The last article looked at the ecological role of fires and the history of fire suppression. While fire is important to a number of ecosystems, in recent years, there have been a number of especially severe wildfires, which have claimed both lives and property. The 2018 fire season was California’s deadliest on record. So, are wildfires getting worse or are we not looking at the larger picture? A changing climate, fire suppression, and invasive species all affect fire length and severity. This article will look at what factors affect wildfire behavior and how we should respond to them.
Faith Ann Heinsch, Greg Dillon, and Chuck McHugh, of the U.S. Forest Service’s Rocky Mountain Research Station, stated in an email that the majority of fires are human caused. W. J. Bond and R. F Keane “Ecological Effects of Fire” (2017), also state that most fires are ignited by people. In spite of some of the fires that have recently made headlines, looking at wildfires through the historical lens can help to put them in perspective. Heinsch, Dillon, and McHugh said that fires were not necessarily more “severe,” even though more area has burned compared to the mid twentieth century, but that the proportion of high intensity fires has remained fairly constant. They also stated that the frame of reference for most Americans is the mid to late twentieth century, which was an especially cooler and wetter epoch. This was largely what caused fire suppression to be successful and in this time period and much less burned than would have had nature been allowed to take its course. Bond and Keane also stated that fires declined after 1870 and areas burnt recently may actually be at the lowest level for the past few millenia. However, the lack of fire in earlier times is one factor which may have affected some more recent ones. Heinsch, Dillon, and McHugh stated that fire suppression leads to fuel buildup. In addition, Bond and Keane also noted that fire suppression allows young trees to become estabished and this can serve as a “fire ladder.” In these instances, “surface fires” which might might otherwise have just burned the underbrush can become “crown fires” and jump to the canopies of mature trees.
While a changing climate is not the only factor to affect wildfire severity, hotter and drier temperatures can cause them to burn longer and spread more quickly. Acccording to W. Matt Jolly, Mark A. Cochrane, Patrick H. Freeborn, Zachary A. Holden, Timothy J. Brown, Grant J. Williams, and David M. J. S. Brown, “Climate-Induced Variations in Global Wildfire Danger 1979- 2013” (July 2015) climate “strongly influences global wildfire activity.” They also said that the factors of dry weather, available fuel, and ignition sources are what causes fires to start and spread. In addition, temperature, relative humidity, and wind speeds also influence wildfire activity. Hot, dry, and windy conditions are what lead to the most severe fires. According to their paper, global temperatures have increased by 0.2 degrees Celsius per decade over the last three decades “possibly” leading to more intense rainfalls and more severe drought. They also stated that climactic changes have been “implicated in global fire variation” and it is “expected” that there will be increases in fire season severity in the coming decades. Heinsch, Dillon, and McHugh stated that there are “indications” that fire seasons are getting longer as a result of climate change. Bond and Keane said that global warming is “predicted” to cause a doubling of burned area and 50% increase in fire occurence by the end of the century in the circumboreal region.
Invasive species can also affect fire length and severity if such species are more fire tolerant than the ones they are replacing. According to Bond and Keane, in Hawaii the invasion, tall nonnative grasses has fueled frequent fires and largely changed forests into grasslands. Likewise, in the western U. S. invasive cheatgrass has also increased fire frequency and severity in the native sagebrush habitat.
The next question then is what should our response be to wildfires and what may be more severe fire seasons in the coming years. Fire is part of a number of ecosystems and there are many species which are not only fire adapted, but even depend on fire. Returning fire to the ecosystems that need it is a way of reducing fuel load and the severity of fires. Heinsch, Dillon, and McHugh state that wildfires are a “key component” of keeping forests healthy, but it is possible to reduce the risk through prescribed burns and treating the area around homes. As with so many other aspects of the world, fire is multifaceted. While fire has its destructive power, it also has its power to maintain ecological balance. Understanding fire’s ecological role as well as what affects its behavior is crucial to accepting it as part of the ecosystem and reducing risk.
Acknowledgement: Faith Ann Heinsch, Greg Dillon, and Chuck McHugh of the U. S. Forest Service’s Rocky Mountain Research Station not only responded to my email inquiry, but also compiled a number of other research materials for both these articles.