• WOOD PRODUCTS VALUE
• IMPORTANCE TO LIVESTOCK AND WILDLIFE
• PALATABILITY
• NUTRITIONAL VALUE
• COVER VALUE
• VALUE FOR REHABILITATION OF DISTURBED SITES
• OTHER USES AND VALUES
• MANAGEMENT CONSIDERATIONS

WOOD PRODUCTS VALUE:

Gambel oak is a good source of fuel wood. Within the Intermountain Region, productivity is high enough to exceed economic thresholds, and profuse vegetative regeneration is ideal for a fuel wood management cycle [107].

Gambel oak is a good source of firewood that produces little smoke and soot. An average weight per standard cord, based upon 80 cubic feet of solid wood in pounds, is summarized below [14]:

It takes 9 months to 1 year to air dry green Gambel oak [14].  Gambel oak provides more energy than other common southwestern trees [92,214]:

• 52 % more than quaking aspen (Populus tremuloides)

• 42 % more than ponderosa pine

• 36 % more than lodgepole pine (Pinus contorta)

• 24 % more than Rocky Mountain juniper (Juniperus scopulorum)

Gambel oak was compared with Colorado pinyon (Pinus edulis), alligator juniper (Juniperus deppeana), ponderosa pine and eastern redcedar (Juniperus virginiana) for specific wood product values.  An average comparative index based upon a weighted combination of specific strength values is summarized below [14]. Final index values were obtained at 20% moisture content.

Small-diameter stems of Gambel oak that are reasonably straight make ideal fenceposts that are decay-resistant and more durable than other oaks [14]. Untreated posts outlast both Emory oak (Quercus emoryi) and Arizona white oak [133].  

IMPORTANCE TO LIVESTOCK AND WILDLIFE:

Gambel oak is an ecologically important species providing food and shelter for many wildlife species. Type and degree of wildlife use corresponds with Gambel oak habit. Brushy growth forms (thickets less than 25 ft² (2.3 m²) and stems less than 15 feet (4.57 m) tall) are utilized as browse by big game and provide habitat for rabbits and rodents. Young pole stands provide sites for foliage-nesting birds. Mature growth forms provide maximum acorn yield for squirrels, birds, elk, and deer. Old stands containing large amounts of dead crown and hollow boles or limbs provide nesting sites for small mammals and birds [119].

Avian: Gambel oak acorns are an important mast crop in many areas. Acorns are a preferred food for band-tailed pigeons during fall and winter. Merriam turkeys also utilize acorns as a major part of their diet [141]. Abert's squirrels feed upon Gambel oak acorns [164]. When a good crop is available, acorns may provide up to 40% of Abert's squirrel fall diet [186].  Patton and others [163] observed squirrels using hollow Gambel oaks over 10 inches (25.4 cm) d.b.h. as nesting sites. Abert's squirrels prefer ponderosa pine forests (201 to 250 trees per acre) where Gambel oak is within a 12 to 14 inch d.b.h. class occurring as 1or 2 trees per acre [162]. 

Gambel oak trees within the ponderosa pine-Gambel oak forests of Arizona provide perching and nest sites for the Mexican spotted owl [81,82]. Illegal cutting of large oak trees within these forests is considered a serious problem for Mexican spotted owl management [79].  Gambel oak is used significantly more (p< 0.01) by juvenile Mexican spotted owls as roosts during dispersal in the fall (August-October) than in winter (November-April) [80].  Conifer/oak forests with relatively high densities of Gambel oak along canyon bottoms of New Mexico are preferred roost sites for Mexican spotted owls [101].

Within a Gambel oak brush community in northern Utah, Marti [140] observed 6 permanent residents: California quail, ring-necked pheasants, scrub jays, black-billed magpies, black-capped chickadees, and rufous-sided towhees. Marti also provides a complete list of birds observed and found nesting.  

Mountain shrub habitats where Gambel oak is codominant with serviceberry provide a summer habitat for Columbia sharp-tailed grouse of northwestern Colorado [85].  In Utah, Gambel oak may provide nesting sites for sharp-shinned hawks [165]. Pygmy owls inhabit ponderosa pine-Gambel oak forest types within the Dixie National Forest, Utah [216].

