Lechuguilla coverage is typically much less on burned sites than unburned sites.
In the Chisos Mountains of Big Bend National Park, Texas, lechuguilla was
present on burned sites. A fire burned on March 21, 1980, during a fall-spring
drought (Oct-May) when vegetation was stressed. Fire severity was variable, and
burned-unburned comparisons were not available. Sites were visited through
the early winter of 1981. The researchers concluded that lechuguilla was able to
recover from "light" to moderate fires [42].
Two years after an August fire in a desert mountain shrub community in Trans-Pecos,
Texas, lechuguilla coverage was 2.41% on unburned sites and 0.03% on burned sites.
No fire behavior or severity characteristics were provided, but precipitation was
above average in both postfire years. The number of lechuguilla rosettes decreased
by 90% after fire; however, the researchers reported that few lechuguilla plants were
killed [8].
Lechuguilla was reduced by more than 50% on burned sites when burned and unburned sites
were compared in the Guadalupe Mountains of New Mexico and Texas. A total of 7 burned sites
were visited 3 to 7 years following fire. Most fires burned in June, but there were single
fires in April, March, and August. The cover of lechuguilla on burned sites was 19% of that
on unburned sites. Surviving plants were slow to recover. A few rhizomatous sprouts were
observed in the 3rd postfire year in an area where lechuguilla had been top-killed. The
researcher noted, however, that scorched lechuguilla plants "showed little evidence
of recovery" [2].
This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g. [44,50,57,74]).
Aboveground growth: Lechuguilla is a long-lived, drought-tolerant perennial. Dense patches of lechuguilla are common due to clonal growth [31,44,74]. A study of 11 lechuguilla populations along a latitudinal gradient from northern to southern Mexico revealed that southern plants grow larger than northern plants [65].
A basal rosette of 20 to 50 upright, thick, fleshy leaves is borne from lechuguilla's woody caudex. The rosette is typically 8 to 24 inches (20-60 cm) tall. Tapered leaves measure 8 to 20 inches (20-50 cm) long by 0.4 to 2 inches (1-4 cm) wide. A 0.7- to 2-inch (18-40 mm) spine occurs at the leaf tip. Leaf margins are lined with downward pointing spines that are 0.1 to 0.4 inch (3-10 mm) long [31,44,45,50,54,63,67]. Leaves may live to be 12 to 15 years old [28] and have been used to age plants [23].
Perfect flowers are produced on a spike-like panicle. The flower stalk bearing this panicle may be 3 to 10 feet (1-4 m) tall [28,29,44,50,57,67,74]. Flower stalks grow rapidly. An 8 inch (20 cm) daily height increase is possible. A height of 8.5 feet (2.6 m) can be reached in 3 to 4 weeks [23]. Flower production occurs once the plant is mature, at typically 10 to 20 years old. After flowering, lechuguilla dies and is replaced by one of many clones [23,50,67]. When northern and southern populations were compared in Mexico, fewer flowers were produced by northern plants [65].
Many dehiscent capsules containing several hundred seeds are produced along the spike-like panicle. Capsules are 0.8 to 1 inch (20-25 mm) long, and seed diameter is 3 to 4.5 mm [21,44,50]. Seeds appear smooth and black when fertile and white and dull when infertile [28].
Belowground growth: Lechuguilla is shallowly rooted. The average depth of 45 below ground structures from 8 plants in Coahuila, Mexico, was 4 inches (10 cm). For average-size plants, approximately 4% of the dry biomass was underground [54]. The lateral underground structures of lechuguilla plants in Big Bend National Park, Texas, were 2 to 3 times the width of the canopy. Root to shoot ratios ranged from 0.09 to 0.21 and averaged 0.14 [77].
