We were out on 18 April 2017 to conduct a post-snow melt, pre-dry season seedling survival survey on our plots in the Jemez Mountains. You can read more about the overall project here, but a quick recap:
We planted seedlings from four species stratified based on aspect (north, south) and cover (shrub, no-shrub) this past fall in the footprint of the 2011 Las Conchas Fire.
We found that our elk deterrent fencing was inadequate in a few areas and that mmmm, soil moisture and temperature sensor wires sure do look tasty to an elk. S.H. Hurlbert in his classic 1984 paper on pseudoreplication states that replication controls for, among other things, “non-demonic intrusion”. He then goes on to state “If you worked in areas inhabited by demons you would be in trouble regardless of the perfection of your experimental designs. If a demon chose to “do something” to each experimental unit in treatment A but to no experimental unit in treatment B, and if his/her/its visit went undetected, the results would be misleading.” Further in the same paragraph he states “Whether such non-malevolent entities are regarded as demons or whether on simply attributes the problem to the experimenter’s lack of foresight and inadequacy of procedural controls is a subjective matter.”
I guess in the case of our planted seedlings, we foresaw the potential for elk to eat our seedlings and therefore exhibited some experimental foresight. However, we didn’t foresee the appeal of sensor cables to elk. Either way, it looks like we’ve got a case of “non-demonic intrusion” and a case of “demonic intrusion”. Fortunately, it is pretty clear when an elk decides to either eat the tasty seedling treat or just ripped it out of the ground and we can look at the effect of including this information or excluding it in a summary presentation of the information.
Even though I still don’t have any resolution regarding whether or not elk qualify as demons, we can at least look at initial survival of the four different seedling species. The labels are as follows: PSME = Douglas-fir, PIPO = ponderosa pine, PIED = pinyon pine, and PIST = southwestern white pine. The strata are labeled as follows: NO = north aspect without shrubs, NS = north aspect with shrubs, SO = south aspect without shrubs, and SS = south aspect with shrubs.
We had higher percent survival on north aspects for all species and lower percent survival on south aspects. Southwestern white pine (PIST) seemed to have an especially tough time on south aspects, as compared to the other species.
One of our hypotheses for this project is that seedlings will have higher survival on north aspects than on south aspects and that on south aspects, survival will be higher with shrubs than without. We’ll see how this plays out during the May-June dry period. So, stay tuned for the next post where we’ll also have some temperature and relative humidity data by strata as well.
Postdoc position in ecosystem modeling
The Earth Systems Ecology Lab (www.hurteaulab.org) at the University of New Mexico is recruiting a postdoctoral researcher with a strong background in ecosystem modeling and programming to contribute to a project aimed at understanding the interaction of climate change and wildfire on post-fire forest recovery. This project will integrate tree seedling data, flux tower data, and ecosystem modeling with the objective of understanding how changing climate will alter forest recovery following wildfire.
The initial appointment is for one year (beginning summer 2017), with the possibility of extension for up to two additional years. A competitive salary and benefits will be provided. Required qualifications include a PhD in ecology, ecosystem science, earth/environmental sciences, or statistics and programming experience with R or Python and C+ or C#. Willingness to periodically participate in field sampling is desirable.
Applicants should submit a cover letter detailing research interests and goals, a complete CV, and names and contact information for three references to Matthew Hurteau (firstname.lastname@example.org). Review of applications will begin on 28 April 2017.
The University of New Mexico is committed to hiring and retaining a diverse workforce. We are an Equal Opportunity Employer, making decisions without regard to race, color, religion, sex, sexual orientation, gender identity, national origin, age, veteran status, disability, or any other protected class.
Shuang Liang successfully defended her dissertation entitled "Simulating the effects of climate change, wildfire, and fuel treatment on Sierra Nevada forests". Congratulations Shuang!
