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Wildlife, Animals, and Plants |
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
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]:
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:
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]:
Related categories for SPECIES: Populus fremontii | Fremont Cottonwood |
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