Adaptations for drought tolerance: Many morphological and physiological adaptations allow lechuguilla to persist in arid habitats. Leaf cuticles resist transpiration, and both leaves and roots have large amounts of mucilage, saponin, and salts that maintain water in solution [50]. In a review, Nobel [52] reports that agaves rapidly initiate root production during rainfall events. Leaf structure and arrangement allow lechuguilla to capture precipitation and deposit it at the shaded base of the plant where evaporation potential is reduced [28].
Fire adaptations: Lechuguilla is not highly adapted to fire, and populations typically suffer losses when burned. Some plants may survive fire by protection of the apical meristem and caudex by tightly packed leaves at the base of the plant or survival of rhizomes that average 4 inch (10 cm) depths [54]. Plants in low-flammability desert microhabitats may avoid direct fire. Dry, rocky areas with low fuel densities or discontinuous fuels or areas protected by topographic relief provide fire protection and would allow lechuguilla to survive, reproduce, and recolonize burned sites [72]. Seeds transported onto burned sites are an unlikely recolonization method, as seedling establishment is rarely observed in the field [21].
FIRE REGIMES: Descriptions of fires in lechuguilla-dominated habitats are rare. The lack of dense continuous fuels in Chihuahuan Desert scrub habitats suggests that fires are infrequent [32].
Fire behavior: The availability of fuels determines the size, frequency, and severity of fires in southern deserts where lightning is common. More arid ecosystems produce less fuels and support fewer fires. Although fires may be infrequent and low in severity, effects on the vegetation may be severe. In the Chihuahuan Desert. low-growing shrubs mixed with other woody vegetation and perennial grasses support occasional fires. Fires are most likely in vegetation next to desert grasslands that burn often [32].
Kittams [35] indicates that dense lechuguilla patches successfully carry fire and burn "hot." Grasses and dead lechuguilla leaves aid in fire spread. Fires are common during dry lightning storms that are common in the Chihuahuan Desert from May to October.
Fire frequency: Fires in the Chihuahuan Desert and in desert shrub communities in Trans-Pecos, Texas are described as infrequent and uncommon [5,8].
Wright [78] reported that semiarid ecosystems, those areas that receive an average of 8 to 20 inches (200-500 mm) of annual precipitation, burned at 5- to 100-year intervals in presettlement time. Fire frequency depended on fine fuel loads, topography, and drought frequency. Fires could be extensive when hot, dry, windy conditions occurred in areas that had 1 to 2 years of abundant herbaceous growth. Wright [78] noted that changes in shrub species composition could be substantial and long lasting following fire.
In Big Bend National Park, Texas, there were 39 fires between 1944 and 1977. Researchers indicated, however, that the number of fires was likely underestimated because small fires that burned out quickly may not have been reported, and fire records for the area were incomplete. Forty-four percent of the fires occurred in those areas with high levels of human impacts and were started by people. This short-term fire frequency for Big Bend National Park likely exceeds that of presettlement time, and may indicate that this area is burning at a frequency greater than that to which the vegetation is adapted [17].
Exotic species and fire: On the Jornada Experimental Range in New Mexico, semiarid black grama (Bouteloua eriopoda)-dominated grasslands have been invaded by Lehmann lovegrass (Eragrostis lehmanniana). Based on other literature and prescribed burning in this area, presence of lovegrass increases available litter and decreases vegetation canopy patchiness. In a prescribed fire, fewer ignitions were necessary and spread was more rapid in invaded than native grasslands. Fire often died out in the native grassland when it burned into wide bare areas. If Lehmann lovegrass invades lechuguilla habitats, fire frequency and size may increase [46].
FIRE REGIMES: The following table provides fire return intervals for plant communities and ecosystems where lechuguilla is important. Find 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) desert grasslands Bouteloua eriopoda and/or Pleuraphis mutica 10 to <100 [47,56] plains grasslands Bouteloua spp. 56,79] blue grama-needle-and-thread grass-western wheatgrass Bouteloua gracilis-Hesperostipa comata-Pascopyrum smithii 56,61,79] blue grama-tobosa prairie Bouteloua gracilis-Pleuraphis mutica <35 to <100 [56] creosotebush Larrea tridentata <35 to <100 [32,56] pinyon-juniper Pinus-Juniperus spp. <35 [56]As indicated in the Fire Ecology section, invasion of Lehmann lovegrass into lechuguilla habitats could increase the fire frequency beyond presettlement frequencies and beyond the range to which Chihuahuan Desert species are adapted.
