A checklist and floristic summary of the vascular ...

Phytotaxa 95 (1): 1–60 (2013) www.mapress.com/ phytotaxa / Copyright © 2013 Magnolia Press

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PHYTOTAXA 95

A checklist and floristic summary of the vascular plants of Napa County, California BENJAMIN J. CRAIN1, 2, 3 & JEFFREY W. WHITE1 ¹Biodiversity Research and Education Laboratory, Department of Biological Sciences, Humboldt State University, 1 Harpst Street, Arcata, CA, 95521; [email protected] 2 Department of Biology, University of Puerto Rico-Rio Piedras, San Juan, PR, 00936; [email protected] 3 Author for correspondence

Magnolia Press Auckland, New Zealand

Accepted by Alexandre Monro: 25 Feb. 2013; published: 23 Apr. 2013

A checklist and floristic summary of the vascular plants of Napa County, California Benjamin J. Crain & Jeffrey W. White (Phytotaxa 95) 60 pp.; 30 cm. 23 Apr 2013 ISBN 978-1-77557-142-1 (paperback) ISBN 978-1-77557-143-8 (Online edition)

FIRST PUBLISHED IN 2013 BY Magnolia Press P.O. Box 41-383 Auckland 1346 New Zealand e-mail: [email protected] http://www.mapress.com/phytotaxa/

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ISSN 1179-3163

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Phytotaxa 95 (1) © 2013 Magnolia Press

CRAIN & WHITE

Table of contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 APPENDIX 1. Checklist of the vascular flora of Napa County, California. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Abstract Napa County contains particularly high levels of biological diversity in a variety of categories and is considered one of ten localized areas in California that contain the highest numbers of native and endemic plant species. Here we present a floristic summary based on a new annotated checklist of the flora of this uniquely diverse region. The checklist was developed by combining several local and statewide floristic data sources that represent herbarium collection records and other observations from Napa County. The final checklist of vascular plants for Napa County consists of 1,716 taxa, including 1,418 native taxa from 101 different families. Alarmingly, 126 native taxa in Napa County were listed as rare or threatened to some degree. The results of this study demonstrate that for its size, Napa County contains remarkably high levels of plant diversity as well as high concentrations of special status taxa as compared to other areas within the California Floristic Province, the State of California as a whole, and other regions within global biodiversity hotspots characterized by Mediterranean climates. In particular, this analysis highlights the floristic significance of Napa County at global and local levels, and thus, this review is an important step to help promote and facilitate long term research and conservation planning in the area. Key words: biodiversity hotspots, California floristic province, Mediterranean biome, rare taxa, species-area models

Introduction California is considered one of the most biologically diverse regions of the world (Myers et al. 2000, Orme et al. 2005, Brooks et al. 2006) and the state ranks high on the list of areas within the USA with unusually large numbers of rare and endangered species (Dobson et al. 1997, Chaplin et al. 2000). Many parts of California also rank in the highest categories for human population densities, a factor contributing directly to habitat degradation, the leading cause of species loss in the state (Parisi 2003). California is classified as both a national hotspot of imperiled biodiversity (Abbitt et al. 2000, Chaplin et al. 2000) and one of the 25 global hotspots of biodiversity (Myers et al. 2000) because of its high diversity levels and the presence of imminent threats. Recent research suggests that species richness patterns are not evenly distributed within global biodiversity hotspots and that local hotspots of diversity need to be identified (Médail & Quézel 1997, 1999, Harris et al. 2005, Murray-Smith et al. 2008). Compared to the majority of of Califonia, Napa County contains particularly high levels of diversity for a number of groups of organisms ranging from plants to amphibians (Parisi 2003) and it is considered one of ten areas in the state that contain the richest concentrations of native and endemic plant species (Stebbins & Major 1965, Thorne et al. 2004). Stebbins and Major (1965) strongly encouraged the development of local level plant checklists and specifically noted the absence of published data from places such as Napa County. Despite Napa’s floristic significance, however, the four-county vascular plant checklist and floristic summary prepared by Major (1963) remains the only checklist containing local level data for the area. Recently several researchers have renewed the argument that developing checklists for all fields of biological research is critical to understanding and conserving

