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Improving Tree Vigor
“Beetle Proofing Stands”
Recent research has shown that lodgepole pine stands that are actively managed may have reduced mortality from mountain pine beetle. This concept can be applied in situations where maintaining a mature forest is desired. The treatment has two effects: it reduces competition between trees increasing their vigor and ability to pitch out beetles and it alters the microclimate to conditions less favorable for the beetles. This tool has only been shown to be effective when the beetle population is low or in the early stages of an outbreak. Once an outbreak is occurring, it may not be able to save stands.
The most important factor in implementing this approach is to leave the largest and healthiest trees evenly spaced throughout the stand. Spacing the leave trees with at least a 14 foot distance between trees is critical. A greater distance may be needed, especially with stands of larger diameter trees. Damage to leave trees must be minimized. It is important that the spacing is even across the treated area; leaving clumps of trees will attract bark beetles. The larger the area treated in this way, the more effective it can be. Also, any trees that become infested should be removed immediately and treated to kill the mountain pine beetle brood so that a beetle population does not develop. This is for lodgepole pine stands and knowledge of its effectiveness in other host species is not as well known.
Additional information can be found at:
“Beetle Proofing Prescription”
“Beetle Proofed” Lodgepole Pine Stands in British Columbia
Fertilization and Watering
These two activities are often used to increase the vigor of individual trees and make them more resistant to insects. The little bit of research done with fertilization and mountain pine beetle suggests that there is no benefit, and fertilizing may actually increase a tree’s susceptibility. There are many factors at play here, so the application of fertilizer is not recommended.
Supplemental watering of trees to increase their vigor is often stated as a possible way to protect pines from mountain pine beetle. There is no research to indicate if this is an effective treatment. It is known that water status of a tree affects the tree’s reaction response to attack through the production of resin. It is presumed increased water availability increases resin production and, therefore, a tree’s ability to defend itself. However, when mountain pine beetle populations are at high or outbreak levels these tree defenses are often overwhelmed and trees are attacked regardless of their vigor.
The chart below is an idealized presentation of how the beetle population and tree vigor interact and affect tree survival. When populations are high, the most vigorous trees can be killed by the beetle. When trees are of very low vigor they can be killed even when the population is at endemic, or low, levels.
