While a trend toward western juniper (Juniperus occidentalis spp. occidentalis) super-dominance in big sagebrush (Artemisia tridentata) communities of the Pacific Northwest since the late 1800s has been well documented, establishment dates of western juniper in less disturbed environments have not. In this paper we document the establishment history of western juniper on 2 minimally disturbed research natural areas that have substantial differences in their physical characteristics. On each site we randomly established twenty 0.05-ha plots to obtain per hectare counts of mature and juvenile western juniper and to obtain a sample of 100 trees closest to the plot center. These trees were then dated using standard dendrochronological techniques. The lower-elevation, more xeric site has an establishment history that suggests it is an emerging western juniper woodland, with the majority of trees sampled establishing since 1978. The higher-elevation site is an older, well-established woodland with a more even temporal distribution of trees. These results suggest that suitable establishment sites may switch from canopy dependence in emerging woodlands to open sites in mature woodlands and that neither domestic livestock grazing nor active fire suppression is a required mechanism for establishment.
Soulé, Peter T. and Knapp, Paul A.
"Juniperus occidentalis (western juniper) establishment history on two minimally disturbed research natural areas in central Oregon,"
Western North American Naturalist: Vol. 60
, Article 3.
Available at: http://scholarsarchive.byu.edu/wnan/vol60/iss1/3