SPECIES: Ceanothus greggii
AUTHORSHIP AND CITATION:
Zouhar, Kristin L. 2000. Ceanothus greggii. 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/ .
Ceanothus greggii ssp. perplexans (Trel.) Beauchamp Mojave buckbrush
Ceanothus greggii ssp. vestitus (Greene) Schmidt Mojave ceanothus 
NRCS PLANT CODE :
The currently accepted scientific name of desert ceanothus is Ceanothus greggii Gray (Rhamnaceae) [16,36,41,45,46,137]. It is a species of the subgenus Cersastes. Natural hybridization is considered prevalent in Ceanothus spp., especially within subgenera, and may complicate taxonomy .
Recognized varieties are as follows:
Ceanothus greggii var. franklinii Welsh Franklin's ceanothus
Ceanothus greggii ssp. greggii Gray Gregg's ceanothus [41,45]
Ceanothus greggii var. perplexans (Trel.) Jepson cupleaf ceanothus 
Ceanothus greggii var. vestitus (Greene) McMinn Mojave ceanothus [16,36]
Common names for varieties are not often encountered in the literature and any reference to varieties in this review will use the scientific name. References in this review to "ceanothus" are general references to the genus Ceanothus.
FEDERAL LEGAL STATUS:
No special status
Desert ceanothus occurs from Trans-Pecos, Texas, through southern New Mexico, Arizona, and southern California, north to the Great Basin region of Utah and Nevada, and south to Oaxoaxa, Mexico [15,16,36,46,137]. Franklin's ceanothus (Ceanothus greggii var. franklinii) is endemic to Grand and San Juan counties in Utah [16,136]. Ceanothus greggii var. greggii is found in and around the Virgin drainage system in Utah . Ceanothus greggii var. perplexans is found in the interior Peninsular ranges of southern California into northern Mexico [36,73]. Ceanothus greggii var. vestitus is found along the desert margin of the southern Sierra Nevada and the Transverse ranges in California, as well as parts of Utah, Nevada, Arizona, Texas, New Mexico, and Mexico [15,16,36,73,136]. The PLANTS database provides a distributional map of desert ceanothus and its infrataxa.
FRES21 Ponderosa pine
FRES28 Western hardwoods
FRES30 Desert shrub
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES40 Desert grasslands
KUCHLER  PLANT ASSOCIATIONS:
K005 Mixed conifer forest
K009 Pine-cypress forest
K019 Arizona pine forest
K023 Juniper-pinyon woodland
K030 California oakwoods
K031 Oak-juniper woodland
K032 Transition between K031 and K037
K034 Montane chaparral
K035 Coastal sagebrush
K036 Mosaic of K030 and K035
K037 Mountain-mahogany-oak scrub
K038 Great Basin sagebrush
K043 Paloverde-cactus shrub
K058 Grama-tobosa shrubsteppe
SAF COVER TYPES :
220 Rocky Mountain juniper
237 Interior ponderosa pine
238 Western juniper
240 Arizona cypress
241 Western live oak
247 Jeffrey pine
248 Knobcone pine
249 Canyon live oak
255 California coast live oak
SRM (RANGELAND) COVER TYPES :
107 Western juniper/big sagebrush/bluebunch wheatgrass
202 Coast live oak woodland
203 Riparian woodland
205 Coastal sage shrub
206 Chamise chaparral
207 Scrub oak mixed chaparral
208 Ceanothus mixed chaparral
209 Montane shrubland
211 Creosotebush scrub
403 Wyoming big sagebrush
405 Black sagebrush
408 Other sagebrush types
412 Juniper-pinyon woodland
413 Gambel oak
414 Salt desert shrub
415 Curlleaf mountain-mahogany
416 True mountain-mahogany
417 Littleleaf mountain-mahogany
503 Arizona chaparral
504 Juniper-pinyon pine woodland
505 Grama-tobosa shrub
507 Palo verde-cactus
509 Transition between oak-juniper woodland and mahogany-oak association
HABITAT TYPES AND PLANT COMMUNITIES:
Desert ceanothus is an important constituent of many chaparral and desert shrub communities and also occurs in drier ponderosa pine (Pinus ponderosa), pinyon-juniper (Pinus-Juniperus) and oak (Quercus spp.) woodlands [14,43,137].
