Prosopis pubescens Benth.

More info for the terms: fire severity, presence, severity

Survival of other mesquite species and riparian vegetation in general
depends on a number of factors including fire severity and site conditions
such as moisture content before the fire and presence and extent of flooding
after fire [5,26,32,111]. In an investigation of both honey and screwbean
mesquite, Anderson [1] states that mesquite recovery from fire, if it occurs,
is very slow.

More info for the terms: competition, fire frequency, frequency, fuel, root crown

Screwbean mesquite is likely to be similar to other southwestern mesquites, in that response
to fire depends on several factors including age of individuals, moisture availability, and
fire frequency and intensity [5,26,27,73,111]. As they mature honey and velvet mesquites
become more resistant to fire [5,26,27,73,111]. Amount of fuel may also influence mortality.
Cable [26] observed higher mortality of velvet mesquite in a site with fuel levels of 4,480
lb/acre than an area with fuels of 2,200 lbs/acre. However, Wright and others [111] found honey
mesquite mortality to be independent of amount of fuel between 4,000 and 7,000 lbs/acre. They did
observe higher mortality of honey mesquite in dry years, due to fires burning the root crown [111].
When the root crown is not damaged, mesquites exhibit basal sprouting after being top-killed [5,26,111].
Mesquites can also sprout from axillary buds on branches within the crown [5,26]. If screwbean
mesquite has the ability to sprout from the root crown after fire, its response could be quite
similar to that of other mesquites. If not, it is likely to be much more susceptible to fires.

Seedling establishment of velvet mesquite on burned sites was less than in unburned plots [27].
There may be multiple causes for this including high seedling mortality [5,73,111], changes to
site conditions which make establishment difficult [24], partially top-killed mesquites producing
fewer seeds [110], and mortality of seeds when exposed to high temperatures. Slightly increased
germination rate of thermally scarified screwbean mesquite seeds compared to nonscarified seeds
was demonstrated in greenhouse studies [34], but has not been reported in field studies (see the Germination section).

In the riparian habitats in which screwbean mesquite occurs, competition from tamarisk also affects
postfire communities. As fire frequency increases, flooding decreases, and water tables drop, the competitive
advantage of tamarisk over other riparian species increases. In addition, fire can increase alluvium
salinity [24], further increasing the competitive advantage of tamarisk in the postfire environment.
A more in depth discussion of the interaction between tamarisk and fire can be found in the FIRE REGIMES and Successional Status sections.

screwbean mesquite

screwbean

tornillo

The Arizona Game and Fish Department lists screwbean mesquite as a harvest
restricted species, meaning permits are required to remove plant by-products
[6]. In addition, Plants Database lists screwbean mesquite as a salvage assessed
species [102]. According to the Arizona Game and Fish Department, permits are
required to remove live individuals of species that are salvage assessed [6].

More info for the terms: indehiscent, perfect, shrub, tree

This description provides characteristics that may be relevant to fire ecology,
and is not meant for identification. Keys for identification are available
[9,65,79,104], including a preliminary key for identification of seedlings
[113].

Screwbean mesquite is a native, deciduous, small tree or shrub [9,64].
It can reach a maximum height of about 30 feet (10 m) with a 1 foot (30 cm)
trunk diameter [36,70,79,104]. In the northernmost portion of its range it
commonly grows to between 8 and 13 feet (2.5-4.0 m) tall [9,109]. Growth is
typically shrubby and branches are long and thin [36,70,79,104]. The bark is
thick and fibrous when mature [70,104]. Spines, 0.2 to 1 inch (5-25 mm)
in length, protect the 0.8 to 3 inch (2-7.6 cm) bipinnately compound leaves,
which typically have 5 to 9 pairs of leaflets that are 0.1 to 0.375 inch long
(3-9.5 mm) [36,65,70,79,104,109]. Flowers are perfect and occur in cylindrical
spikes about 1.6 to 3.1 inches long (4-8 cm) [9,36,65,70,79,109]. The tightly
coiled, indehiscent pods that form after pollination are 0.8 to 2 inches (2 - 5 cm)
in length, 0.16 to 0.25 inch (4-6.4 mm) in diameter, and contain numerous seeds
[36,65,70,79,104,109].

The native range of screwbean mesquite extends from southeastern California west
into southern Nevada, extreme southwestern Utah, southern and western Arizona,
southwestern and south-central New Mexico, western Texas and northern Mexico,
including Baja California, Sonora, Chihuahua, and Coahuila [9,65,70,74,89,109].
Screwbean mesquite has been introduced to areas in India, Pakistan, and southern
and southwestern Africa [20,84]. However, these introductions have rarely been
successful [84].The U.S. Geological Survey provides a distributional map of screwbean mesquite in North America.

