Fire has been an integral part of the natural history of North American forests as a natural disturbance that shapes community composition and ecosystem function. Organized fire suppression beginning in the early 20th century has converted historically fire-tolerant oak dominated ecosystems of the eastern United States to fire-sensitive hardwoods, where the grassy understory that thrived in the open woodlands of oaks as well as the organisms that depend on this understory is no longer present. Currently in upland forests of Mississippi, fire-sensitive mesophytic trees are invading forest gaps and creating a dense canopy that doesn’t allow for oak regeneration or for herbaceous plant growth. These changes in aboveground vegetation along with the absence of fire-produced compounds such as charcoal likely lead to changes in the microbiota of the soil along with changes in soil organic matter quality and quantity, nutrient availability, and microbial activity.
Belowground alterations due to prescribed fire treatments are not explicitly targeted by ecological restoration efforts, but are an unavoidable consequence of the practice that could theoretically lead to changes in the structure and function of the overall ecosystem. Information regarding the effects ecological restoration treatments have on belowground processes could be an invaluable tool for future restoration and management efforts.
To investigate belowground fire-induced changes, soil enzymatic activities for five enzymes involved in organic matter decomposition was determined bimonthly at two sites, each with a control plot, a burn only plot, and a burn plus mechanical thinning plot. The enzymes ß-glucosidase, phosphatase, β-N-acetylglucosaminidase, phenol oxidase, and lignin peroxidase were assayed for activity using p-nitrophenyl (pNP) linked substrates. Leaf decomposition rates of southern red oak (the dominant tree species in these plots) were determined under each treatment through the litterbag technique. Enzyme analysis of the five enzymes was also carried out on the decomposing leaves.
Results/Conclusions
Leaf litter decomposition rates showed a general trend where leaves in burned plots decayed more rapidly than leaves in burned plus mechanically thinned plots. Soil enzyme activity was generally highest in control plots, followed by burned plots, and lowest in plots that have been burned and mechanically thinned. Seasonal trends were also observed, where enzyme activity of phosphatase and β-glucosidase steadily declined between spring and winter. These observed differences in microbial activities between plots undergoing ecological restoration show that restoration treatments are altering belowground processes, and that future management should take these belowground processes into consideration when recommending restorative treatments.