Desert ceanothus is listed as a dominant or indicator species in the following publications:
Arizona chaparral: plant associations and ecology 
New Mexico vegetation: past, present, and future 
Vegetation of the San Bernadino Mountains 
Classification of pinyon-juniper sites on national forests in the southwest 
The vascular plant communities of southern California 
California chaparral: Desert ceanothus occurs in several types of California chaparral communities. Some plants that are common to many types of California chaparral include chamise (Adenostoma fasciculatum), manzanita (Arctostaphylos spp.), ceanothus (Ceanothus spp.), silktassel (Garrya spp.), oak (Quercus spp.), mountain mahogany (Cercocarpus spp.), sumac (Rhus spp.), California buckwheat (Eriogonum fasciculatum), sumac (Rhus spp.), and chaparral yucca (Yucca whipplei) [32,37,82,95]. Herbaceous vegetation is rare, but some annuals that may occur in early seral communities are species of the genera Phacelia, Emmenanthe and Antirrhinum as well as several opportunistic annuals of the genera Cryptantha, Camissonia, Lotus and Filago . Desert ceanothus shares dominance in desert chaparral communities with mountain mahogany, flannelbush (Fremontodendron californicum), bigberry manzanita (A. glauca), and interior live oak (Q. wislizenii) . Chamise or mixed chaparral is dominated by chamise, with desert ceanothus a common secondary species. Additionally, desert ceanothus may be found in communities dominated by Nuttall's scrub oak (Q. dumosa), redshank (Adenostoma sparsifolium), Joshua tree (Yucca brevifolia), antelope bitterbrush (Purshia tridentata), Stansbury cliffrose (Purshia mexicana var. stansburiana), or toyon (Heteromeles arbutifolia). Early seral communities (10-60 years old) are sometimes characterized by a relatively high cover of ceanothus species, including desert ceanothus . Descriptions of several types of chaparral communities of which desert ceanothus is a part (northern mixed chaparral, semi-desert chaparral, desert chaparral) are available [37,39,64,95,117].
Arizona chaparral: Desert ceanothus is found in all Arizona chaparral communities described by Carmichael and others , and is always in association with other species . Arizona chaparral has sparser cover than its California counterpart, and it intergrades with desert scrub or grassland below and ponderosa pine forest or pinyon-juniper woodland above . Shrub live oak (Q. turbinella) is the most common component of Arizona chaparral [54,92]. Other common constituents of Arizona chaparral are manzanita, mountain mahogany, silktassel, sumac, hollyleaf buckthorn (Rhamnus crocea), and cliffrose . Grasses and forbs are usually sparse, but more common than in California chaparral communities.
Mexico chaparral: In Mexico chaparral communities (which may also occur in southern New Mexico and Texas), desert ceanothus is associated mostly with evergreen shrubs of the same genera as those in Arizona and California, including shrub oaks, silktassel, mountain mahogany, sumac, ceanothus, and manzanita and some endemics such as madrone (Arbutus spp.), and sage (Salvia spp.) [54,92]. In the mountain ranges and desert scrub regions of Trans-Pecos, Texas, desert ceanothus is found with sandpaper oak (Q. pungens) mountain mahogany, Spanish bayonet (Yucca faxoniana), smooth-leaf sotol (Dasylirion leiophyllum), ocotillo (Fouquieria splendens), catclaw mimosa (Mimosa aculeaticarpa var. biuncifera), lechuguilla (Agave lechuguilla) and sacahuista (Nolina microcarpa) [87,125].
Pinyon-Juniper: In California pinyon-juniper woodlands, desert ceanothus can be found with singleleaf pinyon (Pinus monophylla), California and western juniper (J. californica and J. occidentalis), big sagebrush (Artemisia tridentata), rabbitbrush (Chrysothamnus spp.), bitterbrush, and flannelbush [75,135]. In pinyon-juniper and oak woodlands of the southwest, desert ceanothus is found with Colorado pinyon (Pinus edulis), singleleaf pinyon, Apache pine (P. engelmannii), Chihuahua pine (Pinus leiophylla var. chihuahuana), alligator juniper (J. deppeana), oneseed juniper (J. monosperma), Arizona white oak (Q. arizonica), Gambel oak (Q. gambelii), shrub live oak, Arizona cypress (Cupressus arizonica), cliffrose, manzanita, mountain mahogany, sumac, Wright silktassel (G. wrightii), prickly-pear (Opuntia spp.), agave (Agave parryi), creosote bush (Larrea tridentata), Wright buckwheat (Eriogonum wrightii), broom snakeweed (Gutierrezia sarothrae), and several grasses including blue grama (Bouteloua gracilis), and pinyon ricegrass (Piptochaetium fimbriatum) [3,18,28,43,77,83,121].
In the desert plains galleta-grama (Pleuraphis -Bouteloua) grasslands of the southwest, desert ceanothus may be found along ravines with other chaparral species . Desert ceanothus may also be found in trace amounts in the Arizona walnut (Juglans majors), Fremont cottonwood-green ash (Populus fremontii-Fraxinus pennsylvanica) and Arizona sycamore (Platanus wrightii) riparian community types in southern Arizona and New Mexico . In the transition zone between the Mojave and Great Basin deserts, desert ceanothus grows in blackbrush (Coleogyne ramosissima) communities with big sagebrush, California buckwheat, and desert needlegrass (Achnatherum speciosum) [4,66]. In Great Basin sage-scrub communities it is found with big sagebrush, bitterbrush, and rubber rabbitbrush (C. nauseosus) .
Ceanothus greggii var. vestitus is described as occurring in montane chaparral, desert chaparral [32,75], sagebrush scrub, and Joshua tree and pinyon-juniper woodlands, in California, Utah and Arizona . Ceanothus greggii var. perplexans is found in montane and desert chaparral , pinyon-juniper woodlands and ponderosa pine forests in southern California . Franklin's ceanothus (Ceanothus greggii var. franklinii) is found in pinyon-juniper, blackbrush, and serviceberry (Amelanchier spp.) communities in Utah [16,136].