More info for the terms: adventitious, cover, fire frequency, fire interval, fire regime, frequency, fuel, litter, root crown, shrub

Fire adaptations:

Screwbean mesquite can survive fire [22,58,78], but little is known of the
adaptations that allow for this. Weak resprouting after fire has been reported
[105], but whether this was from surviving apical buds or adventitious buds on
the root crown, as in other southwestern mesquites [5,110], is not discussed.
Screwbean mesquite colonization of areas recently disturbed by flood has been
reported [43,99]. However, the approximately 15-year lag time before screwbean
mesquite established on an area burned in a 1930 fire in Thousand Palm Oasis, CA,
illustrates that it does take longer for screwbean mesquite to establish on at
least some burned areas [105].


FIRE REGIMES:

Historically fire was probably infrequent in many screwbean mesquite-containing
habitats. In dry areas with low vegetation cover, fire is usually able to spread
only after prolonged wet periods result in increased fuel loads [8,75]. Little is
known of the historic fire frequencies in riparian habitats containing screwbean
mesquite. Northwestern coniferous riparian areas have been shown to have longer
and more variable fire intervals than surrounding uplands [95]. In northern riparian
deciduous communities, fires are infrequent due to typically high moisture content
and high leaf litter decomposition rates [16]. Although site characteristics, such
as moisture conditions and the fire frequency of neighboring habitats, are likely
to result in variation between riparian areas, a relatively infrequent fire interval
is probably applicable to southwestern cottonwood-willow communities as well [24,92].
In mesquite bosque habitats on upper river terraces it is possible that fires were
comparatively more frequent and may have been a factor, along with flooding, in
maintaining the open understory of these forests [58,78]. However, Busch [22] found
significantly smaller area of burned mesquite-dominated or codominated communities
than was expected based on the proportion this type in the riparian areas investigated.
In addition, Busch [22] found that screwbean mesquite communities with less vertical
canopy development burned more often than average stands. Some riparian areas, such as
desert oases, may have experienced more frequent fires [105]. There is evidence that some
wetland areas, at least in the Sonoran region, experienced frequent fires before European
settlement [31]. Although the historic role fire played in southwestern riparian habitats
is not well understood, there is strong evidence that currently fire occurs in riparian
habitats invaded by tamarisk at higher frequencies than other riparian communities [22].
One study of tamarisk stands along the Colorado River found that of 25 sites 21 had burned
over 15 years [4]. Although screwbean mesquite may survive these fires, its recovery is
likely to be much slower than that of tamarisk [1,24,59]. With an increasing frequency of
fire screwbean mesquite will eventually be replaced [22,30,78].


The following table provides fire return intervals for plant communities
and ecosystems where screwbean mesquite can occur. Find further fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Community or Ecosystem Dominant Species Fire Return Interval Range (years)
saltbush-greasewood Atriplex confertifolia-Sarcobatus vermiculatus < 35 to < 100
paloverde-cactus shrub Cercidium microphyllum/Opuntia spp. < 35 to < 100
creosotebush Larrea tridentata 85]
mesquite Prosopis glandulosa 76,85]

Burning at low intensities on sites with relatively unaltered water regimes and little or no tamarisk
is likely to have the least detrimental effects on screwbean mesquite. Fire has been used in programs
to eradicate tamarisk but has generally been unsuccessful [83]. For information on the management of
tamarisk, see the tamarisk summary.

More info on this topic.

More info for the term: phanerophyte

RAUNKIAER [87] LIFE FORM:



Phanerophyte

More info for the terms: habitat type, presence

Screwbean mesquite is found along streams, washes, floodplains, gullies, and in
alkali sinks, oases, arroyos, and bajadas in the desert southwest [9,36,58,105].
It reaches dominance on floodplains in a zone near the edge of the 1st terrace
and on higher alluvial terraces of large perennial waterways, approximately 5 to
20 feet (1.5-6 m) above the river channel [58,72,78,83].


Elevation:
Screwbean mesquite has been reported at elevations from near sea level to 5,500 feet
(1,676 m) [70]. Elevational ranges by state are shown in the table below.


bordercolor="#111111" width="53%" id="AutoNumber2"> State Elevation
Utah 2,400 to 3,300 feet (730 - 1,000 m) [9,109]
Nevada below 3,300 feet (<1,000 m) [9]
Arizona just above sea level to 5,500 feet (<1,675 m)
New Mexico just above sea level to 5,500
feet (<1,675 m) [70]
California below 5,000 feet (1,525 m) [58]
Texas 1,800 to 4,000 feet* (550 - 1,220 m) [107]

* screwbean mesquite is a dominant species in a habitat type that occurs in this
elevational range


Soils:
Screwbean mesquite occurs on a wide range of soil textures [28,72]. Campbell and
Dick-Peddie [28] reported screwbean mesquite on sites with light and sandy to heavy,
clay soil textures. Individual articles have reported screwbean mesquite growing in
silty clay loam [52], rocky clay silt [40], and clay to loam soil textures [99].
Several authors note the presence of screwbean mesquite in sandy areas [9,58,71,100].
Anderson [1] reports that in general, screwbean mesquite does not flourish on clay soils.
Vilela and Ravetta [103] observed higher germination rates and seedling survival in nursery
mix than in soil from a site containing velvet mesquite, which performed better than
adding fertilizer to the same soil. See the Germination and Seedling establishment/growth
sections for more detailed description of these results.