Information regarding the effect of fire on lechuguilla is sparse. Additional studies of fire in lechuguilla habitats are needed before recommendation for or against fire in these habitats is warranted.
Lechuguilla is common on dry hills, plains, rocky slopes, and limestone highlands throughout the Chihuahuan Desert [9,44,50].
Climate: Lechuguilla occupies habitats with semiarid continental climates. The Chihuahuan Desert averages 7.7 to 13.7 inches (196-348 mm) of annual precipitation, and summer temperatures above 100 °F (40 °C) are common [7]. In the northern portion of the Chihuahuan Desert, precipitation averages 9.7 to 10.4 inches (245-265 mm), 70% to 80% of which falls in the summer. The average low winter temperature is 36 °F (2 °C) and mean summer high is 90 °F (31 °C) [49]. In the Trans-Pecos area of Texas, annual rainfall averages 9 to 17 inches (230-430 mm). A majority of the precipitation falls in late summer or early fall when evaporation is rapid [14]. Carlsbad Caverns National Park, New Mexico, receives an average of 14 inches (360 mm) of rainfall, 78% of which comes from May to October in brief but severe thunderstorms. Over a 40-year period, the extreme annual precipitation amounts were 4.5 inches (110 mm) and 43.2 (1,110 mm) inches, and the record low and high temperatures were -10 °F (-23 °C) and 108 °F (42 °C), respectively. In Carlsbad Caverns National Park, lightning, which is often dry, is common from May through October [35].
Elevation: Throughout lechuguilla's range, the densest populations occur below 4,900 feet (1,500 m) [23].
Region Elevation Notes Chihuahuan Desert 3,000 and 7,500 feet [28] Guadalupe Escarpment, NM and TX 3,800-4,600 feet [26] Guadalupe Mountains National Park, TX below 5,500 feet [9] Guadalupe and Sacramento mountains, southern NM 4,000 to 4,600 feet oneseed juniper/lechuguilla vegetation [70] NM 3,00-4,500 feet [44] Trans Pecos, TX below 4,500 feet lechuguilla-smooth-leaf sotol vegetation [71] Uvalde County, TX has been collected at 1,500 feet [28]
Soils: Dry, rocky, limestone and/or calcareous soils are characteristic of lechuguilla habitats [28,31,45,63]. The lechuguilla-smooth-leaf sotol vegetation type of Trans-Pecos, Texas, occupies slopes with shallow rocky soils [71]. Primary limestone sediments or caliche deposits are common in lechuguilla habitats, whereas volcanic deposits are not [28].
Below are the average soil element levels taken from lechuguilla root zones in Coahuila, Mexico [53]:
N (%) K (ppm) Na (ppm) P (ppm) Ca (ppm) Mg (ppm) B (ppm) 0.18 32 50 23 3,330 31 2.5
Lechuguilla provides important habitat and food to a diversity of Chihuahuan Desert mammals, reptiles, and birds but is poisonous to domestic livestock.
Domestic livestock: Lechuguilla causes "goat fever, lechuguilla fever, or swell head" in domestic goats, sheep, and cattle when consumed [45,74]. Saponin is the toxic agent in lechuguilla that is activated by an unidentified photodynamic agent [28,57]. Domestic sheep and goats are poisoned more frequently than cattle. However, most domestic livestock species avoid lechuguilla unless drought conditions are severe and/or other foods are unavailable [28,67].
