triangle-leaf bursage

Ambrosia deltoidea

Summary 11

Ambrosia deltoidea is a North American species of flowering plant in the aster family known by the common names triangle bur ragweed, triangle bursage, and triangleleaf bursage.

Description 12

Ambrosia deltoidea is a shrub growing from a taproot with many lateral and adventitious roots. The plant produces many thin branches growing up to about half a meter tall. It generally has many dead branches tangled in the living crown. It is drought-deciduous. The leaves are no more than 2 centimeters long. The branches and new leaves are coated thinly in woolly fibers; the leaves become hairless with age.

The inflorescence is a spike of several staminateflower heads. There are often some pistillate heads just below these, with some pistillate heads borne on lateral branches. The fruit is an achene covered in spines. The achenes are usually dispersed when they stick to animals. The plant has been observed to have a lifespan of about 50 years.

Distribution 12

The plant is native to the Sonoran Desert region of North America, where it can be found in Baja California, Baja California Sur, and Sonora in Mexico, with its distribution extending north into Arizona in the United States.

This shrub grows in desert habitat, such as desert grasslands and shrublands. It is a dominant or codominant species, and one of the most abundant plants, in the Arizona Upland Subdivision of the Sonoran Desert. It may occur in upper and lower bajadas, but it is most often found in the ecotone between them. It can be found in open areas. It grows on steep, rocky slopes alongside cacti such as the saguaro and paloverde such as the yellow paloverde. Other plants in the habitat include condalia, ocotillo, jatropha, and prickly pears. The bursage easily invades grassland that has been overgrazed. Areas protected from grazing have less bursage.

Fire management considerations 13

More info for the terms: association, controlled burn, cover, density, fire management, forbs, forest, fuel, herbaceous, litter, prescribed fire, wildfire

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].

SPECIES: Ambrosia deltoidea
Marshall, K. Anna., compiler. 1994. Effects of prescribed and wildfires
on triangle bur ragweed on the Tonto National Forest, Arizona.
In: Ambrosia deltoidea. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
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Cave, George Harold, III. 1982. Ecological effects of fire in the upper
Sonoran Desert. Tempe, AZ: Arizona State University. 124 p. Thesis.

Patten, Duncan T.; Cave, George H. 1984. Fire temperatures and physical
characteristics of a controlled burn in the upper Sonoran Desert.
Journal of Range Management. 37(3): 277-280. [23].


The study was located in Bulldog Canyon in Tonto National Forest,
Arizona, at 33 degrees 15 minutes north latitude and 111 degrees 33
minutes west longitude.

The prefire vegetative community was typical of the Upper Sonoran Desert
paloverde-cactus-shrub association (Cercidium spp.-Opuntia spp. and
Carnegiea gigantea-Ambrosia spp.).  Plants occupied about one-third of
the total ground cover.  Triangle bur ragweed (A. deltoidea) occupied about
15 percent of the total ground cover.  Annual forbs and grasses in this
association are abundant after winter and heavy summer rains, providing
enough fuel to carry a fire.

At the time of the fire, triangle bur ragweed would have been flowering
and/or fruiting.

Topography is flat except for one small, dry wash bisecting
the site.  The soil is composed of sandy loam argids with a desert
pavement surface.  Elevation at the site is 1,485 feet (450 m).

The burn site is adjacent to an area burned by wildfire on April 26,
1980.  The 1980 wildfire may have been more severe since both 1979 and
1980 were years of above average precipitation, and the standing
herbaceous vegetation was probably relatively lush.  The study compares
the prescribed fire and the wildfire sites.

The fire was ignited on June 12, 1981.  Conditions were typical for
summer months in the Upper Sonoran Desert.  Air temperatures ranged from
104 degrees Fahrenheit (40 deg C) in the shade to 132.8 degrees
Fahrenheit (56 deg C) 0.4 inches (1 cm) above the unshaded soil surface.
Relative humidity remained at 29 percent during the fire.  Mean air
movement for the duration of the fire was low at 0.001 meters per
second.  Mean wind velocity for gusts was 2.75 meters per second.  Mean
soil moisture percent in the upper 2 inches (5 cm) of soil was 0.61
percent in open areas and 0.80 percent in shaded areas.  Litter fuel
averaged 143.3 grams per square meter.

In 1981, 1 year after the wildfire and immediately following the
controlled burning, the density of triangle bur ragweed was greater on the
wildfire site than on the prescribed fire site, mainly because of the
establishment of triangle bur ragweed seedlings on the wildfire site.
Postfire cover measurements were nearly the same.

Triangle bur ragweed density was reduced by 82 percent on the prescribed
fire site immediately after the controlled burning.  The prefire density
of triangle bur ragweed on the prescribed fire site was 6,275 plants per
hectare.  Immediately after the controlled burning, triangle bur ragweed
density was 1,141 plants per hectare.  One year later, triangle bur ragweed
density had not changed significantly.


Uses 12

This plant acts as a nurse plant for other species, providing shade and increased soil nitrogen for young growing plants. It also protects seedlings from herbivory. It is the main nurse plant for saguaro in Organ Pipe National Monument. It also serves as nurse plant for yellow paloverde, ocotillo, and some prickly pear species. Most bursage plants are associated with a perennial plant.

This plant is not palatable to mammals and it is not grazed by livestock.

Airborne allergens from this plant can cause contact dermatitis in humans.

Sources and Credits

  1. (c) Anthony Mendoza, some rights reserved (CC BY-NC-SA),
  2. (c) anonymous, some rights reserved (CC BY-NC-SA),
  3. (c) anonymous, some rights reserved (CC BY-NC-SA),
  4. (c) anonymous, some rights reserved (CC BY-NC-SA),
  5. (c) anonymous, some rights reserved (CC BY-NC-SA),
  6. (c) sea-kangaroo, some rights reserved (CC BY-NC-ND),
  7. (c) sea-kangaroo, some rights reserved (CC BY-NC-ND),
  8. (c) sea-kangaroo, some rights reserved (CC BY-NC-ND),
  9. (c) Bob Miller, some rights reserved (CC BY-NC),
  10. (c) Bob Miller, some rights reserved (CC BY-NC),
  11. Adapted by Jeny Davis from a work by (c) Wikipedia, some rights reserved (CC BY-SA),
  12. (c) Wikipedia, some rights reserved (CC BY-SA),
  13. Adapted by Jeny Davis from a work by Public Domain,

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