FIRE EFFECTS
SPECIES: Juniperus monosperma | Oneseed Juniper 



IMMEDIATE FIRE EFFECT ON PLANT : 
Oneseed juniper is generally damaged or killed when aboveground foliage
is consumed [43].  Trees less than 4 feet (1.2 m) in height are
particularly susceptible to fire mortality [15].  The length of exposure
to fire required to kill trees generally increases with size [37].

Average mortality following a low-intensity June wildfire in oak-juniper
woodlands of Arizona was 76 percent [43].  Researchers observed 92
percent mortality after a stand of small, bushy oneseed juniper were
burned [9].  Springfield [71] noted that typically 70 to 100 percent of
oneseed junipers less than 4 feet (1.2 m) in height are killed by fire.
Mortality rates are apparently somewhat more variable among larger
trees.  Kills ranging from 30 to 100 percent have been reported in trees
5 to 6 feet (1.5-1.8 m) in height [71].

Relatively little is known about the ways in which fire intensity,
specific weather conditions, understory vegetation, and season of burn
influence the effect of fire on oneseed juniper.  In general, fires of
greater intensity appear to be most damaging to oneseed juniper.
Researchers have found that 100 percent mortality results when 60
percent of the crown is scorched [37].  Temperatures lethal to oneseed
juniper tissue are also related to the degree of desiccation [34], and
thus season of burn may also influence the amount of damage the plant
sustains.  Laboratory experiments have shown that lethal temperatures
tend to be lowest during late spring and summer [34].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
Fires which occur during late spring or summer may be most damaging to
oneseed juniper.  Lethal temperatures have been reported as follows
[34]:

        Lethal temperatures (degrees C) at various dates _

                        1957                     1958
March 5                 80.0    January 7        69.4 
April 3                 73.8    February 7       70.6
April 29                71.2    April 12         70.6
May 29                  72.5    May 1            67.5
June 27                 71.2    May 23           66.2
July 29                 72.5    June 24          62.5
August 19               71.2    July 21          61.8
September 17            71.2    August 19        65.0
October 17              76.2    September 18     70.6
November 7              76.2    Average          67.6
December 10             73.8
Average                 73.6


PLANT RESPONSE TO FIRE : 
Regeneration of oneseed juniper is generally through seed when
aboveground vegetation has been killed or seriously damaged by fire.
Older oneseed junipers can occasionally sprout from the base after fire
[12,40]; approximately 10 percent of oneseed junipers sprouted after a
June wildfire in Arizona.  However, in most cases, sprouting appears to
be a relatively unimportant mode of regeneration.

The length of time required for postfire recovery of oneseed juniper has
not been well documented.  However, researchers have observed that
following other types of disturbance such as mechanical removal, oneseed
juniper only rarely becomes established within the first few years after
the disturbance [69].  A similar response is probable after fire.
Oneseed juniper did not become prominent after an intense wildfire in
Utah until postfire year 40.  This species did not regain dominance on
this site until approximately 70 years after the fire [76].  Evidence
suggests that factors such as soil type and preburn community
composition may significantly influence the length of time required for
recovery [69].  Seedling establishment may be favored in the shade of
dead vegetation, including oneseed junipers [12].  Once established,
oneseed juniper can bear seed as early as 10 years of age on some sites
[69].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
In some intance, oneseed juniper can survive when partially defoliated
by fire [15].  Often the extent of damage is not evident until postfire
year 1 or 2 [15].  The status of oneseed junipers 2 years after a fairly
low-intensity April fire on blue grama-pinyon-juniper range was as
follows:

                total trees             120
                composition             69.8%
                kill                    24.2%
                unharmed                13.3%
                partial defoliation     62.5%
                average % defoliation   
                        (all trees)     44.6%


FIRE MANAGEMENT CONSIDERATIONS : 
Oneseed juniper has been invading grasslands of the Southwest during
much of the past century [35].  In some locations grasslands or open
woods have been replaced by thick stands of pinyon and juniper.
Historically, fire is believed to have played an important role in
maintaining juniper savannas, and grasslands [40,79].  Fire suppression
is believed to have contributed to the relatively recent spread of
oneseed juniper.  Mueggler [56] reported that a fire-free period of 85
to 90 years may be required for the formation of a "well-developed"
juniper woodland.

Oneseed juniper can be burned individually, grasslands burned, or
pinyon-juniper woodlands broadcast burned.  However, not all methods are
equally applicable to all sites, and it is important to tailor the
method chosen to the density of the stand, tree age, fuel levels, and
weather conditions [3,61,71,76,83].

Attempts have been made to enhance forage production through the use of
fire.  In some instances, forage production has increased after oneseed
juniper and other species were removed by fire.  Aro [4] reported
increased forage production of up to 500 pounds per acre following fire
in some pinyon-juniper sites in Arizona.  However, in other instances
little long-term increase in forage production has been noted.  The
presence of a good stand of residual grasses prior to burning may be
important for a favorable reponse.

Removing oneseed juniper by burning individual plants appears to be most
applicable to smaller trees less than 10 feet (3.1 m) in height, in
stands of up to 100 per acre [37,71].  Small junipers reportedly burn
rapidly [37,71].  Larger trees frequently take a considerable length of
time to burn, making this method prohibitively expensive [37].

Light surface fires have been used in attempts to eliminate young
oneseed juniper which have invaded nearby grasslands.  Adequate fuel is
generally available in these areas and young seedlings and saplings 3.2
to 6 feet (1-1.8 m) or less in height are readily killed [9,76].
Fire-induced mortality in larger trees may be somewhat variable, however
[35].  In some areas grazing should be deferred for a time to allow for
sufficient buildup of fuels [71].  Oneseed juniper does not survive in
grasslands where fires occur frequently [83].

Fire may be used in pinyon-juniper woodlands in which oneseed juniper is
well represented when weather conditions are favorable and sufficient
fuels are present.  Dense stands of approximately 400 or more trees per
acre, with a flammable understory, are most suitable for broadcast
burning [76].  In areas with a past history of heavy grazing where
little fuels remain and few residual grasses occur, burning may be
difficult and ineffective.  Burns tend to be most successful when
carried out in June when temperatures are high and the humidity low
[4,61].  Unfortunately, the risk of escape may be great during this time
period [4], and the window for burning very narrow [61].

Related categories for Species: Juniperus monosperma | Oneseed Juniper