Effects of Utah Juniper (Juniperus
osteosperma [Torr.] Little) Litter Leachate
on Germination of Several Range Plant
Species
Chad S. Horman
Val Jo Anderson
Abstract—A growth chamber study was conducted to determine
what allelopathic effects a leachate made from Utah juniper
(Juniperus osteosperma) litter has on seed germination and
germination rate of eight potential understory species. Three
water treatments (distilled water, 1%, and 10% litter leachates)
were tested. Leachates had no negative effect on germination of any
of the eight species. Bluebunch wheatgrass (Pseudoroegneria spicata) and antelope bitterbrush (Purshia tridentata) seeds treated
with leachates had significantly (P <0.05) higher germination
than the control. Leachates initially increased the germination rate
of mountain big sagebrush (Artemisia tridentata ssp. vaseyana),
but later had no effect.
The pinyon (Pinus spp.)-juniper (Juniperus spp.) woodland
is an important ecosystem of the Western United States,
comprising approximately 25 million hectares throughout
Nevada, Utah, Colorado, New Mexico, and Arizona (Hurst
1987). In pre-settlement days, juniper was most abundant
in the southwestern United States, but distinct populations
could be found on rocky mid-elevation foothills of the Great
Basin (Welch and others 1987). Since the mid-1800’s, juniper has slowly encroached into the valleys of the Great
Basin. As juniper has become the dominant species in these
communities, elements of both the biotic and abiotic environments have been modified (Tausch and others 1981).
This has been a serious problem for land managers; when
these trees dominate a site, the herbaceous understory is
severely reduced (Johnsen 1962; Christensen and Johnson
1964; Jameson 1967; Barney and Frischknecht 1974; Tausch
and Tueller 1977; Jeppesen 1978; Young and Evans 1981;
Schott and Pieper 1985). Increased runoff and soil erosion
has been reported as a result of this community shift
(Farmer 1995). Hypotheses to explain how junipers are able
to dominate a site include: (1) increased canopy cover that
creates precipitation interception and shading (Johnsen
1962; Skau 1964; Jameson 1967; Anderson and others 1969;
Gifford 1970; Schott and Pieper 1985; Pieper 1990), (2) deep
In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.
Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.
RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station.
Chad S. Horman is a Restoration Ecologist, Environmental Science and
Research Foundation, Inc., P.O. Box 51838, Idaho Falls, ID 83405-1838. Val
Jo Anderson is an Associate Professor of Range Science, Department of
Botany and Range Science, Brigham Young University, 493 WIDB, P.O. Box
25228, Provo, UT 84602-5228.
280
litter accumulation (Johnsen 1962; Jameson 1966; Everett
and Koniak 1981; Schott and Pieper 1985), (3) allelopathy
(Jameson 1961; Johnsen 1962; Lavin and others 1968;
Jameson 1970a; Peterson 1972), (4) changes in the soil
nutrient composition (Doescher and others 1987; Klopatek
1987; Tiedemann 1987), and (5) competition for soil moisture (Johnsen 1962; Jameson 1970b; Jeppesen 1978; Young
and Evans 1981; Miller and others 1987; Breshears and
others 1997).
It has been reported that juniper litter may be allelopathic (Jameson 1961; Lavin and others 1968; Jameson
1970a; Peterson 1972). Rice (1984) defined allelopathy “…as
any direct or indirect harmful effect of one plant on another
through production of chemical compounds that escape into
the environment.”
The effects of these compounds may be primary or secondary. Primary effects occur at the cellular level and
include such things as: (1) interference with cell elongation,
(2) interference with membrane function, (3) interference
with hormone interaction, or (4) changes in the ultrastructure of the root tip (Lovett and Ryuntyu 1992).
Secondary effects are a result of primary effects and
are the ones more readily seen in the field. These include:
(1) delayed or inhibited germination, (2) delayed or inhibited
stimulation of root or shoot growth, (3) reduced germination rate, (4) reduced biomass or yield, (5) reduced vigor, or
(6) reduced survivability (Winter 1961).
With respect to junipers, the literature contains conflicting evidence as to whether allelopathy really occurs.
