Non‐hierarchical competition among co‐occurring woody seedlings in a resource‐limited environment

Abstract

Abstract Long‐term species persistence in plant communities is contingent in part on the conditions that favor establishment and early survival. In stressful habitats, facilitated seedling establishment can enhance species richness by providing a safe‐site for species unable to establish in open microsites. However, the indirect effects of seedling competition may drive persistence in locations where seedlings occur in high density. This under‐examined dynamic can influence community recovery to stress by favoring competitively dominant species, in particular when stress increases local seedling density in favorable microsites. We present the results of a response surface experiment that examines growth responses among seedlings of Ambrosia dumosa, Eriogonum fasciculatum, and Larrea tridentata that were planted at three densities and four relative frequencies. These species co‐occur at an extensively monitored reference community located in the Colorado Desert, California, USA, where extensive drought caused unprecedented mortality that will require novel recruitment for the community to reach pre‐disturbance composition. Significant, non‐hierarchical competitive responses show that seedling survival is contingent on the species identity and density of neighboring seedlings. This result supports non‐hierarchical competition among these common species. Ambrosia and Eriogonum had faster growth rates than Larrea, but also experienced larger reductions in growth from competition than Larrea. Although drought may intensify seedling competition in favorable locations, the context dependency of competitive outcomes may permit coexistence.

Keywords

• Ambrosia dumosa
• arid systems
• Colorado Desert
• Eriogonum fasciculatum
• indirect effects
• Larrea tridentata