Gom and Rood [32] observed copious sprouting 5 months after a severe April
wildfire along the Oldman River
near Lethbridge, Alberta. Newly emerged sprouts were observed by 2 postfire months.
Buried root crowns of stems less than 3.9 inches (10 cm) diameter were found to produce new
adventitious sprouts even when completely burned, sometimes to several centimeters below
the soil surface. Copious sprouting may occur from buried roots of live trunks with all severities of damage [32].
No evaluations of natural postfire establishment through seed are currently
available.
The degree to which narrowleaf cottonwood provides cover for wildlife species is rated as follows [21]:
CO UT WY MT Pronghorn ---- fair poor ---- Elk fair fair fair ---- Mule deer fair good good fair White-tailed deer fair ---- good poor Small mammals good good good ---- Upland game birds poor good good fair Waterfowl ---- fair poor ---- Small nongame birds good good good ---- Narrowleaf cottonwood is a native deciduous tree with a slender crown [45]. It attains heights up to 60 feet (20 m) [91]; trunks can exceed 30 inches (76 cm) in diameter [57]. The bark of narrowleaf cottonwood is smooth when young, becoming furrowed with age [,39]. Narrowleaf cottonwood is dioecious [10,11,24]. Flowers are borne in catkins, with male flowers smaller than female flowers. Seeds are very small and have cotton tufts [11].
Narrowleaf cottonwood is reported as a facultative wetland species tolerant of frequent and prolonged flooding [39]. It is not drought resistant [31] and is extremely vulnerable to drought induced xylem cavitation [88].
A life span of 100 to 200 years is not uncommon [5].
Narrowleaf cottonwood occurs from southern British Columbia, Alberta, and Saskatchewan south to south-central California, Texas, and Chihuahua, Mexico. It is common throughout Rocky Mountain region of western Montana, central and southern Idaho [36,46]. The Natural Resource Conservation Service's PLANTS database provides a map of narrowleaf cottonwood's distribution in the United States.
Narrowleaf cottonwood can resprout from the roots, root crown, and/or healthy and fire damaged branches after fire [32]. The ability to resprout from branch fragments may also aid in postfire establishment. Fire generally increases the sediment load in streams when the majority of bank stabilizing vegetation is consumed [35]. Narrowleaf cottonwood branch fragments have the ability to trap sediment for localized deposition by impeding stream flow. Fresh, moist, barren alluvium in full sun is very important in the regeneration of narrowleaf cottonwood [11,18,57].
The role of fire in riparian plant community dynamics is closely related to geology and hydrology. Fire alters erosion processes with the magnitude and scale of effects directly related to the size and severity of fire, the topographical components of the stream system, and the size of stream, in conjunction with the amount, intensity, and timing of postfire precipitation. Streamside soils are highly erodible when the majority of vegetation and duff has been removed by fire. Large amounts of precipitation and other hydrologic events that occur soon after fire may result in drastic channel alteration. However, newly deposited alluvium and changes in channel morphology usually increase habitat complexity [35]. In general, fire-induced channel alterations occur most readily during the first 10 postfire years.
Hungerford and others [49] view the role of fire, in what they refer to as wetland systems, as being closely related to adequate ignition sources, the frequency and duration of favorable fire weather, and annual hydrology. Susceptibility to burning increases when annual dry periods are consistent, especially with the accumulation of dead biomass. Fine dead fuels can burn intensely during periods of low humidity, even when the underlying soil is saturated. Upland ecosystems often dictate the frequency of ignitions [49].
FIRE REGIMES:
The following table provides some fire return intervals for communities adjacent to narrowleaf cottonwood. Find further 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".
Community or Ecosystem Dominant Species Fire Return Interval Range (years) silver fir-Douglas-fir Abies amabilis-Pseudotsuga menziesii var. menziesii > 200 grand fir Abies grandis 35-200 maple-beech-birch Acer-Fagus-Betula > 1000 sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [13] basin big sagebrush Artemisia tridentata var. tridentata 12-43 [76] mountain big sagebrush Artemisia tridentata var. vaseyana 5-15 [93] Wyoming big sagebrush Artemisia tridentata var. wyomingensis 10-70 (40)** [90,93] desert grasslands Bouteloua eriopoda and/or Pleuraphis mutica 5-100 plains grasslands Bouteloua spp. Rocky Mountain juniper Juniperus scopulorum wheatgrass plains grasslands Pascopyrum smithii blue spruce* Picea pungens 35-200 pinyon-juniper Pinus-Juniperus spp. Rocky Mountain ponderosa pine* Pinus ponderosa var. scopulorum 2-10 [13] quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [13,37,61] mountain grasslands Pseudoroegneria spicata 3-40 (10)** Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [2] elm-ash-cottonwood Ulmus-Fraxinus-Populus spp. < 35 to 200 [13] *Fire return interval varies widely; trends in variation are noted in the Species Review.Due to decreased probability of postfire sprouting by older mature tress, prescribed fires in narrowleaf cottonwood stands are not recommended past pole and early maturation stages of development [38]. Livestock grazing should be excluded for at least five years after fire, with wildlife browsing monitored [40].