Lechuguilla fever is most common in the spring during periods of drought and/or when range condition is low. Domestic goats and sheep with the fever are lethargic, do not keep up with the herd, and become uninterested in food and water. Affected animals may be jaundiced, excrete yellow liquid from the eyes and nostrils, and have swelling mucous membranes. Animals fed as little as 1% of their body weight in lechuguilla have died [45,67].
A study of non-Angora goat diets from fecal analysis revealed that the amount of lechuguilla in goat diets was a low of 2% in the fall, was 3% in the spring and summer, and was a high of 4% in the winter. The pasture had poor forage productivity. Poisoning of these goats was not mentioned [48].
Mule deer: Feeding observations and fecal analyses indicate that lechuguilla is important in diets of Chihuahuan Desert mule deer [37,40,41]. Mule deer fed on young lechuguilla flower stalks and small 2 to 5 inch (5-10 cm) rosettes throughout the winter [35]. Mule deer feces analyzed from Big Bend National Park, Texas, had the highest frequency of lechuguilla, 9%, in the summer of 1980. These findings differed from other reports of moderate lechuguilla use year round. The researchers noted that the other studies were based on observations or rumen analysis [40].
In Carlsbad Caverns National Park, New Mexico, lechuguilla was more important to mule deer following "poor growing" seasons. Feeding was observed and stomach contents were analyzed from 1967 to 1971. Mule deer consumed flower stalks and fruit, and most lechuguilla feeding occurred from March through April, although some feeding occurred in the winter months. During a nongrowing season that followed a "good growing" season, mule deer fed on lechuguilla in 4 of 95 observations. Following a "poor growing" season, 31 of 186 feeding observations were on lechuguilla. The frequency of lechuguilla in 16 deer stomachs taken after a poor growing season was 69% [36].
Bighorn sheep: Lechuguilla is common in bighorn sheep habitats in the Trans-Pecos area of western Texas [14].
Collared peccaries: Collared peccaries feed heavily on lechuguilla. The tender inner core of leaves, the basal portions of outer leaves, and the roots are consumed [4]. The inner leaf core is an important water source during drought conditions [12].
In a heavily browsed area of Big Bend National Park, 24.4% of lechuguilla plants were browsed. Based on scat analysis, lechuguilla made up 11% to 41% of collared peccary diets from September through June and 3% to 5% in July and August when consumption of prickly pear (Opuntia spp.) fruits was greatest [4]. Stomach contents of 2 collared peccaries from the Trans-Pecos region of Texas were more than 50% lechuguilla [33].
Black bears: In 27 black bear scats left in the late summer (July-September) in Big Bend National Park, Texas, the frequency of agave (Agave spp.) was 7%. Frequency was zero in early summer scats [30].
Other small mammals: Lechuguilla is important in the habitats of several small mammals and is an important food for pocket gophers. In the Guadalupe Mountains National Park, Texas, Botta's pocket gopher habitats contained lechuguilla, and lechuguilla roots were a preferred food item [27]. Southern pocket gophers are thought to affect lechuguilla density in Carlsbad Caverns National Park by feeding on the inner plant core [35].
In Culberson County, Texas, rock squirrels utilize both pinyon-juniper (Pinus-Juniperus spp.) and highlands vegetation in which lechuguilla is common [13]. The smooth-leaf sotol-lechuguilla vegetation association supports large populations of cactus mice and Nelson's pocket mice in the Big Bend region of Brewster County, Texas. In the creosote bush-lechuguilla association the cactus mouse is the most typical mammal. The white-ankled mouse "typifies" the smooth-leaf sotol-juniper-lechuguilla community [15]. In the lechuguilla-creosote bush-cactus vegetation type in the Chisos Mountains of Big Bend National Park, spotted ground squirrels, Botta's pocket gophers, Merriam's kangaroo rats, and black-tailed jackrabbits are characteristic [76]. In Coahuila, Mexico, yellow-faced pocket gopher burrows were found under lechuguilla [62]. For additional information on mammal populations associated with desert vegetation that includes lechuguilla, see [10].
