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

GENERAL BOTANICAL CHARACTERISTICS:

Gambel oak occurs as clones [65] of shrubs in dense patches 3 to 20 feet (0.91-6.1 m) tall, often with a central thicket rising above the others [13], and as widely dispersed trees [43] up to 75.5 feet (23 m) tall [38]. Clones show uniform characteristics in shape, pubescence, and color [92]. Variability in life form corresponds with relative levels of water stress; stunted shrubs are present on xeric sites with moderate-sized trees found in wetter locations [54,107]. Gambel oak bark ranges from 0.5 to 0.75 inch (1.2-1.9 cm) thick. The bark is deeply divided into broad, irregular, often connected, flat ridges. Branches are slender and coated with short, pale, rust-colored hairs when 1stappearing [13]. Leaves of Gambel oak are highly variable, differing in outline, texture, lobing [13,92], pubescence, and size. Acorns are sessile or pedunculate [92], with an oval shape, usually 0.75 inch (1.9 cm) long and 0.63 inch (1.6 cm) broad [13]. 

The underground system of Gambel oak consists of a lignotuber with deep-feeding roots [33]. Lignotubers possess many scattered adventitious buds [213] .Clones are interconnected with rhizomes [198] that intertwine  with lignotubers. Root grafting is common; root-endomycorrhizal associations may also occur [213].

Gambel oak possesses morphological and physiological adaptations to drought [1,116]. Deep roots, xeromorphic leaves and efficient water transport contribute to effective drought tolerance [1]. 

The growth rate of Gambel oak may vary with age. Barger and Ffolliott [14] report Gambel oak grows rapidly in height and diameter at early stages of life, with growth rates steadily declining with age. In contrast,  in central Utah study Wagstaff [206] observed little change in growth rate of Gambel oak diameter during the 1st 100 years of life.

Ecological characteristics compiled by Loehle [132], are summarized below:

RAUNKIAER [168] LIFE FORM:

Phanerophyte

REGENERATION PROCESSES:

Gambel oak reproduces by seed and vegetatively [6,92].

Seed: Production of mature flowers is directly related to moisture availability. Xeric sites often fail to produce mature female flowers, yet male catkins are produced in abundance. On moist sites, flowers of both sexes are produced in large numbers [75]. Acorn production in Arizona was directly related to moisture availability, averaging 188,000 mature acorns/acre (464,548/ha) and over 331,000 per acre (817,900/ha) in heavy moisture years [142]. Although Gambel oak generally possesses distinct male and female inflorescences on a single plant, Tucker and others [200] observed an inflorescence containing both anthers and pistils in Utah. The following year strictly monoecious flowers were produced. Female flowers are found throughout the Gambel oak canopy while male flowers are almost exclusively located at the top [75]. 

Extent of acorn production is also related to stem diameter. Few acorns are produced from stems less than 2 inches (5.1 cm) diameter breast height (d.b.h.), and production rapidly declines when stems are greater than 14 inches (35.6 cm). Maximum acorn production occurs from stems 12 to 14 inches (30.5-35.6 cm) d.b.h. [142,171]. Throughout Utah, 4 to 6 months are required to produce mature acorns [42,92]. Spring freezing may reduce acorn production [156].

Gambel oak may occur at high elevations, where a 60- to 90-day growing season exists. Although at high-elevation ranges the growing season is too short to produce mature acorns, expansion occurs through vegetative reproduction [92]. Limited colonization of the higher-elevational range is thought to be a function of the short growing season [35].

Overall effectiveness of reproduction through seed is directly related to moisture availability [219]. Seedlings are more common in the southern range of Gambel oak [157], where summer rains are heavy and more frequent [155]. Fewer seedlings are found in the northern range [150,155,157]. Neilson [157] found seedling establishment directly relating to consistently high presence of soil moisture. Persistent mesic conditions provide the best conditions for seedling survival. Greater survivorship in winter and summer is also associated with closed canopies [219].

Colonization through seed is enhanced by avian and small mammal acorn dispersal. Acorns of Gambel oak are dispersed by rodents and birds [6]. Band-tailed pigeons, scrub jays, Steller's jays, Lewis woodpeckers, and acorn woodpeckers are agents of dispersal [33,91,92]. The Utah rock squirrel regularly provides short-distance acorn dispersal [167].   

Vegetative: Gambel oak has strong vegetative reproduction capabilities. In most of its range, Gambel oak regeneration depends more on sprouting than establishment from seed [128]. The large underground structure of Gambel oak supports rapid and extensive sprouting following top removal [38]. In Utah vegetative spread of Gambel oak thickets averaged 4-inches (10 cm) per year, with lows of 1.5 inches (3.8 cm) and a high of 12 inches (30.5 cm) [92]. Vegetative reproduction occurs through adventitious buds on lignotubers [198] and freely branched rhizomes [150].  A large difference in ability to regenerate by cloning exists between the southern and northern range of Gambel oak. In Arizona and New Mexico, groupings usually consisted of 1 to 7 ramets per clone [157] compared to 100 to 1,000 ramets per clone observed in the north [26,169].

