Juglans californica Forest & Woodland Alliance
California walnut groves
California walnut groves
USDA Ecological Section Map
Summary Information
- Primary Life FormTree
- Elevation150-900 m
- State RarityS3.2
- Global RarityG3
- DistributionUSA: CA (NatureServe)
- Endemic to CaliforniaYes
- Endemic to California Floristic Province and DesertsYes
- Date Added1995/11/01
Characteristic Species
Juglans californica is dominant or co-dominant in the tree canopy with Alnus rhombifolia, Fraxinus dipetala, Heteromeles arbutifolia, Quercus agrifolia, Quercus lobata, Salix laevigata, Salix lasiolepis, Sambucus nigra and Umbellularia californica.
Vegetation Layers
Trees < 15 m tall; canopy is open to continuous. Shrub layer is sparse to intermittent. Herbaceous layer is sparse or grassy.
Membership Rules
- Juglans californica > 50% relative cover in the tree canopy or > 30% relative cover with Quercus agrifolia present (Keeler-Wolf and Evens 2006).
Habitats
Riparian corridors, but most stands cover all hillslopes. The USFWS Wetland Inventory (1996 national list) recognizes Juglans californica as a FAC plant.
Other Habitat, Alliance and Community Groupings
| MCV (1995) | California walnut series |
| NVCS (2009) | Juglans californica woodland alliance |
| Calveg | Black walnut |
| Holland | California walnut woodland, Walnut forest |
| Munz | Southern oak woodland |
| WHR | Coastal oak woodland |
| CDFW CA Code | 72.100.00 |
National Vegetation Classification Hierarchy
| Formation Class | Mesomorphic Tree Vegetation (Forest and Woodland) |
| Formation Subclass | Temperate Forest |
| Formation | Warm Temperate Forest |
| Division | Madrean Forest and Woodland |
| Macro Group | California Forest and Woodland |
| Group | Californian broadleaf forest and woodland |
Remarks
Juglans californica is a deciduous tree that grows to 15 m tall. Tree morphology varies with age and site conditions, and trees may have multiple trunks. Dense stands tend to be single stemmed. The root system is extensive with a deep taproot. Plants produce large nuts in years with abundant rain. Small mammals and flooding events on seasonal creeks disperse the seeds. Seeds germinate within 4 weeks of dispersal (Esser 1993c). J. californica is a CNPS list 4.2 plant. Stanford et al. (2000) argued for its listing status after studying DNA sequence data.
Juglans californica stands occur in association with annual grassland, mesic chaparral, coastal sage scrub, oak woodland, and riparian vegetation. Holland (1986) divided stands into more open woodlands and more closed forest types. Moisture requirements appear to be similar to those of Quercus agrifolia; the densest forests tend to be equally dominated by these two trees.
Juglans californica stands occur in association with annual grassland, mesic chaparral, coastal sage scrub, oak woodland, and riparian vegetation. Holland (1986) divided stands into more open woodlands and more closed forest types. Moisture requirements appear to be similar to those of Quercus agrifolia; the densest forests tend to be equally dominated by these two trees.
Life History Traits of the Principal Species
| Juglans californica | |
|---|---|
| Life forms | Tree; winter deciduous |
| Seed storage | Transient |
| Seed longevity | Short |
| Mode of dispersal | Animal; gravity; water |
| Germination agents | None |
| Mode of sprouting | Buds on large branches or trunks; underground structures |
| Survivability after fire/disturbance | Fire-hardy; high sprouter |
| Disturbance-stimulated flowering | No |
| Reproductive range | 20-100+ years |
| Recruitment | Low |
| Regional variation | Low |
Fire Characteristics
Juglans californica recovers quickly from fire. It sprouts vigorously when top-killed, but the seeds are killed (Quinn 1990). Plants sprout from lignotuber-like root crowns and from trunks following burning or cutting (Esser 1993c). The tree cover of the stands relates dynamically to fire history and site productivity. In general, J. californica stands are subject to periodic fires. Annual fire is possible when dead annual grasses are present beneath and between the trees during the summer fire season (Quinn 1990).
| Fire return interval | Medium (25-100+ years) |
| Seasonality | Summer-early fall |
| Size/extent | Medium; up to or beyond stand size |
| Complexity | Low to moderate |
| Intensity | Low to moderate |
| Severity | Low to high |
| Type | Surface to passive crown |
| Regional knowledge | Southern California |
Regional Status
- Southern California Coast (261Bb, Bd-g, Bi). The most extensive stands occur from near downtown Los Angeles to the Whittier Hills (Keeley 1990a, Mullally 1992, R. A. Minnich pers. comm. 2007). Those in the Santa Monica Mountains predominantly grow interspersed with chaparral on the slopes (Keeler-Wolf and Evens 2006). Stands also occur in the lower Santa Clara River drainage (Stillwater Sciences and URS 2007).
- Southern California Mountains and Valleys (M262Bf, Bj). Stands occur in the Puente Hills to Chino Hills. Small, fragmented stands also occur along Cajon Wash in western San Bernardino County.
Management Considerations
Juglans californica stands have been reduced historically as a result of urban development, type conversion, and agricultural clearing. A stand’s species composition, density, and tree size have much to do with its fire history.
Associations
- Juglans californica / annual herbaceous [1], [2], [3]
- Juglans californica / Artemisia californica / Leymus condensatus [1], [3]
- Juglans californica / Ceanothus spinosus [1]
- Juglans californica / Heteromeles arbutifolia [1]
- Juglans californica / Malosma laurina [1]
- Juglans californica - Quercus agrifolia [1], [3]
References
- [1] Keeler-Wolf, T.;Evens, J. 2006
- [2] AECOM, 2013
- [3] Reyes, E.;Johnson, D.;Glass, A. 2019
- Barbour, M.G. 1988
- Bowler, P.A. 1989
- Esser, L.L. 1993c
- Holstein, G. 1984
- Keeley, J.E. 1990a
- Mullally, D.P. 1992
- Quinn, Ronald D. 1990
- Stanford, A.M.;Harden, R.;Parks, C.R. 2000
- Stillwater Sciences and URS, 2007
- Swanson, J.C. 1967
- Vogl, R.J. 1976