In the film Death of a Forest shown at last weekend's Wild & Scenic Film Festival here in Nevada City, filmmaker Michael Pellegatti documented how the mountain pine beetle, an insect smaller than your fingertip can be laying waste to forests in Alaska and Canada and parts of the Rocky Mountains.
Bark beetles are part of a natural cycle, but now it’s a “system completely out of balance”, said Sierra naturalist David Lukas, who spoke after the film. And in the film, research entomologist Jesse Logan of the USFS Pine Beetle Project agreed, saying the mountain pine beetle is "a native species that is acting as an invasive species".
Climate change helps the beetles boom with a double-whammy. Higher winter temperatures mean more beetles manage to overwinter - instead of 2% surviving, maybe 60-70% survive, said Logan. And a longer growing season lets the beetle undergo two generations a year, instead of just one. The resultant beetle boom has been especially deadly to high-elevation species like whitebark pine and jack pine, that haven't coevolved with the beetle to evolve defenses like the lower elevation pines have - defenses like drowning the invaders in sap or producing toxins to kill the eggs & larvae.
The beetle has to kill the tree in order to reproduce, Logan said.
In finding & attacking a tree, the beetles have evolved ingenious tactics. They’re more apt to be able to overwhelm a tree’s defenses in a group attack, so the beetles emit pheromones to coordinate an attack, which can involve "literally thousands" of beetles, said Logan.
Another form of coordination comes from one bark beetle subgroup in the Ips family, which makes auditory calls to conspecifics via stridulaton (rubbing a leg against another body part); so one forest pest control research effort has involved mounting speakers on trees to confuse beetles who’d respond to the sound, Lukas said.
And the beetles bring along & use a fungus, for protection, Lukas told us. Pits and crevices hold a “blue stain” fungus, which protects the beetle eggs & larvae - when the beetles have invaded the tree, the fungus colonizes & clogs up the tree's local circulation so it can’t encase and drown the beetle eggs or larvae.
(Online, I've also read that the fungus serves the beetles as food - when eaten, it provides nutrients that wood & sap don’t.)
The whitebark pine is a keystone species, providing food via its pine cones for squirrels, and these cached cones becomes the main food for grizzlies packing in calories to survive the winter; so the tree loss will be felt by animals large and small.
And via the tree loss, climate change has a triple-whammy effect on snowmelt runoff & thus water availability – not only is there likely to be a smaller snowpack due to warmer temperatures, and earlier snowmelt due to an earlier spring, but also, as the pines that currently shade the snow & delay its melt die off, the melt will occur even sooner & be more abrupt, leaving less snow for later in the dry season.
Closer to home, Lukas said Sierra forests have been largely unaffected by this epidemic. He warned landowners that bark beetles are sometimes used as a scare tactic by tree cutters, recommending skepticism when foresters advise you to cut down & remove a beetle-killed tree lest the beetles spread, since the beetles are probably long gone by the time the tree appears dead.
The film also pointed out that global warming could cut trout and salmon fisheries by half or more, since these fish suffer in warmer water. Calling all salmon lovers...
Bark beetles are part of a natural cycle, but now it’s a “system completely out of balance”, said Sierra naturalist David Lukas, who spoke after the film. And in the film, research entomologist Jesse Logan of the USFS Pine Beetle Project agreed, saying the mountain pine beetle is "a native species that is acting as an invasive species".
Climate change helps the beetles boom with a double-whammy. Higher winter temperatures mean more beetles manage to overwinter - instead of 2% surviving, maybe 60-70% survive, said Logan. And a longer growing season lets the beetle undergo two generations a year, instead of just one. The resultant beetle boom has been especially deadly to high-elevation species like whitebark pine and jack pine, that haven't coevolved with the beetle to evolve defenses like the lower elevation pines have - defenses like drowning the invaders in sap or producing toxins to kill the eggs & larvae.
The beetle has to kill the tree in order to reproduce, Logan said.
In finding & attacking a tree, the beetles have evolved ingenious tactics. They’re more apt to be able to overwhelm a tree’s defenses in a group attack, so the beetles emit pheromones to coordinate an attack, which can involve "literally thousands" of beetles, said Logan.
Another form of coordination comes from one bark beetle subgroup in the Ips family, which makes auditory calls to conspecifics via stridulaton (rubbing a leg against another body part); so one forest pest control research effort has involved mounting speakers on trees to confuse beetles who’d respond to the sound, Lukas said.
And the beetles bring along & use a fungus, for protection, Lukas told us. Pits and crevices hold a “blue stain” fungus, which protects the beetle eggs & larvae - when the beetles have invaded the tree, the fungus colonizes & clogs up the tree's local circulation so it can’t encase and drown the beetle eggs or larvae.
(Online, I've also read that the fungus serves the beetles as food - when eaten, it provides nutrients that wood & sap don’t.)
The whitebark pine is a keystone species, providing food via its pine cones for squirrels, and these cached cones becomes the main food for grizzlies packing in calories to survive the winter; so the tree loss will be felt by animals large and small.
And via the tree loss, climate change has a triple-whammy effect on snowmelt runoff & thus water availability – not only is there likely to be a smaller snowpack due to warmer temperatures, and earlier snowmelt due to an earlier spring, but also, as the pines that currently shade the snow & delay its melt die off, the melt will occur even sooner & be more abrupt, leaving less snow for later in the dry season.
Closer to home, Lukas said Sierra forests have been largely unaffected by this epidemic. He warned landowners that bark beetles are sometimes used as a scare tactic by tree cutters, recommending skepticism when foresters advise you to cut down & remove a beetle-killed tree lest the beetles spread, since the beetles are probably long gone by the time the tree appears dead.
We lost a few Ponderosa pines to bark beetle infestation. One of the trees was very near our septic tank, so we speculate that the excavation for the tank probably weakened the root system. We're always on the lookout for these critters, and we have our arborist inspect our 2.5 acres about once a year. We're at about 2500 feet elevation.
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