Natural Disturbance and Coarse Woody Debris

Technician documents felled trees for woody debris studies.

Technician documents felled trees for woody debris studies.

In closed-canopy hardwood forests of the Southern Appalachians, natural disturbance commonly creates canopy openings at scales ranging from single-tree gaps to several hectares. The “background” disturbance regime is generally thought to be primarily single-tree death or crown damage from ice storms. High-intensity, large-scale natural disturbance was relatively infrequent, but integral to forest dynamics at the landscape scale. Changes in light levels to the forest floor, habitat structure, and associated changes in plant and animal communities may be linked to gap size, canopy structure, and coarse woody debris that results from partial-, single-, or multiple tree deaths.

Scientists at the Bent Creek Experimental Forest studied the landscape distribution of canopy gaps created by wind disturbance. They also studied the response of vegetation, rodents, shrews, reptiles and amphibians, and birds to gaps and coarse woody debris levels by comparing these communities in intact, wind-created downburst gaps, salvage-logged gaps, and mature, closed canopy forest.

Our research shows:

  • Some oak species are especially vulnerable to uprooting during the downbursts.
  • High volumes of coarse woody debris are generated by tree blowdowns during high-intensity wind events.
  • Ground-dwelling arthropods are more abundant overall in mature forest than in blow-down patches or salvage-logged blowdowns.
  • Amphibian diversity is similar in mature forest, blowdown patches, and salvage-logged blowdowns. In contrast, reptile diversity and lizard abundance is higher in blowdown patches and salvage-logged blowdowns.
  • Shrew and white-footed mice populations are similar in the mature forest and in the blowdown patches.
  • More mice are captured near coarse woody debris.
  • Bird diversity and the densities of some bird species is higher in blowdown patches than in mature forest.
  • Blowdown patches may increase diversity at a landscape scale by providing patches of young, second-growth forest that are used by many wildlife species.