Fire Refugia are Critical for Conserving Biodiversity

January 25, 2020 Andrew Barton 0 Comments

“Fire refugia are landscape elements that remain unburned or minimally affected by fire, thereby supporting postfire ecosystem function, biodiversity, and resilience to disturbances.” (Meddens et al. 2018)

Andrew M. Barton, Ph.D.

ARTICLE: Meddens, A.H., C.A. Kolden, J.A. Lutz, A.M.S. Smith, C.A. Cansler, J.T. Abatzoglou, G.W. Meigs, W.M. Downing, and M.A. Krawchuk. 2018. Fire refugia: what are they, and why do they matter for climate change. Bioscience68: 944-954.

BACKGROUND

Climate refugia are “areas relatively buffered from contemporary climate change that allow for habitat stability and species persistence over time” (Morelli et al. 2016). In other words, climate refugia are the habitat lifeboats that will help maintain biological diversity during the Anthropocene, because it will be easier for a wide variety of species to exist in these more “normal” areas.

Ensuring the long-term survival of species depends on favorable conditions not just for temperature and moisture, however, but also for predation, food supply, and, very importantly, natural disturbances. Already, scientists have documented warming climates driving natural disturbances — such as hurricanes, floods, and fire — beyond the range that many species evolved to tolerate. Effective refugia, then, include those sites where all of these adverse conditions are moderated.

Wildfire is one of the most widespread natural disturbances, an integral part of ecosystems across much of the world. The photo at the top of this article shows fires across part of the planet on a typical day, 8 October 2019 (NASA Firms). Studies have demonstrated that wildfire prevalence has increased over the past several decades. The Fourth USA National Climate Assessment (US Global Change Research Program 2018), for example, documents that fires in the U.S. are larger, hotter, and more frequent, with resultant loss of resources, life, and property. About half of this change is attributable to hotter, drier weather. Another cause, especially in places naturally characterized by frequent surface fires, is human fire suppression. This leads to larger, hotter fires, as a result of a build-up of live and dead fuels (e.g., more small trees, more fallen branches) that otherwise would have burned in lighter, more frequent fires. Major wildfire blowups across the world are becoming a prominent part of the annual news cycle.

Fire refugia are places where plants, animals, and other organisms can survive this intensified fire regime, persist in the post-fire environment, and then disperse (e.g., by seeds for plants, by locomotion for animals) back into the burned mosaic as it recovers. Fire refugia can occur at many different spatial scales, from small stands (see Figure 1) to larger topographic features (see Figure 2). In fire-prone environments, the survival of many species depends on fire refugia as a necessary complement to climate refugia, especially as both climate and fire change.

Figure 1. Fire refugia can be relatively small, such as this stand of Chihuahua pine (Pinus leiophylla) and Apache pine (P. engelmannii) in the middle of an otherwise severely-burned patch from the Horseshoe Two Fire in 2011 in the Chiricahua Mountains in Coronado National Forest. These trees can serve as important seed sources to recolonize the surrounding burned area.

Figure 2. Fire refugia can be large, such as in Rhyolite Canyon in Chiricahua National Monument, Arizona, shown here, which was unburned or lightly burned by the giant Horseshoe Two Fire in 2011. Pines (P. leiophylla, P. engelmannii, and P. arizonica) grow largely unscathed in large sections of the canyon.

CHARACTERIZING FIRE REFUGIA: A LITERATURE SEARCH

Meddens et. al. (2018) wanted to see what the scientific community already knows about fire refugia. They synthesized the literature on fire refugia in forest ecosystems to define and characterize these crucial habitats, to elucidate the drivers of fire refugia formation and persistence, and to better understand the role of these features in ecosystem resilience to environmental change. Their analysis revealed four fundamental dichotomies.

First, some studies define fire refugia as unburned sites only, surrounded by burned areas—an appropriate approach in situations where very sensitive or understory plants are of conservation concern. In contrast, other studies also include low-severity fires as refugia, a more inclusive approach that is apt to include more species. This makes sense for less sensitive species—trees that can tolerate low fire intensity, for example. Moreover, in some circumstances, low-severity surface fire might actually make these sites more viable as long-term refugia because of the removal of fuel.

A second dichotomy is between whether the study focused on specific species and groups of species of conservation concern vs. on fire refugia across the entire landscape. Species studies might focus on the needs of invertebrates, small mammals, or birds, for example. The landscape approach pays little attention to specific species, instead examining the patterns across the landscape and over time that result in the formation and persistence of all refugial patches. Species-specific approaches are effective at identifying the mechanisms promoting species survival, whereas landscape studies help describe changes in the structure of forests across large areas.

A third dichotomy involves where fire refugia form. Some are produced in predictable ways and places and some are random occurrences. The location of predictable fire refugia is associated with topography, soil types, and human developments such as roads. Rock outcrops, for example, often function as fire breaks, protecting adjacent vegetation from fire. In other cases, fire refugia are created in a stochastic (random) manner, driven by unpredictable wind shifts, fire-created behavior, and changes in weather. Human fire suppression sometimes falls into this category, as fire breaks and other management actions sometimes unpredictably create fire refugia.

Finally, some refugia are ephemeral, lasting through only one fire interval (the time between one fire and the next), whereas others are persistent, lasting through multiple fire intervals. These important persistent fire refugia are generally the result of more stable, predictable topographic patterns on the landscape, as described in the previous dichotomy.

FIRE REFUGIA AND CLIMATE CHANGE

Fire refugia can play many different ecological functions in fire-prone landscapes. They can shelter animals during fires, provide habitat in the post-fire environment, and act as nuclei for reestablishment of species as the burned areas recover. These roles suggest that fire refugia act as biogeographic lifeboats for biota, especially for those particularly sensitive to fire. These functions are likely to become even more important in the future, as both climate and fire patterns shift.

Meddens et. al. (2018) report that, although climate change has intensified wildfires in many places, the evidence for a decline in fire refugia is mixed. Most of these studies have focused on landscape formation of fire refugia and not on species-specific changes in refugia availability, however. Global trends for refugia for specific species are poorly known, but might reveal declines for some species.

Where the climate is projected to become warmer and drier, fire activity is expected to intensify accordingly. This suggests that sites that are both climate and fire refugia for species will become increasingly important. Thus, the locations of fire refugia are critical for landscape heterogeneity to buffer environmental change in the future.

CONCLUSIONS

According to Meddens et al. (2018), “Fire refugia may be at risk…because of changing climate, land management, and fire management practices.” Accordingly, “There is a critical need to prioritize fire refugia for conservation and management under climate change.” The authors conclude, hopefully, that the characteristics and dichotomies outlined above might help land managers actively create and maintain fire refugia through some relatively modest changes to prescribed fire and fire suppression.