What traits give a plant species a competitive edge?

Competition is an interaction between living organisms for resources, space or other prizes where ultimately there is a winner and loser(s). As a society we love competition, it forms an enate part of our character, with some even saying humans thrive on it. Some people might prefer team competitions, e.g. cricket, ice hockey (GO CANADA GO!), baseball; some people might prefer one on one competitions, e.g. boxing, singles tennis, ultimate fighting; then others might (particularly plant ecologists like me) prefer competitive interactions between plant species!

Finding generalised traits that make some plant species competitive suppressors or tolerators, could provide us with key guidelines on the traits to look out for before introducing new plant species. In an interesting new study, Wang et al. (2010) sets up a traditional pairwise competition trial with a twist. They use two ‘phytometers’ or ‘reference species’ (two commonly assessed species for competitive ability, Poa pratensis and Achillea millefolium) and 22 focal species. They then measure different root and shoot traits and correlate these traits to competitive hierarchies. They find that the ability of a plant species to suppress the growth of another species (competitive effect) does not vary with resource availability; while, the ability of a plant species to tolerate competitive interactions (competitive response) does vary with resource availability. I think the ‘twist’ or most interesting part of the experiment comes with the correlations of traits. They find that the ability of a species to suppress the growth of another is correlated with size-related traits and tolerance is related to resource availability. I think this is an interesting finding for restoration because it suggests size/growth traits are inherent but stress tolerance can be managed by changing resource availability. Resource manipulation might be a way of shifting conditions towards favouring the growth of more desirable species if you have a competitive species that you need to get rid of. Although the results of this study are difficult to extrapolate to the field because it was performed under controlled glasshouse conditions, and the short length of the study (60 days), I admire the study for its simple design and think the findings would be interesting to test further in a field trial.

Wang, P., Stieglitz, T, Zhou, D.W. and Cahill, J.F. 2010. Are competitive effect and response two sides of the same coin, or fundamentally different? Functional Ecology, 24, pg. 196-207

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