AUTHORSHIP AND CITATION : Pavek, Diane S. 1993. Carnegiea gigantea. 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 : CARGIG SYNONYMS : Cerceus giganteus Engelm. SCS PLANT CODE : CEGI COMMON NAMES : saguaro sahuaro giant cactus pitahaya TAXONOMY : The currently accepted scientific name for saguaro is Carnegiea gigantea (Engelm.) Britt. & Rose . It is a member of the cactus family (Cactaceae). Carnegiea is a monotypic genus. There are no subspecies, varieties, or forms. LIFE FORM : Cactus FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY
DISTRIBUTION AND OCCURRENCESPECIES: Carnegiea gigantea
GENERAL DISTRIBUTION : Saguaro occurs throughout most of the Sonoran Desert in Arizona, California, and Mexico [65,68]. The northern limits of its distribution are on the edge of the Hualapait Mountains in Arizona and along the Colorado River in southeastern California [30,32,40,65]. The range of saguaro extends southward; the largest populations of this species occur in Sonora, Mexico . ECOSYSTEMS : FRES30 Desert shrub STATES : AZ CA MEXICO BLM PHYSIOGRAPHIC REGIONS : 7 Lower Basin and Range KUCHLER PLANT ASSOCIATIONS : K027 Mesquite bosque K041 Creosotebush K042 Creosotebush - bursage K043 Paloverde - cactus shrub K044 Creosotebush - tarbush SAF COVER TYPES : 241 Western live oak 242 Mesquite SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Saguaro is a dominant or codominant member of the paloverde (Cercidium spp.)/saguaro (also known as the spinose suffrutescent community) and the paloverde/bursage (Ambrosia spp.) desertscrub community types on bajadas (i.e., eroded outwash fans) [35,46,74,75,78]. Infrequently, on the southwestern edge of its range, saguaro occurs in creosotebush (Larrea spp.) communities as a xeroriparian species in arroyos and washes [3,5,11,46]. Saguaro is a community type indicator species in the following publication: Vegetation of the Santa Catalina Mountains: Community types and dynamics .
MANAGEMENT CONSIDERATIONSSPECIES: Carnegiea gigantea
IMPORTANCE TO LIVESTOCK AND WILDLIFE : The flowers, fruits, and seeds of the saguaro are important food sources for wildlife, such as collared peccary, long-nosed bats, heteromyid rodents, western white-winged doves, woodpeckers, and insects [2,19,39,50,56]. Saguaro fruits comprised a small amount (e.g., 1 to 5 percent of collected rumen contents) of mule deer summer diets [38,60,63,79,80]. The fruits were also utilized by desert bighorn sheep; they were present in 10 percent of bighorn fecal pellets analyzed [44,83]. Saguaro provides nesting habitat for birds and small mammals . Saguaro mortality can have a high negative impact on bird species that use it for cover and nesting . PALATABILITY : Saguaro is highly palatable to rodents and jackrabbits; however, saguaro tissue contains oxalates that deter some herbivory [47,68]. NUTRITIONAL VALUE : The nutritional value of saguaro fruits is variable throughout the season and among studies. Saguaro fruits are moderately digestible . The amount of protein reported varied from 10 to 26 percent [33,80]. Acid detergent fiber amounts in the fruits varied from 26 to 62 percent, and dry matter was 11 to 35 percent [33,80]. COVER VALUE : Saguaro is considered a softwood snag . Cavity-nesting birds, especially woodpeckers, and sometimes woodrats nest in saguaro [12,31,43,49,50]. VALUE FOR REHABILITATION OF DISTURBED SITES : NO-ENTRY OTHER USES AND VALUES : Saguaro fruits were a major food staple of the Papago and Pima Indians; the fruits were processed (i.e., dried, fermented, canned) and stored for year-round use [18,21,32]. Seeds, rich in fat, were ground for use as flour and in porridges . Fruits were used for trade and in religious practices by the Papago Indians [21,57]. The internal heavy, woody ribs were used for firewood and building houses and fences [1,6,10]. Saguaro is grown in desert gardens as an ornamental . It is the state flower of Arizona and is used in commercial advertisements of Southwestern living . OTHER MANAGEMENT CONSIDERATIONS : Intensive grazing can prevent recruitment of saguaro seedlings . Various areas in the Sonoran Desert have been protected from domestic livestock grazing for 50 years or more. One early study showed that there was no significant (p>0.05) difference between saguaro abundance on protected and unprotected plots . More recent studies, however, have shown that saguaro increased by 33 to 200 percent in protected areas [27,77]. Saguaro seedlings may be impacted negatively when nurse plants are browsed . Models to predict saguaro age from growth parameters (for example, height-age equivalents) have been developed [28,69]. In transplant experiments, mortality was 100 percent for unshaded saguaro seedlings compared to 65 percent for shaded seedlings . Saguaro are susceptible to few diseases . Healthy saguaro often wall off larvae tunnels, woodpecker holes, or other wounds . Some necroses may occur, however, after mechanical damage to saguaro from breakage, frost, or lightning . Insects, saprophytic yeasts, molds, and bacteria readily inhabit and breed in saguaro necroses [24,66,72]. Temperatures below 23 degrees Fahrenheit (-5 deg C) will damage saguaro. Death will occur after exposure to below freezing temperatures for 29 or more consecutive hours . Fluctuations in saguaro numbers often are due to recurring catastrophic freezes [37,46,69]. Saguaro is protected under the Arizona Native Plant Law. Cactus poaching is of concern around Saguaro National Monument and urban centers . Natural environmental extremes in temperature and drought, however, are more of a threat to the survival of this species .
