Soil Physicochemical and Microbial Responses to High-Energy Fires in a Semi-Arid Savanna

Abstract

Although the risks of industrial denotations in semi-open and congested geometries are often neglected by many safety practitioners, recent studies have shown that detonation onset in industrial installations might be more common than previously believed. Therefore, from the explosion safety perspective, it becomes imperative to assess industrial detonation hazards in order to ensure the robustness of explosion mitigation design, improve emergency response procedures, and provide adequate building siting evaluation. This study investigated flame acceleration and detonation onset under non-idealized obstruction characteristics. Furthermore, it also expanded the application of standard vapor cloud explosion (VCE) models to estimate the likelihood of deflagration-to-detonation transition (DDT) in industrial sites containing less reactive fuels such as propane and other light hydrocarbons. Savannas in the Southern Great Plains are experiencing unprecedented compositional shifts toward woody plant dominance. Recent studies have proposed that high-energy prescribed fires during drought may be an effective method to control undesirable woody species, particularly for resprouters. However, less is known about the effects of high-energy fires on the biogeochemistry of the soil in arid and semi-ari systems. To investigate the impact of fire energy on the soil’s physical, chemical, and biological properties, we sampled soils from two treatments (moderate-energy fire and high-energy fire) and a control (unburned) three days before and immediately (i.e. within hours) after prescribed fires in a semi-arid Texas savanna. We continued to measure the soil properties over a period of 12 months. Around each plot center, 4 soil samples were collected from a 0 to 15 cm depth and combined into a composite sample. The composite sample was then analyzed for physicochemical and microbial properties. We found that the moderate-energy fire and high-energy fire did not appreciably affect the physical (moisture content, water infiltration, aggregate stability, and bulk density) or chemical (pH, total carbon, total organic carbon, and total nitrogen) properties. However, the high-energy fire did negatively reduce enzyme activities responsible for carbon (β-glucosidase, α-glucosidase, cellobiohydrolase) and nitrogen (N-acetyl glucosaminidase) cycling. We also found that immediately after the high-energy fires, two bacterial phyla (Bacteroidetes and FBP) were significantly reduced while two bacterial phyla (Firmicutes and Verrucomicrobia) increased following the high-energyiii and moderate-energy fire, respectively. The effect of the high-energy fire on the microbial structure diminished after one year and was not significant. A complete understanding of both direct and indirect fire energy impacts on the soil dynamics is necessary for effective conservation of arid and semi-arid systems. Additionally, longterm effects of high-energy fires on soil enzyme activity will need further research. Results from this study provide valuable insights into potential belowground consequences of using savanna restoration strategies promoting extreme, high intensity fires as a means of managing woody encroachment.