Most plant species are capable of both sexual and asexual (clonal) modes of reproduction. Species that exhibit clonal reproduction tend to predominate in environments with limited resources compared to individuals that display sexual reproduction. Theory suggests that sexual and clonal populations can be geographically partitioned across the landscape in response to habitat heterogeneity. Populus tremuloides (quaking aspen) displays reproductive flexibility; it reproduces using both sexual and clonal means, although asexual reproduction is reported to be most common. We measured the influence of habitat heterogeneity in P. tremuloides through a genetic analysis of seven population, three from Montana and four from Idaho. Populations were collected from bottomland and upland habitats. Genetic variability was assessed using random amplified polymorphic DNA analysis (RAPD’s). Genetic variability in bottomland populations of P. tremuloides is considerably higher than that detected in upland populations. Three upland populations, Twin Meadow, MT, Brundage Mountain, ID, and Cat Creek Hillside, ID, contained only one to two genotypes. In contrast, three of four bottomland populations contained many more genotypes. Similar to the three upland populations, only two genotypes were detected in the bottomland population from Lake Fork, ID. The average clonal diversity for upland populations was 0.077. The average clonal diversity for bottomland populations was 0.600. These data suggest that upland populations experience considerable clonal recruitment, while sexual recruitment seems more prevalent in bottomland habitats. Habitat heterogeneity appears to be an important process determining mode of recruitment and level of genetic variation within populations of P. tremuloides.

Key words: environmental heterogeneity, genetic variability, mode of recruitment, Populus tremuloides, quaking aspen, salicaceae