| Summary |
Bald cypress (Taxodinm distichum) was studied at three sites along Albemarle Sound in northeastern North Carolina. At each site, there was an offshore stand of bald cypress which we termed a "Cypress Fringe". Behind the cypress fringe was a sandy beach, a small sand berm and finally a swamp forest of mixed bald cypress - t︢p︣elo gum. Observations of the swamps revealed no bald cypress or t︢p︣elo gum seedlings although some young t︢p︣elo gum trees were noted. However, bald cypress seedlings were observed growing on the storm tide driftline along the beach. In order to determine whether the light intensities in these swamps were too low to support the growth of seedlings, bald cypress and t︢p︣elo gum seedlings were grown under controlled environmental conditions. Seed germination experiments using selected temperature regimes revealed that both bald cypress and t︢p︣elo gum seeds germinated best at 30/20°C and 35°C. Following germination of the seed, seedlings were grown to a mean height of 13 cm for use in growth G20981 response experiments. The plant growth chambers supplied four different light regimes. Light intensity, which was measured as Photosynthetically Active Radiation (PAR), roughly simulated field conditions as follows: PAR-27 (swamp), PAR-308 (intermediate), PAR-641 (beach) and PAR-1000 (full sunlight) . After 3 months exposure of the seedlings to long day conditions statistical analysis of the data revealed that the seedlings in treatment group PAR-641 (beach) produced significantly higher values for each parameter measured (p < 0.01), with the exception of chlorophyll concentration per unit leaf area, than did the seedlings in the other three treatment groups. PAR-641 seedlings were taller, sturdier, and exhibited large diameters and higher dry weights. Seedlings grown under "swamp" conditions (PAR-27) produced short, slender stems, and lower dry weights. Species comparison yielded higher values for t︢p︣elo gum seedlings for the following parameters: incremental growth rates; leaf area; wet weight; total dry weight; each compartment of biomass partitioning: leaves, roots, and stems; and stem diameter. Bald cypress seedlings exhibited higher chlorophyll concentrations, higher root/shoot ratios and greater photosynthetic ratios than t︢p︣elo gum seedlings. The bald cypress fringe functions in its own regeneration. It serves as a seed source, dropping its seeds in the water where they are washed up on the driftline. And, as the field studies have shown, the cypress fringe also functions to trap sand and sediment, thus retarding erosion. The offshore bald cypress trees also dampen wind and wave energy that would destroy otherwise unprotected cypress seedlings. Estimation of maximum local erosion rates was shown to be possible in areas with an offshore stand of bald cypress trees. It is proposed that t︢p︣elo gum will, in the distant future, replace bald cypress over most of its range. It appears that, with constant stress from rising sea level, erosion, and angiosperm competition within the swamp, the range of bald cypress may be reduced to cypress domes and protected river systems in Florida. |
