Aliso: A Journal of Systematic and Floristic Botany Aliso: A Journal of Systematic and Floristic Botany A floristic study of Sugarloaf Ridge State Park, Sonoma County, A floristic study of Sugarloaf Ridge State Park, Sonoma County, California California

A ~pecies list of 400 vascular plants was compiled for Sugarloaf Ridge St:ue Park, a 1142 hectare (2820 acre) park in the outer Nonh Coast Ranges within Sonoma County and adjacent western Napa County, California. Relatively undisturbed siJlllds of native perennial bunchgrasses occur a.~ the un derstory In ponions of both the oak woodland and the mixed evergreen forest. Grasslands on serpentine In the park are typically dominated by NasseiiLI. One of the sttlte's eastentmost coast redwood forests occurs in the park. Nonnative Centaurea solstitialis rapidly invades annual grasslands and other dis turbed anea~ in the park. The California Oepanment of Park~ and Recreation (DPR) maintains an active prescribed burn progr.un m an effort to con110l Cenrournt solwtlalis populations. DPR alw Ul>C~ prescribed burning to retard Pseudotsuga men1,iesii estnblt~hment m oak woodlands. DPR biol ogms believe that fire ~uppression in this region results 1n an unn:uural type conversion of oak woodlands to milled evergreen foresL words:

ln this article I tist the vascular plants wh.icb occur within Sugarloaf Ridge State Park. Climate, geology, and vegetation are aJso described. The park occurs in the North Coast Range of northwestern California, mostly in Sonoma County, but including a small area in adjacent Napa County. Until approximately the mid 1800s. the Wappo tribe of indigenous people lived in a village at the headwaters of Sonoma Creek, with.in current park boundaries (Breck Parkman, personal communications). The convergence of several different plant communities makes th.is area species rich, an ideal condition for subsistence Living. Since then. past land uses have included limited conifer logging, ch arcoal maJcing (from oaks}, and Livestock grazing, however, these activities ceased when the park was established in 1964 (California Department of Parks and Recreation 1992).
Given its proximity to urban areas, and many institutions of higher learning, Sugarloaf Ridge State Park is an underutilized teach.ing resource both for secondary and undergraduate education. The park is an excellent resource for teaching basic field plant ecology. North facing slopes support more mesic vegetation than the outh facing slopes facilitating discussion of the impact a pect has on microclimatic conditions. Supporting one of the easternmost Sequoia sempervirens stands, the park provides a means to discuss the biogeography and autecology of a prominent species.
The subject of edaph.ic endemism can be taught using the serpentine chaparral and grasslands in the park. Due to the high oak diversity and resulting hybridization, the opportunity to discuss problems with the species concept exists at Sugarloaf. The successional pattern of Pseudotsuga menziesii invading mature oak woodlands. and invasion of grasslands by Centaurea solstltialis provides an avenue for discussing the influence of fi re in ecosystems and land management. In addition, using the C. solstitialis problem in the park, discussion can easily focus on other issues of exotic plant management, including biological control. G. Ledyard Stebbins (1998) recently tisted the park as one of the "outdoor floristic museums" in the greater San Francisco Bay area which is "accessible to research workers" helping to make Sonoma County "most favorable" for research opportunities.

