SPECIES: Quercus gambelii


INTRODUCTORY

SPECIES: Quercus gambelii
AUTHORSHIP AND CITATION:

Simonin, Kevin A. 2000. Quercus gambelii. 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:

QUEGAM

SYNONYMS:

No entry

NRCS PLANT CODE [203]:

QUGA

COMMON NAMES:

Gambel oak
scrub oak

TAXONOMY:

The scientific name of Gambel oak is Quercus gambelii Nutt. (Fagaceae) [127,210]

Hybridization between oak species is common. Gambel oak hybridizes readily with other oak species and has influenced the evolution of several oaks [92]. Hybridization occurs with Arizona white oak (Q. arizonica) [201], bur oak (Q. macrocarpa) [30,201], chinkapin oak (Q. muehlenbergii), gray oak (Q. grisea) [2,84,201], Mohr's oak (Q. mohriana) [201], and shrub live oak (Q. turbinella) [43,201].

LIFE FORM:

Tree-shrub 

FEDERAL LEGAL STATUS:

No special status

OTHER STATUS:

No entry


DISTRIBUTION AND OCCURRENCE

SPECIES: Quercus gambelii
GENERAL DISTRIBUTION:

Gambel oak occurs from New Mexico west to Arizona and southwestern Nevada and north to Utah, Colorado and southeastern Wyoming [13]. Isolated patches occur in Texas [92]. The Natural Resource Conservation Service provides a map of Gambel oak's distribution in the United States (http://plants.usda.gov/plants/cgi_bin/topics.cgi).

ECOSYSTEMS [83]:

FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES23 Fir-spruce
FRES29 Sagebrush
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES36 Mountain grasslands
FRES40 Desert grasslands

STATES:
AZ CO NM NV TX UT WY

MEXICO

BLM PHYSIOGRAPHIC REGIONS [17]:

6 Upper Basin and Range
7 Lower Basin and Range
11 Southern Rocky Mountains
12 Colorado Plateau

KUCHLER [120] PLANT ASSOCIATIONS:

K018 Pine-Douglas-fir forest
K019 Arizona pine forest
K020 Spruce-fir-Douglas-fir forest
K021 Southwestern spruce-fir forest
K023 Juniper-pinyon woodland
K031 Oak-juniper woodland
K032 Transition between K031 and K037
K037 Mountain-mahogany-oak scrub
K038 Great Basin sagebrush
K055 Sagebrush steppe
K057 Galleta-threeawn shrubsteppe
K058 Grama-tobosa shrubsteppe

SAF COVER TYPES [64]:

217 Aspen
220 Rocky Mountain juniper
237 Interior ponderosa pine
239 Pinyon-juniper
241 Western live oak

SRM (RANGELAND) COVER TYPES [180]:

107 Western juniper/big sagebrush/bluebunch wheatgrass
109 Ponderosa pine shrubland
207 Scrub oak mixed chaparral
210 Bitterbrush
401 Basin big sagebrush
402 Mountain big sagebrush
403 Wyoming big sagebrush
404 Threetip sagebrush
405 Black sagebrush
408 Other sagebrush types
411 Aspen woodland
412 Juniper-pinyon woodland
413 Gambel oak
415 Curlleaf mountain-mahogany
416 True mountain-mahogany
417 Littleleaf mountain-mahogany
418 Bigtooth maple
420 Snowbrush
421 Chokecherry-serviceberry-rose
503 Arizona chaparral
504 Juniper-pinyon pine woodland
505 Grama-tobosa shrub
509 Transition between oak-juniper woodland and mahogany-oak association
733 Juniper-oak
734 Mesquite-oak

HABITAT TYPES AND PLANT COMMUNITIES:

In the southern extent of its distribution, Gambel oak occupies a minor role as an associate within ponderosa pine (Pinus ponderosa) and mixed-conifer habitats. Moving north, long-lived Gambel oak clones form dominant to monotypic overstories [157].

Harper and others [92] constructed a list of common plant associates in a 1985 literature review. The following table lists common plant associates of Gambel oak.