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Desert ceanothus is considered fair to good, staple browse for livestock, especially domestic goats, in winter and early spring [14,43,116,132]. Because of their smaller mouths and more flexible lips, domestic sheep and goats are better able to utilize the intricately branched foliage than are cattle . Angora goats relished desert ceanothus seedlings in Arizona, while use of the mature plants was negligible . Similarly, desert ceanothus was used moderately by domestic goats (Angora and Spanish) in southern California, with 1-year growth preferred to 5-years growth . Spanish goats in chamise chaparral in southern California preferred sandpaper oak and chamise over desert ceanothus for summer browse .
Desert ceanothus is a highly preferred browse of wild ungulates and is used throughout the year in many areas [11,28,102,122,129]. It is particularly valuable as an emergency browse during winter and early spring because of evergreen leaves [55,129]. Desert ceanothus has been described as one of the most important deer browse plants in chaparral ranges of California and the Southwest [9,43,122]. Reports of use by white-tailed and mule deer range from only trace amounts , to more moderate use , to heavy use in late fall and winter. Smaller amounts are used in summer and early fall and moderate amounts in spring [69,85]. Elk and desert bighorn sheep also consume desert ceanothus [7,30,102,115]. Small mammals such as brush rabbits are known to feed on the twigs, stems, and leaves of desert ceanothus [71,72]. Seeds are eaten by mule deer, many small mammals, chukar and other birds, and insects [14,34,131].
Desert ceanothus is highly palatable to most wild ungulates and to many classes of domestic livestock. It is somewhat less palatable to cattle than to deer or domestic sheep and goats . Overall palatability to livestock and wildlife species is as follows [30,40,44,71,85,102,129]:
|Domestic sheep||good-very good||---||fair-good||fair||---|
|Small mammals||---||very good||---||---||---|
|Date||Dry matter||Protein||Acid-detergent fiber||Cell solubles||Ash|
Desert ceanothus exhibits relatively high year-round protein levels, and phosphorus and moisture content were found to be above average, especially during the winter . More detailed nutritional information has been documented for desert ceanothus [115,131].
VALUE FOR REHABILITATION OF DISTURBED SITES:
Desert ceanothus is thought to improve soil fertility by fixing atmospheric nitrogen and is well-adapted for use in stabilizing both neutral and acidic soils. Establishment by seed is often poor, although seedlings may be readily transplanted. This shrub has been successfully planted onto many types of disturbed sites throughout the Southwest and is particularly well-suited for use in southern and northern desert shrub communities and chaparral .
Survival of potted stock of C. greggii var. perplexans planted at 5300 feet (1606 m) elevation in deep soils was 60%. Height growth was 2 to 5 feet (0.6-1.5 m) in 8 years .
OTHER USES AND VALUES:
Desert ceanothus is a potentially good hedge plant in the Southwest . It is also commonly used in low-maintenance landscaping . Ceanothus spp. are esteemed honey plants . The blossoms form a sweet smelling lather when rubbed in water [79,134]. Ceanothus spp. are known for their medicinal value in stimulating lymph and intertissue fluid circulation . The roots of ceanothus species can be used to make a red dye .
OTHER MANAGEMENT CONSIDERATIONS:
Heavy cattle or sheep use of desert ceanothus on summer ranges may be symptomatic of overstocking, and closely hedged plants are often indicative of range deterioration [17,43,129]. Although deer damage is not as severe in desert ceanothus as in other species of ceanothus , it is one of the first species to be reduced on heavily populated deer ranges of the Southwest [11,43,122,139]. Because of its low stature, the whole plant is subjected to use so it cannot withstand, and may be totally eliminated by, continuous heavy browsing [11,122].
To minimize potential adverse impacts on wildlife, managers recommend treating no more than 50% of an area to reduce shrubs, with treated swaths averaging no more than 300 to 400 yards (275-366 m) in width .
GENERAL BOTANICAL CHARACTERISTICS:
Desert ceanothus is an erect or low, rounded, sclerophyllous shrub with intricate, short, rigid branches. It grows 1 to 7 feet (0.2-2 m) tall, seldom more than 5 feet (1.5 m) [46,54,100,102,137]. Although commonly thought to be short-lived (30-40 years) , Keeley  indicates that Ceanothus greggii var. perplexans can live longer than 90 years. Longevity may be increased in desert ceanothus through longitudinal fissioning of the stems. Age can be accurately determined in Ceanothus spp. using growth rings . Aboveground stems are locally even aged and date to the last fire . Nonsprouting species of Ceanothus, such as desert ceanothus, tend to be spatially clumped especially in older stands , and can form dense, impenetrable stands , or grow as lone shrubs . The leaves are evergreen, 0.2 to 0.65 inches (5-16 mm) long, opposite, thick and firm [16,36]. Three ovoid seeds are borne in each rounded capsule [48,132], and are propelled explosively as the capsules mature and dry. Roots tend to be shallow and laterally spreading, with lateral growth far exceeding the depth of penetration (9.8 feet (3 m) of radial spread in a 2.5 foot (0.75 m) diameter plant). More than 90% of the roots occur within the top 12 to 16 inches (30-40 cm) of soil .
