Populus fremontii - Fraxinus velutina - Salix gooddingii Forest & Woodland Alliance
Fremont cottonwood forest and woodland
Fremont cottonwood forest and woodland
USDA Ecological Section Map
Summary Information
- Primary Life FormTree
- Elevation0-2400 m
- State RarityS3.2
- Global RarityG4
- DistributionUSA: AZ, CA, CO, NM, NV, TX, UT, WY. Mexico (NatureServe)
- Endemic to CaliforniaNo
- Endemic to California Floristic Province and DesertsNo
- Date Added1995/11/01
Characteristic Species
Populus fremontii is dominant or co-dominant in the tree canopy with Acer negundo, Baccharis sergiloides, Fraxinus latifolia, Fraxinus velutina, Juglans hindsii, Juglans hindsii × regia, Platanus racemosa, Quercus agrifolia, Salix exigua, Salix gooddingii, Salix laevigata, Salix lasiolepis, Salix lucida ssp. lasiandra and Salix lutea.
Vegetation Layers
Trees < 25 m; canopy is continuous to open. Shrub layer is intermittent to open. Herbaceous layer is variable.
Membership Rules
- Populus fremonitii > 5% absolute cover in the tree layer (Potter 2005).
- Populus fremontii > 50% relative cover in the tree layer (Keeler-Wolf et al. 1998b, Thomas et al. 2004).
- Populus fremontii > 50% relative cover in the tree layer, though sometimes P. fremontii > 30% relative cover if Salix species are co-dominant (Evens and San 2005, Klein and Evens 2005, cf. Stillwater Sciences and URS 2007).
- Populus fremontii > 50% relative cover, or > 30% relative cover with Acer negundo, Juglans, and/or Salix, sometimes with Populus having as little as 5% absolute cover (Sikes et al. 2021, Ratchford et al. 2024a).
- Populus fremontii > 50% relative cover, or > 30% relative cover with Acer negundo, Juglans, and/or Salix, sometimes with Populus having as little as 5% absolute cover in riparian settings with a diverse mix of riparian species (Buck-Diaz et al. 2012, Sikes et al. 2023, Sikes et al. 2025).
Habitats
On floodplains, along low-gradient rivers, perennial or seasonally intermittent streams, springs, in lower canyons in desert mountains, in alluvial fans, and in valleys with a dependable subsurface water supply that varies considerably during the year. The USFWS Wetland Inventory (1996 national list) recognizes Populus fremontii as a FACW plant.
Other Habitat, Alliance and Community Groupings
| MCV (1995) | Fremont cottonwood series |
| NVCS (2009) | Populus fremontii seasonally flooded woodland alliance, Populus fremontii temporarily flooded forest alliance, Populus fremontii temporarily flooded woodland alliance |
| Calveg | Fremont cottonwood |
| Holland | Central Coast cottonwood-sycamore riparian forest, Southern cottonwood-willow riparian forest, Great Valley cottonwood riparian forest, Great Valley mixed riparian forest, Modoc-Great Basin cottonwood-willow riparian forest, Mojave riparian forest, Sonoran cottonwood-willow riparian forest |
| Munz | Not treated |
| WHR | Desert riparian, Montane riparian, Valley foothill riparian |
| CDFW CA Code | 61.130.00 |
National Vegetation Classification Hierarchy
| Formation Class | Mesomorphic Tree Vegetation (Forest and Woodland) |
| Formation Subclass | Temperate Forest |
| Formation | Temperate Flooded and Swamp Forest |
| Division | Western North America Warm Temperate Flooded and Swamp Forest |
| Macro Group | Southwestern North American Riparian, Flooded and Swamp Forest |
| Group | Southwestern North American riparian evergreen and deciduous woodland |
Remarks
Populus fremontii is a fast-growing, short-lived tree that is shade intolerant. Trees produce copious, wind-dispersed seeds in the spring that are viable for up to 5days. Seeds germinate on moist alluvium and other recently disturbed sites. Seedlings establish successfully in areas where subsurface water is available during the growing season. Trees regenerate vegetatively from root suckers and vegetative propagules created during flood-related disturbance (Braatne et al. 1996, Tu 2000), but seed is the primary mode of reproduction. Trees damaged by cutting and fire can sprout if they are not old (Taylor 2000).
Populus fremontii is a common plant at lower elevations, but most stands have endured negative impacts from reduced water availability (through groundwater pumping), livestock use, hydrologic alterations and irrigation schemes, competition from non-native plants, direct habitat destruction, and other human activities.
