Spatial studies in the Chihuahuan Desert of associations with Larrea shrub islands found juveniles more often associated with shrub islands than unassociated. The spatial structure of the shrub islands points to Nurse Plant facilitation of seedlings. Experiments tested the effects of canopy, shrub islands, and understory on five perennials' germination. Longer survival times, but not higher germination, of Zinnia acerosa were found beneath artificial canopies in intershrub areas and cleared shrub islands as compared to intact shrub islands. Therefore, Zinnia may be poor competitor, preferring germination microsites with few competitors, regardless of Nurse Plant effects.

Ogden, UT