• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

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]:

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]:

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)

Related categories for SPECIES: Quercus gambelii | Gambel Oak