Species Common name Zone1
SHRUBS and TREES    
Abies  spp. fir A,B,D,E
Acer spp. maple A,B,C,E
Amelanchier spp. serviceberry A,B,C,D
Artemisia spp. sagebrush A,B,C,D,E
Ceanothus spp.   ceanothus A,B,C,D,E
Cercocarpus spp. mountain-mahogany  A,B,C,D,E
Mahonia repens Oregon-grape A,B,D
Pachistima myrsinites pachistima A,B,C,D,E
Physocarpus malvaceus ninebark A
Pinus ponderosa ponderosa pine B,C,D
Populus tremuloides quaking aspen A,B,C,E
Prunus virginiana chokecherry A,B,C,E
Purshia tridentata antelope bitterbrush A,B,C,D
Rosa spp. wild rose A,B,D,E
Sambucus spp. elderberry A,D
Symphoricarpos spp. snowberry A,B,C,D,E
FORBS    
Achillea millefolium western yarrow A,B,C,E
Aster spp. aster A,B,C,D,E
Balsamorhiza spp. balsamroot A,B,C
Cirsium spp. thistle A,B,D
Erigeron spp. fleabane A,B,C,D
Eriogonum spp. buckwheat A,B,C,D,E
Hydrophyllum capitatum waterleaf A,B
Lathyrus spp. peavine A,B,D
Lupinus spp.  lupine A,B,C,D
Polygonum spp.  knotweed A,B,C,D
Senecio spp. groundsel A,B,D
Solidago spp. goldenrod A,B,C,D
Taraxacum spp. dandelion A,B,D,E
Tragopogon spp. goatsbeard A,B,D
Viola spp. violet A,B,D
Wyethia amplexicaulis mulesears A,B,C
GRAMINOIDS    
Agropyron spp. wheatgrass A,B,C,D
Bromus spp. brome A,B,D
Carex spp. sedge A,B
Elymus spp. wildrye A,B,D
Festuca spp. fescue B,C,D,E
Koeleria macrantha prairie junegrass A,B,D
Melica spp. oniongrass A,E
Poa spp. bluegrass A,B,C,D,E
Stipa spp. needlegrass A,B,C,D
1A = central Utah, B = Colorado, C = southern Utah, D = Arizona, E = New Mexico

Kunzler and others [126] evaluated 23 Gambel oak brush stands in central and northern Utah to compare presence or absence of major plant associates. Gambel oak stands on average supported 25 plant species; cheatgrass (Bromus tectorum) and stickywilly (Galium aparine) were the 2 most abundant species. The most abundant shrub associate was mountain snowberry (Symphoricarpos oreophilus).

Gambel oak is a typical riparian species in New Mexico, occurring from 6,580 to 8,080 feet (2,006 - 2,463 m) within the Black and Sacramento mountain ranges [74]. 

Gambel oak is a dominant species in the central Utah mountain brush zone at 6,500 to 7,800 feet (1,981-2,377 m) on southern exposures. On northern exposures Gambel oak either shares dominance with bigtooth maple (Acer grandidentatum) or is completely replaced by bigtooth maple [36].  Bigtooth maple is a common Gambel oak associate at the southern end of the Wasatch Mountains. On the west flank of the southern and middle Wasatch range, Gambel oak and bigtooth maple form a dense woodland [91].

In Arizona Gambel oak is represented as shrub thickets over the majority of its range. It occurs as a tree throughout the ponderosa pine habitat type. The habit of Gambel oak within ponderosa pine-Gambel oak habitat types corresponds to the overall density of ponderosa pine. In dense ponderosa pine stands, Gambel oak is sparse and short; stems are taller and clumped in open stands [144]. At an elevation range of 8,000 to 8,600 feet (2,440-2,620 m) in Arizona, Gambel oak is subdominant to ponderosa pine with southwestern white pine (Pinus strobiformis) [20]. On heavier-textured soils in Colorado, serviceberry (Amelanchier spp.) is an important associate [185]. 

