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Harvard Forest REU Symposium Abstract 2005

  • Title: Variation of natural abundance δ15N in forest soils and vegetation as a function of historical agricultural land-use
  • Author: David Diaz (Harvard University)
  • Abstract:

    Biogeochemical changes instigated by agricultural land-use are multiple and long-lived. Seemingly innocuous activities such as depositing animal manure as fertilizer and dragging a plow through the earth have produced dramatically altered regimes of nutrient cycling, the effects of which may still be discerned in the ecosystem composition and properties of contemporary forests, even after more than a century of abandonment and reforestation. The extensive historical and ecological research which has been conducted on the Prospect Hill tract of Harvard Forest in Petersham, MA, USA makes this an ideal location to explore the biogeochemical legacies of historical land-use. Distinct values for nitrogen isotope concentrations in forest soils and ferns have been previously documented, establishing the use of N-15 as a meaningful tool in examining the lasting effects of agriculture. To establish the history and trajectory of these changes in the forest following agricultural abandonment, the use of Pinus strobus tree rings may serve as a useful indicator of past variations in soil nitrogen. To evaluate the historical and contemporary effects of different agricultural land-uses on the nitrogen content of the forest, a survey of soil, vegetation (Tsuga canadensis needles, Gaultheria procumbens, and Lycopodium obscurum), and tree rings (P. strobus) is currently underway at the Harvard Forest. These samples will be analyzed for nitrogen isotope concentrations using an Isotope Ratio Mass Spectrometer (IRMS) and used to evaluate potential sources for the biogeochemical variation across land-use types.

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