Wildfires tear across landscapes, moving swiftly, ferociously, and often unpredictably. Yet, once the flames have gone out, sometimes a meadow or even a whole valley may remain intact; surrounded by destruction yet seemingly unaffected.
These island-like refuges—called fire refugia in the scientific literature—can shelter insects, butterflies, birds, and small mammals, and harbor plants and seeds that can later spread out into burned areas, helping nearby fire-damaged ecosystems recover. But for all their importance, not a whole lot is known about fire refugia. However, that is changing.
In recent years, the important role played by fire refugia has started to receive attention from researchers. Case in point: the two journal articles we will be reviewing in this blog.
The first and more recent of the two articles, a literature review published in the journal Bioscience, grapples with how fire refugia have been defined across multiple studies with differing criteria. The second article, published in 2017 in the journal Forests, is a case study examining how previously identified fire refugia fared following the 2012 Wenatchee Complex Fires that burned in central Washington state. The study hints at what this might mean for fire refugia under a changing climate.
Let’s start with the Bioscience article and try to answer, as the article does, what refugia are and why they are important.
Fire refugia, simply described, are unburned areas within the perimeter of a fire. However, if we take a closer look, fire refugia can mean one thing for a tree and something quite different for a small mammal. Individual refugium can range in size from a few square feet to entire hillsides or ravines left in tact.
Fire refugia are commonly found in valleys or near water features, but this isn’t always the case. Fire refugia can also occur sporadically as fires jump and skip across landscapes as result of changing winds and other conditions. And in addition to all these complexities, even partially burned areas can sometimes serve as fire refugia.
In their paper, the University of Idaho’s Arjan Meddens and colleagues consider the many different forms fire refugia can take by creating a framework for understanding fire refugia based on a review of the available scientific literature.
(Full disclosure, the study’s long list of authors includes CIRC’s resident fire-and-its-relationship-to-climate-change expert, John Abatzoglou.)
From their literature review, Meddens and colleagues were able to parse out four key categories that are essential for identifying a fire refugium. Each category—the researchers use the term taxonomic dichotomies—represent a give and take between two competing elements used when defining fire refugia (hence the dichotomies part).
The categories are unburned versus lower severity, species-specific versus landscape-process characteristics, predictable versus stochastic (meaning variable and largely unpredictable) formation, and ephemeral versus persistent.
So, why did Meddens and colleagues go through this categorizing rigmarole? Consider the categories as asking specific questions about how refugia can be defined. For instance, the category unburned versus lower severity essentially asks the question: Does an area need to be completely unburned to qualify as refugia? The answer, the researchers found, differs among species and ecosystems.
For instance, for some rare fire-intolerant species, ground vegetation, and below-ground processes, only strictly unburned areas can serve as refugia. However, in a forested ecosystem, for example, a low-severity ground fire that leaves the canopy intact will not alter the structure of the ecosystem as a whole since taller, older trees can serve as a seed source to help regrow the forest following a fire. A low-severity fire may even serve to protect some forest communities as they tend to reduce the buildup of flammable materials surrounding old growth trees.
The other categories identified by Meddens and colleagues also have implicit questions they are trying to answer. Species-specific versus landscape process characteristics, asks whether the refuge was defined because it sheltered a species or because it protected an entire ecosystem. Because individual species might have different requirements than whole ecosystems, asking the question what is being sheltered from the fire? is key.
Likewise, predictable versus stochastic formation asks whether the conditions that produced a refugium were predictable in some way. While ephemeral versus persistent asks whether the refugium is likely to survive another fire or not. This last question has direct bearing on the 2017 case study in Forests. We’ll get to what this last question might mean for changing climate conditions later.
In the fall of 2012, roughly 25,274 hectares (nearly 98 square miles) of forest in Washington state’s central Cascade Mountains burned in what became known as the Wenatchee Complex Fires. In the destruction, however, was a research boon.
A 1994 study of the burned area had previously examined over 100 plots that were classified for the study as either refugial or nonrefugial. Fast-forward to 2012…many of these same sites are burned in Wenatchee Complex Fires, providing an opportunity to gauge how fire refugia fared when given another opportunity to burn. Because the previous study had divided its plots into refugial or nonrefugial, the fires also provided an opportunity to compare burn severity in fire refugia versus non-refugia. In 2014, a group of researchers led by University of Idaho’s Crystal Kolden went to Washington’s central Cascades to figure this out. The result was a paper published in 2017 in the journal Forests.
