Trees along the West Coast and in the Rocky Mountains face a foe that is killing them by the millions and yet stands only millimeters tall. Bark beetles have affected tens of millions of acres of forest and show no sign of slowing down. Past outbreaks from these beetles have been brief and controlled by precipitation. They even served to balance tree growth in an area by attacking weaker and dying trees to create room for the growth of younger, healthier trees.
Due to an increasingly warm climate, the balance between the beetles and trees has shifted in favor of the beetles. This has caused widespread tree death and ecological destruction not previously seen. Solutions have ranged from spraying trees with carbaryl or cutting down infected trees like amputating a cancerous limb. Yet these are inefficient and at best serve only to slow down the beetles. Ultimately, the climate is the best effective control for this epidemic. Until we can come up with another solution, not much can stand in the way of the Bark beetle epidemic, and it’s possible that nature alone will remedy the problem through natural selection.
Many areas of land throughout the United States and Canada have been drastically affected by this horde. However, those of us in Colorado have a firsthand account of the devastation these little critters can cause. This epidemic has affected Coloradans ecologically and economically, from tourism to clean water production to fires hazards. The death of trees on such a grand scale is costly to humans, trees, and the ecosystem. Unfortunately, this devastation has continued to progress on a widespread scale with no concrete solution in sight. As entomologist Diana Six states, “At this point if you’re a tree, you should not only be worried, but you should be shaking in your roots.”
So, what events led to this change in balance between trees and bark beetles? Bark beetles are native to Colorado and the trees that reside there. Under normal conditions, the beetles only attack the weak and dying trees. Their numbers increase only for a short amount of time. Then they die off either by running out of weak trees to attack or from cold and precipitation. Normally, this brief occurrence serves to regulate both species and benefits the forests as the beetles promote natural selection. They kill off the weaker dying trees and allow younger, healthier trees to grow. This process even furnishes lumber for us to use instead of having to cut down healthy trees.
Yet as the climate warms, the trees become weaker and stressed from lack of water, thus allowing the beetles to overrun their defenses and run rampant. While the trees have their defenses, bark beetles have multiple ingenious tools to overcome them. Their hard exoskeleton allows them to be able to burrow into the trees’ bark into the inner layers where they feed and reproduce. There, the bark beetles disrupt the xylem (tissue that transports water), taking the water for itself and killing the tree by dehydration.
The tree combats this invasion by producing sap to kill the beetles. Under normal conditions, healthy trees can produce enough sap to fend off the insects. Yet during prolonged droughts, the tree is unable to produce as much sap. This leaves it vulnerable to attack. Also, it is an unfair fight as the bark beetle has a fungus ally it uses to stop the tree from producing sap. This fungus grows into the xylem and phloem, further starving the tree and killing it.
As the climate warms, droughts last longer. This stresses the trees and weakens their defenses. They then become succeptible to the invading beetles. The beetles’ population increases massively in a short amount of time, and they feed and reproduce off the weakened trees. As they become stronger in number, they take on healthy trees and spread the infection.
With a warming drier climate, the beetles have been able to expand into higher altitudes and other ecosystems. They have therefore become exotic or a non-native invasive species, attacking trees that have no knowledge or defenses against them. A team of scientists from the University of Wisconsin at Madison reported that “native mountain pine beetles are expanding their range further north into white bark pine forests in the northern Rocky Mountains. Trees at these higher elevations have not evolved defenses to stop the pine beetles.” This cocktail of ideal conditions has caused the bark beetles to prosper in number leading to massive devastation of trees and severely impacting the environment.
The impact of this tree genocide cannot be overlooked as it affects all within the ecosystem. With more dead and dying trees comes an increase likelihood of them falling, causing injury, or acting as kindling. This correlates with hazardous fire conditions. Park services and lumber companies work to remove trees affected by bark beetles but are unable to keep up with the devastation left in their wake.
The increasing number of dead trees also perpetuates the cycle, which further promotes a warmer climate. The forest canopy created by the trees provides shelter for its inhabitants, blocks the sun, and keeps temperatures relatively cool. As the beetles destroy the canopy, the temperature increases further. This leads to drought. The National Science Foundation notes that “The loss of foliage, which blocks and reflects light away from the land, can raise temperatures by about 2 to 4 degrees °F, at least temporarily. This increase can be enough to influence weather patterns, which can lead to drought.”
