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SPINY HOPSAGE SEED GERMINATION
AND SEEDLING ESTABLISHMENT
Nancy L. Shaw
Marshall R. Haferkam.p
high ratings for persistence and resistance to insects and
disease and low ratings for initial establishment and
natural spread. They recommended spiny hopsage for
use in pinyon-juniper, basin big sagebrush (Artemisia
tridentata Nutt. var. tridentata), Wyoming big sagebrush,
shadscale CAtriplex confertifolia [Torr. and Frem.] Wats.),
and blackbrush ( Coleogyne ramosissima Torr.) vegetation
types.
An understanding of requirements for natural or artificial establishment of spiny hopsage seedlings is needed
to permit development of direct seeding techniques for
the species. This paper summarizes current knowledge
of spiny hopsage seed germination, seedbed ecology, and
seedling establishment.
ABSTRACT
Reestablishment of spiny hopsage (Grayia spinosa [Hook.]
Moq.) on disturbed native sites improves shrub diversity,
contributing to development of subcanopy soils, vegetation,
and associated ecosystem stability. Spiny hopsage may be
established by fall or winter planting of seeds or bracted
utricles at a depth of 0.5 em using drills or seeder-packers.
Seeds of Mojave Desert populations germinate in response
to fall or winter rains of at least 160 mm; those from southeastern Oregon and southwestern Idaho germinate in early
spring following overwinter exposure to cool, moist seedbed
microenvironment&. Germination, emergence, and seedling establishment are episodic; success depends on availability of soil water. Survival may be enhanced by site
preparation and planting techniques that reduce vegetative competition and improve water catchment.
Northern Shrub Steppe and Great Basin-Spiny
hopsage plants may remain dormant during dry years,
but large quantities of new branches, leaves, and fruits
(bracted utricles) are usually produced during years with
good spring rainfall (Rickard and Warren 1981; Shaw
1992). Seed quality varies widely with weather conditions, insect infestations, and other factors (Shaw 1992).
Filled utricles ripen from late spring to mid-summer.
Many utricles normally fail to develop; large numbers of
fruiting bracts are normally empty. Consequently, the
quantity of viable seeds contributed to the soil seed bank
and the potential for seedling establishment may vary
considerably from year to year.
Establishment of spiny hopsage is episodic with germination, emergence, and survival dependent on local environmental conditions, particularly precipitation. In
southeastern Oregon and southwestern Idaho, emerging
seedlings were observed only in years with above-average
spring rainfall (Shaw 1992; Shaw and Haferkamp 1990).
Seedlings emerged in early spring from litter accumulations beneath nurse plant canopies or from shrub interspaces slightly downwind. In addition to female spiny
hopsage plants, greasewood (Sarcobatus vermiculatus
[Hook.] Torr.), Wyoming big sagebrush, and male spiny
hopsage plants growing near seed sources also acted as
nurse plants. Compared to interspaces, shrub clumps
provide more favorable water, temperature, light, soil
texture, organic matter, and nutrient conditions for establishment of many species (Pierson and Wight 1991; Rickard
and others 1988; Wallace and Romney 1972; Wallace and
others 1980). Maturation of these seedlings, however, occurs only in canopy openings.
In contrast to the observations of early spring germination, Glazebrook (1941) reported spiny hopsage seedlings
emerged in fall immediately after seeds reached maturity.
Although he collected seeds in eastern Washington, he did
not specify the site of this observation nor did he comment
on the late date of seed maturation. .
INTRODUCTION
Endemic to the Intermountain West, spiny hopsage
(Grayia spinosa [Hook.] Moq.) occurs in Wyoming big
sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis
Beetle & A. Young), pinyon-juniper (Pinus L.-Juniperus
L.), salt-desert shrub, and Mojave Desert communities
(Daubenmire 1970). The species provides cover for birds
and other small animals, spring and early summer forage
for big game and livestock, and soil stabilization on gentle
to moderate slopes (Gullion 1964; McCullough 1969;
USDA-SCS 1968). Growth and nutrient content of vegetation growing near spiny hopsage are enhanced by accumulation of litter rich in potassium and other cations
(Rickard and Keough 1968).
