Post by: E.K. Hammer McWilson
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When left alone a forest will undergo succession. This process consists of several stages, starting from soil and debris, to small plants and vines, then eventually the wooded forest. Each stage has unique species that are specialized to that period’s growing conditions. Frequent fire stops this process and keeps it in one stage, often creating a unique forest that is rich in biodiversity and delicate ecological systems. (6)
Pines and Fire Tolerance
Pinus palustris evolved alongside fire. Pine needles contain oils that are highly flammable. The dry foliage and draped over wiregrass, vines, and shrubs allows oxygen to circulate and creates the perfect conditions to start and feed a fire (5). Seedlings of all Pinus members have soft, green foliage and are therefore vulnerable to fire (3). So how does a longleaf full of flammable material stay safe from the fires? Whether or not a Longleaf survives is often determined by a few elements.
It is a general rule that the seedlings that are healthy before a burn survive, while stressed and diseased seedlings parish in the excessive heat. (6) A longleaf survives to adulthood by shooting its needles up toward the canopy, above the danger of flames (3,6). At three-year burning intervals a longleaf savannah looks healthy, at five-year intervals broadleaf hardwood species and damaging insect infestations start to encroach on the forest.(3,6)
Fire frequency and intensity often aren’t the only variables threatening longleaf seedlings. The Joseph W. Jones Ecological Research Center found that even in the small grass stage, excessive leaf litter, or a lack thereof, can kill a young longleaf. When leaf litter is in over-abundance it can burn too hot and close to a seedling; while when there is not enough litter herbaceous plants are not stunted by the fire enough and can eventually suffocate the young trees. (5)
Fire and Soil
One might expect constant burning to significantly change the chemistry of the soil in the longleaf’s forest floor. A study conducted showed that concentrations of Sulfur, Nitrogen, and Carbon went relatively unaffected. Phosphorus, however, increased from 10 to 30 times. The authors of the study believe that this is not directed resulted from the fire itself, but an effect of the heat slowing microbial activity that causes phosphorus to remain usable in the soil (5). The nutrient content in soil tends to increase after a low-intensity burn because cations trapped in organic material on the forest floor have been chemically converted into a form that living flora can use. It is a general trend that cation concentration with higher vaporization points (i.e. Potassium, Calcium, and Magnesium) tend to increase after a fire, whereas Nitrogen and Sulfur concentrations decrease. The nutrient concentrations left behind after a burn are highly dependent on the intensity of the fire. Low heat burning allow much of the nutrients to remain in the soil while the hottest burns can eradicate almost any cations (2). The effects of soil from fire are complex and layered, often with changes that can be attributed to, but not directly affected by the fire.
Human Interaction
Fire has been a constant in human evolution, even predating today’s Homo sapian sapian (5). As well as being important to humans, fire plays a role in many forest ecosystems, including the longleaf Pine Barrens. Fire was likely first introduced to the pines savannahs by lightning igniting dry grass and pine needles. (7) Evidence from fossils suggest that this has been occurring for around 420 million years (5). It is thought that over time Native Americans started to set fire to the forests themselves. Anthropologists speculate this might be because a frequently burned pine savannah provided low ground cover that is better for hunting, and made use of the trees’ needles, bark, and sap (1). Colonization brought with it a rapid decline in these forests due to logging. Little of the original savannahs remain today.
Human history has been arguably shaped by our ability to harness fire. Although pines cannot use flames in the same way, they adapted to burns long before recorded human history. The excitement of forest fires adds another dimension to an already unique and complex ecosystem.
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Works Cited:
(1) Fowler, Cynthia, and Evelyn Konopik. “The History of Fire in the Southern United States.” Human Ecology Review, 2007, www.humanecologyreview.org.
(2) Fire Effect on Soil, Forest Encyclopedia Network, www2.nau.edu/~gaud/bio300w/frsl.htm.
(3) “5 Five-Year burns.” Five-Year burns - The longleaf pine savanna, www.learnnc.org/lp/editions/cede_longleaf/492.
(4) “A Guide to Soil Quality Monitoring for Long Term Ecosystem Sustainability on Northern Region National Forests.” RMRS - Rocky Mountain Research Station, forest.moscowfsl.wsu.edu/smp/solo/documents/GTRs/INT_280/DeBano_INT-280.php.
(5) Binkley, Dan, et al. “Soil Chemistry in a Loblolly/Longleaf Pine Forest with Interval Burning.” Ecological Applications, vol. 2, no. 2, 1992, pp. 157–164. Jstor, doi:10.2307/1941772.
(6) “General Rules for Burning Longleaf (Longleaf Alliance).” The Longleaf Alliance, 2009, www.americaslongleaf.org.
(7) Wassilieff, Maggy. “ 'Forest succession and regeneration - Plants in a succession'.” Te Ara - the Encyclopedia of New Zealand, 24 Sept. 2007, www.TeAra.govt.nz/en/forest-succession-and-regeneration/page-2 (accessed 20 January 2018)
Images Cited (In order of appearance):
(1) “Pine Needle Basketry.” Heritage Museum of Northwest Florida, www.heritage-museum.org/pine-needle-basketry.html.
(2) Fire Science, www.firescience.gov/projects.
(3) Bottlebrush, E.K. Hammer McWilson
(4) Sap, E.K Hammer McWilson
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