Mountain Pine Beetle in the Black Hills
Forest Management and Timber Sales Succeed at Supressing Mountain Pine Beetle Populations!
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The current Epidemic
As of 2015, approximately 430,000 acres have been impacted to some extent by the mountain pine beetle in the Black Hills region. There have been many successes in the Black Hills at keeping mountain pine beetle populations suppressed through active forest management and timber sales and have only been possible through the collaborative efforts of multiple stakeholders contributing to the suppression efforts. Support from the local counties, State of South Dakota, Federal agancies, and forest products companies has made our successes possible in the Black Hills. Just as some battles have been won, in many other areas the battle has been lost and the region has seen areas of extensive tree mortality as a result of the mountain pine beetle.
The mountain pine beetle (Dendroctonus ponderosae) is one of several common bark beetles native to North America. Originally discovered in the Black Hills in the late 1800’s, this tiny tree killer was first named the “Black Hills Beetle”, which was later changed to “mountain pine beetle” after it was documented throughout the Rocky Mountain West. Pine beetles evolved with western forests of the US and primarily attack ponderosa, lodgepole, scotch, and limber pines.
Beetles like these are omnipresent in nearly all forested systems. Most times, they exist in what are called endemic populations, killing only a few already weakened and stressed trees per year. But when conditions become prime, beetle populations skyrocket to epidemic proportions, otherwise known as an outbreak. The outbreak would typically begin in an especially dense area of forest, spreading outward until it reached a forest type that was inhospitable for the beetles. While there are a number of factors that contribute to the intensity and scope, the main driving force behind an outbreak is over-stocked mature forests.
Historically, these beetles have thrived in scattered pockets of dense trees in pine forests that are otherwise not overcrowded. As those pockets of dense, mature trees develop the beetles would naturally "thin" the isolated stand of trees. However, what we have seen with the most recent outbreak is a forest that is generally overcrowded with too many mature trees and only pockets where forest management has occurred to aleviate the overcrowded conditions. This leads to prime forest structure across the landscape for the beetles and some of the few places not at risk of infestation are those areas where forest management and timber sales have "thinned" the forest, reduced mountain pine beetle habitat, and promoted increased tree vigor. It has often been quoted by researchers and biologists studying this mountain pine beetle, that “the Black Hills don’t have pine beetle problem, they have a tree problem”.
other words, there are too many
trees that are all relatively the same age class. Most mountain pine
epidemics have originated in even-aged, high density stands.
numerous factors contribute to epidemic mountain pine beetle
over-stocked ponderosa pine stands are the major contributor to
The mountain pine beetle completes its life cycle in one year. In late July to early August, the beetle emerges from last year’s host tree (now dead) and seeks out the next available suited host tree. This annual phenomenon is typically referred to as the “flight”. Mountain pine beetle flights are unique in that they are synchronized, meaning that while some beetles may fly early, and some may fly later, the critical mass of beetles seem to emerge and fly simultaneously within a matter of days. When a pine beetle lands on a suitable host tree, they emit a pheromone that attracts other beetles to mass-attack. This is how these tiny beetles are able to overcome a tree’s defenses. Pitch tubes on a pine tree are sure signs of beetle attack.
Boring through the bark, the pine beetle kills its host by disrupting the movement of food from the needles to the roots through the construction of tunnels known as galleries underneath the bark of the tree. Here the pine beetles lay their eggs in late summer/early fall. Each beetle also carries a fungus known as blue stain from tree to tree; blue stain fungi plug the water-conducting tissue of the tree, blocking the flow of water from the roots to the needles. This combined attack almost always kills an infected tree within one year. Soon the eggs hatch into the larvae stage, which then become dormant in preparation for winter. In the process, the larvae produce glycol, similar to motor antifreeze, which allows them to be nearly immune to any cold temperatures they might experience during the winter. The following spring, the larvae continue to mature and complete their metamorphosis into the adult stage.
a tree is attacked, it is too
late to do anything to save it. The best prevention against
mountain pine beetles is maintaining less stocked, unsusceptible
stands. This means having a healthy, thinned forest that is
to pine beetles and does not allow them the opportunity to
Areas thinned by timber harvest resist beetle infestation and extensive mortality.
The future of beetle impacted forests
Go anywhere in the Black Hills and it is clear the forest has been subjected to a devestating mountain pine beetle epidemic. However, while some areas have lost a substantial portion of the mature trees, many beetle impacted areas have a component of young trees that will release and grow much quicker - similar to following a timber harvest. Barring any further disturbance, these stands of young trees will begin recruitment into the overstory. Unfortunately, the likelihood of another disturbance has been significantly heightened as the dead trees fall to the forest floor and accumulate as fuel for catastrophic wildfires. Forest recovery could be set back hundreds of years if such a fire burns through these stands of beetle impacted forest. Evidence of this can be found in the footprint of Jasper Fire which burned in 2000. Fifteen years later, areas that burned at high severity have yet to begin recovering to forested conditions.