Areas within the native range of spiny hopsage have
been depleted or damaged by livestock grazing, wildfires,
invasions of weedy annuals, mining, off-road vehicle use,
road and pipeline construction, and other human activities (Blaisdell and Holmgren 1984). Reestablishment
of the species on these sites is often desirable. Billings
(1949), Dayton (1931), Monsen and Christensen (1975),
and Plummer (1966), encouraged development of spiny
hopsage as a revegetation species. Plummer and others
(1968) evaluated its revegetation attributes, assigning
Paper presented at the Symposium on Ecology, Management, and Restoration oflntermountain Annual Rangelands, Boise,ID, May 18-22, 1992.
Nancy L. Shaw is Botanist, Intermountain Research Station, Forest
Service, U.S. Department of Agriculture, Boise, ID; Marshall R. Haferkamp
is Range Scientist, Fort Keogh Livestock and Range Research Laboratory,
Agricultural Research Service, U.S. Department of Agriculture, Miles City,
MT.
252
The episodic nature of seedling establishment may partially explain seemingly contradictory reports of native
spiny hopsage seedling occurrence. For example, the
USDA-SCS (1968) reported spiny hopsage establishes
rapidly in eastern Washington bluebunch wheatgrass
(Agropyron spicatum [Pursh] Scribn. & Smith) or needleand-thread (Stipa comata Trin. & Rupr.) communities
depleted by overgrazing or other disturbances. By contrast, Daubenmire (1970) found no spiny hopsage plants
with fewer than 16 xylem rings after extensive searches
in eastern Washington.
Natural recovery of spiny hopsage on disturbed sites
was studied at the U.S. Atomic Energy Commission,
Nuclear Test Site (USAEC-NTS) in the southern Great
Basin. Shrub recovery was monitored at Pahute Mesa
following nuclear testing in 1965. Elevation of the site
is 1,800 to 1,890 m and mean annual precipitation 119
to 279 mm. Following testing, no spiny hopsage seedlings
remained in the totally killed area (Wallace and others
1977, 1980). Shrub recovery began rather quickly, even
though the totally killed area was dominated by Russian
thistle (Salsola iberica Sennen and Pau) and the partially
killed area by grasses during the first 5 years. In an unusually good precipitation year, a large number of spiny
hopsage seedlings emerged and grew to heights of 0.3 to
0.4 m (Wallace and Romney 1972). By 1976, spiny hopsage
and total shrub seedling density had increased to the
point that shrub recruitment appeared adequate for replenishing the site. Density of new spiny hopsage seedlings was 34 per hectare in the totally killed area, 55 per
hectare in the partially killed plot, and 14 per hectare in
the control area. Seedlings in the totally killed area presumably established from external seed sources.
many size classes. The mean dry weight of spiny hopsage
plants was 74.3 ± 85.8 g. Approximately 66 percent of the
plants weighed less than the modal size class (24.4 to
64.6 g) and 17 percent weighed more, again indicating
an abundance of small (young) plants. They concluded
this distribution possibly reflected emergence and
survival of many seedlings in response to good rainfall
2 years prior to sampling.
The impact of supplemental water on seedling emergence and establishment in a community dominated by
goldenhead (Acamptopappus shockleyi Gray) and bursage
(Ambrosia dumosa [Gray] Payne) was examined near
Mercury, NV, in the northern Mojave Desert (Hunter
and others 1980). Plots of native vegetation were sprinkler irrigated to maintain soil water content above 5 percent, increasing annual water input from an average of
100 to 150 mm to about 350 to 450 mm (Wallace and
Romney 1972). After 3 years of irrigation followed by
4 years of natural rainfall, spiny hopsage density increased from 288 to 438 plants/ha and biomass from 41
to 241 kglha. On nonirrigated plots density increased
from 356 to 465 plants/ha and biomass from 59 to 109
kg/ha. Possible reasons for the increase on nonirrigated
plots were not discussed.
