SPECIES: Populus fremontii


Populus fremontii: INTRODUCTORY

INTRODUCTORY

SPECIES: Populus fremontii
AUTHORSHIP AND CITATION:
Taylor, Jennifer L. 2000. Populus fremontii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

ABBREVIATION:
POPFRE

SYNONYMS:
Populus fremontii var. mesetae (Eckenwalder) Little [108]
     = P. f. ssp. mestae Eckenwalder [82,95,96]
Populus fremontii var. pubescens Sarg. [97]
     = P. f. ssp. fremontii [96]

NRCS PLANT CODE [155]:
POFR2
POFR3
POFRM

COMMON NAMES:
Fremont cottonwood
Arizona cottonwood
Alamo cottonwood


TAXONOMY:
The currently accepted scientific name of Fremont cottonwood is Populus fremontii S. Wats. (Salicaceae) [82,95,96,97,162].

Recognized infrataxa are as follows:

Populus fremontii ssp. fremontii Wats.    Fremont cottonwood [49,82,96]
Populus fremontii ssp. mesetae Eckenwalder    meseta cottonwood [82,95,96]

Fremont cottonwood hybridizes with narrowleaf cottonwood (P. angustifolia) to produce P. × hinkleyana Correll [45,94,108] and with black cottonwood (P. trichocarpa) to produce P. × parryi Sarg. [45,108].  In California, where the ranges of black and Fremont cottonwood overlap, the 2 species are reported to occur together without hybridization [86].

LIFE FORM:
Tree

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
In Texas, the Fremont cottonwood-Goodding willow (Salix gooddingii) Series is listed as "very rare and local throughout range or found locally in restricted range, 21 to 100 occurrences (threatened throughout range)" and "rare or uncommon, 21 to 100 occurrences" [151].


DISTRIBUTION AND OCCURRENCE

SPECIES: Populus fremontii
GENERAL DISTRIBUTION:

Fremont cottonwood occurs in riparian habitats from western Texas west through New Mexico, Arizona, and California, northward into Nevada and Utah [49,82,92,97,104,108,120,128,139,162]. It also occurs in the Sonoran and Chihuahuan deserts of Mexico [88,128]. The Natural Resource Conservation Service's PLANTS database provides a distributional map of Fremont cottonwood and its infrataxa in the United States. Distribution by subspecies is as follows [73,82,108,162]:

Populus fremontii ssp. fremontii --- southwestern New Mexico westward through Arizona and California, extending north into southern and western Nevada, and southern and eastern Utah

P. f. ssp. mesetae --- southwestern and Trans-Pecos Texas to southwestern New Mexico and Arizona and extending south on the Central Plateau into northern Mexico

Fremont cottonwood does not occur in Colorado. Cottonwoods previously misidentified there as Fremont cottonwood have been reassigned as Rio Grande cottonwood (Populus deltoides var. wislizeni) [160,161].

ECOSYSTEMS [64]:

FRES29 Sagebrush
FRES28 Western hardwoods
FRES30 Desert shrub
FRES35 Pinyon-juniper
FRES34 Chaparral-mountain shrub
FRES40 Desert grasslands

STATES:

AZ CA NV NM TX UT
MEXICO


BLM PHYSIOGRAPHIC REGIONS [20]:

3 Southern Pacific Border
4 Sierra Mountains
6 Upper Basin and Range
7 Lower Basin and Range
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains

KUCHLER PLANT ASSOCIATIONS [101]:

K023 Juniper-pinyon woodland
K027 Mesquite bosques
K030 California oakwoods
K031 Oak-juniper woodland
K032 Transition between K031 and K037
K037 Mountain-mahogany-oak scrub
K038 Great Basin sagebrush
K039 Blackbrush
K040 Saltbush-greasewood
K041 Creosotebush
K042 Creosotebush-bursage
K051 Wheatgrass-bluegrass
K055 Sagebrush steppe
K057 Galleta-threeawn shrubsteppe

SAF COVER TYPES [55]:

68 Mesquite
222 Black cottonwood-willow
235 Cottonwood-willow
239 Pinyon-juniper
240 Arizona cypress
242 Mesquite
255 California coast live oak

SRM (RANGELAND) COVER TYPES [140]:

202 Coast live oak woodland
203 Riparian woodland
211 Creosote bush scrub
212 Blackbush
303 Bluebunch wheatgrass-western wheatgrass
401 Basin big sagebrush
412 Juniper-pinyon woodland
413 Gambel oak
422 Riparian
501 Saltbush-greasewood
503 Arizona chaparral
504 Juniper-pinyon pine woodland
509 Transition between K031 and K037

HABITAT TYPES AND PLANT COMMUNITIES:

Fremont cottonwood can occur in pure stands but more often grows in association with willows (Salix spp.), other trees, and shrubs [26,49].  Groves of cottonwoods were used as an indicator of water, especially in low desert areas, during the early exploration of the western United States [104].  Historically, Fremont cottonwood dominated many of the riparian woodlands of the Central Valley of California [86].

Published classification systems listing varieties of Fremont cottonwood as indicator species or as dominant components of community types or plant associations are listed below.

Community ecology and distribution of California hardwood forests and woodlands [12]
Forest and woodland habitat types (plant associations) of Arizona south of Mogollon Rim and southwestern New Mexico [16]
Vegetation and soils of the Churchill Canyon Watershed [21]
Flora and vegetation of the Rincon Mountains [23]
Southwestern wetlands - their classification and characteristics [30]
Association types in the North Coast Ranges of California [38]
Riparian vegetation and flora of the Sacramento Valley [39]
A framework for plant community classification and conservation in Texas [42]
New Mexico vegetation: past, present, and future [43]
Classification of riparian vegetation [44]
Vegetation and community types of the Chihuahuan Desert [81]
Preliminary descriptions of the terrestrial natural communities of California [84]
Vegetation types of the San Bernardino Mountains [87]
Preliminary classification for the coniferous forest and woodland series of Arizona and New Mexico [107]
Biotic communities in the sub-Mogollon region of the inland Southwest [109]
Wetlands [115]
A series vegetation classification for Region 3 [119]
Classification of riparian habitat in the Southwest [124]
A survey of riparian forest flora and fauna in California [133]
Desert grassland (riparian community in desert grassland region) [138]
Riparian forest and scrubland community types of Arizona and New Mexico [148]
Riparian habitat classification in the southwestern United States [150]
Plant communities of Texas (Series level) [151]
Vegetation of the Huachuca Mountains, Arizona [158]
Vegetation of the Santa Catalina Mountains, Arizona [163]

In Nevada, Fremont cottonwood is listed as a community codominant with Goodding willow, with a basin big sagebrush (Artemisia tridentata var. tridentata)-cheatgrass (Bromus tectorum) understory [21].  

In California riparian woodlands, Fremont cottonwood is associated with northern California walnut (Juglans hindsii) [19,80,112], coast live oak (Quercus agrifolia) [14], valley oak (Q. lobata) [19,54,80,110], Goodding willow [28,65], sandbar willow (Salix exigua) [28], arroyo willow (S. lasiolepis) [28,121], red willow (S. laevigata) [111,112,121], Oregon ash (Fraxinus latifolia) [19,110,111,112], green ash (F. pennsylvanica) [65], white alder (Alnus rhombifolia) [14,110,111,112,118], California sycamore (Platanus racemosa) [14,19,67,110,118,125], box elder (Acer negundo) [19,67,110], bigleaf maple (A. macrophyllum) [118], red alder (Alnus rubra) [67], Arizona alder (A. oblongifolia) [80], Tecate cypress (Cupressus forbesii) [7], Russian-olive (Elaeagnus angustifolia) [28], and saltcedar (Tamarix ramosissima) [28]. Understory species include Oregon false goldenaster (Heterotheca oregona var. oregona), California wild grape (Vitis californica) [19,80], Douglas' sagewort (Artemisia douglasiana) [19,80], Pacific dewberry (Rubus vitifolius) [19,80], lemonade sumac (Rhus integrifolia), woolly bluecurls (Trichostema lanatum), wedgeleaf ceanothus (Ceanothus cuneatus), toyon (Heteromeles arbutifolia), bush rue (Cneoridium dumosum), hollyleaf cherry (Prunus ilicifolia) [7], rubber rabbitbrush (Chrysothamnus nauseosus), Wood's rose (Rosa woodsii), Torrey's saltbush (Atriplex torreyi) [28], common elderberry (Sambucus nigra ssp. canadensis), trailing blackberry (Rubus ursinus) [121], California wildrose (Rosa californica) [19], and stretchberry (Forestiera pubescens) [28].  