LOCATION AND PHYSICAL GEOGRAPHY
Encompassing 1142 hectares (2820 acres), Sugarloaf Ridge State Park ranges in elevation from 183 m (600 feet) to 832 m (2729 feet). The park is located in the mountain range between the Sonoma and Napa vaJleys. Mount Saint Helena lies to the north-northwest 24 km (15 air miles). The mouth of the Russian River at the Pacific Ocean is due west 55 km (34 air miles). Lake Berryessa is roughly 29 km (18 air miles) to the northeast. Santa Rosa is 16 km (J 0 air miles) to the west. The small town of Kenwood lies 5 km (3 mjJes) to the southwest. The park encompasses Bald Mountain, Red Mountain, the upper reaches of Adobe Canyon, and part of Sugarloaf Ridge (Fig. 1). Sonoma Bowcutt AUSO Creek bisects the park. Most of the headwaters of this creek are included within the park boundaries. Sonoma Creek ultimately drains, via Sonoma Valley, into San Pablo Bay 32 km (20 air miles) south of the park. Also included in the park are portions of Bear Creek which also drains into Sonoma Creek. Adobe Canyon Road provides access from Highway 12. Hood Mountain County Park connects to the western boundary of Sugarloaf Ridge State Park. GEOLOGY Sugarloaf Ridge State Park is relatively diverse geologically (Wagner and Bortugno 1982). Serpentinized ultramafic rocks (peridotite) of Jurassic age are best represented in the northwestern portion of the park. Quaternary landslide deposits are found primarily at the toe of the south-facing slopes below outcrops of serpentinized ultramafic rocks. This pattern is unsurprising given the instability of serpentinized material when wet. The northeastern portion of the parlc is characterized by the Franciscan Complex. This complex is common in the North Coast Ranges and is a melange of sandstone, shale, conglomerate, chert, greenstone, and metagraywacke with inclusions of serpentinized ultramafic rocks. Sonoma volcanics of Pliocene age characterize Sugarloaf Ridge. A relatively small outcrop of Lower Cretaceous-Upper Jurassic Great Valley Sequence occurs in the eastern portion of the park. This sequence is a melange of marine mudstone, siltstone, sandstone, and conglomerate. CLIMATE Like most of northern California, Sugarloaf Ridge State Park receives a majority of its precipitation during late fall , winter, and spring (Fig. 2). On average, the total annual rainfall is 888.5 mrn (35 inches) in Santa Rosa, which, at 16 km (10 air miles) to the west of the park, is the closest weather station (NOAA 1993). The average annual temperature in Santa Rosa is 14.7 C (58.4 F). Being at an inland location, the park has a wide daily temperature range, particularly in summer. During summer the park is hot and dry, and as a result evapotranspiration rates are high (Elford 1964). The evapotranspiration rate is approximated using the Thornthwaite method (Fig. 2). As this approach averages the high and low daily temperatures, it underestimates the actual evapotranspiration rate (Shelton 1978 Based on climatic data from the National Oceanic and Atmospheric Administration collected between 1961 and 1990. nial grassland, cham.ise chaparral, serpentine chaparral, white alder riparian woodland, oak woodland, mixed evergreen forest, and coast redwood forest. In general, plant community boundaries intergrade thus creating a complex vegetation mosaic. This is particularly true of the oak woodland and mixed evergreen forest. Roadsides and other disturbed places serve as habitat for a variety of weedy species which are primarily nonnative.

Annual Grassland
Nonnative annual grasses and forbs from Europe dominate most of the grasslands in the park. Dominant species vary and include Avena barbata, Afatua, Bromus diandrus, B. hordeaceus, and Cemaurea solstitialis. Common associates include Aira caryophyllea, Briza minor, Lolium multiflorum, L. perenne, Taeniatherum caput-medusae, Lathyrus cicera, Trifolium spp., and Vicia villosa. Livestock grazing of park grasslands occurred between 1942and 1964, and possibly earlier (California Department of Parks and Recreation 1992. This past land use probably helped to favor nonnatives over native species. Occasional native species within the annual grassland include Calochortus luteus and Lupinus bicolor. Elymus glaucus, a native perennial grass, often occurs where the grasslands border with oak woodland.
Park staff bum the grasslands to increase native plant populations and control Cenraurea ~olstitialis.
After two consecutive years of prescribed burning in the park, the percent cover of native grassland species increased. In addition, after the burns in July 1993 and1994, C. solstitialis percent cover and the number of its seeds in the seed bank declined significantly (Hastings and DiTomaso 1996). C. solstitialis continues to plague many grassland areas considered impractical to bum due to limited access for fire control crews. State parks plans to continue herbicide use in these areas (Hastings and DiTomaso 1996).

