Western juniper woodlands have been the focus of extensive research and management due to range expansion and infilling that began over a century ago. Understanding juniper seed dispersal is vital to identifying processes behind this expansion. Dispersal of Juniperus seeds has generally been attributed to consumption of female juniper cones (“berries”) by frugivorous birds and mammals, which then defecate seeds after gut passage. However, recent studies have found that scatter-hoarding rodents harvest and cache juniper seeds. Rodents caching and failing to recover juniper seeds that have been removed from feces may constitute a secondary mode of dispersal that accounts for more seedling recruitment than primary dispersal by frugivores. We considered implications of juniper seed dispersal by frugivorous birds and subsequent removal of bird-passed seeds and secondary dispersal by scatter-hoarding rodents by examining the distribution of western juniper seeds after dispersal by birds along transects extending from a juniper woodland into a 30-year-old burn. In winter 2016, we surveyed 4 microsites (open, shrub canopy, juniper canopy, and rock) across the wooded and burned habitats for bird-dispersed seeds and repeated surveys 6 months later to determine the degree to which rodents had removed seeds. Western juniper seeds were more abundant in winter than in summer surveys, in the woodland than in the burned habitat, and under juniper canopies compared with the other microsites. There was a significant inverse relationship between the number of bird-dispersed seeds in each microsite and the distance of the microsite from the woodland. We suggest that scatter-hoarding rodents are important to the dispersal process, as they remove seeds from high-density microsites, such as tree canopies, and redistribute them. We consider the relevance of these findings to western juniper woodlands experiencing infilling and expansion, as well as to those impacted by climate-induced mortality.
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13 July 2017
Distribution of Western Juniper Seeds Across an Ecotone and Implications for Dispersal
Lindsay A. Dimitri,
William S. Longland
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Western North American Naturalist
Vol. 77 • No. 2
July 2017
Vol. 77 • No. 2
July 2017