Big game: Gambel oak is a major forage species for deer and elk in Utah [147]. Gambel oak is moderately used, relative to other forage and browse species, by Rocky Mountain mule deer in winter and spring with heavier use occurring in summer and fall [124]. In its southern range, Gambel oak is a desirable species for desert mule deer and white-tailed deer in the San Cayetano and Dos Cabezas mountains of southeastern Arizona. Greatest use of Gambel oak occurs mid-July to October, with white-tailed deer showing greater utilization than mule deer. Gambel oak, however, is not located in habitats used by mule and white-tailed deer of Arizona during the winter [11].  

Gambel oak communities in Colorado provide important winter ranges for big game animals [130]. Based upon a review of 3 studies, Kufeld [121] reports Gambel oak as highly valuable winter forage for Rocky Mountain elk. Smith [181] and Smith and Hubbard [183] monitored winter forage preference of deer in Utah. Gambel oak ranked 7th out of 17 forage species based on time spent browsing and plant weight consumed. Mule deer and white-tailed deer utilized new growth and sprouts as forage [107,171]. Gambel oak ranges in southwestern Colorado provide the majority of black bear spring habitat [86] and fall food for black bear in southwestern Colorado [86].

In Colorado, bighorn sheep utilize Gambel oak as a minor component of their summer diet. On low elevation summer ranges, Gambel oak may comprise up to 17% of the June diet [177], although, in most cases, bighorn sheep avoid dense stands of Gambel oak [174]. Within north-central Utah, porcupines use Gambel oak as their primary winter food and cover source [190].

Acorns can also provide a food source for collared peccary in Arizona [115].

PALATABILITY:

Gambel oak may contribute up to 50% of diet without cattle showing any ill effects.  Poisoning occurs when more than 50% is consumed, with death often resulting when more than 75% of cattle's diet is Gambel oak [26]. Freezing enhances toxic properties of Gambel oak browse; young foliage turned black by freezing is extremely toxic [189]. 

The palatability of Gambel oak to livestock and wildlife species in several western states has been rated as follows [55] :

NUTRITIONAL VALUE:

Mature and juvenile Gambel oaks provide valuable forage with nitrogen and energy in excess of maintenance requirements for Spanish goats [52]. At 5.4% crude protein, Gambel oak does not meet the protein requirement of wintering mule deer [208]. Protein content of Gambel oak leaves was found to decrease starting June to September while phosphorus and gross energy remained constant [47]. As winter browse, Gambel oak is low in essential nutrients [182], with crude protein less than 10% [198].

The percent nutrient content of Gambel oak during January from 9 geographic areas throughout Colorado is summarized below [123]:

Welch [209] reports Gambel oak to have 26.6% in-vitro digestibility and a crude protein content of 5.3% in winter.

Dick and others [52] compared chemical composition of juvenile and mature Gambel oak:

Juvenile Gambel oak contains higher tannin levels than mature trees, but also has higher digestibility of dry matter and fiber [52].  Concentration of tannins in Gambel oak forage is greatest in spring [202].

A nutritional difference exists between Gambel oak sprouts on burned and unburned areas. Postfire bud tissue is higher in tannin content (4.1 mg/100 mg burned plant tissue compared to unburned with 3.4 mg/100 mg). Burned stem tannin content was twice that of unburned, 1.6 to 0.7 respectively. Although high in tannin, postburn buds had higher nutritional value than either buds and twigs of unburned areas or twigs on burned areas [198]:

COVER VALUE:

The Gambel oak type of the Intermountain West provides good winter habitat for mule deer and offers high cover potential [107]. However, tall, dense stands of Gambel oak provide poor winter ranges for deer and elk. Tall Gambel oak reaches beyond browse height of deer and elk and leads to shade-induced suppression of forbs and grasses [122]. Dense stands may also exclude some big game animals. In White River Plateau, Colorado, Boyd [21] observed Gambel oak densities  exceeding 51% canopy cover, which physically excluded elk. 

The degree to which Gambel oak provides cover for wildlife species is as follows [55] : 

VALUE FOR REHABILITATION OF DISTURBED SITES:

Gambel oak has not been used extensively for environmental rehabilitation of disturbed sites. The majority of research has been centered toward control or eradication. However, Gambel oak has a moderate value for long-term revegetation. The extensive root system helps provide soil stability and reduce erosion [33].

Propagation of Gambel oak using stem cuttings has shown little success [92,179]. Sopp [184] recommends stratification of Gambel oak seeds for 2 weeks at 35.6 degrees Fahrenheit (2 ^o C) to obtain maximum germination results. Sopp also recommends disinfecting acorns to prevent contamination by pathogens.

