FIRE EFFECTS
SPECIES: Ambrosia deltoidea | Triangle Bursage 



IMMEDIATE FIRE EFFECT ON PLANT : 
Triangle bursage is usually top-killed or killed by fire [18,26].



DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Burning generally decreases bursage (Ambrosia spp.) cover
[2,7,18,26,34].

It is not clear whether top-killed triangle bursage sprout after fire.
One study found 1 percent of top-killed triangle bursage sprouting 4
years after a fire [18].  No other research describes the ability of
triangle bursage to sprout.

Triangle bursage produces a large amount of seed, and seedlings
establish after fire.  Following fires that occurred in 1974 in
south-central Arizona, no triangle bursage sprouted, but several
survived in unburned patches.  Density of triangle bursage in postfire
year 1 was 275 plants per 1,500 square meters; 3 to 4 years later,
density was 49 plants per 1,500 square meters.  Eighty-two percent of
all seedlings were triangle bursage [26].

Desert fires reduce perennial plant cover, often for several years [26].
In an Upper Sonoran Desert site on the Tonto National Forest, prefire
coverage of perennial plants, including triangle bursage, was 30.7
percent.  Perennial cover immediately after fire was 9.3 percent.  The
physical characteristics of the study site, including soil surface
albedo, microsite maximum and minimum temperatures, and soil water
repellency were not greatly altered [23].

The killed portion of a woody, desert plant such as triangle bursage
usually represents many years of growth.  Repeated fires, even when they
do not kill woody taxa outright, keep them in a juvenile, nonfruiting
stage [12].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
A low-severity lightning fire occured in late June of 1979 in the
Sonoran Desert near Florence, Arizona.  The prefire vegetative community
was typical of the Arizona Upland Subdivision of the Sonoran Desert.
The dominant species were triangle bursage, yellow paloverde,
creosotebush, saguaro, buckhorn cholla (Opuntia acanthocarpa), hedgehog
(Echinocereus fasciculatus), barrel cactus (Ferocactus wislizenii), and
prickly pear (Opuntia phaeacantha).  Small patches of vegetation were
skipped throughout the burn.  With the exception of these skips, nearly
all trees and shrubs were completely top-killed [18].

The density of triangle bursage 19 months after the fire was 540 plants
per hectare, compared to 6,790 plants per hectare in the unburned control
area.  Percent cover of triangle bursage was 0.7 percent in burned areas
and 7.4 percent in control areas.  Ninety-three percent of all triangle
bursage plants in burned areas were top-killed; overall mortality of
triangle bursage was 92 percent.  By 1981, only 1 percent of top-killed
triangle bursage plants were sprouting [18].


FIRE MANAGEMENT CONSIDERATIONS : 
McLaughlin and Bowers [18] hypothesized that two consecutive wet winters
may be required for the development of a fuel load adequate to sustain
fire in the Sonoran Desert.  The first wet winter would result in higher
production of annuals and the addition of large numbers of seeds to the
soil.  The second wet winter would facilitate sprouting of the increased
number of seeds and production of enough annuals to sustain fire.

Native American Hohokam farmers (A.D. 11150-1350) cleared fields,
ditches, and broad patches of the desert by fire.  Hohokam farmers found
that burning could increase the variety of plants available to be
gathered and mammals to be hunted.  The fossil record shows about 40
percent bursage (Ambrosia spp.) pollen in Hohokam times compared with 74
percent in modern times [2].

Desert fires may create potential soil stability problems [23].

Related categories for Species: Ambrosia deltoidea | Triangle Bursage