More info for the terms:
adventitious,
cactus,
caliche,
climax,
codominant,
competition,
cover,
density,
fire management,
fire regime,
forest,
frequency,
fuel,
grassland,
herb,
litter,
natural,
phanerophyte,
presence,
root crown,
seed,
series,
severity,
shrub,
shrubs,
succession,
top-killThe scientfic name of triangle bur ragweed is Ambrosia deltoidea (Torr.) Payne [
24].
It is a member of the aster family (Asteraceae). There are no recognized subspecies,
varieties, or forms.
LIFE FORM: Shrub
FEDERAL LEGAL STATUS: No special status
OTHER STATUS: NO-ENTRY
DISTRIBUTION AND OCCURRENCE
SPECIES: Ambrosia deltoidea
GENERAL DISTRIBUTION: Triangle bur ragweed occurs throughout much of the Sonoran Desert. It
extends southward from southwestern Arizona into Sonora and Baja
California, Mexico [
2,
3,
16,
24,
27].
Distribution of triangle bur ragweed in Arizona. Map courtesy of USDA, NRCS. 2018. The
PLANTS Database.
National Plant Data Team, Greensboro, NC [2018, June 28] [
41].
ECOSYSTEMS: FRES30 Desert shrub
FRES40 Desert grasslands
STATES: AZ MEXICO
BLM PHYSIOGRAPHIC REGIONS: 7 Lower Basin and Range
12 Colorado Plateau
KUCHLER PLANT ASSOCIATIONS: K042 Creosotebush - bursage
K043 Paloverde - cactus shrub
SAF COVER TYPES: 242 Mesquite
SRM (RANGELAND) COVER TYPES:
506 Creosotebush-bursage
508 Creosotebush-tarbush
HABITAT TYPES AND PLANT COMMUNITIES: Triangle bur ragweed is a dominant or codominant member of the Arizona
Upland Subdivision of the Sonoran Desert [
5,
8,
16]. Although it mostly
occurs in the ecotone between upper and lower bajadas, it also grows on
upper bajadas, in lowland communities dominated by creosotebush (Larrea
tridentata), and in desert grassland communities [
3,
4,
10,
16,
33].
In the ecotone between upper and lower bajadas, characterized by steep,
gravelly slopes, triangle bur ragweed occurs in a paloverde (Cercidium
spp.)-cacti-mixed scrub series and the desert scrub community type.
Associated species include yellow paloverde (C. microphyllum), saguaro
(Carnegiea gigantea), condalia (Condalia lycioides), ocotillo
(Fouquieria splendens), jatropha (Jatropha cardiophylla), and prickly
pear (Opuntia spp.) [
3,
8,
16].
On upper bajadas, triangle bur ragweed is codominant with jojoba (Simmondsia
chinensis), yellow paloverde, mesquite (Prosopis juliflora), and
ironwood (Olneya tesota) [
4].
In desert grassland communities that have been overgrazed, triangle
bursage can be found among other invading perennial shrubs including
corvillea (Corvillea tridentata), yellow paloverde, jojoba, ocotillo,
wolfberry (Lycium spp.), acacia (Acacia spp.), canotia (Canotia
holacantha), velvet mesquite (Prosopis juliflora var. velutina), and
saguaro [
33].
Publications listing triangle bur ragweed as a dominant or codominant
species include:
The Natural Vegetation of Arizona [
19]
Sonoran Desertscrub [
32]
Vegetation of the Santa Catalina Mountains: community types and
dynamics [
20]
Other species associated with triangle bur ragweed but not previously
mentioned are brittle bush (Encelia farinosa), false-mesquite
(Calliandra eriophylla), Berlandier wolfberry (Lycium berlandieri),
hedgehog cactus (Echinocereus engelmanii), ferocactus (Ferocactus
acanthodes), and white ratany (Krameria grayi).
MANAGEMENT CONSIDERATIONS
SPECIES: Ambrosia deltoidea
IMPORTANCE TO LIVESTOCK AND WILDLIFE: According to Stubbendieck and others [
28], triangle bur ragweed is
worthless as forage for livestock.
PALATABILITY: Triangle bur ragweed is unpalatable [
31]. McAuliffe and others [
43] report that
it is highly unpalatable to mammalian herbivores.
NUTRITIONAL VALUE: NO-ENTRY
COVER VALUE: NO-ENTRY
VALUE FOR REHABILITATION OF DISTURBED SITES: Triangle bur ragweed may stabilize critical areas such as surface-mined
lands in arid regions. It can be established by direct seeding or with
containerized plants [
30].
OTHER USES AND VALUES: The paloverde/triangle bur ragweed community is an aesthetically attractive
plant community, and it is often preserved as a form of landscaping when
urban development occurs [
20].