Populus fremontii may dominate stands or mix with other trees in riparian settings. Some uncertainty exists about the proper classification of mixed stands of P. fremontii and Salix gooddingii. Vaghti (2003) places these in the P. fremontii alliance; Hickson and Keeler-Wolf (2007), in a larger survey from the Sacramento Delta, suggest they are better placed in the Salix gooddingii alliance. Furthermore, uncertainty exists about mixed stands of P. fremontii and Platanus racemosa. Klein and Evens (2005) and Evens and San (2005) place co-dominant stands in a mixed alliance, but we place them in the Platanus racemosa alliance. Populus fremontii also occurs in mixed stands with additional co-dominant species in southern California, including S. laevigata and other willows (S. lucida and S. lasiolepis), Quercus agrifolia, and Juglans californica (Klein and Evens 2005, Stillwater Sciences and URS 2007).
This alliance was cited as Populus fremontii Forest Alliance in the 2009 book, A Manual of California Vegetation, second edition. The name has been updated to agree with the National Vegetation Classification.
Populus fremontii is a common plant at lower elevations, but most stands have endured negative impacts from reduced water availability (through groundwater pumping), livestock use, hydrologic alterations and irrigation schemes, competition from non-native plants, direct habitat destruction, and other human activities.
Populus fremontii may dominate stands or mix with other trees in riparian settings. Some uncertainty exists about the proper classification of mixed stands of P. fremontii and Salix gooddingii. Vaghti (2003) places these in the P. fremontii alliance; Hickson and Keeler-Wolf (2007), in a larger survey from the Sacramento Delta, suggest they are better placed in the Salix gooddingii alliance. Furthermore, uncertainty exists about mixed stands of P. fremontii and Platanus racemosa. Klein and Evens (2005) and Evens and San (2005) place co-dominant stands in a mixed alliance, but we place them in the Platanus racemosa alliance. Populus fremontii also occurs in mixed stands with additional co-dominant species in southern California, including S. laevigata and other willows (S. lucida and S. lasiolepis), Quercus agrifolia, and Juglans californica (Klein and Evens 2005, Stillwater Sciences and URS 2007).
This alliance was cited as Populus fremontii Forest Alliance in the 2009 book, A Manual of California Vegetation, second edition. The name has been updated to agree with the National Vegetation Classification.
Life History Traits of the Principal Species
| Populus fremontii | |
|---|---|
| Life forms | Tree; winter deciduous |
| Seed storage | Transient |
| Seed longevity | Short |
| Mode of dispersal | Gravity; water/hydrological; wind |
| Germination agents | None |
| Mode of sprouting | Buds on small branches; buds on large branches or trunks; underground structures |
| Survivability after fire/disturbance | Fire-sensitive; thin epidermis to fire-hardy; no/low sprouter |
| Disturbance-stimulated flowering | No |
| Reproductive range | 10-130 (5-300) years |
| Recruitment | High |
| Regional variation | High |
Fire Characteristics
Fluvial processes of major flood events and consequent flood scour, overbank deposition of water and sediments, and stream meandering primarily disturb stands. The fire interval was probably long or moderate with a low-intensity surface fire regime in original stands. Stands invaded by Tamarix have short fire intervals (10-20 years) in Arizona (Ohmart and Anderson 1986) and California (Brooks and Minnich 2006). Surface fuels provided by Tamarix also increase fire intensity and the probability of crown fires that result in high mortality rates in Populus fremontii (Brooks pers. comm. 2007). Many stands in southern California and the Central Valley have been invaded by Arundo donax, which has a similar effect in increasing fuel load and fire intensity and in reducing fire interval, often resulting in high mortality of native cottonwoods and willows and increased post-fire dominance by Arundo (Coffman 2007).
| Fire return interval | Medium |
| Seasonality | Late summer-fall |
| Size/extent | Less than stand size or larger |
| Complexity | High |
| Intensity | Low to high |
| Severity | Low to high |
| Type | Passive crown fire |
| Regional knowledge | Sierra Nevada foothills |
Regional Status
- Central California Coast (261Aa, Ac, Ae, Ah). Gray and Greaves (1984) describe coastal stands.
- Central California Coast Ranges (M262Aa-h, Aj-k). Stands occur in San Benito and western Fresno Cos. (Evens et al. 2006). Stands of Populus fremontii with Salix gooddingii also exist along the Salinas River (B. Orr pers. comm. 2008). Other stands occur at Pinnacles National Monument (Kittel et al. 2012).
- Colorado Desert (322Ca-d). Small stands occur at Anza-Borrego Desert State Park (Keeler-Wolf et al. 1998b, Spolsky 1979). Stands are scattered at oases throughout the section. Several stands exist along the Colorado River and All-American Canal.
