Growth and Survival of Giant Ragweed (Ambrosia trifida L.) in a Delaware River Freshwater Tidal Wetland

Abstract

SICKELS, F. A. AND R. L. SIMPSON (Biology Department, Rutgers University, Camden, NJ 08102 and Biology Department, Rider College, Lawrenceville, NJ 08648). Growth and survival of giant ragweed (Ambrosia trifida L.) in a Delaware River freshwater tidal wetland. Bull. Torrey Bot. Club 112:368-375. 1985.-The survivorship, phenology, production, and distribution of the annual species Ambrosia trifida L. in a Delaware River freshwater tidal wetland were studied during 1982. Germination began in mid April with maximum seedling density (x = 104.5, S.D. = ?58.1 m-2) reached in mid May. Survivorship exceeded 92% through June and then declined gradually to 23% by late September. Flowers were initiated in late July with seeds ripening in September. Maximum height (298.8 ? 33.7 cm plant-') was attained in late September as was maximum shoot (73.8 ? 45.6 g plant-') and root (32.7 ? 37.0 g plant-') biomass. Peak standing crop (3265.6 g m-2 shoot and 1500.9 g m-2 root) occurred in late August. Leaf mortality was 162.1 g m-2. Net production corrected for leaf loss and survivorship was 6573.8 g m-2, the highest rate of production yet reported for a freshwater tidal wetland macrophyte. Seed production, estimated in late September, was 12,9'58 seeds m-2 with 17% showing signs of predation; apparent survival was 1% based on maximum seedling density. Transplant experiments showed that Ambrosia seedlings survived to reproduce in two locations, its normal levee habitat and near the upland forest border, a habitat isolated from a seed source. Transplants did not survive in the stream channels, apparently due to scouring and length of inundation or in the poorly drained high marsh due to lack of tolerance of seedlings to water-logged soils and to shading by other species. Thus, although Ambrosia trifida can dominate the levee habitat, its colonization of other habitats seems doubtful.