In January 2017, while doing forest inventory it was discovered that approximately 6 acres of a 16-acre tamarack (Larix laricina) stand had likely been killed by eastern larch beetles (Dendroctonus simplex). ELB is a native insect that can occasionally reach large population numbers and kill otherwise healthy stands of trees. Salvage cutting and thinning was prescribed and approved but unable to be implemented due to lacking the frozen ground needed for stand entry to prevent rutting, compaction, or root damage on wet site conditions. The ground never adequately froze enough during the 2016-2017 winter season to meet these requirements and consequently the beetle infestation spread and caused additional tree mortality within the stand. Colder temperatures are forecasted for winter 2017-2018 to sufficiently freeze the ground and allow operations to salvage the marked trees for firewood.
Figure 1: Tamarack stand with evidence of beetle kill.
The primary areas with beetle killed trees within the cross-hatched areas (see Figure 2) consist of two smaller patches, one each on the north and south sides. Porcupine damage may have weakened several trees which allowed the bark beetle populations to rise high enough to start killing undamaged and otherwise healthy trees.
Figure 2: Map of effected stand and proposed treatment area.
- Salvage about 6 acres of standing dead beetle killed tamarack.
- Thin stand to improve the growth rate, form, and health of residual living trees and make them more resilient to future insect outbreaks.
Figure 3: More evidence of ELB-caused mortality within tamarack stand.
Pre-treatment stand description and condition
Stand establishment and management history:
Stand planted in wet area of abandoned pasture land in 1963.
Pre-treatment species composition:
Figure 4: Photo of dense pre-treatment stand structure within ELB-infested tamarack stand (stem exclusion stage).
Pre-treatment growth and stocking:
The average basal area on this stand is 137 sq. ft. The average DBH is approximately 9 inches.
Pre-treatment forest health issues:
Eastern larch beetle infestation-caused mortality.
- Salvage dead timber and thin stand to increase resilience to ELB.
- Prevent the spread of ELB to other tamarack stands.
Figure 5: Premature yellowing of tamarack trees indicate evidence of ELB infestation.
Standing dead trees and dense clumps of living trees were marked for removal. Frozen ground is required for thinning operations due to wet site conditions. When site conditions allow, trees will be crown thinned, with an objective of making crop trees free-to-grow on at least 3 sides. Windfallen trees may also be removed to reduce the amount of bark beetle food in the stand.
What actually happened during the treatment
No treatment occurred due to inadequately frozen ground.
Since the treatment was not implemented we cannot know if the prescription would have had any impact, positive or negative on the stand itself, or slow the spread of the ELB into adjacent stands. Though not officially quantified, in the absence of doing anything the ELB infestation appears to have spread to other trees, allowing us to make inference that a no action treatment in this stand did not meet our goals and objectives of increasing resilience to ELB.
Plans for future treatments
The permit will be re-offered once conditions are favorable for stand entry.
Costs and economic considerations
Volume: Tamarack, 42 cords @ $1/cord = $42 worth of timber.
Wood will likely be used as firewood.
This case study was developed with support from the United States Department of Agriculture's National Institute for Food and Agriculture (USDA-NIFA), Renewable Resources Extension Act (RREA). Project #MIN-44-E02, principal investigator Eli Sagor, University of Minnesota.
Summary / lessons learned / additional thoughts
The forest ecosystems that make up this site are vulnerable to climate change scenarios with warmer winter temperatures with less snow pack. These conditions may allow for increased outbreaks of eastern larch beetle1. A warmer, drier climate may lead to tamarack stands that are less resilient or adaptable to disturbance from pests, drought, or fire1. A warmer, drier climate may further complicate the timing for harvesting or salvage operations in stands with wet site conditions. Though anecdotal evidence exists, additional study is necessary to know exactly how eastern larch beetle will be affected by the proposed sanitation and thinning operations and whether or not these actions have the desired effect.
1Handler, S., & United States. Forest Service. Northern Research Station, issuing body. (2014). Minnesota Forest Ecosystem Vulnerability Assessment and Synthesis: A Report from the Northwoods Climate Change Response Framework Project