Screwbean mesquite can often be found in slightly to moderately saline soils [65,71].
Screwbean mesquite was found to be more salt tolerant than Fremont cottonwood and Goodding
willow at shallow [61] and deep [1] soil levels. In a laboratory study Jackson and others
[61] observed 100% survival over 120 days when salt concentrations were 36,000 mg/l or less.
After 120 days of exposure to 60,000 mg/l salt concentrations 70% of screwbean mesquite survived.
There was a trend for less stem growth in the 36,000 and 60,000 mg/l treatments. It is possible
that screwbean mesquite responses were lower than those of other species due to the slow growth
of screwbean mesquite. Percent germination showed a dramatic change, with 98%-100% germination
at or below 6,000 mg/L and 0% germination at salt concentrations of 18,000 mg/L and higher
[61]. When revegetating Bosque del Apache National Wildlife Refuge, NM, screwbean mesquite was
planted on sites with salinities between 3 and 8 dS/m [99].


Screwbean mesquite occurs on alkaline sites, as well. For instance, Goel and Behl [52] performed
experiments in which screwbean mesquite was grown in an area with pH ranging between 8.5 and 10.6
and the soil from a site with velvet mesquite used in Viela and Ravetta's [103] experiments had a
pH of 8.2.


In addition, many mesquite species have been shown to fix nitrogen [45]. Although nitrogen fixation
in screwbean mesquite has been reported [84], data demonstrating this is lacking.


Water
Although a drought-tolerant species, depth to subsurface water is important to screwbean mesquite
[28,56,83,100]. It is considered an obligate riparian species in most of its range [33]. Depths of
subsurface water greater than 13 feet (4 m) are likely to be inhospitable to screwbean [1] and in
revegetation efforts on the Bosque del Apache National Wildlife Refuge it was not planted in areas
where depth to the water table was greater than approximately 4 feet (1.2 m) [99]. Reports of screwbean
mesquite on upland areas have not included information, such as water table depths, that would assist
in determining what is allowing for screwbean mesquite occurrence outside the riparian zone [60,101].
Annual precipitation in the mesquite habitat type, in which screwbean mesquite can be a dominant
species, is between 3 to 20 inches (7.5-50 cm) [72].


Historically, flooding was a typical disturbance in habitat types in which screwbean mesquite occurs
[1,58,83]. It can survive 1 to 3 months of flooding during the growing season [106], and establishes on
recently flooded areas [43,99].

More info on this topic.

This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

More info for the term: cover

SAF COVER TYPES [41]:





68 Mesquite

235 Cottonwood-willow

242 Mesquite

More info on this topic.

This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

More info for the term: shrub

ECOSYSTEMS [49]:





FRES30 Desert shrub

FRES33 Southwestern shrubsteppe

More info on this topic.

This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

More info for the term: shrub

KUCHLER [68] PLANT ASSOCIATIONS:





K027 Mesquite bosques

K040 Saltbush-greasewood

K041 Creosote bush

K042 Creosote bush-bursage

K043 Paloverde-cactus shrub

K044 Creosote bush-tarbush

K059 Trans-Pecos shrub savanna

More info on this topic.

This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):

More info for the terms: cover, woodland

SRM (RANGELAND) COVER TYPES [93]:




203 Riparian woodland

211 Creosote bush scrub

501 Saltbush-greasewood

506 Creosotebush-bursage

507 Palo verde-cactus

508 Creosotebush-tarbush

729 Mesquite

Screwbean mesquite can survive some fires [22,105], but the mechanisms involved or
conditions required have not been investigated.

More info for the terms: cactus, cover, pericarp, seed, shrubs

Screwbean mesquite is important as cover and food to wildlife and is eaten
by livestock.


Palatability/nutritional value:
Many animals find the pods of screwbean mesquite palatable. Coyotes, rodents,
roadrunners, Gambel's quail and Mearns quail all eat screwbean mesquite pods
[53,83,104]. The species of rodents eating screwbean mesquite pods have not been
reported, but in a review Bogusch [15] lists many rodents which feed on southwestern
mesquites, including Merriam's kangaroo rat, desert pocket mouse, and the
white-throated woodrat. Other species noted to eat mesquite pods or leaves were
white-winged doves, ravens, hooded skunks, and deer. Cattle are also known
to eat screwbean mesquite pods [10,65]. However it is possible that the spines of
screwbean mesquite deter some browsers [83].

