Long‐Term Soil Chemistry Changes in Aggrading Forest Ecosystems

Abstract

AbstractAssessing potential long‐term forest productivity requires identification of the processes regulating chemical changes in forest soils. We resampled the litter layer and upper two mineral soil horizons, A and AB/BA, in two aggrading southern Appalachian watersheds 20 yr after an earlier sampling. Soils from a mixed‐hardwood watershed exhibited a small but significant decrease in soil pH. Extractable base cation content declined substantially in both mineral horizons. For example, Ca2+ levels in the A horizon fell from 236 kg ha−1 in 1970 to 80 kg ha−1 in 1990. Proportionally, the decline was greatest for Mg2+, which dropped from 111 to 20 kg ha−1. A white pine (Pinus strobus L.) plantation was planted in 1956, after clear‐felling hardwoods and recutting sprouts for 15 yr. Soil pH and base cation concentrations declined in the A horizon from 1970 to 1990. Soil pH declined from 5.9 to 5.0 and Ca2+ levels from 534 to 288 kg ha−1. Cation content did not change significantly in the AB/BA soil horizon. Nutrient budgets were constructed using these soil and litter data plus existing data on weathering rates, forest productivity, and hydrologic fluxes and associated chemistry. Decreases in soil base cations and soil pH are attributed to leaching and to the sequestration of nutrients in biomass.