Mountain pine beetle

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 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 approximately 5 mm, about the size of a grain of rice.

In western North America, the current outbreak of the mountain pine beetle and its microbial associates has destroyed wide areas of lodgepole pine forest, including more than 16 million of the 55 million hectares of forest in British Columbia. The current outbreak in the Rocky Mountain National Park began in 1996 and has caused the destruction of millions of acres of ponderosa and lodgepole pine trees. According to an annual assessment by the state's forest service, 264,000 acres of trees in Colorado were infested by the mountain pine beetle at the beginning of 2013. This was much smaller than the 1.15 million acres that were affected in 2008 because the beetle has already killed off most of the vulnerable trees (Ward).[1]

Mountain pine beetles inhabit ponderosa, whitebark, lodgepole, Scotch, jack pine,[2] 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, unusually hot, dry summers and mild winters throughout the region during the last few years, along with forests filled with mature lodgepole pine, have led to an unprecedented epidemic.[3]

It may be the largest forest insect blight ever seen in North America.[4] Climate change has 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.[5]

Because of its impact on forestry, the transcriptome[6] and the genome[7] have been sequenced. This is only the second beetle genome to be sequenced to date.

Tree infestations

Mountain pine beetles can damage whole regions of forest.

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.[8] 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.[3]

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°) can reduce the beetle populations and slow the spread, but the insects can recover quickly and resume their attack on otherwise healthy forests.

Life cycle

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.[9]

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

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:[10]

The concept of natural plant defense holds hope for eliminating pine beetle infestation. Beneficial microbial solutions are being researched and developed that work with the plant to activate and enhance its resistance mechanisms against insects and disease.

The US Forest Service tested chitosan,[11][12] a biopesticide, to pre-arm pine trees to defend themselves against MPB. The US Forest Service results show collodial chitosan elicited a 40% increase in pine resin (P<0.05) in southern pine trees. One milliliter 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 chitosan was responsible for eliciting natural defense responses of increased resin pitch-outs, with the ability to destroy 37% of the pine beetle eggs.[13] Dr. Jim Linden, Microbiologist, Colorado State University, stated the chitosan increased resin pitch-outs to push the mountain pine beetle out of the tree, preventing the MPB from entering the pine tree and spreading blue stain mold.[14]

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, permethrin and bifenthrin 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.[15]

Colorado’s forests are densely wooded, making them much more susceptible to bark beetle attack. 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 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.

Fall and burn is the technique being used in Alberta where there is hope of limiting the outbreak to western Canada, preventing its spread to northern Saskatchewan and further towards eastern Canada where jack pine may be vulnerable as far east as Nova Scotia.[16]

Commercial use of affected trees

Timber quality

Wood from beetle-affected trees retains its commercial value for 8 to 12 years after the tree has died, but the level of value drops rapidly, for within several months, as the moisture retained in the tree seeks to escape, it blows large checks and cracks from the outer diameter deep into the heart of the tree. The balance of the moisture escapes more slowly, but in doing so, small cracks occur throughout the timber. In short, this causes difficulties for modern high-output automated sawmill operations and greatly increases the lumber losses and the labor to produce high quality wood products. 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.[17] The blue staining of the wood that occurs in the outer diameter of the tree, the sapwood, as a result of the fungus that is carried by the beetles and results in the trees death has no effect on the wood’s strength properties, nor are there any harmful health effects. Blue stain is considered to be a defect in the lumber grading standards and thus is considered a 'down-grade' that results in a lower commodity market price. This fact, combined with the increased cost of lumber production in processing dead, dry, cracked timber, results in very low, if any, profitability, and has thus resulted in a very limited desire to produce blue stain wood products when there is an obvious and very great need to better utilize these resources.

