THE DECLINE OF SOIL ORGANIC-MATTER, TOTAL-N, AND AVAILABLE WATER CAPACITY FOLLOWING THE LATE-HOLOCENE ESTABLISHMENT OF JACK PINE ON SANDY MOLLISOLS, NORTH-CENTRAL MINNESOTA

This paper examines the rate at which prairie soils (Mollisols) were converted to forest soils (Entisols or Alfisols) following a late-Holocene invasion of brush prairie by jack pine. Nine study sites were ranked by their respective dates of jack pine forest establishment as determined from historical records, or inferred from the pollen stratigraphy of six lakes, spanning the past 2,500 radiocarbon years. Percentage dry weight of soil organic matter, total N, and available water capacity, all highly correlated, declined rapidly in both the epipedon and rooting zone during the first 1,000 radiocarbon years after jack pine replaced brush prairie. One-time measurements of nitrate and ammonium were not related to the period of jack pine forest occupation, and changes in the flux of these mineral N species over time were not investigated. A three-parameter negative-exponential function was used to model the soil changes. The model predicts declines from 5.7 to 1.4% for soil organic matter, 0.220 to 0.034% for total N, and 14.3 to 4.2% for available water capacity within the epipedon during a 2,500-year period following the establishment of jack pine forest on sandy Mollisols. © 1990 Williams & Wilkins.