Prescribed fire burning through longleaf pine understory – Houston Chandler

            I get asked all the time if I worry about venomous snakes while working in the field.  Well-meaning friends and family members encourage me to be on the lookout for snakes at all times.  These comments generally come from people who have the mindset that venomous snakes are lurking around every corner or are at least abundant enough to be encountered regularly.  In reality, I seldom worry about venomous snakes, even when working with them directly and often spend days in the field without seeing a snake of any kind.  There are many other aspects of fieldwork that present a much more acute problem than venomous snakes.  Don’t take this the wrong way, we work very hard to be as safe as possible around venomous snakes, but, the fact is, bites are incredibly rare when using appropriate handling procedures and wearing appropriate safety gear.

            Driving to and from survey sites is almost always the most dangerous thing that I do when conducting fieldwork.  However, it’s hard to worry too much about the dangers of daily commutes as it is a part of everyday life.  No, the things that I worry about more than anything are the things that you cannot actually see.  If you talk to a group of field biologists who regularly work outside, you will likely find someone who has at some point in their career encountered some form of infectious disease.  In the eastern half of the United States, tick-borne infections are particularly common, and I know many people who have had one of the many different infections that ticks can transmit.  Lyme disease is probably the most well-known tick-borne illness in the U.S., and there are many places where anyone who spends a significant amount of time outside is likely to encounter this disease (CDC).  Luckily for me, the Coastal Plain in Georgia has low rates of Lyme disease cases (although the number of cases across the eastern U.S. has increased in recent years), but other tick-borne illnesses are more prevalent in this region.

Amblyomma maculatum – Photo from the CDC, Dr. Christopher Paddock

Ixodes scapularis – Photo from the CDC, Michael L. Levin, PhD

            There are many species of ticks that call the southeastern Coastal Plain home, and these species can carry a variety of pathogens, some of which are infectious to humans.  Prescribed fire’s impacts on tick populations has been of interest to habitat managers for many years.  Research has indicated that regular prescribed burning does, in fact, reduce tick population size when compared to unburned plots of land (Gleim et al. 2014).  During growing season fires, many ticks are killed as fire burns through the herbaceous understory and small shrubs.  Importantly, these results depended on maintaining the vegetation characteristics of fire-maintained longleaf pine forests (open canopy and lack of woody mid-story).  A one-time burn was not sufficient for long-term reductions in tick populations.  Direct mortality from fire and a lack of mid-story vegetation appear to have a sustained effect on tick abundance, likely reducing tick numbers to a more natural level.

            Follow-up research conducted by Gleim et al. (2019) found that these reductions in tick populations do in fact reduce the chances of encountering a tick-borne illness.  Pathogenic bacteria prevalence was not reduced in tick populations, but the reduction in the number of ticks decreased the likelihood of encountering an infected tick.  Interestingly, some non-pathogenic bacteria (Rickettsia spp.) did occur at a lower prevalence in burned sites, indicating that burning disrupts the transmission of these bacteria (Gleim et al. 2019).  The results of these studies add to the already long list of benefits to ecosystems and the surrounding communities of regular prescribed burning in the southeastern U.S.

            Ticks are not the only animals that carry pathogens capable of infecting humans, although along with mosquitos, they are probably the most well-known.  Some pathogens can also be picked up in the environment without traveling through an intermediary host (brain-eating amoeba [Naegleria fowleri] comes to mind).  The unseen nature of these hazards makes them a more-concerning aspect of fieldwork than venomous snakes ever will be.  In fact, venomous snakes eat a lot of ticks while consuming their normal prey items, performing an important ecosystem service.

Even though some species of ticks carry diseases, they are still important parts of the ecosystem. The Gopher Tortoise tick (Amblyomma tuberculatum) is commonly found attached to soft spots on tortoises and is one of the many species dependent on tortoises in the southeast. – Houston Chandler

Literature Cited

Gleim, E. R., L. M. Conner, R. D. Berghaus, M. L. Levin, G. E. Zemtsova, and M. J. Yabsley. 2014. The phenology of ticks and the effects of long-term prescribed burning on tick population dynamics in southwestern Georgia and northwestern Florida. PLoS ONE 9:e112174.

Gleim, E. R., G. E. Zemtsova, R. D. Berghaus, M. L. Levin, M. Conner, and M. J. Yabsley. 2019. Frequent prescribed fires can reduce risk of tick-borne diseases. Scientific Reports 9:9974.

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