Platanus racemosa - Quercus agrifolia Woodland Alliance
California sycamore - coast live oak riparian woodlands
California sycamore - coast live oak riparian woodlands
USDA Ecological Section Map
Summary Information
- Primary Life FormTree
- Elevation0-2400 m
- State RarityS3
- Global RarityG3
- DistributionUSA: CA. Baja California, Mexico (TJM2)
- Endemic to CaliforniaNo
- Endemic to California Floristic Province and DesertsYes
- Date Added1995/11/01
Characteristic Species
Platanus racemosa and/or Quercus agrifolia is dominant or co-dominant in the tree canopy in riparian habitats with Alnus rhombifolia, Juglans californica, Populus fremontii, Quercus lobata, Salix exigua, Salix gooddingii, Salix laevigata, Salix lasiolepis, Salix lutea, Schinus molle and Umbellularia californica.
Vegetation Layers
Trees < 35 m; canopy is open to intermittent. Shrub layer is open to intermittent. Herbaceous layer is sparse or grassy.
Membership Rules
- Platanus racemosa > 30% relative cover in tree canopy; Quercus agrifolia, Salix species, or Populus fremontii may be co-dominant. (Evens and San 2005, Klein and Evens 2005, Keeler-Wolf and Evens 2006, Stillwater Sciences and URS 2007).
- Platanus racemosa > 5% absolute cover in tree layer; in mixed stands, Populus fremontii < 5% absolute cover in the tree canopy (Potter 2005).
- Platanus racemosa > 50% relative cover in the tree layer (Keeler-Wolf et al. 1997).
- Quercus agrifolia > 50% relative cover in a riparian setting, or Platanus racemosa > 30 relative cover or sometimes > 15% relative cover as a characteristic tree with Acer macrophyllum, Acer negundo, Aesculus californica, Juglans hindsii, Quercus agrifolia, Quercus lobata, Salix laevigata, or Umbellularia californica (Sikes et al. 2023).
- Quercus agrifolia > 50% relative cover in a riparian setting, often with Salix spp. and Toxicodendron diversilobum (Sikes et al. 2021, Buck-Diaz et al. 2021)
Habitats
Gullies, intermittent streams, springs, seeps, stream banks, and terraces adjacent to floodplains that are subject to high-intensity flooding. Soils are rocky or cobbly alluvium with permanent moisture at depth. The USFWS Wetland Inventory (1996) recognizes Platanus racemosa as a FACW plant.
Other Habitat, Alliance and Community Groupings
| MCV (1995) | California sycamore series |
| NVCS (2009) | Platanus racemosa temporarily flooded woodland alliance |
| Calveg | California sycamore |
| Holland | Central Coast cottonwood-sycamore riparian forest, Sycamore alluvial woodland, Southern sycamore-alder riparian woodland |
| Munz | Not treated |
| WHR | Valley foothill riparian |
| CDFW CA Code | 61.310.00 |
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
Platanus racemosa is a fast-growing, deciduous tree that can grow up to 25 m in height and live to 400 years in age. Trees produce plumed, wind-dispersed achenes annually. Fresh seeds germinate on moist, clayey sediments. Young trees readily stump-sprout, but they are not very vigorous epicormic sprouters (Sullivan 1994).
Quercus agrifolia is a drought-resistant evergreen tree that grows to 25 m in height. The root system contains both roots that tap groundwater and ones that surface-feed extensively (Callaway 1990). It is the most susceptible of the California oaks to soil drought. Acorns develop in the first year, and crops vary greatly in size. Crop failures are common. Most acorns drop in fall, and scrub jays and California ground squirrels disperse and cache them, but some remain attached to trees until spring. Seed predation is high. Seeds germinate soon after they fall and develop deep lateral roots. Shoot growth can be rapid, but browsing by livestock, black-tailed deer, pocket gophers, grasshoppers, cutworms, and feral pigs is high (Steinberg and Howard 2002). Seedlings survive best under larger nurse plants or in rock outcrops (Callaway and Davis 1998, Parikh and Gale 1998a).
