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Harvard Forest Symposium Abstract 2005
- Title: Impacts of chronic N amendments on tree reproduction in an oak-dominated stand at Harvard Forest
- Primary Author: Hilary Callahan (Barnard College - Columbia University)
- Additional Authors: John Aber (University of New Hampshire - Main Campus); Angelica Patterson (Barnard College - Columbia University); Hina Zafar (Barnard College - Columbia University); Katrina del Fierro (Barnard College - Columbia University)
- Abstract:
Beyond the primary goal of analyzing how ecosystem functions may change in response to rising N deposition, the long-term Chronic N plots are a superb opportunity for linking such changes with organismal or population ecology mechanisms. Our recently initiated efforts include investigating how control vs. artificially elevated N inputs influence (1) the reproductive portion of litterfall, (2) acorn abundance, and (3) seed and seedling viability and quality. We have sorted and analyzed the non-foliage portion of litterfall samples collected from 1997-2002. Biomass of these tissues varied interannually, with a large increase in 2001 not observed in leaf tissue samples. Biomass also increased significantly with N inputs (Fig. 1), as did acorn biomass and acorn abundance in 2003 and 2004 (Fig. 2). In these years, seed size was significantly lower in control plots, known to be N-limited, but non-significant differences among treated plots did not correspond to N input levels, possibly reflecting genetic differences among trees on these plots. We have also quantified the impact of common insects that consume acorns, reducing seed viability. In 2003 and 2004, damage was uniformly severe across control and treated plots. We plan to expand efforts to include assessing N content of flower, fruit and seedling tissues, and of seed predator abundance, and to extend our monitoring activities across mast and non-mast years.
- Research Category:
