Index of Species Information

SPECIES:  Prosopis velutina

Introductory

SPECIES: Prosopis velutina
AUTHORSHIP AND CITATION : Uchytil, Ronald J. 1990. Prosopis velutina. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

ABBREVIATION : PROVEL SYNONYMS : Prosopis juliflora var. velutina Prosopis chilensis var. velutina SCS PLANT CODE : POVE COMMON NAMES : velvet mesquite TAXONOMY : The currently accepted scientific name of velvet mesquite is Prosopis velutina Woot.(Fabaceae). There are no infrataxa [17,18,28,61,65,125]. Inter- and intraspecific hybridization within mesquites (Prosopis spp.) is common. Many intermediate forms exist, making identification difficult at the specific or varietal level. Before settlement of the Southwest by Europeans, speceis were separated by geographic barriers. With the introduction of livestock, mesquites have spread, and now have a more or less continuous distribution across the Southwest, which allows for increased hybridization [65]. The ranges of velvet mesquite and western honey mesquite (P. glandulosa var. torreyana) overlap in western Arizona [56] and hybrids are common [6]. Plants in the vicinity of Guaymas, Sonora, and La Pas, Baja California combine characteristics of velvet mesquite, western honey mesquite, and honey mesquite (P. glandulosa var. glandulosa) [65]. LIFE FORM : Tree, Shrub FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


DISTRIBUTION AND OCCURRENCE

SPECIES: Prosopis velutina
GENERAL DISTRIBUTION : The main distribution of velvet mesquite is confined to central and southern Arizona, extreme southwestern New Mexico, and adjacent northern Mexico [56,73].  The eastern boundary of its range is near the Continental Divide in southern New Mexico [115].  The Continental Divide forms a natural boundary between populations of velvet mesquite and honey mesquite (var. uncertain) [115].  In California, velvet mesquite is represented by only a few individuals that occur in Imperial, Riverside, and Kern counties [57].  This population is believed to be from human introductions.  A small, isolated population occurs in the Rio Grande Valley, near El Paso, Texas [65], that is also thought to be introduced. ECOSYSTEMS :    FRES30  Desert shrub    FRES33  Southwestern shrubsteppe    FRES34  Chaparral - mountain shrub    FRES35  Pinyon - juniper    FRES40  Desert grasslands STATES :      AZ  CA  NM  TX BLM PHYSIOGRAPHIC REGIONS :     7  Lower Basin and Range    12  Colorado Plateau KUCHLER PLANT ASSOCIATIONS :    K023  Juniper - pinyon woodland    K027  Mesquite bosque    K031  Oak - juniper woodland    K033  Chaparral    K042  Creosote bush - bursage    K043  Palo verde - cactus shrub    K044  Creosote bush - tarbush    K046  Desert: vegetation largely lacking    K058  Grama - tobosa shrubsteppe SAF COVER TYPES :    235  Cottonwood - willow    239  Pinyon - juniper    241  Western live oak    242  Mesquite SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Velvet mesquite occurs in low elevation vegetation types, including paloverde (Cercidium microphyllum)-bursage (Franseria deltoidea) cacti (Opuntia spp.), desert grasslands, oak woodlands, and pinyon-juniper (Pinus edulis-Juniperus spp.) woodlands [55].  In desert grasslands, it may be found in high enough densities to form "brushy ranges", but in the other vegetation types it is generally found as scattered individuals.  Along major water coarses and their tributaries, however, deciduous woodlands or "bosques" are often dominated by velvet mesquite. Shrubby associates in desert grasslands include viscid acacia (Acacia vernicosa), whitethorn acacia (A. constricta), catclaw acacia (A. greggii), graythorn Condalia lycoides), ironwood (Olneya tesota), burroweed (Haplopappus tenuisectus), hackberries (Celtis spp.), tarbush (Flourensia cernua), and paloverde [15,30,55].  In drainage basins, velvet mesquite often occurs in relatively pure stands of tobosa grass (Hilaria mutica).  On heavy-textured upland soils, velvet mesquite occurs in pure stands of tobosa or sacaton (Sporobolus wrightii) [30]. Velvet mesquite is often interspersed in low elevation oak woodlands dominated by Emory oak Quercus emoryi), Mexican blue oak (Q. oblongifolia) and Arizona white oak (Q. arizonica) [55]. Mesquite bosques were typically open and parklike.  Velvet mesquite often forms nearly pure stands in these riparian situations but may also be interspersed with other trees and shrubs such as netleaf hackberry (Celtis reticulata), wolfberry (Lycium spp.), Mexican elder (Sambucus mexicana), Southwestern condalia (Condalia obovata), and fourwing saltbush (Atriplex canescens) [30,87,93].  The understory was historically dominated by vine mesquite grass (Panicum obtusum), careless weed (Amaranthus palmeri), and in saline areas, by saltbushes (Atriplex spp.).  Today, because of grazing and other disturbances, many bosques have been invaded by introduced grasses and forbs, including cutleaf filaree (Erodium cicutarium), mustard (Sisymbrium irio), red brome (Bromus rubens), and schismus (Schismus barbatus) [86].

MANAGEMENT CONSIDERATIONS

SPECIES: Prosopis velutina
WOOD PRODUCTS VALUE : The chief use of velvet mesquite wood is for firewood.  Mesquite (Prosopis spp.) wood is easily sawed and split, is dry and heavy, ignites readily, and produces intense heat [54].  During the settlement of southern Arizona, velvet mesquite provided dimension lumber for buildings and bridges, walls for corrals, fence posts, tombstones, and fuel for domestic and industrial uses [92,93].  During the 1880's many velvet mesquite bosques were clearcut to obtain wood for these purposes. The wood is still used locally for fence posts and lumber.  In recent years, mesquites have been increasingly used to produce charcoal briquets [35]. IMPORTANCE TO LIVESTOCK AND WILDLIFE : Livestock:  Cattle, horses, sheep, goats, hogs, mules, and burros eat large quantities of ripe velve mesquite fruit when available [29]. Livestock often remove the fruits as high on the tree as they can reach and eat fallen pods lying on the ground [3,51].  Livestock do not consume the foliage to any great extent [80].  Foliage consumption by livestock is greatest during drought years, especially in the early spring when other forage is lacking [29,49].  Most livestock consume mesquite (Prosopis spp.) flowers when available [80].  In some areas of Mexico, mesquite beans are collected, ground, and fed to cattle [31]. Wildlife:  Velvet mesquite annually provides an abundant and nutritious food source for numerous wildlife species when the pods ripen between June and late October [51,71].  The beans and seeds form an important part of the diet of mice, kangaroo rats, woodrats, chipmunks, ground squirrels, rock squirrels, cottontail rabbits, skunks, quail, doves, ravens, jackrabbits, the racoon, coyote, collared peccary, white-tailed deer, mule deer, wild turkey, and mallard [2,9,29,51,52,101,105,122]. Many species of small rodents derive a large portion of their diet from velvet mesquite seeds.  These animals frequently store seeds and whole beans in dens or caches [51].  Many species of birds eat flower buds and young inflorescences of velvet mesquite.  Insectivorous birds feed on the numerous insects that are attracted to velvet mesquite flowers [113].  Many species of quail eat mesquite buds and flowers in the spring, and seeds during the fall and winter [122].  Mesquite seeds often comprise 10 to 25 percent of the diet of Gambel's and scaled quails [31].  Collared peccaries in Arizona feed heavily on velvet mesquite beans from July to September [34].  In south-central Arizona, velvet mesquite fruits comprised 9 percent of the white-tailed deer's and 29 percent of the mule deer's summer diet, but use of any velvet mesquite parts during the rest of the year was minimal [82].  A study in semidesert grass-shrub habitats of southern Arizona found mule deer use of velvet mesquite to vary seasonally.  Velvet mesquite leaves comprised 0.3 percent of the mule deer's diet during the spring, 2.9 percent during the autumn, and 4.9 percent during the winter, while fruits comprised 24.0 percent of the mule deer's summer diet [110]. Mesquite browse is generally not a very important wildlife food source. The wild turkey, ground squirrels, cottontails, and woodrats consume some leaves [9,52].  Jackrabbits often consume large amounts of mesquite and may crop leaves, buds, and bark as high as they can reach [124]. Velvet mesquite seedlings up to about 2 years old are often eaten by jackrabbits and cottontails.  Kangaroo rats frequently eat recently germinated velvet mesquite seedlings [51].  Locally, mule deer consume large quantities of mesquite foliage, but this may reflect a scarcity of other browse rather than a preference for mesquite [109]. PALATABILITY : The sweet, nutritious seed pods of velvet mesquite are highly palatable to all classes of livestock and to numerous small and large wildlife species.  For both livestock and wildlife, the palatability of leaves and twigs is relatively low.  Livestock browse small amounts of leaves and twigs as they green up in the spring, but velvet mesquite browse is otherwise seldom eaten [29].  Leaf consumption may increase during drought years when other forage is lacking, or following a killing frost in the fall [49]. NUTRITIONAL VALUE : Velvet mesquite's fruits are nutritious.  The thick and spongy pericarp is high in sugars and the seeds contain large amounts of protein. Fruits also supply a good source of minerals for herbivores.  Because plants fix nitrogen, the leaves are high in protein.  Nutritional information concerning velvet mesquite fruit is presented below [4]:                 % N    % crude   % fat    % fiber   % ash   % total                        protein                               sugars seed            5.13    29.44    5.68      7.12     3.83      ---- pericarp        1.13     6.88    2.24     23.48     5.52      31.6 whole pod       1.95    11.81    2.36     22.61     4.83      22.2 The mineral composition of velvet mesquite fruit is as follows [4]:                % Ca   % Mg   % Na   % K   ppm Cu  ppm Zn  ppm Mn  ppm Fe seed           .26    .18    .06    .68    13.6    49.6    24.2    46.6 pericarp       .63    .09    .04   1.16     6.4     9.6    11.6    48.8 whole pods     .53    .09    .03   1.27     8.3    26.4    14.5    40.4 Nutritional information concerning velvet mesquite leaves and fruits collected in southern Arizona is presented below [110]:           season      % protein    % K    P/Ca ratio    % In Vitro           collected                                     digestibility leaves    spring        17.6       .23       .28            62.3 fruit     summer        9.5        .16       .23            66.5 leaves    autumn        16.4       .10       .05            44.8 leaves    winter        15.8       .10       .05            44.9 COVER VALUE : Velvet mesquite provides needed security cover for large wildlife species.  Its invasion into grasslands has benefited brush dependent wildlife species such as the collared peccary and mule deer [2,15]. Southern Arizona studies indicate that velvet-mesquite-dominated vegetation types are a preferred habitat of desert mule deer, but that white-tailed deer seldom use velvet mesquite habitats [2,108].  Small mammals such as antelope jackrabbits, woodrats, and kangaroo rats are often found in brushy velvet mesquite habitats.  A southern Arizona study found that 99 percent of available velvet mesquite shrubs housed Merriam kangaroo rat dens [103].  In fact, many species of rodents place their burrows under the protection of velvet mesquite plants [76]. Found in desert environments, velvet mesquite provides shade for livestock and wildlife.  Jackrabbits often use the shade that mesquites provide to help regulate their heat balance [76]. Brushy velvet mesquite ranges provide excellent habitat for the zebra-tailed lizard, desert spiny lizard, western whiptail, and tree lizards.  The desert spiny lizard and tree lizards are primarily arboreal and are often found in mesquite trees.  Tree lizards may aggregate in large numbers in the winter, using the underside of protruding velvet mesquite bark as hibernating sites [47]. Velvet mesquite riparian communities provide important habitat for numerous nesting bird species during both summer and winter.  Along the lower Verde River floodplain in Arizona, 19 species and 244 pairs of breeding birds per 100 acres (40 ha) were found in a velvet mesquite bosque community [117].  In another velvet mesquite bosque community in southern Arizona, 476 pairs of nesting birds were found per 100 acres (40 ha) [46]. VALUE FOR REHABILITATION OF DISTURBED SITES : Saltcedar (Tamarix ramosissima), an introduced species from Eurasia, has invaded and replaced many native Southwestern riparian communities. Since saltcedar communities are much less valuable to wildlife than native communities, methods have been developed for removing the saltcedar and revegetating with native species [70].  Along the lower Colorado River on the border of southern California, nursery-grown western honey mesquite seedlings have been planted with other native species to revegetate riparian areas following saltcedar removal [25,123].  Velvet mesquite can probably be used for these rehabilitation purposes within its range. Ninety-day-old nursery grown velvet mesquite seedlings were successfully transplanted onto 2 feet (0.6 m) of topsoil covering asbestos waste tailings near Globe, Arizona.  Three years after planting, 96 percent of the seedlings were alive and showed better growth and vigor than other shrub species planted [98].  Stem cuttings of several species of mesquite (Prosopis spp.) have been successfully rooted in greenhouse experiments when treated with a rooting compound [41].  Fresh seed that has not been dried will germinate readily without any pretreatment.  Seed that has been stored must first have the hard seed coat scarified, which can be done by knicking individual seeds with a knife or by soaking numerous seeds in sulfuric acid [81].  Nursery-grown velvet mesquite seedlings have reached heights of 2.6 inches (6.6 cm) in 7 months, 6.75 inches (17.1 cm) in 12 months, 8.68 inches (22 cm) in 18 months, and 14.8 inches (37.6 cm) in 21 months [51]. Members of the genus Prosopis are being developed for rehabilitation and biofuel production in developing countries due to firewood shortages, erosion, and other problems associated with desertification [39,40]. North American mesquites, however, appear best adapted to their area of origin. OTHER USES AND VALUES : Velvet mesquite is used as an ornamental shade tree.  It needs little or no watering and can survive on limited rainfall [1,31].  Velvet mesquite provides an excellent source of nectar for honey bees and is one of the most valuable honey plants in Arizona [80]. Mesquite pods have been proposed as a source of food for human consumption because they are very nutritious.  Velvet mesquite pods contain large amounts of sugar and the protein content of the seeds is similar to soy beans.  Flour made from velvet mesquite seeds and pods mixed in small amounts with wheat flour has been tested in various recipes including breads and cookies with favorable results [85]. Research suggests that velvet mesquite could be managed as an agricultural multiple product crop, yielding both nutritious pods and biomass for fuel. Mesquites (Prosopis spp.) were probably the most important wild plant staple of indigenous Southwest peoples [5,37].  The pods were a very reliable food source because fruiting occurred even during drought years.  In some places velvet mesquite bosques extended for miles along river bottoms.  These bosques provided an abundance of beans, allowing indigenous peoples to harvest selectively from trees producing high quality fruits [101].  Pods were collected in large quantities and stored in grainery baskets on the roofs of houses or sheds [5].  The beans were ground into a flour which was used to prepare cakes and breads, the main staple of the diet [5,37].  Various refreshing drinks were made from the sweet pods.  An intoxicating beerlike drink was sometimes prepared by allowing the juices of the pods to ferment. Flowers were eaten raw or roasted, formed into balls, and stored in pottery vessels [37]. Mesquites were not only an important food supply for Southwest peoples but also provided fuel, shelter, weapons, tools, dyes and paints, medicines, cosmetics, baskets, furniture, clothing, rope, glue, and many other everyday items [5,37]. OTHER MANAGEMENT CONSIDERATIONS : Velvet mesquite infests millions of acres of grazing land in Arizona. Introduction of livestock in the Southwest resulted in overgrazing, dispersal of mesquite seed by cattle, and a reduction of range fires due to insufficient fuels which allowed velvet mesquite to increase in density and spread into grasslands [66,95].  Today dense velvet mesquite thickets occur over vast areas that were essentially free of velvet mesquite 100 years ago.  Velvet mesquite is considered a range pest or weed because infestations greatly reduce herbaceous forage available for livestock and makes moving and handling livestock more difficult. Adaptive features that make control difficult include (1) abundant, long-lived seed that is disseminated by livestock and wildlife, (2) high rate of seed germination over a wide range of environmental conditions, and (3) its ability to resprout following injury [42,95].  Areas which have been cleared in the past, either by chemical or mechanical methods, generally were reinfested with seedlings and/or resprouts.  Herbicidal control attempts often resulted in only low to moderate mortality.  Many or most plants resprouted after treatment and developed into multistemmed bushes. Chemical control:  Aerial application of herbicides generally resulted in the greatest herbaceous forage production following treatment. Banned for use on rangelands in the early 1980's, 2,4,5-T was one of the most commonly used methods of velvet mesquite control in the 1950's, 60's, and 70's.  The most effective herbicide for killing mesquites (Prosopis spp.) available for use today is clopyralid; however, it is much more expensive than 2,4,5-T.  Velvet mesquite is probably susceptible to aerial applications of clopyralid, which often results in 50 to 85 percent mortality of honey mesquite [12,62,63,64].  Recent research suggests that even greater mesquite mortality, over 90 percent, can be acheived by mixing clopyralid with picloram or triclopyr [12]. Moderate control has also been achieved with aerial applications of tebuthiuron pellets [49,129]. Mechanical control:  Mechanical methods devised for controlling mesquites include tree dozing, cable chaining, roller chopping, root plowing, tree grubbing, and land imprinting.  For mechanical measures to be effective, the dormant buds which occur along the underground stem must be damaged or removed to prevent sprouting.  If only the aboveground portion of the plant is removed, velvet mesquite will quickly resprout.  Tree grubbing with blades attached to crawler tractors which severs roots 6 to 12 inches (15-30 cm) below the soil surface and root plows which uproot trees are effective control measures, often achieving over 90 percent mortality [78].  Areas root plowed or mechanically grubbed are often seeded with native grasses. Without seeding, serious soil disturbances caused by these control methods often reduces perennial grass cover for several years.  On areas with moderate shrub density, an alternative to root plowing, cabling, or grubbing which disturbs the soil, is land imprinting followed by seeding.  The land imprinter is a heavy roller, set with pyramid shaped teeth, 4 to 6 inches (10-15 cm) long, attached in an irregular pattern and pulled behind a caterpillar tractor.  As the roller passes over the ground it leaves the area looking like a huge waffle.  The tractor and roller crush and shred the vegetation and deposit the mulch into the funnellike depressions [49]. Hand grubbing mesquite seedlings, although very labor intensive, is an effective preventive measure used for removing mesquites during early stages of invasion.  When the roots are severed 4 inches (10 cm) below the soil surface, hand grubbing effectively kills plants under 1 inch (2.5 cm) in diameter [78].  Biological control:  Although not used to date, seed, legume, and flower feeding insects have been proposed as agents for biological control of mesquites [31]. Grazing:  No matter what method of control is used, it needs to be done in conjunction with a proper grazing program to ensure maximum benefits. Due to its reproductive potential and regenerative capabilities, velvet mesquite will probably never be eliminated from sites where it has become established [29].  Dahl [29] suggests that a proper rotation grazing system in coordination with controlled burning promises to be most effective. Wildlife:  Control methods which leave selected individuals, scattered patches, or strips of velvet mesquite can increase forage production for cattle while retaining enough cover for wildlife.  Aerial applications of herbicides is often detrimental to collared peccary populations because prickly pear (Opuntia spp.), an important food source, is susceptible to spraying.  Root plowing disturbs or kills burrowing rodents. Threat to Bosques:  Velvet mesquite bosque communities today cover only a fraction of the acreage covered in presettlement times.  During the settlement of southern Arizona, many bosques were cleared for fuelwood, lumber, and to convert land to agricultural use.  Today, bosque destruction continues due to fuelwood cutting, clearing for further agricultural needs and housing developments, and the lowering of underground water tables [44,86].  Pumping of underground water for agricultural use, has resulted in the total destruction of entire velvet mesquite bosques when water tables were lowered below the rooting depth of the mesquites, about 50 feet (14 m) [67,86].  Remaining bosques are threatened in areas where pumping of underground water continues.  These bosques are extremely important avian habitat [46]. [See Cover Value] Toxicity:  Mesquite pods are normally considered excellent feed for cattle and horses, however when large amounts of beans are consumed continuously over a 2-month period serious digestive disturbances or death may occur [32,116].  The disease known as "jaw and tongue trouble" is characterized in cattle by profuse salivation, continuous chewing, a protruding tounge, and a tilted head.  Animals gradually become emaciated and may lose up to 50 percent of their weight.  If acute symptoms, such as loss of apetite, rapid weight loss, nervousness, a wild expression, and bulging eyes, develop, animals usually die within 2 to 4 days [116].  In cattle excessive buildup of mesquite beans in the rumen apparently destroys the rumen bacteria that digest cellulose and synthesize B vitamins [32].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Prosopis velutina
GENERAL BOTANICAL CHARACTERISTICS : Velvet mesquite is a deciduous, thorny shrub or small tree.  Plants may grow into single-stemmed trees up to 50 feet (15 m) tall with a trunk diameter up to about 2 feet (61 cm) or they may develop into an erect, multistemmed bush [51,69].  The largest trees are often found along water courses or floodplains where the deep root system has access to year-round water.  In general, tree forms are found on alluvial soils whereas smaller forms are found on tighter, rocky upland soils [51]. Velvet mesquite has a strong tendency for apical dominance and a well-developed crown [89].  Undisturbed plants therefore develop into single-stemmed trees.  If the aboveground growth is damaged or removed, such as by freezing weather, drought, fire, trampling, browsing, or cutting, dormant buds located on the underground stem initiate new growth, resulting in the many-stemmed growth form.  In many semi-desert grasslands the shrubby form predominates because years of browsing, trampling, and repeated chemical or mechanical control attempts resulted in many plants sprouting from the base [114]. The bark on older branches and the trunk is dark brown, rough and thick, and separates into long narrow strips [75].  Young branches may be green and photosynthetic [119].  Stout, yellow thorns are about 0.25 to 1 inch (0.6-2.5 cm) long and generally occur in pairs on young branches [75]. The yellowish-green flowers occur on a 2 to 3 inch (5-7.6 cm) long cylindrical, pedunculate, spikelike raceme [51,113].  The flattened, straight or curved legume-type fruits are 3 to 8 inches (7.6-20 cm) long, occur singly or in drooping clusters, and may be yellow, red, black, or mottled [114]. Velvet mesquite is a facultative phreatophyte which extracts moisture from a large volume of soil through a well-developed root system.  In true desert environments plants are often restricted to wash areas where the taproot can penetrate several meters to underground water.  Roots probably do not extend much more than 50 feet (14 m) [67,86], although they have been found at depths of 175 feet (53 m) [99].  