Timber Uses

The timber can be used for any wood product from standard framing lumber to engineered wood products, such as glue-laminated products and cross-laminated panels. The epidemic in British Columbia is also creating opportunities for the emerging bio-energy industry. Though there are many small wood working and craft shops that are making furniture and crafts out of this beautiful and exotic appearing blue-stained wood, and despite the massive supply and the increasingly apparent need to utilize this dead timber, there are very few companies that have aggressively gone after the need to use this otherwise wasted and hazardous natural resource by creating product lines that require large volumes of these dead trees. This is of course largely due to the significant difficulties and increased expense inherent to processing dead timber, and the correspondingly lowered profitability.

Biofuel/alternative energy production from beetle-killed trees

There has been concern that the huge number of beetle-killed trees may pose a risk of devastating forest fires. Forest thinning to mitigate fire danger is expensive and resource-intensive.[18] Attention is turning to ways to turn this liability into a source of cellulosic ethanol.

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.[19]

Fire hazards

The long-held belief that beetle infestations and resulting deadkill lead to more devastating forest fires is currently being challenged. Although some disagree, ongoing NASA studies have shown beetle kill may actually reduce available small fuels and consequently limit the effect and reach of fires.[20]

Current outbreak

The current outbreak of mountain pine beetles is ten times larger than previous outbreaks.[21] 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.[22] 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.[23] 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.

As of May 2013, the Pine Beetle is aggressively devastating forests in all 19 Western States and Canada, effectively decimating approximately 88 million acres of timber at a 70-90% kill rate. Over 13,000 miles of power lines are being endangered with falling trees that increasingly raise the risk of fires that could cause widespread problems for millions of customers. The mountain pine beetle has affected 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 4,500,000 acres (18,000 km2) in Colorado and southeastern Wyoming; other outbreaks encompass the Black Hills of South Dakota and extend as far south as Arizona, and as far north as Montana and Idaho. 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.[24]

Previously, cold spells had killed off bark beetles which are now attacking the forests.[25][26] The longer breeding season is another factor encouraging beetle proliferation. The combination of warmer weather, attack by beetles, and mismanagement during past years has led to a substantial increase in the severity of forest fires in Montana.[26][27] According to a study done for the U.S. Environmental Protection Agency by the Harvard School of Engineering and Applied Science, portions of Montana will experience a 200% increase in area burned by wildland fires, and an 80% increase in air pollution from those fires.[28][29]

Effect on the carbon cycle

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, but many scientists believe we are at a 'tipping point' of our Western Forests becoming a source of carbon off-put that is greater than that of a 'carbon sink'.[21]

Effect on water resources

Hydrologists from the University of Colorado have investigated the impacts of beetle-infested forests on the water cycle, in particular, snow accumulation and melt. They concluded that dead forests will accumulate more snowpack as a result of thinner tree canopies and decreased 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.[30] Augmented snowpack coupled with dead trees that no longer transpire will likely lead to more available water.