Jameson (1961) showed that extracts from one seed juniper
(J. monsperma), Utah juniper (J. osteosperma), and alligator juniper (J. deppeana) inhibited growth of wheat (Triticum spp.) radicles. Jameson (1970a) later identified two
compounds from Utah juniper that were considered possible
growth inhibitors. Peterson (1972) found that Rocky Mountain juniper (J. scopulorum) produced both water soluble
and volatile inhibitors that reduced germination of several
herbaceous species. Lavin and others (1968) reported that
allelopathy in Utah juniper was species specific. Johnsen
(1962) found one seed juniper extracts did not significantly
reduce blue grama (Bouteloua gracilis) germination.
Much of the work done on allelopathy has focused on
juniper species other than Utah juniper and little has been
done in the foothill environment of central Utah. Thus, this
study was conducted to determine what allelopathic effects
a leachate made from Utah juniper litter would have on
total seed germination and germination rate of eight potential understory species.
USDA Forest Service Proceedings RMRS-P-11. 1999
Methodology ___________________
Differences were deemed significant at P <0.05 unless otherwise noted.
The experiment tested the effects of 1 and 10% leachates
made from Utah juniper litter leachate on total germination and germination rate of eight potential understory
species: bluebunch wheatgrass (Pseudoroegnaria spicata
[Pursh] Love ‘Secar’), bottlebrush squirreltail (Elymus
elymoides [Raf.] Swezey), cheatgrass (Bromus tectorum L.),
orchardgrass (Dactylis glomerata L.’Paiute’), Lewis flax
(Linum lewisii Pursh ‘Appar’), small burnet (Sanguisorba
minor Scop. ‘Delar’), antelope bitterbrush (Purshia tridentata [Pursh] DC.), and mountain big sagebrush (Artemisia
tridentata spp. vaseyana [Rydb.] J. Boivin).
The leachate was made from litter collected beneath Utah
juniper trees in the Tie Fork drainage of Spanish Fork
Canyon, Utah County, Utah. The litter was sifted through
#20 hardware mesh to separate soil from litter.
A 1% leachate solution was prepared by soaking 1 g of
litter in 100 ml of distilled water for 24 hours at 20 °C
(Jobidon 1986). The leachate was then poured through a #60
mesh filter. A 10% leachate was made in the same fashion
except that 10 g of litter per 100 ml of water was used.
The experiment was a completely randomized design with
three treatments: distilled water (control), 1%, and 10%
leachate, replicated four times. Each grass sample contained 50 seeds and each forb or shrub sample contained
25 seeds. In each petri dish, the seeds were placed on two
1-mm thick blotter pads saturated with one of the treatment solutions. Due to their large diameter, small burnet
and antelope bitterbrush seeds were placed between blotter
pads to insure adequate imbibition. The dishes were then
double-sacked in plastic bags. In order to have constant
humidity, a petri dish with two saturated blotter pads was
placed at the bottom and top of each stack in the bags. The
dishes were then placed in cold storage (1 °C) for 8 weeks
to simulate overwintering that normally occurs in the field.
Following the cold storage, the dishes were moved to a
growth chamber with a 20/15 °C temperature regime consisting of 12 hours each. Number of seed germinated were
recorded during the cold treatment and for 21 days following
placement in the growth chamber or until all seeds had
germinated, whichever came first. Germination was defined
as 1 mm of radicle emergence.
Percent germination data were arcsine transformed prior
to analysis. Analysis of variance (ANOVA) was performed
using Minitab (1995) statistical package and a Fisher’s
protected LSD was used for mean separation (Ott 1993).
Results ________________________
The results of the two leachate treatments were not
significantly different and were therefore pooled. Leachate
treatments had no negative effects on germination of any
of the eight species (table 1). Germination of bluebunch
wheatgrass and antelope bitterbrush seeds treated with
leachate was significantly higher, 3 and 7%, respectively,
than the control treatment. Mountain big sagebrush was
the only species whose germination rate was affected by
the leachate treatment (table 1). Seeds watered with leachate
reached 25% germination 6 days faster than did those
watered with distilled water. However, by the time 50% of
the mountain big sagebrush seeds had germinated, there
was no difference in germination rate between control and
treated seeds (table 1).