BOTANICAL AND ECOLOGICAL CHARACTERISTICSSPECIES: Carnegiea gigantea
GENERAL BOTANICAL CHARACTERISTICS : Saguaro is a native, arborescent, stem succulent that grows from 9.8 to 52.5 feet (3-16 m) tall and 5.9 to 29.5 inches (5-75 cm) in diameter [6,10,64,65]. It is the largest of the columnar cacti growing in the United States . Saguaro has a deep anchoring taproot (up to 3.2 feet [1 m] deep) and extensive lateral roots (13 to 98 feet [4-30 m] long) [14,65]. The stems are simple with one to five (rarely up to 49) lateral, erect branches [6,10]. Saguaro trunks have many prominent ribs, armed with dense, stout spines that are up to 2.8 inches (7 cm) long [6,10,32]. Flowers are 3.4 to 4.9 inches (8.7-12.5 cm) long and occur at the ends of branches [6,32,45]. Fruits are oblong and contain up to 2,500 seeds [1,10]. RAUNKIAER LIFE FORM : Stem succulent REGENERATION PROCESSES : Saguaro reproduce sexually and are self-incompatible . Reproduction begins when a plant is approximately 7.2 feet (2.2 m) tall [29,68]. Growth is extremely slow [47,68]. At the end of 2 years, seedlings will be about 0.25 inch (0.6 cm) tall . At 3.2 feet (1 m), plants may be 20 to 50 years old . Flowers only develop at branch and main stem tips. An increase in branch number increases the reproductive potential of an individual . Many different animals pollinate the nocturnally blooming saguaro flowers and are detailed elsewhere [2,39,40]. Flowers are open for less than 24 hours . A plant averages four open flowers per day for about 30 days . Plants commonly have more than 100 fruits [47,68]. Seeds germinate readily . Conditions for germination are detailed elsewhere [1,89,91]. Saguaro seeds are short-lived; seed reserves are not maintained in the soil [58,76]. In random soil samples, relative densities of saguaro seeds were between 0.3 and 2.0 percent . Less than 1 percent of the annual seed production germinates due to predation or moisture stress [15,48]. Heavy seedfall can occur during the summer rains . Drought during the 12 to 14 months following germination is the most critical factor threatening seedling survival [48,67]. Perennial shrubs, such as foothills paloverde (Cercidium microphyllum), are important as nurse plants for facilitating saguaro establishment [22,29,36,62]. Seed dispersal by frugivorous birds is a primary factor in saguaro establishment beneath shrub canopies . Saguaro seedling density significantly (p<0.05) decreased from the center to the outer edges of nurse plant canopies . On the margins of its range, recruitment has not kept pace with mortality caused by freezing temperatures and drought [52,76]. Saguaro has lower fruit production at the drier western edge of its range . In some areas where cattle grazing has not occurred, recruitment appeared to occur in pulses correlated with above-normal precipitation . SITE CHARACTERISTICS : Compared to other columnar cacti, saguaro occurs over the broadest range of habitats from gently sloping alluvial flats of the lower bajadas to steep, rocky, high-elevation volcanic slopes [51,53,74]. The greatest densities of saguaro are found in the more mesic eastern parts of its range . Saguaro occurs on shallow soils that are light, coarse-textured, and rocky. The soils are underlain at 3.2 to 9.6 feet (1-3 m) depths by an impervious caliche layer [8,88]. There is usually no differentiation of the soil into horizons [87,88]. Saguaro is found at elevations from 1,640 to 5,000 feet (500-1,525 m) [35,50,56,86]. Saguaro has been reported on all aspects [77,88]. However, most individuals occur on open east- and west-facing slopes, and the fewest occur on north-facing slopes [6,77,86]. The Sonoran Desert is a warm desert with a semiarid to arid continental or an arid subtropical climate [27,67,82]. Precipitation is bimodal, falling December to February and July to August, and amounts vary from year to year [19,42,51]. Average amounts of rain per year are 6 to 15 inches (152-400 mm) [3,14,42,84]. Common arborescent associated species