Surface Soil Acidification under Red Pine and Norway Spruce

Abstract

AbstractNear‐tree patterns of forest‐soil pH under red pine (Pinus resinosa Ait.) and Norway spruce [Picea abies (L.) Karst.] were examined in order to evaluate the role of trees in acidification processes of surface soils. Variability in soil pH was analyzed by comparing samples obtained at different distances and directions from the base of a tree, at different times within a year, under live and dead trees, trees of different sizes, and trees of the same species growing on different soil types. Accumulation of soil organic matter, pH of freshly fallen litter, and the concentration of oxalate in water extracts of Oe horizons were measured as a function of distance from the base of selected trees. A significant decrease in soil pH from the edge of the canopy to the base of the tree was found in the upper mineral soil and organic horizons beneath live trees of both species. In general, the direction of sampling, the percent organic matter within a soil sample, and the time of year for sampling did not significantly affect soil pH. Mass of organic matter above the mineral soil did not exhibit a distinct pattern with distance from a tree. Twelve years after thinning red pine trees, a significant depression in pH existed in Oi and Oe horizons near the base of a dead tree or stump. Near‐tree depression in pH of the Oi horizon, where tree roots are not present, and of the Oi and Oe horizons around previously thinned trees where no stemflow occurs, suggests that soil fungi endemic or more active in the near‐tree environment of red pine and Norway spruce could make a significant contribution to acidification of soil surface horizons.