Resource pulses drive spatio-temporal dynamics of non-native bark beetles and wood borers.

Abstract

Clear-fell harvesting of non-native plantation forests in the southern hemisphere creates large amounts of woody debris that is used for breeding by non-native bark beetles and wood borers. Limited competition and a shortage of natural enemies allow some invasive pine bark beetles and wood borers to become highly abundant and cause phytosanitary issues. Replicated transects (550-750 m long) of funnel traps baited with alpha-pinene and ethanol spanning even-aged Pinus radiata stands were established in New Zealand's largest plantation forest and monitored from pre-harvest until up to 5 years post-harvesting to test the effects of harvesting residue resource pulses on the spatio-temporal population dynamics of Hylurgus ligniperda, Hylastes ater and Arhopalus ferus. Generalised additive mixed model analyses of trap captures of >687,000 H. ligniperda, >7600 H. ater and >5000 A. ferus individuals showed greatly elevated populations for the first 2-3 years post-harvest. Subsequently, populations returned to very low levels once the resource pulse was exhausted. Spatial patterns of captures reflecting beetle dispersal from breeding material showed a curvilinear decline along the breeding resource gradient by up to 95% from the interior of a recently harvested stand into an adjacent, previously harvested stand with exploited resources. Synthesis and applications. The results show that forest management characterised by ongoing harvesting of neighbouring stands facilitates the build-up of large populations of bark beetles and wood borers of phytosanitary concern. This is due to recurrent resource pulses caused by the supply of substantial amounts of breeding material from tree felling. Our findings can inform forest planning aimed at avoiding such harvesting patterns, by assisting with the development and implementation of strategies for the management of beetle populations across the landscape. Most beetles dispersed <400 m beyond the source stand edge, although some beetles are likely to have dispersed further. Keeping a distance of 1-2 km between recently felled stands and those scheduled for felling would be expected to reduce rapid population growth. This knowledge can also be used to reduce seedling attack, minimise infestation of logs, and ultimately, mitigate pathway and biosecurity risks, with important implications for forest product exports and quarantine measures.

Key words

• population dynamics
• spatial variation
• temporal variation
• invasive species
• introduced species
• plant pests
• insect pests
• forest pests
• pests
• arthropod pests