The Long-Term Effects of Land-Use History on Nitrogen Cycling in Northern Hardwood Forests

• Published in: Ecological applications 2001-02, Vol.11 (1), p.253-267
• Main Authors: Goodale, Christine L., Aber, John D.
• Format: Article
• Language: English
• Subjects: Acer rubrum; Acer saccharum; Betula papyrifera; C:N ratio; disturbance; Fagus grandifolia; fire; Forest ecology; Forest ecosystems; Forest litter; Forest soils; Hardwood forests; land-use history; logging; Mineral soils; New Hampshire; Nitrification; Nitrogen; nitrogen mineralization; nitrogen saturation; old growth; Old growth forests; Soil organic matter; succession; USA, North Carolina; White Mountains (New Hampshire, USA)
• ISSN: 1051-0761; 1939-5582
• DOI: 10.1890/1051-0761(2001)011[0253:TLTEOL]2.0.CO;2

Nearly all northeastern U.S. forests have been disturbed by wind, logging, fire, or agriculture over the past several centuries. These disturbances may have long-term impacts on forest carbon and nitrogen cycling, affecting forests' vulnerability to N saturation and their future capacity to store C. We evaluated the long-term (80-110 yr) effects of logging and fire on aboveground biomass, foliar N (%), soil C and N pools, net N mineralization and nitrification, and NO3 -leaching in northern hardwood forests in the White Mountain National Forest, New Hampshire. Historical land-use maps were used to identify five areas each containing previously logged, burned, and relatively undisturbed (old-growth) forests. Aboveground biomass averaged 192 Mg/ha on the historically disturbed sites and 261 Mg/ha on the old-growth sites, and species dominance shifted from early-successional and mid-successional species (Betula papyrifera and Acer rubrum) to late-successional species (Fagus grandifolia and particularly A. saccharum). Forest floors in the old-growth stands had less organic matter and lower C:N ratios than those in historically burned or logged sites. Estimated net N mineralization did not vary by land-use history (113 kg· ha-1· yr-1); mean (± 1 SE) nitrification rates at old-growth sites (63 ± 4.3 kg· ha-1· yr-1) doubled those at burned (34 ± 4.4 kg· ha-1· yr-1) and logged (29 ± 4.7 kg· ha-1· yr-1) sites. Across all plots, nitrification increased as forest floor C:N ratio decreased, and NO3 -concentrations in streamwater increased with nitrification. These results indicate that forest N cycling is affected by century-old disturbances. The increased nitrification at the old-growth sites may have resulted from excess N accumulation relative to C accumulation in forest soils, due in part to low productivity of old-aged forests and chronic N deposition.