Birds: Thirteen breeding bird species utilized lechuguilla-creosote bush-cactus habitats for nesting in the Chisos Mountains of Big Bend National Park. Common nesters included Say's phoebes, verdins, mocking birds, black-tailed gnatcatchers, house finches, ash-throated flycatchers, and cactus wrens [76]. For additional information on bird populations associated with desert vegetation that includes lechuguilla, see [10].
Reptiles: Many lizards and snakes utilize habitats where lechuguilla is important. Gray-checkered whiptails occupy the upper San Antonio Canyon of Trans-Pecos, Texas [75], and canyon lizards are found in Big Bend National Park, Texas [19]. In both areas, lechuguilla is important. The lechuguilla-creosote bush-cactus vegetation in the Chisos Mountains of Big Bend National Park supports populations of canyon lizards, round-tailed horned lizards, tiger whiptails, Couch's spadefoot, coachwhips, western patch-nosed snakes, and western diamond-backed rattlesnakes [76].
Greater earless lizards, round-tailed horned lizards, and common checkered whiptails were significantly (p-value not reported) associated with succulent desert vegetation in Guadalupe Mountains National Park. The researcher indicated that these reptiles may be valuable vegetation type indicators, as they typically remain in the area even when some dominant plants disappear in early secondary succession. For a description of the succulent desert vegetation, see Habitat Types and Plant Communities [26].
Palatability/nutritional value: The average concentration of elements in leaf tissue taken from the center of mature leaves from plants growing in Coahuila, Mexico is provided below [53]:
N K Ca Mg Na P Mn Cu Zn Fe B
(%)
(ppm)
1.14 1.27 6.11 0.40 45 1,220 14 6.9 36 77 18Lechuguilla leaves from plants in New Mexico averaged 30.7% crude fiber, 7% ash, and 3.6% protein. Not all protein was digestible [6].
Cover value: The presence of lechuguilla in the habitats of many mammals, birds, and reptiles suggests that it provides useful cover. For additional information on the importance of lechuguilla in wildlife habitats, see the species group of interest within Importance to livestock and wildlife.
Lechuguilla is a dominant or subdominant species in the following vegetation classifications:
United States:
New Mexico:
oneseed juniper
(Juniperus monosperma)/lechuguilla and oneseed juniper/sacahuista
(Nolina microcarpa)-lechuguilla vegetation types in the Guadalupe and/or Sacramento
mountains in the southern portion of the state [70]
semidesert
grasslands that surround the Chihuahuan Desert in the south [7]
smooth-leaf sotol
(Dasylirion leiophyllum)-lechuguilla and oneseed juniper/lechuguilla
communities in the Guadalupe Escarpment [25]
desert
and mountain chaparral vegetation in the west-central part of the state [55]
disturbance
scrub communities with blue grama (Bouteloua gracilis), sideoats grama (B.