In New Mexico riparian woodlands, Fremont cottonwood is listed as a codominant with Goodding willow, sandbar willow, box elder, Arizona walnut (Juglans major), Arizona sycamore (Platanus wrightii) [27,52,54,89], Arizona white oak (Quercus arizonica), Emory oak (Q. emoryi) [109], green ash, velvet mesquite (Prosopis velutina), alligator juniper (Juniperus deppeana), catclaw acacia (Acacia greggii), saltcedar, and box elder [27]. Understory species include stretchberry, desert false indigo (Amorpha fruticosa), mule's fat (Baccharis salicifolia),  screwbean mesquite (Prosopis pubescens), arrowweed (Pluchea sericea) [52,56,89], and western soapberry (Sapindus saponaria var. drummondii) [27].

Riparian forests in Arizona consist of Fremont cottonwood, black cottonwood [121], Goodding willow [27,75,83,88], velvet ash (Fraxinus velutina) [83,113], Arizona sycamore [27,83,88,92,113], Arizona walnut [27,88,92,113,116], box elder [27,116], green ash [27,88], true pinyon (Pinus edulis) [61], Emory oak, Ajo Mountain scrub oak (Quercus ajoensis), Bonpland's willow (S. bonplandiana) [109], alligator juniper, catclaw acacia, velvet mesquite [27], western honey mesquite, screwbean mesquite, Athel tamarisk (Tamarix aphylla), saltcedar, and arroweed [74,75,88]. Understory species include annual rabbitsfoot grass (Polypogon monspeliensis), tree tobacco (Nicotiana glauca), Cleveland's tobacco (N. clevelandii), pricklyburr (Datura inoxia), giant Spanish needle (Palafoxia arida var. gigantea), cattle saltbush (Atriplex polycarpa), big saltbrush (A. lentiformis), fourwing saltbush (A. canescens), small coastal germander (Teucrium cubense var. densum), coyote gourd (Cucurbita palmata), Thurber's sandpaper plant (Petalonyx thurberi), spiny chloracantha (Chloracantha spinosa) [75], mule's fat [75,88] and western soapberry [27].

In Utah, Fremont cottonwood, saltcedar, sandbar willow, peachleaf willow (Salix amygdaloides), Russian-olive, saltgrass (Distichlis spicata), and whorl-leaf watermilfoil (Myriophyllum verticillatum) make up the lowland woody community around Utah Lake. The understory consists of grasses and annuals or aquatic herbs  [29]. Fremont cottonwood also occurs in Utah with Utah juniper (Juniperus osteosperma) [83], water birch (Betula occidentalis), thinleaf alder (Alnus incana ssp. tenuifolia), red-osier dogwood (Cornus sericea), Gambel oak, (Q. gambelii), box elder, bigtooth maple (A. grandidentatum), narrowleaf cottonwood (Populus angustifolia), and lanceleaf cottonwood (P. ×  acuminata). Understory species include chokecherry (Prunus virginiana), Wood's rose (Rosa woodsii), thimbleberry (Rubus parviflorus), Saskatoon serviceberry (Amelanchier alnifolia), northern black currant (Ribes hudsonianum), golden currant (R. aureum), blue wildrye (Elymus glaucus), fernleaf biscuitroot (Lomatium dissectum), Oregon-grape (Mahonia repens), sweetcicely (Osmorhiza berteroi), Canada bluegrass (Poa compressa), Kentucky bluegrass (P. pratensis), starry Solomon-seal (Maianthemum stellatum), feathery false lily-of-the-valley (M. racemosum ssp. racemosum), and Canada goldenrod (Solidago canadensis) [51].  


