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.
This has been a big year for wildfires so far and an especially impactful year for some communities that have been devastated by fire. Several of us were keeping an eye on the Rough Fire as it looked like it was going to cross the north fork of the Kings River and head to the Teakettle Experimental Forest. In addition to media coverage of big wildfire events has been heightened attention to the rising costs of fire suppression and the ever larger fraction of US Forest Service budgets that suppression is consuming.
The news reports, the Rough Fire, and the focus on suppression costs caused me to take a look at some fire figures for the past decade posted on the National Interagency Fire Center (NIFC) website. So far, 2015 is second only to 2006 for number of acres burned and the 2015 fire season isn’t over yet. From 2005-2015, total acres burned ranged from 2.9 million acres in 2010 to 9.03 million acres in 2006. During this 10 year period we averaged 58,195 fires per year and we spent between $984 million and $1.92 billion fighting the fires. In the table below I have pulled the yearly fire data from the NIFC website and made a couple of calculations.
You might think that there is a relationship between the number of fires and the number of acres burned in a given year. However, the number of fires only accounts for about 12% of the variability in number of acres burned each year. As it turns out, the number of fires 100,000 acres or larger in a given year explains much more of the variability in acres burned each year.
The number of fires 100,000 acres or larger accounts for 81% of the variability in acres burned in a given year from 2005 to 2014. These larger fires account for between 16% and 45% of the acres burned over this time period and only 0.009 to 0.03% of the number of fires. These so-called megafires have accounted for a large fraction of the area burned this year.
The number of large wildfires in the western US have been increasing since the mid-1980s and are correlated with warmer temperature and earlier spring snowmelt. The National Research Council estimated that each degree Celsius of additional warming will increase the area burned by 200-400% in parts of the western US. Recent work has argued that we need to reevaluate the way we manage fire and fund wildfire suppression efforts. These ideas are especially salient considering that as the climate warms further, we can expect more large wildfires, which will not only impact communities where wildfires burn, but also impact communities that are further away with degraded air quality.