The fire triangle (oxygen, heat, fuel) applies to wildland fire as much as it does to any other type of fire. Fire suppression involves “removing” one of the legs of the triangle, usually fuel. The fire behavior triangle (fuels, topography, weather) influences how fire behaves when burning through a forest. Things like steep slopes, high temperatures, and gusty winds can all cause more active fire behavior. In a recent paper, Brandon Collins analyzed 40 years of weather data in the northern Sierra Nevada. He found that the frequency of extreme fire weather (hotter, drier, and windier conditions) has increased. We tend to get our largest and hottest wildfires under extreme fire weather.
In a recent paper led by Dan Krofcheck, we set out to better understand how extreme fire weather influences the effects of forest treatments on moderating fire behavior (i.e. surface fire rather than crown fire) in the Dinkey Creek watershed in the southern Sierra Nevada. Since we wanted to isolate the effects of fire weather, we created two different sets of fire weather inputs. The first was generated using 13 years of data from three different weather stations located in or near the Dinkey Creek watershed. The second set of weather was generated using weather station data from the 2013 Rim Fire, which burned 141,131 ha of the Stanislaus National Forest and Yosemite National Park. The figure below shows the differences in model inputs generated from these two different sets of weather data. The distributions from the 13 years of weather data (labeled contemporary) have a lower build-up index (panel B) and fine fuel moisture code (panel C), which are measures of how much moisture is in the fuel and lower values mean the fuel is wetter and less available to burn. While these two parameters both had fairly big differences, the biggest difference was in mean daily wind speed (panel D). The weather station near the Rim Fire (labeled extreme) recorded much higher daily wind speeds than we see in the contemporary data.
We ran simulations with no management activities, thinning, and thinning followed by regular prescribed burning under both distributions of weather. Under contemporary fire weather, we didn’t find a big difference between the management scenarios in terms of fire severity (0 = no fire; 5 = tree-killing fire). When we ran the same management scenarios with the extreme fire weather, the results were quite striking (Figure 2).
The no-management and thin-only scenarios both had large increases in fire severity across the majority of the watershed (Figure 3). We also found increasing fire severity under the thin and maintenance burning scenario, but across the majority of the watershed, severity was considerably lower with regular prescribed fire use. When we looked at the variability in fire severity between model runs for a particular management scenario we found that the no-management and thin-only scenarios consistently burned more severely.
The most interesting finding for us was the large difference between the thin-only and thin and maintenance burning treatments. The increase in fire severity for the thin-only treatment was driven by the big increase in shrub growth that occurred following thinning. Opening up the canopy allows more light to reach the forest floor and shrubs are able to grow in more continuous patches that carry fire. When we followed the thinning with regular prescribed fire, the repeated surface fire held the shrubs in check and reduced the fuel available to carry fire. As fire weather continues to become more extreme with changing climate, our results suggest that restoring surface fire is central to reducing the chance of high severity, tree-killing wildfire.
In a previous study we looked at the effects of forest treatments to restore surface fire and how they influence forest carbon storage. That study used historical climate to grow the forests, which left me wondering if how carbon dynamics and the influence of restoring surface fires might be altered by changing climate. To answer this question, I used the same forest landscape model as the previous study and obtained projected climate data from the climate models that were run in support of the IPCC’s Fifth Assessment Report.
Using all of these climate projections, I developed monthly climate distributions for early, middle, and late 21st century. As the figure on the right shows, each period is progressively warmer and the amount of precipitation falling each month is quite variable.
The figure below shows the influence of climate change and wildfire without treatments to restore surface fire (solid lines) and with treatments to restore surface fire (dotted lines). Without treatments, the combination of tree-killing wildfire and warmer temperatures cause the amount of carbon stored in ponderosa pine trees to decline over time. With treatments, the amount of carbon initially decreases because of the removal of trees by thinning and then increases over time. This is because fewer ponderosa pine trees are killed when wildfire occurs. The treatment simulations (dashed lines) also show how climate affects tree growth. The blue line and shaded area represents carbon under late-century climate (2090-2099) and it is significantly lower than under early-century climate (2010-2019).
