• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

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]:

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]:

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].

Species Index

Related categories for SPECIES: Quercus gambelii | Gambel Oak