MANAGEMENT CONSIDERATIONS

SPECIES: Populus fremontii
WOOD PRODUCTS VALUE:

Fremont cottonwood is moderately light in weight and color, uniform in texture, and has a fairly straight grain.  The wood is relatively soft and weak, but its strength-to-weight ratio is high [13,45].  The untreated wood of all cottonwoods (Populus spp.) has low resistance to decay when in contact with the ground [45].

Primary wood products include lumber, veneer, and pulpwood [13,92,103]. Finished products include crates and boxes for food storage and pallets [13,88].  The wood is used locally in the southwestern United States for fenceposts and firewood [13,18,88,92,103] and is preferred for kilning bricks in Arizona [10].

The wood shavings from Fremont cottonwood are used in livestock bedding, mulches, packing material, and insulation [13,88].

IMPORTANCE TO LIVESTOCK AND WILDLIFE:

Riparian habitats occupied by Fremont cottonwood add diversity to the arid and semiarid environments of the American Southwest [91,127].  Fremont cottonwood and Fremont cottonwood-willow stands provide valuable habitat for many species of birds and other wildlife in Arizona, California, Colorado, Nevada, New Mexico, and Texas.  Species such as golden eagle, Swainson's hawk, red-tailed hawk, and Bell's vireo build their nests in the crown [17,72,131,137], while various cavity-nesting birds nest in the dead trunks and limbs of Fremont cottonwood [60,65,79].  In Nevada, Fremont cottonwood sites are breeding areas for great blue heron [66].  Birds known to have a high affinity for Fremont cottonwood stands include hawks (gray, black, zone-tailed, red-tailed) [61,89,131], bald eagle [74], and woodpeckers (downy and ladder-backed) [52].  Fremont cottonwood communities also provide cover, nesting, and foraging habitats for other birds [11,52,53,60,89,90,102,109,130], ringtail [19], squirrels, beavers [103], and other rodents [3,109].  

In California, Fremont cottonwood-willow and willow communities provide the greatest overstory canopy coverage of any desert riparian vegetation type.  Consequently, they provide a wider range of perches, nest sites, and foraging substrates; they are known to support roughly 2 to 5 times more breeding bird species than vegetation types with less overstory [54].  More than 50% of the bird species breeding in the homogeneous Fremont cottonwood stands along the Verde River in Arizona depended exclusively on this vegetation type [37].

Fremont cottonwood communities provide shade for domestic livestock, provide a food source for beavers, elk, deer, and squirrels, and help maintain mesic habitats for upland amphibian and reptile species in the Sonoran Desert [28,94,103].

PALATABILITY:

The palatability of Fremont cottonwood to domestic livestock and wildlife has been rated as follows [47,135]:

CA UT
Cattle poor fair
Domestic sheep poor to fair fair
Horses useless poor
Mule deer poor to fair ----
White-tailed deer poor to fair ----


This species has been called "sweet cottonwood" because horses eat the inner bark [104].

NUTRITIONAL VALUE:

Fremont cottonwood is rated as fair for both energy and protein content. The nutritional value of Fremont cottonwood for wildlife has been rated as follows [47]:

  UT
Pronghorn fair
Elk fair
Mule deer fair
Small mammal fair
Small non-game bird fair
Upland game bird poor
Waterfowl fair


COVER VALUE:

The value of Fremont cottonwood as cover for domestic animals and wildlife has been rated as follows [47]:

  UT
Pronghorn poor
Elk fair
Mule deer fair
White-tailed deer fair
Small mammals good
Small non-game birds good
Upland game birds fair
Waterfowl fair


VALUE FOR REHABILITATION OF DISTURBED SITES:

Fremont cottonwood's rapid early growth makes it well suited for revegetating riparian sites [47,126].  It has been successfully planted in many riparian rehabilitation projects [36,82,92,126,164] and is recommended for revegetating areas in the Southwest where invasive saltcedar has been removed [88,99].  Fremont cottonwood, along with willows and other native plants, has also been used to restore, enhance, or create bird habitat in riparian areas [46,63].