Although screwbean mesquite is an important part of the diet for many species, it is not
recommended as animal feed. Like other mesquites, screwbean mesquite is
high in seed protein and pericarp sugar [11]. However, in a feeding trial on young
chickens screwbean mesquite was shown to result in a negative protein efficiency ratio,
which means individuals fed on this diet exhibited a net nitrogen loss [11]. The following
table shows the composition of screwbean mesquite pods [11].

bordercolor="#111111" width="72%" id="AutoNumber1">
% H2O
% Protein (N x 6.25)*
% Fiber
% Ash
% Sugar
Whole pod 5.9 11 17 3.8 25
Seeds 7.4 26 - - -

*not corrected for nonprotein nitrogen


Cover value:
Screwbean mesquite-containing habitats provide good cover for birds, and several bird
species nest in screwbean mesquite communities [7]. Johnson and others [63] state
"some of the cottonwood-willow and associated mesquite riparian vegetation types
are the most productive avian habitats in the western U.S." Gullion [53] notes the
high quality of cover for Gambel's quail provided by vegetation comprised of screwbean
mesquite and other shrubs. Abert's towhee, mourning dove and Gambel's quail nest in
screwbean mesquite communities year round [77]. Verdin and black-tailed gnatcatchers are
resident summer species in mesquite communities [77,82]. Some summer nonresidents include
ash-throated flycatcher, Lucy warbler, northern oriole, and the white-winged dove [77].
In winter, ruby-crowned kinglets and yellow-rumped warblers occur [77,82]. Engel-Wilson
and Ohmart [39] cite their previous finding that during winter more avian habitat
specialists were found in cottonwood-willow and screwbean mesquite communities, even
though only 99 acres (40 ha) within the 49,420-acre (20,000 ha) study area were comprised
of these types. Other bird species that inhabit screwbean mesquite-containing habitats include
black-chinned hummingbirds, cactus wrens, ladder-backed woodpeckers, pyrrhuloxias and Crissal
thrashers [18,82,107].


Screwbean mesquite communities also provide cover to small mammals. Thickets of Sonoran
desertscrub support desert cottontail as well as several rodents [101]. Screwbean mesquite
habitat types have relatively high diversity of nocturnal rodents including cactus mouse,
desert pocket mouse, Merriam's kangaroo rat, and the white-throated woodrat [2].

More info for the terms: cover, forbs, habitat type, herbaceous, series, shrubs, tree, woodland

Screwbean mesquite is associated with desert riparian woodland and scrub habitats.
Saltbush (Atriplex spp.), arrowweed (Plucea sericea), and introduced
tamarisk (Tamarix spp.) co-occur with screwbean mesquite throughout most
of its range [25,28,33,58,78].

Screwbean mesquite can be a dominant species in the mesquite bosque habitat type
[7,58,86,107]. In southern California, Baccharis (Baccharis spp.) and desert
lavender (Hyptis emoryi) are associated understory species in mesquite
woodland [86]. Along the Colorado River this habitat type may include honey mesquite
(Prosopis glandulosa), velvet mesquite (P. velutina), netleaf hackberry
(Celtis reticulata), creosotebush (Larrea tridentata), wolfberries
(Lycium spp.), white bursage (Ambrosia dumosa), fourwing saltbush
(Atriplex canescens), big saltbrush (A. lentiformis), cattle saltbush
(A. polycarpa), blue paloverde (Parkinsonia florida), common elderberry
(Sambucus nigra ssp. canadensis), Mojave seablite (Suaeda moquinii)
and forbs such as carelessweed (Amaranthus palmeri) and gourds (Cucurbita spp.)
[58]. Along the Rio Grande River in southern New Mexico mesquite bosques frequently contain
screwbean mesquite with skunkbush sumac (Rhus trilobata), wolfberries, seepwillow (B.
salicifolia), arrowweed, and the grasses alkali sacaton (Sporobolus airoides)
and saltgrass (Distichlis spicata) [28,33].