Plants growing on sites where the soil is shallow or moisture does not penetrate deeply have an extensive system of lateral roots that reach several meters away from the plant base1w.  Under these circumstances laterals are often concentrated in a zone 6 to 12 inches (15-30 cm) below the soil surface [90].  Plants can also extract water from soil held at high matric forces [89].  These adaptations allow velvet mesquite to retain an entire complement of leaves during all but the most severe droughts. The primary botanical characteristics used to differentiate velvet mesquite, honey mesquite, and western honey mesquite are the size, shape, and hairness of the leaflets.  Velvet mesquite leaflets are generally short, hairy, and closely spaced; those of honey mesquite are long, linear, glabrous and widely spaced; those of western honey mesquite are intermediate [6].  Several manuals and keys are available to aid in proper identification [6,61,75,91]. RAUNKIAER LIFE FORM :    Phaneropyte REGENERATION PROCESSES : Velvet mesquite reproduces sexually by producing an abundance of seeds. Vegetative regeneration commonly occurs following damage to the aboveground portion of the plant. Seed production:  Velvet mesquite flowers are pollinated by insects, predominately bees.  Although mesquite inflorescences contain hundreds of flowers, generally only one to a few fruits develop per inflorescence [113].  This ensures enough resources for proper development of a limited number of fruits per inflorescence.  Insufficient soil moisture can cause early spring flowers to be entirely aborted before pollination occurs.  New flowers will develop if there is sufficient rainfall later in the season.  Due to fluctuations in the weather, fruit production can be quite variable from year to year for plants growing in semi-desert grasslands [51].  Plants growing along washes or in riparian areas, where they have access to permanent underground water, produce fruit quite predictably from year to year.  The seeds are glossy brown, oval, 0.2 to 0.28 inch (5-7 mm) long and 0.12 to 0.2 inch (4-5 mm) wide [6]. There are about 13,418 seeds per pound (29,573/kg) [51].  The reproductive potential of velvet mesquite is often greatly reduced by seed-feeding insects.  The life cycle of Bruchid beetles (Algarobius spp.) and the amical weevil (Bruchus amicus) are dependent upon mesquite fruit.  Female beetles and weevils lay eggs on the pods and as the larvae hatch they burrow into the fruits and feed on the seeds [71].  A small, brown, circular spot often forms on the pod showing evidence of larvae entry.  Fruit collected within a 25 mile (40 km) radius of Tucson had as high as 70 to 80 percent of the seeds attacked by insect larvae [51].  Although flower and pod attacking insects significantly reduces the production of pods and viable seeds per plant, velvet mesquite produces pods in such abundance that numerous viable seeds are still produced [71]. Seed dispersal:  Animals - Pods are eaten and then dispersed by domestic and wild animals.  Cattle and rodents are the primary dispersers of velvet mesquite seed; numerous other animals also consume the pods [see Importance To Livestock And Wildlife].  Studies involving honey mesquite showed that when pods were fed to livestock, 97, 79, and 16 percent of the seeds passed through the digestive tracts of horses, yearling steers, and ewes with the greatest number of seeds passing through between 42 and 60 hours after feeding [43].  When velvet mesquite seed pods were fed to domestic sheep, 32 percent of the seed passed through the digestive tract intact and sound.  Examination of cattle dung piles on velvet mesquite-grasslands at a time when ripe pods were plentiful, showed that each dung pile averaged 1,535 seeds, of which about 65 percent were sound [51].  Because it takes days for seeds to pass through the digestive tracts of domestic animals, seeds are dispersed great distances.  The digestive juices of domestic animals also kills some seed-eating insects [89].  Many rodents collect and store velvet mesquite seeds or pods in caches.  Merriam kangaroo rats often transport seeds more than 100 feet (30 m) [51,103].  Seelings commonly germinate from uneaten seed in rodent caches [103,105].  Sampling in 1948, 1950 and 1951 on the Santa Rita Experimental Range, showed that during these years 37.4, 23.3, and 8.4 percent of seedlings emerging, respectively, were from kangaroo rat caches [51]. Water - Velvet mesquite pods float and are carried downslope by flowing water.  Intense summer rainstorms often cause overland flows of water on areas with only minor slope gradients in the Sonoran Desert.  On the Santa Rita Experimental Range, seedlings are abundant in the alluvium along small water courses and in the alluvial fans formed by these drainages [51]. Seed viability and germination:  Velvet mesquite seeds contain a bony, protective endocarp.  Scarification of this hard seed coat must occur before the seed can germinate.  Scarification of the seed occurs naturally when seeds pass through the digestive system of animals. Seeds remaining in pods not consumed by animals remain dormant until the seed coat is broken by weathering.  Tests of various aged sound seed showed that 1- to 45-month-old scarified seed displayed better than 94 percent germination, 1-month-old unscarified seed had only 20 percent germination, and germination of 5- to 45-month-old unscarified seed never exceeded 7 percent.  Most germination of velvet mesquite seeds within pod segments buried 1 inch (2.5 cm) below the soil surface in Arizona occurred within 3 years, with about 35, 9, and 1 percent germination occurring 1, 2, and 3 years after planting [118].  The protective endocarp allows seeds to remain viable for long periods. Seeds in dry storage have remained viable for decades.  Germination of stored seed has been reported as follows [51]: Age in years            Germination of sound seed                         Unscarified     Scarified     11                     ----            97.5%     44                      20%            60%     50                      30%            60% Planting of unscarified seeds in the field showed that germination of seeds within pod segments was 2 to 3 times greater than that of hulled seeds.  Over a 3-year period, 44.7 percent of seeds planted in pod segments germinated, but only 15.8 percent of hulled seeds germinated [118]. Velvet mesquite seeds germinate over a wide range of temperatures and soil conditions.  Better than 80 percent germination was achieved at temperatures ranging from 61 to 100 degrees F (16-38 C) [112].  High germination occurs over a wide range of soil pH (4-10) and on soils of high salinity [112]. Seedling emergence and establishment:  Velvet mesquite seeds must be covered with a small amount of soil or dung for seedlings to become established.  