Stands of P. racemosa are well adapted to intermittent flooding conditions of the streams in the Mediterranean climate of cismontane California. P. racemosa also appears to have specific germination requirements that limit its ability to colonize areas that are not frequently scoured by natural flooding events.
This alliance includes Platanus racemosa woodlands whose status and distribution throughout California were summarized by Keeler-Wolf et al. (1997). We have also included stands of co-dominant P. racemosa and Populus fremontii within this alliance, though Klein and Evens (2005) placed these stands in a separate Platanus racemosa-Populus fremontii alliance. In addition, this alliance has been expanded since the 2009 publication, A Manual of California Vegetation, second edition, to include riparian stands dominated by Quercus agrifolia. Upland stands of Q. agrifolia remain in the Quercus agrifolia Alliance.
Quercus agrifolia is a drought-resistant evergreen tree that grows to 25 m in height. The root system contains both roots that tap groundwater and ones that surface-feed extensively (Callaway 1990). It is the most susceptible of the California oaks to soil drought. Acorns develop in the first year, and crops vary greatly in size. Crop failures are common. Most acorns drop in fall, and scrub jays and California ground squirrels disperse and cache them, but some remain attached to trees until spring. Seed predation is high. Seeds germinate soon after they fall and develop deep lateral roots. Shoot growth can be rapid, but browsing by livestock, black-tailed deer, pocket gophers, grasshoppers, cutworms, and feral pigs is high (Steinberg and Howard 2002). Seedlings survive best under larger nurse plants or in rock outcrops (Callaway and Davis 1998, Parikh and Gale 1998a).
Stands of P. racemosa are well adapted to intermittent flooding conditions of the streams in the Mediterranean climate of cismontane California. P. racemosa also appears to have specific germination requirements that limit its ability to colonize areas that are not frequently scoured by natural flooding events.
This alliance includes Platanus racemosa woodlands whose status and distribution throughout California were summarized by Keeler-Wolf et al. (1997). We have also included stands of co-dominant P. racemosa and Populus fremontii within this alliance, though Klein and Evens (2005) placed these stands in a separate Platanus racemosa-Populus fremontii alliance. In addition, this alliance has been expanded since the 2009 publication, A Manual of California Vegetation, second edition, to include riparian stands dominated by Quercus agrifolia. Upland stands of Q. agrifolia remain in the Quercus agrifolia Alliance.
Life History Traits of the Principal Species
| Platanus racemosa | Quercus agrifolia | |
|---|---|---|
| Life forms | Tree; winter deciduous | Tree; evergreen |
| Seed storage | Transient | Transient |
| Seed longevity | Short | Short |
| Mode of dispersal | Water/hydrological; wind | Animal; gravity |
| Germination agents | Stratification—winter | None |
| Mode of sprouting | Buds on large branches or trunks; underground structures | Buds on large branches or trunks; underground structures? |
| Survivability after fire/disturbance | Fire-sensitive; thin epidermis; (sensitive to anthracnose) | Fire-hardy; thick epidermis; low flammability; high sprouter |
| Disturbance-stimulated flowering | No | No |
| Reproductive range | 25-400 years | 25-250+ years |
| Recruitment | Episodic | Low to medium; episodic |
| Regional variation | Unknown | High |
Fire Characteristics
Since stands of Platanus racemosa occur exclusively in drainages and on north-facing lower slopes, the extent and severity of fire within stands is dependent on adjacent vegetation. However, stands appear to have low fire severity and complexity, probably because the surface fuels, if present, do not easily carry fire. They remain moist longer during the year. With many shrubs present, the fire complexity may be higher.
| Fire return interval | Short to medium (partly dependent on neighboring alliances) |
| Seasonality | Summer-early fall |
| Size/extent | Medium; up to stand size |
| Complexity | Low to moderate |
| Intensity | Low to moderate |
| Severity | Low to high |
| Type | Surface |
| Regional knowledge | Sierra Nevada and foothills |
Regional Status
- Central California Coast (261Ac, Ae-h, Aj-l). Stands of riparian Quercus agrifolia occur in San Mateo County (Sikes et al. 2021). Platanus racemosa stands are widespread in Santa Clara Co. with some presence in Santa Cruz Co. along Soquel Creek (Sikes et al. 2023). Stands are common in the northeastern subsections away from the immediate coast. Stands occur in the Santa Lucia Mountains above and east of the summer fog belt (Keeler-Wolf et al. 1997). Several stands are altered by dam construction and resulting summer water flow (Grossinger et al. 2006).