Published classifications listing Gambel oak as an indicator or dominant are listed below:

A classification of forest habitat types of the northern portion of the Cibola National Forest, New Mexico [3]
A classification of forest habitat types of the Lincoln National Forest, New Mexico [4]
Douglas-fir habitat types of northern Arizona [5]
Classification of the forest vegetation of Colorado by habitat type and community type [6]
Forest Vegetation on National Forests in the Rock Mountain and Intermountain Regions: habitat and community types [7]
Forest vegetation of the Medicine Bow National Forest in southwestern Wyoming: a habitat classification [8]
Classification of the forest vegetation on the National Forests of Arizona and New Mexico [9]
Climax forest series of northern New Mexico and southern Colorado [49]
Forest habitat types south of the Mogollon Rim, Arizona and New Mexico [50]
A classification of forest habitat types of northern new Mexico and southern Colorado [51]
Forest habitat types in the Apache, Gila and part of the Cibola National Forests, Arizona and New Mexico [70]
Grassland, shrubland and forestland habitat types of the White River-Arapaho National Forest [99]
Forest vegetation of the Routt National Forest in Northwestern Colorado: a habitat classification [103]
Forest vegetation of the Gunnison and parts of the Uncompahgre National Forests: a preliminary habitat type classification [117]
Forest and woodland habitat types (plant associations) of northern New Mexico and northern Arizona [129]
A classification of spruce-fir and mixed conifer habitat types of Arizona and New Mexico [146]
Aspen community types of Utah [148]
A classification of forest habitat types: southern Arizona and portions of the Colorado Plateau [149]
Plant associations (habitat types) of the forests and woodlands of Arizona and New Mexico [191]
A management-oriented classification of pinyon-juniper woodlands of the Great Basin [211]
Forest habitat types on the Medicine Bow National Forest, southeastern Wyoming: preliminary report [215]
Coniferous forest habitat types of central and southern Utah [220]


MANAGEMENT CONSIDERATIONS

SPECIES: Quercus gambelii
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]:

Oven Dry Air-dry (12% moisture) Green (65% moisture)
3168 3548 5227

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]:

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.

Property Gambel oak Colorado pinyon alligator juniper ponderosa pine eastern redcedar
Bending strength 70 60 63 65 67
Comprehensive strength 67 75 76 69 87
Stiffness 78 108 60 112 80
Hardness 137 73 107 41 81
Shock resistance 78 65 79 58 114
Volumetric shrinkage 121 99 73 97 78

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] :

  CO UT WY
Cattle Fair Fair ----
Domestic sheep Fair Fair ----
Horses Fair Poor  
Pronghorn ---- Good Poor
Elk Good Good Fair
Mule deer Good Good Good
White-tailed deer Good ---- Good
Small mammals Fair Good Good
Small nongame birds Poor Poor Good
Upland game birds Good Good Good
Waterfowl ---- Poor Poor
 

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]:

Nutrient Mean Coefficient of variation (%)
Dry matter component 64.1 1.7
Crude protein 5.1 6.1
Soluble carbohydrate 27.8 8.2
Ether extract 3.9 21.8
Soluble ash 4.0 6.2
Lignin 24.0 9.2
Hemicellulose 10.1 19.7
Cellulose 24.1 10.8
Holocellulose  34.1 5.7
Insoluble ash 0.7 30
In-vitro digestible dry matter 28.1 3.7

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 oak Mature oak
Dry matter (%) 35.2 44.8
Cell wall (%) 36.2 43.8
Lignin (%) 7.8 11.8
Nitrogen (%) 2.1 1.9
Gross energy (Kcal/g) 4.6 4.3
Tannin (mg protein ppt./mg sample) 0.231 0.176
Tannin (mg tannic acid equivalent/g) 40.4 34.7

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]:

  Crude protein (%) Phosphorus (%) Digestibility (%)
Burned stands      

Buds

9.5 0.36

0.17 34.0 0.59

Twigs

7.5 0.22 0.13 29.8 0.70
Unburned stands      
Buds  6.5 0.09 0.12 26.2 1.68
Twigs 5.7 0.10 0.11 23.5 1.15
 

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] : 

  CO UT WY
Pronghorn ---- Fair Poor
Elk Good Good Good
Mule deer Good Good Good
White-tailed deer Good ---- Good
Small mammals Good Good Good
Small nongame birds Good Good Good
Upland game birds Good Good Good
Waterfowl ---- Poor Poor
 

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].