Seeds that germinate on the soil surface normally die.  In Arizona, seedling emergence is most common during July and August when soil moisture is adequate due to summer rains, but may occur anytime between March and November [51].  Recent research on honey mesquite in Texas suggests that past grazing history has little influence on mesquite establishment in grasslands, but that herbaceous defoliation during the year of seed dispersal is a key factor [16].  In semi-desert grasslands of Arizona, velvet mesquite seedling establishment was similarly found to be much higher in grazed habitats and in areas denuded by drought than in vigorous stands of perennial grasses [51]. In true desert environments, conditions that favor plant establishment may occur only once every 5 to 10 years following intense rains [123]. Because velvet mesquite seeds can remain viable for several years, seeds stored in the soil may germinate following such events.  In a crater in northern Sonora, Mexico, velvet mesquite seedlings became established following two unusually intense rainfalls in 1970 and 1972 which induced ponding [120]. Seedling development:  Soil moisture stress and browsing by rodents and insects often result in very slow development of velvet mesquite seedlings.  Seedlings exhibit more rapid growth on coarse-textured soils than fine-textured soils.  Velvet mesquite seedlings rapidly develop a deep root system which allows them to reach water and nutrients for later growth before upper soil layers become dry [13].  Top and root growth of seedlings found on upland sites at the Santa Rita Experimental Range that were protected from browsing was as follows [51]: age in months       average maximum plant        average maximum root                           height                      penetration                    (inches)  (centimeters)      (inches)  (centimeters)     9                2.1         5.3              20.1        51.0    14                3.0         7.6              27.1        68.8    24                3.7         9.4              ----        ----    38                4.5        11.4              33.4        84.8    50                5.0        12.7              ----        ---- Another study found that on upland sites, 94 percent of all velvet mesquite plants established over a 17-year period were under 3.0 feet (0.9 m) tall [50].  Vegetative regeneration:  Velvet mesquite plants have numerous perennial dormant buds located along an underground stem.  These dormant buds generally occur from the basal portion of the plant to about 6 inches (15 cm) below the soil surface [95].  When aboveground growth is damaged or killed, new sprouts arise from the bud zone. SITE CHARACTERISTICS : In southern Arizona, precipitation and temperature change along an elevational gradient to produce distinct vegetation zones.  Annual precipitation ranges from only a few inches at the lowest elevations to about 19 inches (480 mm) at the highest elevations [55].  Velvet mesquite occurs primarily below 5,500 feet (1,676 m) in the three lowest elevation vegetation zones described below:   (1) The paloverde-bursage-cacti association is low elevation desert and       occurs from about 1,000 to 3,000 feet (305-914 m) in elevation and       receives about 7 to 12 inches (17.5-30 cm) of annual precipitation       [55].  In this zone velvet mesquite's abundance is influenced by       edaphic factors.  The processes of weathering and erosion has       resulted in a soil particle gradient along the bajadas.  This       gradient is from coarser textured soils on the upper bajada to       finer textured soils on the lower bajada and valley fill [11].       Velvet mesquite is often restricted to the coarse soils of the       upper bajada, which have more available soil moisture than the       finer textured soils [10].  Plants also occupy washes,       intermittent streams, or playas of the lower bajada where they       may have access to underground water, but are generally absent       from the middle slopes of the bajada.   (2) Desert grasslands dominated by grama grasses (Bouteloua spp.) and       threeawns (Aristida spp.) occur between about 3,000 and 5,000 feet       (914-1,524 m) in elevation and receive about 12 to 16 inches       (300-400 mm) of annual precipitation.  Velvet mesquite occurs in       various densities throughout desert grasslands.  On some sites it       occurs as scattered plants forming mesquite savannas, but on       others its persistence has converted many grasslands to "brushy       ranges".  In southeastern Arizona, velvet mesquite-grasslands were       found primarily on level or rolling upland areas with coarse- or       medium-textured soils [30].      (3) Oak woodlands with velvet mesquite generally occur between about       3,650 and 5,500 feet (1,113-1,676 m) in elevation [55].  Velvet mesquite woodlands are found along major water courses and their tributaries.  These bosques attain their maximum development on alluvial deposits where plants may reach over 50 feet (15 m) in height and comprise over 95 percent of the trees [86,87].  Bosques may also occur, but are less common, on fine-textured soils and in side canyons [87]. Bosques are commonly on a terrace 5 to 20 feet (1.5-6 m) above the river channel [55,86].  SUCCESSIONAL STATUS : The geographical range of velvet mesquite has probably changed very little since settlement times, but its abundance within its range has increased dramatically.  Its widespread occurrence in desert grasslands, and to a lesser degree in oak woodlands, is a relatively recent event. Velvet mesquite thickets and scattered plants were occasionally found in desert grasslands before settlement times but are widespread today [55]. Velvet mesquite's dramatic invasion into grasslands has been attributed to a combination of (1) overgrazing by livestock which reduced herbaceous fuels and thus reduced the frequency and intensity of range fires and (2) the concurrent dispersal of mesquite seed by livestock into grazed habitats.  Both factors are discussed below. Fire - The role that range fires played in controlling velvet mesquite density in desert grasslands prior to settlement by Europeans is unclear.  Some researchers feel that fires had the ability to keep velvet mesquite at very low densities within grasslands [60].  Fire has killed up to 50 percent of velvet mesquite plants smaller than 1 inch (2.5 cm) in basal stem diameter [51].  In desert grasslands it often takes velvet mesquite 10 to 20 years to reach this size [51].  Prior to grazing by livestock, herbaceous fuels were probably sufficiently abundant to carry a hot fire.  