A study of nucleation during primary succession was carried out on age sequences of communities at two sites in the Canadian Rocky Mountains: one at the Mount Robson moraines, British Columbia, the other at Southeast Lyell Glacier, Alberta. The study concentrated on the associations of species with the nitrogen-fixing plants Hedysarum boreale var. mackenzii at Mount Robson moraines and Dryas drummondii at Southeast Lyell Glacier because those plants might serve as nuclei for colonization by other species, thus facilitating succession. The data show that recruitment of later successional species is greater in patches of the two pioneer species, but the fact that recruitment takes place away from the plants also suggests that although there is nucleation, it is not necessary for succession at these sites. Key words: colonization, nitrogen fixation, nucleation, succession.