Screwbean mesquite occurs in other riparian woodlands, such as the desert microphyll and
cottonwood (Populus spp.)- willow (Salix spp.) cover types. For example, in
New Mexico the gallery forests of the Rio Grande River contain Rio Grande cottonwood
(P. deltoides var. wislizeni), Fremont cottonwood (P. fremontii), sandbar willow
(S. exigua), Goodding willow (S. gooddingii), black willow (S. nigra),
New Mexico olive (Forestiera pubescens var. pubescens), false indigo (Amorpha fruticosa),
seepwillow, and tamarisk, with screwbean mesquite having varied importance [37,38,99,112]. Herbaceous
species typical in these areas include common lambsquarters (Chenopodium album) , narrowleaf
globemallow (Sphaeralcea angustifolia), white sweetclover (Melilotus alba), and silverleaf
nightshade (Solanum elaeagnifolium) [99]. On the Rio Grande River in western Texas, screwbean
mesquite occurs with lanceleaf cottonwood (Populus x acuminata), willows, seepwillow,
buttonbush (Cephalanthus occidentalis), desert willow (Chilopsis linearis),
tamarisk, blackbrush acacia (Acacia rigidula), catclaw acacia (A. greggi), tree tobacco
(Nicotiana glauca), and Texas paloverde (Parkinsonia texana) [91,107,108]. Screwbean
mesquite is an associate of Chihuahuan Desert riparian forests, which may contain Fremont
cottonwood, willows, desert willow, honey mesquite, velvet ash (Fraxinus velutina),
seepwillow, common reed (Phragmites australis), tamarisk, and giant reed (Arundo donax)
[55]. Similarly, Sonoran streams and rivers which support riparian woodland can contain Fremont
cottonwood and Goodding willow with either velvet ash, western honey mesquite (Prosopis glandulosa
var. torreyana), velvet mesquite, or screwbean mesquite [98]. The vegetation of Sonoran
alkali sinks also contains Fremont Cottonwood, Goodding willow, screwbean mesquite, as well as
seepwillow, and big saltbrush, and spiny chloracantha (Chloracantha spinosa),
but is frequently dominated by tamarisk and arrowweed in areas with no to moderate salinity [19].
Another mesquite-containing woodland is the desert microphyll woodland described by Thorne [100].
The vegetation may include blue paloverde, catclaw acacia, smoketree (Psorothamnus spinosus),
western honey mesquite, desert willow, desert ironwood (Olneya tesota), creosotebush, desert
lavender, plus smaller shrubs, such as singlewhorl burrobush (Hymenoclea monogyra), Anderson
wolfberry (L. andersonii), broom baccharis (B. sarothroides), fairyduster (Calliandra
eriophylla), lotebush (Ziziphus obtusifolia var. obtusifolia), and desertsenna
(Senna armata) [100]. Additionally, Sonoran oases contain screwbean mesquite along with California
palm (Washingtonia filifera), Olney threesquare (Scirpus americanus), singlewhorl burrobush,
arrowweed, saltgrass, alkali goldenbush (Isocoma acradenia), cattle saltbush, wheelscale saltbush
(Atriplex elegans), desertholly, (A. hymenelytra), and sweetbush (Bebbia juncea)
[88,105].

Screwbean mesquite also occurs in scrub vegetation. For instance, along the
lower Colorado and Gila rivers and in the Salton Sea basin, vegetation is
typically dominated by tamarisk with some sites also containing arrowweed, big
saltbrush, iodinebush (Allenrolfea occidentalis), Mojave seablite, cattle
saltbush, honey mesquite, and/or screwbean mesquite [78]. Haigh [54] reported screwbean
mesquite, arrowweed, iodinebush, and broom baccharis occurring in a tamarisk-dominated
community along an intermittent stream in southern Nevada. The riparian scrub habitats
of southern Nevada valleys are comprised of species such as screwbean mesquite, sandbar willow,
common reed, tamarisks, arrowweed, seepwillow, and saltbush [30,53]. Mohave wash scrub may
consist of screwbean mesquite, catclaw acacia, desert saltbush, desert willow, Mojave rabbitbush
(Ericameria paniculata), smoketree, white burrobrush (H. salsola), pygmy cedar
(Peucephyllum schottii), western honey mesquite, desert almond (Prunus fasciculata),
and skunkbush sumac (Rhus trilobata) [58]. Mesquites (Prosopis spp.) are
also common associates of desert saltbush in some areas of the saltbush series of Sonoran
desert scrub vegetation [101].

Classifications in which screwbean mesquite is a characteristic or associate
species are listed below by location.

California: [3,19,58,78,86,89,100]

Arizona: [78,89]

New Mexico: [28,33,89]

Texas: [28,55,89]

Mexico: [55,78,89]

More info for the terms: shrub, tree

Tree-shrub

As an invasive, screwbean mesquite is much less of a concern than other southwestern mesquites
[47]. It does have some weedy tendencies [84], and Northington and Burgess [81] report a probable
introduction of 3 screwbean mesquite trees in Guadalupe Mountains National Park, TX. The source
of a small population in the San Joaquin Valley, CA, is uncertain, but it may have been introduced
as well [57]. However, widespread invasion of screwbean has not been reported. Being largely
restricted to riparian habitats is a likely factor limiting the potential spread of screwbean
mesquite.

