DISPLACEMENT OF ANDROPOGON SCOPARIUS ON THE NEW JERSEY PIEDMONT BY THE SUCCESSIONAL SHRUB MYRICA PENSYLVANICA

Andropogon scoparius, a perennial grass found in old fields on the New Jersey Piedmont, can be invaded and displaced by a nitrogen-fixing shrub, Myrica pensylvanica. The progression of Andropogon displacement was followed over a season, and possible contributing mechanisms (shading, allelopathy, physical effects of Myrica litter) were tested through field and greenhouse experiments. In the field, Andropogon seedling growth was inhibited beneath Myrica clumps, and mature plant living crown area was reduced. In the greenhouse, Andropogon seedling growth was reduced significantly in pots with mature Myrica. Both seedling and mature growth of Andropogon were reduced under shaded conditions. No inhibitory physical effects of Myrica litter on Andropogon seed germination or mature plant growth were found; however, there may ba allelopathic effects of Myrica litter leachate on Andropogon seedlings growing under shade or within grass litter, and on mature Andropogon in shaded conditions. Andropogon displacement appears to be the result of a complex interaction of Myrica shade, allelochemic, and competitive effects, rather than being attributable to any single mechanism.