- Posted By: Rob York
- Written by: Reproduced from the website, www.foreststeward.com
Article reviewed: Interacting disturbances: wildfire severity affected by stage of forest disease invasion
By M.R. Metz, K.M. Frangioso, R.K. Meentemeyer, and D.M. Rizzo, published in the journal Ecological Applications, vol. 21: 313-320
The plot line: These researchers evaluated the influence of Sudden Oak Death (SOD) on wildfire severity. They were able to do so because they had measured forests that were infected to various degrees (ranging from no infection to very advanced infection) by SOD prior to a wildfire (the Basin Complex fire) occurring. They found that, where SOD had recently infected forests and caused lots of standing dead trees, fire severity was greater but SOD infection was not the primary determinant of fire severity. Burn severity was very patchy and influenced by many other factors besides whether or not the area had been infested with SOD. In areas where SOD infection was advanced (i.e. several years since first infections), there was greater burn severity at the forest floor but again SOD infestation was not a major determinant of fire severity. They suggest that management efforts may be more effective if targeted in areas where SOD is still in the initial stages of infestation (i.e. where there are lots of standing dead trees with dead leaves and branches).
Relevant quote: “Our results indicate that the timing of fire relative to disease progression is an important predictor of burn severity in infested areas because differences among fuel types were more important indicators of damage than pathogen presence alone.”
Relevance to landowners and stakeholders:
Wildfire risk is often grossly over-simplified. During this time of year, for example, we begin to hear reports on the news that this year’s fire danger will be “especially high.” If it is a wet spring, they say that fire danger will be “especially high” because of all of the growth of fuels (vegetation) that is occurring. If it is a dry spring, they say that fire danger will be “especially high” because of the dry fuel conditions. And if it is an average year, they usually wait until we have a hot and dry week and then claim that it is actually a very dry year and, you guessed it, fire danger will be “especially high.” The reality is that fire behavior is a result of a huge complexity of factors that include how much fuel is available to burn, the structure of the fuel, the local topography, and the weather conditions at the time of the fire.
Historically, fires in central coast forests of California have not occurred as frequently as they have up in the Sierra Nevada. But as a landowner, I am actually more comfortable in the Sierra Nevada than in central coastal forests when it comes to altering the behavior of fire when occurs. Fires in the coastal forests appear to be more weather-driven and less fuel-driven than those in the Sierra Nevada. And as a forester, I know that I can alter fuels on my land to manage fire behavior. Weather? Not so much. This research suggests that treating areas of recent SOD infestation might lower fire severity a little, but that other factors will accumulate to have more of an influence on fire behavior. For forestland owners in the central coastal forests of California, you should hope that insurance companies don’t read this article.
Relevance to managers:
While infestation occurs as a gradual process, there appears to be 4 logical stages of SOD infection:
1. Initial infection- trees lose vigor and slowly decline over about 6 years.
2. Crown mortality- over 1 or 2 more years, leaves and small branches die and slowly shed off of the dead trees
3. Snag decomposition- snags either gradually crumble apart of fall over
4. Log buildup- Logs are on the ground and gradually decompose
As discussed in a previous post, Sudden Oak Death is anything but sudden. As the authors of this article point out, SOD truly is a “chronic and progressive stress” rather than a sudden one.
It is during stage 2 above where the authors of this research seem to be recommending that managers focus on in terms of reducing fire risk. This could mean prioritizing fuel-reduction treatments to occur in areas that have high densities of standing dead trees with lots of dead biomass still in the crowns.
Fire severity may be just as high or higher in stage 3, but this study did not measure fine surface fuels so it is unknown. But it would make some intuitive sense to me that a buildup of litter and debris from SOD may increase fire severity. As the authors mention, this needs further study. See a related post on the interaction of bark beetles and fire severity in lodgepole pine forests.
Of course, the most effective management would be to try to stop SOD in the first place, but this is obviously difficult. I heard one of the authors of this article give a talk about management options with respect to lowering SOD infection. He mentioned two things that I recall:
1. Thinning + burning might be effective (presumably by increasing individual tree vigor and by reducing future fire severity)
2. A no-host buffer around critical areas (e.g. removing host species around a park core area, for example) would be very difficult because most hosts sprout.