 

OTHER 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]:

Density/ha Mean stem diameter (mm) Range of stem diameter (mm) Mean stem height (m) Range of stem height (m) Mean stem age (year) Range of stem age (year)
5,000 87 17-124 3.42 1.47-4.42  60.8 40-64
5,000 117 37-180 3.50 2.36-4.65 36.8 16-68
7,600 61 13-120 3.65 2.34-4.83 109.8 78-142
12,000 52 15-80 2.68 1.75-3.51 66.8 66-67
13,514 74 40-97 3.99 2.34-4.80 69.0 49-88
16,800 42 11-99 2.58 1.02-3.15 73.0 19-138
30,400 36 10-107 2.38 1.02-3.56 54.6 32-115
34,444 41 17-65 2.27 1.62-2.74 44.0 17-62

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]:

Soil depth (ft) Open areas between oak thickets   Oak thickets Herbicide- controlled oak
0-1 7.37 10.52 9.32
1-2 7.94 9.61 10.46
2-3 9.68 9.94 13.13
3-4 11.01 10.31 14.36
4-5 11.79 10.86 13.71

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]:

Nutrient (g/kg)  ponderosa pine Gambel oak Significance (p-value)
C 487 446 0.001
N 3.98 9.70 0.001
P 0.44 1.85 0.001
S 0.48 0.82 0.001
Ca 3.67 8.28 0.005
Mg 1.32 3.51 0.001
K 1.30 4.64 0.005
C:N 122 46 0.001

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].


BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Quercus gambelii
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:

Typical age of mortality (years) Maximum Longevity (years) Specific gravity Relative growth rate Relative Decay Resistance
90 120 0.62 Medium High
 

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]:

  Unit  surface-10 10-20  20-30  30-40 40-50 50 +
Adventitious buds Number 1293 4325 1978 727 671 133
  % 14 48 22 8 7 1
Rhizomes Number 0 7 2 7 6 1

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 185o 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:

  Understory Open area
Litter depth (cm) 2.3 0.2
Perennial forbs (%) 15.6 27.4
Annuals (%) 32.9 40
Shrubs (%) 27.7 18.4
Light intensity1 (foot candles) 76 242
1 Light intensity was measured in July from 12 to 2 pm.

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]:

Flower buds bursting Leaf buds bursting In full leaf In full bloom Fruit ripe Fruit dropped
May 25 May 23 June 17 June 5 September 25 October 10

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].


FIRE ECOLOGY

SPECIES: Quercus gambelii
FIRE ECOLOGY OR ADAPTATIONS:

Gambel oak is a fire-adapted species [143]. It responds to fire by vegetative sprouting from the lignotuber and rhizomes. Tree forms may survive low-severity fire [92].

Fire frequency within Gambel oak stands varies with plant associates. In most associations, little fuel is available for fires to occur in successive growing seasons [44,144]. Pure Gambel oak stands in southwestern Colorado burn most readily between October 1 and snowfall, when dead leaves remain on branches and the National Fire Danger Rating System burning index is between 40 and 75 [22]. Fall fires carry most readily through pure Gambel oak stands after leaf senescence but before leaf fall [144]. Dry, windy weather readily spreads flames through oak crowns [22]. Gambel oak stands burn well during dry summer conditions, especially on steep, south aspects [22,142].

Fire succession: Fire in Gambel oak stands may promote a brief grass-forb stage depending upon fire intensity and frequency [44]. In most situations, Gambel oak resprouts vigorously the 1st growing season following fire [13,26,44,53,76,143,144]. If successive fires occur at this stage, Gambel oak stands may be reduced to a grass-forb stage [44,144]. Repeated fires in Gambel oak ranges may deplete stored resources of rhizomes and lignotubers [144]. As sprouts continue to grow, natural thinning occurs, adding dead stems to the fuel. Fire occurring at this stage also sends Gambel oak stands back to a seral grass-forb stage. In absence of fire, sprouts form young poles. At this stage fires are stand replacement, either creating openings within stands for colonization by resprouts or a complete recycling back to a grass-forb stage. In the absence of fire, Gambel oak stands reach maturity in 60 to 80 years. Fire response in mature stands is similar to that in young poles. A severe fire will recycle the stand; low-severity fires create openings for resprouts. At 80 years Gambel oak stems die naturally, creating more openings for sprouts [44].

