SPECIES: Populus angustifolia
Simonin, Kevin A. 2001. Populus angustifolia. 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/ .
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) , balsam poplar (P. balsamifera) [12,33,53], and eastern cottonwood (P. deltoides) [12,33].
No special status
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
PLANTS database provides
a map of narrowleaf cottonwood's distribution in the United States.
FRES21 Ponderosa pine
FRES30 Desert shrub
FRES36 Mountain grasslands
FRES38 Plains grasslands
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
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
K056 Wheatgrass-needlegrass shrubsteppe
K057 Galleta-threeawn shrubsteppe
K063 Foothills prairie
K068 Wheatgrass-grama-buffalo grass
210 Interior Douglas-fir
216 Blue spruce
219 Limber pine
220 Rocky Mountain juniper
237 Interior ponderosa pine
238 Western juniper
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
Narrowleaf cottonwood is a dominant species of Central Colorado riparian areas of upper foothills
and lower montane zones . It is also a principal tree species along streams of semiarid
regions of southern Alberta . Few narrowleaf cottonwood colonies are found east of the
southern Sierra Nevada Crest . Common plant associates of narrowleaf cottonwood are listed
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) , ponderosa pine (P. ponderosa), [1,44], Rocky Mountain juniper (Juniperus scopulorum) [43,44], and blue spruce (Picea pungens) . In Arizona and New Mexico, white fir (Abies concolor), blue spruce, Douglas-fir, ponderosa pine, and Gambel oak (Quercus gambelii) are common associates . Limber pine (Pinus flexilis), Douglas-fir, eastern cottonwood (Populus deltoides), and black cottonwood (P. trichocarpa) are common associates in Montana . In Utah, water birch (Betula occidentalis), thinleaf alder (Alnus incana) , box elder, bigtooth maple (Acer grandidentatum), Gambel oak, Fremont cottonwood, and Rocky Mountain juniper are common associates .
Shrubs: In Colorado, Rocky Mountain maple (Acer glabrum), Saskatoon serviceberry (Almelanchier alnifolia) , 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 . In Arizona and New Mexico, thinleaf alder, Arizona alder (Alnus oblongifolia), willow, box elder, currant (Ribes spp.), and rose (Rosa spp.) are common . In Montana, narrowleaf cottonwood is commonly found with red-osier dogwood, kinnikinnick (Arctostaphylos uva-ursi), big sagebrush (Artemisia tridentata), and Wood's rose . In Utah common associates are rose, mountain snowberry, willow, and red-osier dogwood .
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.) . 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 .
Forbs: Northern bedstraw (Galium boreale), cow parsnip (Heracleum lanatum), and American vetch (Vicia americana) are common associates of narrowleaf cottonwood in Colorado . 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 .
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 
Classification of the riparian vegetation of the montane and subalpine zones in western Colorado 
Forest and woodland habitat types (plant associations) of Arizona south of the Mogollan Rim and southwestern New Mexico 
Classification and management of Montana's riparian and wetland sites 
Riparian reference area in Idaho: a catalog of plant associations and conservation sites 
Preliminary riparian community type classification for Nevada 
A physical and biological characterization of riparian habitat and its importance to wildlife in Wyoming 
Riparian community type classification of Utah and southeastern Idaho 
Plant associations (habitat types) of the forests and woodlands of Arizona and New Mexico 
Riparian forest and scrubland community types of Arizona and New Mexico 
Riparian community type classification of eastern Idaho - western Wyoming 
Narrowleaf cottonwood timber is strong, light weight, and resistant to impact and splitting
but susceptible to decay . Historically, narrowleaf cottonwood was used for crates,
boxes and pallets . In Utah, fuelwood and fenceposts were common uses . Narrowleaf cottonwood timber
is also good for pulp [6,51].
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 .
Narrowleaf cottonwood and other Populus species community types in Colorado provide habitat for over 200 species of vertebrates .
Narrowleaf cottonwood provides good avian nesting and breeding habitat  for the greater pewee , sharp-shinned hawk , and bald eagle . Narrowleaf cottonwood is a major food plant of beaver  and is most commonly harvested when greater than 1 inch (3 cm) d.b.h. .
The palatability of narrowleaf cottonwood for livestock and wildlife species is rated as follows :
|Small nongame birds||----||fair||fair|
|Upland game birds||----||poor||poor|
Within streamside woodlands of Wyoming, narrowleaf cottonwood is relatively unpalatable to game and domestic livestock .
Nutritional value (mean %) of immature leaves of narrowleaf
cottonwood is summarized below :
The degree to which narrowleaf cottonwood provides cover for wildlife species is rated as
|Upland game birds||poor||good||good||fair|
|Small nongame birds||good||good||good||----|
|Establishment by seed||Establishment by transplant||Seed production and handling||Natural spread (seed)||Natural spread (vegetative)||Growth rate||Soil stability||Adaptation to disturbance||Soil pH|
|very poor||good||poor||medium||good||good||good||poor||acid to alkaline|
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 .
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 . Damming generally reduces the number and quality of narrowleaf cottonwood regeneration sites .
