- The purpose of this study was to develop a plant
association classification for the mature coniferous
forests of the McDonald and Paul M. Dunn Research Forests.
A secondary objective was to quantify diversity within the
plant associations. This Forest is approximately 11,000
acres and is located 6 miles to the north of Corvallis
Oregon. This forest is owned and managed by the College of
Forestry at Oregon State University.
This study, and a companion study by Leavell (1991),
was funded by the Research Forest to broaden their
understanding of the plant communities on the Forest. The
companion study developed relationships between the plant
associations and the environment.
Classification was based on 108 plots, using percent
cover of trees, shrubs, forbs, and grasses. This sampling
density of approximately 1 plot per 100 acres is much greater than most community classifications in the area
(Hemstrom & Logan, 1986; Hemstrom et al., 1987; Topik et
al., 1988; Juday, 1976). A total of 117 vascular plant
species were encountered; 68 of these were used in
classification. Stands sampled for this classification
were primarily seral, yet the most mature available. Few
climax stands were available for sampling.
Plant associations were developed using TWINSPAN, a
two-way indicator species analysis (Hill, 1979b). Six
plant associations were developed and described in this
Tsuga heterophylla/Acer circinatum-Gaultheria shallon
Abies grandis/Acer circinatum-Gaultheria shallon
Abies grandis/Disporum hookeri-Thalictrum occidentale
Abies grandis/Polystichum munituin
Abies qrandis/Rubus ursinus-Rhus diversiloba
Abies randis/Brachypodium sylvaticum
One plant association, Abies grandis/Acer circinatum-
Gaultheria shallon, parallels a previously described plant
association described by Juday in the Valley Margin Zone
(Juday, 1976). The other 5 plant associations described in
this study are original descriptions.
The TSHE/ACCI-GASH, ABGR/ACCI-GASH, and the ABGR/RUURRHDI
plant associations are shrub-dominated. ABGR/DIHOTHOC
and ABGR/POMU are forb-domjnated associations, and
ABGR/BRSY is a grass-dominated plant association. Plant associations were shown to have significant
differences in species richness, heterogeneity, evenness,
and in vertical structure. Average species richness per
plot is highest in the ABGR/ACCI-GASH and ABGR/DIHO-THOC
plant associations, which also has high relative diversity
(Shannon's index) and evenness. Species richness is lowest
in the TSHE/ACCI-GASH plant association, probably because
it was represented only by seral stands.
Structural diversity included an analysis of snags.
Snag number, size, and distribution were not related to
plant associations. Current snag levels indicate that at
most, 30 percent of the maximun populations for six
woodpecker species could be supported on this Forest.
A description of each plant association is given. The
description for each includes: extent, location,
characteristic species, species richness and percent cover
within four strata (trees, shrubs, forbs, and grasses),
heterogeneity (Shannon' s diversity index), and an evenness