In a prairie it is a grass or a forb. In the tundra, it is a shrub, herb, or lichen. If more than one species make up the dominant cover, then individuals in the suite of species are called codominants . Dominant species are often called visual essence species , for they are the ones that give a plant community its unique look. Dominance is determined by density in a plant community - that is, the total number of stems or individual plants within a given area.
Ecologists use precise sampling techniques to determine dominance.
One common technique is the use of quadrats, or plots of land with fixed dimensions. Within each quadrat, the trees, saplings, shrubs, and herbs are counted and measured. In forests, relative density, relative cover, and relative frequency are weighted to determine dominance. In herbaceous communities, dominance is determined by relative cover and frequency. You need look only as far as your garden for the answer to this question.