A Comparison of the Structure, Primary Productivity, and Transpiration of Cypress Ecosystems in Florida

Abstract

To investigate how inputs of water and nutrients influence the structural and functional characteristics of cypress wetlands, primary productivity, respiration, transpiration, tree growth, biomass, basal area, stem density, standing stocks of phosphorus, and litterfall were measured in several kinds of Florida cypress ecosystems subjected to varying inflows of water and nutrients. A scrub cypress forest, natural and sewage—enriched cypress domes, and a cypress floodplain forest were studied. Floodwaters in these ecosystems ranged from stagnant and phosphorus poor (0.01—0.08 mg P/L) to flowing and phosphorus rich (0.66—5.86 mg P/L). Inputs of total phosphorus transported by water to these forests varied from 0.11 g P°m—2°yr—1 in the scrub cypress forest to 1625 g P°m—2°yr—1 in the floodplain forest. Phosphorus content of aboveground biomass (ranging from 0.25 to 4.78 g P/m2) appeared to be positively related to phosphorus inputs. Biomass and other structural characteristics of the study sites appeared to be related to stand history rather than to phosphorus inputs. For example, there was little difference in aboveground biomass between natural cypress domes (20.6—26.6 kg/m2), a sewage—enriched dome (21.7 kg/m2), and a floodplain forest (28.4 kg/m2). Aboveground biomass for the scrub cypress forest was low (3.6 kg/m2). Net daytime photosynthesis (2.1—13.7 g C°m—2 ground surface°d—1), plant respiration (0.9—10.9 g C°m—2) ground surface°d—1) and an estimate of gross primary productivity increased with increasing inputs of total phosphorus. Aboveground biomass production (sum of wood production, ranging from 44 to 1080 g°m—2°yr—1, and litterfall, ranging from 224 to 941 g°m—2°yr—1) increased with increasing total phosphorus inputs in the low range, but biomass production leveled in the high input range. Total water loss from cypress forests increased with increasing P inputs. Mean daily transpiration rates from the scrub cypress forest (1.0 mm) and cypress domes (3.1—3.8 mm) were lower while those from the floodplain forest (5.6 mm) were similar to evaporation rates from open water bodies. Ratios of transpiration to net daytime photosynthesis were also low (156—221 g H2O/g organic matter), showing that cypress is efficient in its water use. In cypress domes and scrub cypress forest, where water may be limiting, trees appear to adjust t potential water stress through leaf morphology adaptations and minimum canopy development (leaf area index, LAI = 0.53—3.4 m2/m2). When water is not potentially limiting, as in the floodplain forest, adaptations to conserve water were lacking (e.g., LAI = 8.5 m2/m2). A dome with added sewage effluent had higher leaf biomass, leaf area index, and chlorophyll ° content, and more phosphorus stored in leaves than untreated domes. Net primary productivity, litter production, and wood production increased approximately twofold over pre—effluent rates or untreated cypress domes.