RELATIONSHIPS BETWEEN SEED FATES AND SEEDLING ESTABLISHMENT IN AN ALPINE ECOSYSTEM

On exposed soils relationships between soil surface characteristics and seed morphological attributes often determine the microsites of seed entrapment and influence patterns of seedling establishment. I examined seed and seedling fates of alpine species with varying morphology over a range of uniform- and mixed-particle-size soils on the Beartooth Plateau, Montana. Physical relationships between seeds and surface soils determined entrapment and retention within the zone of potential emergence (0-1 cm depth). Seed size (length or mass), the presence or absence of specialized appendages or seed coats, and the nature of the appendage or seed coat influenced numbers of seeds trapped and seed distributions among the particle sizes. Antrorse hairs, hygroscopic awns, pappuses, and mucilaginous seed coats all resulted in higher entrapment over the range of particle sizes. The effectiveness of different seed morphologies was decreased by prolonged exposure (1 yr) to the environment. In contrast to seed entrapment and retention, seedling emergence and survival depended on the ability of the different particle-size soils to meet the biological requirements of the species. Although some seedling emergence occurred in particle sizes that ranged from <0.5 to 4-8 mm, almost no seedlings survived in particle sizes larger than 1-2 mm. In particle sizes in which emergence occurred, a higher percentage of the total seeds trapped survived the first, growing season as seedlings for large-seeded than for small-seeded species. For most species, the highest entrapment and retention occurred in particle sizes in which there was little or no emergence. Seedling emergence and survival were related to seed entrapment only for species with reasonably high emergence, and the R(2) values were often low. Understanding seedling establishment patterns in different-particle-size soils requires knowledge of how relationships between seed morphology and soil characteristics affect entrapment patterns, and knowledge of soil particle size thresholds for seedling establishment.