curtipendula), beebrush (Aloysia spp.), acacia (Acacia spp.), and
tulip pricklypear (Opuntia phaeacantha) and grass/rosette scrub communities with
sideoats grama, gypsum grama (B. breviseta), and/or hairy grama (B. hirsuta)
in Big Bend National Park [17]
creosotebush-tarbush
(Larrea tridentata-Flourensia cernua) desert scrub vegetation
found on the desert plains adjacent to Brewster County's Chisos Mountains [51]
smooth-leaf
sotol-lechuguilla, creosotebush-lechuguilla, and smooth-leaf sotol/oneseed juniper/lechuguilla
vegetation associations in Brewster County [15]
Colorado
pinyon-alligator juniper (Pinus edulis-J. deppeana) vegetation association with
some oak (Quercus spp.) and highlands vegetation dominated by oneseed juniper
with some ocotillo (Fouquieria splendens), smooth-leaf sotol, and
javelin bush (Condalia ericoides) in Culberson County [13]
papershell
pinyon (P. remota)/smooth-leaf sotol-lechuguilla vegetation
type is common on Del Norte Mountain slopes [10]
creosotebush-lechuguilla community in El Paso County [60]
succulent
desert vegetation in Guadalupe Mountains National Park
dominated by lechuguilla and smooth-leaf sotol with resinbush (Viguiera stenoloba) and
Pinchot juniper (J. pinchotii) common [26]
lechuguilla-smooth-leaf sotol vegetation type in the Trans-Pecos region [16,71]
semidesert
grasslands that surround the Chihuahuan Desert in Trans-Pecos [7]
lechuguilla
is indicative of Chihuahuan Desert grasslands and scrub vegetation [49]
succulent-scrub vegetation type where Torrey's yucca (Yucca torreyi), smooth-leaf sotol, and
hechtia (Hechtia spp.) are commonly associated with lechuguilla [7]
lechuguilla
scrub vegetation with Texas false agave (H. texensis), feverfew (Parthenium spp.),
ocotillo, and/or viscid acacia (A. neovernicosa) possible [31]
cactus desert
vegetation in the north dominated by plumed crinklemat (Tiquilia greggii),
saltbrush (Atriplex spp.), and crown of thorns (Koeberlinia
spinosa); lechuguilla is considered subdominant [39]
semidesert
grasslands that surround the Chihuahuan Desert in southwestern
Chihuahua and western Coahuila [7]
Utilization of lechuguilla fibers, soaps, foods, and drinks by southwestern people was extensive historically and continues today. Lechuguilla fibers called "istles," Ixtili, or Tampico are strong and durable. Fibers were used to make ropes, twine, sacks, saddle cloths, basketry, paint brushes, sandals, hair brushes, and when formed into a cord was used in clothing construction [11,50,57,74]. In a review, Nobel [52] reported that lechuguilla fibers were used in sandals made 8,000 years ago. Lechuguilla fibers are still desired for power-driven polishers and scrubbers for floors and brushes used in steel mills and metal fabricating plants. Fibers are also found in brooms and pastry brushes [63].
Material in lechuguilla's leaves and roots has strong cleansing properties. Soap from lechuguilla plants leaves hair, scalp, and skin soft and shiny. As a detergent, lechuguilla does not dull colors and removes spots from fine materials [28,50,63,74]. Softer plant parts including the inner cluster of unopened leaves can be boiled and eaten or fermented into an alcoholic drink. Large flower stalks have been used in the construction of walls and roofs and as fishing poles [50,63]. Juice from lechuguilla leaves has been used to poison arrows, and agave juice when mixed with plaster works as an insecticide that deters white ants [28,50]. Today hecogenis, one of lechuguilla's sapogenins, is used in steroid drugs [28].
Lechuguilla is also used as an ornamental in southern desert areas [68].
Lechuguilla is described as producing ample seeds and clones [28]. Despite high seed output, seedlings are rarely observed. Reproduction is predominantly vegetative through rhizome and daughter plant production [21].
Pollination: Lechuguilla flowers receive a diversity of visitors making cross pollination probable [9,65], but indeterminate flowering makes self pollination possible as well [23]. Flowers open in late afternoon and last almost 96 hours. Anthers usually wither within 24 hours of flower opening, and the stigma is receptive nearly 66 hours after blooming [23].
Lechuguilla nectar attracts hummingbirds, wasps, bees, butterflies, and beetles [9]. During a study of 11 lechuguilla populations in Mexico that amounted to a total of 114 observation hours, the most abundant flower visitor was the honeybee, which accounted for 50.5% of the visits. However, the small size of this insect caused researchers to doubt its pollination potential. Larger bumblebees and carpenter bees made up 23.4% of the visits, a nocturnal hawkmoth constituted 9.5% of visits, and hummingbirds were 4.1% of the visits [65].