VASCULAR PLANTS OF NAPA COUNTY, CALIFORNIA


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biodiversity as these lists allow us to monitor species’ statuses and trends, to support research and education, and to promote the benefits arising from biodiversity (Droege et al. 1998, Crane 2004). Consequently documenting the plant species that occur in Napa County is an important task. To this end, the goal of this study is to develop a comprehensive vascular plant checklist for Napa County. An additional aim is to present detailed comparisons of Napa’s flora to the State of California, to other areas within the California Floristic Province, and to other botanically diverse regions within hotspots characterized by the Mediterranean biome. Largely due to its importance for the production of grapes a great deal of geographical data has been collected from Napa County (Stoms et al. 2005). Napa County is located north of San Pablo Bay in the coastal mountains between 38.15° and 38.86°N latitude and between 122.64° and 122.06°W longitude. Napa County’s total surface area comprises 2,052 km² and it covers 0.5% of California’s total surface area of 403,932 km² (U. S. Census Bureau 2000), making it the eighth smallest of the 58 counties within the State. Napa County encompasses much of the Napa River, Putah Creek, and Suisan Creek watersheds (Lambert & Kashiwagi 1978). As part of the California Coast Range, elevation in Napa County varies from sea level to around 1,307 meters in the Mayacamas Mountains which roughly define the County’s northern and western borders. The Blue Ridge, the Rocky Ridge, and the Vaca Mountains represent Napa’s eastern extent (Lambert & Kashiwagi 1978, Miles et al. 1998). The geology of Napa County is characterized by several major bedrock units composed mainly of sedimentary, volcanic and ultramafic rocks from the Cenozoic and Mesozoic periods (Miles et al. 1998, Harden 2004). Each of these units contributes distinctive parent material to the variety of soils found in the area. Lambert and Kashiwagi (1978) describe four of the resulting soil associations which cover roughly 16% of the county, as well drained to poorly drained, nearly level to moderately steep soils on alluvial fans, on flood plains, in basins, on tidal flats, and on terraces. They describe seven other associations in Napa County which cover 84% of the area as excessively drained to well drained, gently sloping to very steep soils on uplands (Lambert & Kashiwagi 1978). The diversity of substrates in Napa County would be expected to directly influence floristic patterns. Napa County is located within one of five climate regions in the world generally characterized by a Mediterranean climate (see Dallman 1998). Relatively mild wet winters, warm dry summers and long growing seasons are standard for the county (Hickman 1993, Ornduff et al. 2003, Parisi 2003). Regional maps show that Napa County encompasses at least three unique climatic zones that combine maritime and interior influences (Hickman 1993). Mean maximum temperatures range from approximately 10° to over 37° C and annual rainfall in the County ranges from around 38 to 139 cm per year (Lambert & Kashiwagi 1978). This climate offers ideal growing conditions for a number of unique plant species (Dallman 1998). Despite Napa County’s relatively small size, it includes portions of two geographical regions and three geographical sub-regions found within the California Floristic Province. The majority of the county is included in the North Coast Ranges sub-region of the Northwestern California region. The remaining portion of the county is included in the San Francisco Bay Area and Central Coast sub-regions of the Central Western California region (Hickman 1993). Consequently, nearly 60 vegetation types that grow in a variety of ecological niches have been identified and mapped in Napa County (Thorne et al. 2004). Thus the extraordinarily unique and diverse flora of Napa County is largely a consequence of the overall heterogeneity of the area (Hickman 1993, Ornduff et al. 2003, Parisi 2003).

Methods To create the plant diversity checklist of Napa County several local and statewide data sources based on herbarium collections from Napa County and published floras from California were combined. Initially available data from Napa were pooled from four databases: 1) The Jepson Herbaria Online Interchange for California Floristics SMASCH database (Jepson Flora Project 2005), 2) the Consortium of California Herbaria database (CCH 2010), 3) the California Native Plant Society (CNPS) Inventory of Rare and

