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Description of Pinyon-Juniper and Juniper
Woodlands in Utah and Nevada From an
Inventory Perspective
Renee A. O'Brien
Sharon W. Woudenberg
Abstract-Forests composed mostly of pinyon and/or juniper species cover more than 45.3 million acres in the Intermountain West.
About 40 percent (18.0 million acres) of that area is in Nevada and
Utah, where roughly 71 percent of the total forest land is pinyonjuniper and juniper forest type. The net volume of pinyon and
juniper species in the two States is estimated at over 10.3 billion
cubic feet, or about 137.5 million cords. Juniper makes up 63 and
47 percent of the pinyon-juniper volume in Utah and Nevada,
respectively. Fifty-eight percent of the total number of pinyon and
juniper trees in Nevada, and 49 percent in Utah are pinyon. About
53 percent of pinyon-juniper and juniper stands in Utah and about
67 percent in Nevada are estimated to be between 40 and 120 years
old. Almost 20 percent of stands in Utah and 9 percent of stands in
Nevada have an age over 200 years. Only about 6 percent of Utah
stands and less than 1 percent of Nevada stands show evidence of
chaining.
The objective of this paper is to present an overview of
composition, structure, and productivity of pinyon-juniper
and juniper ecosystems, focusing on data from recent Utah
and Nevada State inventories. This paper will also demonstrate the use oflarge-scale inventory data for planning and
decision making.
Forest types composed of pinyon and/or juniper species
cover approximately 45.3 million acres in the western States
of Montana, Idaho, Wyoming, Nevada, Utah, Colorado,
Arizona, and New Mexico. The Interior West Resource
Inventory, Monitoring, and Evaluation (IWRIME) Program
of the U.s. Forest Service, Rocky Mountain Research Station, conducts forest land inventories in these eight States
as part of its national Forest Inventory and Analysis (FIA)
duties. About 40 percent of the pinyon-juniper and pure
juniper ecosystems in the area inventoried by IWRIME
occurs in Nevada and Utah, where roughly 71 percent of the
total forest land is pinyon-juniper or pure juniper forest
type.
This paper will focus only on the pinyon-juniper and
juniper forest types in Utah and Nevada, with special
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.
Renee A. O'Brien is Analysis Team Leader and Sharon W. Woudenberg is
Supervisory Forester with the Interior West Resource Inventory, Monitoring,
and Evaluation Program of the U.S. Forest Service, Rocky Mountain Research Station, Ogden, UT 84401.
USDA Forest Service Proceedings RMRS-P-9. 1999
emphasis on Utah. Utah is the Interior West State with the
most complete and current forest inventory data base. In
the past, IWRIME did not usually inventory National Forest
System (NFS) lands, obtaining the numbers instead from
NFS inventories for State and regional reporting. However,
a cooperative agreement and funding from the U.S. Forest
Service Intermountain Region resulted in a comprehensive
inventory of Utah's forests that included NFS lands and all
reserved lands and was completed in 1995. A Utah State
report is currently being prepared (O'Brien, in preparation).
Nevada also has a fairly comprehensive State inventory,
which was conducted between 1978 and 1982. An area
update was done in 1989, and the results of the Nevada
inventory were published in 1992 (Born and others). The
number of field plots on pinyon-juniper and juniper forest
types in Nevada was 1,104, and in Utah, 1,212 (fig. 1).
Also shown in figure 1 are parts of six ecoregions that
occur in Nevada and Utah, as described by Bailey (1995):
(1) American Semi-Desert and Desert Province, (2) Colorado
Plateau Semi-Desert Province, (3) Intermountain SemiDesert Province, (4) Intermountain Semi-Desert and Desert
Province, (5) Nevada-Utah Mountains-Semi-DesertConiferous Forest-Alpine Meadow Province, and (6) Southern Rocky Mountain Steppe-Open Woodland-Coniferous
Forest-Alpine Meadow Province.
Figure 1-Utah and Nevada ecoregions and IWRIME
pinyon-juniper or juniper field plots.
55
Table 1-Area and net volume with percent standard error for pinyon-juniper and juniper
forest types in Utah 1993, and Nevada 1989.
State
Utah
Forest type
Attribute
Pinyon-juniper
Area
Volume
Area
Volume
7,766,307
Area
Volume
Area
Volume
7,155,970
Juniper
Nevada
Pinyon-juniper
Juniper
Sampling Procedures _ _ _ _ __
IWRIME uses a two-phase sampling procedure for State
inventories, described in detail by Chojnacky (1998). The
first, or photo interpretive, phase is based on a grid of sample
points systematically located every 1,000 m across all lands
in a State. Forestry technicians use maps and aerial photos
to obtain ownership and stratification information. Field
crews conduct the second, or field, phase of the inventory on
a subsample ofthe phase one points that occur on forest land.