Desert ceanothus contains nitrogen-fixing bacteria within its root nodules, which may increase its abundance on nitrogen poor sites. Based on fairly limited observations of root nodules in desert ceanothus in southern California chaparral, Kummerow and others  estimated N fixation at the rate of 0.09 pounds N per acre (0.1 kg per ha) per year in a stand with 32% cover. Desert ceanothus has a relatively low photosynthetic rate 90.85nM/cm2/sec-1 in full sunlight .
Desert ceanothus relies on production of numerous seedlings to maintain dominance or subdominance in chaparral communities [14,47,53,55]. It regenerates almost exclusively from long-lived seeds that accumulate in the soil [92,146] and germinate prolifically following fire . It is, therefore, fire dependent, with sharp population increases after fire and an intervening period during which there is mortality but little establishment . Minnich and Howard  report the establishment of Ceanothus greggii var. vestitus, en masse, after pinyon fires, despite the absence of adults previous to the burn. There are some reports of desert ceanothus sprouting from the stem or root crown after fire or mechanical removal, although sprout survival is poor [56,73,94,97,98].
Seed production: Desert ceanothus plants reach sexual maturity and begin producing seed between 3 and 15 years of age [12,54,145]. Obligate seeding species of ceanothus produce several times the number of seeds as sprouting ceanothus plants. Quantity of seed produced varies significantly (p<0.01), sometimes by orders of magnitude, from year to year , and may be influenced by plant size and density, stand location and fluctuations in climate [48,144]. One-year annual seed production at a California site was estimated at 33.8 million seeds per acre (83 million per hectare) . Seed production is thought to be related to the amount of precipitation received in the previous year, with high precipitation leading to greater seed production [48,145]. Zammit and Zedler  found that the rate of seed production increases with shrub height and was maximized within two decades after fire. They observed no evidence of decline in seed production with age of shrub up to 86 years. Average annual seed production ranged from 0 seeds up to 21,092 seeds per plant. Seed production requires flower pollination and is therefore dependent on insect populations.
Seed dispersal: Seeds are propelled explosively as the capsules mature and dry. This mechanism aids dispersal as seeds are sent outward from the parent plants, and may represent an antipredator strategy . Rodents, birds, and ants may also play a role in seed dispersal .
Seed banking: As many as 1.0 to 1.4 million seeds per acre (2.6 to 3.7 million seeds per hectare) have been observed in the soil at a given time . Seed reserves are influenced primarily by site-specific patterns of seed production and by the intensity of postdispersal seed predation and are not correlated with time since fire [143,144]. Zammit and Zedler  observed a significant (p<0.05) increase in density of germinable seeds with increasing live crown cover, and found highest density (180/ft2 (2000/m2)) in stands of intermediate age. Density of the soil seed bank is almost always lower than the density of annual seed rain [48,104,144]. Failure of seeds to accumulate over time may be due to losses by erosion, predation or infestation, and severe fire [48,54,143]. Seed of desert ceanothus stored in the soil may remain viable for decades [27,91,92]. Keeley  observed about 50% viability of desert ceanothus seeds stored in the soil.
Seed predation: Most seeds produced in a year are consumed or removed within a few months of dispersal. Desert ceanothus seeds may be used by harvester ants that rapidly and selectively remove seeds from the soil surface , or they may be infested by the phytophagous chalcid wasps . In some areas rodents may consume up to 99 % of annual ceanothus seed production . An estimate of seed loss is 34% of annual production .
Germination: Germination between fires is negligible, but after fire, seedlings are produced in abundance [14,48,51,144], assuming a quantity of viable seed is present in the soil. Heat stimulation or scarification (5 min at 158 degrees Fahrenheit (70 oC)) is required for germination of desert ceanothus [12,27,49,91,143,145]. Severe fires can kill more shallowly buried seed, while stimulating those buried more deeply . Increasing fire severity resulted in better and earlier germination of desert ceanothus seeds compared with chamise seeds and sprouts. Fewer seeds germinated in the field when compared with greenhouse germination studies, suggesting that the number of seedlings emerging in the field is a fraction of the postfire readily germinable seeds, and that suitable microsites for germination are an important factor .
Seedling establishment: Establishment of desert ceanothus seedlings occurs during the 1st year postfire, although a few seedlings may continue to emerge during the 2nd season or later [53,94,107]. Competition for light and water is often intense . Seedlings are vulnerable to the effects of drought and damage by insects, rabbits or rodents . Early mortality is often high. Keeley and Zedler  report 95% seedling survival during the 1st year of regrowth at a southern California chaparral site, while Kummerow and others  report only 7.8% survival of desert ceanothus seedlings the 1st year.
Desert ceanothus grows on dry, rocky slopes, foothills, canyons, gullies, and in erosion channels [84,92,127,137]. It flourishes on a variety of soil types, is tolerant of both basic and acidic soils, and most often grows on dry, poorly developed soils [43,96,126,129]. It is most commonly found in areas with 20 to 30 inches (500-750 mm) precipitation . Desert ceanothus is a chaparral species that grows in several different community types in several geographic locations, each with specific site characteristics. Attempts to ascribe site preferences for most chaparral species have generally produced weak correlations and indicate that preferences may change with the region .