See also

References

  1. ↑ "Bob Ward: Colorado Wildfires Are Linked to Global Warming". Huffingtonpost.com. 2013-06-19. Retrieved 2014-02-14.
  2. ↑ Erbilgin, Nadir; Ma, Cary; Whitehouse, Caroline; Shan, Bin; Najar, Ahmed; Evenden, Maya (30 October 2013). "Chemical similarity between historical and novel host plants promotes range and host expansion of the mountain pine beetle in a naïve host ecosystem". New Phytologist 201 (3): 940–50. doi:10.1111/nph.12573. PMID 24400902.
  3. 1 2 Archived August 11, 2010 at the Wayback Machine
  4. ↑ Petit, Charles (2007-01-30). "In the Rockies, Pines Die and Bears Feel It". The New York Times. Retrieved 2009-02-09.
  5. ↑ "Mountain pine beetle and forest carbon feedback to climate change". 2008-04-24. Retrieved 2009-07-16.
  6. ↑ Keeling, Christopher I.; Henderson, Hannah; Li, Maria; Yuen, Mack; Clark, Erin L.; Fraser, Jordie D.; Huber, Dezene P.W.; Liao, Nancy Y.; Roderick Docking, T.; Birol, Inanc; Chan, Simon K.; Taylor, Greg A.; Palmquist, Diana; Jones, Steven J.M.; Bohlmann, Joerg (2012-08-31). "Transcriptome and full-length cDNA resources for the mountain pine beetle, Dendroctonus ponderosae Hopkins, a major insect pest of pine forests". Insect Biochemistry and Molecular Biology (Dx.doi.org) 42 (8): 525–36. doi:10.1016/j.ibmb.2012.03.010. PMID 22516182.
  7. ↑ "Abstract | Draft genome of the mountain pine beetle, Dendroctonus ponderosae Hopkins, a major forest pest". Genome Biology. Retrieved 2014-02-14.
  8. ↑ "Mountain Pine Beetle". Ext.colostate.edu. 2014-01-08. Retrieved 2014-02-14.
  9. ↑ "US Forest Service Forest Insect and Disease Leaflet Mountain Pine Beetle" (PDF). Fs.fed.us. Retrieved 2014-02-14.
  10. ↑ "Mountain Pine Beetle - Ministry of Forests, Lands and Natural Resource Operations - Province of British Columbia". For.gov.bc.ca. Retrieved 2014-02-14.
  11. ↑ Mason, M. (1997). "Defense Response in Slash Pine: Chitosan Treatment Alters the Abundance of Specific mRNAs". US Forest Service{{inconsistent citations}}
  12. ↑ Klepzig, K. (2003). "Cellular response of loblolly pine to wound inoculation with bark beetle-associated fungi and chitosan". US Forest Service{{inconsistent citations}}
  13. ↑ O'Toole, Erin (2009-09-10). "Solution for Pine Bark Beetles May Help Front Range Trees". NPR Morning Edition - KUNC 91.5 FM Greeley, CO.
  14. ↑ Porter, Steve (2009-09-11). "Arming trees against pine beetle invasions". Northern Colorado Business Report.
  15. ↑ "Colorado State University Spraying Trees to Protect Against Mountain Pine Beetle: Common Questions for Landowners to Consider" (PDF). Csfs.colostate.edu. Retrieved 2014-02-14.
  16. ↑ Hillary Rosner (April 2015). "Pine Beetle Epidemic". National Geographic. Retrieved March 23, 2015.
  17. ↑ "British Columbia Forest Facts" (PDF). Naturallywood.com. Retrieved 2014-02-14.
  18. ↑ (Kumar 2009)
  19. ↑ (MacLachlan)
  20. ↑ "NASA Satellites Reveal Surprising Connection Between Beetle Attacks, Wildfire". Nasa.gov. Retrieved 2014-02-14.
  21. 1 2 "Beetles may doom Canada's carbon reduction target: study". Terradaily.com. 2008-04-23. Retrieved 2008-04-28.
  22. ↑ "Mountain Pine Beetle - Ministry of Forests and Range - Province of British Columbia". For.gov.bc.ca. Retrieved 2014-02-14.
  23. ↑ Archived August 8, 2010 at the Wayback Machine
  24. ↑ "Rocky Mtn. Bark Beetle- Bark Beetle Managementhttp://www.2003firestorm.gov.bc.ca/". Fs.usda.gov. Retrieved 2014-02-14. External link in |title= (help)
  25. ↑ "Beetles shaping Montana's forest lands". The Missoulian. July 31, 2005. Archived from the original on August 8, 2009.
  26. 1 2 "Forest Service finds varied beetle activity". The Missoulan. February 14, 2010.
  27. ↑ "UM climate expert says triple-digit Julys will be norm". Billings Gazette. August 27, 2007.
  28. ↑ "Forecast: More air pollution, Study predicts global warming will increase fires in Northern Rockies". Billings Gazette. July 29, 2009.
  29. ↑ "Impacts of climate change from 2000 to 2050 on wildfire activity and carbonaceous aerosol concentrations in the western United States" (pdf). Journal of Geophysical Research (Acmg.seas.harvard.edu) 114. Bibcode:2009JGRD..11420301S. doi:10.1029/2008jd010966.
  30. ↑ "Mountain pine beetle activity may impact snow accumulation and melt". ScienceDaily. Retrieved 2014-02-14.

External links

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