HYDROGEOMORPHIC CONDITIONS LIMITING THE DISTRIBUTION OF BALDCYPRESS IN THE SOUTHEASTERN UNITED STATES

Baldcypress is a dominant species in the alluvial valleys of the Coastal Plain of the southeastern United States. It is mostly absent, however, in the surrounding regions. An investigation of the northern boundary of baldcypress along streams flowing into the Coastal Plain indicates that a major factor limiting its distribution is high seasonal water-level fluctuations. Initial seedling establishment is dependent on water-level fluctuations. Seeds are dispersed by flood water, and germination occurs after their deposition on exposed surfaces as the water recedes. However, baldcypress seedlings are killed when completely submerged for longer than a few days. Seasonal water-level fluctuations increase with distance upstream, and eventually a point is reached along these streams where seedlings almost always are killed by high flood waters during the years following their establishment. This appears to be an important factor controlling the upstream boundary of baldcypress. The natural hydrology of most Coastal Plain streams has been altered by efforts to control flooding, mostly through dams and channelization. Baldcypress regeneration requires a narrow range of hydrologic conditions, and human-induced changes in seasonal water-level fluctuations likely will affect the northern boundary of baldcypress. Key words: Coastal Plain, floodplain, Taxodium, wetland.]