B is for Beetle

When I hear the word ‘beetle’ I automatically think of mountain pine beetle (Dendroctonus ponderosae):

Actual beetle is smaller than shown (Photo: NRCAN).

Much of my research in the past 6 years has focused on the effects of mountain pine beetle (MPB) on forest structure, and the subsequent impacts on snow accumulation and melt under the forest canopy. And since large areas of MPB-killed forest can increase wildfire risk (a recent synthesis paper in Forest Ecology and Management discusses this in detail), my research also examines the effects of wildfire on snow processes and hydrology.
But MPB isn’t the only insect affecting our forests on such a large scale. Many different insects feast on our forests each year, and the scale of attack and subsequent impact on forest health and structure is closely related to climate.
Spruce (Dendroctonus rufipennis) and Douglas-fir (Dendroctonus  pseudotsugae) beetles
Douglas fir beetle (Photo: USDA – Region 4 Intermountain Archive).

Spruce beetle (Photo: BC Forest Practices Branch)

These two beetles are from the same Dendroctonus family as the mountain pine beetle, but affect different  tree species. Spruce beetle outbreaks appear episodically in the century-long stand history  of spruce-dominated regions, with the most recent one from 1990-2000 occurring on the Kenai Peninsula  of Alaska, and the Bowron Lakes area of British Columbia. Given the relationship between   beetle attack and air  temperature, studies suggest  these outbreaks may increase with warming climate. Outbreaks of Douglas-fir beetle also occur episodically, with the most recent happening in Washington right now. These beetles thrive in areas that have recently been affected by wildfire or blowdown – so with increasing  wildfire  incidence and extreme weather events leading to treefall,  Douglas-fir beetle may continue to thrive.
Ips spp.
Pine engraver beetle (Ips spp.) (Photo: Jeff Schalau, University of Arizona Ag Extension).

Ips – also called the pine engraver or engraver beetle – is prevalent in pine and spruce forests of the western Cordillera, and has many different subspecies that specialize in which trees they attack  (spruce, pinon pine, lodgepole, limber pine, etc.). It looks a lot like the pine beetle, but with a dent in its bum. Ips will attack drought-stressed trees, but is also drawn to newly cut ones. Ips infestations are not as aggressive as Dendroctonus infestations, and are of more limited spatial extent and severity.
Budworm (Choristoneura spp.)
This one is a killer of spruce and  Douglas-fir, from the West to the East coasts of Canada and up into the Territories and Alaska. Episodic outbreaks of budworm have been linked to weather conditions  – namely winters with below average precipitation followed by early springs with average air temperature.
So why do we care about all these bugs? Our forests are affected by pests – and have been cyclically for at least the past century. But recent – and predicted – changes in climate can significantly alter  the  recurrence interval of  infestation, and the resulting severity and extent. For example, pine beetle populations explod­ed partially as a result of warmer winters that failed to kill larvae overwintering beneath  tree bark. Now, warmer summer temperatures are allowing them to breed twice as fast. Increased air temperatures are also implicated in spruce and Douglas-fir beetle outbreaks, and indirectly  with Ips, which is attracted to drought­ stressed trees. Given the variety of tree species affected, the spatial range of each of these species, and the  likelihood  of enhanced  climatic changes – we can expect more insect attacks in the coming years.
This will have  implications for everything from hydrology to land surface albedo. Snowmelt-dominated headwater basins that feed downstream systems are  likely to see major hydrologic effects. If large areas of forest are affected by these types of pests – similar to the large area of BC now in the grey stage of mountain pine beetle attack – the surface albedo can increase with subsequent cooling effects on the overlying atmosphere.
It’s an excellent reminder of the interconnections between environmental systems, in this case forests, water, and atmosphere, and the cascading effects of change in just one small part of this system.

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