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Dr. David J. Mladenoff
Department of Forest Ecology and Management
University of Wisconsin-Madison

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Experimental manipulation of northern hardwoods forest structure

Contact Jodi Forrester

Background:

The management and use of natural resources represent a fundamental way in which humans affect ecological systems. There is concern among scientists that continual biomass removal is detrimental to the long-term sustainability and maintenance of biodiversity of forested ecosystems through its effects on nutrient capital and structural complexity. Begun in 1994 as a collaboration between the Wisconsin Department of Natural Resources and UW-Madison, the precursor observational phase of the current experimental study noted two major changes in forest structure resulting from harvest: (1) Depleted amounts of coarse woody debris (CWD); and (2) Alterations in canopy architecture. First, old-growth forests contain more and larger (by about 70%) fallen timber and snags than second-growth stands. Second, individual gaps in the canopy are twice as big in old-growth stands. Based on these observational studies, we now seek to experimentally modify forest management, in order to allow second-growth stands to more rapidly develop the structural features found in old-growth stands.

Research question:

The overall research goal is to integrate key structural characters of old-growth forests that promote forest sustainability and biodiversity with common forest management practices. In practice, this goal is two-fold: (1) Develop a mechanistic understanding of the feedbacks between forest structure (CWD and canopy gaps) and function [carbon (C) and nitrogen (N) cycling]; and (2) Integrate science and education through collaborative research between the university and young researchers, including undergraduate and graduate students and an internship program.

Approach:

Project Director Dr. David Mladenoff and others in UW-Madison's Department of Forest Ecology and Management devised the Flambeau Experiment, a unique 50+-year project to examine the research questions. At the 320-hectare field site in the Flambeau River State Forest, we propose a replicated, experimental manipulation of two factorial treatments: CWD loads and canopy openings, in order to understand the mechanisms of how common forest management practices alter long-term forest productivity and diversity through functional changes. The overall project has both long- and near-term objectives. The current work focuses on our near-term expectations, specifically that C and N dynamics are predominantly influenced by changes in the soil and mid- and understory plant communities brought about by gap alterations. At longer time scales, we expect the effects of the CWD manipulations to be manifested as plant-soil feedbacks incorporate the changes in the quality and quantity of detritus. We focus on key functional groups of forest biodiversity, structural components, and ecosystem processes. We will (1) Quantify decomposition effects based on interactions and feedbacks of microclimate with key functional biota, including vegetation and soil microorganisms; (2) Determine resulting impacts and feedbacks on key structural components, including over- and understory vegetation plus detrital and mineral-soil C and N pools; and (3) Directly measure management effects on sustainability, including net primary production, net C sequestration, and long-term N availability.

Results to date:

We have completed the third year of a three-year pre-treatment field study. Current field tasks encompass diverse ecological field sampling and monitoring, including plant communities (species identification and cover estimates by strata), forest structure (stem map), canopy gaps (hemispherical photos), coarse woody debris, C and N dynamics, soil organic matter pool sizes (litter fall, decomposition, floor and mineral-soil sampling), soil CO2 flux, forest surveying/mapping (GPS, GIS), and meteorological monitoring. Related laboratory and computer activities include sample preparation and analysis using sensitive equipment, large database management, statistics, and logistical planning.

Previous work:

Click here for a list of publications from the first phase of this project, where we examined and quantified the structural, compositional, and functional differences between old growth and managed northern hardwood forests in the upper Great Lakes region.

Other Principal Investigators involved in the project:

Dr. Tom Gower, Univ of Wisconsin-Madison, Dept of Forest Ecology & Management
Dr. Erika Latty , Hollins Univ, Dept of Biology
Dr. Craig Lorimer, Univ of Wisconsin-Madison, Dept of Forest Ecology & Management