Competition intensity is linked to the co‐occurrence status and height differences of plant species found growing together in an old‐field community

Abstract

Abstract Experimental evidence suggests that larger plant species generally have a competitive advantage and thus should dominate communities where competition for limiting resources (i.e. water, soil nutrients, light, space and/or mutualists) is intense. Additionally, researchers have postulated that competition can generate negative co‐occurrence patterns. However, neither expectation is strongly supported by empirical evidence. In a relatively undisturbed old‐field plant community, we explored the interdependency of these expectations by examining pairwise species co‐occurrences, and pairwise species maximum height differences (measured here as the maximum potential height of the species), and by estimating competition intensity for sample plots using field transplants grown with and without neighbours. Specifically, we tested whether maximum species height differences were greater for negatively co‐occurring species pairs than for positively co‐occurring pairs found growing together. We also tested whether the maximum species height differences and co‐occurrence status of species pairs were associated with the average competitive environment they tended to be found growing in. Negatively co‐occurring species pairs found growing together differed more in maximum height than in positively co‐occurring species pairs that were more similar in maximum height. Additionally, species maximum height differences between negatively co‐occurring species pairs where higher in less competitively intense plots, whereas species maximum heights were more similar between positively co‐occurring species pairs found growing together in less competitively intense plots. Synthesis. Our results suggest an association between estimates of competition intensity generated using transplant experiments and co‐occurrence patterns. These findings contribute to our understanding of the association between size‐mediated competition and spatial organization in plant communities and provide a framework for future research in this area.