Narrowleaf cottonwood is common to alluvial benches of high plains to low mountains [46]. It occurs on a wide range of soil textures [39], inhabiting loamy sand to sandy loam with high percentages of coarse fragments [44], and gravel bars [39].
Regional: Narrowleaf cottonwood is rare in California where it is restricted to mid-elevation streamsides [45]. It is common to drainages greater than 6,000 feet (1828 m) in Arizona [6]. Narrow benches, small streams, and floodplains of larger streams are common sites in central Colorado [44]. In Montana, narrowleaf cottonwood is most abundant on medium to coarse-textured, well-drained soils [39]. Mid- to high-elevation streambanks or canyon bottoms are common sites in Utah [51].
The elevational ranges for narrowleaf cottonwood in several states are listed below:
210 Interior Douglas-fir
216 Blue spruce
217 Aspen
219 Limber pine
220 Rocky Mountain juniper
237 Interior ponderosa pine
238 Western juniper
239 Pinyon-juniper
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES23 Fir-spruce
FRES29 Sagebrush
FRES30 Desert shrub
FRES35 Pinyon-juniper
FRES36 Mountain grasslands
FRES38 Plains grasslands
K011 Western ponderosa forest
K012 Douglas-fir forest
K018 Pine-Douglas-fir forest
K020 Spruce-fir-Douglas-fir forest
K021 Southwestern spruce-fir forest
K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K038 Great Basin sagebrush
K051 Wheatgrass-bluegrass
K056 Wheatgrass-needlegrass shrubsteppe
K057 Galleta-threeawn shrubsteppe
K063 Foothills prairie
K066 Wheatgrass-needlegrass
K068 Wheatgrass-grama-buffalo grass
110 Ponderosa pine-grassland
302 Bluebunch wheatgrass-Sandberg bluegrass
303 Bluebunch wheatgrass-western wheatgrass
314 Big sagebrush-bluebunch wheatgrass
412 Juniper-pinyon woodland
413 Gambel oak
418 Bigtooth maple
503 Arizona chaparral
504 Juniper-pinyon pine woodland
Fire will partially or completely kill narrowleaf cottonwood depending upon severity. Mature narrowleaf cottonwood possesses thick-furrowed bark; however, the bark does not always provide adequate insulation, leaving trunks vulnerable to heat-induced xylem cavitation and scarring. Even low-severity fires may wound trees, resulting in either complete or partially killed crowns [32]. Due to limited root systems, narrowleaf cottonwood seedlings and saplings on well-drained alluvial bars are very susceptible to severe fires [41].
Riparian habitats are sites for many migratory and non-migratory wildlife species. Even where narrowleaf cottonwood communities do not directly benefit specific species, indirect benefits occur through maintenance of healthy streamside habitats. Narrowleaf cottonwood is an excellent bank stabilizing species [39,51], contributing to the development of stable riparian communities for use by wildlife. The clonal reproduction of established narrowleaf cottonwood stands leads to heterogeneous trunk size and spatial clumping, increasing habitat richness for wildlife [33]. Narrowleaf cottonwood and other Populus species community types in Colorado provide habitat for over 200 species of vertebrates [79].
Narrowleaf cottonwood provides good avian nesting and breeding habitat [75] for the greater pewee [15], sharp-shinned hawk [69], and bald eagle [85]. Narrowleaf cottonwood is a major food plant of beaver [57] and is most commonly harvested when greater than 1 inch (3 cm) d.b.h. [5].
Narrowleaf cottonwood is a dominant species of Central Colorado riparian areas of upper foothills
and lower montane zones [44]. It is also a principal tree species along streams of semiarid
regions of southern Alberta [32]. Few narrowleaf cottonwood colonies are found east of the
southern Sierra Nevada Crest [47]. Common plant associates of narrowleaf cottonwood are listed
below.
Trees: In Colorado narrowleaf cottonwood is commonly found with box elder (Acer negundo), balsam poplar (P. balsamifera), Fremont cottonwood (P. fremontii), Douglas-fir
(Pseudotsuga menziesii) [1], ponderosa pine (P. ponderosa), [1,44], Rocky Mountain juniper (Juniperus scopulorum) [43,44], and blue spruce (Picea pungens) [27].