- Central California Coast Ranges (M262Aa-f, Ah, Aj). Stands exist at the base of Coyote Ridge (Evens and San 2004) along Coyote Creek and other creeks in the Diablo and Gabilan ranges (Kittel et al. 2012, CCH 2017+, Calflora 2018+). Some stands exist along the Salinas River adjacent to stands of the Salix gooddingii alliance and on slightly higher surfaces than stands of the Populus fremontii alliance (B. Orr, pers. comm. 2008).
- Great Valley (262Aa-d, Af-i, Ak-l, Ap-q, As-u). Stands of Platanus racemosa occur sporadically in this section, including those mapped at the Sacramento-San Joaquin River delta (Hickson and Keeler-Wolf 2007). Stands of Quercus agriolia occur as riparian stringers, often associated with Q. lobata and with willows, in the Sacramento-San Joaquin River delta (Hickson and Keeler-Wolf 2007). Stands along the Sacramento River north to Redding are composed primarily of Platanus racemosa with Quercus agrifolia or Quercus lobata (VegCAMP and GIC 2013).
- Northern California Coast (263Ak-m). Riparian stands dominated by Quercus agrifolia occur in Marin County (Buck-Diaz et al. 2021)
- Northern California Interior Coast Ranges (M261Cb). Scattered stands occur along the Sacramento River on the eastern edge of this subsection and near Redding (VegCAMP and GIC 2013).
- Sierra Nevada (M261Ep, Es). Stands occur south of the Kern River and near Lake Isabella at low-montane elevations (Potter 2005). Stands dominated by Platanus racemosa occur in the Kaweah River drainage along the western edge of Sequioa National Park (NPS-SEKI 2009).
- Sierra Nevada Foothills (M261Fa-e). Stands occur in the southern subsections between the Kern and San Joaquin rivers (Keeler-Wolf et al. 1997). A few exist in the northernmost subsection; for example, stands line Big Chico Creek and other creeks in Butte and Tehama Cos. that feed into the Sacramento River. Stands mixed with Populus fremontii in the northern subsection (Klein et al. 2007) have been placed in this alliance.
- Southern California Coast (261Ba-b, Bd-j). Stands occur in watercourses across the section, such as in the Santa Monica Mountains (Keeler-Wolf and Evens 2006), along the Santa Clara River drainage (Stillwater Sciences and URS 2007), and in areas further north into Santa Barbara Co. and the Santa Ynez River (B. Orr pers. comm. 2008) area. Introduced plants grow on Santa Cruz Island (Junak et al. 1995).
- Southern California Mountains and Valleys (M262Ba-d, Bf-g, Bj-p). Stands in western Riverside Co. (Klein and Evens 2005) and in central San Diego Co. (Evens and San 2005) occur along low-elevation streams. Several studies (Brothers 1985, Finn 1991, Zembal 1989) report tree densities for this section. Some interesting stands along several creeks on the north side of the San Gabriel Mountains almost reach the Mojave Desert near Littlerock and Valyermo in Los Angeles Co.
Management Considerations
This is one of the state’s rarer alliances, enduring habitat modification. Platanus racemosa does not compete well with more obligate wetland trees such as Salix gooddingii and Populus fremontii. Such wetland species have reduced and invaded several stands, particularly after the construction of dams along streams that now flow through the summer. Grazing reduces tree regeneration (Shanfield 1984). Anthracnose (a group of diseases that blight trees in the spring) affects trees throughout California. Although anthracnose does not typically kill trees outright, it does appear to limit capsule development and seed set.
This alliance is currently ranked rare with a state ranking of S3, and was ranked in January of 2022 using the NatureServe Rank Calculator version 3.186. Primary factors resulting in a rare rank are severe threats from drought, groundwater pumping, changes in flooding regimes, and competition from invasive species, all in addition to the threats mentioned in the preceding paragragh.