Field procedures for Utah are described in detail in USDA
(1994), and in USDA (1982) for Nevada.
For the most part, the IWRIME sampling intensity on
lands outside NFS lands in the Interior West is one field plot
every 5,000 m, or about every 3 miles. The sampling intensity on NFS lands in Utah was double that of outside lands.
In Nevada, National Forest System lands were not field
sampled. Most data summaries presented in this report for
Nevada are based on the 6,526,784 acres that were actually
sampled. Area estimates for the 2,312,752 acres of NFS
lands were based on photo interpretation information, and
volume estimates in tables 1 and 2 were developed using
stratum means (field plots) fr9m other ownerships.
The IWRIME sample was designed to meet national
standards of precision for forest attributes at State and
regional levels. Standard errors, which denote the precision
of an estimate, were computed for State totals of area and
volume of the pinyon-juniper and juniper types in Nevada
and Utah, and are presented in table 1. Standard errors are
usually higher for smaller subsets of the data.
Area
Volume
acres
thousand
Area
error
2.3
3.2
7.3
8.9
5,365,955
1,382,400
660,683
1.3
2.9
5.6
7.7
3,498,881
1,683,566
560,305
usually on drier and lower elevation sites. The total area
of pinyon-juniper and juniper combined is 8,839,536. An
additional 25,043 acres of pinyon-juniper is estimated to
occur on reserved areas, for a total of 8,864,579, with about
19 percent being pure juniper. Sixty-nine percent of the
pinyon-juniper and juniper forests in Nevada are administered by the Bureau of Land Management (BLM), 26 percent
by NFS, and 5 percent are privately owned.
It is estimated that Utah has 7,766,307 acres of pinyonjuniper forest type composed mainly of two needle pinyon or
occasionally singleleaf pinyon in association with Utah
juniper or occasionally Rocky Mountain juniper. Approximately 1,382,400 acres are occupied by juniper species
occurring without pinyon. The total area of pinyon-juniper
and juniper combined is 9,148,707 acres, with 15 percent
being pure juniper (fig. 2). Sixty-one percent of the pinyonjuniper and juniper forests in Utah are administered by
the BLM, 15 percent by NFS, 10 percent by other public, and
13 percent are privately owned.
Number of Trees
The composition of the forest by individual tree species is
one measure of forest structure. In Utah, it is estimated
that the number of pinyon and juniper trees is about equal
10,000
(/)
Forest Composition and
Structure
Percent standard
1'1
[J
8,000
Utah
Nevada
Q)
"C,)
co
6,000
"0
C
co
(/)
::J
0
4,000
..c
FIA differentiates pinyon-juniper forest type (stands that
have juniper and any pinyon present) from juniper forest
type (purely juniper). It is estimated that Nevada has
7,155,970 acres of pinyon-juniper forest type, composed
mostly of singleleaf pinyon (Pinus monophylla) in association with Utahjuniper (Juniperus osteosperma) or occasionally Rocky Mountain juniper (Juniperus scopulorum). Two
needle pinyon (Pinus edulis) may also occasionally be found.
Juniper occurs without pinyon on about 1,683,566 acres,
56
I-
2,000
°
Pinyon-juniper
Pure juniper
Combined
Forest type
Figure 2-Area of pinyon-juniper and juniper foresttypes
in Utah and Nevada.
USDA Forest Service Proceedings RMRS-P-9. 1999
(49 and 51 percent). Utah juniper makes up 92 percent, and
Rocky Mountain juniper makes up 8 percent of the juniper
trees. Twoneedle pinyon makes up 78 percent, and singleleaf
pinyon makes up 22 percent of the pinyon trees. Pinyon
makes up more of the small trees, with juniper comprising
more of the trees greater than 7 inches diameter at root
collar (d.r.c.). Fifty-eight percent of the total number of
pinyon and juniper trees in Nevada are pinyon, but more of
the trees 11 inches d.r.c. or greater are juniper.
40
ro
ro
Q)
III
Utah
30
~
......
c
Q)
()
20
~
Q)
a..
