Engelmann Oak [Quercus engelmannii Greene]

Engelmann Oak [Quercus engelmannii Greene]

Listing CNPS List 4 R-E-D Code 1-2-2

State/Federal. Status -- None FAGACEAE Apr.-May

Global Rank G3 State Rank S3.2

Distribution: San Diego County, Orange County, and Riverside County, Santa Catalina Island; Baja California, Mexico

Habitat: Oak Woodland and Southern Mixed Chaparral are both utilized by this tree. Larger oaks sometimes occur in vast savannah grasslands such as at Guejito (Fallbrook sandy loam), Ballena (Las Posas fine sandy loam), and near Santa Ysabel and Mesa Grande (Holland stony fine sandy loam, Crouch rocky coarse sandy loam). In the foothills the Engelmann Oak may also occur as a shrubby element within the chaparral. Typically in such a situation the understory is relatively dense and the small oaks (even mature oaks in this habitat usually remain stunted) are concentrated on the periphery of watercourses or mesic slope aspects. Along larger creeks Quercus agrifolia usually predominates.

Known Sites: The Engelmann Oak is relatively abundant in the Echo military sector on Camp Pendleton, in the Santa Margarita Mountains, on the Guejito Ranch, on Rancho Cuca, and near Mesa Grande. It is well represented in the vicinity of Alpine such as on slopes near South Grade Road, in Pamo Valley, east of Dulzura, and on the old Daley Ranch north of Escondido. In numerous other areas it is locally common. These include Japatul Valley, along Deerhorn Valley Road, near Cole Grade Road and Oak Glen Road, Tecolote Drive in the Pala Mesa area, off Clevenger Canyon Road, at Glen Lonely, at Stallion Oaks near Boulder Creek Road, in Lee Valley, east of Victoria Lane in Alpine, near Ramona View Drive in east Ramona, and in the hills south of Bonsall and the San Luis Rey River. Numerous isolated trees and small copses occur in north coastal San Diego County such as in Lux Canyon in Encinitas, and west of Ramblas de las Flores in Rancho Santa Fe. Often these trees show some introgression with Quercus dumosa, and apparent hybrids with this species are often common nearby. Also reported from Buckman Springs, Rancho Bernardo, Banner, Lost Valley, San Felipe, and the Vulcan Mountains. Herbarium specimens were examined from Monrovia in Los Angeles County and from Santa Catalina Island (one tree reported extant). Reported by Roberts in Orange County at Casper's Regional Park and Rancho Mission Viejo. This tree is abundant on the Santa Rosa Plateau in western Riverside County west to Tenaja Road.

Three specimens are found at the San Diego Natural History Museum south to 32 31' North; where collected by Moran (SD 104373) at the edge of a valley near El Pedregal. Such limited collection numbers underscore its rarity in Mexico.

Status: Engelmann Oak populations in Southern California are still relatively abundant and stable. Poor reproduction is an apparent problem with this oak. This may be due to a variety of reasons, foremost of which is cattle overgrazing. Other factors may include herbivory from small mammals, birds, and insects on the acorns; as well as browsing from deer, and a need for specific weather conditions to promote optimal seedling establishment. Frequent Engelmann Oak hybrids, presumably with species of scrub oak, are often noted in the chaparral; typically these individuals are shrub-sized and exhibit much leaf variation.

Single-leaf Basketbush [Rhus trilobata Nutt. var. simplicifolia (Greene) Barkley)

Listing CNPS List 2 R-E-D Code 3-1-1

State/Federal. Status -- None ANACARDIACEAE Mar.-Apr.

Global Rank G5T? State Rank S1.3

Distribution: San Diego County; Arizona; Utah; Colorado; Oklahoma

Habitat: Desert Basketbush occurs in open Sonoran Desert Scrub on Whale Peak.

Known Sites: This variety of the common Basketbush is reported by Shreve and Wiggins from the Sierra Juarez and Sierra San Pedro Martir of Baja California, eastward to southern Utah, Colorado, and Oklahoma. It grows in San Diego County in a drainage among the Pinyon Pines at about 4000 feet on a north-facing slope of Whale Peak.

Status: The isolated population of Single-leaf Basketbush is well defended on Whale Peak and this species is stable in San Diego County. This variety of basketbush is not addressed within the Jepson Manual (1993), although a note mentions that geographic variation for Rhus trilobata within western North America needs study. Provisionally, it is recommended that all Southern California populations should be protected.

Copyright May 1994 Craig H. Reiser.

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