After identifying and siting the plots, Kolden and colleagues analyzed the differences between refuge and non-refuge plots. Of the 109 plots, 36 were identified as fire refugia, 73 as non-refugia. Only six of the identified plots (one refugia plot and five non-refugia plots) were left unburned by the fire.
On a whole, the researchers determined, refugia sites burned more severely than non-refugia plots. In fact while 50% of plots experienced no change in their forest structure, a larger proportion of previously identified fire refugia experienced some change in the composition of their ecosystems.
Of the 36 plots defined as historic fire refugia, 35 burned, and burned more severely than the surrounding non-refugia plots. At first this seems a bit surprising, but if we break down this result, it makes more sense. Remember that it had been longer since the fire refugia sites had burned. This allowed more growth to build up, supplying additional fuel for the fires, leading to higher burn severity.
Does this mean that the historic fire refugia plots had outgrown their status as refugia? Not necessarily. The refugia plots, as Kolden and colleagues point out, may still be able to return to their function as persistent fire refugia. That, of course, could depend on another factor: climate change.
The western United States has seen larger fire extents in recent decades in part attributed to the long legacy of fire suppression and warmer and drier conditions brought on by climate change. With the additional growth built up over the years, historically persistent fire refugia may be at risk of intense burns. This means many may outgrow their refugia status. This brings us back to the Bioscience study and the dichotomy of ephemeral versus persistent.
How to gauge whether a refugium is likely to continue serving as a refugium will be complicated by climate change, Meddens and colleagues write. Fire refugia have not been studied extensively and no trends have been detected, but it appears that landscape features that have historically supported refugia—such as local topography, valleys, and streams—show a diminishing capacity to aid refugia status as fuels build up and climate and weather conditions become more likely to produce fires.
In a warmer future climate, the fire season is expected to be longer and hotter, resulting in dry flammable vegetation. With drier—or more arid—vegetation, fires may burn more severely, which reduces the potential for fire refugia to persist.
(For more information on projected future changes in wildfire see our previous post “Wildfire and Area Burned.”)
Meddens and colleagues end their study with a discussion of what their findings might mean for resource managers.
The bottom line, the researchers conclude, is that fire refugia are important for maintaining ecosystem resiliency for plants and animals. Meddens and colleagues call for management actions to identify, maintain, and promote fire refugia.
Two suggestions made by the researchers are to actively work to protect sensitive fire refugia as a part of fire suppression (something that’s been done for giant sequoia) and to embed fire refugia protection into national and global conservation plans.
How and if these suggestions become policy and how the body of scientific knowledge surrounding fire refugia grows in the coming years will be worth keeping an eye on in the decades ahead.
Meddens, Arjan J.H., Crystal A. Kolden, James A. Lutz, Alistair MS Smith, C. Alina Cansler, John T. Abatzoglou, Garrett W. Meigs, William M. Downing, and Meg A. Krawchuk. “Fire Refugia: What Are They, and Why Do They Matter for Global Change?.” BioScience 68, no. 12 (2018): 944-954. https://doi.org/10.1093/biosci/biy103.
Kolden, Crystal A., Tyler M. Bleeker, Alistair Smith, Helen M. Poulos, and Ann E. Camp. “Fire Effects on Historical Wildfire Refugia in Contemporary Wildfires.”Forests 8, no. 10 (2017): 400. https://doi.org/10.3390/f8100400.
Linnia Hawkins is a PhD candidate studying atmospheric science at Oregon State University. Working with the Oregon Climate Change Research Institute since 2014, Linnia’s research interests include, regional climate modeling and the impacts of climate change on forests in the western US. She is a regular contributor to The Climate CIRCulator. Other Posts by this Author.
Nathan Gilles is the managing editor of The Climate Circulator, and oversees CIRC’s social media accounts and website. When he’s not writing for CIRC, Nathan works as a freelance science writer. Other Posts by this Author.