- Great Valley (262Aa-d, Af-z). Mixed stands occur in the section and are generally small and fragmented. They occur in the Sacramento Valley (Bahre and Whitlow 1982, Conard and Robichaux 1980), the northern Sacramento River (Vaghti 2003), the delta (Hickson and Keeler-Wolf 2007), and the San Joaquin River and its major tributaries (McBain and Trush, Inc. 2000, Stillwater Sciences 2001, Moise and Hendrickson 2002, Stella et al. 2003).
- Klamath Mountains (M261Ac, Ai, Am, Ar, Au). Small stands occur along the Sacramento and Trinity rivers.
- Mojave Desert (322Aa-j, Al-p). Stands occur in the Owens Valley (Brothers 1984) and are described for the central, southern, and eastern subsections (Thomas et al. 2004, Keeler-Wolf et al. 2005).
- Mono (341Df, Dh-i). Stands are common in the upper Owens Valley near Bishop. A few stands also occur at freshwater springs on the western shores of Mono Lake. Two stands are mapped in Fish Slough Ecological Reserve (VegCAMP 2014b).
- Northern California Coast (263Aj, Am). Stands exist scattered such as along the Napa River. Several surveyed stands along the Russian River (Klein et al. 2015).
- Northern California Coast Ranges (M261Ba-f). Small stands occur in inland areas at low elevations.
- Northern California Interior Coast Ranges (M261Ca-c). Small stands occur in the section such as along the Thomes, Stony, and Elder creeks. One of the largest stands is aptly along Cottonwood Creek.
- Sierra Nevada (M261Er-s, Eu). Small stands exist at lower montane elevations in the southern subsections (Potter 2005).
- Sierra Nevada Foothills (M261Fa-e). Mixed stands of P. fremontii with Alnus rhombifolia, Platanus racemosa, or Salix laevigata are common in the section (Potter 2005). Some stands have well-developed shrubs and lianas, such as Cephalanthus occidentalis, Rubus armeniacus, and Vitis californica (Klein et al. 2007). Cottonwood forest restoration efforts in the Kern River Preserve by Audubon California have been quite successful.
- Sonoran Desert (322Ba-b, Bd-e). Many stands from the Colorado River bottomlands contain Tamarix spp.
- Southeastern Great Basin (341Fc, Fe). Stands surveyed in Cottonwood Canyon, Saline Valley, and at China Garden Spring.
- Southern California Coast (261Ba-j). Stands exist scattered along the upper Ventura, Santa Clara, San Gabriel, and Los Angeles rivers. The largest occur in flood-control basins. Arundo donax has invaded many stands along the Santa Clara River (Stillwater Sciences and URS 2007, Coffman 2007) and other rivers in this region. Tamarix is also present in some stands. Junak et al. (1995, 2007) cite stands from Santa Cruz and Santa Catalina islands.
- Southern California Mountains and Valleys (M262Ba-d, Bf-g, Bi-p). Stands occur along the Santa Margarita and Santa Ana rivers (Hanes 1984, Zembal 1989), in western Riverside Co. (Klein and Evens 2005), and in central San Diego Co. (Evens and San 2005); these vary in composition.
Management Considerations
Most of the larger stands of Populus fremontii exist downstream from dams. Regulating stream flows below large dams to mimic key components of natural flood regimes in terms of flood duration, peak flow, and timing appears to be critical for restoring and maintaining healthy stands with successful seedling establishment in these managed systems (McBain and Trush, Inc. 2000, Rood et al. 2003, 2005, Stillwater Sciences 2006 and 2007b).
