The LHS (Leaf-Height-Seed) model has been proposed as a simple trait based functional classification.  We investigated whether the two components of competitive ability i.e. competitive response (CR) and competitive effect (CE) are captured by the LHS model and whether these two components are independent for 12 coexisting Mediterranean grasses.

Two greenhouse experiments were conducted to estimate competitive effect and response of 12 coexisting grass species.  We applied a phytometer design and we calculated CR and CE using the relative interaction index (RII).  Mature plant height, seed mass and leaf dry matter content (LDMC, used as leaf traits) were measured for each species.  Correlations and tradeoffs between the three traits and the components of competitive ability CR and CE were analyzed with Principal Component Analysis (PCA).

Results/Conclusions

The LHS model was a good predictor of competitive ability but CR and CE were independent and related to different traits. CR was positively correlated with seed mass and CE with plant height.  LDMC was neither correlated to CR nor to CE.  Based on these findings, we suggest that there are three primary strategies allowing coexistence which are related to competition rather than to the commonly assumed differences in resource use, 1) large CE, i.e. large negative impact on other species, 2) large CR, i.e. resistance to competition and 3) small seeds allowing competition avoidance.