Chaparral occurs on rocky, nutrient-poor soils and is best developed on steep slopes . California chaparral is characterized by a Mediterranean climate with cool, moist winters, and hot, dry summers. Water availability is likely the primary determinant of community structure in areas where desert ceanothus grows . In general, obligate-seeding species such as desert ceanothus increase in abundance, diversity and longevity with increasing aridity. Seedlings of these species are also more tolerant to drought than those of associated sprouting species [47,54]. Poole and Miller  found desert ceanothus to maintain leaf conductance at very low water potentials compared with associated chaparral shrub species. However, Zammit and Zedler  found that shrubs on north aspects tend to grow larger and produce more seed than those on south aspects, likely due to better moisture availability on these aspects. Also, nonsprouting ceanothus may experience mass mortality within a stand in severe drought years . Desert ceanothus seems to capture and use more water by using it lavishly while it is readily available, and still maintaining conductance at very low water potentials [90,101]. Data suggest that water stress may inhibit nodulation in ceanothus, which may help explain the low densities of N-fixing nodules found in desert ceanothus compared with densities found under other ceanothus species in northern California . Availability of phosphorus may also limit growth of ceanothus . Desert ceanothus is a poor competitor under shaded conditions .
In Arizona, chaparral sites are most common on coarse textured, poorly developed soils with granitic parent material . Desert ceanothus is usually found on the upper portions of slopes and /or relatively level sites where other shrubs are scarce . It is commonly found on north slopes at lower elevations in the desert zone and south slopes at upper elevations, increasing in abundance with increasing elevation up to 5,000 feet (1515 m) in Arizona [24,69]. In the desert plains grassland in southern New Mexico, Arizona and southwestern Texas, desert ceanothus can be found along ravines and similarly favorable sites .
Generalized elevation and precipitation ranges by state are as follows:
|AZ||3,000-7,100 feet (914-2151 m)||16-26 inches (400-650 mm)||[12,46,83]|
|CA||3,500-7,000 feet (1060-2121 m)||15.2-25.4 inches (380-635mm)|||
|TX||3,500-8,000 feet (1067-2438 m)||----|||
|UT||4,000-9,400 feet (1220-2870 m)||----||[136,137]|
|Mexico||3,465-9,900 feet (1050-3000 m)||----|||
Ceanothus greggii var. vestitus is found on dry slopes from 3,500-7,500 feet (1067-2286 m) in California, Utah and Arizona. Ceanothus greggii var. perplexans is found on dry slopes from 3,465 to 8,085 feet (1050 to 2450 m) in California .
Desert ceanothus is considered to be part of a fire-induced climax in chaparral communities of southern California and the Southwest . Hanes  aptly described succession in a Ceanothus greggii var. vestitus stand as "more of a gradual elimination of individuals present from the outset than a replacement of initial shrubs by new species".
Desert ceanothus produces a large number of seeds and, with fire, a small number of mature plants are replaced by an abundance of seedlings which require 3 to 15 years to reach sexual maturity [12,48]. Parker  found that maximum transpiration rates are consistently higher for shallow-rooted obligate-seeding Ceanothus species than for deeper-rooted sprouting shrub species and that this results in more rapid seedling growth for these species . As seedlings grow and shrub cover increases, there is intense intra- and interspecific competition for light and moisture resulting in heavy mortality [47,50,55]. Ceanothus dominated chaparral accumulates aboveground biomass at an exponential rate through at least 2 decades after stand establishment . Ceanothus greggii var. vestitus was found to have greatest canopy coverage in chaparral stands 22 to 40 years after disturbance , and desert ceanothus was most abundant in 10-22 year old burns . Mortality of ceanothus was observed to consistently decrease over time up to 120 years . Hanes  observed that over one-half of the population of C. crassifolius and C. greggii var. vestitus was dead in stands older than 40 years. Desert ceanothus plants are well adapted to competing in mature chaparral and are seldom entirely eliminated from a stand . If these "short-lived" species escape close competition they can be quite long-lived [47,113]. Keeley  observed that the C. greggii var. perplexans was still an important constituent of southern California chaparral which had remained undisturbed for 90 years. Similarly, Zammit and Zedler  showed no decline in seed production in desert ceanothus 6-82 years after fire.
It has been suggested that senescence occurs in older chaparral due to the formation of allelochemicals and/or sequestering of nutrients in biomass and recalcitrant soil compounds. Larigauderie and others  observed little change in growth rate or vigor of desert ceanothus with stand age, suggesting that desert ceanothus is not a short-lived species and its elimination from older stands is likely due to reasons such as decline in nutrient availability, rather than a physiological decline of the shrub. Fenn and others  found no evidence that N stored in the microbial biomass in soils under desert ceanothus is involved in nutrient deficiencies in older California chaparral stands. Marion and Black  observed an accumulation of available N over time up to 60 years, after which it declined; and a steady decline in soil P over time.
