Burton Lab Michigan Gradient Study

Michigan Gradient Study


  • Nitrogen (N) saturation of terrestrial ecosystems is one of the most important contemporary ecological issues

  • Researchers at Michigan Technological University, the University of Michigan and the University of Idaho are adding nitrate (NO3-) to northern hardwood forests in Michigan to learn how this common Lakes States forest type responds to chronic N additions.
    Text Box:  Project History: The Michigan Gradient study was established in 1987 to examine the effects of climate and atmospheric deposition on ecosystem processes in the Great Lakes region and continues today with support from NSF. Four northern hardwood study sites extend 500 km from northwestern Upper Michigan to southern Lower Michigan. The experiment was deliberately established to range from the northern edge of the northern hardwoods region in western Upper Michigan to the transition zone in the middle of the Lowe Peninsula, encompassing most of the hemlock-white pine-northern hardwoods biome defined by Braun (1950).
    In 1994, we began studying the effects of chronic N additions on northern hardwood forests by experimentally adding NO3- (30 kg N ha-1 yr-1) to three treatment plots per site and comparing C and N cycling in these to that in three control plots per site. A variety of changes indicate chronic N additions have altered ecosystem processes. These include much greater leaching losses of dissolved organic carbon, dissolved organic nitrogen and NO3-, and reduced soil respiration. The NO3- treatment has also increased ecosystem C storage both by reducing rates of organic matter decomposition and by increasing aboveground woody growth. The research team is continuing the NO3- additions in order to learn the specific mechanisms behind these changes and to determine which will persist and which are transient effects that will diminish as the ecosystems adjust to altered N availability.


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