Interestingly, the results from simulations that don’t include treatments are heavily influenced by a large increase in Gambel oak. This species can resprout after fire and provide a fuel source to carry a subsequent fire before the pine trees are large enough to withstand fire. As shown in the photos below, this is an outcome that we are already seeing in the southwestern US following large, hot wildfires.
The results from this study suggest that by restoring natural fires to this ponderosa pine forest, we can maintain a pine forest for a longer period of time under changing climate.
Trees can live for hundreds to thousands of years. With that kind of lifespan they certainly experience a range of climatic conditions. When we move from thinking about the tree to thinking about the forest and how changing climate might impact a forest, we’ve got to consider how climate influences tree regeneration. There is a body of research that has examined the climatic conditions under which different tree species will regenerate. The range of climatic conditions that a seedling will tolerate is generally much narrower than the range of conditions a mature tree will tolerate.
In a recent study led by Shuang Liang, we examined how future climate change and wildfire might alter the distribution of tree species across the Sierra Nevada Mountains of California and Nevada. We used the LANDIS-II simulation model, projected climate data from three climate models, and area burned projections to simulate the forests of the Sierra Nevada. The climate models show that with unabated human carbon emissions we can expect about 3-5°C of warming by 2099, which will dry out the environment leaving forests with less water for growth.
When we ran simulations we used the three climate projections in Figure 1 and we also ran simulations with climate from the period 1980-2010 to create the baseline scenario. This baseline case included area burned data from the same period and provides a comparison with the future climate and wildfire scenarios. When we looked at how future climate and wildfire impacted where different tree species were on the landscape, we found small changes for the mature trees (Fig 2 a,b). At the lowest elevations, we found slight declines in tree species like white fir that prefer more precipitation, but changes in the distributions of other species were quite small. However, when we looked at tree regeneration, we found large differences between the baseline scenario and the future climate scenario. In the middle elevation band (3900-6900 feet), we found sharp declines in the amount of regeneration events for the more moisture loving species like white fir and we found that more drought-tolerant species like ponderosa pine had accounted for more of the regeneration (Fig 2c,d).
Fig 2: The spatial distribution of dominant tree species by biomass (a) and by elevation band (b). The spatial distribution of dominant tree species by number of regeneration events (c) and by elevation band (d). The results use baseline climate and wildfire (BSWF) and projected climate and wildfire (CCWF).
We also found sharp declines in the number of regeneration events over the 90 year simulation (Fig 3). The majority of the mountain range had 50% fewer regeneration events with future climate and wildfire than did the baseline scenario.
When you’ve got forests that experience wildfire, reduced regeneration is important because it means that areas that burn will take longer to recover to forest. When we compared the percentage of the Sierra Nevada that was not forested in 2099, we found that it had increased by about 5% over the baseline climate scenario. Now, 5% doesn’t seem like much, but when you are talking about the whole Sierra Nevada mountain range that is approximately 170,000 hectares (656 square miles).
These results suggest that we can expect some pretty large changes in the species that make up the forests of the Sierra Nevada and the amount of area that has forest cover as the climate changes.
2016 has been an interesting year for wildfire research. A couple of studies published this year have identified linkages between the increasing area burned by wildfire and increasing temperature. Leroy Westerling published a study where he looked at the increase in area burned by large wildfires over the period 1970-2012. He found that across the western US, area burned by large wildfires has increased by 556% over the 1983-1992 average (Figure 1 top). His analysis shows that increasing temperatures correlate with longer fire seasons. Average fire season length increased by 84 days between the first decade of his analysis (1973-1982) and the last decade (2003-2012)
John Abatzoglou and Park Williams published a study where they looked at the relationship between fuel aridity and area burned in the western US. Fuel aridity is a measure of how dry the material in the forest is and the drier it is the more flammable it is. Their results show a strong relationship between this measure of dryness and area burned (Figure 1 bottom). Increasing temperature is also playing a role here and they attribute approximately half of the forest area burned by wildfire to human-caused climate change over the period 1984-2015.
