Understory Response to Canopy Gaps of Varying Size in a Mature Oak Forest

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Abstract
Canopy gaps were studied in a mature oak forest to determine whether gap size is an important variable controlling the mode of response of the understory vegetation. A severe gypsy moth defoliation produced single- and multiple-tree openings, and the vegetation in these openings and in matched control sites was censused to see whether new plants became established or whether existing plants reorganized their division of resources within the gap area. Apparently no new establishment of plants had occurred. The vegetation had reorganized itself with understory species, principally Cornus florida, becoming the most important element in the lower stratum. The understory species evidently occurred in patches of high relative density, within which canopy-tree reproduction was apparently inhibited or excluded. Because most of the gypsy moth-caused gaps were smaller than these patches of understory growth, gap size did not appear to affect the mode of response of the vegetation. Gap dynamics can probably be understood, and perhaps predicted, by superposing the pattern of canopy openings on the patchwork of understory-species growth in the disturbed sand.