In Arizona and New Mexico, white fir (Abies concolor), blue spruce,
Douglas-fir, ponderosa pine, and Gambel oak (Quercus gambelii) are common
associates [7]. Limber pine (Pinus flexilis), Douglas-fir, eastern
cottonwood (Populus deltoides), and black cottonwood (P. trichocarpa)
are common associates in Montana [40]. In Utah, water birch (Betula occidentalis), thinleaf alder (Alnus incana)
[51], box elder, bigtooth maple (Acer grandidentatum), Gambel oak, Fremont
cottonwood, and Rocky Mountain juniper are common associates [68].
Shrubs: In Colorado, Rocky Mountain maple (Acer glabrum), Saskatoon serviceberry (Almelanchier alnifolia) [1], willow (Salix spp.), water birch, thinleaf alder [1,44], red-osier dogwood (Cornus sericea), Wood's rose (Rosa woodsii), western snowberry (Symphoricarpos occidentalis) and mountain snowberry (S. oreophilus)
are common associates of narrowleaf cottonwood [44]. In Arizona and New Mexico,
thinleaf alder, Arizona alder (Alnus oblongifolia), willow, box elder, currant (Ribes spp.), and rose (Rosa spp.) are common
[7]. In Montana, narrowleaf cottonwood is commonly found with red-osier dogwood,
kinnikinnick (Arctostaphylos uva-ursi), big sagebrush (Artemisia tridentata), and Wood's rose [40]. In Utah common associates are rose, mountain
snowberry, willow, and red-osier dogwood [68].
Graminoids: In Colorado, narrowleaf cottonwood is commonly found with slender wheatgrass (Elymus trachycaulus), nodding brome (Bromus anomalus), bluejoint reedgrass (Calamagrostis canadensis),
and sedge (Carex spp.) [44].
In Montana, creeping bentgrass (Agrostis stolonifera), timothy (Phleum pratense), Kentucky bluegrass (Poa pratensis), bluegrass (Poa
spp.), bearded wheatgrass (Elymus caninus), slender wheatgrass, other wheatgrasses
(Triticeae),
redtop (Agrostis gigantea), and reed canarygrass (Phalaris arundinacea) are common associates [40].
Forbs: Northern bedstraw (Galium boreale), cow parsnip (Heracleum lanatum), and American vetch (Vicia americana) are common associates of narrowleaf cottonwood in
Colorado [44].
In Montana dandelion (Taraxacum officinale), western yarrow (Achillea millefolium), Canada thistle (Cirsium arvense), yellow sweetclover (Melilotus officinalis), white clover (Trifolium repens), and Canada goldenrod (Solidago canadensis)
are common associates [40].
Published classifications listing narrowleaf cottonwood as an indicator or dominant are
listed below:
Classification of the forest vegetation of Colorado by habitat type and community type [1]
Classification of the riparian vegetation of the montane and subalpine zones in western Colorado [4]
Forest and woodland habitat types (plant associations) of Arizona south of the Mogollan Rim and southwestern New Mexico [7]
Classification and management of Montana's riparian and wetland sites [40]
Riparian reference area in Idaho: a catalog of plant associations and
conservation sites [50]
Preliminary riparian community type classification for Nevada [59]
A physical and biological characterization of riparian habitat and its importance to wildlife in Wyoming [66]
Riparian community type classification of Utah and southeastern Idaho [68]
Plant associations (habitat types) of the forests and woodlands of Arizona and New Mexico [82]
Riparian forest and scrubland community types of Arizona and New Mexico [86]
Riparian community type classification of eastern Idaho - western Wyoming [94]
Anthropogenic modification of riparian systems may adversely affect ecosystem
health. Drastic declines in the reproductive ability of cottonwoods and other native species
is common. Disturbances such as irrigation diversions, reservoirs, farming, and grazing have
profoundly altered natural stream ecology [20].
Dams: Dams alter annual water table fluctuations [48,58] by reducing downstream flow, altering sediment transport, decreasing organic
matter transport, and decreasing sediment deposition [11,20]. These modifications
to river hydrology generally have negative impacts on downstream narrowleaf
cottonwood communities [11,48,72,73].
Annual spring flooding is a controlling factor behind species composition and population dynamics
of narrowleaf cottonwood communities [48,60]. Annual floods usually coincide with seed
dissemination [58]. Damming generally reduces the number and quality of
narrowleaf cottonwood regeneration sites [48].
