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Changes in Plant Composition within a
Pinyon-Juniper Woodland
Dennis D. Austin
Ahstract-Vegetal composition and photo comparisons were determined during 1974,1984, and 1997 on seven permanent 50 m 2 plots
within a mature pinyon-juniper community in northeastern Utah.
Data and photo comparisons showed few changes over 23 years.
Within the Intermountain Region, pinyon-juniper habitat
provides a major proportion of big game and livestock winter
ranges. While it is clearly recognized that available forage of
shrubs and other species declines as density and cover of
pinyon-juniper increases, few longitudinal studies have defined the rate of change, particularly in mature woodlands.
This paper presents data and supporting photographs defining the slow rate of successional change.
Table 1-Number of plants per seven permanent, 50 m2 plots.
Year
Species
Trees
Juniperus osteosperma - mature
Juniperus osteosperma - juvenile
Pinus edulis - mature
Pinus edulis - juvenile
1974
22
16
6
2
1984
22
17
6
6
1997
22
16
6
6
52
13
76
56
9
84
63
11
74
10
67
86
15
80
68
14
34
8
13
19
8
6
11
249
110
88
34
5,366
35
259
14
215
14
15
286
99
48
19
4,468
99
244
25
154
193
40
81
9
4,444
110
241
8
104
4
18
Shrubs
Artemisia arbuscula
Artemisia tridentata
Ephedra viridis
Gutierrezia sarathrae
Other shrubs
Shrubs-Dead skeletons
77
Perennial Grasses
Methods _ _ _ _ _ _ _ _ _ __
Poa secunda
Sitanion hystrix
Data were collected in the exact methodology during 1974,
1984, and 1997 (Austin 1987), with the only exception that
data collected in 1997 were taken only from selected plots
with photo points.
Each plot measured 5.5 x 9.1 m and was marked by steel
reinforcement rods on all corners. Plot boundaries were
defined by connecting the four corners with a string or tape.
All perennial plant species within the plot were counted and
recorded by species. To assure that individual plants were
not missed on these large plots, a separate search was made
for every perennial species, previously identified in the area.
Mature trees were defined with height greater than 120 cm.
Annual plants were not considered in this report.
Perennial Forbs
Results and Discussion
of perennial grass and forb species varied by individual
species during the three measurement periods, but no distinct changes in population by species could be defined.
Photo points confirmed no measurable changes in the
plant community. Figures 1-6 are representative of the
woodland during 1974, 1984, and 1997. All photos were
taken between June 15 and July 5. Figures 1A and 2A were
taken in 1974 and compared with photos taken in 1997,
figures 1B and 2B, respectively. Likewise, figures 3A, 4A,
5A, and 6A were taken in 1984 and compared with photos
taken in 1997.
A few notes: Mter 23 years all reinforcement rods marking
the plot corners, and after 13 years all reinforcement rods
marking the photo positions were intact. The photo points
established in 1974 were not marked by reinforcement rods.
Comparing figures 1A and 1B, note the increase in size of the
Ephedra (Ephedra viridis) in the center of the photos.
Increase or decrease in size of individual Ephedra plants or
clumps was variable. Comparing figures 2A and 2B, note the
dead sagebrush skeleton next to the rock in the lower left
corner in 1997, but absent in 1974. Establishment and death
Changes in plant community composition were not detected during the 23 year interval (table 1). The number of
mature U tahj uni per (J unipe r osteosperma) and pinyon pine
(Pinus edulis) were unchanged. A single juvenile Utah
juniper became established but later died. An additional
four juvenile pinyon pines were recorded suggesting slow
change towards pinyon dominance. A numerical increase in
the number oflow sagebrush (Artemisia arbuscula) was due
to a number of small seedlings established within the last
one to three years. The number of dead shrub skeletons
declined numerically during the three periods. The number
In: Monsen, Stephen B.; Stevens, Richard, comps. 1999. Proceedings:
ecology and management of pinyon-juniper communities within the Interior
West; 1997 September 15-18; Provo, UT. Proc. RMRS-P-9. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Rocky Mountain Research
Station.
Dennis D. Austin is a wildlife biologist with the Division of Wildlife
Resources and is associated with the Department of Rangeland Resources,
Utah State University, Logan, UT 84322-8430.
138
Aster arenosus
Cryptantha spp.
Erysimum spp.
Gilia congesta
Opuntia spp.
Penstemen spp.
Petradoria pumila
Physaria chambersii
Sisymbrium linifolium
Townsendia incana
Other Forbs
6
22
USDA Forest Service Proceedings RMRS-P-9. 1999
Figure 1A-1974 plot 19.
Figure 18-1997 plot 19.
Figure 2A-1974 plot 20.
Figure 28-1997 plot 20.
Figure 3A-1984 plot 21.
Figure 38-1997 plot 21.
of individual sagebrush plants was common during the
periods. Comparing figures 3A and 3B, note the consistency
in density ofthe small perennial desert aster (Aster arenosus).
Although found on few plots, once established this species,
like most perennial forb species, persisted. Comparing figures 4A and 4B, note the fire scarred stump in the center of
USDA Forest Service Proceedings RMRS-P-9. 1999
139
Figure 4A-1984 plot 8.
Figure 48-1997 plot 8.
Figure 5A-1984 plot 26.
Figure 58-1997 plot 26.
Figure 6A-1984 plot 28.
Figure 68-1997 plot 28.
the photos. Very little change or decomposition for dead
limbs oftrees was found. Comparing figures 6A and 6B, note
the increase in the size of diameter of the pinyon on the left.
Growth rates of height and diameter for pinyon pine were
about 1.0 em/year.
Reference ---------------------------------
140
Austin, D. D. 1987. Plant community changes within a mature
pinyon-juniper woodland. Great Basin Naturalist. 47: 96-99.
USDA Forest Service Proceedings RMRS-P-9. 1999