The Utah woodlands at 5,500 to 7,800 feet (1,676-2,377 m), where Gambel oak and/or bigtooth maple are dominant, codominant, or long-term seral dominants, have low combustibility. However, environmental conditions occasionally permit severe wildfires [22]. Gambel oak leaves killed by a late spring freeze may provide dried tinder during summer or early fall [214]. With increasing bigtooth maple cover, fire susceptibility lessens through relatively rapid decomposing leaf litter and a reduced understory [22]. Susceptibility increases where conifers are encroaching, due to resinous foliage and persistent litter [92].

In Zion National Park, Utah, fires are more frequent in ponderosa pine stands with a Gambel oak understory than in Gambel oak-dominated stands without ponderosa pine litter [144]. The mean historical fire return interval in ponderosa pine-Gambel oak forests near Tucson, Arizona, was 3.7 years between 1637 and 1883. Only a single fire scar was recorded between 1883 and 1951. With fire exclusion, Gambel oak and ponderosa pine densities have increased. A reconstruction of 1883 presettlement forest structure compared with contemporary forest structure from a 1994/1995 inventory at Camp Navajo, Arizona, is summarized below [77]:

Species Presettlement  mean Contemporary mean
Trees/ha    
     Ponderosa pine 65.3 720.2
     Gambel oak 79.4 471.4
Basal area (m2/ha)    
     Ponderosa pine 11.7 18.2
     Gambel oak 1.0 6.6

Fire in ponderosa pine stands of Arizona may convert stands to thickets of Gambel oak [170], initiating a Gambel oak successional stage after the competing ponderosa pine overstory is removed [44,53]. Dense understories of Gambel oak may serve as ladder fuels that carry fire to overstory tree crowns, increasing fire risk to ponderosa pine [22]. A detailed description of fire-induced succession within ponderosa pine-Gambel oak habitat types can be found in Crane [44].

Gambel oak is a seral species in quaking aspen, pinyon-juniper, and mixed-conifer forests [44]. Gambel oak occupies a seral postfire successional stage in pinyon-juniper woodlands [61,218]. Reestablishment of pinyon pine and most juniper species after disturbance is dependent entirely upon seed production. The vegetative reproductive capabilities of Gambel oak provide it with an inherent postfire advantage. Gambel oak occupies a seral postfire stage within pinyon-juniper woodlands of Mesa Verde, Colorado. Gambel oak dominates for approximately 25 postfire years, and may persist up to 100 years before canopy suppression by pinyon pine and juniper species [62]. Floyd [71] presents the Gambel oak vegetation type as successional in Colorado, altering the habitat and facilitating invasion and eventual succession to pinyon-juniper woodland. Within Douglas-fir forests of the White Mountains of Colorado, Hanks and Dick-Peddie  [89] describe Gambel oak as occupying a postfire successional stage that may persist up to 100 years before being shaded out by coniferous overstory. Within the Huachuca Mountains of Arizona, Gambel oak was found in Douglas-fir communities after fire. As Gambel oak matured, Douglas-fir seedlings occupied the understory, suggesting eventual return to Douglas-fir dominance [23]. Hypothetical postfire succession in Rocky Mountain habitats where Gambel oak occurs is described by Crane [44].

The following table describes fire return intervals in some communities where Gambel oak occurs [27]:

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
mountain-mahogany-Gambel oak scrub Cercocarpus ledifolius-Quercus gambelii < 35 to < 100 
western juniper Juniperus occidentalis 20-70 
Rocky Mountain juniper J. scopulorum < 35 [27]

POSTFIRE REGENERATION STRATEGY:

Tree with adventitious bud/root crown/soboliferous species root sucker
Tall shrub, adventitious bud/root crown
Secondary colonizer (on-site or off-site seed sources)


FIRE EFFECTS

SPECIES: Quercus gambelii
IMMEDIATE FIRE EFFECT ON PLANT:

Fire may top-kill Gambel oak [26]. Gambel oak habit and community structure affect susceptibility to fire. Tree forms are less likely to be top-killed in a low-severity fire compared to shrubs with branches closer to the burning surface fuels [92].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

No entry

PLANT RESPONSE TO FIRE:

Fire usually stimulates sprouting of Gambel oak after top-kill [13,26,53,76,143], increasing density of previously open stands and merging scattered stands into continuous thickets [26]. Gambel  oak regeneration after fire is usually vigorous [143]. Sprouts may be observed within 10 postfire days [198].

