Seed production, dispersal, predation and germination of seven high elevation Rocky Mountain legume species
Date
1987
Authors
Smyth, Clinton Ross
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Abstract
A three year study of seed production, dispersal, predation, and germination was done on seven high elevation Southern Canadian Rocky Mountain legume species: Astragalus alpinus, A. bourgovii, A. robbinsii, A. vexillliflexus var. nubilus, Hedysarum sulphurescens, Oxytropis podocarpa, and O. sericea. Initiation of vegetative and reproductive activity was one to two weeks earlier each year and was related to the successively warmer springs each year.
Seed production varied with species and year. The number of viable seeds produced each year was constantly high for Oxytropis podocarpa, whereas the number of viable seeds produced by ). sericea, Hedysarum sulphurescens and t he Astragalus species was variable. The number of abnormal or aborted seeds was low except for Astragalus alpinus in 1985, Astragalus bourgovii in 1983 and O. sericea in each year. Seed production of the Astragalus and Hedysarum species was reduced by pre-dispersal seed predation by species of Bruchophagus (Hymenoptera : Eurytomidae). The magnitude of seed damage was related to habitat. Pre - dispersal seed predation by weevils (Coleoptera: Curculionidae) was low for the Oxytropis speci es. However, seed predation of O. podocarpa by ptarmigan (Lagopus lagopus) was high in two populations each year. Foraging by elk (Cervus elaphus), rocky mountain bighorn sheep (Ovis candensis) and the golden mantel ground squirrel (Spermophilus lateralis) also reduced seed production .
Seed germination varied with species, population and year. All of the viable seeds of H. sulphurescens germinated each year, whereas seed germination varied for the other species. The variation in seed germination is attributed to environmental factors such as day length, temperature or soil moisture which may have affected the production of impermeable 'hard' seeds. Various physical and chemical treatments were applied to break the dormancy of these seeds, the results of which showed that with the exception of H. sulphurescens, all species have a seed coat imposed dormancy . Seed germination in H. sulphurescens was found to be temperature regulated . Seeds of all species were observed to germinate at 2°C to 5°C. Therefore, seeds of these species may germinate in the fall and overwinter as small seedlings although seedling mortality would limit recruitment.
Oxytropis sericea was considered to be the most suitable species for revegetation of high elevation disturbances, although this evaluation was based primarily on technical factors. Several of the remaining species would be suitable , provided the technical difficulties associated with seed collection could be overcome.