HERBACEOUS WETLANDS OF THE YUCATAN PENINSULA - COMMUNITIES AT EXTREMEENDS OF ENVIRONMENTAL GRADIENTS

Distribution of wetland communities and growth characteristics of domi nant macrophyte species were studied in the SE and NW parts of the Yuc atan Peninsula. Plant, water and soil samples were collected from 30 m arshes ranging from permanently flooded to seasonally drying. Marsh so ils were identified as either peats, marls or clays with many intergra des. Water quality ranged from mesosaline (chloride or sulfate dominat ed) to fresh (carbonate dominated). Nutrient concentrations, specifica lly phoshorus, were low. The dominant species were Typha domingensis ( TD), Cladium jamaicense (CJ), Eleocharis cellulosa (EC), E. interstinc ta (EI), and algal mats composed mostly of blue green algae (BG). EC a nd BG dominate marshes with marry soils and high salinities. CJ grows well on peaty soils and is well adapted to extremely low phosphorus co ncentrations and occasional drying. TD dominates nutrient rich marshes with deep water and clayey soils. The species differ significantly in their growth, death and decomposition rates. All these rates are high est for TD, followed closely by EC, and slowest for CJ.