Photo Credit: Using small controlled burns to assess fire behavior in basal duff mounds. Photo by Eamon Engber
As I write this, I’m flying over the dry deserts of the southwest, en route to Jacksonville for the annual meeting of the FAC Net and the FLN. It’s been almost exactly 5 years since I was last in Florida, and I’m excited to be going back. In spring 2011, my husband and I spent four months in north Florida working on a research project, and it was the end of April that year that we and our Australian shepherd loaded into our old red Toyota pick-up, hitched up a U-Haul trailer full of longleaf pine duff samples (really!), and started the grueling journey west on I-10. After 50 straight hours of driving and two separate trailer tire blowouts in the middle of the desert, we crossed home into California—and I’ve been wanting to come back to north Florida ever since.
As someone who grew up in one of the most fire-prone parts of northern California, it was hard for me to imagine a more pyrophytic landscape. Before 2011, I envisioned Florida consisting mostly of beaches and amusement parks—much like the uninformed stereotypes people have of my own home state. What I found instead was a magical place where the “soil” is sand, clear blue spring water wells up from nowhere, old-growth trees are small enough to wrap my arms around, lightning strikes more than anywhere else in the country and fire is the defining force on the landscape. It didn’t take long for north Florida to win me over.
Back to the U-Haul full of duff samples: while we were in Florida in 2011, we were working on some research on duff flammability in long-unburned longleaf pine savannas. That project stemmed from years of related research that Morgan Varner (then with Humboldt State University, now with the USDA Forest Service Pacific Northwest Research Station) had conducted in longleaf pine stands in the southeast. His earlier research had documented some of the novel, problematic effects of restorative burning in long-unburned, old-growth longleaf, including basal duff smoldering that was disproportionately causing mortality in larger, older trees. In a 2005 paper in Restoration Ecology, Varner and his colleagues synthesized findings from various case studies of burning in longleaf, and they found that a majority of restoration burning projects were causing excessive, unintended tree mortality—sometimes killing more than 50% of trees. With longleaf pine area already at 3% of historical coverage, these additional losses were cause for serious concern, and the research helped call out the need for more strategic, adaptive restoration efforts. Likewise, their findings translated well to other frequent fire-adapted species that develop basal duff mounds in the absence of fire, including ponderosa pine in the West.
Using infrared imagery to understand patterns of duff ignition and fire spread. Credit: Eamon Engber
The 2011 project aimed to pick apart the mechanics of duff ignition and consumption, and provide more detail on duff moisture and other conditions that could limit or moderate fire severity and effects. The project included micro burns of individual basal duff mounds, with detailed measurements of soil heating and duff moisture, depth, and bulk density, as well as infrared imagery to assess patterns of fire spread, duration of smoldering, and the role of “vectors” like pine cones and heavier fuels. These field-based measurements were corroborated with lab-based burning of intact duff samples, which traveled with us from Florida (in the U-Haul trailer) to be burned in the Humboldt State University fire lab. The results of that study are still in development, though the duff moisture data resulted in a nice little paper that assessed the utility of digital duff moisture meters for restorative burning in longleaf (Engber et al. 2013). These projects are true examples of fire science informing and enabling adaptive management and restoration.
As a Californian, I think Florida is interesting not only for its abundant fire-adapted plants and highly volatile fuels, but also for the relatively intact connection that people have with fire—something that has largely been lost where I come from. Prescribed fire is a part of life in north Florida. If you’ve never read Francis Putz’s 2003 article titled “Are rednecks the unsung heroes of ecosystem management?”, I highly recommend it! It tells us, in an entertaining way, about the everyday cultural connections between people and fire in the southeast, and it reminds us that it takes all types to maintain fire on our landscapes. We’re all working for a noble cause, but it’s got to be fun, too!
References:
Engber, E.E., Varner, J.M., Dugaw, C., Quinn-Davidson, L., and J. Hiers. (2013). Utility of an instantaneous moisture meter for duff moisture prediction in long-unburned longleaf pine ecosystems. Southern Journal of Applied Forestry. 37(1): 13-17. https://www.researchgate.net/profile/J_Varner/publication/274444842_Utility_of_an_Instantaneous_Moisture_Meter_for_Duff_Moisture_Prediction_in_Long-Unburned_Longleaf_Pine_Forests/links/55915daa08ae1e1f9bafe810.pdf
Varner, J. M., Hiers, J. K., Ottmar, R. D., Gordon, D. R., Putz, F. E., & Wade, D. D. (2007). Overstory tree mortality resulting from reintroducing fire to long-unburned longleaf pine forests: the importance of duff moisture. Canadian Journal of Forest Research, 37(8), 1349-1358. https://cdnsciencepub.com/doi/abs/10.1139/x06-315
Varner, J.M., Gordon, D.R., Putz, F.E., and HIers, J.K. (2005). Restoring fire to long-unburned Pinus palustris ecosystems: novel fire effects and consequences for long-unburned ecosystems. Restoration Ecology. 13(3): 536-544. http://labs.bio.unc.edu/Peet/Courses/Bio255_2005F/papers/VarnerEtAl2005.pdf
Putz, F.E. (2003). Are rednecks the unsung heroes of ecosystem management? Wild Earth. 13(2/3): 10-14. http://www.sfrc.ufl.edu/fire/Fire_Science_Lab/Fire_Ecology_and_Management_files/Putz%202003.pdf
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