Fremont cottonwood can be successfully planted in chaparral-mountain shrub, big sagebrush, pinyon-juniper, and desert shrub communities where there is sufficient moisture [126,127].  It can grow on disturbed sites removed from groundwater as long as good moisture is available in the spring, but on such sites it will exhibit a shrubby growth form [26].  Plants readily establish from nursery-grown containerized stock and rooted cuttings [36].  Growth of seedlings is rapid on favorable sites, and the roots of established seedlings are effective stabilizers of alluvial soil [47,82,126].

OTHER USES AND VALUES:

Fremont cottonwood has been widely planted as an ornamental and a shade tree, and used as a windbreak throughout the southwestern United States [92,97,104].  

Native Americans ate the inner bark of Fremont cottonwood for antiscorbutic [18,100]. The bark and leaves were used to make poultices to relieve swelling, treat cuts, cure headaches, and wash broken limbs, and to treat saddle sores and swollen legs of horses [18,166].  The twigs were used by the Pima for basket materials [100], and Cahuilla tribes used the wood for mortars and tools [18]. In northern Mexico,  small industries utilize the wood to make bowls and small statues [88]. Fremont cottonwoods were used by the Pueblo tribes for drums and were the preferred wood species for Quechan cremations [114]

OTHER MANAGEMENT CONSIDERATIONS:

Fremont cottonwood communities are declining as a result of human activities.  A 1914 survey along the Gila River of Arizona showed 1,584 acres (641 ha) - 33% of the survey area -  was occupied by Fremont and other cottonwoods. Fremont cottonwood was the most widespread riparian community of the Southwest. A 1944 survey of the same area showed on 160 acres (65 ha) so occupied; by 1964, Fremont cottonwood was no longer a cover type: only a few scattered trees remained [154]. 

Cattle grazing prevents successful regeneration of Fremont cottonwood seedlings [8], and exclusion of grazing in Fremont cottonwood riparian zones has been recommended [68,134,137,159].  However, Asplund and Gooch [8] maintain that the impacts of grazing are unclear and that recruitment is affected more by flooding and the creation of suitable habitat than by grazing pressure.

Fremont cottonwoods and other components of riparian streamside stands are important in erosion control and fisheries production; they stabilize banks and provide for thermal cover and debris recruitment [77,126]. If possible, buffer strips of these woodlands should be maintained upland from streams, rivers, lakes, and ponds  [78].  

Regulating stream flows to mimic the natural flood regime (duration, peak flow, and timing) could be used to establish Fremont cottonwood and decrease saltcedar [144].  Decreased flooding, stabilized flows, introduction of exotics (saltcedar, Russian-olive, and leafy spurge (Euphorbia esula)), water diversion due to damming and agricultural use, and stream channelization have led to drought stress and the subsequent decrease in Fremont cottonwood and associated riparian species [26,36].  The loss of Fremont cottonwoods could mean the loss of the riparian woodland ecosystem [26]. See black cottonwood for further information on the effects of watercourse damming and stream diversion on Fremont and other cottonwoods.


BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Populus fremontii
GENERAL BOTANICAL CHARACTERISTICS:

Fremont cottonwood is a native, deciduous hardwood tree [1,11,13,24,35,49,50,75] that ranges from 19.7 to 112 feet (6-34 m) [22,48,49,72,89,90,97,128,148,162] in height and has a broad, rounded or cylindrical crown [120,123].  The trunk diameter at breast height ranges from 19.7 inches to 12.8 feet (0.5-3.9 m) [22,48,49,61,72,90,97,128,148,162]. 