More info for the term: fuel

According to literature reviews and some ethnographic investigations [10,38], screwbean
mesquite was a food source for many southwestern tribes, including the Chauilla, Pima,
Apache, Cocopa, and Quechan [10,29,44]. The Chauilla Indians prepared and used the sweet,
dried pods in the much same way as other mesquite pods, by grinding them into meal for bread
or gruel [10,12,15,104]. Other tribes, such as the Pima, preferred to pit-cure the pods before
eating or further processing [10,29]. In addition, the pods or meal could be used to
make beverages [12,15,29,104] and a syrup was made by boiling the pods [15,36].

Screwbean mesquite was used by many southwestern tribes in a variety of other ways. The bark
and roots had medicinal value and were used to treat wounds [10,15,65,104]. The use of gum,
bark, and blossoms as food, medicine, dyes, and in making pottery have been reported for
other southwestern mesquites [10,12,88], but it is uncertain if screwbean mesquite was also
used for these purposes.

Currently use of screwbean mesquite is limited. Besides a small market for
timber products, the current main use of mesquite is in the production of honey
[42]. However, honey mesquite is typically used and the extent of screwbean mesquite
use has not be reported.

Wood Products:



The wood of mesquites is hard, durable, and attractive [69,80]. Due to the slender nature
of the branches and often shrubby growth form screwbean mesquite is most typically used for
fuel and fence posts [13,29,65,70,80,104]. Native Americans used the wood for fuel as well as
for weapons, tools, and construction [10,29]. The wood is also used locally for small items,
such as tool handles and trinkets [13,65,104]. Custom woodworkers use mesquite wood, including
that of screwbean mesquite, for making small pieces of furniture and specialty items [69].

More info on this topic.

Flowering typically starts in May [9,65,74,79] and pods begin ripening in July [9]. Campbell and
Dick-Peddie [28] note an approximate 20-day delay in the development of screwbean mesquite floral
and vegetative parts in Albuquerque, NM, compared to El Paso, TX.

More info for the terms: cover, frequency

Current available evidence suggests that screwbean mesquite will most likely decline
due to fire, although the extent can vary. Busch and Smith [23] note screwbean
mesquite's absence from a site severely burned 3 years previously, despite unburned
areas having scattered individuals. Egan [35] suggests boron or salt accumulations may
explain the lack of growth on sites 5 growing seasons after a severe fire. In at least
some situations, it can take about 15 years for screwbean mesquite to establish after
fire [105]. Busch [21] found that although honey and screwbean mesquite occurred on
recently burned sites, mesquite did not dominate any sites after fire, not even those
areas that had been classified as mesquite-dominated before fire. However, screwbean
mesquite did occur on burned sites of every vegetation type, and Busch and Smith [25]
found only slight effects of fire on screwbean mesquite cover and frequency in cottonwood-willow
communities.

POSTFIRE REGENERATION STRATEGY [97]:




Reports of screwbean mesquite's occurrence in burned areas do not explain its postfire
regeneration strategy.

More info for the terms: fruit, layering, peat, restoration, scarification, seed, tree

Screwbean mesquite reproduces by seed which is typically scarified by the
digestive tracts of animals. Some mesquite species have dormant buds on the root
crown that sprout when plants are top-killed [5,46,111]. There are no reports of these
structures on screwbean mesquite.

Breeding system:
Screwbean mesquite is monoecious 
[109].
Given that most species of this genus are self-incompatible [52], it is likely true
of screwbean mesquite.

Pollination:
Mesquites are typically insect pollinated [66,94]. Although pollination information
specific to screwbean mesquite is not available, there is no evidence to suggest
that is not insect pollinated as well. Screwbean mesquite is one of several mesquite
species that make excellent bee forage and is also a source of nectar for butterflies [42,64].
Bees use both the pollen and nectar of screwbean mesquite [50,64].

Seed production:
Although there is a lack of information specific to screwbean mesquite, seed
production has been investigated for other members of the genus. Ffolliott [46]
noted the estimate for seed production of mesquite species in Latin America, obtained
in his previous work, as 104 to 105 seeds per tree in a given
reproductive season. This is despite a reportedly low proportion of flowers that produce
fruit with viable seeds [46]. Glendening and Paulsen [51] reported their largest velvet
mesquite pod harvest as 39.5 pounds (17.9 kg), which equated to approximately 142,000
seeds and was obtained from a 10.5-foot (3.2 m) tall tree with a crown diameter of 19 feet
(5.8 m). However the 4 year average of pods produced by velvet mesquite trees at
elevations between 3,000 and 4,500 feet (914-1372 m) in southern Arizona was
1.38 pounds (0.62 kg). It is probable that seed production and variation between
individuals of different sizes is comparable to screwbean mesquite; however the
degree of similarity is unknown. 