The distribution of adventitious buds and rhizomes (in cm) within the soil profile of a Gambel oak stand in central Utah was as follows [198]:

Adventitious buds were concentrated in the top 11.8 inches (30 cm) of soil. More adventitious buds were found on lignotubers than on rhizomes [198]. Lignotubers provide the primary source for regeneration after top-kill; rhizomes possess fewer buds and facilitate widespread development of clones [108]. 

SITE CHARACTERISTICS:

The upper and lower limits of Gambel oak's range are established by the Arizona monsoons that generates a gradient of increasing cold stress in winter and spring and a summer drought stress with increasing latitude [175]. Gambel oak prefers a mean annual temperature of 44.6 to 50 degrees Fahrenheit (7-10 ^oC) with winter temperatures below negative 0.4 degrees Fahrenheit (-18 ^oC) [39]. Gambel oak does not occur in areas where winter precipitation falls below 10 inches (250 mm) or where subfreezing temperatures persist for long periods of time [35]. Annual mean precipitation measured over 14 years (1934 to 1948) at 7,655 feet (2,333 m) within Gambel oak habitats of the mountain brush zone was 20.10 inches (510 mm) [134]. Throughout its distribution Gambel oak occurs between 3,250 and 10,200 feet (990-3,110 m) [92]. Elevation limits are the widest at the southern extent, narrowing northward [155]. A preference for south slopes was observed between 8,200 and 8,700 feet (2,500-2,650 m) in southwestern New Mexico [41]. At 7,500 to 8,000 feet (2,286-2,438 m) in Mount Livermore, Texas, Gambel oak occurs on ledges and bordering talus slopes [100].   

Several environmental parameters were evaluated in Gambel oak stands, comparing understory and open areas between oaks in the lower Unita mountains, Utah. Elevation is 7,218 feet (2,200 m); slope is 10% with an 185^o exposure. Mean annual precipitation is 17.7 inches (450 mm), 60% of which is received in winter [212]. Litter was deeper, shrubs had greater cover, and light was less intense under Gambel oak:

Elevational ranges of Gambel oak are:

southwestern Colorado:  4,000 to 8,500 feet (1200-2550 m) [93]
Utah:  5,500 to 7,500 feet (1700-2300 m) [26,40]

SUCCESSIONAL STATUS:

Canopy suppression is a successional trend when Gambel oak is associated with bigtooth maple, white fir, ponderosa pine, Rocky Mountain juniper, or Colorado pinyon [34,36,56,71,96,143,159]. Across its range, Gambel oak occupies a seral, postfire successional stage with late successional associates more susceptible to fire [22,62,214].  

Gambel oak is listed as a persistent seral stage in the ponderosa pine of northern Arizona, with he majority of Gambel oak occurring as trees. Populations of Gambel oak increase with disturbance in ponderosa pine woodlands [90].  

In southern and southwestern Colorado, Gambel oak occupies a secondary successional stage in ponderosa pine and Douglas-fir (Pseudotsuga menziesii) stands removed by fire or logging [26,93]. It is a persistent subclimax to conifers or a climax species of foothill ranges [56,59,96,134]. 

Mountain brush vegetation where Gambel oak and bigtooth maple are codominant tend to develop into a bigtooth maple-dominated brush type. The successional transition to a bigtooth maple dominant overstory is attributed to the greater reproductive potential and shade tolerance of bigtooth maple [159]. Within Gambel oak-bigtooth maple brush, bigtooth maple seedlings grow readily under and on the periphery of bigtooth maple and Gambel oak canopies. Gambel oak seedlings are rarely observed under dense bigtooth maple canopies [36]. Bigtooth maple successfully invaded Gambel oak brush in the Wasatch Mountains of Utah, while Gambel oak had difficulty invading bigtooth maple stands [159]. 

In central Utah, Gambel oak/bigtooth maple brush communities at 6,500 to 7,800 feet (1,981-2,377 m) may succeed to conifer-pinyon-juniper at the low elevations and to white fir at upper elevations [134]. 

SEASONAL DEVELOPMENT:

Gambel oak flowers usually appear in late March to early April with acorns ripening in August or September [92]. In Utah, flowers appear when leaves are nearly half grown, usually May or June [13]; at the lower elevation limits in Utah, flowers occasionally appear in early May [28,200]. Acorns mature in northern Utah from September to early October [35]. The following table provides a summary of Gambel oak seasonal development during a 160 to 175 day growing season at 7,655 feet (2,333 m) in northern Utah [42]:

Gambel oak produces buds in winter for the following spring. Not all buds produced in winter become active; some dormancy is maintained. Dormant buds may become active if new shoots are defoliated [59].

In southwestern Colorado, at least 5 weeks are required after snowmelt before onset of spring growth. Photoperiod requirements prevent bud burst occurring earlier than the 3rd week of May. Shoot elongation is generally 24 to 27 days and is not dependent upon date of bud burst [192].

Related categories for SPECIES: Quercus gambelii | Gambel Oak