Gap Size and Succession in Cutover Southern Appalachian Forests: An 18 Year Study of Vegetation Dynamics

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We used clearcut logging in establishing four replicated sizes of canopy openings (0.016, 0.08, 0.4, and2.0 ha) in a southern Appalachian hardwood forest in 1981 to examine the long-term effects of disturbance size on plant community structure, biomass accumulation, aboveground net primary productivity (NPP), and mode of recovery. The reestablishment of NPP and biomass following logging was6 –7-fold greater in large than small openings by 17 years. Total biomass in the 2.0 ha openings(127.3 Mg ha)1) recovered 59.5% as NPP (19.7 Mg ha)1yr)1) reached 225% of precut forest levels.Biomass accumulation was 2.6 –3.6-fold greater in interior than edge locations of all but the 0.016 hagaps. The absence of significant patch size or edge vs. interior differences in tree densities suggests thatgrowth rates of individual trees were enhanced in more insolated microenvironments. Sprouting (86 –95% of tree NPP) was much more important than advance regeneration (4 –10%) or seedling germination (<2%) during early recovery in all opening sizes. Canopy dominant Quercus and Carya treesexhibited limited sprouting following disturbance. Instead, shade-intolerant Robinia pseudoacacia andLiriodendron tulipifera were major sprouters that used N-fixation (Robinia) and rapid growth (Liriodendron) in attaining 7.4 and 5.9 fold greater biomass accumulation, respectively in 2.0 ha than 0.016 haopening sizes. Seedling germination and understory production were extensive in all openings followinglogging, but declined rapidly as the young tree canopy began closing by 4 –6 years. The relative importanceof shade-intolerant tree biomass approximately doubled over 17 years as shade-tolerant tree seedlings,herbs, and shrubs gradually regained importance under the emerging canopy. Sprouting caused the persistence of a tree species composition in all openings that remained relatively similar to the precut forest.Large disturbances on mountain slopes of the southern Appalachians generally promote sprouting andrapid recovery, whereas small disturbances in low-elevation cove forests lead to a gradual recovery throughseedling germination and/or advance regeneration. Continued logging in the southern Appalachians willincrease the relative size and frequency of large disturbances, further the importance of sprouting of shadeintolerant species, and lead to more even-aged forest stands throughout the region.