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Endangered Plants (CNPS 2005), and 4) the Calflora: Information on California Plants for Education, Research and Conservation database (Calflora 2000). We chose these data sources based on their representation of large plant collections at significant local and regional herbaria and because of their collaborative efforts with several state and federal government agencies, botanical gardens and universities. The preliminary Napa County plant checklist was further augmented with personal observations and data collected by local botanists. These observations mainly confirmed the presence of taxa reported from Napa County but for which no voucher specimen existed. Local landowners were also helpful and although their extensive knowledge of the plants on their lands added no new species to the final checklists, they did provide valuable information on several undocumented populations of rare taxa. Once collected all data records were compiled into a provisional checklist. Each taxonomic record (species, sub-species, or variety) was subjected to a rigorous screening process. During this process, synonymous records, nomenclatural inaccuracies (e.g. orthographical variants) and taxonomic errors were eliminated whereas taxonomic revisions were incorporated. Taxonomic authority was based on the Jepson Manual: Higher Plants of California (Baldwin et al. 2012) and the Angiosperm Phylogeny Group III system (APG 2009) in addition to more recent publications for specific taxa. The process began by using Fred Hrusa’s CROSSWALK (Hrusa 2005) database for plant taxonomic synonymy to screen each record. In the few cases where records were unavailable on CROSSWALK records were verified by using the California Native Plant Society’s Inventory of Rare and Endangered Plants of California (Tibor 2001) and the Jepson Manual (Hickman 1993). Taxonomic records that did not survive the screening and records listed as genera only were rejected from the checklist while the verified records were put on a list for accepted taxa. Lastly, we removed taxa that were presumed to exist in Napa County based on reports or other literature (see Calflora 2000) but could not be confirmed by an authoritative data source or herbarium records. In all cases each record on the final checklist was either confirmed by herbarium collection records or by reports from at least two published floras. After completing this screening process we catalogued all accepted and confirmed plant records in a final checklist divided into the native and exotic floras of Napa County (Appendix 1). Once completed we annotated the native plant checklist with information on rarity status by using data from the California Department of Fish and Game Natural Diversity Database (CNDDB), NatureServe’s Element Ranking System (CNDDB 2013, NatureServe 2006), and Crain & White (2011). Using the final checklist we compared total richness and rarity richness (including area adjusted measures) for Napa County to the same measures for California as well as other counties in the state. Special attention was given to the flora of Sonoma County (Best et al. 1996) as it is adjacent to Napa County and shares many of Napa’s geographical features. Similar attention was given to Roberts’ (1998) plant checklist for Orange County as well as to Howell et al.’s (2007) checklist for Marin County as they have the most similar overall areas to Napa County. Nonetheless we compared our results to all counties in California with available data to incorporate as much of the California Floristic Province into the analysis as possible (Hoover 1970, Smith & Wheeler 1992, Oswald & Ahart 1994, Moe & Twisselmann 1995, Matthews 1998, Clifton 2003, Rebman & Simpson 2006). Likewise we conducted similar comparisons to subsets of other global biodiversity hotspots within the Mediterranean biome for which comparable data on plant diversity was available (Médail & Quézel 1997, Goldblatt & Manning 2002, Judd et al. 2008). Specifically we compared the flora of Napa County to subsets of the Mediterranean Basin, the Southwest Australia, and the Cape Floristic Provence biodiversity hotspots. Collectively these comparisons provided a local and global perspective on the flora of Napa County. To account for the effects of area on our analysis we developed species area models based on the available data for each of the locations we considered in this study to determine if Napa County contained more plant species than expected for its overall size. We used log transformed data and the linear form of the power function, i.e., log S = log c + z log A, where S is species richness, A is area (km2) and c and z are data specific constants to calculate species area curves (see Veech 2000). Two curves were calculated, one for all locations in California with available data on total number of plant species and another for locations within hotspots occurring in the Mediterranean biome with data on total native plant species numbers. Following methods VASCULAR PLANTS OF NAPA COUNTY, CALIFORNIA


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employed by Pomeroy (1993), Ceballos and Brown (1995) and Estill and Cruzan (2001) we identified locations that were furthest above the expected values predicted by the species area curves to determine which locations furthest exceeded their expected richness values. This analysis allowed us to account for the effects of area on species richness.

Results The final checklist of the flora of Napa County included 1,716 native and exotic taxa representing 110 families (Appendix 1). The native plant checklist included 1,418 taxa representing 82.6% of Napa County’s total vascular flora and 101 different families. Ten families contained the largest proportion of the native vascular flora in Napa County (Table 1). These ten families included 693 taxa representing 48.8% of Napa’s native flora (40.3% of the total flora). In addition to the native plants, there were also 298 exotic plant taxa comprising 17.4% of the county’s total vascular flora. These exotic taxa were members of 48 different families including nine families unique to the checklist for exotic plants. The most represented families on the exotic plant checklist (Table 2) included 219 taxa representing approximately 73.4% of Napa’s exotic flora (12.7% of the total county flora). In terms of rarity, 126 native taxa representing 8.8% of the native flora of Napa County (7.3% of Napa’s total flora) were listed as rare or threatened at the global or state level (CNDDB 2013). These special status taxa were from 38 different families, 11 of which were the best represented (Table 3). These 11 families contained 84 special status taxa representing over 65% of all special status plants in Napa County. In summary, it is apparent that the diversity of plants occurring in Napa County makes a substantial contribution to the overall diversity of California and the United States. TABLE 1. Ten best represented families in the Napa County native flora. Family

Number of native taxa in Napa

Percentage of native Napa flora

Percentage of total Napa flora

Asteraceae

197

13.9

11.5

Fabaceae

88

6.2

5.1

Poaceae

85

6.0

5.0

Boraginaceae

57

4.0

3.3

Brassicaceae

50

3.5

2.9

Polemoniaceae

46

3.2

2.7

Apiaceae

45

3.2

2.6

Cyperaceae*

42

3.0

2.5

Orobanchaceae*

42

3.0

2.5

Polygonaceae

41

2.8

2.3

* indicates a tie.

