Competitive responses of the rare Viola elatior and the common Viola mirabilis

Viola mirabilis is abundant in Estonia; Viola elatior is rare. We tested whether these species differ in their competitive responses to a common grass. We used a pot experiment in which individuals of each violet species grew with 0, 2, 4, or 8 individuals of Festuca ovina in natural soil. The response patterns of shoot and root mass and leaf numbers of the two species were similar: the biomass and leaf number of both violet species decreased with increasing grass density. The decrease of root mass of the rare V. elatior was significantly greater, and the decrease of leaf number tended to be greater, than that of the common V.␣mirabilis. We conclude that the stronger competitive response of V. elatior compared to V. mirabilis might be one reason behind its lower regional and local abundance.