In pinyon-juniper woodlands of southern California, desert ceanothus is part of the understory shrub component that will dominate a site for about 50 years following fire, followed by a slow recolonization of singleleaf pinyon . Wangler and Minnich  observed skeletons of desert ceanothus but no living stems on burns greater than 47 years old in these communities. Cover of desert ceanothus peaked at about 18-33 years after fire at 10-13% cover and 3,232-4,094 stems per ha. It is considered a perennial nurse shrub for single leaf pinyon. Desert ceanothus was present only in the earliest successional stage (grass-forb) as described by Koniak and Everett  in another southern California pinyon-juniper woodland.
Seasonal development of desert ceanothus varies with geographic location. In the Mediterranean scrub communities, growth rhythms are related to moisture availability, with the majority of annual growth and flowering occurring in the spring [84,109,129], growth all but ceasing at the onset of hot summer temperatures in late May, and the fruiting period typically completed by June . Desert ceanothus plants flower on old growth from floral buds initiated in the previous growing season . Plants may flower a second time during August through October if sufficient summer precipitation is received [46,129]. Shoot growth lasts only a fraction of the time of seasonal root growth .
Desert ceanothus has the capacity to fix carbon year-round , and data indicate that it will grow whenever conditions are favorable . Stomatal conductances are high (0.5 cm sec-1) in desert ceanothus in the winter when compared with other chaparral evergreen shrubs. It is also likely to maintain more active photosynthesis into the drought than many deep-rooted shrubs, but later in the season may have complete stomatal shut-down for a month or more [54,88]. Sparks and others  measured seasonal photosynthate allocation in desert ceanothus and chamise and observed relatively low structural allocation in spring and higher in summer; and increased proportional allocation to storage in the fall.
|initiation of growth||March||Mar.-Apr.|
|shoot growth||Mar.-May; Aug.-Sept.||mid-Apr.-mid-June|
|fine root growth||end of Feb.-Aug.|
|duration of growth days||68-70|
|flowers||March-May (sometimes Sept.)||early spring|
FIRE ECOLOGY OR ADAPTATIONS:
Desert ceanothus is a component of chaparral communities in which fire is a dominant part of the environment. These communities are adapted to particular fire regimes defined by intensity, season and frequency of fire. In California chaparral communities of which desert ceanothus is a common component, the context is high-intensity canopy fires that usually come in the late summer or fall every 20-30 years on average . Chaparral appears to be resilient to fire-recurrence intervals of 100+ years . Although Zammit and Zedler  estimate that desert ceanothus shrubs will die out locally in chaparral unburned for 85-155 years. Wildfires are less frequent in Arizona chaparral communities supporting desert ceanothus, occurring every 50-100 years .
It is suggested that occasional long fire-free periods (100 years or more) are an important evolutionary stimulus for the obligate seeding strategy. The region of California with the lowest lightning-fire frequency is the coastal range which is also the area which supports the greatest abundance and diversity of nonsprouting species such as desert ceanothus. With shorter fire frequency (20-30 years) both seeding and sprouting species regenerate, but sprouting species may gain advantage after several cycles . Desert ceanothus may require 5-15 years to reach sexual maturity, and fires at intervals this frequent may cause local extinctions [54,98]. Seedlings are rare except after fire and populations are locally even aged and regionally a mosaic of different aged populations dating to past fires . Fire return intervals for plant communities and ecosystems where desert ceanothus occurs are as follows:
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|California chaparral||Adenostoma and/or Arctostaphylos spp.||< 35 to < 100 |
|basin big sagebrush||Artemisia tridentata var. tridentata||12-43 |
|Wyoming big sagebrush||A. t. var. wyomingensis||10-70 (40**) [133,142]|
|coastal sagebrush||A. californica||< 35 to < 100|
|desert grasslands||Bouteloua eriopoda and/or Pleuraphis mutica||5-100|
|blue grama-needle-and-thread grass-western wheatgrass||B. gracilis-Hesperostipa comata-Pascopyrum smithii||< 35|
|blue grama-buffalo grass||B. gracilis-Buchloe dactyloides||< 35|
|California montane chaparral||Ceanothus and/or Arctostaphylos spp.||50-100|
|paloverde-cactus shrub||Cercidium microphyllum/Opuntia spp.||< 35 to < 100 |
|curlleaf mountain-mahogany*||Cercocarpus ledifolius||13-1000 [1,114]|
|mountain-mahogany-Gambel oak scrub||C. l.-Quercus gambelii||< 35 to < 100|
|blackbrush||Coleogyne ramosissima||< 35 to < 100|
|Arizona cypress||Cupressus arizonica||< 35 to 200|
|juniper-oak savanna||Juniperus ashei-Quercus virginiana||< 35|
|western juniper||J. occidentalis||20-70|
|Rocky Mountain juniper||J. scopulorum||< 35|
|creosotebush||Larrea tridentata||< 35 to < 100|
|pine-cypress forest||Pinus-Cupressus spp.||< 35 to 200|
|pinyon-juniper||Pinus-Juniperus spp.||< 35 |
|Mexican pinyon||P. cembroides||20-70 [78,123]|
|Colorado pinyon||P. edulis||10-49|
|Rocky Mountain ponderosa pine*||P. ponderosa var. scopulorum||2-10|
|Arizona pine||P. p. var. arizonica||2-10|
|California oakwoods||Quercus spp.||< 35|
|oak-juniper woodland (Southwest)||Quercus-Juniperus spp.||< 35 to < 200|
|coast live oak||Q. agrifolia||<35 to 200|
|white oak-black oak-northern red oak||Q. alba-Q. velutina-Q. rubra||< 35|
|canyon live oak||Q. chrysolepis||<35 to 200|
|blue oak-foothills pine||Q. douglasii-P. sabiana||<35|
|California black oak||Q. kelloggii||5-30|
|interior live oak||Q. wislizenii||< 35|
|elm-ash-cottonwood||Ulmus-Fraxinus-Populus spp.||< 35 to 200 |
Heat stimulation or scarification (5 min at 158 degrees Fahrenheit (70 oC)) is required for germination of desert ceanothus seed [12,27,49,91,143,144]. Seed mortality varies with fire severity and depth of burial . Quinn  observed 90% mortality in hoaryleaf ceanothus (C. crassifolius) seed 1 week after wildfire.
DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Timing of fire, soil moisture, plant size, and physiological condition may all play a role in whether plants and seeds are killed by fire. Plants are usually killed, although there are reports of damaged plants surviving and sprouting [54,56,94]. Sprouts tend to be weak and easily succumb to stress form drought, competition, herbivory, or further burning [98,107]. Severe fires can kill the more shallowly buried seed, while stimulating those buried more deeply . Seed predation may occur following fire as rodents and birds may dine on roasted seed .
PLANT RESPONSE TO FIRE:
Mature plants (3-15 years) of desert ceanothus produce seed annually and disperse it in the vicinity of the plant. Numbers produced can vary by orders of magnitude from year-to-year [48,145]. Seed that is not lost to predation or erosion accumulates in the soil around parent plants during fire-free intervals. The soil seed pool is thought to be greatest in stands of intermediate age . Seed can remain viable for decades and is stimulated by heat to germinate following fire [8,27,146]. Scarified, viable seed in suitable sites will germinate if not lost to granivorous rodents or birds. Keeley  found about 50% of desert ceanothus seed in the soil was viable at a southern California chaparral site.
Most seeds germinate the 1st spring after fire , although some seedling establishment has been observed in subsequent springs [53,91,93,94]. Fire must be severe enough to scarify seed, although a case was reported in which seed was not scarified by fire, but by temperatures reached by sun on the blackened soil the 2nd postfire season .
The 1st 1 to 3 years after fire are critical in determining composition of mature chaparral communities [2,72]. Seedling mortality affects the species balance of shrub seedlings and stump sprouts, is generally greatest during the 1st postfire year, and varies as a result of herbivory, competition and climate . Mortality of desert ceanothus may be high in early postfire years when compared with other shrubs [48,62,93]. Although Keeley and Zedler  report only 2% mortality of desert ceanothus seedlings in the 1st postfire year at a California chaparral site, while chamise and manzanita species experienced 39 to 71% mortality. Abundant seedlings usually provide more than enough plants to insure perpetuation even after high initial mortality .
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Postfire seed germination and seedling establishment are a function of severity, size and season of fire, as well as climatic conditions, competition and herbivory following fire. The number of desert ceanothus seeds that germinate is a function of seed production during the preceding fire-free interval, consumption or removal of seeds by animals and insects, degree of heat scarification and postfire survival of seeds . The year and season in which a fire occurs may have important consequences for the reproduction of desert ceanothus due to the fluctuations of seeds stored in the soil .
Fires of greatest intensity would occur at some intermediate fire-free interval, as fuel loads increase up to a point and then decrease as more and larger plants die and decompose. This is also the time when the soil seed pool would be the greatest .
Pase  observed greater seedling establishment in Arizona chaparral following a severe burn (2,618 seedlings/acre (6466/ha)) than following a less severe burn (636 seedlings/acre (1571/ha)). Moreno and Oechel  found that seedling abundance of desert ceanothus was positively correlated with fire severity. Variability in distribution of desert ceanothus may be due to local fluctuations in fire severity . Prescribed burns conducted when soils are moist may reduce the response of desert ceanothus because the intensity and duration of heat may be too low to stimulate germination .
Large fires may harm population levels of nonsprouting shrubs that have suffered heavy soil seed predation . However, a larger burn may help protect seedlings from herbivory by small mammals that cannot reach them due to lack of cover [72,128].
Season of burn may affect establishment of desert ceanothus. Following early spring (low severity) fires, establishment of ceanothus was poor compared with more severe summer season fires [2,89]. A chaparral stand dominated by desert ceanothus and chamise was burned in the early winter, and desert ceanothus seedlings failed to germinate the 1st postfire spring. Seedlings were unable to compete with established vegetation the following spring, resulting in a stand dominated by chamise .
Drought following seedling establishment may favor ceanothus over chamise [25,71,80]. However, Moreno and Oechel  found mortality of desert ceanothus seedlings was strongly related to depletion of soil moisture the first few months after germination. While desert ceanothus demonstrates a greater adaptability to the physical environment, it is also subject to a greater degree of interspecific interference by plant and animal interaction than chamise.