Wallace and Romney (1972) studied seedling emergence
in disturbed creosote bush (Larrea tridentata [DC.] Cov.)
communities of the Mojave Desert within the USAEC-NTS.
They found few spiny hopsage seedlings emerged unless
artificial irrigation was applied.
GERMINATION STUDIES
Threshed seeds and northern shrub steppe and Great
Basin seed sources have been utilized in most studies of
spiny hopsage seed germination and in full-scale plantings.
Work with bracted utricles and Mojave Desert populations is more limited.
Dry afterripening reduces seed dormancy of several
shrubby chenopods (Ansley and Abernethy 1985;
Pendleton and Meyer 1990; Springfield 1969, 1972).
Shaw and others (in press), found no consistent differences between laboratory germination or field seedling
establishment of 2- and 4-year-old spiny hopsage seed
collections from one southwestern Idaho and one southeastern Oregon site. King (1947) found germination
of a 6-year-old seed lot from eastern Washington was enhanced by a 2-week moist prechill at 5 oc, but a 12-week
moist prechill was required for a 4-year-old seed lot from
the same area. He suggested the differences might be attributed to duration of dry afterripening.
Laboratory studies by Glazebrook (1941) indicated light
had no influence on germination when 1-year-old spiny
hopsage seeds harvested in eastern Washington were incubated at 22 to 26 °C. The positive response (92 percent
germination in 35 days) of this seed lot to an alternating
temperature regime of 30/20 oc (8 h/16 h) and work indicating seedlings could be "frozen solid while still very
young and yet survive" led him to recommend early spring
or late fall sowing for nursery production.
Mojave Desert-Manning and Groeneveld (1990)
found that spiny hopsage seedlings in the Transition Zone
between the Great Basin and Mojave Desert in Owens
Valley, CA, also developed beneath nurse plants, particularly in heavily grazed areas. Beatley (1979/80) made a
similar observation for the northern Mojave Desert.
Wallace and Romney (1972) reported Mojave Desert
populations of spiny hopsage produced nondormant seeds
capable of germinating rapidly when adequate water was
available. Ackerman (1979) found seeds of 11 common
Mojave Desert shrubs including spiny hopsage germinated following fall or winter rains (October to March)
of at least 160 mm. Establishment of these species was
considered episodic as only one of 201 seedlings emerging
on study plots between 1971 and 1975 survived until
spring 1977. Of 63 spiny hopsage seedlings emerging,
62 succumbed the first year and one the second year.
Further evidence for episodic seedling establishment
was provided by El-Ghonemy and others (1980) who examined size-class distributions of spiny hopsage and nine
other perennial species in undisturbed areas of Rock
Valley in the northern Mojave Desert. Size classes were
defined on the basis of plant biomass. Frequency histograms for size-class distribution on a natural log basis
showed a somewhat negatively skewed distribution for
spiny hopsage, resulting from segregation of the numerous smaller, and presumably younger, individuals into
253
constant and alternating temperatures. Bracts did not
decrease water uptake by the seed or provide mechanical
restraint to embryo emergence, consequently inhibition
of oxygen uptake was suggested as a possible mechanism
for their action. Whether bracts remain intact in the field
through winter has not been investigated.
Differences in seed dormancy noted by Glazebrook
(1941), Shaw (1992), and Wood and others (1976) may
have resulted from genetic variation, seed cleaning procedures, or both. Lack of a moist-prechill requirement
might be expected for Mojave Desert populations. Shaw
(1992) found southwestern Idaho and southeastern Oregon
seeds were rendered germinable by partial or complete
removal of the testa. Both normal and abnormal germination were increased by threshing techniques that disrupted the testa.
Smith (1974) reported moist prechilling for 60 or 90 days
at 4 oc improved the rate of spiny hopsage germination.