The bark is smooth on the trunk, twigs, and branches of young trees, but trunk bark becomes deeply furrowed at maturity [48,49,97,123,162]. Fremont cottonwood is dioecious [26,49,50], with small (approximately 0.04 inch (1 mm) in length), fragile seeds [58]. The catkins range from 1.25 to 3.25 inches (3.75-8.26 cm) for the staminate and 4 to 5 inches (10.16-12.70 cm) for the pistillate [156]. Fremont cottonwood is inundation and siltation tolerant [26].  This tree has a lifespan of more than 130 years [26].

RAUNKIAER LIFE FORM [129]:

Phanerophyte 

REGENERATION PROCESSES:

Fremont cottonwood is a fast-growing [88,92] obligate seeder [28], and reproduction primarily comes from establishment of  wind-borne seeds [31,68,69,88]. Asexual regeneration occurs following crown and branch damage, uprooting, or flood-related disturbance [26]. Regeneration is tied to the annual runoff regime of the area [28].  Mortality of both saplings and mature trees can be great following major flooding events, but recruitment takes place on the newly created microsites [26].

Sexual reproduction: Fremont cottonwood reaches reproductive maturity between 5 and 10 years of age [26]. Flowers are produced early in the spring and are entirely wind pollinated [50,58].  Large crops of seed are produced in the spring; the seeds have a cottony tuft of trichomes that enables them to float long distances in the wind [58] and on water.  Seeds may not be fully viable when dispersed [26]. Seeds typically germinate within 24 to 48 hours on suitable seedbeds, but seeds may remain viable for 1 to 5 weeks after dispersal [26,57,58]. Viability is lost if a suitable microsite is not found within 2 or 3 days of seed becoming wet [26]. 

Suitable recruitment sites are created by the floodwaters of spring run-off.  Seeds germinate almost exclusively on the freshly deposited, exposed alluvium left by receding floodwaters. The availability of this type of moist, exposed habitat during and 6 to 8 weeks after seed dispersal is crucial because of the limited period of seed viability [88].  Abandoned secondary and tertiary stream channels are valuable recruitment sites because subsurface water is available and some protection from scouring is provided [8].  

Vegetative regeneration: Cottonwood species (Populus spp.) reproduce vegetatively by sprouting from stumps and root crowns, by forming suckers (adventitious shoots on roots) [2,26,49,50,79], and from stem cuttings [92].  Root suckering has been observed to be the predominant method of regeneration of Fremont cottonwood in some areas in Utah [91].  Root or bole sprouting often occurs after some injury (uprooting, broken branches) [34].  Sprouting from lateral buds on stems occurs when there is contact with moist alluvial soil [143]. 

Growth: Root growth of young Fremont cottonwood seedlings is very rapid on favorable sites. Average growth rate is 0.16 to 0.47 inch (4-12 mm) [26,143], and a growth rate of 0.5 inch (13.5 mm) per day has been observed over a 4-day period [57].  Because the upper layers of the moist alluvium dry rapidly with the onset of warmer summer temperatures, rapid root growth is essential in order to reach depths where a supply of water is available. Fremont cottonwood is vulnerable to droughts before the roots reach seasonal alluvial water tables [26].  Rooting depths in mature stands are 9.8 to 16.4 feet (3-5 m) [26,166].  

SITE CHARACTERISTICS:

Fremont cottonwood occurs in riparian communities throughout the Southwest and much of California [26,41]. It grows primarily on alluvial soil and on other sites where subsurface water is available during the growing season, such as near water tanks, along irrigation ditches, dry washes, floodplains of major rivers, large perennial streams, springs, and in desert oases [48,49,66,68,69,71,76,112,143,153].  Large, mature trees are generally found close to the main channel, while the seedlings and saplings are located on the widest parts of the floodplain [8,143].    

