Fire & Fire Suppression

By NABCANABCA, on 17 Mar 2017 06:04

Threat Description

The impact of fire suppression and fire management activities on foraging and roosting habitat. Potential impacts include mortality and/or disturbance of bats due to prescribed fire activities, loss of habitat diversity due to fire suppression (or lack thereof), reduction in insect prey abundance or diversity due to fire suppression (or lack thereof), loss of roosting habitat due to fire suppression and toxicity of fire suppressant chemicals on house-roosting bats.

Perceived Importance of this Threat

The impact of fire on bat populations is widespread. Wildfires are a seasonal occurrence in the western United States, and intermittently affect all fifty states. Prescribed fire is used throughout all states for wildfire control and forest management.

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Mitigation Measures

Fire has become an important and effective tool for forest and ecosystem management. Several studies have been conducted on the potential impacts of prescribed fire on bat populations in North America, particularly in the southeastern United States. These studies have demonstrated that bat species, along with several other wildlife species, appear to benefit from prescribed fire in the long-term (Harper et al. 2016). Habitat characteristics that influence bat species presence and activity on the landscape include degree of clutter and roosting resources. Prescribed fire and associated management methods, such as overstory thinning, help reduce clutter and can increase snag incidence on the landscape (Loeb & Waldrop 2008; Zarnoch et al. 2014; Cox et al. 2016). In many studies, bat activity increased in burned landscape. Community or species composition of that activity does relate strongly to vegetation or clutter structure (Armitage et al. 2012; Silvis et al. 2015). One documented decrease in bat activity after burning was in habitat with higher post-burn timber harvest rates, where the removal of roosting habitat likely outweighed the foraging benefits of reduced clutter (Silvis et al. 2015).

Prey abundance and diversity is another habitat characteristic that can change with prescribed burning. It has been hypothesized that prey abundance and diversity increases post-burn due to insect attraction to dead wood (Frame 2010). However, insect community response to prescribed fire varies with burn protocol, habitat differences, and species studied (Lacki et al. 2009; Armitage et al. 2012). The impacts of fire on prey abundance and whether those impacts significantly affect bat activity remains unclear (Cox et al. 2016). Changes to forest structure and clutter reduction appear to have the more significant effect on bat activity post-burn.

Bats are more likely to be negatively impacted by fire management immediately after fire application, when individuals are not able to escape the burn quickly enough and are therefore injured or killed. Mitigation of fire threats involve safely managing the application of fire to ensure bats are able to escape from roosts (Frame 2010). This includes the following methods:

Choosing appropriate burn weather and season: Prescribed fire should be applied during the late winter and early spring months so bats are less likely to be in deep hibernation and more likely to wake from torpor. Bats can then more easily arouse to escape approaching fire. During later growing season burns, protecting snags and known roosts is critical to preventing loss of roosting habitat.

Using appropriate ignition tactics: Ignition tactics should include slow-start operations and low fireline intensity. This ensures bats have enough time to detect arousal cues such as smoke and increasing temperatures, and will not be injured by high flames or heat as they flush.

Ensuring large roost snags are available for shelter: Forest management practices, including burning, should focus on leaving a selection of large trees available on the landscape that can become snags and provide roosting habitat. Bats will roost in larger than average trees or snags; and the larger the tree or snag, the higher up the bats will roost. This allows for a safer height above critical plume temperature at which injury can occur. Leaving a large proportion of snags available for shelter on the landscape will reduce risk to bats from fire, and will provide suitable habitat for maternity colonies as well.

By encouraging burn methods such as those listed above, the benefits of prescribed burning can be achieved while the risk to bats from fire is reduced. Fire suppression can impact bat populations negatively in the long-term, so maintaining prescribed burning practices is important. By suppressing fire on the landscape, habitats remain cluttered and prey biodiversity or abundance present in foraging habitat may be less than in burned landscape. Fire use or wildfire in a fire-suppressed landscape is also more difficult to control making destruction, rather than restoration, of habitat more likely.

Below are some more resources on fire and bat populations in the United States.

Joint Fire Science Program firescience.gov

Consortium of Appalachian Fire Managers and Scientists appalachianfire.org

Challenges/Barriers to Addressing this Threat

The majority of prescribed burning practices fall in line with the methods outlined above, and do reduce risk to bats, as well as other small mammals. For bats, the main challenge to addressing the impact fire can have on bat populations is the elusive quality of roost locations.

Roost locations are often difficult to assess, but important knowledge for mitigating the impacts fire may have on bat populations. If roost locations are known, entities conducting prescribed burning can proactively manage burning protocol to minimally affect the roost. However, most roost locations are unknown. Thus, operating as if potential roosts are inhabited is essential to mitigating the fire threat. While minimal disturbance to roosts usually ensures the survival of these species, when fire is involved disturbance may be inevitable. Following the burn methods outlined above will ensure most bats are able to escape compromised roosts.

The other challenge to mitigation of the fire threat is negative perceptions of fire and the resulting fire suppression. Once a wildfire is moving through the landscape, there is little that can be done to salvage the burned habitat and bats that may have succumbed to the fire. This is why it is important to allow prescribed burning on landscapes where it is needed; it will ultimately reduce the risk of unmanageable wildfires and habitat destruction. By reducing the risk of habitat destruction, the effects of several other threats to bats – such as white-nose syndrome, residential and commercial development, or logging – may be somewhat reduced through the provision of alternate or refuge habitat.

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