 2005, critical levels of bark beetle infestation were detected in 2007/8 via a programme of ongoing monitoring. Following strategic and timely intervention of the part of the State Forest Service research institute (‘Silava’) and Latvian Forest Service staff, this outbreak was effectively contained to manageable levels by 2010 (Smits, A. pers. comm.). Damaged timber is useable but stained blue and logistical and financial costs are involved in removing infected timber from sites and between sites as well as treating it at processing sawmills. Although spruce bark beetle is therefore an endemic threat and damage is common, especially in the Eastern part of the Latvia, damage can be minimized and the extent of the spread of beetle infestations can be controlled to sustainable levels. In Latvia as in Scotland, there are no known natural controls for Ips typographus, and although climate can influence both vulnerability of tree stands as well as the extent of distribution of Ips there is a growing concern at the risk posed to timber production and nature conservation in (mature) European and UK spruce forests (see above). Additionally, in the context of controlling outbreaks in Latvia and where some lessons may be learned in anticipation of potential outbreaks in Scotland, ownership status and management priorities of forest stands bear considerable relevance. For example, in the Latvian setting, stands of trees in a given forest area may often be owned by different individuals/agencies where different importance is placed on for example timber production and conservation. In some sites, different management objectives e.g. leaving fallen windthrow, or mature trees unharvested, may lead to differing levels of risk from infestation by Ips typographus due to an increase in substrate stems allowing high levels of bark beetles to accrue. Furthermore, once infestation has been detected and established in a stand, there may reasons to allow outbreaks to run their course to comply with nature conservation objectives. Where stands have been affected, standard practice by the Latvia State Forest Service is to clear-fell the affected stand/area and thereafter establish monitoring and control via pheromone traps, which although requiring some input to establish and empty periodically, are relatively effective and simple way of reducing beetle numbers.
Currently the UK has Protected Zone status for Ips typographus, and as consequence has experienced little threat from significant outbreaks. However, some threat and occurrence in recent years has led to the Plant Health (England) Order 2019 for introduction of emergency measures in response to outbreaks. Regular inspections and interception at ports where poor quality timber is returned to host country or contained at port if risk of importing spruce bark beetle (or other pathogens) is detected as high are part of strict controls already in place. Conditions on import standards e.g. all timber treated, kiln dried, covered by a plant passport and officially stamped are further measures designed to maintain the Protected Zone status (B. Fairgrieve pers. comm.).
Given the extent and value of both Norway and Sitka spruce stands in both Scotland and the wider UK, it is vitally important economically and environmentally as described above to minimize and control any outbreaks of dangerous forest pests in coming years. Lessons learned in Latvia as well as other European countries indicate the importance of early detection through annual monitoring and indeed the important relevant intervention to control outbreaks and minimize losses as well as preventing further spread of infestations.
What struck me particularly as well as the learning experience during the Latvia exchange was the extremely delicate situation when influences of climate change and pest migration are concerned. Working with efforts to control an invasive mammal, the North American Grey squirrel, to conserve native Red Squirrel populations I have direct experience of the efforts required to control introduced species and conserve an iconic native mammal. With regard to plant pests and pathogens it was made very apparent during this exchange the risks posed and costs associated with invasive management in a European context for the timber sector in both Scotland and the UK.
I would like to extend special thanks and great appreciation to our Erasmus+ host, Andis Purs, and in particular for the presentation and site visits offered on Ips typographus, I would like to thank Senior Researchers Dr. Agnis Smits, Oskars Zalkans and Janis Petersons of the SILAVA institute, Latvian State Forest Service.
Lopatka, J. (2018) https:/uk.news.yahoo.com/climate-change-blame-bark-beetles-ravage-central-europes-142631203.html
Stokmane, M, Smits, A., and Zalkans, O.: Bistamakie meza kaitekli un slimbas Latvija (Ed Purs, A.) Valsts meza dienests 2018.