Fremont cottonwood is found in areas where the annual range of temperatures is 9 to 67 degrees Fahrenheit (-5 to 37 oC) [25,35,40,83,86] and the majority of the annual precipitation occurs during the winter. Mean annual precipitation ranges for Fremont cottonwood are as follows [8,21,25,61,152]:

AZ 12 to 18 inches (305-457 mm)
CA 1 to 4.5 inches (25.4-114.3 mm)
NV 9.2 inches (234 mm)
UT 8 to 11 inches (203-279 mm)

Soils: Fremont cottonwood is found in alluvial valleys, on terraces of floodplains, stabilized gravel bars, and adjacent to disturbed sites (agricultural lands and forest clearings) [8,26,88]. Soil types and structures include well-drained, alluvial, sandy to sandy clay loams with varying degrees of organic matter [29,57], clay or other fine soil and rock deposits [31], coarse, rocky and sterile soils [7], and fine-grained alluvial substrates [143].  It has also been described as fairly salt tolerant (< 1,500 mg/L) [26].

Elevational ranges for Fremont cottonwood are as follows:

P. f. ssp. fremontii   References
AZ 2 to 9,428 feet (0.6-2,857 m)   [8,13,27,49,59,65,88,90,94,98,143,148,149]
CA 0 to 6,500 feet (0-1,981 m)  [7,31]
NM 789 to 9,428 feet (239-2,857 m)  [148,149]
NV 2,162 to 5,460 feet (659-1,664 m)  [9,21]
UT 2,494 to 6,103 feet (760-1,860 m)  [47,51,52,83,92,123,162]
P. f. ssp. mesetae    
TX 2,600 to 4,800 feet (792-1,463 m)  [128]


SUCCESSIONAL STATUS:

Fremont cottonwood is a shade-intolerant pioneer that typically establishes on freshly exposed alluvium, sand or gravel bars, streambanks, or other floodplain sites following winter/spring floods [26,79,80,111,112,143,144]. Communities dominated or codominated by Fremont cottonwood and other cottonwoods (Populus spp.) are naturally maintained by periodic winter and spring floods [31,58,115]. Dams and reservoir systems that change the natural timing and volume of water flow reduce the recruitment and vigor of Fremont cottonwood stands [58]. In the absence of periodic flooding, succession proceeds, and the cottonwoods are eventually replaced by more shade-tolerant species (for example, western honey mesquite) [115]. Flooding and time between floods are the driving successional forces in these communities [93].

Lowe [109] has called Fremont cottonwood associations a "distinctive climax biotic community." According to Johnson [93] Fremont cottonwood is both a "climax" and "pioneer" in Clementsian successional terminology. In Arizona, Asplund and Gooch [8] found that germination and establishment of Fremont cottonwood could take place in the absence of other species. Replacement of species does not occur; therefore, biological succession is not a good descriptor of the interspecific dynamics of these riparian communities [8]. Fremont cottonwood is "considered an important member of the climax riparian vegetation in the Sacramento Valley" of California.  In Utah, Fremont cottonwood occurs in mid-seral successional stages, not climax [79].  

SEASONAL DEVELOPMENT:

In general, Fremont cottonwood 1st flowers early in the spring, before leaf emergence, and finishes by the end of May. Seed drop roughly coincides with the receding of spring floodwaters. Cottonwoods are dormant during the fall. Leaf senescence occurs in late September and abscission in mid-October. General dates for some phenological stages of Fremont cottonwood are as follows [8,26,27,31,58]:

Location Begins flowering Full flower Ends flowering Seeds ripen & disperse
AZ ---- ---- ---- April-June
central AZ ---- Feb 15-March 15 ---- March-April
west-central AZ ---- ---- ---- Feb-March
CA April-May
UT May  May May ----

FIRE ECOLOGY

SPECIES: Populus fremontii
FIRE ECOLOGY OR ADAPTATIONS:

Fire adaptations: Fremont cottonwood sprouts after fire or other injury. Coppice sprouting is the predominant mechanism of vegetative reproduction in most areas. However, root suckering is the predominant method in some areas of Utah [34,70,79,91,145].