Perennial Grassland
Most of the perennial grasslands occur on serpentine substrates at the interface between annual grassland and serpentine chaparral. The perennial grasslands are dominated by Nassella spp. Native wildflower diversity is higher in this plant community as compared to the nonnative grassland. Percent cover of vegetation is lower than the nonnative grassland which approaches 100 percent.

Chamise Chaparral
Cham.ise chaparral occurs primarily on south-facing slopes. Species diversity is relatively low, with Adenostoma fasciculatum forming a closed shrub canopy. Occasional shrub associates include Arctostaphylos manzanita ssp. manzanita, Hereromeles arbutifo/ia, and Quercus berberidifolia. The sparse understory is made up primarily of Nassella cemua. During the first few years after bums and other forms of disturbance, herbaceous species diversity increases. Post fire associates include Apiastrum angustifolium and Emmenanthe penduliflora. Lomatium repostum, which is on the California Native Plant Society watch list (List 4), occurs in this community.

Serpentine Chaparral
A distinctive chaparral community occurs on serpentine-derived soils (Hennecke Series in the park). Ceanothus jepsonii var. jepsonii and Quercus durata serve as indicator species. The native perennial bunchgrass, Melica torreyana, frequently dominates the sparse understory. Other understory associates include Galium porrigens var. tenue, Lessingia ramulosa, and Malacothrix jloccifera. A healthy population of Ceanothus sonomensis occurs along Goodspeed Trail , on the south-facing slope west of Bear Creek. This species is considered rare statewide by the California Native Plant Society (Skinner and Pavlik 1994 ).

White Alder Riparian Woodland
Alnus rhombifolia is the dominant tree along much of Sonoma Creek. Associated riparian species include Acer macrophyllum, Artemisia douglasiana, Umbellularia califomica, and Urtica dioica ssp. holosericea. Rhagadiolus stellatus, a nonnative herb not reported from elsewhere in Sonom a County, has established in several locations within the riparian corridor . In the lower stretches of the Sonoma Creek, white alder riparian woodland intergrades with coast redwood forest.

Oak Woodland
Oak woodlands within the park are highly variable. Quercus agrifolia dominates a majority of the oak woodlands in the park. The understory is sparse except in tree gaps where a variety of herbs grows, including Lathyrus vestitus, Lotus scoparius, and Madia gracilis. Shade-tolerant species in this community include Sanicula crassicaulis and Toxicodendron diversilobum. Stands of Q. kelloggii occur in scattered locations in the park, frequently with a dense understory of Festuca califomica. On the eastern side of Red Mountain, oak woodland is dominated by Q. chrysolepis and Q. kelloggii with Umbellularia califomica and Acer macrophyllum interspersed. Quercus garryana is abundant from near the confluence of Rattlesnake Creek and Sonoma Creek upstream to approximately the confluence of Malm Fork Sonoma Creek and Sonoma Creek.
In the Sonoma Mountains, Pseudotsuga mem.iesii is invading mature oak woodlands (Barnhart et al . 1996).
The oak woodlands may represent a disclimax created by native people through burning (Breck Parkman, pers. comm.). Impetus existed to manage for oak acorns, which served as a staple food. Without burning, portions of the oak woodlands in the park may ultimately become mixed evergreen forest (Barnhart et al. 1996). To maintain habitat and species diversity, state parks staff burn some of the oak woodlands to reduce P. menziesii populations (Marla Hastings, pers. comm.). Based on two 20 m X 50 m plots, one in the oak woodland and one in the mixed evergreen forest, there is some support for this management strategy, albeit limited by the small sample size (Bowcutt unpubl. data). The relative floristic similarity of the two plots was estimated by calculating the Jaccard community coefficient (J), where J = (C/(A + B +C)) X 100 with A = total of number of species in stand A, B = total number of species in stand B, and C = total number of species in both stands A and B (Barbour et al. 1987). My University of California at Santa C ruz Field Ecology students and 1 found a lower vascular plant species richness in the oak woodland (36 species vs. 46); however. the Jaccard similarity coefficient between the two communities is low (30). Based on this coefficient value, relatively few species occur in both communities; therefore, the total species richness in the park could decline if oak woodland succeeded to mixed evergreen forest. Barnhart et al. ( 1996) also corroborate this conclusion, stating, " P. menziesii invasions will result in reduction of biological diversity in this region of California."