Recurrent fires every 10 to 20 years would have killed many plants and kept others in a low stature, nonflowering state [51,60]. Seed dispersal - Some researchers hypothesize that low densities of mesquites in Southwestern grasslands prior to the introduction by livestock resulted primarily from limited seed dispersal [16].  Since mesquites evolved with New World megafauna, such as camelids, stegomastodons, notoungulates, and edentates [89], dispersal of mesquite seeds became very restricted when most of these herbivores became extinct at the end of the Pleistocene.  With the introduction of livestock by European settlers, mesquite invaded grasslands as cattle transported seed from plants which were primarily found in draws and drainageways.  Livestock deposited the seeds into grazed habitats. Studies have shown that vigorous stands of grass significantly reduce velvet mesquite seedling establishment and survival when compared to nearby stands weakened by grazing [51]. Saltcedar has become established along many rivers of the Southwest. In some areas it has invaded and replaced velvet mesquite bosque communities.  Salt cedar spread seems to be related to the altering of natural river flow by dams [130]. Flooding of rivers can cause the destruction or formation of mesquite bosque communities.  If channel widening and clearing occur bosques can be destroyed by the undercutting and collapse of the terrace.  Following the receding of floodwaters, velvet mesquite seedlings may become established on freshly deposited alluvium.  When seedlings successfully establish themselves on river bars, they further enhance the accumulation of alluvium, which in time, progressively elevates the surface above the river, allowing the development of the mesquite bosque [88]. SEASONAL DEVELOPMENT : Spring bud break in velvet mesquite can vary from year to year and from site to site.  Bud break seems to depend on both photo and thermal periods and rarely occurs until after the last spring frost [29,84]. Bud break and flowering generally begins earlier in warmer locations such as at lower elevations, lower latitudes, and in warm microhabitats [27].  Following bud burst, twig elongation and leaf growth are rapid and are generally completed in about 4 weeks [24].  Inflorescences emerge and develop simultaneously with the leaves.  Flowers develop and are fertilized about 25 days after they begin growth.  Insufficient soil moisture can cause spring flowers to be entirely aborted before pollination occurs. Flowers can also be destroyed by hail, heavy rain, or strong winds [51].  New flowers will form after abortion or destruction if favorable conditions later arise.  Pods mature about 7 to 9 weeks after bud burst [24,51].  In Arizona, fruits generally mature in July and drop from the plant in September; however, mature fruits have been observed from June through October [51].  Leaves usually drop by late December [24], but during warm winters, plants may retain their leaves until just before new ones begin growing in the spring [89].  If summer rainfall is high, velvet mesquite can develop a smaller number of second cohort of leaves [113].  A second set of flowers and fruit are also possible with abundant summer rainfall. Variation in the phenological development of velvet mesquite plants growing at different elevations on the Santa Rita Experimental Range in Arizona over a 4-year period is summarized below [51]: year and                              elevation (feet) phenological stage      3,000        3,500        4,000        4,500                           1949 leaf bud burst        late March   early April  late March   late April flowering begins      early April  mid-April    mid-April    late April flowering ends        early May    early June   mid-May      early July first pods mature     mid-May      early June   mid-May      early July all pods mature       early July   early July   early July   early Aug    1950 leaf bud burst        mid-March    late March   mid-March    mid-March flowering begins      late March   late March   mid-March    late March flowering ends        late April   late April   late April   mid-May first pods mature     late April   mid-May      late April   mid-May all pods mature       early July   mid-July     late July    mid-July    1951 leaf bud burst        mid-April    mid-April    mid-April    mid-April flowering begins      early May    mid April    early April  mid-April flowering ends        early June   early June   mid-May      early June first pods mature     early June   early June   late May     early June all pods mature       early July   early July   late June    late July    1952 leaf bud burst        mid-April    mid-April    mid-April    mid-April flowering begins      mid-April    mid-April    mid-April    mid-April flowering ends        mid-May      early June   early May    mid-May first pods mature     early June   early June   late May     late May all pods mature       early July   mid-July     mid-July     late July

FIRE ECOLOGY

SPECIES: Prosopis velutina
FIRE ECOLOGY OR ADAPTATIONS : Velvet mesquite plants contain numerous, dormant buds on an underground stem.  Soil and rough bark sufficiently insulate the buds from the heat of most fires [22,51].  Even 8-month-old seedlings have sufficiently developed underground stem buds to allow some plants to survive burning [19].  Following top-killing fires, numerous sprouts arise from the underground buds. Numerous wild and domestic animals consume and disperse velvet mesquite seed.  Seed from off-site plants can be transported to burned areas by animals. POSTFIRE REGENERATION STRATEGY :    Geophyte, growing points deep in soil    Initial-offsite colonizer (off-site, initial community)

FIRE EFFECTS

SPECIES: Prosopis velutina