Seed: Caches of acorns gathered by rodents are a source of postfire regeneration [158].

Sprouting: First-year responses to fire show vigorous Gambel oak regrowth. Adventitious buds located on rhizomes and lignotubers may produce stems reaching up to 18 inches (45.7 cm) in height. Surviving stems also resprout from buds [144]. Dormant buds on rhizomes are stimulated by fire [143]. Rhizomes generally lie between 4 and 20 inches (10-50 cm) below soil surface, so they are protected from all but the most severe fires [198]. Wright [217] predicts continued growth after fire in Gambel oak, inducing a natural thinning of continuous thickets that ultimately decline to coverage equaling the previously unburned stand within 18 years. 

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Postfire stand recovery time varies according to fire severity, climatic factors, and site characteristics. Recovery after fire is fastest on warm, south-facing slopes at low elevations [125].

Postfire regrowth was greatest the 1st year following a summer (July) and fall (September to October) fire between 4,600 and 6,400 feet (1,402-1,950 m) in northern Utah. August 1 postfire growth was 16 to 18 inches (41-46 cm), with 2nd-year growth at  4 to 8 inches (10-20 cm) [13]. Other studies show similar, rapid Gambel oak recovery from fire. New shoots with flowers were produced 26 days after an August fire in Orem Park, Provo Canyon, Utah, on stems that were defoliated but not killed [92]. Gambel oak shrublands were nearly half-covered with resprouting oaks 1 year after an August fire in Mesa Verde National Park, Colorado [72]. Also in Mesa Verde National Park, Gambel oak crown sprouted and leafed within a few months after a mid-July to August lightning-ignited wildfire at 7,500 feet (2,286 m) [61]. Resprouting of Gambel oak after an October prescribed burn in Grand Mesa National Forest, Colorado, was greatest at the 1st postburn growing season, decreasing the 2nd and following growing seasons.

FIRE MANAGEMENT CONSIDERATIONS:

In mature Gambel oak stands ( > 60 years), severe fires top-kill all or most of the stand; low-severity fires create openings for sprouts [144].   

Gambel oak leaf moisture content varies greatly from year to year. Moisture content decreases from May to August [160]; August foliage has less than half the moisture of May foliage [161]. Within Waterton Canyon, Colorado, the moisture content of Gambel oak leaves decreased significantly (p < 0.001) in both the upper and lower canopy from May to August. This was true regardless of aspect and elevation. Ogle [160] constructed a model to predict fire behavior in relation to fuel moisture in Gambel oak.

Gambel oak produces a large amount of leaf litter that contributes, in most cases, 70% of total stand litter. In Utah, accumulated litter biomass of approximately 33,335 pounds per acre (37,348 kg/ha) was about equivalent to the bole biomass of 36,328 pounds per acre (40,702 kg/ha) [38]. 

The distribution of belowground nitrogen (kg/ha) and the percent of total belowground nitrogen was evaluated in a Gambel oak stands near Ephraim, Utah [199]:

Aboveground kg/ha % of N capital
Leaves 43 0.45

Live Branches

19 0.20

Stem

124 1.3
Dead branches 40 0.43
Dead down 30 0.30
Standing dead 55 0.60
Litter 582 6.2
Belowground    
Soil 8455 87.9
Roots 240 2.6

Based on this data, harvest followed by broadcast burning may result in a 10% loss in nitrogen capital depending upon fire intensity [199].

