Competition, survivorship and growth in macrophyte communities

SUMMARY. 1. Transplant experiments tested the proposition that the intensity of competition within macrophyte communities varies with standing crop in a freshwater marsh in Ontario, Canada.
2. Transplants of three species ( Carex lasiocarpa, Juncus brachycephalus, Scripus validus ) were grown at sixty-six locations chosen to represent a range of standing crop values. At each location, transplants were grown in plots with all neighbours removed and in adjacent plots with all neighbours present.
3. The effect of neighbours on transplant growth did not vary with standing crop, soil, or water depth, with the exception of one species which was most suppressed by neighbours in shallow water. In contrast, the effect of neighbours on the survivorship of transplants was greatest on organic soils supporting high values of standing crop in shallow water, and least on mineral soils supporting low values of standing crop in deeper water.
4. The results indicated that establishment and survivorship of vegetative propagules was most likely to be affected by neighbours in shallow water, but that the growth of established plants was not influenced by neighbours anywhere. Growth results corroborate earlier findings that competition has little effect on aquatic macrophytes.