Controlled annual burning is a common management technique used to control invasive understory plants and promote oak regeneration. However, prescribed burning effects on oak forest and woodland soils remain largely unknown. Fire has marked an often disproportionate impact on soil carbon (C), nitrogen (N), and phosphorus (P). Evaluating the impacts of repeated low-intensity prescribed burning on oak forest soils is critical for understanding and predicting burning effects on vegetation dynamics and ecosystem functions. The goal of this study was to evaluate relative changes in soil C and nutrient dynamics in response to repeated low-intensity controlled burning in an oak-dominated forest. We used a stoichiometric approach to analyze soil biogeochemical responses to controlled burning in forest plots and better understand the microbial dynamics in burned soils. Because of the exhibited effects of burning on C, N, and P concentrations, availability, enzyme activities, and microbial biomass, we expected repeated burning to alter the stoichiometric ratios of these factors in the soil.
Results/Conclusions
We found a significantly higher pH (p=0.0033), soil organic matter (p=0.0320), total Carbon (p=0.0014), and total nitrogen (p=0.0073) and no change in soil moisture in burned plots. We tested the activity of soil enzymes including β- 1,4- glucosidase (BG), N-acetyl-β-D-glucosaminidase (NAG), and acid phosphatase (AP) which break down organic C, N and P respectively. We found significantly higher ratios of BG:AP (p=0.0381) and NAG:AP (p=0.0001) and lower ratios of BG:NAG (p=0.0613) in the burned soils. We expect that these changes are driven by relative increases in NAG or decreases in AP activity in burned soils. We found lower ratios of microbial biomass C to microbial biomass P (MBC:MBP) in burned soils (p=0.0845). This is likely driven by a relative increase in MBP in burned soils (p=0.0545). MBN was also significantly higher in burned soils (p=0.0453), however MBC:MBN ratios were unchanged with burning treatment. Burning increases light available on the forest floor and increases organic matter, carbon, and nitrogen, which may benefit oak regeneration. However, increased understory herbaceous plants in the burned areas are likely shading out many of the oak seedlings. These results should be considered when predicting the benefits of controlled burns and analyzing the use of controlled burns in the future.