Breeding system: Indeterminate lechuguilla flowers are capable of self fertilization [23], and cross pollination by insects is encouraged through nectar production [9,65]. A study of 11 lechuguilla populations along a north-south latitudinal gradient in Mexico revealed high levels of genetic variation as compared to other long-lived perennials. The highest levels of homozygosity and likely a lower amount of outcrossing occurred in northern populations, and the highest levels of heterozygosity and more outcrossing occurred in southern populations. Southern populations received a greater number of insect visits than northern populations [66].
Seed production: Seed production by lechuguilla is prolific [1,50]. Numerous capsules are produced along the panicle, and each capsule can contain up to several hundred seeds [21]. Seed production requires a large reallocation of biomass. Nonflowering plants typically have 85% of their biomass as leaves, 15% as basal mass; when flowering is almost complete, 40% of lechuguilla's biomass is in the inflorescence, 50% is in the leaves, and 10% is basal mass [23].
Lechuguilla plants studied in Mexico revealed fruit production differences among northern and southern populations. Fruit set was highest in southern populations [65].
Predation affects lechuguilla seed production. Mule deer relish young lechuguilla flower stalks and likely limit seed production [35]. Moth larvae also affect lechuguilla seed production. Larvae feed on unopened flowers, and of those flowers with entry scars, 90% to 95% were aborted. Lechuguilla flowers provide water and nutrients in the May and June dry season, so may be utilized by any opportunistic feeder [23].
Seed dispersal: Wind and animals aid in the dispersal of lechuguilla seeds. Seeds are released from splits in the capsule through movement of the tall flower scape. When winds are strong, seeds may be dispersed hundreds of feet from the flowing plant [28,50].
Seed banking: Lechuguilla's lack of germination restrictions suggests that seed banks are short lived. However information on this topic is lacking.
Germination: Seeds readily germinate [50]. Temperatures exceeding 95 °F (35 °C), however, decrease germination percentages [22]. Lechuguilla seeds harvested in the fall from plants in Guadalupe Mountains National Park, Texas, showed 88% to 93% germination. Seeds received no pretreatments and were kept moist in petri dishes under variable light and temperature conditions. It took an average of 4 days to see 50% germination [1].
Similarly, seeds collected in the late summer from El Paso County, Texas, and northern Mexico showed no dormancy period. Germination was not affected by light and dark treatments. However, temperature extremes of approximately 50 °F (10 °C) and 100 °F (40 °C) limited germination to less than 2%. Optimal germination, 80% to 95%, occurred at temperatures of 77 to 86 °F (25-30 °C). Seeds germinated well with water stress levels up to -5.0 atmospheres, and germination was best at 6.15 pH, although lechuguilla abundance is typically greatest in soils where pH range is typically 7.8 to 8.5 [21].
Lechuguilla seeds collected in El Paso County, Texas, showed significantly (p<0.05) decreased germination when exposed to 95 °F (35 °C) for more than 18 hours or exposed to 100 °F (40 °C) for 2 hours. Germination after late summer rains in the Chihuahuan Desert is likely restricted by this temperature sensitivity. Germination may be restricted to cool winter periods, as 100 °F (40 °C) soil temperatures would be common in the summer or fall in the Chihuahuan Desert [22].
Seedling establishment/growth: Seedling establishment is rare. Freeman [21] suggests that the lack of "specialized germination requirements" may limit lechuguilla's ability to establish by seed.
Growth: Elevation and climate affect lechuguilla growth. Of 52 plants studied in the Chihuahuan Desert of Coahuila, Mexico, an average of 6.6 leaves were produced per plant per year. When conditions were wet in the summer and early fall, more than 1 leaf could unfold per month per plant. Total plant productivity was 0.38 kg/m²/year and exceeded that of most other Chihuahuan Desert plants [54].