The checklist developed during this study, had significant numerical differences when compared to four other lists and databases that include taxa from Napa County (Table 4). Our checklist included more taxa than both Major (1963) and the Jepson Herbaria SMASCH list for Napa County (Jepson Flora Project 2005). The higher number of taxa was largely due to newly discovered taxa, more recent collections, and taxonomic revisions and updates. In contrast, the number of taxa listed on Calflora (2000) and the Consortium of California Herbaria (2012) was larger than on our checklist. This was primarily due to these sites inclusion of numerous taxa presumed to exist in Napa County in addition to taxa listed at the genus level only, i.e. taxa that we excluded from our final checklist. As these taxa were not included in the checklist used for this analysis the Calflora and Consortium of California Herbaria lists were expected to be larger.

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TABLE 2. Ten best represented families in the Napa County exotic flora. Family

Number of exotic taxa in Napa

Percentage of exotic Napa flora


Poaceae

67

22.4

3.9

Asteraceae

46

15.4

2.6

Fabaceae

30

10.0

1.7

Brassicaceae

18

6.0

1.0

Amaranthaceae*

10

3.3

0.5

Apiaceae*

10

3.3

0.5

Caryophyllaceae*

10

3.3

0.5

Plantaginaceae*

10

3.3

0.5

Solanaceae*

10

3.3

0.5

Geraniaceae

8

2.6

0.4

* indicates a tie. TABLE 3. Eleven families best represented by special status taxa in the Napa County native flora. Family

Number of special status taxa

Percentage of special status Napa flora

Percentage of native Napa flora


Asteraceae

18

14.2

1.2

1.0

Polemoniaceae

12

9.6

0.8

0.7

Fabaceae

11

8.8

0.8

0.6

Brassicaceae

9

7.2

0.6

0.5

Apiaceae*

6

4.8

0.4

0.3

Orobanchaceae*

6

4.8

0.4

0.3

Liliaceae*

5

4.0

0.3

0.2

Polygonaceae*

5

4.0

0.3

0.2

Lamiaceae*

4

3.2

0.3

0.2

Linaceae*

4

3.2

0.3

0.2

Rhamnaceae*

4

3.2

0.3

0.2

* indicates a tie. TABLE 4. Comparison of the total number of listed plant taxa among available data sources for Napa County.

Publication/data source

Total number of taxa listed for Napa County

Major (1963)

1253

The Jepson Herbaria SMASCH List (2007)

1044

Calflora (2005)

2238

Consortium of California Herbaria (2012)

2055

Present Study

1716

Several interesting features came to light when the floristic characteristics of Napa County were compared to the characteristics of other areas. For example, Baldwin et al. (2012) indicate that taxa from 187 families exist in California, although taxonomic revisions are ongoing. According to our analysis the 110 native and exotic families occurring in Napa County equate to 58.8% of California’s total familial diversity, a substantial portion for such a small area. The two largest families in California, Asteraceae and Poaceae

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(Baldwin et al. 2012) were also the largest families in Napa County. Notably Asteraceae is also the largest family in the Cape Flora Region of South Africa (Goldblatt & Manning 2002) and in Morocco (Rankou et al. 2013), which like California, are characterized by Mediterranean climates 2013). With regard to species diversity, a recent assessment indicates that California contains 7,601 unique taxa including 6,502 native taxa (Baldwin et al. 2012). Accordingly the 1,716 taxa present in Napa County represent 22.5% of California’s total floristic diversity (Table 5) while Napa’s 1,418 native taxa represent 21.8 % of California’s native flora, again a substantial proportion considering the size of Napa County. Additionally, of the taxa currently known to occur in California 85.5% are native while 1,099 exotic species represent the other 14.4% of California’s flora (Baldwin et al. 2012). Both the floras of California and Napa County contained comparable percentages of native and exotic taxa, an indication that Napa County is quite representative of the state as a whole based on this measure. In total there are 2,142 special status plant taxa in California representing 32.9% of the native flora, or 28.1% of the total flora (CNDDB 2013). The 126 special status plant taxa from Napa County comprise 5.8% of all special status plants in California, or 1.9% of the California native flora (1.6% of California’s total flora) (CNDDB 2013). Furthermore after adjusting for area, Napa had more taxa per km² and more rare taxa per km² than the State of California as a whole, again highlighting the significance of the county’s flora (Table 5). TABLE 5. Floristic comparison of Napa County to California (CA) and other selected California counties. Sources for total number of taxa are listed with their respective counties. All county area measures from United States Census Bureau (2000). Rare taxa numbers from CNPS (2005).