Critique (I always have one, no matter how good the article is):
The primary limitation is the fact that only large logs were measured as surface fuel prior to the fires. Obviously if the researchers had known that a fire was going to happen, they would have been more comprehensive in measuring surface fuels. But just measuring “1000 hour fuels” leaves a lot of the surface fuel equation unaccounted for.
- Author: Rob York
[originally posted at www.foreststeward.com]
Article reviewed: Responses of oaks and tanoaks to the sudden oak death pathogen after 8 years of monitoring in two coastal California forests
By B.A. McPherson, S.R. Mori, D.L. Wood, M. Kelly, A.J. Storer, P. Svihra, and R.B. Standiford, published in Forest Ecology and Management 2010 Vol 259 pp 2248-2255
The plot line: The researchers closely monitored the progression of Sudden Oak Death (SOD) over 8 years, tracking the rate of mortality in coast live oaks, California black oaks, and tanoaks. They compared SOD-caused mortality with mortality not related to SOD (i.e., the “background level” of mortality). Over the monitoring period, they observed a steady increase in SOD infections (bad news for oaks) coupled with a steady decrease in trees without SOD infections (also bad news for oaks). It was much more common for trees to die from SOD infections than for reasons not related to SOD, by a factor of 7 to 9 (very bad news for oaks).
Relevant quote: “Under the pressure of this aggressive pathogen, the presence and propagation of resistant genotypes among the host oaks and tanoaks may provide the best chance for sustainable wildland populations of these species and for management of these forests.”
Relevance to landowners and stakeholders:
When SOD was first identified as the cause of widespread oak mortality in 2000, there was a huge amount of attention drawn to it. Whoever gave it the name “Sudden Oak Death” was a genius if they were trying to draw media attention to the disease. In addition to the name being inherently catchy, “Sudden Infant Death” was in the news at the same time so SOD got some bonus hype via phonetic-association. The disease deserved the attention it received (although I wonder what kind of attention and funding it would have received had it occurred somewhere other than coastal California). At the time, scientists and managers were wondering if SOD would march through all of the western US, leaving billions of dead trees in its destructive path.
Permanent monitoring plots that are revisited year after year are a good way (perhaps the best way) of tracking how forests change. It appears that the range of the SOD impact on native forests has not expanded in the last decade, but the disease continues to have a profound influence on the forests where it has been established (central and northern coastal forests of California). Mature tanoak, California black oak, and coast live oak trees are dieing at a much faster rate than they otherwise would. If the mature trees are not replaced with resistant trees, the decline of these species’ populations in SOD-impacted areas will continue.
Relevance to managers:
The relevant metric in this case is the comparison of SOD-caused mortality rate to background mortality rate. The SOD-caused mortality rate for live oak was 3.1% per year. It was 5.4% per year for tanoak. This may not sound like a lot, but it is indeed a very high mortality rate, especially when compared against the background rate of 0.33% per year for live oak and 0.75% per year for tanoak.
Besides the relevant quote given above, no explicit relevance is provided for managers in this paper. My inference is that this paper provides documentation that SOD-related mortality rates continue to be very high and that managers should be anticipating very significant change in SOD-affected forests. Managers should expect species composition shifts, and therefore shifts in processes such as nutrient cycling and fire behavior as well.
As was the case when this disease was first discovered, a lot of attention and funding is still being given to SOD research and outreach programs. More information is available at here.
Critique and/or limitations (there’s always something, no matter how good the article is) for the pedants:
For an article in Forest Ecology and Management, it has very little content in terms of explicit management implications. The one sentence referring to management suggests that propagation of resistant genotypes could be a worthwhile management response. This idea could have been developed more. How much do we know about current levels of resistance? Are there resistant breeding programs in place? Not that it couldn’t be done, but it would seem to take a lot of work to create an operational nursery program and infrastructure for oak species that currently are not widely planted.
It was unclear to me whether or not IN-GROWTH was measured in these plots. If it was just tracking individual trees over time without also tracking in-growth of new trees, then we are only getting one side of the equation in terms of knowing long-term population trends. I am assuming that in-growth was indeed measured, but the authors did not explicitly say that this was the case so I’m not sure.
It also would have been very helpful to report the overall change in basal area over time. Given the rapid mortality rates and the fact that mature trees are infected readily, I would expect that basal area declined substantially over the monitoring period. Knowing the change in basal area over time gives more information about how competition-related stand dynamics might be interacting with the pathogen. Since they did not report change in basal area, it makes me think that perhaps in-growth was not measured?/span>