Germination of prechilled seeds incubated at 22 °C or 30/
20 °C (day/night) was complete in 8 or fewer days compared to 30 days for controls. Both moist prechilling periods were also effective in increasing total germination of
seeds incubated at 22 °C (maximum of 36 percent compared to 21 percent for controls); only the 90-day moist
prechill improved total germination (29 compared to
25 percent) when seeds were incubated at 30/20 °C.
Shaw (1992) found a 45-day moist prechill at 3 to 5 oc
improved both total germination and germination rate
of bracted utricles and seeds of one southwestern Idaho
and one southeastern Oregon seed source. For the incubation temperatures tested (10, 15, 20, 25, 30, 15/5, and
10/2 °C [8/16-h alterations]), germination increased from
9 to 64·percent with moist prechilling. Days to 50 percent
germination declined from 24 to 11.
Wood and others (1976) examined the germination response of four Nevada (Great Basin) and one California
(Mojave Desert) spiny hopsage seed sources to 55 constant
and alternating temperatures. All seed sources were nondormant. Highest constant temperature germination percentages were obtained at 10 and 15 °C (66 to 74 percent).
A 5 °C low temperature alternating with high temperatures between 0 and 30 °C, inclusive, provided the highest
germination percentages (70 to 90 percent) for all five
seed lots. After 1 week, greatest seedling elongation of a
Dayton, NV, seed lot occurred at 5, 15/20,20, and 5/25 °C.
Shaw (1992) found total germination of moist-prechilled
(45 days) bracted utricles and seeds from southwestern
Idaho and southeastern Oregon incubated at 5/15 °C was
similar to constant temperature germination over the 20to 30-°C range, but the rate was slower. The findings of
Shaw (1992), Smith (1974), and Wood and others (1976)
may be typical of species adapted to germinate in late fall
or early spring when soil water content is most likely to
be favorable for seedling establishment.
Wood and others (1976) suggested the drifts of spiny
hopsage fruiting bracts that sometimes accumulate under
and around shrubs, mixing with leaves and other debris
to form a thick mulch, may modify the seedbed environment. They found that air-dried bracted utricles are highly
hygroscopic, increasing 41 percent by weight when placed
over water in a desiccator. Bracted utricles of a Mojave
Desert seed source were highly tolerant of osmotic stress.
When incubated in polyethylene glycol solutions of -0.8
to -1.2 MPa, their germination was not reduced compared
to controls incubated in water, suggesting bracts might
function to regulate the osmotic potential of the utricles,
enabling them to attain the osmotic potential required
for germination. Germination of bracted Mojave Desert
utricles incubated in NaCl solutions occurred only at water potentials greater (less negative) than -1.3 MPa, suggesting ion toxicity might be occurring at lower potentials.
Wood and others (1976) found constant temperature
germination of bracted utricles and seeds of a Mojave
Desert seed source did not differ over the 2- to 40-°C
range. In contrast, Shaw (1992) reported bracts reduced
germination of moist-prechilled southwestern Idaho and
southeastern Oregon seed sources incu~ated at several
DIRECT SEEDING
Stark (1966) and Plummer and others (1968) recommended use oflocal spiny hopsage seed sources for rangeland plantings. Few data on population differences have
been reported. Shaw and others (in press) found germination and establishment of seed lots collected from similar
environments in southwestern Idaho and southeastern
Oregon and planted at two southern Idaho sites did not
differ consistently. Wood and others (1976) found bracted
utricles and seeds of a Mojave Desert seed source from
California germinated at higher temperatures than did
four Great Basin sources from Nevada. Common garden
studies of spiny hopsage were recently initiated in southeastern Idaho by the USDA-SCS (Hoag 1992) and should
provide considerable information on variability among
populations and site requirements for their establishment.