Associations
Stands with a Mixed Tree Canopy
- Populus fremontii / Acer negundo [9], [12], [14]
- Populus fremontii / Acer negundo / Rubus armeniacus [9]
- Populus fremontii - Fraxinus velutina [19]
- Populus fremontii - Juglans californica [7]
- Populus fremontii - Prosopis spp. [1], [2]
- Populus fremontii - Quercus agrifolia [7]
- Populus fremontii - Salix gooddingii [12], [13], [18], [19], [23]
- Populus fremontii - Salix gooddingii / Baccharis salicifolia [1], [5], [11]
- Populus fremontii - Salix laevigata [1], [4], [5], [6], [10], [12], [13], [22], [23]
- Populus fremontii - Salix (laevigata, lasiolepis, lucida ssp. lasiandra) [7]
- Populus fremontii - Salix laevigata / Salix lasiolepis - Baccharis salicifolia [5], [7], [21], [24]
- Populus fremontii - Salix laevigata / Salix lasiolepis / Vitis girdiana [5]
- Populus fremontii - Salix lasiolepis [7], [12], [16], [19], [22], [23]
- Populus fremontii - Salix lucida ssp. lasiandra [8]
- Populus fremontii - Sambucus nigra [7]
Stands with a Simple Tree Canopy
- Populus fremontii [9], [16], [22], [24]
- Populus fremontii / Baccharis (emoryi, salicina) [13]
- Populus fremontii / Baccharis salicifolia [1], [5], [7], [10], [11], [12], [15], [17], [20], [22], [24]
- Populus fremontii / Baccharis sergiloides [13]
- Populus fremontii Great Valley [9], [12], [17]
- Populus fremontii / Rubus ursinus [9], [21]
- Populus fremontii / Salix exigua [3], [12], [14], [16], [19], [22], [23]
- Populus fremontii / Vitis californica [4], [9], [12], [23]
References
- [1] Evens, J.;San, S. 2005
- [2] Keeler-Wolf, T.;Roye, C.;Lewis, K. 1998b
- [3] Keeler-Wolf, T.;Thomas, K. 2000
- [4] Klein, A.;Crawford, J.;Evens, J.;Keeler-Wolf, T.;Hickson, D. 2007
- [5] Klein, A.;Evens, J. 2006
- [6] Potter, D.A. 2005
- [7] Stillwater Sciences and URS, 2007
- [8] Spolsky, A.M. 1979
- [9] Vaghti, M.G. 2003
- [10] Kittel, G.;Reyes, E.;Evens, J.;Buck, J.;Johnson, D. 2012
- [11] Sproul, F.;Keeler-Wolf, T.;Gordon-Reedy, P.;Dunn, J.;Klein, A.;Harper, K. 2011
- [12] Buck-Diaz, J.;Batiuk, S.;Evens, J.M. 2012
- [13] Evens, J.M.;Sikes, K.;Hastings, D.;Ratchford,J.S. 2014
- [14] Klein, A.;Keeler-Wolf, T.;Evens, J. 2015
- [15] Buck-Diaz, J.;Evens, J. 2011a
- [16] Buck-Diaz, J.;Evens, J. 2011b
- [17] CNPS Vegetation Program, 2015
- [18] Hickson, D.;Keeler-Wolf, T. 2007
- [19] Reyes, E.;Evens, J.;Glass, A.;Sikes, K.;Keeler-Wolf., T.;Winitsky, S.;Johnson, D.;Menke, J.;Hepburn, A. 2020a
- [20] Sikes, K.;Buck-Diaz, J.;Evens, J. 2021
- [21] Sikes, K.;Buck-Diaz, J.;Vu, S.;Evens, J. 2023
- [22] Buck-Diaz, J.;Sikes, K.;Vu, S.;LaFever-Jackson, A.;Evens, J. 2023
- [23] Ratchford, J.;Harbert, B;Boul, R.;Keeler-Wolf, T.;Evens, J. 2024a
- [24] Sikes, K.;Buck-Diaz, J.;Vu, S.;Bibbo, M.;Evens, J. 2025
- Barry, W.J. 1989a
- Barry, W.J. 1989b
- Bowler, P.A. 1989
- Capelli, M.H.;Stanley, S.J. 1984
- Cheatham, N.H.;Haller, J.R. 1975
- Conard, S.G.;Robichaux, R.F. 1980
- Evens, J.M.;Klein, A.;Taylor, J.;Hickson, D.;Keeler-Wolf, T. 2006
- Faber, P.M.;Keller, E.;Sands, A.;Massey, B.M. 1989
- Griffin, J.R.;Critchfield, W.B. 1972
- Holstein, G. 1984
- MacMahon, J.A. 1988
- McBride, J.R. 1994
- Menke, J.;Reyes, E.;Hepburn, A.;Johnson, D.;Reyes, J. 2013
- Minckley, W.L.;Brown, D.E. 1982
- NatureServe, 2007
- Paysen, T.E. 1982
- Paysen, T.E.;Derby, J.A.;Black, H.;Bleich, V.C.;Mincks, J.W. 1980
- Reyes, E.;Fulton, J.;Buck-Diaz, J.;Sikes, K.;Vu, S.;LaFever-Jackson, A.;Evens, J.;Johnson, D. 2023b
- Sands, A. 1980
- Shiflet, T.N. 1994
- Stromberg, J.C.;Patten, D.T.;Richter, B.D. 1991
- Taylor, J.L. 2000
- Thomas, K.;Franklin, J.;Keeler-Wolf, T.;Stine, P. 2004
- Thorne, R.F. 1976
- VegCAMP (CDFW Vegetation Classification and Mapping Program);AIS, 2013