OTHER MANAGEMENT CONSIDERATIONS: Domestic grazing has caused a decrease in grasses and subsequent lack of
fuel for burning in the Sonoran Desert. As a result, bursage (Ambrosia
spp.) has increased in the Sonoran Desert [
2]. During a 30-year period
of protection from grazing, triangle bur ragweed decreased while perennial
grasses and palatable shrubs increased [
1]. Hessing and Johnson [
11]
found that removing woody plants, including triangle bur ragweed,
contributed to greater herb growth.
Because of its dense, low-lying canopy, triangle bur ragweed may protect the
seedlings of other species from herbivory. McAuliffe [
17] found that
rabbits consumed a greater proportion of seedlings in the open than
under triangle bur ragweed.
Triangle bur ragweed is the principal nurse plant for saguaro at Organ Pipe
National Monument. Its shade reduces maximum soil surface temperatures,
and it also provides a microhabitat with elevated soil nitrogen levels
[
9].
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Ambrosia deltoidea
GENERAL BOTANICAL CHARACTERISTICS: Triangle bur ragweed is a native, drought-deciduous, microphyllous shrub
growing up to 1.65 feet (50 cm) tall [24, 29]. Innumerable slender and
brittle branches spring up from the base forming a compact, roughly
hemispherical crown [27, 35]. Mature triangle bur ragweed crowns contain
many dead branches which are shed only as a result of weathering [
27].
The branches and young leaves of triangle bur ragweed are tomentulose and
resinous. Leaves become glabrous above with age. Leaf length is 0.6 to
0.8 inches (1.5-2 cm) or smaller [
24,
27].
Staminate heads are borne terminally. Two-flowered, pistillate
involucres are clustered below the staminate spikes or on lateral
branches. They produce globose, spiny achenes [
24,
27].
Triangle bur ragweed possesses one long taproot with well-developed laterals
[
35]. Triangle bur ragweed roots are slender, brittle, and longitudinally
ridged with cork [
6]. They are confined to the soil above the caliche
hardpan--about 8 to 16 inches (20-40 cm) deep [
6,
35]. Besides roots
arising from the main root, Cannon [
6] found 50 adventitious roots about
0.12 inches (3 mm) in diameter which arose from the root crown, growing
horizontally. Filamentous rootlets formed on many roots of triangle
bursage after the soil had been moistened by rains, but such rootlets
were short lived [
6].
Triangle bur ragweed is relatively short lived for a desert shrub. It has
an observed longevity of about 50 years [
10,
27].
RAUNKIAER LIFE FORM: Phanerophyte
REGENERATION PROCESSES: Triangle bur ragweed reproduces sexually. Seed is produced abundantly, and
seedlings establish in open space. In the Sonoran Desert, the relative
abundance of triangle bur ragweed seedlings was some 45 times the density of
mature triangle bur ragweed plants. The density of mature triangle bur ragweed
was similar to that of mature creosotebush, but 1,001 triangle bur ragweed
seedlings were counted while only 124 creosotebush seedlings were found
[
17].
Triangle bur ragweed seeds are spiny and are probably dispersed by mammals.
One study reports that triangle bur ragweed has very limited ability to
sprout after top-kill [
18]. No other research describes the ability of
triangle bur ragweed to sprout.
Triangle bur ragweed reproduces from cuttings with the application of auxin
[
15].
SITE CHARACTERISTICS: Triangle bur ragweed commonly grows in open spaces [
17] on pediments, upper
bajada surfaces, and basin floors on a variety of substrates including
volcanic, granitic, metamorphic, alluvial, and caliche soils. There was
no significant difference in cover of triangle bur ragweed among volcanic,
granitic, metamorphic, and alluvial substrates [
21].
Triangle bur ragweed is a frequent dominant on gravel outwashes, bajadas,
and the ecotone between upper and lower bajadas [
3,
17,
35]. Triangle
bursage occurs almost entirely on very coarse soils that are relatively
uniform in composition with little differentiation into horizons
[
3,
14,
15], although it occurs rarely on sand [
27]. Precipitation
percolates rapidly through the soil and drains quickly away along the
underlying caliche layer [
1,
35].
Rainfall averages 4 to 12 inches (100-300 mm) annually with a bimodal
distribution [
16,
25]. Temperatures at Organ Pipe National Monument and
elsewhere in the Sonoran Desert fluctuate daily and seasonally. The
mean frost frequency at the monument from 1956 to 1985 was 17 frosts per
year (standard deviation=7, range=5-34) [
21].
