Managing Mountain Pine Beetle After a Wildfire
7-9-12
S. Sky Stephens
970-491-7282 or sky.stephens@colostate.edu
Recent wildfires throughout Colorado have raised a number of questions about managing post-fire forests. In this document I hope to address a number of issues that have come up concerning mountain pine beetle (MPB), including the impacts of wildfire on the beetles and which management activities may be appropriate post-fire. Given the diversity of burn severity and the range of impacts on individual trees throughout a burn area, all information provided will be general. Please contact me with specific questions and we at the CSFS will do our very best to assist you in making post-fire management decisions.
Direct Impacts of Recent Fires on Beetles:
• Recent fires have impacted large areas of our forests; however, the area impacted by MPB is much larger.
• Depending on the level of burn severity in an area, the direct impacts on beetle populations are highly varied within the fire area and along its boundaries.
• Some fires (High Park, Hewlett and others) have destroyed numerous trees that harbored this season’s MPB population.
• There are also many unaffected trees within the burn areas which still harbor beetles.
• The increased stress on trees scorched by the fire will increase their susceptibility to MPB.
• Recent fires haven't stopped the MPB outbreak.
• Douglas-fir beetle and Ips beetles typically show an increase in activity after a fire.
• Trees with scorched bark have an increased susceptibility to Ips and Douglas-fir beetle.
• We will likely see an increase in these beetles’ activity in and around fire areas.
Impacts on Previously Applied Preventive Products:
• Chemical sprays exposed to high heat or directly to fire will have lost some, if not all, of their effectiveness. - We are not aware of any studies that have looked at the impacts of heat, smoke or fire on chemical preventive products for MPB.
- Most chemicals degrade faster when exposed to heat; depending on levels of heat exposure, some preventive products may have a reduced efficacy after a fire.
- Products applied directly to bark that has now burned have also been burned and are not likely to have any remaining efficacy.
• Pheromones exposed to high heat or directly to fire also will have lost some, if not all, of their effectiveness. - We are not aware of any studies that have looked at the impacts of heat, smoke or fire on pheromones.
- Direct impacts of fire and extreme heat may have melted pheromone packets, making them ineffective.
- Pheromones are chemicals, and increased rates of degradation would be expected with exposure to heat; depending on levels of heat exposure, pheromones may have a reduced efficacy after a fire.
• Considerations for Reapplication of Preventive Products: - Proper application of preventive products will remain key to their effectiveness.
- Some trees impacted by the fire will survive, others will not. This is very difficult to predict and tree loss will not be apparent in many trees until next spring.
- Trees that do not currently show any signs of beetle activity may be suitable for reapplication of a preventive product this year.
- Preventive chemical sprays may adhere less effectively to scorched bark, due to presence of soot/ash/charred bark.
- Pheromone packets can be reapplied without concern other than monetary costs.
- With increased stress on trees in fire areas and fewer host trees available, all preventive products may have a reduced effectiveness.
• Future Seasons After a Fire - Post-fire bark beetle impacts will occur and change over several seasons.
- Post-fire survival of trees will be dependent on each tree’s adaptability to fire; for example, ponderosa pine is more fire resilient than lodgepole pine, and the conditions of the seasons following a fire event, including levels of precipitation and changes in soil condition, will vary for each location.
- Management of MPB in forests and on individual trees in post-fire areas will remain important while MPB remains active on those landscapes.
- Management of MPB will be dictated by each landowner’s management objectives.
• Final Thoughts - Preventive treatment of remaining trees may be more important than ever over the next few seasons because in fire-impacted areas, the trees remaining represent a smaller selection of hosts and those remaining trees will likely have experienced additional stressors (and may be less success at defending themselves against MPB).
- For 2012, the window of opportunity to reapply preventive products is rapidly closing. No products are currently proven effective in trees already impacted by MPB.
- Efficacy of any preventive product will remain dependent on proper application, adequate coverage, correct dosage and good timing.
