SEED DISPERSAL, SEEDLING SURVIVAL AND HABITAT AFFINITY IN A SNOWBED PLANT - LIMITS TO THE DISTRIBUTION OF THE SNOW BUTTERCUP, RANUNCULUS-ADONEUS

We studied the roles of seed dispersal and seedling survival in limiti ng the distribution of Ranunculus adoneus to alpine snowbed habitats. Achenes of R. adoneus fall directly below the infructescence within 15 cm of the maternal plant. Secondary seed movement is also restricted, with seeds transported only, on average, an additional 10 cm during s nowmelt the following spring. The distribution of R. adoneus seeds in the soil mirrors this view of highly restricted dispersal. Snowbed soi l contains an average of 0.033 seeds per cm3, but snow buttercup seeds are not found 20-40 m away in meadows bordering the snowbed. These fi ndings suggest that limited seed dispersal acts to confine recruitment to locations within parental habitats. Transplanted seedlings in mead ow and snowbed microsites had statistically indistinguishable survival rates over their first growing season. However, causes of seedling mo rtality differed between habitats. Risk of seedling desiccation was fo urfold higher in snowbed than meadow vegetation. In contrast, predatio n by small mammals occurred only in meadow microsites. These findings imply that genotypes appropriate for regeneration in the snowbed are p robably poorly suited for colonization of adjacent plant communities. Experimental modification of transplanting destinations in the meadow showed that microsites most conducive to growth and survival of snow b uttercup seedlings provided opportunities for rapid infection by VA my corrhizae in the absence of neighboring vegetation. Such combinations of environmental factors are probably rare and ephemeral.