Mixed Evergreen Forest
Mixed evergreen forest is dominated by Pseudotsuga menziesii, Quercus spp., and Umbellularia calijomica. Total tree canopy cover is roughly 85 percent. Common to occasional tree associates include Lithocarpus densijlo rus and Arbutus men~iesii. The herbaceous understory is highly variable and species rich. Common fern and herb associates include Dryopteris arguta, Melica spp., Stachys ajugoides var. rigida, Sanicula crassicaulis, Toxicodendron diversilobum, and Trientalis latifolia. Mixed evergreen forest is primarily restricted to the north-facing slope of Sugarloaf Ridge on Sonoma volcanics and the Lower Cretaceous-Upper Jurassic Great Valley Sequence. The soil type mapped for the area is Rock land which is described as being, " in rough mountainous areas where there is little soil material " (U. S. Department of Agriculture 1972). The county soil survey describes the vegetation on this soil as sparse with occasional stunted trees, which is not representative of the area under study. Much of this vegetation in the park grows near the toe of Sugarloaf Ridge, possibly because of ero- sional material which accumulates, allowing the vegetation to develop more fully.

Coast Redwood Forest
Coast redwood forest is restricted to the more mesic portions of Adobe Canyon, along Sonoma Creek, at lower elevations where the creek has deeply incised the canyon. This stand of Sequoia sempervirens represents one of the easternmost in the state; another stand occurs near the small town of Angwin approximately 15 km (9 air miles) to the north-northeast, also in Sonoma County. Within the park, coast redwood forest is a riparian community. On average, the percent cover of Sequoia sempervirens within this community in the park is 75 percent. Based on seven tree cores, the age of the older coast redwood trees is roughly 120 years, thus the trees were logged circa 1875 (Bowcutt unpubl.). Evidence of stump sprouting from trees cut during this time is common. Lithocarpus densiflorus is a frequent tree associate, although percent cover is low at approximately 5 percent. The herbaceous cover is sparse with low species richness. Herb and fern associates include Adenocaulon bicolor, Dryopteris arguta, and Polystichum munitum. Based on geologic and soil maps, coast redwood forest in the park occurs on Sonoma volcanics (Wagner and Bortugno 1982) in either Rock land or Laniger Loam (U. S. Department of Agriculture 1972).

HISTORY OF BOTANICAL RESEARCH IN THE PARK
Three unpublished vascular plant species lists exist for the park: DiTomaso (1996), Stocking (s.d.), and Wright (1975). Vouchers appeared to be lacking except for a limited number from DiTomaso's list, which was based primarily on vegetation research in the grasslands. Several of his specimens added taxa to the park flora. A floristic study of Sonoma County was recently completed . Specimens collected in the park by a variety of individuals are cited in the county flora and included in this flora when they add taxa. Whatford (1994) Table  1). The three largest families in the park are Asteraceae, Poaceae, and Fabaceae, in descending order. Asteraceae and Poaceae are the two largest families in the state, so their prominence is unsurprising. The high number of leguminous plants is largely due to the high diversity of Trifolium. With 15 taxa, it is the best represented genus in the park. Asteraceae, Poaceae, and Fabaceae combined represent 35% of the flora. Further floristic work in the park will no doubt add species to the list; however, the majority are represented in this publication.
Collections made as a part of this study added four taxa to the known flora of Sonoma County: Carex amplifolia, ]uncus nevadensis, Montia parvifolia, and Rhagadiolus stellatus. Carex amplifolia and R. stellatus were included in the county flora based on unpublished findings of this floristic research. ]uncus nevadensis, and M. parvifolia represent additions not included in Best et al. (1996). In addition, this work provides vouchers for species listed in Best et al. (1996) without the benefit of a voucher specimen; included in this category are the newly introduced Trifolium striatum not included in Hickman' (1993) and Claytonia parviflora.

