Joe Lowe, the Wildland Fire Coordinator for the State of South Dakota has written an opinion article for the Rapid City Journal about the relationship between pine beetle outbreaks and fire. Here are some excerpts:
In recent days, there has been much discussion about bark beetles and fire. With over 400,000 acres of our Black Hills attacked by pine beetles, the issue must be aggressively addressed.
[…]
The pine beetle attacks present three different and unique set of fire problems depending on when the attacks occurred.
The first phase is in the early stages of the beetle attack. The trees are dying or dead with the needles still on them and the crowns are close together.
Under the tree canopy we have ladder fuels that allow the surface fire to step up into the dead trees. This is called a crown fire. In this example I would expect to see a rapidly spreading fire of great intensity to occur.
The fire does not have to drive off moisture in the trees to sustain combustion. Every firefighter understands these basic fire principles.
In the second phase the needles have fallen off and the tree trunk and branches are still standing. In this phase the fire would mainly be a surface fire with opportunities to suppress it.
During the third phase the trees start to fall and create timber litter on the forest floor.
The heavy fuels are now horizontally distributed, and will contribute to higher intensity surface fires.
Make no mistake about it. In my opinion, a fire problem does exist in the Black Hills Ponderosa forest that has been attacked by pine beetles.
In the article, Chief Lowe makes some very good points. He also mentions research being done on the relationships between fire and beetle outbreaks in lodgepole pine and Douglas fir forests which we covered on September 8, 2010. One research project, funded by the Joint Fire Science Program, is being conducted by William Romme and Philip Townsend in the greater Yellowstone ecosystem. Other related research is being done by Monica Turner and Martin Simard.
One of the key facts from the research that has come to light so far is that the very flammable volatile oils which fuel a fire in green pine needles begin to break down when the needles die, making them less likely to sustain a fire according to the researchers. Previously, this has not been widely recognized by firefighters and may seem counter-intuitive.
Research needs to specifically determine how the reduced volatile oil content in dead needles may or may not counter-balance the lower moisture content in the dead needles. Which fuels a fire more, the oils, or a lower fuel moisture? If it is the oils, as the research at this point leads us to believe, then beetle-killed trees with dead needles would be less of a fire problem than green trees. That is, the rate of spread, likelihood of a crown fire, and the resistance to control would be reduced.
And there is little argument among wildland fire professionals that dead standing pines without needles are less likely to sustain a crown fire than green trees. After the dead trees fall, a ground fire would produce a great deal of heat, but I believe the rate of spread and resistance to control would be much less than a fire in standing green trees.
As Chief Lowe correctly points out, other factors may also be considered when decisions are made about a beetle outbreak, including the monetary value of commercial timber, and the aesthetics of dead trees compared to a green forest in an area visited by tourists. The safety of firefighters and hikers can also be an issue as the trees fall. Fighting fire in a snag forest may not be feasible.
As you hear so often, more research is needed, especially in Ponderosa pine forests.
========================
UPDATE January 29, 2010
A paper has been recently published, titled “Do mountain pine beetle outbreaks change the probability of active crown fire in lodgepole pine forests?” Here is an excerpt from the abstract:
Modeling results suggested that undisturbed, red, and gray-stage stands were unlikely to exhibit transition of surface fires to tree crowns (torching), and that the likelihood of sustaining an active crown fire (crowning) decreased from undisturbed to gray-stage stands. Simulated fire behavior was little affected by beetle disturbance when wind speed was either below 40 km/h or above 60 km/h, but at intermediate wind speeds, probability of crowning in red- and gray-stage stands was lower than in undisturbed stands, and old post-outbreak stands were predicted to have passive crown fires. Results were consistent across a range of fuel moisture scenarios. Our results suggest that mountain pine beetle outbreaks in Greater Yellowstone may reduce the probability of active crown fire in the short term by thinning lodgepole pine canopies.
The paper is written by Martin Simard, William H. Romme, Jacob M. Griffin, and Monica G. Turner.
During the early 2000’s we had a bark beetle epidemic wipe out huge tracts of our pinon pine in Northern New Mexico. We had the debate then about whether or not we were going to be more vulnerable or less to raging wildfires. I believe, in the end, the consensus was that we would be less vulnerable because the “turps” (turpentine) emitted from green trees with needles would be a much more volatile fire.
The often overlooked factor is that the reason the trees die is that they have lost their ability to produce the turpentine related sap. The beetles girdle or stop the upward flow of sap by the fact that they feed on the phloem or cambium layer of the tree which is what allows the water and sap to rise throughout the tree, thus systemically killing the trees by robbing them of their ability to hydrate and to draw nutrients through what amounts to their vascular system.
We all thought that the firewood would not be any good because of the lack of sap but now, several years later, we are still burning the larger trees that have recently fallen. They burn fine, tho I don’t really think these fires put out as many btu’s as those trees not affected by beetle. Locally, we have had some small wildfires in our pinon stands that have, luckily, been put out rather quickly before spreading too far and fast. This could be an indication that they are not as volatile as their green cousins. Where people have elected to just let the trees rot and not remove them, looks like they are creating excellent compost for the next generation. I think that the bark beetle die off is a natural phenomeon for this purpose, but if you have a stand of beautiful ponderosa on your property (as we do), that is small comfort when they die off.
On another note, after studying the bark beetle epidemic in order to save our own property, we discovered that Masterline Permethrin Pro available through Univar is an excellent product for protecting your trees. It is sprayed topically. The reason this particular brand of permethrin is so good is that it is encapsulated in cellulose which makes it stick to the trees and lasts for a full year, making it more cost effective and environmentally friendly. We were able to save almost all of our trees while we have neighbors who lost huge portions of their pinons.
It’s important to remember that the UW study attributes to forests of Douglas Fir, lodgepole pine, and Engelmann spruce.
Turpentine distilled from the California pines such as Ponderosa Pine (Pinus ponderosa) and Gray Pine (Pinus sabiniana) yield a form of turpentine that is almost pure heptane. When producing chemical wood pulp from pines or other coniferous trees with the Kraft process, turpentine is collected as a byproduct. Often it is burned at the mill for energy production. The average yield of crude turpentine is 5–10 kg/t pulp.
In 1946, Soichiro Honda used turpentine as a fuel for the first Honda motorcycles as gasoline was almost totally unavailable following World War II.
Ponderosa pine burns with far more explosivity, especially when needled.
The Black Hills have not been a natural forest since the mid-1800s when a nearly Hills-wide fire cleared open spaces for native aspen. Mining activities high-graded every species and left doghair pine to infest a previously diverse forest system.
It seems to me that another factor which needs to be addressed, is whether beetle kill affects the “seasonality” of wildland fires. Once the tree has died, it does not receive any moisture during wet seasons, so even during relatively wet periods there will be low fuel moisture in the heavy fuels. Could this lead to more fires outside of the so-called “normal” fire season?