Markus Melin, Tiina Ylioja, Leena Aarnio, Katri Hamunen, Seppo Nevalainen, Antti Pouttu, Heli Viiri. (2021). Emergence levels of pine shoot beetles from roundwood piles of Scots pine and the cascading damage in the surrounding forests. Silva Fennica vol. 55 no. 5 article id 10525. https://doi.org/10.14214/sf.10525

Keywords: forest management; forestry; Tomicus piniperda; Tomicus minor; roundwood; legislation; timber storage

Highlights: Emerged pine shoot beetles were counted from piles of harvested Scots pine, and the shoot damage in the surrounding forests was measured; Damage was noticeable up to a distance of 40–60 m, being more severe near large piles; For piles smaller than 50 m³ the level of damage (fallen shoots) was mainly below known thresholds for growth losses; Logs with harvester-damaged bark were significantly less colonized by the beetles.

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Bark beetles are amongst the most aggressive pest agents of coniferous forests. Due to this, many boreal countries have designated laws aiming to lower the risk of bark beetle epidemics. Finland’s forest legislation has pre-emptive measures targeted against bark beetles, and for Scots pine (Pinus sylvestris L.), the law concerns pine shoot beetles (Tomicus spp.). This study used data collected around 25 piles of Scots pine roundwood that were harvested in the winter but left in the forest until the following November. Thus, the pine shoot beetles were able to use the piles for breeding. We assessed the number of emerged insects from the piles and the cascading damage they caused in the surrounding forests. All roundwood piles, regardless of their volume, were used by the beetles for breeding. Highest densities of beetle exit holes were found from the parts of the log with thick and intact bark. If the bark of the log was damaged by the harvester head, the number of beetles decreased significantly. Depending on the volume of the roundwood pile, the cascading damage (fallen shoots) was noticeable up to ca. 40–60 m from the roundwood pile. Storing of piles smaller than 50 m³ did not cause excess damage. The number of fallen shoots per tree was generally below the known thresholds for when growth losses can occur. However, the study was conducted in mature forests, and it can be assumed that the recorded damage levels would severely affect the growth of young pines, raising the question of where to store the roundwood. As with other bark beetles, the role of Tomicus beetles as damage agents may change in the future, but based on this as well as past studies, the species can be viewed as a notable damage agents only around long-term wood storage sites in the current northern conditions.

Melin, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Yliopistokatu 6b, FI-80100 Joensuu, Finland E-mail: markus.melin@luke.fi
Ylioja, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, FI-00790 Helsinki, Finland E-mail: tiina.ylioja@luke.fi
Aarnio, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, FI-00790 Helsinki, Finland E-mail: leena.aarnio@luke.fi
Hamunen, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Yliopistokatu 6b, FI-80100 Joensuu, Finland E-mail: katri.hamunen@luke.fi
Nevalainen, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Yliopistokatu 6b, FI-80100 Joensuu, Finland E-mail: seppo.nevalainen@gmail.com
Pouttu, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, FI-00790 Helsinki, Finland E-mail: antti.pouttu@kolumbus.fi
Viiri, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Yliopistokatu 6b, FI-80100 Joensuu, Finland; UPM-Kymmene Oyj, UPM Forest, Peltokatu 26 C, PL 85, FI-33100, Tampere, Finland E-mail: heli.viiri@upm.com

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