ORGANIC MATTER AND NITROGEN ACCUMULATION DURING 70 YEARS OF OLD-FIELD SUCCESSION IN CENTRAL NEW HAMPSHIRE (ECOLOGY, PRODUCTIVITY, NUTRIENTS)

An old-field succession was studied within a small farming community (Bald Mountain) of central New Hampshire. Ecosystem accumulation of organic matter and nitrogen was documented using an eight member chronosequence including open-field and forested sites ranging in age from 33- to 65-years-old. Sites were located within a 2 km('2) area (except for one site) for which a detailed history was constructed using census records, town tax records, deeds, and interviews.; Ecosystem trends were examined in the old-field chronosequence by dividing the ecosystem into four compartments and measuring each separately: living biomass, dead wood, forest floor, and mineral soil. The mineral soil was examined using a new approach involving quantitative pits.; Rates of aboveground productivity of the old-field succession (2.6 Mg/ha/yr) were indistinguishable from those following stem-only clear-cutting (2.4 Mg/ha/yr) in the same area. Forest floor organic matter increased rapidly (0.8 Mg/ha/yr). Net ecosystem productivity of the chronosequence was 4 Mg/ha/yr.; Nitrogen accumulation in the old-field chronosequence was 21 kg-N/ha/yr. Ap horizon mineral soil showed large significant decreases in nitrogen of -16 Kg-N/ha/yr, equal to the increases in forest floor nitrogen. The Ap horizon nitrogen pool seems to represent a major source of nitrogen for regrowing vegetation. A nitrogen budget of the old-field chronosequence showed unaccounted for inputs of nitrogen of 14 kg-N/ha/yr. However, when the B horizon (which does not show significant trends) is not included in the ecosystem budget only 5.5 kg-N/ha/yr are unaccounted for.; Presettlement forests of the Bald Mountain community were examined using witness trees and 1903 forest inventory data. The forests were comprised of equal amounts of spruce and beech and lesser amounts of birch, maple and hemlock.; The Bald Mountain community was: settled 1790-1835, a stable farming community 1835-1880, and abandoned 1880-1950. The history of the community and its fields were typical of hill farms of northern New England. Abandonment of Bald Mountain appears to have been less related to problems with soil fertility than social and economic pressures.