10
Stand Density
Stand density index (SDI), as developed by Reineke (1933)
is a relative measure of stand density that quantifies the
relationship between trees per acre, stand basal area, average stand diameter, and stocking of a forested stand. The
concept was developed for even-aged stands, but can also be
applied to uneven-aged stands (Long and Daniel 1990). SDI
is usually presented as a percentage of the maximum SDI
for the type. A maximum SDI value of 465 was used for
pinyon-juniper, and 344 for purejuniper. SDI was computed
for each plot using those maximums, and the results were
grouped into three classes. Figure 3 shows the three classes
of SDI for each State. A site was considered to be fully
occupied at 35 percent of SDI maximum, which marks the
onset of competition related stresses and slowed growth
rates. IWRIME estimates that 53 percent of pinyon-juniper
stands in Utah and 49 percent in Nevada are at or above 35
percent of SDI maximum.
Stand Age
Age information is relatively difficult to obtain for pinyonjuniper stands because of tree form and the difficulty of
counting growth rings. In Nevada, 3 trees reflecting the
average or above average size in the stand were bored to get
stand age. Junipers were not included because of perceived
60
Utah
50
ro
ro
(l)
~
+-'
c
(l)
40
30
()
~
(l)
a..
20
10
0
Understocked
(0-34.9%)
Fully-stocked
(35-59.9%)
Overstocked
(60%+)
Stand Density Index (SOl) class
Figure 3-Percent area of combined pinyon-juniper
and juniper forest types by SDI class, Nevada 1989 and
Utah 1993.
USDA Forest Service Proceedings RMRS-P-9. 1999
o
1-404180
81120
121160
161200
201250
251300
300+
Stand age class
Figure 4-Percent area of combined pinyon-juniper and
juniper forest types where ages were collected by stand
age class, Nevada 1989 and Utah 1993.
difficulty in boring, so ages on pinyon-juniper forest land in
Nevada only came from pinyons. This represents a bias,
because pure juniper stands were not aged. Age data were
obtained for about 62 percent of stands sampled in Nevada.
In Utah, only one woodland tree of any species reflecting the
average of the stand (based on cruiser judgement) was aged,
but cores were collected at all locations. Cores for all woodland trees sampled in Utah were sent into the office for aging
and storage.
Even though the two States had different protocols for tree
selection, the pattern of age distribution was similar for both
States. Based on this admittedly scanty age data, it is
estimated that about 53 percent of the stands in Utah, and
about 67 percent of the stands where age was sampled in
Nevada were between 40 and 120 years old (fig. 4). Only
about 20 percent of the stands in Utah and 9 percent in
Nevada were over 200 years. A report on old growth, "Characteristics of Old-growth Forests in the Intermountain Region" (USDA 1993), defines old-growth criteria for pinyonjuniper forest types using trees per acre, tree diameters,
and tree ages. Screening with a combination of just two of
the criteria, stand age and stand-size class, showed that
14 percent of all Utah stands had an age of 200 years or
greater and a stand size of 9 inches (d.r.c.) or greater.
Figure 5 presents the percent area ofpinyon-juniper and
juniper forest types (combined) by stand age class and
ecoregion, and gives a rough indication of the differences
among ecoregions. For example, more of the pinyon-juniper
and juniper forest types in the Colorado Plateau SemiDesert Province have a stand age between 161 to 300 years
than in the other ecoregions. The American Semi-Desert
and Desert Province has the most extreme differences by
age class, due probably to the small number of plots in that
ecoregion.
Because 120 years is roughly the amount of time since
significant impacts from mining and settlement would have
first been felt in these areas, the data for stands 120 years old
or less was separated from stands greater than 120 years for
57
90
B Colo Plat
. Desert
40%
co
Q)
-fr Nv-Ut Mtns.
Q)
10-
S.Rockies
co 30%
c
Q)
()
B- American
20%
C
Q)
III
tEl
60
50
1-120 years (NV)
121+ years (NV)
40
10-
Q)
0...
30
20
Q)
0...
co
()
+-'
10-
10-
1-120 years (UT)
121+ years (UT)
70
50%
co
•
80
·9 Semi
10%
10
0
0%
None
1-40
4180
81120
121160
161200
201250
251300
Cutting
Other
Fire
Chaining
301
Type of disturbance
+
Stand age class
Figure 5-Percent area of combined pinyon-juniper and
juniper forest types by stand age class and ecoregion,
Nevada 1989 and Utah 1993.
additional analysis. About 71 percent of the pinyon-juniper
stands sampled for age in Nevada, and about 57 percent in
Utah are estimated to be less than 120 years old. Crews
make a subjective field assessment of the predominant
human or natural disturbance on each plot that impacts the
entire condition. The percent of area with stand age 120
years or less is compared to the percent of area with stand
age greater than 120 years in terms of evidence of disturbance in figure 6. The overwhelming majority of pinyonjuniper or juniper stands have no visible evidence of disturbance in either State. One of the categories of disturbance
was chaining, which was evident on about only 6 percent of
Utah plots 120 years old or less, and about 1 percent of
Nevada plots 120 years old or less.