Fire suppression costs by year from the National Interagency Fire Center website show that from 1985 to 2015 we spent approximately $36.6 billion on fire suppression in 2015 dollars. While the year with the highest total fire suppression cost was 2015 ($2.13 billion), the year with the highest per acre suppression cost was 1998 ($455/acre, Figure 2). Area burned in any particular year explains about 51% of the variability in suppression costs. A number of factors account for the remainder of the variability in suppression cost, including proximity to developed areas. As an example, the 2016 Soberanes fire in southern California burned 132,127 acres and cost an estimated $260 million to suppress, that works out to $1967/acre.
When we look at how decadal averages in suppression cost have change over time, the picture is similar to Leroy Westerling’s results (Figure 3). It is important to note that the first average suppression cost only covers the period 1985-1992 and the last average suppression cost bar is only for the years 2013-2015. The majority of the suppression expenditures are by the US Forest Service and in a 2015 report they showed that fire suppression accounted for 52% of their budget. Given that area burned by wildfire in the western US is increasing as the temperature goes up and suppression expenditures are on the rise, this really begs the question – how sustainable is our current relationship with fire?
The 2011 Las Conchas fire burned 156,593 ac (63,370 ha) on the east flank of the Jemez Mountains in northern New Mexico. While certainly not the largest fire in recent years, this particular fire burned through three areas previously impacted by wildfire. This New York Times article provides a good overview of the issues facing this particular landscape and many western landscapes in general.
In the southwestern US, the area burned by wildfire has increased 1266% over the 1973-1982 average. A recent estimate suggests that climate change contributed an additional 10.3 million ac (4.2 million ha) of forest fire over the period from 1984-2015, meaning that in the absence of climate change we would have expected about 50% less burned area over that period. As a result, severely burned landscapes like the east flank of the Jemez Mountains are becoming more common.
Increasing fire size and larger patches of severe fire, where the majority of trees are killed, create a challenge for reforestation. The first challenge is distance to mature trees that provide the seed for tree establishment. This challenge can be overcome by planting seedlings. However, trees modify the climate conditions at ground level. Under the canopy of a forest, the air temperature is cooler and the relative humidity is higher, making it a moister environment. These factors matter because hot, dry conditions can be lethal to seedlings. In a burned patch where all of the overstory trees have been killed, these microclimatic conditions may be too harsh for seedlings to establish.
We are in the process of establishing an experiment funded by the Joint Fire Science Program to figure out how the post-fire environment influences the ability of planted seedlings to survive and grow. The post-Las Conchas fire landscape has a mix of shrub and grass cover. Our hypothesis is that shrub cover could create more favorable growing conditions for tree seedlings. To test this hypothesis, we constructed exclosures in shrub and non-shrub patches and are in the process of planting seedlings.
We are instrumenting these sites with sensors that measure temperature and relative humidity at the height of the seedlings.
We’ll link the temperature and humidity data with data collected at weather stations that we are deploying around the experiment. This will allow us to model how microclimate (ground level temperature and relative humidity) vary across the larger area and predict how these factors influence tree seedling survival and growth. Stay tuned for updates on this project.
The Earth Systems Ecology Lab is recruiting 1-2 PhD students to begin fall 2017. Current research topics in the lab include: understanding factors controlling post-wildfire tree establishment, quantifying the influence of changing climate and wildfire on tree species distributions and carbon dynamics, and quantifying the influence of forest management activities on forest carbon dynamics. Additional detail about ongoing projects can be found here. Student support will include some combination of teaching and research assistantships and only US citizens/legal residents will be considered.
If you are interested in being considered, send your CV, a one-page statement of research interests, unofficial transcripts, and unofficial GRE scores to email@example.com. Additional details about student expectations can be found here. Review will begin on 7 November.