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You are here >1Up Info > Wildlife, Animals, and Plants > Plant Species > Shrub > Species: Quercus dumosa | Nuttall's Scrub Oak
 

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FIRE EFFECTS

SPECIES: Quercus dumosa | Nuttall's Scrub Oak
IMMEDIATE FIRE EFFECT ON PLANT : California scrub oak often occurs in highly flammable chaparral stands which burn at relatively high frequency. The total effect of fire on oaks varies according to fire intensity and severity, fire behavior, season of burn, and size of the plants. Because most Nuttall's scrub oak is relatively small (generally less than 8 inches [20.3 cm] d.b.h.) and has thin, flaky bark, it is almost always top-killed by fire [48,50]. Seedlings are almost always killed by fire [31]. Larger, older Nuttall's scrub oaks with slightly thicker bark and higher crowns tend to be somewhat more resistant to fires than smaller individuals [48]. Stems of lightly charred trees with d.b.h.'s greater than 6 inches (15 cm) can occasionally survive fire [48,50]. Trunks of oaks are, in general, more seriously damaged by slower moving, low intensity fires than those of shorter duration and high intensity. However, the heat-sensitive crowns are generally seriously damaged by high-intensity fires, even those of relatively short duration. Greater damage occurs as the growing season progresses, with least damage produced by winter fires [50]. Oaks are usually less severely damaged when burned at lower ambient air temperatures. Stem and bark: The full extent of bole damage may not become evident for some time. However, the trunks of most scrub oak exhibit medium to heavy charring soon after fire. Young oak stems damaged by heat generally change from a gray to reddish-gray in color. The subsurface layer of the bark changes from a green to tan or brown, and inner bark appears yellow instead of the normal white or pink. Damaged inner bark often has a characteristic fermented aroma. A pattern of vertical cracks often develops in the charred bark of scrub oak, and the bark may be burned through to the wood. The loose, outer bark is generally consumed if heavily burned. The cambium can be considered dead, with overall survival unlikely, if the bark has been consumed, or if it appears to be cracked and separated from the wood. Trunk char of oaks may be categorized as follows [50]: light charring - spotty char or scattered pitting of the bark medium charring - continuous charring, areas of minor reductions in bark thickness heavy charring - pronounced reductions in bark thickness; wood sometimes exposed Crown: Crown damage is variable in oaks and the degree of damage can differ even within an individual crown [48]. The degree of damage may range from essentially none to total removal of the foliage. Oaks less than 6 inches (15.2 cm) d.b.h. are usually top-killed by even low intensity fires [50]. However, underground portions of scrub oak generally survive fire even though top-killed, and overall adult mortality is often quite low [31,65]. Nearly 100 percent survival of belowground or surface level regenerative structures has been documented after spring or summer fires in southern California chaparral [39]. Mortality may be more likely after hot fires with the potential to damage regenerative structures. Some California oaks are killed if burned at frequent intervals [52]. Seed: The heat-sensitive acorns of Nuttall's scrub oak are poorly adapted to survive fire [74]. Most acorns still present on the trees are killed readily by fire [73], as are the majority of those stored on-site in the soil or litter [20,28,31]. Occasionally, acorns buried in rodent caches are sufficiently protected from heat to survive and germinate [73,74]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : It may be necessary to wait for at least one growing season, and preferably three, before the true potential for survival can be accurately determined [50]. Fire-related injuries can increase oak's susceptibility to attack by insects, fungus, or windthrow [48]. Various methods have been developed for assessing damage to oaks including chemical, electrical, and visual techniques [48,50]. PLANT RESPONSE TO FIRE : Nuttall's scrub oak typically sprouts prolifically after fire [6,27,36]. Stump-sprouting is commonly observed where portions of the stump remain intact [18,39,44]. Nuttall's scrub oak also resprouts from the root crown [9,50]. Older root crowns which have been burned repeatedly can develop into large structures at, or below, the soil surface [20]. However, scrub oak "does not usually form a distinct burl" [31]. Establishment from seed does occur but appears to be less common than sprouting [30,29,73]. Vegetative response: Sprouting is generally both vigorous and rapid [20]. Plants usually sprout by the first growing season after fire, but delayed sprouting has also been observed [48,50]. Sprouts may emerge as soon as 10 days after fire, or sprouting may be deferred for up to 2 years. The ability to remain dormant for at least one growing season prior to sprout production may enhance survival as sprouting is delayed until a favorable moisture regime is encountered [47]. Speed of recovery depends on such factors as topography, aspect, and weather [30]. Sprouting appears to be unrelated to season of fire. The availability of soil moisture is probably the primary factor controlling sprouting [47]. Sprouting of Nuttall's scrub oak is most common and most rapid on deep, moist soil, particularly on north-facing slopes [20,46,47]. Generally, fewer plants sprout on more xeric rocky sites, and sprouting is often delayed until the following spring [46,47]. Seedling establishment: Regneration by seed does occur but may be limited to periods of abundant rainfall [30,74]. Many Nuttall's scrub oak seedlings