Reproductive Output of Pinus albicaulis (whitebark pine) at Alpine Treelines

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University of Montana Conference on Undergraduate Research (UMCUR)

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Bunker, Jesse Austin
ScholarWorks at University of Montana
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Subalpine Pinus albicaulis (whitebark pine) are experiencing high rates of mortality due to outbreaks of native Dendroctonus ponderosae (mountain pine beetle) and the exotic fungal pathogen Cronartium ribicola (the cause of white pine blister rust). P. albicaulis in the alpine treeline ecotone appear to escape D. ponderosae attack. This habitat may serve as a refuge for P. albicaulis during periods of extreme beetle pressure. However, treeline ecotones can only be functional refuges if they’re able to reproduce. To date, no one has documented cone production, seed set, or seed viability in treeline P. albicaulis individuals, although reproductive output has been studied at lower elevations. We surveyed reproductive characteristics of P. albicaulis in treeline ecotones at six sites in five mountain ranges in the northern Rocky Mountains to quantify sex allocation and cone density. We harvested seed-cones to record seed-cone traits and seed quality for P. albicaulis at two of our treeline sites. We also compared x-ray imagery and float test techniques for determining seed viability in P. albicaulis. We found that: the majority of individuals within treeline ecotones are not currently reproductive, and those with reproductive structures are mostly male (83.3%); cone density is substantially lower than it is in subalpine stands; and cone size, seed potential and set, and seed size and viability appear to be drastically lower at treeline ecotones than subalpine forests.