Associations
Stands Lacking a Well-Developed Shrub Layer
- Platanus racemosa / annual grass [2], [4], [5], [6], [7], [9], [10], [13], [14], [20]
- Platanus racemosa / Bromus hordeaceus [5]
Stands with a Mixed Tree Canopy
- Platanus racemosa - Aesculus californica [19]
- Platanus racemosa - Populus fremontii / Salix lasiolepis [3], [4], [7], [9], [12], [13]
- Platanus racemosa - Quercus agrifolia [4], [5], [6], [7], [9], [11], [12], [14], [15], [20]
- Platanus racemosa - Quercus lobata [13], [20]
- Platanus racemosa - Salix laevigata / Salix lasiolepis - Baccharis salicifolia [7], [9], [10], [13], [20]
- Umbellularia californica - Platanus racemosa [6], [20]
Stands with a Well-Developed Shrub Layer
- Platanus racemosa / Adenostoma fasciculatum [1]
- Platanus racemosa / Baccharis salicifolia [5], [10], [12], [20]
- Platanus racemosa / Toxicodendron diversilobum [8], [20]
- Quercus agrifolia / Salix lasiolepis [4], [6], [7], [12], [14], [15], [16], [17], [18], [20]
References
- [1] Bendix, J. 1994
- [2] Campbell, B. 1980
- [3] Evens, J.;San, S. 2004
- [4] Evens, J.;San, S. 2005
- [5] Keeler-Wolf, T.;Lewis, K.;Roye, C. 1997
- [6] Keeler-Wolf, T.;Evens, J. 2006
- [7] Klein, A.;Evens, J. 2005
- [8] Potter, D.A. 2005
- [9] Stillwater Sciences and URS, 2007
- [10] White, S.D. 1994a
- [11] Kittel, G.;Reyes, E.;Evens, J.;Buck, J.;Johnson, D. 2012
- [12] Sproul, F.;Keeler-Wolf, T.;Gordon-Reedy, P.;Dunn, J.;Klein, A.;Harper, K. 2011
- [13] Buck-Diaz, J.;Batiuk, S.;Evens, J.M. 2012
- [14] AECOM, 2013
- [15] Reyes, E.;Johnson, D.;Glass, A. 2019
- [16] Sikes, K.;Buck-Diaz, J.;Evens, J. 2021
- [17] Hickson, D.;Keeler-Wolf, T. 2007
- [18] Buck-Diaz, J.;Sikes, K.;Evens, J.M. 2021
- [19] Ratchford, J.;Boul, R.;Keeler-Wolf, T.;Evens, J. 2023a (in progress)
- [20] Sikes, K.;Buck-Diaz, J.;Vu, S.:Evens, J. 2023
- Barry, W.J. 1989a
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- Boyd, S.D.;Ross, T.S.;Bramlet, D. 1995
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- Calflora, 2018+
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- CCH (Consortium of California Herbaria), 2017+
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- Griffin, J.R.;Critchfield, W.B. 1972
- Grossinger, R.M.;Askevold, R.A.;Striplen, C.J.;Brewster, E.;Pearce, S.;Larned, K.;McKee, L.;Collins, J. 2006
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- Menke, J.;Reyes, E.;Hepburn, A.;Johnson, D.;Reyes, J. 2013
- Minnich, R.A. 1976
- NPS-SEKI, 2009
- Parikh, A.;Gale, H. 1998a
- Paysen, T.E.;Derby, J.A.;Black, H.;Bleich, V.C.;Mincks, J.W. 1980
- Paysen, T.E.;Derby, J.A.;Conrad, C.E. 1982
- Sands, A. 1980
- Shanfield, A.N. 1984
- Steinberg, P.D.;Howard, K.L. 2002
- Sullivan, J. 1994
- Thompson, K. 1961
- Thorne, R.F. 1976
- VegCAMP (CDFW Vegetation Classification and Mapping Program), 2015a
- VegCAMP (CDFW Vegetation Classification and Mapping Program);AIS, 2013
- VegCAMP (CDFW Vegetation Classification and Mapping Program),;GIC, 2013
- Vogl, R.J. 1976
- Zembal, R. 1989