Aboveground Forest Biomass and Litter Production Patterns in Atlantic White Cedar Swamps of Differing Hydroperiods

Abstract

Ecosystems dominated by Chamaecyparis thyoides (Atlantic White Cedar) are critically endangered due to hydrologic alterations associated with ditching, logging, development, and agricultural conversion. Few studies have related structural and functional characteristics of this plant community to water tables, yet hydrologic management options may be critical to establish a peat-based seed refugium and allow Atlantic White Cedar self-maintenance in this ecosystem. In this study, we assessed aboveground forest biomass, litter production, and depth to water table at a mature (60–70 y) and an intermediate (20–35 y) age-class stand in two national wildlife refuges, Alligator River (AR) and Great Dismal Swamp (DS) in North Carolina. We calculated forest biomass from morphometric data gathered within randomized study plots. We made monthly litter collections at each study plot from November 1998 to April 2000; litter was sorted by species and type for the first 12 months. Wells installed at each study plot recorded water-table levels, which were at or near the surface at AR but >30 cm below the soil surface at DS throughout the study. Although Atlantic White Cedar was a dominant species at all sites, community structure differed between refuges. Total aboveground biomass was similar among age classes; however, Atlantic White Cedar stem density was greater and mean diameter at breast height was lower at AR. Mean annual litter production was higher at AR sites for each age class despite a persistently high water table. We conclude that the rates of primary production associated with high water tables at AR represent favorable conditions for Atlantic White Cedar self-maintenance.