Frenzel Creek

The area covers 935 acres (378 ha). Elevations range from 1390 to 3090 ft (424-942 m). The entire drainage of Frenzel Creek, a small north-flowing, permanent tributary of Little Stony Creek, is included. Slopes are predominantly eastern- and western- facing and steep, except for the majority of the two main ridgetops.

Distinctive Features

Distribution and Regeneration of Sargent and MacNab Cypress: These are the only two sympatric species of cypress in California. MacNab cypress is an interior, xerophilic cypress, occurring on ridgetops, never overlapping with Sargent cypress in the drainage. Sargent cypress is a mesophilic coastal type near its most inland distribution here. Hybridization was not seen in the RNA and is rare elsewhere (Griffin and Critchfield 1976). Sargent is apparently less fire-dependent than MacNab, regularly reseeding in riparian areas of drainage, without fire. In contrast, MacNab cypress rarely reseeds without fire. Sargent cypress is relatively shade-tolerant in the seedling stage.

Numbers and Types of Serpentinite Endemics: About 36 taxa in the RNA are generally considered serpentinite endemics or indicators (Kruckeberg 1984). Most are herbaceous neo-endemics; five are likely to be paleo-endemics (Raven and Axelrod 1978).

Rare Flora: Eight taxa found in the drainage are listed by CNPS, including Astragalus clevelandii (List 4), Antirrhinum subcordatum (List 1B), Hersperolinum drymarioides (List 1B), Mimulus brachiatus (List 3), Mimulus glaucescens (List 4), Senecio clevelandii (List 4), and Streptanthus morrisonii (List 1B).

New and Undetermined Taxa: Two plant taxa, Castilleja miniata ssp. nov. and Allium cratericola ssp. nov., have been collected in the RNA. The Castilleja was collected for the first time during the fieldwork for the RNA ecological survey. It is a serpentine riparian species locally common at Frenzel Creek and along portions of Little Stony Creek. It also was seen at Cook’s Springs, about 2 miles (3 km) east of the RNA. L. Heckard of the Jepson Herbarium believes this is a distinctive subspecies of the widespread C. miniata complex. The Allium occurs on serpentinite barrens and has previously been collected in the inner N. Coast Ranges by Dale McNeal and his students at University of the Pacific, but it is still undescribed.

Association Types

Vegetation sampling consisted of five 100-m² plots in the Sargent cypress dominated area, and six 100-m² plots in the MacNab cypress stands. Acreage of each type is based on the ecological survey (Keeler-Wolf 1983), and the sum does not match the total area.

Serpentinite Chaparral (37600, 71321, 83220): 580 acres (235 ha). Two subtypes are divided into four phases.

The mixed subtype 1 is most extensive, dominated by Arctostaphylos viscida and Quercus durata, with Ceanothus jepsonii var. albiflorus, Garrya congdoni, Heteromeles arbutifolia, and Eriodictyon californicum. It includes the A. viscida phase on most xeric exposures; the Q. durata phase dominates on east, northeast, and northwest exposures. Foothill pine (Pinus sabiniana) forms a very open canopy in some places. Thirty-five species of herbs are listed as typical for this subtype, including the serpentine endemics Allium falcifolium, Clarkia gracilis ssp. albicaulis, Claytonia gypsophylloides, Calystegia subacaulis, Nemacladus montanus, Senecio greenei, Silene campanulata ssp. glandulosa, and Streptanthus breweri. 

Subtype 2 is dominated by MacNab cypress (51 acres, 21 ha). Two phases occur: exposed and sheltered. The exposed phase on ridgetops is most extensive, with subdominant serpentine chaparral shrubs and relatively high cover of Adenostoma fasciculatum. Stands are of uniform height (3-4 m) and age (mostly 60-80 years). Herbs are similar to mixed serpentinite chaparral. The sheltered phase is restricted to northern slopes and heads of ravines. MacNab Cypress is more often a tree up to 7 m tall and 64 cm dbh. Density of woody plant stems varies from 2400 to 9600/ha. Basal area of MacNab cypress ranges from 2.7 m²/ha on the 1950 burn to 86 m²/ha on the sheltered phase.