MANAGEMENT RECOMMENDATIONS
California Department of Parks and Recreation manages the park for the preservation of native plant biodiversity. Three aggressively invasive exotics, Cytisus scoparius, Foeniculum vulgare, and Genista monspessulana, are currently rare in the park, bowever, a vigilant manual removal. program is recommended to keep these species from becoming management problems in the future. Continued efforts to control Centaurea solstitialis and feral pigs are encouraged. Recreational use of horses in the park presents a means for introduction of nonnative species (e.g., Trifolium striatum). Given the recreational value of horseback riding, 1 do not recommend prohibiting their use. However, attention should be given to controlling new introductions to keep them from becoming invasive problems. This would include frequently monitoring trails used by the horses and around the corral.
Future acquisitions are desired to connect, at least with trail corridors, several local parks to Sugarloaf Ridge State Park including Annadel State Park, Bothe Napa State Park, and Jack London State Park (Bud Getty, pers. comm.). Sugarloaf Ridge State Park is already contiguous with Hood Mountain Regional Park, which is 608 hectares (1500 acres).

FUTURE RESEARCH NEEDS
A thorough survey of 410 hectares ( lOll acres) added to the park in 1997 was beyond the scope of this effort and is worthy of future attention. With this addition, the park's total area is 1552 hectares (3831 acres). Voucherless taxa listed in the county flora as being from "Sugarloaf Ridge" are not included in this study. Neither are voucherless taxa on the three unpublished checklists for the park (DiTomaso 1996; Stocking s.d.;and Wright 1975). Voucher specimens are needed to confirm the presence of these and other taxa not included in this study.
ACKNOWLEDGMENTS I received much research support for which I am grateful. Kate Mawdsley made significant contributions by assisting with collecting, identification, and manuscript editing. Bud Getty of the California Department of Parks and Recreation and his staff provided logistical support. My students in California Floristics at the University of California at Davis collected specimens in spring 1993 and 1994. My students in Ecology Field Quarter at University of California at Santa Cruz helped to collect vegetation data in the park in May 1996. Dr. Ellen Dean and Jean Shepard graciously provided space to work at the University of California Davis Herbarium. They also identified several grasses joyfully. Dr. Michael Vincent identified the Trifolium striatum. Dr. Ann Howald gave a phone consultation. Karen Knoll provided field assistance in July 1997. The Davis Herbaria Society helped defray the cost of hiring a cartographer and paid for some travel expenses. Dr. R. K. Benjamin and two anonymous reviewers contributed helpful criticisms on an earlier draft.

ANNOTATED CHECKLJST OF THE VASCULAR PLANTS
Voucher specimens are housed in the University of California Davis Herbarium at the University of Cal-ifomia (DAV) unless otherwise noted. Voucher specimens exist for 97% of the taxa represented in this floristic study. Nomenclature follows Hickman (1993). Common names were gleaned from several sources: Abrams (1940;1944;and 1951), Abrams and Ferris (1960). Best et al. (1996), Hickman (1993), Mason (1957), and Munz and Keck (1973). Herbarium abbreviations follow Holmgren et al. (1990). In addition the following notations were used: * for nonnative species and + for unnaturalized garden rel icts not included in the numerical analyses.  Stocking (s.d.) and Wright ( 1975). Collected in Adobe Canyon and several other inland Sonoma County locations . Constance ( 1993) reports this species as occurring only along the north and central coast.   (1996), Stocking (s.d.), and Wright (1975). Collected "probably in the vicinity of MI. Hood''     (Best et al. I 996). Also reported by Stocking (s.d.) and Wright ( 1975  . Also reported by DiTomaso (1996) and Wright ( 1975 (1993), however, Best et al. (1996)   . Also reported in park by Stocking (s.d.) and Wright (1975