Fire alters the plant community in which Gambel oak occurs. Gambel oak communities are usually tolerant of fire, but herbage yields of associated species do not appear to improve [25]. Frequency and cover of major plant species on Gambel oak-dominated sites in oak brush near Wasatch Mountains State Park, Utah, were evaluated 1 year after an August wildfire [166]:

  Unburned Cover  Burn  
Species Frequency (%) (%) Frequency (%)  Cover (%)
Gambel oak  100 51.12 92.8 38.36
pale agoseris  (Agoseris glauca 11.8 1.06 0.90 < 0.01
bluebunch wheatgrass  29.40 0.59 0 0
Saskatoon serviceberry (Amelanchier alnifolia) 23.50 1.09 8.1 0.95
big sagebrush  17.60 1.09 0 0
China aster (Callistephus chimensis) 5.90 0.03 0 0
cheatgrass  23.5 4.17 18.90 0.16
lambsquarters (Chenopodium album) 0 0 24.30 1.24
narrowleaf goosefoot (C. leptophyllum) 5.90 0.03 19.8 0.39
maiden blue-eyed Mary (Collinsia parciflora) 29.40 0.15 27.9 0.32
tapertip hawksbeard (Crepis acuminata) 47.10 1.38 3.60 0.02
stickywilly  11.80 0.21 24.30 0.69
Brown's pea (Lathyrus spp.) 58.80 2.59 7.20 0.30
biscuitroot (Lomatium triternatum) 35.30 0.77 1.8 0.01
tansyaster (Machaerantera canescens) 0 0 0.9 0.03
Kentucky bluegrass  52.90 16.81 17.1 1.23
bushy knotweed (Polygonum ramosissimum) 0 0 6.3 0.03
chokecherry  29.40 8.38 10.80 0.84
threeawn goldenrod (Solidago velutina) 0 0 2.7 0.19
mullein (Verbascum thapsus) 0 0 19.8 1.2
goldeneye (Heliomeris multiflora) 0 0 24.3 0.86

Control: Fall burning provides the least amount of Gambel oak control. Gambel oak is dormant in the fall and total nonstructural carbohydrate reserves are at their peak [137]. Gambel oak is most severely harmed by successive fires when carbohydrate reserves are low. Top-killing Gambel oak in the summer may produce resprouts within 6 weeks. However, by fall, resprouts are still immature and carbohydrate recovery cannot begin until the following spring leaf-out, producing a 9- to 10-month period without carbohydrate replacement. Control may occur though carbohydrate stress imposed by 2 summer burns. However, effective burning may require biennial treatments due to light litter accumulation within a single growing season [94].

Observations within a ponderosa pine stand in southwestern Colorado at 7,600 feet (2,316 m) suggest frequent burning during mid-August provides control for Gambel oak. Vigorous Gambel oak sprouting was observed regardless of burn season. Twice-burned spring and fall treatments resulted in resprout densities equal to once-burned areas. Twice-burned summer treatments resulted in decreased oak density, frequency, and cover. Resprouts after twice-burned summer treatments were confined to top-killed oak thickets; sprouting after fall and spring burns was not restricted; and previous Gambel oak thicket boundaries were extended[94]. Frischknect and Plummer [76] suggest seeding competitive grasses after fire, but additional studies are required to substantiate findings [92].


FIRE CASE STUDY

SPECIES: Quercus gambelii
FIRE CASE STUDY CITATION:
Tirmenstein, D., compiler. 1988. Gambel oak recovery after prescribed burning in a Colorado Rocky Mountain ponderosa pine stand. In: Quercus gambelii. 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/ [ ].

REFERENCES:

Harrington, M. G. 1982. Stand, fuel, and potential fire behavior characteristics in an irregular southeastern Arizona ponderosa pine stand. Res. Note RM-418. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 6 p. [221].

Harrington, M. G. 1985. The effects of spring, summer, and fall burning on Gambel oak in a Southwestern ponderosa pine stand. Forest Science. 31(1): 156-163. [94].

SEASON/SEVERITY CLASSIFICATION:

Fall 1977/fire severities not reported
Spring 1978
Summer 1978
Fall 1979
Spring 1980
Summer 1980

STUDY LOCATION:

The study was conducted on 2.5-acre (1 ha) plots within the San Juan National Forest in southwestern Colorado.

