Disturbed Alpine Ecosystems: Seedling Establishment of Early and Late Seral Dominant Species

This study examined the effects of seedbed and seedling environment on establishment of early and late seral dominant alpine species. Species studied included late seral dominant forbs (Geum rossii, Artemisia scopulorum, and Polemonium viscosum), early seral dominant forbs (Potentilla diversifolia and Sibbaldia procumbens), a late seral dominant grass (Festuca idahoensis), and early seral dominant grasses (Calamagrostis purpurascens and Deschampsia cespitosa). Germination responses of each species to wet vs. dry cold stratification and light vs. dark conditions were investigated. No statistical differences were observed in the seed germination of early and late seral dominant forbs or early and late seral dominant grasses, but significant differences were observed in the responses of grasses and forbs. Seed germination of forbs was greater under light than dark conditions and following wet cold storage. Effects of fertilization on growth responses and nutrient uptake of G. rossii and D. cespitosawere evaluated in a factorial greenhouse experiment in which seedlings of each species were grown at four levels of nitrogen (N) and phosphorous (P). The late seral dominant forb responded more like a species from a low-nutrient environment exhibiting lower relative growth rates, higher root:shoot ratios, and a smaller response to N than the early seral dominant. A field experiment on the Beartooth Plateau, Montana, examined the soil environment and seedling emergence, growth, and survival of seeded early and late seral dominants on loamy sand soils of a severe disturbance and on peat soils of an undisturbed area during two growing seasons. Effects of fertilizer and mulch were examined on the severely disturbed area. Differences between uncleared turf and turf cleared of vegetation (gap disturbance) were evaluated on the undisturbed area. The gap disturbance had higher levels of N and P and warmer soil than the severe disturbance or vegetated undisturbed area. Soil water potentials were never low enough to result in plant stress. Seedling growth was slow - .005 g to .04 g dry weight the first growing season and .02 g to .20 g the second growing season. Growth was greatest on the gap disturbance and on fertilized plots of the severely disturbed area. Early seral dominants had the largest seedlings and the smallest R/R+S ratios. Mortality was low - odds of .50 were rarely exceeded even after two years. Survival was higher on warm, nutrient rich soils of the gap disturbance. Mulch increased emergence and survival on the severe disturbance. Fertilization increased mortality, probably because an initial pulse of N was followed by a rapid decline. Higher mortality occurred in 1986 than 1985 as 1986 had a shorter growing season and cooler air and soil temperatures early in the growing season