Resource competition and suppression of plants colonizing early successional old fields

Early colonizing annual plants are rapidly suppressed in secondary successi on on fertile midwestern old fields, while later colonizing perennials pers ist. Differences in competitive ability for above- and belowground resource s may be partly responsible for differences in species persistence during s uccession, as both light and nutrient availability may change rapidly. We f ound that, although both above- and belowground competition suppress growth of colonizing plants, belowground competition was the dominant factor in t he suppression of the annual Ambrosin artemisiifolia in 2nd-year-old fields near the W.K. Kellogg Biological Station in southwestern Michigan. Despite an ability to persist in later successional fields, seedling transplants o f the perennial Achillea millefolium were also suppressed by above- and bel owground competition, with belowground competition having the strongest eff ect. As in many old fields, nitrogen availability is the primary factor lim iting plant productivity. There was no clear difference between the species in ability to compete for N-15 from an enriched patch, although there was an indication of greater precision of foraging by Achillea. Life history di fferences between these species and consequent differences in the phenology of root growth relative to other old-field plants are likely to play a lar ge role in the persistence of Achillea in successional fields where Ambrosi a is suppressed.