| Mountain pine beetle | |
|---|---|
| Adult mountain pine beetle Dendroctonus ponderosae |
|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Family: | Curculionidae |
| Subfamily: | Scolytinae |
| Genus: | Dendroctonus |
| Species: | D. ponderosae |
| Binomial name | |
| Dendroctonus ponderosae Hopkins, 1902 |
|
The mountain pine beetle (MPB) Dendroctonus ponderosae, is a species of bark beetle native to the forests of western North America from Mexico to central British Columbia. It has a hard black exoskeleton, and measures about 5 millimeters, about the size of a grain of rice.
Mountain pine beetles inhabit ponderosa, lodgepole, Scotch and limber pine trees. Normally, these insects play an important role in the life of a forest, attacking old or weakened trees, and speeding development of a younger forest. However, unusual hot, dry summers and mild winters in central British Columbia during the last few years, along with forests filled with mature lodgepole pine, have led to an unprecedented epidemic.[1]
It may be the largest forest insect blight ever seen in North America.[2] Climate change is said by some to have contributed to the size and severity of the outbreak, and the outbreak itself may, with similar infestations, have significant effects on the capability of northern forests to remove greenhouse gas (CO2) from the atmosphere.[3]
Contents |
Mountain pine beetles affect pine trees by laying eggs under the bark. The beetles introduce blue stain fungus into the sapwood that prevents the tree from repelling and killing the attacking beetles with tree pitch flow. The fungus also blocks water and nutrient transport within the tree. On the tree exterior, this results in popcorn-shaped masses of resin, called "pitch tubes", where the beetles have entered.[4] The joint action of larval feeding and fungal colonization kills the host tree within a few weeks of successful attack (the fungus and feeding by the larvae girdles the tree, cutting off the flow of water and nutrients). When the tree is first attacked, it remains green. Usually within a year of attack, the needles will have turned red. This means the tree is dying or dead, and the beetles have moved to another tree. In three to four years after the attack, very little foliage is left, so the trees appear grey.[5]
As beetle populations increase or more trees become stressed because of drought or other causes, the population may quickly increase and spread. Healthy trees are then attacked, and huge areas of mature pine stands may be threatened or killed. Warm summers and mild winters play a role in both insect survival and the continuation and intensification of an outbreak. Adverse weather conditions (such as winter lows of -40 °C) can reduce the beetle populations and slow the spread, but the insects can recover quickly and resume their attack on otherwise healthy forests.
Beetles develop through four stages: egg, larva, pupa and adult. Except for a few days during the summer when adults emerge from brood trees and fly to attack new host trees, all life stages are spent beneath the bark.[6]
In low elevation stands and in warm years, mountain pine beetles require one year to complete a generation. At high elevations, where summers are typically cooler, life cycles may vary from one to two years.
Female beetles initiate attacks. As they chew into the inner bark and phloem, pheromones are released, attracting male and female beetles to the same tree. The attacking beetles produce more pheromones, resulting in a mass attack that overcomes the tree’s defenses, and results in attacks on adjacent trees.
Natural predators of the mountain pine beetle include certain birds, particularly woodpeckers, and various insects.
Management techniques include harvesting at the leading edges of what is known as “green attack”, as well as other techniques that can be used to manage infestations on a smaller scale, including:[7]
The US Forest Service tested chitosan,[8][9] an ecofriendly biopesticide, to pre-arm pine trees to defend themselves against MPB. The US Forest Service results show AgriHouse's EPA-registered ODC Collodial Chitosan elicited a 40% increase in pine resin (P<0.05) in southern pine trees. One milliliter ODC chitosan per 10 gallons water was applied to the ground area within the drip ring of loblolly pine trees. The application was repeated three times from May through September in 2008. The ODC chitosan was responsible for eliciting natural defense responses of increased resin pitch-outs, with the ability to destroy 37% of the pine beetle eggs.[10] Dr. Jim Linden, Microbiologist, Colorado State University, stated the chitosan increased resin pitch-outs to push the boring pine beetle out of the tree, preventing the MPB from entering the pine tree and spreading blue stain mold.[11]
Aggressively searching out, removing, and destroying the brood in infested trees is the best way to slow the spread of mountain pine beetles; however, it may not protect specific trees. Spraying trees to prevent attack is the most effective way to protect a small number of high-value trees from mountain pine beetles. Carbaryl (Sevin SL and XLR, and others), permethrin (Astro, Dragnet, and others), and bifenthrin (Onyx) are registered in the United States for use in the prevention of pine beetle infestations. Carbaryl is considered by the EPA to likely be carcinogenic to humans. It is moderately toxic to wild birds and partially to highly toxic to aquatic organisms. Permethrin is easily metabolized in mammalian livers, so is less dangerous to humans. Birds are also practically not affected by permethrin. Negative effects can be seen in aquatic ecosystems, as well as it being very toxic to beneficial insects. Bifenthrin is moderately dangerous to mammals, including humans; it is slightly more toxic to birds and aquatic ecosystems than permethrin, as well as extremely toxic to beneficial insects.[12]
Spraying is very effective at protecting the pines, but is not recommended for large-scale use due to ecological and financial reasons. Pines should be sprayed before the beetle flight in July, so May or June will yield the best results. Spraying one's own trees requires both spraying and safety equipment; a licensed applicator is highly recommended.[13]
Verbenone is the main compound for the anti-aggregate pheromone for the mountain pine beetle. This compound is produced by three companies: Contech, Synergy Semiochemicals Corp. and Hercon Environmental. Verbenone is a behavior-modifying pheromone that tricks the pine beetle into believing the tree is no longer useful to more beetles and they will leave the tree alone. It is useful in campsites and places close to creeks and rivers where spraying cannot be used. Verbenone does not kill the insects; it simply pushes them away to another tree or area. It has been fairly successful in areas with low beetle populations, but has not been very successful in areas with higher populations. It is only useful in small-scale operations.[14]
Colorado’s forests are much more densely wooded, making them much more susceptible to the beetles. Current legislation is in place to help with the growing beetle problem. Colorado Senators Mark Udall and Michael Bennet announced that Colorado will receive $30 million of the $40 million dollars being diverted by the U.S. Forest Service to fight the millions of acres of damage caused by the mountain pine beetle in the Rocky Mountain region.