Another one of Colorado’s concerns from the invasion is tourism. Rocky Mountain National Park is one of the ten most visited national parks in the United States and could experience a costly drop in tourism as its forests are reduced by the epidemic. Ski resorts such as Vail, Breckenridge, Steamboat Springs, and Winter Park have suffered extensive beetle damage, which, if continued, could severely financially impact the state. An economic study reveals the skiing industries provide $4.8 billion of annual revenue to Colorado. With so much at stake economically and financially, there is a desperate need for a solution to this outbreak.
It would be grand if one simple solution could correct this issue; however, nature is adaptive and dynamic. To fix the problem, many steps and processes are needed to be put into place, some of which are already underway. In the short-term, removing the dead and dying trees can prevent damage to powerlines, waterways, and humans. This can also provide lumber for construction as the beetles do not damage the integrity of the wood. In fact, lumber industries have moved from chopping down healthy trees to using the dead trees from the beetle infestation. Unfortunately, the beetles can survive in the wood, and as it’s transported to other places, the beetles spread the infection.
Another short-term solution is to spray the trees with carbaryl, a manmade pesticide that is toxic to insects when ingested. However, this is rarely used as it is toxic to other animals and birds as well and therefore is not a viable widespread solution. Bark and Wood Boring Beetles of the World lists its techniques for bark beetle control as follows: salvage or using any feasible wood leftover, cut the trees before they fall on their own to reduce damage, pile and burn the trees or use chemical applications. While these can be affective short-term solutions or cleanup methods, none of these techniques address the complete issue of the bark beetle infestation. UC IPIM, California’s state pest management program, notes, “Except for general cultural practices that improve tree vigor, little can be done to control most bark beetles once the trees have been attacked.”
While a long-term solution may seem unlikely, entomologist Diana Six has stumbled upon a hidden but obvious discovery–nature. While comparing tree core measurements of pines, she noticed after looking at a bark-beetle-ravaged site that some trees were unaffected. These trees were the same species, age, and size as their affected kin, yet they were completely unharmed. Six suspected that a genetic component made the surviving trees more adaptable to a warmer environment. In other words, natural selection was at play, killing off the trees that failed to adapt while those whose DNA mutated survived.
So, the simple solution might be to do nothing. Maybe this could be a temporary shift in balance, and the trees will respond to by adapting. In a review concerning management for mountain pine beetle outbreak suppression, the authors stated,
It is perhaps no accident that the beetle treatments that have been most aggressively pushed for in the political landscape allow for logging activities that might provide revenue and jobs for the commercial timber industry. The result is that the push to ‘do something,’ uncertainty, and political pressures might lead us to act to respond to climate change before we understand the consequences of what we are doing, in the end producing more harm than good.
It’s worth remembering that action can mean many things, from waiting to gathering information to not doing anything through direct methods. As the authors noted, information must be gathered with science, not politics. Further genetic research is being conducted to estimate the relative risk to change in temperature, moisture, and pathogen of a tree to obtain more information regarding susceptibility of pathogen infection. This could lead to an evidence-based plan to combat the bark beetle’s invasion.
The war between beetles and trees has had social and economic impacts on the Colorado government and populace. A correlation between the bark beetle population and an increasingly warm climate has changed the natural balance of the bark beetle / tree relationship. But nature has its checks and balances, and as Six answered when asked at TEDx how she wants to change things, she responded, “I don’t want to change the world. We have changed the world to a point that it is barely recognizable. I think it’s time to stop thinking change and try to hold on to what beauty and function remains.”
Therefore, it’s vital to act to find a solution to this outbreak but also prudent to remember that the action required may be to just gather information and allow science to point in the direction or present a solution. Short-term solutions such as chemical sprays end up causing more harm to the environment and should not be considered a long-term viable solution. To look ahead, we must accept that we might not be needed for a solution. To combat this invasion, more research is required. Maybe scientists should keep looking into the genetic component of trees that are unaffected by the bark beetle and learn how best to rectify this human propelled event without causing further harm.
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Kevin Ciano-McGee lives in Colorado Springs. He spent six years serving as a corpsman (physical therapy technician) at the United States Naval Academy. He recently left the military and moved back with his wife Caitlin to Colorado to pursue a degree in medicine. His goal is to attend Rocky Vista University to pursue a degree in osteopathic medicine (DO).