OTHER USES AND VALUES:

Native Americans of the Southwest used Gambel oak acorns for food [29].

MANAGEMENT CONSIDERATIONS:

Silviculture:  Effective management of Gambel oak forests requires methods to assess current stand conditions and predict changes in relation to treatments imposed.  

Several studies provide evidence regarding Gambel oak's ability to suppress other plant species. Allelopathic toxins produced by Gambel oak may limit the natural regeneration ability of ponderosa pine seedlings [95], but research results are limited. As an understory component of a ponderosa pine forest in central Arizona, Gambel oak did not limit the growth of overstory ponderosa pine [19].  Gambel oak suppresses herbaceous species in open rangeland [106].  

Density of Gambel oak stems within a stand is significantly (p < 0.05) related to stand height. According to McKell [143] and Brown [26], young Gambel oak thickets are generally dense, but thin out with age. Stand characteristics for Gambel oak between 6,890 and 8,200 feet (2,100-2,500 m) receiving annual precipitation of 14 to 20 inches (360-510 mm) in Utah were evaluated. As stand height increased, stem density decreased. A summary of stand characteristics is given below [38]:

Stand height is not directly related to age. Stands with stems up to 142 years old produced trees similar in height to stands 1/3rd to 2/3rds as old. The same study found that lignotubers compromised 72% of the total belowground biomass of Gambel oak [38].

In general, heavy logging of ponderosa pine favors Gambel oak [170]. Clearcutting of a ponderosa pine overstory in a forest with a Gambel oak and alligator juniper understory was evaluated 23 years later. Gambel oak stocking had increased 1.5 times, mostly in the form of vegetative sprouts, with regeneration averaging 1,090 ± 167 stems per acre. Clearcutting resulted in establishment of a Gambel oak-brushfield in what was previously a ponderosa pine forest [95]. Gambel oak consistently sprouted adjacent to slash windrows in a ponderosa pine clearcut in Arizona [193].

Chojnacky [31,32] provides volume equations for Gambel oak in Arizona. Hutchings and Lamar [104] provide equations to estimate Gambel oak yields from foliage cover and basal area on various range sites in Utah.  

An evaluation of snag density and composition on 2 national forests in Arizona reported that Gambel oak contributed 18% of snags in ponderosa pine forests, with ponderosa pine contributing 76.4% (alligator juniper was 2.3%). Within mixed-conifer forests Gambel oak contributed 24.3%, with white fir (Abies concolor) at 25.1%, ponderosa pine at 4.9%, and quaking aspen at 8.3% [78].

Inonotus andersoni is a fungus with the ability to girdle Gambel oak and kill the cambium. Although Inonotus andersoni is a functional member of Gambel oak habitats, it does not pose a major threat. Decay is a slow process most often occurring in older trees and does not seriously affect regeneration. Wildlife habitat is created through fungal-induced snags and live trees with snag characteristics [66].

A rotational fuel wood harvest cycle of 65 years allows Gambel oak clones to grow stems greater than the minimum fuel wood size of 3.5 inches (8.8 cm) in north-central Utah [207]. 

Soil ecology: Gambel oak places a heavy draw on soil moisture both within oak thickets and in open areas between oak thickets. Tew [195] observed soil moisture utilization by Gambel oak in northern Utah.  An oak stand of 65 square foot basal area/acre (6 m²/ha) used 11 to 13 inches (28-33 cm) of water per year from the upper 8 feet (2 m) of soil. Initial water uptake occurs within the upper 4 feet (1.2 m) with additional water removed from the 4 to 8 foot (1-2 m) zone [195]. In northern Arizona Gambel oak was more effective at avoiding soil water stress and atmospheric water stress than old- growth ponderosa pine [116]. A comparison of mean soil moisture content (%) among 4 Gambel oak rangeland sites in southwestern Colorado was conducted over the course of 3 years. Results show higher soil moisture content (%) within herbicide controlled oak rangelands [138]:

Leaf litter produced by Gambel oak has a positive effect on soil nitrogen within the surface (upper 5.9 inches (15 cm) of soil) [113,114].  Gambel oak leaves contain 2 to 4 times the N, P, S, Ca, Mg, and K of pine needles. Leaves also contain 8% less C than ponderosa pine needles. Gambel oak enhances nutrient release of ground cover within ponderosa pine stands by decaying faster than ponderosa pine litter. Presence of oak leaf litter may alter the distribution of nutrients within ponderosa pine forest floors [113].

