Plant reproductive ecology and community structure along a subalpine snowmelt gradient Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1831cn47r

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  • The seasonal duration of snow cover is a primary factor influencing the patterns of vegetation in high subalpine and alpine environments, but little is known concerning the responses of plant reproduction and seedling recruitment to gradients of snow-release. Vegetation patterns of a high subalpine site in the Oregon High Cascades were described and related to important environmental factors. Life history stages constraining reproduction and recruitment of five perennial alpine species were investigated by monitoring phenology, reproduction, and the emergence and survival of experimentally sown seedlings. Abundance of the persistent buried seed bank was assessed. Detrended Correspondence Analysis ordination revealed timing of snow-release to be the primary factor influencing vegetation patterns on the site. Degree of soil development was next in importance. Nine community types were identified, representing shifts in species dominance in response to these two gradients. Seven of these community types are widespread in alpine or high subalpine areas in the Pacific Northwest. Reproductive phenologies of four of the five species were significantly compressed in response to late snow-release. The short growing season does not limit seed production in four of the five species; fertilization failure, fruit abortion, and seed predation did limit seed production of four species in one year. Seedling emergence and establishment were extremely low, occurring almost exclusively in protected microsites away from mature plants. For all species, the primary loss of potential offspring occurred between seed dispersal and seedling emergence, and was attributed to lethal effects of high soil surface temperatures and drought. The abundant persistent seed bank was heavily dominated by two species with very low cover in the standing vegetation. Even bare soils contained large numbers of seeds, indicating that the establishment of vegetation on the site is not limited by availability of seeds, but of seedling safe sites. Patterns of reproduction and recruitment explain much of the existing vegetation patterns on this site. A more complete explanation would also require an understanding of the responses of reproduction and recruitment to longterm environmental fluctuations.
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