Serpentinite Barrens (no Holland equivalent): 81 acres (33 ha). Vegetation is very sparse and herb dominated. Species include Streptanthus morrisonii, S. breweri, Allium cratericola ssp. nov., Asclepias cordifolia, A. solanoana, Eriogonum vimineum, E. nudum, E. dasycarpum, and E. ursinum var. nervulosum.

Non-Serpentinite Chaparral (37110, 37E00): 66 acres (27 ha). Two subtypes (mesic and xeric) occur. The mesic subtype occurs on northeast-facing slopes and is dominated by tall shrubs of Cercocarpus betuloides, Ceanothus cuneatus, Quercus wislizenii var. fructescens, and Heteromeles arbutifolia. Herbs are often dense and include 20 typical species, the majority of which are not present on serpentinite chaparral.

The xeric subtype occurs on ridgetops and is dominated by thick stands of Adenostoma fasciculatum and Ceanothus cuneatus with lesser numbers of Arctostaphylos manzanita, A. glandulosa, A. canescens, Quercus wislizenii var. fructescens, Q. durata, Q. x morehus, Heteromeles arbutifolia, Cercocarpus betuloides, Ribes malvaceum, and Haplopappus linearifolius. Herbs and grasses are few, with annual Bromus dominant.

Serpentinite Riparian and Valley Bottom (83220 in part): 57 acres (23 ha). This is the most hydrophilic vegetation in the RNA. It is subdivided into three types: strict riparian (permanent water), mesic valley bottom (moist and shady, but no year-round water), and rivulet herbaceous association (along intermittent, sunny streams). Characteristic woody species of the strict riparian type include Rhododendron occidentale, Salix breweri, Calycanthus occidentalis, Sargent cypress, and Rhamnus californica ssp. crassifolia. Understory species include Aquilegia exima, Achillea millefolium, Lilium pardalinum, Stachys albens, Epipactis gigantea, Castilleja miniata ssp. nov., Carex serratodens, Scirpus americanus, Senecio clevelandii, Heleocharis sp., Helenium bolanderi, Angelica tomentosa, and Juncus mexicanus.

The mesic valley bottom type is dominated by Sargent cypress and California bay (Umbellularia californica) (often mutually exclusive). Other woody species include Ceanothus integerrimus var. californicus, Rhamnus californicus ssp. crassifolius, Toxicodendron diversilobum, and Cercis occidentalis. Many species of herbs are shared with adjacent serpentinite chaparral. Tree densities range from 700 to 6200/ha. Seedling densities (all Sargent cypress) range from 100 to 600/ha. Basal area ranges from 6.5 to 72.3 m²/ha. Mean dbh ranges from 3.5 to 31.0 cm. 

The rivulet herbaceous association type species include Mimulus brachiatus, Centaurium sp., Mimulus bicolor, M. glabrescens, Epilobium minutum, and Gayophytum sp. Shading restricts growth of the characteristic herbs.

Pine-Oak Woodland (71322, 83210): 36 acres (15 ha). This association occurs on north, northeast, and northwest-facing slopes at the head of the drainage, off serpentinite. Canyon live oak (Quercus chrysolepis) is dominant, with knobcone pine (Pinus attenuata) and, occasionally, foothill pine emerging from the canopy. Understory species are Cercocarpus betuloides, Heteromeles arbutifolia, Arctostaphylos manzanita, A. canescens, Toxicodendron diversilobum, Berberis dictyota, Lotus crassifolius, Cynoglossum grande, Symphoricarpos acutus, Ribes californicum, Dodecatheon hendersonii, Sanicula crassicaulis, and Keckiella lemmonii.

Non-Serpentinite Riparian (no Holland equivalent): 3 acres (1 ha). This association is restricted to a small area of Frenzel Creek on Franciscan rocks. Species include California bay (dominant), Fremont cottonwood (Populus fremontii), Salix laevigata, Sambucus mexicana, Vitis californica, Rubus ursinus, Rhus trilobata, Clematis ligusticifolia, Potentilla glandulosa, Cystopteris fragilis, Adiantum jordanii, Perideridia kelloggii, Lotus sp., and Datisca glomerata.

Plant Diversity

One hundred eighty species are listed.

Conflicting Impacts

Off-road vehicle use adjacent to the RNA may have light impact on upper drainage. Fire suppression practices may necessitate controlled burning to maintain MacNab cypress stands in the future.