After a December prescribed burn in 54-year-old California chaparral desert ceanothus seedlings numbered 4 seedlings per foot2 (44 per m2) in May. Most of these seedlings died in May and June, leaving 7.8% alive in December. Mortality was not affected by stump sprouters, but was likely due to drought and/or herbivory by rabbits .
Seedlings of desert ceanothus are lacking physical and chemical defenses against herbivores that may develop later and are especially vulnerable to herbivory . Mills  observed that preferential consumption of desert ceanothus by brush rabbits could eliminate its competitive advantage over chamise. In the absence of herbivory, chamise experienced higher mortality. Desert ceanothus plants that were located among the dense branches of chamise were taller than plants in uncovered microsites on open plots. This suggests that chamise may act as a nurse plant, protecting desert ceanothus from herbivory by rabbits. Ceanothus seedlings were also heavily infected by psyllids during the 2nd and 3rd postfire years. This infection significantly (p<0.01) reduced growth and survivorship of ceanothus seedlings, killing around 13% of seedlings .
FIRE MANAGEMENT CONSIDERATIONS:
It is important for managers to consider the natural fire regime of desert ceanothus plant communities when planning prescribed burns since deviations from the natural regime will change community composition and structure . Desert ceanothus may be an important component in postfire communities because of its ability to fix nitrogen [20,21]. Opportunities for population expansion of desert ceanothus increase after fire . Prefire plant community and soil seed bank composition, along with timing, season, severity, and size of burn, as well as postfire competition and herbivory will affect composition of the postfire plant community.
Desert ceanothus requires 5 to 15 years after fire before substantial seed crops are produced, so fires at more frequent intervals can produce localized extinctions [54,98]. A diversity of fire-free intervals at one site is suggested for maintenance of community diversity. Season of burn is also an important consideration. The observation that fewer species germinate in chaparral communities after winter and spring burns may be explained by the fact that these communities evolved in a fire regime with late summer and fall fires . Since soil seed bank density is rarely as high as a single years seed rain, a fire that occurs closer to the time of seed dispersal (usually late spring or early summer), operates on a larger seed bank and will likely result in a greater number of seedlings than would a fire later in the season . It is important to consider the relationship between prefire shrub age, vigor and seed production, and postfire seedling establishment .
Fire must be severe enough to scarify seed . Similarly, prescribed burns conducted when soils are moist may reduce the response of the seed bank, if the intensity and duration of the heat is too low to stimulate germination . High severity fires favor desert ceanothus over chamise. A high severity spot occupied by a burned out chamise plant will likely succeed to desert ceanothus due to its greater resistance to fire severity .
Size of fire may also affect survival of desert ceanothus. The interior of large burns may be relatively free of small mammals, thereby favoring desert ceanothus. On smaller burns access may be immediate and frequent, resulting in reduced cover of desert ceanothus [9,71].
Seeding with grasses after fire may impede establishment of ceanothus seedlings . In the absence of herbivory, desert ceanothus exhibits a competitive advantage over chamise [9,72]. Crown cover of desert ceanothus was unchanged in an Arizona chaparral community that was seeded to weeping lovegrass (Eragrostis curvula) and grazed by cattle after a severe wildfire .
There is increasing dead biomass in a stand as shrubs age and die, resulting in increased flammability . Brush management burning guidelines are available [8,19]. Some flammability characteristics of desert ceanothus are given in Rundel . Chaparral types dominated by ceanothus will burn only under conditions of very low fuel moisture or high winds and it is not unusual to find stands over 100 years old in this type .
The study was located in the Sierra Ancha Experimental Forest in central Arizona, near the community of Globe.
PREFIRE VEGETATIVE COMMUNITY:
Prefire vegetation was dominated by shrub live oak (Quercus turbinella) and true mountain -mahogany (Cercocarpus montanus). Other important species included: Wright silktassel (Garrya wrightii), pointleaf manzanita (Arctostaphylos pungens), Pringle manzanita (A. pringlei), desert ceanothus (Ceanothus greggii), banana yucca (Yucca baccata), narrowleaf yerba santa (Eriodictyon angustifolium), and Wright buckwheat (Eriogonum wrightii). Many plants were decadent, and some dead before the site was burned.
TARGET SPECIES PHENOLOGICAL STATE:
Elevation: 5,300 feet (1615 m)
Annual precipitation: 25.0 inches (640 mm), 30% received June through September
Soils: coarse, poorly developed
Parent material: weathered diabase
Average slope length: 120 to 190 feet (37-58 m), few > 200 feet (61 m)
Slope steepness: moderate, averaging 30%
|September 1961||September 1962||September-October 1963||October 1964|
|rate of spread index||15-20||10-20||10||10|
|maximum air temperature (oF)||69||85||80||79|
|relative humidity (%)||46||34||25||33|
|wind speed (mph)||17||5||6||5|
|litter moisture (%)||13||8||6||7|
|pretreatment||post-treatment||year 1||year 2||year 3||year 4||year 5|
|Postfire year||seedlings per acre|
FIRE MANAGEMENT IMPLICATIONS:
Plants are killed by fire. Heat stimulates germination of large numbers of stored seed. Prescribed fire can enhance the browse quality of decadent ceanothus stands, as numerous seedlings emerge after fire.
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