• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

GENERAL BOTANICAL CHARACTERISTICS:

Shrub live oak is a clump-forming or clonal evergreen shrub or less commonly a small tree [81,84,94,101]. It typically grows from 3 to 8 feet (0.9-2 m) in height with stem diameters to 8 inches (20 cm) [8,99,101]; however, it can reach 15 feet (5 m) or more [8]. The somewhat leathery leaves are 0.5 to 1.6 inches (1.3-4 cm) in length, 0.3 to 0.9 inch (0.7-2.4 cm) in width [94,101]. Leaves persist through the winter [93]. Fruits of shrub live oak are slender, annual acorns 0.5 to 1 inch (1.3-2.5 cm) in length, with turbinate cups [94].

Belowground structure: Root depths of over 25 feet (8 m) have been reported in parts of Arizona [81]. Roots and rhizomes may spread 16 feet (4.9 m) or more horizonally [16]. Shrub live oak forms colonies by sprouting from rhizomes [8,100]. Thousands of individual stems may form from a single or only a few individuals [8]. Davis and Pase [16] report "what appears to be a relatively open stand of shrub live oak aboveground, may actually be a relatively closed system" of overlapping roots and rhizomes. The top foot of soil typically contains a dense network of small surface laterals that aid in the absorption of surface soil moisture. In central Arizona, the greatest accumulation of belowground biomass occurred in the top 2 feet (0.6 m) of soil, with biomass decreasing with depth as follows [16]:

Soil depth (m)    Weight (g)                             
0 - 0.3           	7053
0.3 - 0.6         	7883
0.6 - 0.9         	5068
0.9 - 1.2         	3403
1.2 - 1.5         	2602
1.5 - 1.8         	1575

RAUNKIAER LIFE FORM:

Phanerophyte

REGENERATION PROCESSES:

Shrub live oak reproduces through both sexual and vegetative means.

Sexual reproduction: Shrub live oak produces small acorns which usually germinate and establish from late July through mid-September [8,93]. Germination often occurs shortly after acorn maturation and coincides with the summer rainy season [63]. Under laboratory conditions germination capacity may reach 95% [61].

Acorn production is largely dependent on the amount of precipitation received during the previous winter [63]. Dry summers may inhibit or retard acorn production [79,80]. In "good" years shrub live oak produces an abundance of acorns [79]. Total acorn failure, although rare, can occur [63,79]. Total crop failures may occur when October-March precipitation is less than 15 inches (38 cm) [63]. Generally, good crops are produced at 3- to 5-year intervals [61].

The vast majority of shrub live oak seedling mortality is apparently attributable to drought. In an Arizona study, seedling mortality during the first spring drought period following germination was 53%. Mortality rates appeared to decline by 3 years after germination [63].

Shrub live oak acorns do not require a ripening period and frequently germinate while in storage. Shrub live oak acorns are characterized by a short period of viability, and seedbanking is unlikely. Pase [63] reports "there is probably a negligible carryover of seeds from 1 year to the next." Very few viable seeds remain 1 year after burial, due in large part to predation by insects, birds, and mammals [63].

Acorns are dispersed by numerous birds and mammals which eat and/or cache the acorns. Shrub live oak seeds tend to be somewhat heavy, weighing an average of 0.046 to 0.053 ounce (1.3-1.5 g) per seed [30], and are consequently not transported long distances by most seed-dispersing animals. Scrub jays are particularly important dispersal agents. These birds generally "plant" single acorns at depths of 1.5 to 2 inches (4-5 cm), a few feet to a hundred feet from the parent plant. Rodents more often cache multiple seeds, which can germinate and produce groups of 10 to 20 or more seedlings at a single location. Seedling distribution indicates that, at least in many of the central Arizona sites studied, scrub jays play a much more significant role as dispersers than do rodents [63].

Seedlings are rarely encountered in the field [8,79,63]. Successful establishment is thought to require 15 inches (38 cm) or more of precipitation from October through March, followed by 10 inches (25 cm) or more from July to September [8,63]. These conditions are met in only 1 year out of 10 at many Arizona sites [63]. In laboratory experiments seedling roots grew to a depth of 1 foot (30 cm) prior to leaf development [16]. Plants only 12.9 inches (7.4 cm) in height had roots that extended to 21 inches (53 cm) in depth [8].

Vegetative reproduction: Shrub live oak tends to increase more through rhizome sprouting than by seedling establishment [63,79]. Shrub live oak sprouts vigorously after fire, application of herbicides, or mechanical treatment [8,16,65,79,100,105].

SITE CHARACTERISTICS:

Shrub live oak is particularly common on many low winter ranges in southern Utah and Nevada and in chaparral-desert grassland ecotones in Arizona [8,94]. Shrub live oak often grows in scattered patches in swales and canyons [94].

Soil: Shrub live oak grows well on dry hillsides and mesas and tolerates a wide range of soil types [94]. Growth is best on sandy to clay loams [20]. Soils are often slightly acidic [16]. This oak is not restricted to deep soils and can grow on shallow, broken and fractured substrates [16,79]. Soils are typically coarse-textured and poorly developed in shrub live oak chaparral [24].

In eastern Yavapai County in central Arizona, soils developed from quartz diorite provide more favorable moisture regimes than do heavy clay soils developed from volcanics. In north-central Arizona, shrub live oak growing on less favorable, drier, sedimentary and volcanic substrates may be more susceptible to drought damage. Where root penetration is restricted, plants are more susceptible to damage from drought or fire [79].

Climate: Shrub live oak is drought tolerant and typically occupies drier and warmer sites than Gambel oak [57,58]. In the northern part of its range, shrub live oak often grows on warm, dry, southern exposures [21]. Arizona chaparral is characterized by a biseasonal precipitation pattern with summer and winter precipitation and spring and fall droughts [16]. Annual precipitation averages 16 to 25 inches (410-640 mm) [24].

Elevation: Ranges of shrub live oak are as follows [20,32,56,80,101]:

4,000 to 8,000 ft (1,220-1,525 m) in AZ
3,934 to 10,492 ft (1,200-2,000 m) in CA
2,689 to 5,607 ft (820-1,710 m) in UT

SUCCESSIONAL STATUS:

Shrub live oak may have climax or seral status. This long-lived oak is considered to be an indicator of climax in parts of Arizona and New Mexico [8,53]. During the 2nd and 3rd years after fire in shrub live oak-dominated chaparral in Arizona, forbs and grasses dominate. Shrubs, including shrub live oak, assume prominence the 5th through 7th year after disturbance, although it may take more than 11 years for shrubs to reach preburn levels [8]. A typical successional pathway in pinyon-juniper is as follows [33]:

bare soil
annuals
perennial grasses and forbs
shrubs (including shrub live oak)
shrubs and open trees
climax pinyon-juniper

Pond [68] reports that weeping lovegrass dies out as the density of shrub live oak increases.

SEASONAL DEVELOPMENT:

Shrub live oak flowers from April through June. In Ventura County, California, shrub live oak usually flowers in April [89]. In Utah, flowering begins by April and ends by May [20].

Shrub live oak acorns mature by the summer or early fall. Acorns were present on shrub live oak from late August to early September at 1 Arizona site [79]. Acorns often germinate during the summer rainy period, with germination and emergence occurring from late July to mid-September [63].

Related categories for SPECIES: Quercus turbinella | Shrub Live Oak