Lechuguilla plants from sites in southern Coahuila and central Neuvo Leon grew more slowly on low-elevation, low-moisture sites than on higher elevation, higher moisture sites. Leaves unfolded at an average rate of 8.7/plant/year on a site receiving 2.2 inches (56 mm) of mid- to late summer precipitation but unfolded more slowly, 3.9 leaves/plant/year, on the sites receiving 0.9 inch (23 mm) of mid- to late summer precipitation. Low elevation (3,300 feet (1,000 m)) populations had an average of 22 leaves and an annual leaf unfolding rate of 5.1/plant/year; mid-elevation plants (4,600 feet (1,400 m)) averaged 36 leaves/plant, and leaf unfolding rates averaged 7.5 leaves/plant/year; high elevation populations (6,200 feet (1,900 m)) averaged 47 leaves per plant, and leaves unfolded at an average rate of 10.8 leaves/plant/year [58].
Asexual regeneration: Vegetative reproduction through rhizome expansion and sprouting is the predominant means of regeneration [21,23,63]. Damage to flower stalks or inner leaf cluster can stimulate rhizome production. Animal browsing of the flower stalk stimulates rhizome and daughter plant production [35,67]. When the tight inner cluster of unopened leaves is cut off, regeneration of the unopened leaf stalk will be complete in 6 months to a year. The removal of this unopened leaf cluster stimulates clonal growth from rhizomes [63].
The concept of succession, in which community composition changes over time as a site is modified by past and present species, was developed in mesic eastern forests and does not apply well to the dynamics of southern desert ecosystems. In eastern forest ecosystems, pioneer species are typically not present in climax communities. In southwestern deserts, species that make up the predisturbed vegetation are the same species that make up the recovering vegetation [51].
Lechuguilla is present in a community characterized by cyclical vegetation change along Tornilla Creek in Brewster County, Texas. As clay beds accumulate layers of gravel and sand, they support a creosote bush-tarbush desert scrub community. Erosion of the soil leaves a very fine-textured, tightly compacted clay material that is virtually impenetrable by water. Without a soil layer the site typically cannot support plant life. As thin layers of sand and gravel are washed onto the clay beds, the site supports shallowly-rooted grasses such as alkali sacaton (Sporobolus airoides) and tobosa (Pleuraphis mutica). As soil development improves, the site supports a sparse cover of shrubs that tolerate shallow soils (≤1 foot (0.3 m)), including creosote bush, smooth-leaf sotol, and lechuguilla. In time shrub density increases and eventually the site again supports the creosote bush-tarbush desert scrub community. If soil is eroded again, species intolerant of shallow soils disappear, and if severe erosion exposes the clay beds once again the site is void of plant life until soils build again. The author suggests that the creosote bush-tarbush is a "super-climax" vegetation type since it is the predisturbed and recovered vegetation type [51].
Lechuguilla coverage increased significantly (p<0.05) over a 30-year period on alluvial fans and steep slopes in Big Bend National Park, Texas. Grazing hadn't occurred in the park since 1945, and no major disturbances were reported for the area during the study period. Lechuguilla coverage on alluvial fans was 3.7% in 1955, 3.6% in 1961, and 5.9% in 1981. Lechuguilla coverage on rocky steep hillslopes was significantly greater in 1981 than in 1961. Lechuguilla had 6.3% cover in 1955, 5.6% in 1961, and 8.1% in 1981 [43].
Some suggest that lechuguilla's presence in grama (Bouteloua spp.) grasslands indicates a "degraded" or disturbance community. In the Chihuahuan Desert, overgrazed and eroded grama grasslands support increased lechuguilla density and are considered "degraded" [31]. Heavy grazing of Chihuahuan Desert grasslands has facilitated lechuguilla increases [35]. In the Big Bend National Park of Texas, lechuguilla occurs in disturbance scrub communities that are considered a product of heavy grazing and reduced fire frequency [17].
The scientific name of lechuguilla is Agave lechuguilla Torr. (Agavaceae) [34,44,50,57].
When lechuguilla and thorncrest century plant (A. univittata) habitats overlap,
there are intermediate forms considered hybrids [28].
