DigitalCommons@Linfield

Seedling Growth and Survival of Western Red Cedar (Thuja Plicata), Six Years Later

Jereld R. Nicholson Library

In 2005, western red cedar (Thuja plicata) seedlings were planted in Forest Park in Portland, Oregon to ascertain whether mammalian predation had a role in low seedling recruitment in the park. Nine study sites, three in each section (urban, middle and rural) of the park were located along an urban-rural land use gradient. At each site, 27 seedlings were planted. Each tree was randomly assigned to one of three groups: deer exclusion, rodent exclusion or control. Each was measured prior to installation of exclusion devices (March 2005). Tree height, width, basal diameter, percent of branches grazed and mortality rate has been measured annually. Preliminary results for the measurements made in summer 2011 showed that trees in the middle and far sections of Forest Park grew significantly more in terms of height, width and basal diameter than trees in the city section. Control trees grew significantly less than trees protected by rodent or deer exclusion devices. Trees in the far section had significantly more grazing by deer and elk than those in the city section, although trees in deer exclusion devices had significantly less grazing. Seedling mortality at the sites ranged from 3.7% to 70.4%. Mortality did not appear to relate to predation.