ABOVEGROUND BIOMASS AND NET PRIMARY PRODUCTION ALONG THE HOG ISLAND CHRONOSEQUENCE

John J. DiLustro and Frank P. Day

Aboveground biomass was examined along the Hog Island dune chronosequence. The dominant species were Ammophila breviligulata and Spartina patens. Aboveground biomass was harvested monthly from ten quadrats on dunes 6, 24, 36, and 120 years old. Sampling was conducted from April to November 1993. Biomass values were greater for younger dunes. Total aboveground biomass decreased with increasing site age and ranged from 152 g m^-2 on the 120 year old dune to 205 g m^-2 on the 6 year old dune in October 1993. Spartina patens biomass was greater than Ammophila breviligulata for the 6, 24, and 36 year old dune ridges. It also showed a pattern of decreasing biomass with increasing dune age; in July it ranged from 72 gm^-2 to 5 gm^-2. The same month showed less variation in Ammophila breviligulata; it increased from 17 g m^-2 to 39 gm^-2 across increasing dune age. Ammophila breviligulata had greater biomass for only the 120 year old dune. Net aboveground primary productivity did not vary greatly among different age dunes. There appeared to be a midsummer decline in biomass due to drought conditions. The aboveground net primary production (ANPP) from the sum of species peaks was 259 g m^-2yr^-1 for the 6 year old dune, 226 g m^-2yr^-1 for the 24 year old dune, 256 g m^-2yr^-1 for the 36 year old dune and 274 g m^-2yr^-1 for the 120 year old dune. Nitrogen and phosphorus concentrations in plant tissue were low. Biomass and nutrient values are reflective of production in a stressed environment. The variation in production of aboveground biomass across dune age may be controlled by moisture, microclimatic conditions and soil nitrogen levels.