Plant ecology's guilty little secret: understanding the dynamics of plant competition

Abstract

Summary1. Plant competition has been studied for decades. Yet, it is still an elusive concept that means different things to different people, is resistant to direct study and is shrouded in semantic and statistical complexity. We still lack basic information about many competitive mechanisms, processes and outcomes and their relationship to other ecological processes, and about how local interactions between individuals are propagated through communities. We suggest here that two critical issues have been overlooked in previous studies. 2. First, there is a need for direct measurements of the process of competition as opposed to indirect mechanisms of competitive outcomes. Biomass has become the 'industry standard' for measuring competition, but we suggest that biomass cannot provide unambiguous insights into plant competition because it is the product of too great a range of factors and processes. 3. Second, the use of a single measure of competition at an arbitrarily assigned end point of an experiment misses much of the complexity of dynamic interactions between competing plants and can lead to erroneous interpretations. Here, we suggest approaches to handle these difficulties, using new techniques or the application of well-known methods in a novel way. We also provide examples of systems or questions where the improved understanding these approaches could bring would be of particular benefit. 4. Ultimately, we suggest the need for a major shift in the way in which we consider and measure plant competition to identify broadly agreed rules for variation in its importance, its role in different communities and habitats, and how and whether it influences or drives patterns of species diversity and abundance.

Functional Response (FR) and Relative Growth Rate (RGR) Do Not Show the Known Invasiveness of Lemna minuta (Kunth)

“…Moreover, our results underline the fact that comparing RGRs of monocultures only depicts the potential direct competition and neglects more important indirect competition and interactions on the long run [53]. Consequently, the relative growth rate provides information on biomass-based competition and dominance [50], though is insufficient to describe or predict the invasive potential of macrophytes as no significant differences in RGR were observed.…”

Resource competition in plant invasions: emerging patterns and research needs

“…They showed that native perennial grasses were subject to both intra- and interspecific competition with invasive annual species during early growth stages, but the type of competition differed among four harvests. This suggests that the relative importance of intra- vs. interspecific competition varies among harvests during the early stages of plant growth (Mangla et al, 2011b; see Trinder et al, 2013) and emphasizes the importance of examining competition at several points in time (Foster and Gross, 1997, 1998; Gibson et al, 1999), particularly when comparing species characterized by different life cycles (Gibson et al, 1999). …”

Growth trajectories and interspecific competitive dynamics in wheat/maize and barley/maize intercropping

“…Plant biomass at one harvest is an outcome of plant growth up to that point, so a single harvest cannot reveal the processes involved (Trinder et al 2012). Plants' competitive interactions are dynamic and change over the course of growth (Zhang et al , 2012Trinder et al 2012Trinder et al , 2013. Studying plant competition dynamically can provide a better picture of how interspecific interactions develop over the course of the growing season (Andersen et al 2007) and improve our understanding of the mechanisms underlying plant-plant interactions.…”