Mast-Seeding in Perennial Plants: A Test of the Pollen Coupling Hypothesis

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Seed output fluctuates dramatically over time in many plant populations. These fluctuations, often called mast seeding, directly affect numerous plant and animal species. Nonetheless, empirical tests of the proximate causes of mast seeding are virtually nonexistent. Crone and Sala will test proximate mechanisms of mast seeding in two plant species: Astragalus scaphoides (bitterroot milkvetch), a bee-pollinated wildflower, and Pinus albicaulis (whitebark pine), a wind-pollinated tree. For each species, Crone and Sala will test whether pollen availability limits seed production, and the effect of seed production on stored resources. These experiments test the assumptions of "pollen coupling" a recently proposed, but untested, hypothesis for how mast-seeding occurs. Crone and Sala will also evaluate predictions of pollen coupling models, using wide-scale geographic patterns of synchrony in whitebark pine and whole-plant manipulations of fruit set and pollen availability in bitterroot milkvetch. Fluctuations in the fruit or seed output of mast-seeding plants are a key factor regulating economically important wildlife and pest species. Whitebark pine exemplifies the importance of understanding mast seeding for management. In Yellowstone National Park, whitebark cone crop failures cause human-grizzly conflicts; managers need to predict non-mast years in order to deal with these conflicts and associated public relations. In Glacier National Park, whitebark pine has been decimated by an introduced pathogen, white pine blister rust. Predicting mast years will help managers locate and collect seeds of resistant trees, and design restoration strategies that maintain key elements of mast-seeding. In addition to direct application of research results, this project will provide educational opportunities for undergraduate and graduate students, and integrate with ongoing programs that provide research opportunities for inner-city and Native American undergraduate students.