Understanding and predicting fire spread across landscapes – and the impacts of these fires on ecosystems – is increasingly important for natural resource management. Unfortunately, the spread of fire is notoriously unpredictable and this issue is compounded by the rising prevalence of unusually large wildfires that can have major – even catastrophic – impacts on ecosystems. A new paper in Ecological Applications by Miranda Gray and Brett Dickson confronts these issues by applying circuit theory to model the spread of fire across the lower Sonoran Desert in the Southwestern United States. Circuit theory treats a landscape like an electrical circuit to evaluate the conductance of a particular process – for example, the movement of organisms or, in this case, spread of fire.
Their model shows that the areas within their landscape that are most likely to burn are at lower elevations, on shallower slopes, and on less topographically rough terrain – the ‘hot’ colors on the map to the right. They then go on to consider the effects of fires within these areas that are most likely to burn. The areas with high fire likelihood overlap with 21% of the currently-occupied habitat of the federally endangered Sonoran pronghorn, with much of this area predicted to be strongly negatively impacted by a fire. Moreover, nearly 15% of areas with high fire likelihood are within National Wilderness Areas, such as Cabeza Prieta and Kofa Wilderness Areas. Gray and Dickson suggest that the results of their model can help natural resource management. For example, areas of high fire likelihood could be targets for treatments that reduce the amount of fuel for fires and, thus, their likelihood of burning.
This work helps to inform long-standing questions about how alterations to landscape connectivity – particularly through the use of corridors – might influence the spread of fire (Simberloff and Cox 1987, Haddad et al. 2014). Might flammable corridors result in unwanted spread of fire between patches, posing a conservation ‘danger’?
The answer, it turns out, may not be so straight forward. Corridors can promote fire in open landscapes (Brudvig et al. 2012), but whether this constitutes a danger depends on the desirability of fire in ecosystem management. In fire-maintained ecosystems, such as many of the world’s grasslands and savannas, corridors might facilitate the spread of prescribed fire used in management. On the other hand, in ecosystems experiencing unnaturally high fire frequencies, such as Gray and Dickson’s Sonoran desert system, reducing the spread of unwanted fire may be a priority; in such cases, corridors may present undesirable impacts.
Of course, this doesn’t mean that we should avoid corridors and other connectivity measures in fire-prone ecosystems. In all cases, it is important that we weigh the undesirable (e.g., fire spread) and desirable (e.g., Sonoran pronghorn gene flow) impacts of corridors. In some instances, rectifying pros and cons may require creative solutions – such as corridors that have breaks in fuel continuity, but provide movement conduits for species of conservation concern.
Gray, M.E., and B.G. Dickson. 2015. A new model of landscape-scale fire connectivity applied to resource and fire management in the Sonoran Desert, USA. Ecological Applications 25:1099-1113.
Brudvig, L.A., S.A. Wagner, and E.I. Damschen. 2012. Corridors promote fire via connectivity and edge effects. Ecological Applications 22:937-946.
Haddad, N.M., L.A. Brudvig, E.I. Damschen, D.M. Evans, B.L. Johnson, D.J. Levey, J.L. Orrock, J. Resasco, L.L. Sullivan, J.J. Tewksbury, S.A. Wagner, and A.J. Weldon. 2014. Potential negative ecological effects of corridors. Conservation Biology 28:1178-1187.
Simberloff, D., and J. Cox. 1987. Consequences and costs of conservation corridors. Conservation Biology 1:63–71.