Part 1: Bark beetle just getting started on a continent-wide rampage
Pacific Northwest old-growth forests are superlative at capturing and storing vast amounts of CO2. Even after 200 years in existence, second-growth low-elevation forests could not compete with the magnificent storage capacity of the ancient forests … [while up north, the] boreal forests contain 47 per cent of the Earth’s stored carbon.
But all is not well. As the author is quick to point out: "in order to flourish and provide these and other benefits, forests have specific requirements and optimal conditions that need to be fulfilled."
It turns out that overheating the forests and unleashing hordes of voracious bark beetles isn't one of them.
The bark beetles
Enter, stage right, the insatiable bugs:
These destructive insects – each about the size of a plump grain of rice – number in the hundreds of billions and have killed billions of mature pine, spruce and Douglas-fir trees.
…bark beetles are devastating the forests like never before in modern times, perhaps in the entire history of conifers. Moreover, the beetles are advancing into regions of high-elevation forests, which typically rarely experience outbreaks. They are also venturing into the northern boreal forest, which has not evolved to defend itself…
The future of our forests in western North America is precarious.
How can such a tiny insect threaten the very existence of giant and ancient forests spanning thousands of kilometres? Dr. Halter goes on to weave the fascinating story of the bark beetles' sophisticated communication systems, biological tricks, chemical toolkits and evolutionary flexibility. These are no simple "bugs". They are formidable, well-armed and hyper-organized predators from which conifers have fled for their lives throughout their mutual history.
The targeted species of trees have survived only where they could effectively use their two main forms of defence against bark beetles:
1) gobs of gooey resin that literally block the beetles
2) the ability to survive extreme cold temperatures that kill the beetles
By warming the climate we are destroying both these tree defences across vast stretches of forests.
Rising temperatures are shifting the water cycle causing increasing summer droughts and water stress for trees. Thirsty trees can't make enough resin, or food, to fight off beetle attacks. Those rising temperatures are not just weakening the trees, they are also banishing the extreme cold that held back the beetles.
As Dr. Halter explains, if there is one thing cold-blooded insects thrive on, it is rising temperatures. Every aspect of the bark beetles lives is governed by temperature. Increasing the temperature is like turbo-charging the beetles.
Energized and unleashed into weakened and exposed new forest lands -- from piñon pines in Arizona to boreal jack pines in Alberta -- the bark beetle hordes are now on full attack. And what an attack it is!
I'll highlight just a few of the beetles' fascinating attacking tricks and tactics that the book reveals.
The bark beetles have a suite of specialized abilities that allows them to zero in on water-stressed trees. Water stressed trees can't make enough resin to defend themselves. The beetles can literally hear the ultrasonic noises given off as microscopic water columns in trees break when dried out. They can also detect infrared reflectance, plant surface temperatures, leaf yellowing and biochemical changes in distressed trees.
Bottom line: if a tree is temporarily weakened from a lack of water the beetles know it. And now global warming is increasing the number of trees suffering water stress. The table is set.
Once the victims are identified, the first scout beetles arrive. If the tree is suitable the beetles transform the tree's own defensive compounds into a chemical signal that: