One of the most visible and unintended consequences of global warming are bark beetles. Drought beget beetles. The U.S. is experiencing its worst drought in more than 50 years. The first 9 months of 2012 have been the warmest of any year on record in the contiguous U.S. These warm temperatures are fueling the largest tree-killing, bark beetle epidemic ever recorded throughout western North America.
Rising temperatures across western North America between 1.8 and 3.6 degrees Fahrenheit are having a deleterious affect on the conifer forests. These forests evolved to withstand temperatures in excess of minus 40 degrees Fahrenheit, and these frigid temperatures prevent bark beetle epidemics from occurring.
Global warming has effectively removed nature's cold-curtain enabling the indigenous mountain pine bark beetles to speed up their life cycles (formerly two years and now two generations within one year), and move-up into the high elevation forests throughout the western half of the continent.
The extent of the current bark beetle infestation is staggering; in British Columbia for example, half the commercial forests have been killed in the past 15 years. That's enough wood to build a city of over five million homes. Furthermore, instead of absorbing CO2 from the atmosphere these graveyard forests are decomposing and contributing greenhouse gases to an ever-rising pool. They will add over 250 million metric tons over the next decade or the equivalent of all the cars and light truck emissions in Canada over a period of five years.
It doesn't even begin to end there. The spruce beetles in the far north of British Columbia and into Yukon's Kluane National Park and Reserve have accomplished something never recorded in modern or past times. Since the cold ecological constraint has been removed they have killed over 864,000 acres of white spruce. Prior to this, the largest spruce attack was a modest 610 acres in 1977.
Bark beetles have killed over 69 million acres of mature forests across western North America. And nowhere is it more evident than across the western mountains of the U.S. The temperature over the past 40 years have risen in excess of 3.6 degrees Fahrenheit and the high elevation whitebark and limber pines are disappearing at an incredible rate as many forests have experienced 90 percent mortality rates. The sentinels of the high country have become the tsunami sirens of global warming, showing scientists that a warming world is irrevocably altering the landscape across the entire mountainous region of western North America.
In a whitebark or limber pine's lifetime, say 700 years, it can provide over 504,000 individual seeds. Not only do some of those seeds go onto to create entire treeline ecosystems; but also each tree goes on to act as a healthy restaurant that feeds a whole neighborhood of critters. The well-being of the entire community depends upon these pines for they cast shade, altering the micro-climate enabling shade-dependent trees like spruce and fir an opportunity to grow.
Whitebark and limber pines have co-evolved with an intelligent member of the Corvid family (including crows, ravens, rooks, magpies and jays) a Clark's nutcracker, which must harvest and disseminate the pine seeds. Clark's rely on the pine seeds for its main source of food especially in the winter as these birds reside full-time in the high mountains. As the whitebark and limbers die the birds are adapting by foraging in lower elevation forests.
Unlike the Clark's who can feed elsewhere, the monarch of Wyoming's wilderness - Yellowstone National Park's grizzly bears - are facing an uncertain future. These giant bears rely upon whitebark's large, protenacious seeds as a main food source. It's well documented that three times as many grizzly bears die in bad whitebark pine seed years as good ones.
The loss of these magnificent high elevation pine forests will also impact the way people live across the West. These mountain pine forests attract and hold snowpacks. In the springtime pine roots slowly regulate the mountain moisture that feeds water to intensive agriculture systems, mighty industries and a burgeoning population of over 50 million people.
The warfare between tree killing bark beetles and conifers is a fascinating story dating back a couple hundred million years to the Triassic Period.
Members of the Pinaceae family including pines, spruces and others possess primary defense mechanisms made up of a resin, or pitch, system. When an insect bores into a tree, the tree releases a sufficient flow of resin to preclude the insect from going any further. The resin contains monoterpenes, diterpene acids and stilbene phenolics, which are known to have antibiotic and other repellent properties to fight beetles, fungi, bacteria and mites.
When members of the Pinaceae become stressed by drought they stop producing copious amounts of gooey pitch; they become sitting ducks. The bark beetles, dark in color and about the size of a plump rice grain are able to detect higher stressed plant surface temperatures, leaf yellowing, increased infrared reflectance, biochemical changes and likely hear ultrasonic stressed-induces cavitation when cells desiccate.
Bark beetles have evolved a clever predatory strategy of turning the plant's terpenoid defense system against itself. Beetles overcome mature trees with a synchronous mass attack. Sheer numbers completely overwhelm the stressed tree, or even a healthy one.
Trees emit chemicals - known as kairomones - that actually attract more invaders. Initially in August however, it is the pioneer female mountain pine beetle that penetrates the bark and oxidizes the tree's monoterpenes alpha-pinene - a type of terpene - to produce trans-verbenol, a pheremone that attracts males. When this has occurred, the tree's kairomones of alpha-pinene and myrcene blend together, and this signals that the tree has relinquished the fight. Basically, the tree itself sends out the signal that sparks a mass attack of thousands of mountain pine beetles, lasting for about 48 hours.
Once completely colonized, mountain pine beetles halt the attack by using yet another chemical cue as an anti-aggregate. High concentrations of trans-verbenol emitted from the attacked tree sends a signal to surrounding trees of impending death and acceptance of the forthcoming onslaught.
In addition to synchronous mass attacks the beetles carry with them a blue-stain fungi and bacteria, which proliferates inside the tree impairing the water conducting tissue, or xylem cells, in the sapwood.
In northeastern British Columbia the climate has warmed so quickly that formerly a range uninhabitable for the beetles, are now accessible. The northern pines are more chemically attractive to the beetles compared to the southerly lodgepole pines (its main host). In fact, northeastern lodepoles' lack the terpenoid defense mechanism to fight the beetles, because they did not expend energy resources to a build such a defense system against a non-existent (at the time) beetle predator. The beetles have advanced into those naïve forests and are breeding with much higher success than in the southerly lodgepole pine forests.
In 2002 and 2006 billions of British Columbian mountain pine beetles were sucked up into the upper atmosphere and spat out hundreds of miles on the eastern side of the Albertan Rocky Mountains. Millions of beetles survived this forced migration and successfully reproduced within a year, and made a transition from hybrid lodepole/Jack pines into pure Jack pines - an a priori.
With warming temperatures and a plentiful food source, the harbingers of global warming - bark beetles - are now for the first time ever into Earth's emerald crown or the boreal forest, which extends all the way across the continent to Labrador and the Atlantic Ocean.