• 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:

Shrub live oak is top-killed by fire [15,18]. The degree of damage and subsequent mortality rate of shrub live oak following fire depends largely on fire intensity and severity, site characteristics that influence fuel levels, and climatic factors [87]. On most sites, shrub live oak is difficult to kill by burning [70].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

Shrub live oak is more susceptible to fire-induced damage on drier, unfavorable sedimentary or volcanic substrates than on more favorable sites and can occasionally be eliminated from these marginal sites by fire. Evidence suggests that shrub live oak is especially difficult to kill on soils with relatively favorable moisture relationships [79,80].

Fires of high severity generally result in increased mortality. Seedling survival tends to be higher following "light" fires [8,79,80]. Survival of 1-year old shrub live oak seedlings was as follows after fires in central Arizona chaparral [64]:

intense burn*  light burn**
48%            91%

*leaves and twigs mostly consumed
**shrubs dead, but leaves and twigs mostly intact; 
    "largely a cool or ground fire"

PLANT RESPONSE TO FIRE:

Shrub live oak typically sprouts from the root crown and rhizomes following fire [8,16,79,80,100,104,105]. In Arizona chaparral communities, shrub live oak may be favored by repeated burning [75].

Although sprouting is apparently the most common form of regeneration after fire, seedling establishment may also be important. A "moderate population" of shrub live oak seedlings was observed on Arizona chaparral burned 1 and 2 years earlier. Survival after 3 years was 26% with most mortality attributable to drought [63]. Postfire seedling emergence and survival after fall burning in Arizona chaparral site were as follows [65]:

Seedling emergence -

# years 
after burn        1     2     3     4     5

seedlings/acre    62    12    16    0     9 = 99 (total)

Seedlings surviving at the end of the growing season -

# years
after fire        1     2     3     4     5

seedlings/acre    57    50    36    36    9     

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Recovery times after fire for shrub live oak range from 4 to 8 years or more [87]. Cable [7] observed that shrub live oak had regained preburn density within 5 years after fire in Arizona. After an early fall prescribed burn in a shrub live oak-true mountain-mahogany (Cercocarpus montanus) community in central Arizona, shrub live oak exceeded pretreatment cover within 5 years. Crown canopy over (%) of shrub live oak was as follows [65]:

           Postfire year

Prefire    0      1      2       3       4       5
22.7       1.3    9.0    14.1    14.7    17.8    25.6

Cover values (%) of shrub live oak 1 to 8 years after fire in 2 Arizona studies were as follows:

1st study - based on line intercepts following June 1956 burn [8] -

1956    1957    1958    1960    1961
81.0    80.4    69.4    70.5    68.0

                Unburned-    Burned-      Burned-
                native       reseeded*    reseeded*-
                                          herbicide
Treatment year
1955 site        21.8        16.8         ---
1956 site        29.6        25.5         3.8
1958 site        27.2        19.8         2.1
1959 site        18.4        13.8         ---             
average          24.2        19.0         3.0

*seeded to Lehmann lovegrass and weeping lovegrass or a combination

              Stem counts before burning in indicated year - 

Yrs. between  1953     1954    1955   1956    1957    1958   1959
burns         (pretmt)                
1             121       710     330    371     161      38     17
2             152       ---    1231   1161    1142     ---    662
3             276       ---     ---    ---     ---     ---   1469
4             170       ---     ---    ---     790     ---    773
5              94       ---     ---    ---     ---     436   1107

FIRE MANAGEMENT CONSIDERATIONS:

Davis and Dieterich [17] report "people experienced with fire characteristics in Arizona oak chaparral have always maintained that chaparral either burns fiercely or does not burn at all." A critical rate of spread threshold has been estimated at 20 feet per minute. For fire to spread, conditions must be suitable for generating spread at or above that rate. Minimum sustained spread of 1/4 mile per hour (22 ft/min) has been reported in prescribed burns [17]. Details are available on rate of spread in shrub live oak-dominated chaparral [17].

Flammability of shrub live oak is increased by preheating which may cause chemical changes. Detailed information is available [88].

Prescribed fire: Prescribed fires have resulted in temporary reduction of shrub live oak [65]. At some sites fuels are sparse, and broadcast burning may nearly impossible [70]. Several years may be needed for shrub live oak chaparral to produce enough fuel to carry a fire. Ten to 20 years may be required for shrub live to reburn at some sites [6,8]. Herbicides may be applied prior to prescribed burning to increase flammability and kill the tops of shrub live oak without removing litter [65]. In an Arizona study, late summer application of 'Dinoxol' (a mixture of 2 lbs/gallon (acid equivalent) of the butoxyethanol esters of 2,4-D and 2,4,5-T herbicides) killed 80% of the leaves and twigs. Moisture content of herbicide-killed leaves was 8 to 15% (oven-dry) compared with 85 to 97% for untreated leaves [65]. Shrub live oak leaves contain approximately 6.2% volatiles [27]. Regressions have been developed for foliar moisture of shrub live oak [48].

Grass production: The production of introduced perennial grasses may increase following fire in shrub live oak communities. Productivity may be increased for 5 to 7 years following fire. In an Arizona study, comparative production values by treatment were as follows [87]:

            Perennial grass production

            Unburned-      Burned-        Burned-
            native         reseeded       reseeded-
                                          herbicide
1956 site     3 lb/acre    ----           280 lb/acre
1958 site    31 lb/acre    179 lb/acre    803 lb/acre

        Shrub live oak cover (%)

        grazed    ungrazed
1952    20.40     18.46
1956    33.93     30.27
1958    36.37     31.04

Soils: Fire acts as a mineralizing agent quickly volatilizing the litter and standing fuels of shrub live oak. These compounds then condense within the soil and on the soil surface. Immediately after a prescribed fire amounts of exchangeable ammonium and extractable phosphorus in the soil increased under shrub live oak [62].

Related categories for SPECIES: Quercus turbinella | Shrub Live Oak