Long-term Effects of Prescribed Fire and Fire Surrogate Treatments on Southern Appalachian Mountain Forest Soil Chemistry

• Main Author: Dukes, Christopher Jered
• Other Authors: Forest Resources and Environmental Conservation
• Format: Others
• Language: en
• Published: Virginia Tech 2020
• Subjects: ForestrySoil Chemistry; Ecosystem Restoration; Wildfire Hazard
• Online Access: http://hdl.handle.net/10919/96593

As a response to rising wildfire hazard and forest structure and composition concerns, the National Fire and Fire Surrogate Study was established in 2000 to determine how fuel reduction and ecosystem restoration techniques might affect ecosystem properties and processes across the United States. Soil chemistry and the southern Appalachian Mountains were an ecosystem property and ecoregion of interest, respectively. Treatments utilized at this site included: prescribed fire alone (3 burns), mechanical cutting of understory shrubs and midstory trees alone (2 cuttings), and a combination of the two (2 installations). Soils were sampled in 2018 to determine potential treatment impacts for: O horizon and mineral soil (0-10 cm depth) carbon (C), nitrogen (N), carbon:nitrogen (C:N) and mineral soil calcium (Ca), magnesium (Mg), phosphorus (P), potassium (K), and pH. Results suggested slight, but statistically significant changes in O horizon C and N and mineral soil C, N, C:N, Ca, and P values from 2001-2018 differed statistically between the treatments. Soil responses differed significantly between the replications utilized in this study and also did not fully agree with results from previous sampling that occurred following the first implementation of these treatments. This research highlights the spatial and temporal nature of soil responses to management. When considered with previously reported vegetation and fuels results from this site, it appeared that prescribed burning with and without mechanical cutting presented the most promise to achieve ecosystem restoration and fuel reduction properties without altering forest soil chemistry. === Master of Science === Fire was historically present in the southern Appalachian Mountains from both natural and anthropogenic sources. A common natural cause resulted from lightning ignitions while some common anthropogenic sources resulted from Native American ignitions. Their fire-use goals included understory clearing, reduction of pests and diseases, hunting, and even warfare. These practices were adopted by early European settlers and were implemented regularly across the landscape through the late 19th century. In the early 20th century, however, fire exclusion policies were implemented across broad acreages of the continental United States. Over 80 years later, such policies led to forests that have been altered from their historic composition. Some of these alterations include changes to plant species composition. In portions of eastern United States forests, fire intolerant, shade tolerant species now exert a dominant influence beyond what would be expected in a frequently altered state. This process, referred to as mesophication, is a positive-feedback cycle that changes the composition of the forest floor, as well, as a result of the vegetative composition alterations. This cycle has led to substantial forest floor fuel accumulations comprised of vegetative litter and duff. Essentially, this policy shift and subsequent fuel alteration has potentially increased wildfire hazard when dry weather conditions and ignitions coalesce. In 2000, the National Fire and Fire Surrogate Study (FFSS) was designed and implemented to study ecosystem responses to fuel reduction treatments in 13 locations across the United States. One of these locations was the southern Appalachian Mountains near Hendersonville, North Carolina. For this particular study, soil chemistry was the observed ecosystem trait. The treatments included untreated control, prescribed fire, mechanical cutting of vegetation, and a combination of prescribed fire and cutting. From 2001-2018, 4 prescribed burns, 2 cutting treatments, and 2 combination treatments have been implemented. Prior to the first treatments in 2001, soils were sampled to determine pre-treatment soil chemistry. In 2018, soils were re-sampled to determine the potential long-term impacts of repeated implementations of these management techniques on forest soil chemistry. Overall, the results suggested that forest soil chemistry was altered in ways that do not appear biologically significant and may in fact fail to alter soils in ways that might benefit and sustain long-term ecological restoration objectives. Continued treatment applications may be necessary to obtain more desirable conditions.