County (source)

Area (km²) (% total CA area)

Total taxa (% of CA flora)

Rare taxa (% of CA rare flora)

Taxa/ km²

Rare taxa/ km²

Napa (Present study)

2052 (0.5%)

1716 (22.5%)

126 (5.8%)

0.836

0.061

Marin** (Howell et al. 2007)

2145 (0.5%)

1679 (22.0%)

117 (5.4%)

0.782

0.054

Orange** (Roberts 1998)

2455 (0.6%)

1193 (15.6%)

88 (4.1%)

0.485

0.035

Butte (Oswald & Ahart 1994)

4343 (1.1%)

2023 (26.6%)

105 (4.9%)

0.465

0.024

Sonoma* (Best 1996)

4579 (1.1%)

1921 (25.2%)

171 (7.9%)

0.419

0.037

Plumas (Clifton 2003)

6768 (1.7%)

2085 (27.4%)

121 (5.6%)

0.308

0.017

San Luis Obispo (Hoover 1970)

9365 (2.3%)

1583 (20.8%)

202 (9.4%)

0.169

0.021

Monterey (Matthews 1998)

9767 (2.4%)

2055 (27.0%)

182 (8.4%)

0.210

0.018

Mendocino (Smith & Wheeler 1992)

10,044 (2.5%)

2746 (36.1%)

165 (7.7%)

0.273

0.016

San Diego (Rebman & Simpson 2006)

11,722 (2.9%)

2314 (30.4%)

256 (11.9%)

0.197

0.021

Kern (Moe & Twisselmann 1995)

21,137 (5.2%)

1875 (24.6%)

161 (7.5%)

0.088

0.007

California (Baldwin et al. 2005)

403,932

7601

2142

0.018

0.005

* Indicates adjacent county ** Indicates counties with most similar overall surface area.

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The importance of Napa County’s floristic diversity was further emphasized after comparing it to the floras of other counties in California (Table 5). For instance Napa County had a comparable number of taxa to the two adjacent counties with available data despite being smaller than both of them; Marin County is approximately 100 km² larger while Sonoma County is more than twice the size of Napa County (United States Census Bureau 2000). Even though Marin County and Orange County are approximately the same size as Napa County (United States Census Bureau 2000) their floristic diversity differs. Marin County has 37 fewer taxa and 9 fewer rare taxa than Napa County while Orange County contains 522 fewer taxa and 37 fewer rare taxa than Napa (Table 5). Markedly Napa County had more taxa per km² and more rare taxa per km² than every county included in the comparison (Table 5). This measure is a strong indication of Napa’s high diversity levels. When the flora of Napa County was compared to the floras of other botanically rich areas found within the biodiversity hotspots characterized by a Mediterranean climate (Myers et al. 2000), the significance of the county is again confirmed (Table 6). Médail and Quézel (1997) give estimates of the number of species that occur within several smaller regions of the Mediterranean Basin biodiversity hotspot. These regions include both insular and mainland portions of the Mediterranean region that vary in overall size. When the number of native taxa per km² and the number of rare taxa per km² are compared, only the Madeira Archipelago exceeded Napa in these richness measures (Table 6). Likewise, Judd et al. (2008) documented plant diversity in grid cells with approximate areas of 3091 km² covering the eastern portion of the Southwest Australian biodiversity hotspot. When considering the five cells (labeled cell 1-5 in Table 6) from the Australian study area with the greatest overall richness and rarity richness values, Napa County surpassed each cell in all diversity measures (Table 6). Moreover Goldblatt and Manning (2002) quantified plant diversity in subsets of another biodiversity hotspot, the Cape Flora Region of South Africa. Again Napa County exceeded each of the study areas in the Cape Flora Region when considering the number of species per km² (Table 6). Thus, the overall significance of the floristic diversity in Napa County is not solely limited to the United States; it extends to the global scale. The results from the species-area curves further demonstated Napa’s flouristic significance (Fig. 1, Fig. 2). The regression model using the linear form of the power function of log area against log number of species in regions of California (n = 12, see Table 5) showed a clear trend of increasing species richness with increasing area and explained much of the variation in the data (R2 = 0.77, p =