Plant response to heterospecific neighbor removal and nutrient addition ina subarctic coastal dune system (northern Quebec, Canada)

Removal of heterospecific neighbors and addition of nutrients were performe d In the field, on a subarctic coastal dune system in northwestern Quebec ( Canada), to test for the significance of interspecific interactions and nut rient availability on plant performance. Elymus mollis and Lathyrus japonic us, the major species found on the second ridge (approximately 150 years ol d) of the dune system were studied. Nutrient addition increased the perform ance of bath E. mollis and L, japonicus. However. heterospecific neighbor r emoval had no significant effect on either species. Most importantly, there were no significant interactions between heterospecific neighbor removal a nd nutrient addition in any of the analyses of variance performed on the re sponse variables, for either one of the two species. These results suggest that nutrient availability does not influence species interactions in the s ystem, and that limiting abiotic conditions may restrict plant-plant intera ctions even on somewhat older ridges. Temporal and/or architectural niche s egregation between the two species studied may also explain, in part, the a bsence of biotic interactions.