were observed in the spring following a December prescribed fire during a period of unusually abundant rainfall. However, because of the timing of dispersal, acorns are poorly adapted to survive fire [74]. Seedbeds created by fire do not favor germination or growth of Nuttall's scrub oak [31]. Rarely, seedlings buried in rodent caches or in stands with unusually deep litter survive fire and subsequently germinate [73]. Rate of postfire recovery: Nuttall's scrub oak generally recovers fairly rapidly after fire, particularly on better sites. It, along with ceanothus, commonly dominates southern California chaparral by the fourth year after fire [30]. Impenetrable cover can develop in oak chaparral within 5 to 10 years after fire [41]. In coastal sage communities, Nuttall's scrub oak generally becomes dominant by the second decade after fire [20]. Growth of sprouts is somewhat variable [46], but is generally rapid during the first 3 years after fire [24]. Sprout heights of more than 2 feet (0.6 m) have been observed within only 2 months after fire [47]. Approximately 4 to 5 months after a July wildfire, some sprouts had reached 2 to 3 feet (0.6-0.9 m) in height, and most were at least 12 inches (31 cm) tall [46]. Biswell and Gilman [6] observed that some sprouts had reached 24.9 inches (63 cm) within 10 months after a September wildfire, and maximum heights of 78 inches (198 cm) had been reached by the end of the second growing season. Maximum heights of 95 inches (236 cm) were recorded by the end of the third growing season, and a few oaks had reached 8 feet 9 inches (236 cm) by the end of the fourth growing season. Sprouts tend to grow more rapidly than seedlings during the first few years after fire. Comparative heights of Nuttall's scrub oak seedlings and sprouts by the end of the spring of the first postfire year were as follows [30]: high elevation mid. elevation low elevation resprouts 30 cm 47 cm 55 cm seedlings ----- 12 cm 7 cm DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : Fuels and flammability: Nuttall's scrub oak tends to be somewhat less flammable than many other chaparral species. Flammability is reduced because of the relatively high fuel moisture of living plants, a lower proportion of dead-to-live fuels, and fewer volatiles [18]. The volatile content is approximately 3.7 percent, and leaf energy content averages 20.33 kJ -1 [18,46]. Heat content has been calculated as follows [48]: density (lb/ft 3) heat content (Btu/lb) flaky outer bark 37 8350 outer bark 45 8250 inner bark 63 6750 wood 57 8060 Nitrogen volatilization: Approximately 25 percent of the aboveground biomass and surface soil was volatilized in fires which consumed 60 percent of Nuttall's scrub oak biomass [55]. Prescribed fire: Limited evidence suggests that burning may be difficult in stands dominated by Nuttall's scrub oak [3,18]. In mature chaparral stands with significant amounts of fine fuels, burning without damaging oaks is often difficult [20]. Repeated fires can maintain Nuttall's scrub oak as a small, multistemmed shrub [50]. Hot fires tend to be most effective in reducing sprouters such as Nuttall's scrub oak. Riggan and others [55] observed that low fuel moisture and winds consistently greater than 5 to 8 miles per hour (8-12 km/hour) are required to spread fire in Nuttall's scrub oak communities. Flame lengths of 20 to 33 feet (6-10 m) were produced by prescribed fires which released just enough energy to achieve steady spread rates. A threshold for fire propagation in communities with little dead wood is overridden by higher wind speeds which increase the efficiency of heat transfer to unburned fuels. Postfire harvest: The degree of damage must be correctly determined before appropriate harvest recommendations can be made. Plumb and Gomez [50] suggest waiting for at least 1, and if possible, 3 growing seasons before cutting oaks in which crown survival is in doubt. Once damage has been accurately assessed [See Fire Effects], the following guidelines may be used for Nuttall's scrub oak [48]: plant size and degree of trunk char light medium heavy < 6 inches d.b.h. cut cut cut 6-12 inches d.b.h. leave cut cut Harvesting of oaks is generally recommended if 75 percent of the trunk is girdled on plants less than 6 inches (15.2 cm) d.b.h., or if more than 50 percent is girdled on plants greater than 6 inches (15.2 cm) d.b.h. [48]. Postfire productivity: Total postfire production of Nuttall's scrub oak has been reported at 2.5 pounds per acre (2.8 Mg/ha) in the first year after fire. Annual biomass production over a 35-year period was estimated at 2.8 pounds per acre (3.2 Mg/ha), but foliar biomass averaged .97 pounds per acre (1.1 Mg/ha) by the first postfire year [55], suggesting rapid recovery after fire. Wildlife considerations: Tender Nuttall's scrub oak sprouts provide wildlife browse after fire [66]. Following fires in southern California chaparral, new sprouts are browsed by deer during late June through early July. An average of 20 percent of all shoots on 23 percent of the plants were browsed by deer during this time period. Small mammals such as the brush rabbit browsed stump-sprouts most heavily during October and November. Postfire utilization of Nuttall's scrub oak by small mammals in southern California chaparral was as follows [39]: year % shrubs browsed % shoots browsed per plant 1982 20 4.5 1983 45 8.0 Livestock: Recently burned chaparral comprising Nuttall's scrub oak can provide an adequate maintenance diet for domestic goats during the spring and summer [62].

Related categories for Species: Quercus dumosa | Nuttall's Scrub Oak

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Information Courtesy: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Fire Effects Information System

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