Microtopography and vegetation in Atlantic white cedar swamps: the effects of natural disturbances

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Abstract
Disturbance may alter patterns of microtopography within wetlands, and may consequently alter the relationship between woody plants and microtopography. I measured microtopographic relief and the relationship of shrubs and tree seedling distributions to microrelief in undisturbed Atlantic white cedar (Chamaecyparis thyoides (L.) Mills.)) swamps in the New Jersey Pinelands, and in stands disturbed by blowdowns and fire. In undisturbed stands, hummock–hollow structures, at a scale of about 1 m, are poorly defined and often obscured by smaller scale and larger scale patterns of elevation. The swamp floor is, on average, 25 cm above the lowest hollows, but sites ≥ 100 cm high occur in undisturbed swamps and within blowdown gaps. Burned sites tend to lack microsites with high elevations, and have less well-developed pattern than undisturbed sites. In blowdowns, there is an increase in the frequency of high-elevation microsites, and more pronounced hummock–hollow patterning. All woody plant species occupy sites of intermediate elevation, are absent from the lowest 20% of the forest floor, and display little evidence of habitat differentiation among species along the microtopographic gradient. In disturbed sites, the species' ranges shift in response to disturbance-induced changes in the availability of microsites. Key words: microtopography, microsites, forested wetlands, swamps, spatial pattern, disturbance, Chamaecyparis thyoides, shrubs.