Parker [
22] studied the soil characteristics of sites dominated by
triangle bur ragweed at Organ Pipe National Monument. Overall, triangle
bursage was most abundant on flat terrain, but its cover was reduced on
the lower bajadas and in the western portion of the Monument where pH
was relatively high [
22]. In the Ajo Mountains on south-facing slopes,
sites had low pH and high available magnesium. In the Blanco Mountains,
Senita Basin, and Quitobaquito Hills, available magnesium was low. In
the Bates Mountains, Puerto Blanco Mountains, lower elevations of the
Ajo Mountains, and flats in Senita Basin, triangle bur ragweed grew on
north-facing slopes in volcanic soil. In the Sonoyta Mountains,
triangle bur ragweed grew on northwest- to northeast-facing slopes. Leitner
[
14] found that triangle bur ragweed preferred the cooler, more humid
conditions of north-facing slopes at Punta Cirio, Sonora, Mexico,
although it occurred on both north- and south-facing slopes. Triangle
bursage grows from 1,000 to 3,000 feet (300-900 m) [
13].
SUCCESSIONAL STATUS: Triangle bur ragweed is often the first plant to occupy an open area.
Recruitment of other species rarely occurs in the open. Once
established, triangle bur ragweed acts as a nurse plant for other species,
providing improved microhabitat and protection from herbivory [
17,
9].
Most mature triangle bur ragweed plants have an associated perennial.
Eighty-two out of 103 triangle bur ragweed plants lacking associated
perennials were small (and presumably young)--2 inches (5 cm) or less in
root crown diameter. Only 2 of 101 triangle bur ragweed plants that had
other perennials associated with them had basal diameters of 2 inches (5
cm) or less [
17].
Succession in the desert is difficult to characterize. Although changes
in relative abundances of species may occur, plants rarely disappear
from the ecosystem altogether because severe disturbance is usually
lacking [
17]. McAuliffe [
17] described changes in desert vegetation in
terms of community dynamics instead of succession. For instance, in
communities codominated by triangle bur ragweed, triangle bur ragweed colonizes
open space and acts as a nurse plant for other perennial shrubs. Some
larger, presumably older individuals within the population bear no
evidence of former associations with triangle bur ragweed, probably because
they have outlived it. Triangle bur ragweed continues to colonize other
open space. Relative abundance of species may be altered, but triangle
bursage presence is maintained [
17].
Triangle bur ragweed is known to establish on overgrazed desert grasslands.
Tueller [
31] suggested that partial or complete protection from grazing
on triangle bur ragweed-invaded rangeland will promote secondary succession.
Secondary succession results in the establishment of climax grasses and
palatable shrubs and a decrease in unpalatable shrubs such as triangle
bursage.
When growing among creosotebush and jumping cholla (Opuntia fulgida),
triangle bur ragweed occupies a distinct root zone so interspecific
competition is minimized [
35]. In one study, no roots of neighboring
plants grew near triangle bur ragweed roots [
6].
SEASONAL DEVELOPMENT: Most new leaves on triangle bur ragweed develop and mature during the winter
and early spring [
29]. Triangle bur ragweed flowers from February to July
[
33]. Seeds are produced after both summer and winter rains [
27].
FIRE ECOLOGY
SPECIES: Ambrosia deltoidea
FIRE ECOLOGY OR ADAPTATIONS: Because triangle bur ragweed establishes in open spaces, it survives fires
that burn with a mosaic pattern [
26].
Although triangle bur ragweed seedlings establish after fire, the literature
does not mention whether the seed originates on- or off-site.
Fires occur frequently in the desert grassland at the eastern margin of
the Sonoran Desert. Fires in the desert proper, however, are infrequent
and generally of low severity because production of annual and perennial
herbs seldom provides a fuel load capable of sustaining fire [
18].
Fires occur occasionally in the Sonoran Desert, mostly in the Arizona
Upland where the biannual rainfall produces relatively lush rangeland
[
23,
26]. Following a moist year, the desert floor is covered with
sufficient annual plant fuel and litter to carry a fire [
23]. When
winter annuals thrive, fire is more likely [
2,
17]. Exotic annuals may
be more productive than native species and fuel more frequent, more
severe fires [
2].
FIRE REGIMES: Find fire regime information for the plant communities in which this
species may occur by entering the species name in the
FEIS home page under
"Find FIRE REGIMES".
POSTFIRE REGENERATION STRATEGY: NO-ENTRY
FIRE EFFECTS
SPECIES: Ambrosia deltoidea
IMMEDIATE FIRE EFFECT ON PLANT: Triangle bur ragweed 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 bur ragweed sprout after fire.
One study found 1 percent of top-killed triangle bur ragweed sprouting 4
years after a fire [
18]. No other research describes the ability of
triangle bur ragweed to sprout.
Triangle bur ragweed produces a large amount of seed, and seedlings
establish after fire. Following fires that occurred in 1974 in
south-central Arizona, no triangle bur ragweed sprouted, but several
survived in unburned patches. Density of triangle bur ragweed 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 bur ragweed [
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 bur ragweed, 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 bur ragweed
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 bur ragweed, 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 bur ragweed 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 bur ragweed 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 bur ragweed was 92 percent. By 1981, only 1 percent of top-killed
triangle bur ragweed 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].
FIRE CASE STUDIES
SPECIES: Ambrosia deltoidea