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 . Summer water table levels are a critical component of narrowleaf cottonwood establishment . 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 . 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 . 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 . Grazing disturbance may initiate stable communities of invasive species such as Kentucky bluegrass, smooth brome (Bromus inermis), dandelion, and white clover .
Narrowleaf cottonwood is a native deciduous tree with a slender crown . It
attains heights up to 60 feet (20 m) ; trunks can exceed 30 inches (76
cm) in diameter . 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 .
Narrowleaf cottonwood is reported as a facultative wetland species tolerant of frequent and prolonged flooding . It is not drought resistant  and is extremely vulnerable to drought induced xylem cavitation .
A life span of 100 to 200 years is not uncommon .
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 .
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 .
Narrowleaf cottonwood seeds possess a small window of viability , generally 2 days . 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 . Baker  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 .
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 . 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 , promoting colonization of bare gravel bars . Steep gradients, coarse streambeds, and constrained channels also promote clonal regeneration .
Cloning is important in narrowleaf cottonwood gallery maintenance. Male and female trees have similar clonal abilities. In southern Alberta, Gom and Rood  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 
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 .
Narrowleaf cottonwood is common to alluvial benches of
high plains to low mountains . It occurs on a wide range of soil textures
, inhabiting loamy sand to sandy loam with high percentages of coarse
fragments , and gravel bars .
Regional: Narrowleaf cottonwood is rare in California where it is restricted to mid-elevation streamsides . It is common to drainages greater than 6,000 feet (1828 m) in Arizona . Narrow benches, small streams, and floodplains of larger streams are common sites in central Colorado . In Montana, narrowleaf cottonwood is most abundant on medium to coarse-textured, well-drained soils . Mid- to high-elevation streambanks or canyon bottoms are common sites in Utah .
The elevational ranges for narrowleaf cottonwood in several states are listed below:
|Arizona||6,200 to 7,700 feet (1,900-2,350 m) |
|California||3,937 to 5,905 feet (1,200-1,800 m) |
|Colorado||5,000 to 8,000 feet (1,900-2,450 m) |
|Eastern Idaho||< 6,700 feet (2,000 m) |
|Southern Idaho||5,000 to 6,000 feet (1,500-1,800 m) |
|New Mexico||6,200 to 7,700 feet (1,900-2,350 m) |
|Texas||> 3,500 feet (1,000 m) |
|Northern Utah||5,000 to 6,000 feet (1,500-1,800 m) |
|Southern Utah||6,200 to 8,000 feet (1,900-2,450 m) |
|Western Wyoming||< 6,700 feet (2,000 m) |
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 .
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  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  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  for southern and eastern Idaho.
Phenological development of narrowleaf cottonwood is directly related to annual hydrologic events .
Flowering and pollination generally coincide with springtime peaks in river flow . Catkins
appear before leaf emergence  on twigs of the previous year  from specialized buds of preformed
inflorescences . 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 .
In general, flowering occurs May to June with leaf fall taking place from mid-September to October . Leaf primordia are formed in the fall. New leaves continue to form throughout the growing season .
Narrowleaf cottonwood can resprout from
the roots, root crown, and/or healthy and fire damaged branches after fire .
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 . 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 . In general, fire-induced channel alterations occur most readily during the first 10 postfire years.
Hungerford and others  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 .
The following table provides some fire regime intervals for communities adjacent to narrowleaf cottonwood:
|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|
|sagebrush steppe||Artemisia tridentata/Pseudoroegneria spicata||20-70 |
|basin big sagebrush||Artemisia tridentata var. tridentata||12-43 |
|mountain big sagebrush||Artemisia tridentata var. vaseyana||5-15 |
|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.||< 35|
|Rocky Mountain juniper||Juniperus scopulorum||< 35|
|wheatgrass plains grasslands||Pascopyrum smithii||< 35|
|blue spruce*||Picea pungens||35-200|
|pinyon-juniper||Pinus-Juniperus spp.||< 35|
|Rocky Mountain ponderosa pine*||Pinus ponderosa var. scopulorum||2-10 |
|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 |
|elm-ash-cottonwood||Ulmus-Fraxinus-Populus spp.||< 35 to 200 |
Tree with adventitious bud/root crown/soboliferous species root sucker
Initial off-site colonizer (off-site, initial community)
Fire will partially or completely kill narrowleaf cottonwood depending upon
severity. Mature narrowleaf cottonwood possesses thick-furrowed bark; however, the bark does not
adequate insulation, leaving trunks vulnerable to heat-induced xylem cavitation
Even low-severity fires may wound trees, resulting in either complete or partially killed crowns
Due to limited root systems, narrowleaf cottonwood seedlings and saplings on
well-drained alluvial bars are very susceptible to severe fires .
Narrowleaf cottonwood resprouts from roots, healthy and fire damaged branches,
and root crowns .
Postfire sprouting generally occurs after light- to moderate-severity fire in pole sized and recently mature
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 . See black cottonwood for further information on sprouting response of narrowleaf and other cottonwoods.
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Gom and Rood  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 .
No evaluations of natural postfire establishment through seed are currently
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
. Livestock grazing should be excluded for at least five years after fire, with wildlife
browsing monitored .
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