Future Range Shifts Suggest That the Six-Spined Spruce Bark Beetle Might Pose a Greater Threat to Norway Spruce in Europe than the Eight-Spined Spruce Bark Beetle

Abstract

Both the eight-spined spruce bark beetle (eight-spined beetle, Ips typographus) and the six-spined spruce bark beetle (six-spined beetle, Pityogenes chalcographus) have major deleterious effects on Norway spruce (i.e., Picea abies, the host tree) in Europe. However, future potential range shifts of the two pests and their range overlap with Norway spruce have not yet been characterized. Through range dynamic models, we characterized their future range expansions, as well as their range overlap with their host tree under current–future change scenarios in 2100. Host availability was the greatest contributor to the range shifts of the two pests, and climatic changes were the main drivers of the range expansion of the host. The potential range, expanded range, and overlapped range were larger for the six-spined beetle than for the eight-spined beetle. The host tree, i.e., Norway spruce, might face increasing threats from the two pests in the future. Future climate change will likely indirectly facilitate range shifts of pests by promoting increases in the area capable of sustaining the host tree. The six-spined beetle might pose a greater threat to Norway spruce than the eight-spined beetle, albeit the latter has previously been considered to have more deleterious effects on Norway spruce.