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Harvard Forest Symposium Abstract 2013

  • Title: Masting and mortality in whitebark pine (Pinus albicaulis)
  • Primary Author: Joshua Rapp (Massachusetts Audubon Society)
  • Additional Authors: Elizabeth Crone (Tufts University); Casey Mangnall (Harvard Forest); Eliot McIntire (Pacific Forestry Centre, Natural Resources Canada)
  • Abstract:

    In western North America, mountain pine beetles and white pine blister rust are causing wide-spread tree mortality in whitebark pine (Pinus albicaulis), a mast-seeding tree species whose nutritious cones benefit many wildlife species. We are studying patterns of masting and mortality risk in whitebark pine at 36 sites throughout western Montana and adjacent Idaho, to shed light on the mechanisms of masting and implications of mortality for masting patterns. Since the initial surveys of these trees in 2004-2006, a mountain pine beetle epidemic has killed millions of trees in large parts of the study area. In 2011 and 2012, we resurveyed 34 of these sites to collect data on pollen and seed cone production, stem growth, pine beetle and blister rust infestation, and site characteristics. Using these data we analyzed patterns of sex allocation and the role of pollen limitation in driving masting dynamics, and are now examining the relationship between growth, cone production, and site characteristics is determining mortality risk from mountain pine beetle.



    Whitebark pine seed cone maturation increased with site pollen cone production, indicating pollen limitation, and pollen and seed cone production were positively correlated across years.

    Positively correlated pollen and seed cone production improved mature seed cone crop compared with scenarios of no synchrony between pollen cone production and seed cone initiation, negative correlation (trade-off) between seed cone initiation and pollen cone production, or no masting. Preliminary analyses suggested that trees suffering pine beetle-induced mortality had lower growth rates prior to the outbreak than surviving trees.



    Our results support a role for pollination efficiency in both increasing long-term seed production and as a proximate mechanism for synchronizing masting in P. albicaulis. Pollen limitation combined with stand isolation and reduced tree density due to mortality from forest pests and climate change may lead to reduced seed cone maturation and changes in masting patterns. Background tree health likely influences tree mortality risk from mountain pine beetle infestation. Further analyses will test whether masting patterns change in stands that have experienced declining tree density as a result of the observed mortality.

  • Research Category: Conservation and Management
    Historical and Retrospective Studies
    Invasive Plants, Pests & Pathogens
    Physiological Ecology, Population Dynamics, and Species Interactions
    Regional Studies