Recent studies [54,72,74] have focused on dam-related decreases in summer
water tables. Many dams do not alter spring discharge. Dams that have no effect on spring discharge
rates may not affect the production of alluvial deposits for narrowleaf cottonwood
regeneration. However, seedling establishment is generally adversely affected by exposing
seedlings to artificial drought [72]. Summer
water table levels are a critical component of narrowleaf cottonwood establishment [54].
In Alberta narrowleaf cottonwood abundance declined from 1951 to 1994. Ground surveys conducted over 9 years
(1985-1994) recorded an absence of seedlings and saplings. Declines were drought induced, through insufficient flow rates
during summer months together with the abrupt reductions following high spring flow rates [74].
Narrowleaf cottonwood seedlings
are not tolerant of abrupt declines in water table levels. Slow daily declines
of 1.6 inches per day (4.0 cm/day) in water table levels over a 28-day period were
found to stimulate root growth
without causing profound decreases in shoot height. Larger declines of 4 inches
per day (10 cm/day) drastically slowed
shoot height [54]. See black cottonwood
for further information on the effects of watercourse damming and
stream diversion on narrowleaf and other cottonwoods.
Grazing: Damage from livestock grazing (defoliation, soil compaction, or floodplain water table subsidence due to channel
widening or downcutting) has decreased cottonwood (Populus spp.) populations [17]. Grazing disturbance
may initiate stable communities of invasive
species such as Kentucky bluegrass, smooth brome (Bromus inermis),
dandelion,
and white clover [44].
Nutritional value (mean %) of immature leaves of narrowleaf
cottonwood is summarized below [64]:
AZ CA CO ID MT
The palatability of narrowleaf cottonwood for livestock and wildlife species is rated as follows [21]:
Within streamside woodlands of Wyoming, narrowleaf cottonwood is relatively unpalatable
to game and
domestic livestock [8].
Phenological development of narrowleaf cottonwood is directly related to annual hydrologic events [72]. Flowering and pollination generally coincide with springtime peaks in river flow [11]. Catkins appear before leaf emergence [57] on twigs of the previous year [23] from specialized buds of preformed inflorescences [24]. Male flowers appear earlier than females with both occurring approximately 1 to 2 weeks prior to leaf initiation. Seed dispersal generally coincides with annual declines in river flow [11].
In general, flowering occurs May to June with leaf fall taking place from mid-September to October [34]. Leaf primordia are formed in the fall. New leaves continue to form throughout the growing season [24].
Narrowleaf cottonwood resprouts from roots, healthy and fire damaged branches, and root crowns [32]. Postfire sprouting generally occurs after light- to moderate-severity fire in pole sized and recently mature stands [41].
The ability to produce postfire sprouts is greatly affected by stand age and location of the water table. Sprouting potential decreases proportionally as mature trees age. High water tables aid in the sprouting ability and subsequent sprout survival [38]. See black cottonwood for further information on sprouting response of narrowleaf and other cottonwoods.
Tree with adventitious bud/root crown/soboliferous species root sucker
Initial off-site colonizer (off-site, initial community)
Narrowleaf cottonwood shows both asexual and sexual regeneration. Channel narrowing and redistribution of sediment are the 2 main fluvial processes providing suitable narrowleaf cottonwood establishment sites [62].
Sexual: Pollen is wind dispersed with fertilization occurring within 24 hours of pollination. Subsequent seed maturation is temperature dependent, generally requiring 3 to 6 weeks. Seed dispersal through wind and water is aided by fluffy cottonlike hairs [11].
Narrowleaf cottonwood seeds possess a small window of viability [33], generally 2 days [57]. Seeds readily germinate when deposited in favorable environments. Successful germination and establishment is dependent upon a suite of abiotic and biotic conditions, with insolation and moisture availability the most limiting factors. Seedlings require wet alluvium in full sunlight [11,18,57]. Narrowleaf cottonwood seedlings are poor competitors in vegetated sites because lack of endosperm food reserves limits successful establishment in shaded areas [11]. Baker [3] found narrowleaf cottonwood seedlings uncommon in stands older than 45 to 60 years. Seedlings are intolerant of dry conditions [11,18] and are most vulnerable during summer drought [11,54,72] before roots reach late-season alluvial water tables [11].
Asexual: Narrowleaf cottonwood sprouts from the root crown and roots [11,33,77]. Sprouting is often linked to disturbance that scarifies stems and/or roots [33]. Narrowleaf cottonwood also sprouts from branch and root fragments when adequate sediment deposition is present [33,54]. Vegetative propagation is a dominant mode of reproduction within foothill rivers and relatively clear streams with coarse substrates [73], promoting colonization of bare gravel bars [39]. Steep gradients, coarse streambeds, and constrained channels also promote clonal regeneration [33].
