Plant species number, biomass accumulation and productivity of a differentially fertilized Michigan old-field.

The response of old-field vegetation to fertilization at the rate of 450 kg·N·ha-1 under different application schedules was evaluated using measurements of plant species number, biomass accumulation and structurefunction group productivity. Application of fertilizer under differing schedules at the same seasonal rate differentially affected plant species number, but not biomass accumulation. The structure-function groups productivities were differentially stimulated in response to fertilization under different schedules. These responses are discussed in terms of generated dominance and site resource availability.Structure-function groups are defined as a level of biological organization greater than the population, but less than the community. The use of such groupings is discussed as a means of viewing community interactions at a level higher than the population.