IMMEDIATE FIRE EFFECT ON PLANT : Fire mortality of velvet mesquite is generally low.  Following most fires, plants sustain little or no damage, have their aboveground foliage partially destroyed, or are completely top-killed.  Only a small percentage are killed. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : Based on observations following prescribed fires and wildfires, top-kill and mortality appear to be most influenced by the size of the velvet mesquite plant and the intensity of the fire.  Size of the plant:  Percent top-kill and mortality of velvet mesquite following fire are inversely related to plant height and basal stem diameter.  At the Santa Rita Experimental Range in southern Arizona, fall burning on areas with 303 pounds per acre (340 kg/ha) of herbaceous fuel and about two burroweed plants per meter square resulted in greater than 80 percent top-kill of velvet mesquite plants up to 2 inches (5 cm) in basal stem diameter.  The percentage of plants top-killed, on a size class basis, gradually decreased to near zero as basal stem diameter increased to 10 inches (25 cm) [79].  Evaluation of several other prescribed fires at Santa Rita showed that young velvet mesquites less than 0.5 inch (1.25 cm) in basal stem diameter suffered about 50 percent mortality, but only 8 to 15 percent of plants greater than 0.5 inch in basal stem diameter died [51].  In southern Arizona, an accidental June fire in Lehman lovegrass (Eragrostis lehmanniana) resulted in 30 percent mortality of velvet mesquite less than 0.5 inch in basal stem diameter and 18 percent mortality of plants with basal stem diameters from 2 to 6 inches (5-15 cm) [20].  At Santa Rita, 4- to 6-inch-tall (10-15.5 cm) seedlings were burned in a "good stand" of grass.  Of the 8-month-old seedlings burned in March, 67 percent were killed and 23 percent were top-killed only.  Of the 12-month-old seedlings burned in June, 65 percent were killed and 25 percent were top-killed only [19]. The effects of fire on velvet mesquite 10 months following a June prescribed fire (mesquites in bloom at time of burn) in an area with 40 percent grass cover dominated by curly mesquite (Hilaria belangerii) is summarized below [8]:                              basal stem diameter (inches) fire effects         0-.5    .5-1    1-2    2-3    3-4    >4    total                                   (number of plants) no crown damage       1        4      5      7      8     12     37 partial top-kill     16       14      8      1      0      1     40 total top-kill       73       11      1      0      0      0     85 dead                  8        1      0      0      0      0      9              total   98       30     14      8      8     13    171 Fire intensity:  In some locations, velvet mesquite has displaced grasses to the extent that the herbaceous fuels are insufficient to carry anything but a cool or spotty fire [104].  Low intensity fires occur under these circumstances and usually inflict no damage or only partially kill the aboveground crown.  High intensity fires may kill many young plants, but mature plants are often only top-killed and then resprout.  Fire intensity is influenced most by the amount of herbaceous fuel and the time of year burning takes place.  Plants seem to be more susceptible to burning during late spring and early summer, which is the hottest and driest time of the year in Arizona, than during other times of the year [22].  At the Santa Rita Experimental Range, about 29 percent of velvet mesquites were killed on areas burned in June, compared to about 10 and 4 percent on areas burned in November and February [51].  Following a June fire at Santa Rita, velvet mesquite suffered 25 percent mortality in an area with 4,480 pounds per acre of herbaceous fuel (4,973 kg/ha) dominated by Lehman lovegrass, but on areas with 2,200 pounds per acre (2,465 kg/ha) of herbaceous fuel dominated by black gramma (Bouteloua eriopoda), velvet mesquite suffered only 8 percent mortality [20]. The fire effects on velvet mesquite on the Santa Rita Experimental Range as influenced by plant size and season of burn are summarized below [51].  Since herbaceous fuels were lacking, barley hay was added to increase the fine fuel to 800 pounds per acre (896 kg/ha). basal stem diameter                       Month and fire effect                                 Feb     June    Nov     Oct up to 0.5 inch                 top alive                       3%      1%     13%     ---  top-kill                       74%     39%     66%     ---  dead                           23%     60%     21%     --- 0.5 to 1.0 inch             top alive                      35%      5%     12%      5%  top-kill                       50%     62%     73%     90%  dead                           15%     33%     15%      5% 1.0 to 2.0 inches  top alive                      50%      6%     41%     28%  top-kill                       50%     74%     52%     62%  dead                            0%     20%      7%     10% 2.0 to 5.0 inches  top alive                      78%     20%     63%     62%  top-kill                       22%     65%     32%     31%  dead                            0%     15%      5%      7% over 5.0 inches  top alive                      82%     40%     82%     90%  top-kill                       18%     49%     18%     10%  dead                            0%     11%      0%      0% PLANT RESPONSE TO FIRE : The response of velvet mesquite following fire depends on the amount of damage the fire inflicted on the plant.  Plants may initiate new growth from either aerial crown or underground stem buds.  Following low-intensity fires which only partially top-kill plants, velvet mesquite often sprouts from axillary buds on the branches of the crown. Following severe, top-killing fires which char or completely consume the crown, plants survive by producing numerous basal stem sprouts [20,126]. Some plants which are lightly or moderately damaged survive by both refoliating undamaged portions of the crown and by producing basal sprouts.  In general, smaller plants receive more crown damage and thus tend to recover by basal sprouting, while larger plants tend to produce crown sprouts.  Cable [20] observed that basal sprouting predominated on trees with a stem diameter less than 2 inches (5 cm), while crown sprouting predominated on plants with basal stem diameters less than 2 inches. Following a fall burn at Santa Rita, heights velvet mesquite resprouts were 105 percent of preburn levels in 4 years.  Six years after burning, some resprouts flowered and set seed [79]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : Prescribed burning has not been effective in controlling velvet mesquite because of the species' fire survival strategies.  On grasslands in good condition with a low density of velvet mesquite, repeated prescribed fires have the potential to kill small plants under 0.5 inch (1.25 cm) in basal stem diameter and keep others low in stature and from producing seed [22].  However, on some sites velvet mesquite has reduced the native grass cover to the extent that there is now insufficient fuel to carry anything more than a "spotty" or "cool fire" [42].  In general, fire will not carry in Southwestern grasslands having less than 600 pounds per acre of herbaceous fuel (654 kg/ha) unless there is a good stand of burroweed present [127].  When there is less than 892 pounds per acre (1,000 kg/ha), a windspeed of 8 miles per hour (12.8 km/hr) is needed to carry the fire [127].

REFERENCES

SPECIES: Prosopis velutina
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