Cloning is important in narrowleaf cottonwood gallery maintenance. Male and female trees have similar clonal abilities. In southern Alberta, Gom and Rood [33] found cloning was important to narrowleaf cottonwood population structure and expansion. Ramet spacing ranged from inches to 164 feet (50 m) depending upon mechanism of clonal propagation. Shoot sprouting produced tightly clustered clones around buried root crowns. Root suckers produced wider spacing than shoot sprouting. Beavers influenced clonal propagation, perpetuating clonal expansion and encouraging regeneration near stream channels.
Schier and Cambell [77] found the majority of root suckers occurred from suppressed buds embedded in periderm of undisturbed roots after death or injury of aboveground parts. Roots with damaged vascular cambium were most likely to sprout.
Branch fragments provide an important mode of asexual propagation. Beavers, high winds, heavy rain, hail, snow, and flooding all produce branch fragments capable of regeneration. Branches have the ability to impede stream flow and trap sediment for localized deposition, and may promote narrowleaf cottonwood establishment in areas lacking unvegetated sediment deposits [54].
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands
Narrowleaf cottonwood is a rapidly growing pioneer species, showing natural stand replacement adjacent to riparian systems with undisturbed hydrology. However, narrowleaf cottonwood shows slower growth rates than the majority of cottonwood species, requiring a longer time for adequate establishment [81].
Although successional events in communities dominated by narrowleaf cottonwood are different between sites, common attributes are shared. Narrowleaf cottonwood colonizes moist, barren, newly deposited alluvium exposed to full sunlight. Shade intolerance, and lack of successful sexual regeneration under its own canopy prevent narrowleaf cottonwood communities from achieving climax status. In Montana Hansen and others [40] observed asexual sprouting within narrowleaf cottonwood communities, but sustained population maintenance was limited. They considered eventual replacement of narrowleaf cottonwood by later stages inevitable. Merigliano [62] provides a detailed outline of narrowleaf cottonwood ecology and other associated riparian species of the South Fork Snake River, Idaho. Successional trends in narrowleaf cottonwood communities are provided by Hall and Hansen [38] for southern and eastern Idaho.
The currently accepted scientific name of narrowleaf
cottonwood is Populus angustifolia James (Salicaceae) [45,46,52,92].
Narrowleaf cottonwood hybridizes naturally with Fremont cottonwood (P. fremontii) [29], balsam poplar
(P. balsamifera) [12,33,53], and eastern cottonwood (P. deltoides) [12,33].
Narrowleaf cottonwood timber is strong, light weight, and resistant to impact and splitting [6], but susceptible to decay [51]. Historically, narrowleaf cottonwood was used for crates, boxes and pallets [6]. In Utah, fuelwood and fenceposts were common uses [51]. Narrowleaf cottonwood timber is also good for pulp [6,51].
Populus angustifolia, commonly known as the narrowleaf cottonwood,[2] is a species of tree in the willow family (Salicaceae). It is native to western North America, where it is a characteristic species of the Rocky Mountains and the surrounding plains.[3] It ranges north to the provinces of Alberta and Saskatchewan in Canada and south to the states of Chihuahua, Coahuila, and Sonora in Mexico.[3] Its natural habitat is by streams and creeks between 3,900 to 7,900 feet (1,200 to 2,400 m) elevation.[1][3]
The tree is slim in profile, and can grow in tightly packed clusters.[4] Its leaves are yellow-green, lanceolate (lance-shaped), and with scalloped margins. It produces catkins in the early spring. The fruiting capsules are fluffy and white.
Old catkins and emerging spring leaves
Where their ranges come into contact, this species will readily hybridize with Populus balsamifera, Populus deltoides, Populus fremontii, and Populus trichocarpa. These hybrids can form extensive populations in some regions. Due to the frequency and morphological consistency of P. angustifolia × P. deltoides hybrids, they were initially described as a fully separate species ("P. acuminata") until its hybrid origin was firmly established in the 1980s.[3]
The buds are sticky and gummy and were enjoyed as a sort of chewing gum by local Native American peoples, including the Apache and Navajo. The tree is the host species of the sugarbeet root aphid (Pemphigus betae).
Populus angustifolia, commonly known as the narrowleaf cottonwood, is a species of tree in the willow family (Salicaceae). It is native to western North America, where it is a characteristic species of the Rocky Mountains and the surrounding plains. It ranges north to the provinces of Alberta and Saskatchewan in Canada and south to the states of Chihuahua, Coahuila, and Sonora in Mexico. Its natural habitat is by streams and creeks between 3,900 to 7,900 feet (1,200 to 2,400 m) elevation.
