Are soils beneath coniferous tree stands more acidic than soils beneath deciduous tree stands?

Authors: BURGESS-CONFORTI, JASON - University Of Arkansas; Moore, Philip; Owens, Phillip; MILLER, DAVID - University Of Arkansas; Ashworth, Amanda; HAYS, PHILLIP - Us Geological Survey (USGS); EVANS-WHITE, MICHELLE - University Of Arkansas; ANDERSON, KELSEY - University Of Arkansas

Submitted to: Environmental Science and Pollution Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2019
Publication Date: 3/26/2019
Citation: Burgess-Conforti, J.R., Moore Jr, P.A., Owens, P.R., Miller, D., Ashworth, A.J., Hays, P.D., Evans-White, M., Anderson, K.R. 2019. Are soils beneath coniferous tree stands more acidic than soils beneath deciduous tree stands? Environmental Science and Pollution Research. 26:14930–14931. https://doi.org/10.1007/s11356-019-04883-y.
DOI: https://doi.org/10.1007/s11356-019-04883-y

Interpretive Summary: A potential cause of watershed acidification is the shift in dominate forest species from deciduous hardwood forest to coniferous pine forest. Although coniferous vegetation has been linked to the acidification of soil in the past, there was no statistically significant differences in four measures of soil acidity between the hardwood and pine stands. The coniferous needle litter was more acidic than the hardwood litter which may contribute acidity to the watershed via runoff. The study was limited to the top 15 cm of soil which limits interpretations on the effect of pine trees on soil chemistry.

Technical Abstract: In 2008, the Mulberry River, a National Wild and Scenic River, was listed as impaired due to low pH (below pH 6.0). Over the last 50 years, the volume of conifers in the Ozark region has increased 115% since 1978 which may result in the acidification of nearby aquatic ecosystems. The objective of this study was to determine if differences exist in soil and litter chemical properties between deciduous and coniferous tree stands. Aboveground litter (n=200) and soil (n=400) at 0- to 5- and 5- to 15-cm depths were collected at paired deciduous and coniferous stands at 10 locations within the Mulberry River watershed (1010 km2) and analyzed for a suite of chemical parameters. There were no differences (P>0.05) in several measures of soil acidity between deciduous and coniferous stands. Litter collected from the coniferous stands was more acidic than deciduous litter (4.4 vs 4.7; P<0.05). Cation exchange capacity, exchangeable Ca and Mg, and water soluble P and Mg contents differed (P<0.05) by stand and depth. Cation exchange capacity and exchangeable Ca and Mg were greatest in the 0- to 5-cm depth interval of the coniferous stands. Water soluble P and Mg contents were greatest within the 0- to 5-cm depth interval which did not differ (P>0.05) between stand but were greater than the 5- to 15-cm depth interval. Although limited to the top 15-cm of soil, the similarity in soil acidity between stands suggests that conifer growth may not be a substantial source of acidity to the Mulberry River.