Seed dispersal:
Seeds of screwbean mesquite are transported by water and domestic and wild animals,
including coyotes and rodents [11,65,83]. When eaten, seeds get the added advantage
of avoiding insects, thus decreasing insect-caused mortality [67]. Digestion also
scarifies the seeds, which is generally required for germination [34,67,103]. The sprouting
of uneaten velvet mesquite seeds from rodent caches has been reported [51] and, given the
use by rodents, could occur in screwbean mesquite as well.

Seed banking:
After 44 years, 60% of scarified velvet mesquite seeds from herbarium specimens germinated
on damp filter paper in a dark oven set to 80 °F (26.7 °C) [51]. Although no similar information
is available for screwbean mesquite, it is probable that their seeds also can remain dormant for long
periods.

Germination:
Scarification is necessary for screwbean mesquite seeds to germinate [34,67,103]. This
typically occurs naturally by passing through the digestive tract of animals, but also
occurs due to weathering [65,67,83,103]. Rates of germination in the wild are unknown; however,
several laboratory studies have been performed. Typical rates of germination were between 60% and
70%, for treatments which included chemical or mechanical scarification [34,90,103]. Jackson and others
[61] obtained the highest germination rates, with 98%-100% of seeds germinating in treatments with
salt concentrations at or below 6,000 mg/l. They used a chemical scarification method in which seeds
were soaked in 98% sulfuric acid for 25 minutes. Thermal scarification may increase germination rates
compared to nonscarified controls, but have been substantially less effective than mechanical and
chemical treatments. Dreesen and Harrington [34] demonstrated an increase in germination rates compared
to nonscarified seeds when using a thermal scarification method where water heated to 194 °F (90 °C) was
poured over seeds and then steeped for 4 hours. The mean increase was 7% for one seed source and 18% for
another. However, mechanical scarification using a commercial scarifier, which uses a spinning paddle to
throw seeds against an drum lined with 100 grit sand paper, showed a much larger increase to a mean of 62%
germination from one seed source and 92% from the other [34]. Vilela and Ravetta [103] reported germination
rates of just under 60% for a mechanical scarification method in which seeds were nicked with a razor blade;
this was much higher than the thermal method which had germination rates of less than 5%. Chemical
scarification showed an even larger improvement, with a germination rate of approximately 64%. In this case,
thermal scarification involved dropping seeds in boiling water until it reached room temperature and chemical
scarification was performed by soaking seeds in sulfuric acid 1 N for 15 minutes, rinsing them in running water
3 times for 2 minutes, and then soaking them in water for 15 to 30 minutes [103]. Tumble scarification, in
which seeds were placed in a rock tumbler with pea gravel and coarse grit for 2 to 3 hours, resulted in
slightly less germination than nonscarified seeds [34].

Soil also has an effect on germination. In a laboratory study, the soil with the highest germination rate
(65%) was nursery mix (ground sphagnum (Sphagnum spp.), peat moss, and vermiculite in 1:1:1 ratio).
Soil from a site with velvet mesquite resulted in 35% germination of screwbean mesquite, while only 25% of
seeds germinated when fertilizer was added to the soil from the site with velvet mesquite. These figures are
from seeds scarified by chemical, mechanical, or thermal methods randomly planted in 1 of the 3 mixtures [103].

Seedling establishment/growth:
Although mesquite seeds can germinate on the soil surface, seedlings require a covering of 0.4 to 0.8
inches (1-2 cm) to provide anchorage and moisture [46].

Survival of screwbean mesquite seedlings in laboratory studies has been varied.
Jackson and others [61] observed 100% survival for 120 days in all treatments with
salt concentrations of 36,000 mg/l or less. Vilela and Ravetta [103] also obtained high
seedling survival, with seedlings in the nursery potting mix having nearly 100% survival
to 60 days after germination. Those in soil from a site with velvet mesquite had about 87%
survival, while approximately 84% of those growing in the fertilized velvet mesquite soil
survived 60 days after germination. In contrast, Rhodes and Felker [90] found screwbean mesquite
a difficult species to grow in a greenhouse. Over the first few weeks of their trial screwbean
mesquite seedlings exhibited a 68% survival rate. All seedlings subsequently died, but it is
unknown whether the mortality was due to disease or the experimental increase in salt concentrations
to 1.2%. Again, field data are not available.

Asexual regeneration:
There are no records in the literature of screwbean mesquite propagating vegetatively in the
wild. However, Goel and Behl [52] classified screwbean mesquite as "easy to root"
in an investigation of techniques for increasing output of genetically desirable individuals
for use in restoration planting. Between 80% and 90% of attempts resulted in rooting of screwbean
mesquite, depending on the method used. Eighty percent of cuttings rooted. Air layering, a rooting
method in which a ring of bark is removed and covered in sphagnum, then covered in plastic, was
slightly more successful, and air layering with the application of the root promoting indole acetic
acid resulted in 90% of samples rooting [52].

More info on this topic.