Wood from beetle-affected trees retains its commercial value for eight to 12 years after the tree has died. This so-called ‘shelf life’ is dependent on a number of factors, including economic and stand site conditions. The trees remain commercially viable longer under drier conditions. In areas where it is wetter, the trees tend to rot at the base and fall faster, especially if they are larger.[15] The blue stain fungus has no effect on the wood’s strength properties.
The timber can be used for anything from standard framing lumber to engineered wood products, such as glue-laminated (glulam) products and cross-laminated panels. The epidemic in British Columbia is also creating opportunities for the emerging bioenergy industry.
The long-held belief that beetle infestations and resulting deadkill lead to more devastating forest fires is currently being challenged. Ongoing NASA studies have shown that beetle kill may actually reduce available small fuels and consequently limit the effect and reach of fires.[16]
The current outbreak of mountain pine beetles is ten times larger than previous outbreaks.[17] Huge swaths of central British Columbia (BC) and parts of Alberta have been hit badly, with over 40 million acres (160,000 km2) of BC's forests affected.[18] Under the presumption that the large areas of dead pine stands represent a potential fire hazard, the BC government is directing fuel management activities in beetle areas as recommended in the 2003 Firestorm Provincial Review.[19] Harvesting affected stands aids fire management by removing the presumed hazard and breaking the continuity of the fuels. These fuel management treatments are specifically designed to reduce interface fire threats to communities and First Nations located in the infestation zone. The interface is the area where urban development and wilderness meet.
The mountain pine beetle has impacted more than 900 miles (1,400 km) of trail, 3,200 miles (5,100 km) of road and 21,000 acres (85 km2) of developed recreation sites over 3,600,000 acres (15,000 km2) in Colorado and southeastern Wyoming. The US Forest Service is working on a hazard tree removal strategy, prioritizing high-use recreation areas, such as campgrounds, roads and National Forest Service lands adjacent to vulnerable public infrastructure such as power lines and near communities.[20]
Researchers from the Canadian Forest Service have studied the relationship between the carbon cycle and forest fires, logging and tree deaths. They concluded by 2020, the pine beetle outbreak will have released 270 megatonnes of carbon dioxide into the atmosphere from Canadian forests. There is yet to be an accepted study of the carbon cycle effect over a future period of time for North American forests.[17]
Hydrologists from the University of Colorado have investigated the impacts of beetle-infested forests on the water cycle, specifically, snow accumulation and melt. They concluded that dead forests will accumulate more snowpack as a result of thinner tree canopies and increased snow sublimation. These thinned canopies also cause faster snow melt by allowing more sunlight through to the forest floor and lowering the snowpack albedo, as a result of needle litter on the snow surface.[21] Augmented snowpack coupled with dead trees that no longer transpire will likely lead to more available water.
The huge number of beetle-killed trees poses a substantial risk of devastating forest fires. Forest thinning to mitigate fire danger is expensive and resource-intensive (Kumar 2009). Attention is turning to ways to turn this liability into a source of cellulosic biofuels.
Leaders in western U.S. states and Canadian provinces have promoted legislation to provide incentives for companies using beetle-killed trees for biofuel or biopower applications. Sellable commodities resulting from MPB damage can help subsidize the cost of forest thinning projects and support new job markets. Colorado's Department of Energy recently provided $30 million toward construction of the state's first cellulosic ethanol plant, to convert beetle kill into ethanol. Lignin, a byproduct of the process, can be sold for applications in lubricants and other goods (MacLachlan).