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Coarse Woody Debris

by Christopher Burdette

Winter 2008

Amongst the towering oaks and ever-elusive animals of Black Rock Forest is an equally interesting and integral forest element: dead wood. Termed coarse woody debris (CWD) within the scientific community, it consists of both standing dead trees (snags) and material that has fallen to the ground; it is defined as wood pieces larger than 10 cm in diameter and more than 1 m in length

CWD is added to ecosystems by numerous mechanisms, including wind, fire, insect attack, pathogens, competition, and geomorphic processes.  During decomposition, logs and other forms of CWD reduce erosion and affect soil development, store nutrients and water, provide a source of energy and nutrient flow, serve as seedbeds, and provide habitat for decomposers and heterotrophs (organisms that need organic substances to grow).

Last summer, I investigated the abundance, distribution, and mass loss of CWD in 18 sites on the North Slope of Black Rock Mountain.  This area was selectively thinned for firewood twice in the mid-20th century.  Our investigation found CWD volumes were at the low end of the scale (40 m³/ha) compared to similarly aged northeastern forests, which range from 28 to 166 m³/ha.  We then calculated the amount of carbon stored in this source at 8.9 Mg/ha, which was also low compared to published findings from similarly aged and composed northeastern forests. 

Red and chestnut oaks (Quercus rubra and Q. prinus) represented 72% of the volume of CWD found, and sugar and red maples (Acer saccharum and A. rubrum) approximately 18%, with other species representing less than 10%.

We also looked at the distribution and range of decay.  Classes are used to categorize the degree of decay, ranging from decay class I in which CWD is largely intact and resembles a living tree to decay class V in which the material is thoroughly decomposed and easily breaks down into the soil.  Decay class III, in which the material has no bark but still retains its shape, was the most abundant across all species, indicating that a specific event, either natural or historical, led to the high prevalence of this class.

There were sufficient snags of all size classes to support cavity-nesting wildlife, according to forest management guidelines.  Low CWD amounts limit ecosystem function on a carbon storage and strict volume per hectare basis, thus constraining the ability of CWD to reduce erosion and promote seedbeds.

This research reflects the current state of our knowledge on this important resource, and also provides a baseline study for comparison and evaluation of forest health as changes occur in Black Rock Forest.

Christopher Burdette is a senior in the Department of Ecology, Evolution, and Environmental Biology (E3B) at Columbia.  He worked with Drs. Kevin Griffin (Lamont-Doherty Earth Observatory), Matt Palmer (E3B), and Bill Schuster (Black Rock Forest).