The C:N ratio in ponderosa pine forest litter decreases when Gambel oak is a member of the understory compared to ponderosa pine without Gambel oak [131]. A comparison of nutrients between freshly fallen Gambel oak leaves and ponderosa pine needles from trees growing side by side shows significantly higher nutrient content in Gambel oak litter [114]:

Grazing: Beef production per acre is much greater in Gambel oak-controlled pastures than in pastures with no Gambel oak control. In southwestern Colorado herbicides have been used to decrease Gambel oak and increase livestock productivity [138]. In general, cattle are safe from poisoning if other forage is available. Cattle should not be released when hungry on Gambel oak ranges with little forage other than oak [189].

Jefferies [106] found greater herbage production of needle-and-thread (Hesperostipa comata), western wheatgrass (Pascopyrum smithii), and blue grama (Bouteloua gracilis) in openings between oak stands than under Gambel oak canopies in both grazed and protected pastures. Kentucky bluegrass (Poa pratensis) had greater production under canopy than in the open [106]. Seeding of Gambel oak rangeland in Utah should occur in the fall, just before leaf fall. Stevens and Davis [187] recommend aerial seeding followed with mechanical disturbance. Further information including a summary of recommended species, depending upon community type, is found in Stevens and Davis [187].

Gambel oak is most susceptible to insect herbivory early in the growing season, with young expanding leaves preferred [65]. Gambel oak leaves support a higher insect biomass per unit of foliage than ponderosa pine [37].  

Control methods: Top-kill of Gambel oak promotes vegetative sprouting. Numerous studies document the sprouting ability of Gambel oak after mechanical crushing [59] or herbicide treatment [59,92,98,139]. In general, the best strategy for reducing vigor of sprouting species is to apply control methods during periods of low carbohydrate reserves [16]. However, total eradication of Gambel oak is rare due to prolific vegetative regeneration from roots, rhizomes and basal stems [59]. Most control options provide short-term benefits that eventually produce Gambel oak thickets [130]. 

Control of Gambel oak with herbicides is extremely variable depending upon growing season and herbicide used.  Herbicides may induce prolific sprouting, producing rangelands of lower quality than the original stand [139]. The herbicide application rates of picloram, 2,4-D, or 2,4,5-T necessary to control Gambel oak kill most desirable shrubs and forbs. Fenuron kills Gambel oak but is persistent, producing a soil sterilization effect and a subsequent elimination of desirable plants [205]. Effective control can be obtained from a mixture of  picloram and 2,4,5-TP [139]. Picloram pellets are an ineffective control for Gambel oak [45,46].  

Application of hormone-type herbicides is recommended before full leaf stage or in late August before the end of fall regrowth corresponding to downward translocation. August applications, however, may be less effective due to wax accumulations on existing mature leaves [60]. Applications corresponding with downward assimilate translocation maximize herbicide concentrations in the underground parts, where effective plant damage occurs [151].    

Lauver and others [130] suggest integrated management for optimum control of Gambel oak. High application rates and high treatment costs are usually required for herbicide control of Gambel oak [204]. Thinning programs, when conducted correctly, promote growth of remaining Gambel oak stems (not resprouts) allowing forage increases [130]. 

Combined with other nutritious forage low in tannin content, Gambel oak provides a healthy diet for domestic goats [152]. When domestic goat browsing was initiated in late spring with periods of high intensity short duration grazing throughout the growing season in Northern Utah, Gambel oak showed a 78% reduction after 2 successive years [172]. 

When Gambel oak is abundant, domestic goats may prefer it to other available browse. Davis and others [47] provide several management considerations for obtaining maximum oak control from goats: all oak brush foliage should be accessible; time of goat browsing should center around late June (full leaf stage) and August (late summer regrowth); stocking rates of 5 to 10 goats per acre are preferred  [47].  

Wildlife: Kufeld [122] recommends fall prescribed burns rather than chaining or spraying to manage Gambel oak brush rangelands for elk, deer and cattle. Domestic goats were found to reduce the amount of Gambel oak browse available to wintering deer in Utah. Deer responded with greater consumption of sagebrush (Artemisia spp.) and rabbitbrush (Chrysothamnus spp.) [173]. A detailed description of the management of Gambel oak associations for wildlife and livestock was prepared by Steinhoff [185].

Related categories for SPECIES: Quercus gambelii | Gambel Oak