Disturbances such as fire may favor seedling regeneration. Fire thins the overstory and surrounding vegetation, allowing light to penetrate, and exposes mineral soil [143].

Fire regimes: Fremont cottonwoods are not fire dependent [145]. Historical fire regimes for Fremont cottonwood-dominated riparian zones bordering drier ecosystems are poorly described [154]. Fire scars are rare on Fremont cottonwood and when found, usually have such extensive heartrot that the tree's fire history cannot be reconstructed [146,147].Wildland fires appear to have been infrequent in riparian communities dominated by Fremont cottonwood, Goodding willow, and mesquite species prior to invasion by saltcedar [34]. Fire regimes for plant communities and ecosystems bordering Fremont cottonwood communities are summarized below. For further information regarding fire regimes and fire ecology of communities and ecosystems where Fremont cottonwood is found, see the `Fire Ecology and Adaptations' section of the FEIS species summary for the plant community or ecosystem dominants listed below.
Community or Ecosystem Dominant Species Fire Return Interval Range (years)
California chaparral Adenostoma and/or Arctostaphylos spp. < 35 to < 100 
sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [33]
basin big sagebrush A. t. var. tridentata 12-43 [136]
saltbush-greasewood Atriplex confertifolia-Sarcobatus vermiculatus <35 to <100 
mountain-mahogany-Gambel oak scrub Cercocarpus ledifolius-Quercus gambelii <35 to <100 
blackbrush Coleogyne ramosissima <35 to <100 
creosotebush Larrea tridentata < 35 to 100
mesquite Prosopis glandulosa < 35 to < 100 
California oakwoods Quercus spp. < 35 
coast live oak Quercus agrifolia <35 to 200 
Arizona cypress Cupressus arizonica < 35 to 200 
pinyon-juniper Pinus-Juniperus spp. < 35 
tamarack Larix laricina 35-200 
California steppe Festuca-Danthonia spp. < 35 
desert grasslands Bouteloua eriopoda and/or Pleuraphis mutica 5-100 
galleta-threeawn shrubsteppe Pleuraphis jamesii-Aristida purpurea < 35 to 100 [33]


POSTFIRE REGENERATION STRATEGY [141]:

Tree with adventitious bud/root crown/soboliferous species root sucker
Initial off-site colonizer (off-site, initial community)


FIRE EFFECTS

SPECIES: Populus fremontii
IMMEDIATE FIRE EFFECT ON PLANT:

Mature Fremont cottonwood trees are  top-killed by moderate fire [2,5,14,15].  The cambium layer is damaged by even low-severity surface fire [143,154].  In California, a severe wildland fire completely consumed the understory vegetation of a Fremont cottonwood community. Fremont cottonwoods that were top-killed by the fire were sprouting vigorously from the root crowns [15].  

PLANT RESPONSE TO FIRE:

Most cottonwoods (Populus spp.) readily coppice following an injury such as fire; Fremont cottonwood sprouts primarily from the bole [34,70,145].  This ability presumably depends on fire severity.  Fremont cottonwood also sprouts from roots [91], but there is no fire-related documentation of this regeneration method.  Sprouting ability of cottonwood species is reported to decline after 25 years of age [62]. See black cottonwood for further information on sprouting response of Fremont and other cottonwoods.

Fremont cottonwood regenerates from off-site seeds if suitable site conditions exist during seed dispersal (see Botanical Characteristics, Regeneration Process).

FIRE MANAGEMENT CONSIDERATIONS:

In the southwestern United States, many riparian areas have been invaded by saltcedar [53]. Saltcedar-dominated communities accumulate fuels more rapidly than Fremont cottonwood-dominated communities and consequently burn about every 10 to 20 years [122,154]. Native vegetation, including Fremont cottonwood, is often absent from these burned areas despite prefire presence.  The native vegetation is usually replaced by the fire-adapted saltcedar [33,99,122].  For the remaining Fremont cottonwood woodlands to survive, saltcedar needs to be removed and replaced with natural vegetation.  Once this is done, a more natural fire regime can be reestablished [99].


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