Ecosystem response to 15 years of chronic nitrogen additions at the Harvard Forest LTER, Massachusetts, USA

https://doi.org/10.1016/j.foreco.2004.03.033Get rights and content

Abstract

Humans have altered the global and regional cycles of nitrogen more than any other element. Alteration of N cycling patterns and processes in forests is one potentially negative outcome of accelerated N deposition worldwide. To assess potential impacts of N deposition on temperate forests, a series of chronic nitrogen additions in two contrasting forest types (red pine plantation and mixed hardwood stand) were designed as a core experiment of the Harvard Forest (HF) Long-term Ecological Research (LTER) program. This paper describes the chronic N experimental study site in detail and presents the long-term baseline measurements established at the beginning of treatments in 1988.

Results reported here continue or accelerate trends presented in previous papers. Losses of inorganic N remain high in the high N plots (higher in pines than hardwoods) and low N plots in the pine stand also have measurable DIN losses. Foliar and fine root N concentrations are elevated significantly. Mortality of red pine reached 56% by 2002 in the pine high N plot, and biomass accumulation has stopped altogether. The high N hardwood stand shows increased ANPP, but excess N availability and a severe drought in 1995 contributed to mortality of 72% of red maple trees by 2002. Species importance and litterfall patterns were altered in several plots after 1995. Roots, foliage and wood have diminished as net sinks for added N, re-emphasizing the role of soils in N retention. Two mechanisms for large net retention of added N were suggested in a review paper in 1998. Of these, abiotic immobilization is supported by a growing set of papers, while assimilation and re-exudation by mycorrhizae is suggested by increased DON concentrations.

Introduction

Our introductory paper for this special section (Aber and Magill, 2004) presents a brief review of the literature on global patterns of N deposition, and the long-term effects of this deposition on forests through nitrogen saturation. This paper describes the Chronic N Amendment Study at the Harvard Forest (HF) (Petersham, MA, USA) in detail and presents the long-term baseline measurements established at the beginning of treatments in 1988. Long-term measurements trace the retention and loss of added N, changes in pool size or concentration in different parts of the system, and the effects of N accumulation on plant and microbial processes, all in the context of the nitrogen saturation hypothesis (Aber et al., 1989, Aber et al., 1998). These basic measurements present the context for the detailed studies reported in other papers in the chronic N special section of this issue.

Section snippets

Study site and experimental design

The chronic nitrogen addition experiment is a core experiment of the Harvard Forest Long-term Ecological Research (LTER), and is located at the Harvard Forest in central Massachusetts (42°30′N, 72°10′W). Two contrasting forest stands were selected for this study, each with different land-use histories that have been well documented as part of the Harvard Forest silvicultural and land management records. The red pine (Pinus resinosa Ait.) plantation was established in 1926 and is located on the

Nitrogen inputs and losses

Background nitrogen deposition at the Harvard Forest (0.66–0.8 g N m−2 per year) is moderate for the northeastern United States (Munger et al., 1996, Ollinger et al., 1993, Lovett and Lindberg, 1993) and substantially lower than many experimental sites in Europe (Dise and Wright, 1995, Dise et al., 1998, Gundersen et al., 1998). We assume that deposition has remained relatively constant over the course of the experiment, as total US emissions of NOx have not changed during the experimental period (

Comparisons with previous work and other studies from the chronic N plots

Many of the findings reported in this paper continue or accelerate trends seen in earlier data summaries of the chronic N study. Losses of inorganic N remain high in the high N plots (higher in pines than hardwoods) and low N plots in the pine stand also have measurable DIN losses. Foliar and fine root N concentrations are elevated significantly. Trends in tree decline in the pine high N plot have accelerated and complete mortality in that stand is likely in the near future. Canopy condition

Acknowledgements

This research was funded by the National Science Foundation Long-Term Ecological Research Program and the USDA National Research Initiative Competitive Grants Program. Many people have contributed to the success and longevity of this project, including Gloria Quigley, Steve Newman, Richard Bowden, Joe Hendricks, Matt Kizlinski, Shannon Cromley, Jeremy Fontenault and Colin Pinney. Special thanks goes to the root sorting crew of 1999: Alex Sherman, Dan Vorosmarty, Cheryl Parker and Tracey

References (55)

  • J.D Aber et al.

    Nitrogen saturation in northern forest ecosystems

    BioScience

    (1989)
  • J.D Aber et al.

    Predicting the effects of climate change on water yield and forest production in the northeastern U.S.

    Climate Res.

    (1995)
  • J.D Aber et al.

    Nitrogen saturation in temperate forest ecosystems: hypotheses revisited

    BioScience

    (1998)
  • E.S Azhar et al.

    Binding of nitrate-N on polyphenols during nitrification

    Plant Soil

    (1986)
  • G.A Baron-Gafford et al.

    Nutrient concentrations and contents, and their relation to stem growth, of intensively managed Pinus taeda and Pinus elliotti stands of different planting densities

    Forest Sci.

    (2003)
  • Bauer, G.A., Bazzaz, F.A., Minocha, R., Long, S., Magill, A., Aber, J., Berntson, G.M., 2004. Effects of chronic N...
  • C Beier et al.

    Field-scale “clean” rain treatments to two Norway spruce stands within the EXMAN project-effects on soil solution chemistry, foliar nutrition and tree growth

    Forest Ecol. Manage.

    (1998)
  • K.L Bolster et al.

    Interactions between precision and generality in the development of calibration for the determination of carbon fraction and nitrogen concentration in foliage by near infrared reflectance

    Can. J. Forest Res.

    (1996)
  • A.W Boxman et al.

    Vegetation and soil biota response to experimentally-changed nitrogen inputs in coniferous forest ecosystems of the NITREX project

    Forest Ecol. Manage.

    (1998)
  • M.K Burke et al.

    Fine root growth phenology, production, and turnover in a northern hardwood forest ecosystem

    Plant Soil

    (1994)
  • D.A Clark et al.

    Measuring net primary production in forests: concepts and field methods

    Ecol. Appl.

    (2001)
  • W.S Currie et al.

    Leaching of nutrient cations from the forest floor: effects of nitrogen saturation in two long-term manipulations

    Can. J. Forest Res.

    (1999)
  • D.B Dail et al.

    Rapid abiotic transformation of nitrate in an acid forest soil

    Biogeochemistry

    (2001)
  • E.A Davidson et al.

    A mechanism of abiotic immobilization of nitrate in forest ecosystems: the ferrous wheel hypothesis

    Global Change Biol.

    (2003)
  • N.B Dise et al.

    Synthesis of nitrogen pools and fluxes from European forest ecosystems

    Water Air Soil Pollut.

    (1998)
  • N.B Dise et al.

    Nitrogen leaching in European forests in relation to nitrogen deposition

    Forest Ecol. Manage.

    (1995)
  • C.T Driscoll et al.

    Longitudinal and temporal trends in the water chemistry of the North Branch of the Moose River

    Biogeochemistry

    (1987)
  • Cited by (0)

    View full text