Volume _ _ _ _ _ _ _ _ _ _ __
The total volume of wood in live pinyon and juniper trees
on all forest types in both States is estimated to be in excess
of 10.3 billion cubic feet. This number divided by a standard
FIA conversion factor of75 gives an estimate of the number
of cords-137.5 million. Table 2 displays cubic foot volume
by species, owner, and State.
Figure 6-Percent area of combined pinyon-juniper
and juniper forest types in each age category by type
of visible disturbance, Nevada 1989 and Utah 1993.
Volume of all species on pinyon-juniper andjuniper forest
types averages about 459 cubic feet (6.1 cords) per acre in
Nevada, and 659 cubic feet (8.8 cords) per acre in Utah.
Figure 7 shows the difference in cubic foot volume per acre
between ecoregions. The range is from less than 200 cubic
feet per acre in the American Semi-Desert and Desert
Province to over 800 cubic feet per acre in the Southern
Rocky Mountain Steppe-Open Woodland-Coniferous Forest-Alpine Meadow Province. These differences in average
volume per acre may reflect the climatic and geographic
differences among the ecoregions. These estimates include
other species that might occur on pinyon-juniper andjuniper
forest types.
Growth and Mortality _ _ _ __
Growth for pinyon and juniper species is characteristically low, and is difficult to measure. However, it is estimated that the gross growth rate for Nevada and Utah is 1
percent or less per year. The total mortality observed was
only about 5 percent of growth in Nevada, and 15 percent of
growth in Utah.
Table 2-Net volume of pinyon and juniper species by state and owner group, (thousand cubic feet).
State
National forest
Owner
Other public
Private
Total
Utah
Pinyon
Juniper
501,116
694,610
1,536,240
2,800,847
258,148
491,095
2,295,504
3,986,552
Nevada
Pinyon
Juniper
548,906
361,110
1,437,842
1,407,143
153,811
120,898
2,140,559
1,889,151
2,105,742
7,182,072
1,023,952
10,311,766
Total
58
Species
USDA Forest Service Proceedings RMRS-P-9. 1999
900
CD
800
(lj
700
t5
Q;
Q.
1i5
2
600
500
()
:0
400
.s.
300
::J
CD
E
::J
(5
>
200
100
0
Amer.
Colo.
Plat.
Semides.
Desert
NV-UT
Mtns.
S.Roe.
Mtns.
Ecoregion
Figure 7-Cubic foot volume per acre on combined
pinyon-juniper and juniper forest types, by ecoregion in
Nevada 1989 and Utah 1993.
References ---------------------------------Bailey, Robert G., compiler. 1995. Descriptions of the ecoregions of
the United States. 2nd ed. Misc. Pub. No. 1391. Washington DC:
U.S. Department of Agriculture, Forest Service, Washington,
DC. 108 p.
USDA Forest Service Proceedings RMRS-P-9. 1999
Born, J. David; Tymcio, Ronald P.; Casey, Osborne E. 1992. Nevada
Forest Resources. Resour. Bull. INT-76. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research
Station. 64 p.
Chojnacky, David C. 1998. Double sampling for stratification: a
forest inventory application in the Interior West. Res. Pap.
RMRS-RP-7. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 15 p.
Long, James N.: Daniel, Theodore W.1990. Assessment of growingstock in uneven-aged stands. Western Journal of Applied Forestry 5(3):93-96 .
O'Brien, Renee A. [In preparation]. Utah forest resources. Resour.
Bull. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station.
Reineke, L. H. 1933. Perfecting a stand-density index for even-aged
forests. J. Agric. Res. 46:627-638.
U.S. Department of Agriculture, Forest Service. 1982. Nevada
forest survey field procedures. Unpublished field guide on file at:
U.S. Department of Agriculture, Forest Service, Rocky Mountain
Research Station, Forestry Sciences Laboratory, Interior West
Resource Inventory, Monitoring, and Evaluation Program, Ogden,
UT.
U.S. Department of Agriculture, Forest Service. 1993. Characteristics of old-growth forests in the Intermountain Region. Hamilton,
Ronald C., compiler. Unpublished report on file at Ogden, UT:
U.S. Department of Agriculture, Forest Service, Intermountain
Region.
U.S. Department of Agriculture, Forest Service. 1994. Utah forest
survey field procedures, 1994-1995. Unpublished field guide on
file at: U.S. Department of Agriculture, Forest Service, Rocky
Mountain Research Station, Forestry Sciences Laboratory, Interior West Resource Inventory, Monitoring, and Evaluation Program, Ogden, UT. 232 p.
59