are Organ Pipe Cactus (Lemierocereus thurberi), barrelcactus (Ferocactus wislizeni), cholla (Opuntia spp.), ocotillo (Fouqueria splendens), catclaw acacia (Acacia greggii), ironwood (Olneya tesota), and jojoba (Simmondsia chinensis) [8,13,26,50]. Other associated species are littleleaf krameria (Krameria parvifolia), fluffgrass (Erioneuron pulchellum), tobosa (Hilaria mutica), Indian-wheat (Plantago insularis), and thelypody (Thelypodium lasiophyllum) [13,23,61]. SUCCESSIONAL STATUS : Obligate Climax Series Succession in desert systems is difficult to define . Saguaro may be considered a climax species. Establishing in the shade of perennial shrubs, saguaro usually outlives and surpasses the nurse plants. Regeneration of saguaro continues in suitable areas of its range. SEASONAL DEVELOPMENT : Saguaro flowers from late April to June [1,32,39,45]. Fruits mature during June and July before the summer rains [6,65]. Most growth of saguaro occurs during the summer rainy season .
FIRE ECOLOGYSPECIES: Carnegiea gigantea
FIRE ECOLOGY OR ADAPTATIONS : Saguaro is not truly adapted to fire because there is no postfire stimulation of flowering or seed production . It has several prominent morphological characteristics, however, that may aid its survival when burned. The apex is protected to some degree by tissue folds and spines. Vascular tissue is protected by a thick cortex that has a high thermal capacity close to that of water. As saguaro ages, ribs at the base of a plant may develop a woody bark which is more resistant to burning than young tissue . Although mortally injured by fire, death may be delayed if the saguaro can live off of its reserves, which may enable a plant to flower for 1 to 6 years more . Singed saguaro have been observed to flower from unburned branches. However, scorched plants may die due to reduced vigor . Fire may remove spines from a saguaro, making it vulnerable to herbivory . Nurse plant species influence saguaro fire survival. Although desert fire temperatures are variable, fire temperatures beneath foothills paloverde were lower than under triangleleaf bursage (Ambrosia deltoidea) . Fire-free periods in the Sonoran Desert are greater than 250 years . Saguaro would be eliminated under a fire frequency of less than 30 years . Fires that do occur are usually of low intensity due to small fuel loads . FIRE REGIMES : 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". POSTFIRE REGENERATION STRATEGY : Tree without adventitious-bud root crown Secondary colonizer - off-site seed
FIRE EFFECTSSPECIES: Carnegiea gigantea
IMMEDIATE FIRE EFFECT ON PLANT : Fire top-kills saguaro, and it may kill existing seedlings . Because there is a lag time between time of injury by fire and time of death, postfire mortality may be underestimated . Small saguaro, less than 6.6 to 13 feet (2-4 m) tall, with large amounts of fuel at the plant base do not survive. Larger saguaro may survive with limited damage [16,41]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Postfire recovery is dependent upon individual plant recovery and seed dispersal from unburned plants . Surviving saguaro with little or no injury will resume growth . Absorption of rain following fire-caused injuries can result in fire scars splitting, which opens the plant to insects and infections . Vegetation surveys done the third and fourth years following an early summer fire found no sprouting of saguaro and no seedlings . Two studies that compared burn and adjacent wildfire areas 2 years after prescribed burning found that 100 percent of saguaro present in plots had died. Plots were read before and after fire. There were no sprouts or seedlings [16,17]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : Fire would be an effective tool to control saguaro invasion or density [68,73]. Along major highways in Arizona, motorist-caused fires have completely eliminated the saguaro over large areas .
REFERENCESSPECIES: Carnegiea gigantea
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