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S. Appalachian forest succession described in 20-year study

A Western Ecology Division scientist and colleagues in Georgia have completed a 20-year study of forest productivity, species composition, and diversity responses to disturbance in the southern Appalachian Mountains. In 1981, in cooperation with the U.S. Forest Service, clearcut logging was used to create four sizes of forest openings ranging downwards in five-fold increments from 2 hectares to 0.016 hectares. These clearings, smaller than typical logging clearcuts, simulated openings caused by natural disturbances such as blow-downs or insect attacks. The researchers found by the end of the study that recovery of the forestís net primary production and biomass was seven times greater in the largest compared with the smallest openings. Biomass in the 2-hectare openings had returned to 60 percent of what it had been and productivity reached 225 percent of pre-disturbance levels.

Shade-intolerant black locust trees, which enrich soil through nitrogen fixation, grew rapidly in the larger openings. Their nitrogen contribution may have resulted in more rapid growth of the forest even after they were shaded out by larger trees of other species. The researchers reported that in this type of mixed deciduous forest, sprouting from stumps and roots rather than from seed germination was the most important mode of forest regeneration in openings of all size. This type of sprouting moderated the differences in species composition in response to gradients of light, moisture and nutrient resources in openings of all sizes. (Contact D.L. Phillips, 541-754-4485; phillips.donald@epa.gov)

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