Interspecific Competition for Space Between Wetland Plants with Clonal Growth

Abstract

Several plant species of wetland habitats expand through clonal growth, often forming dense, nearly monospecific stands. Adjoining interspecific colonies represent an ideal model for testing hypotheses about competitive interactions between clonal species and developing predictive theories on plant competition for space. In this study, we evaluated the outcome of competition between colonies of Phragmites and Typha. First, we compared the progression and density of colonies in roadside ditches 1) at the zone of contact of two well-established monospecific colonies, and 2) in zones where the progression fronts are free from competition. Second, we used an experimental mesocosm approach to simulate competition for space between two plant colonies. The experiment was done under three salinity levels in order to better understand how deicing salt may influence interspecific competition. In roadside ditches, Typha did not slow down Phragmites progression. In the mesocosm experiment, both species showed optimal growth in low salinity, but Phragmites was superior at all salinity levels. In opposition to previous classical pair-wise experiments, the results of our experiments on Phragmites – Typha interactions concur with field evidence of dynamics between neighboring colonies. Our experiment approach succeeds in better simulating competitive interactions for space between plants with clonal growth.