Failures of early spiny hopsage plantings in Utah were
attributed to planting the small seeds (869 to 932/g) at excessive depths (Plummer 1984; Smith 1974). Glazebrook
(1941) recommended seeds be surface broadcast, while
Kay and others (1977) recommended a seeding depth of
10 mm. Wood and others (1976) found few or no seedlings
established when seeds were broadcast on smooth or
packed surfaces in a greenhouse study. Broadcasting
bracted utricles on a rough soil surface resulted in 18 percent seedling establishment. Establishment of 48 percent
from seeds and 51 percent from bracted utricles was obtained by planting at a depth of 5 nun.
Recommended seeding rates range from 0.6 to 4.4 kg/ha
(Anderson and Shumar 1989; Rosentreter and Jorgenson
1986). Shaw and others (in press) reported first-year establishment ranged from 0 to 23.5 percent of viable seeds
planted in late fall at two southern Idaho sites during
2 years. Seeds were direct seeded or broadcast and covered.. Planting depth in both cases was about 5 nun.
Planting spiny hopsage seeds in late fall or winter in
southern Idaho exposed seeds to cool, moist seedbed environments, permitting early spring emergence when soil
water conditions were favorable for growth prior to the
onset of summer drought (Shaw and others, in press).
During 1 year, seeds at two sites began germinating in
late February and early March when maximum and minimum air temperatures averaged 8 and 0 °C and surface
254
soil temperatures averaged 4 and -2 oc. Seedlings
emerged in March and early April when maximum and
minimum air and surface soil temperatures averaged 12
and0°C.
Shaw (1992) reported field emergence from southwestem Idaho plantings was severely limited if soil water was
low. The possibility that some nongerminating seeds may
have entered secondary dormancy _was indicated by high
viability and low to moderate laboratory germination of
seeds recovered from late fall or winter plantings in early
summer. Early and late-spring plantings did not provide
temperature or moisture conditions necessary to permit
germination and emergence. Longevity of field-planted
seeds in primary or secondary dormancy was not examined, but limited second and third year emergence was
noted.
Shaw and Haferkamp (1990) reported developing seedlings produced a single shoot and a taproot system with
few lateral roots during the first growing season. They
found some seedlings in southwestern Idaho plantings
were damaged or destroyed by seed harvester ants (/'ogonomyrmex salinus Olsen) and nymphs of an unidentified
plant bug CMelanotrichus spp.). Wallace and Romney
(1972) recommended control of herbivores and competing
vegetation for establishment of spiny hopsage and other
desert shrubs.
REFERENCES
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Southwestern Naturalist. 24: 399-408.
Anderson, Jay E.; Shumar, Mark L. 1989. Guidelines for
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DISCUSSION
Until additional research is completed, general guidelines for reestablishing shrubs should be followed when
direct seeding spiny hopsage. In the absence of seed
transfer guidelines, seeds from local sources should be
planted. Bracted utricles and seeds can be drilled or
planted through seeder-packers. Large fruiting bracts
may clog some drill drops, but bracted utricles must be
threshed carefully to avoid embryo ·damage. Bracted
utricles and seeds should be planted about 0.5 em deep.
As the ability of spiny hopsage seedlings to compete with
herbaceous species is poorly known, the species should
be planted separately or in mixtures with other shrubs.
Shrub seeds with different planting depth requirements
must be planted through separate drill drops; seeds of
most shrubs can be mixed together for planting through
seeder-packers. Spiny hopsage may be mixed with other
grass, forb, and shrub seeds for aerial seeding, but seeds
should be covered. A rate of 66 seeds/m2 is frequently
used for planting shrub mixes. The planting rate for
spiny hopsage often may be dictated by seed availability.
Late fall or winter planting is required for spiny hopsage in southwestern Idaho and southeastern Oregon to
permit exposure of bracted utricles or seeds to cool, moist
seedbed conditions. Fall planting may also be required in
the Mojave Desert to permit germination and emergence
following fall or winter precipitation.
Microenvironmental conditions in prepared seedbeds
differ sharply from those in natural seedbeds beneath
nurse plants. Consequently, spiny hopsage establishment
may be enhanced by mulching or water catchment techniques that moderate soil water, temperature, or nutrient
conditions.
255
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