PREFIRE VEGETATIVE COMMUNITY:

The study site consisted of a multiple-aged Rocky Mountain ponderosa pine overstory averaging 300 trees and 124 square feet (11.5 m2) basal area per acre. There was a dense Gambel oak (Quercus gambelii) understory. Herbaceous and other shrubby understory vegetation was sparse.  The majority of Rocky Mountain ponderosa pine (75%) occurred as trees in the 4- to 11-inch (10-28 cm) d.b.h. class. In forest openings, Gambel oak reached heights of 15 feet (4.8 m) with 4-inch (10 cm) basal diameters. The majority of Gambel oak was less than 4 feet (1.2 m) tall and 2 inches (5 cm) in basal diameter.   

TARGET SPECIES PHENOLOGICAL STATE:
Spring Summer Fall
full leaf stage 2nd growth period dormant, near peak root carbohydrate levels
 

SITE DESCRIPTION:

Burned areas were located on a south aspect with less than 5% slope at 7,600 feet (2,316 m). Average annual precipitation in Mancos, Colorado, 5 miles southwest of the study site is 17 inches (430 mm), with the least amount of precipitation occurring in June and the greatest amount in August. Fire has not occurred since 1877. Before 1877 fire intervals were 1 to 16 years with an average of 6 years.  

FIRE DESCRIPTION:

Initial burn:

  Fall Spring Summer
Temperature (F) 56-63 65-79 72-77
Humidity (%) 32-41 14-41 21-37
Wind speed (mph) 2-5 1-6 1-5
Moisture (%)      
       Litter layer 7.2 5.4 6.0
       Fermentation layer 11.8 6.9 7.5
       Humus layer 18.9 11.5 9.2
Spread rate (ft/min) 6 8 5
Flame length (ft) 3.0 3.5 3.5

2nd burn:
  Fall Spring Summer
Temperature (F) 48-53   77-83 68-72
Humidity (%) 25-30 19-24 20-27
Wind speed (mph) 1-3 2-7 2-6
Moisture (%)      
       Litter layer 13.1 3.6 4.5
       Fermentation layer --- --- ---
       Humus layer 26.2 5.8 9.2
Spread rate (ft/min) 3 10 6
Flame length (ft) 1.0 3.5 3.0

Fuels were dry during the 2nd spring burn, resulting in rapid-fire spread that consumed 35% of the forest floor fuels. Nearly all the new litter was consumed, along with 10% of the residual fuels. The summer burn consumed 17% of the forest floor, 70% of which was new litter.  

FIRE EFFECTS ON TARGET SPECIES:

Single-burn treatments resulted in 100 to 150% increases in Gambel oak density and a 10 to 40% increase in frequency. Cover of Gambel oak was only reduced temporarily. Reductions 1 year after the initial burns were as follows:

Oak d.b.h (in) Reduction (%) Reduction numbers (stems/200 ft2)
1/4-1 80 2.6-13.7
1-2 70 0.7-2.2
 > 2 50 0.4-0.8

Overall cover of Gambel oak was reduced 20 to 35% 1 year after the initial burn. Cover of fall and spring burn plots equaled those of control plots 2 years after the burn.

Consecutive fall and spring burns resulted in slight increases in Gambel oak sprouts with successive summer burns reducing Gambel oak density by 20%, frequency by 16%, and cover by 12%. Gambel oak frequencies after the twice-burn spring and fall treatments increased 10% by postfire year 4. Cover of the twice-burned plats was reduced, particularly on the summer treatment. However, all treatments had slight Gambel oak cover increases by postfire year 4.   

FIRE MANAGEMENT IMPLICATIONS:

Single burns in any season are unlikely to remove Gambel oak from ponderosa pine understories. However, results of this study suggest consecutive summer burns reduce Gambel oak populations. Gambel oak burned during the summer regrowth period, when carbohydrate levels are reduced, is unable to sprout and accumulate carbohydrates before fall dormancy. Successive burns in this period can place additional stress on Gambel oak. Spring burns generally allow good recovery prior to dormancy. Similarly, fall burns after carbohydrate reserves are accumulated have little effect on Gambel oak.

The deep-rooted Gambel oak can compete effectively with ponderosa pine for available water and nutrients. When Gambel oak sprouts prolifically after fire or other disturbance, it is capable of inhibiting ponderosa pine regeneration. Consecutive burns in ponderosa pine-Gambel oak stands could, in time, favor the growth and regeneration of pine.


Quercus gambelii: References


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