Emergence date effects on resource partitioning between diffuse knapweed seedlings.

Abstract

Diffuse knapweed (Centaurea diffusa Lam.) has reduced forage production, watershed quality, and biodiversity, and increased soil erosion on millions of hectares of rangeland. Diffuse knapweed has evolved mechanisms that allow it to dominate sites in nearly monotypic stands. Understanding these mechanisms may provide useful information in developing weed management strategies. Objectives of this study were to investigate interference, growth rates, and resource partitioning between early and late emerging diffuse knapweed seedlings. Seeds of diffuse knapweed were planted 21 March (early emerging) and 14 April (late emerging) 1993 in addition series mixtures with total stand densities ranging from 1,000 7,000 plants m-2. Shoots were harvested on 1 and 2 June 1993. The greatest interference was among coemerging seedlings. Resource partitioning ratios (51 and 1398) indicated substantial partitioning between seedlings having different emergence dates. Continuous seedling emergence may allow diffuse knapweed to occupy all available safe sites.