This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

BLM PHYSIOGRAPHIC REGIONS [14]:





7 Lower Basin and Range

13 Rocky Mountain Piedmont

(key to state/province abbreviations)


UNITED STATES


AZ CA NV NM TX UT





MEXICO
B.C.N. Chih. Coah.
Son.

More info on this topic.

More info for the terms: fuel, succession

Shade tolerance: Screwbean mesquite is moderately shade
tolerant, with a layer occasionally forming under cottonwood and willow canopies [28]. Vilela and
Ravetta [103] found high nitrogen concentrations in green screwbean mesquite stems and pose the possibility
that they could be photosynthetically active.

Although typical succession, from one community type to another, has not been demonstrated in desert
riparian habitats of the American southwest [22,62], this could be changing. Historically species
establishing on disturbed sites would be the same species present before the disturbance and were
likely to persist until another disturbance occurred [62]. However, Cleverly and others [30] found
tamarisk dominating older sites. Over time, changes to water regimes including less frequent flooding,
lowering water tables, and increasing salinity will favor tamarisk [25,30]. Dick-Peddie [33] classifies
communities dominated by tamarisks as a successional-disturbance vegetation type. In addition, tamarisk
dominance seems to result in more frequent fires, likely due to deeper water tables and decreased flooding
producing larger and drier fuel loads [4,21,22]. Due to better regeneration than other burned riparian
species [24], tamarisk and arrowweed replace more original vegetation with each successive fire [22].
Smith and others [96] provide a review of these studies.

The currently accepted scientific name of screwbean mesquite is Prosopis
pubescens Benth. (Fabaceae) [9,64,65,102,104,109]

Screwbean mesquite has been used in revegetation efforts in areas dominated by
tamarisks [17,35,99]. It can be planted on sites with higher salt concentrations
than many other native riparian species can tolerate [61,99]. However results of
screwbean mesquite plantings in revegetation efforts have been mixed. Successes are
mainly attributed to planting on sites within the requirements of screwbean mesquite
[17,99]. See the Asexual regeneration section for
success rates of different propagation techniques.

Perennial, Trees, Shrubs, Woody throughout, Nodules present, Stems erect or ascending, Stems or branches arching, spreading or decumbent, Stems greater than 2 m tall, Trunk or stems armed with thorns, spines or prickles, Stems solid, Stems or young twigs sparsely to densely hairy, Leaves alternate, Leaves clustered on spurs or fasicles, Leaves petiolate, Extrafloral nectary glands on petiole, Stipules inconspicuous, absent, or caducous, Stipules persistent, Stipules free, Stipules spinose or bristles, Leaves compound, Leaves bipinnate, Leaf or leaflet margins entire, Leaflets opposite, Leaflets 10-many, Leaves hairy on one or both surfaces, Inflorescences spikes or spike-like, Inflorescence ament-like, Inflorescence axillary, Inflorescence or flowers lax, declined or pendulous, Flowers sessile or nearly so, Flowers actinomorphic or somewhat irregular, Calyx 5-lobed, Calyx glabrous, Petals united, valvate, Petals greenish yellow, Stamens 9-10, Stamens completely free, separate, Stamens long exserted, Filaments glabrous, Style terete, Fruit a legume, Fruit unilocular, Fruit freely dehiscent, Fruit oblong or ellipsoidal, Fruit twist ed, Fruit spirally coiled or contorted, Fruit coriaceous or becoming woody, Fruit exserted from calyx, Fruit internally septate between the seeds, Fruit compressed between seeds, Fruit glabrous or glabrate, Fruit hairy, Fruit 3-10 seeded, Fruit 11-many seeded, Seeds embedded in gummy or spongy pulp, Seed with elliptical line or depression, pleurogram, Seeds ovoid to rounded in outline, Seed surface smooth, Seeds olive, brown, or black.

Prosopis pubescens, mezquite dulce o tornillo, és una arbust o arbret que és planta nativa de les regions àrides de Mèxic, (Baja California, Chihuahua, Coahuila i Sonora) i del sud-est dels Estats Units (de Texas a Califòrnia).

Flower spikes

Prosopis pubescens, commonly known as screwbean mesquite, is a species of flowering shrub or small tree in the pea family, Fabaceae, that is native to the southwestern United States (Texas, Arizona, New Mexico, California, southern Nevada and Utah) and northern Mexico (Baja California, Chihuahua, Coahuila, Sonora).

El mezquite dulce o tornillo (Prosopis pubescens) es un pequeño árbol o arbusto nativo de las regiones áridas de México (Baja California, Chihuahua, Coahuila y Sonora) y el sudoeste de EE. UU. (de Texas a California).

Prosopis pubescens là một loài thực vật có hoa trong họ Đậu. Loài này được Benth. miêu tả khoa học đầu tiên.