Discussion _____________________
This study indicated leachate from Utah juniper litter
had no allelopathic affect on seed germination. Surprisingly,
the leachate was found to cause a slight, but significant,
increase in percent germination of bluebunch wheatgrass
and antelope bitterbrush over the control. Lavin and others
(1968) reported one seed juniper extract caused a slight
increase in four-wing saltbush (Atriplex canescens) germination. With respect to germination rate, Utah juniper
leachate caused a decrease in the number of days for mountain big sagebrush to reach 25%, but then had no effect by
the time 50% emergence had occurred.
Allelopathy has been reported to occur in some juniper
species. Jameson (1961) reported a 5% water extract made
from fresh foliage of Utah juniper, alligator juniper, and one
seed juniper reduced wheat radicle germination by 85, 83,
and 79%, respectively. Lavin and others (1968) found Utah
juniper leaf and stem extracts decreased germination of
crested wheatgrass (Agropyron cristatum), blue grama, and
side oats grama (B. curtipendula). They reported no effect on
Luna pubescent wheatgrass (Elytrigia intermedia) and weeping lovegrass (Eragrostis curvula). Peterson (1972) reported foliage extracts of Rocky Mountain juniper negatively affected germination of some herbaceous plants.
Johnsen (1962) reported leachate made from old and fresh
Table 1—Effects of leachate made from Utah juniper litter on seed germination and germination rate.
Species
Bluebunch wheatgrass
Cheatgrass
Orchardgrass
Bottlebrush squirreltail
Lewis flax
Small burnet
Mountain big sagebrush
Antelope bitterbrush
Germination (%)
Control
Leachate
91.3 a*
84.6 a
56.4 a
69.6 a
82.2 a
95.3 a
99.0 a
88.9 a
94.6 b
85.8 a
59.0 a
81.2 a
74.5 a
96.4 a
98.1 a
95.7 b
# of Days to 25% germination
Control
Leachate
57.0 a
41.0 a
60.5 a
56.7 a
57.0 a
57.0 a
57.5 a
57.0 a
57.0 a
42.7 a
58.9 a
55.5 a
57.0 a
57.0 a
51.5 b
57.0 a
# of Days to 50% germination
Control
Leachate
57.0 a
48.0 a
72.5 a
57.0 a
57.0 a
57.0 a
55.0 a
57.0 a
57.0 a
46.2 a
68.0 a
57.0 a
57.6 a
57.1 a
54.1 a
57.0 a
*Values in rows followed by a different letter were significantly different at P <0.05.
USDA Forest Service Proceedings RMRS-P-11. 1999
281
litter and fresh foliage of one seed juniper had no effect on
blue grama germination.
Differences in the results of this study and those previously reported may be due to methodology. The majority of
studies have been conducted by making the leachate
from fresh foliage. The negative effects observed in those
studies may have been due to allelopathic compounds that
are quickly degraded and lost once the foliage begins to
decompose. Jameson (1970a) identified two potentially allelopathic compounds in Utah juniper foliage and litter that
behaved in just such a manner. The first compound, although allelopathic, degraded quickly enough that it never
reached toxic concentration. The second compound had a
slower decomposition rate and could accumulate to toxic
levels when the right conditions occurred. This same principle may apply to other compounds in Utah juniper litter.
When extracts are made and tested from fresh foliage, they
may contain harmful compounds that decompose or volatilize quickly and never reach toxic levels in a natural setting.
This may explain why no allelopathic effects were observed
in the present study when decomposing leaf litter was used.
Conclusions ____________________
In this study, leachate made from Utah juniper litter had
no negative effect on seed germination on any of eight
species tested. The leachate significantly increased germination of bluebunch wheatgrass and antelope bitterbrush.
Germination rates were largely unaffected by the leachate.
Mountain big sagebrush did show an initial increase in
germination rate, but, by the time 50% of the seeds had
germinated, no difference was found between leachate and
control treatments. These findings indicated, with respect to
seed germination, allelopathy of Utah juniper litter is not a
major force in reducing understory vegetation.
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