Spatial Patterns of Biomass and Aboveground Net Primary Productivity in a Mangrove Ecosystem in the Dominican Republic

Abstract

The objective of this study was to quantify spatial patterns in above- and belowground biomass, primary productivity, and growth efficiency along a tidal gradient in a 4700-ha mangrove forest in the Dominican Republic. We tested the hypothesis that spatial patterns of forest structure and growth following 50 years of development were associated with variations in the soil environment across the tidal gradient. Twenty-three plots were monitored from 1994 to 1998. Aboveground biomass and biomass accumulation were estimated by applying allometric regression equations derived from dimension analysis of trees harvested at our study site. Soil porewater salinity ranged from 5 to 38 g kg -1 across the tidal gradient, and most measurements of forest biomass and productivity were inversely related to salinity. Mean standing biomass (233 ± 16.0 Mg ha -1 ; range, 123.5-383.5), biomass increment (9.7 ± 1.0 Mg . ha -1 y -1 ; range, 3.7-18.1), annual litterfall rates (11.4 Mg . ha -1 yr -1 ; range, 10.2-12.8), leaf area index (LAI) (4.4 m 2 . m -2 ; range, 2.9-5.6), aboveground net primary productivity (ANPP) (19.7 Mg . ha -1 y -1 ; range, 15.6-25.0), and growth efficiency (1.6±0.2 kg . ha -1 y -1 ; range, 1.0-3.6) all showed an inverse linear relationship with salinity. Fine-root biomass (≤ 2 mm) (9.7 ± 1.2 Mg . ha -1 ; range, 2.7-13.8) showed a weak tendency to increase with salinity, and the ratio of root to aboveground biomass increased strongly with salinity. Our results suggest that physiological stresses associated with salinity, or with some combination of salinity and other covarying soil factors, control forest structure and growth along the tidal gradient. The higher allocation of carbon to belowground resources in more saline sites apparently contributed to reductions in ANPP along the tidal gradient.