Flora of the Huachuca Mountains, Cochise County, Arizona

Janice E. Bowers and Steven P. Mclaughlin 1

Abstract.-The Huachuca Mountains, Cochise County, Arizona, are one of about two dozen "sky islands" in southeastern Arizona. A herbarium search revealed that, prior to 1990, 849 species had been documented from the Huachuca Mountains. Field work conducted between 1990 and 1994 added another 144 species to the flora. Altogether, 993 species in 467 genera and 101 families are now known from the range. Of these, 65 are introduced. Madrean floristic elements dominate the flora, accounting for 69.9% of all native species. Sonoran elements (5.0% of all native species) are relatively poorly represented in the Huachuca Mountains compared to more arid mountain ranges in southeastern Arizona. The flora of the Huachuca Mountains is comparatively rich for an Arizona local flora, with 29-39% more species than expected based on its elevational range and collecting history. Substrate complexity and the presence of many well-watered canyon habitats and springs contribute to the high species diversity.

INTRODUCTION

The Huachuca Mountains (fig. 1), located in southwestern Cochise County on the United States-Mexico border, are one of two dozen moun­tain ranges in southeastern Arizona. Often referred to as "sky islands" (Heald 1951), these ranges form a floristically diverse archipelago that has been of keen interest to botanists for more than a century. The Huachuca Mountains in par­ticular have a long and illustrious botanical history. Plant collection dates back to the botanical explorations of John Gill Lemmon and Sara Plum­mer Lemmon in 1882 (Crosswhite 1979) and has continued until the present day (fig. 2). Floristic work includes an enumeration of Timothy E. Wil­cox and Marcus E. Jones collections (Britton and Kearney 1894, Jones 1930) and checklists for Fort Huachuca, Ramsey Canyon, Garden Canyon and Coronado National Memorial (Goodding 1950a, 1950b; Pratt 1963; Toolin 1980; Yatskievych 1980-81; Ruffner and Johnson 1991; Parfitt and Christy 1992). Altogether, 84 collectors have taken more than 4000 specimens from the range.

1 University of Arizona, Tucson, AZ.

135

Our initial objective was, based on the work of these many collectors, to assemble a plant check­list for the entire range so that we could detemine if the flora was indeed, as Wallmo (1955) charac­terized it, "quite well known." Eventually, we also becalne interested in how plant checklists grow and shrink. In this paper, we compare the flora of the Huachuca Mountains with floras of other sky islands in southeastern Arizona, and demonstrate that species composition of local floras is dy­namic, subject to historical changes in climate, land use, and other factors. The checklist will be published at a later date.

STUDY AREA

The north-south trending Huachuca Moun­tains belong to the Basin and Range Province (Hunt 1967). Maximum elevations are 9,466 feet (2885 m) on Miller Peak, 9220 feet (2810 m) on Carr Peak, 8725 feet (2659 m) on Ramsey Peak, and 8410 feet (2563 m) on Huachuca Peak. Several major canyons with perennial reaches drain the precipitous eastern slope and eventually flow into the San Pedro River. The western slope, part of the Santa Cruz River watershed, has only a few streams with perennial reaches. Overall, the

This file was created by scanning the printed publication.Errors identified by the software have been corrected;

however, some errors may remain.

Fort

Arizona

. , . . , I , , , ,

...... ,-" "

Military /" "

,..,f .:~ Aeservation,""':

~ .... . ' . .' ''"''. , , I

" ,'" ............

Forest

.--, .... -_ ... , ~: C'o;~n.do " " National

~ ".morlal

I I

J~f 1:1 J:a

I I I

,

, ,,'

~~/

//

/ . 1/ if

Mlle. I 2 I I

i , , i , 2 3 ..

Kilometer.

Sierra

Vista

",

.. .... -.... ,,"' .. ,

" .--

N

~

Figure 1.-Huachuca Mountains and vicinity. The .... vy blllell line shows the study area boundary. A, Location of the Huachuca Mountains In Arizona; B, admlnlstrlltlw units In and near the Huachuca Mountains; C, major drainages and peaks of the Huachuca Mountains.

500

! 400

t 300 U)

~ 200 J 1 100

o

Vear

Figure 2.-Plant collection by YMr, Huachuca Mountain. (omitting all years In which fewer tMn 10 apeclmen. we,. collected). Based on specimen. depo .... at the University of Arizona herbarium

136

Huachuca Mountains appear highly dissected, with a large ratio of canyon to ridge habitat.

Our study area had an elevational range of 4466 feet (1361 m) and covered about 122 square miles (31,600 ha). The northern and eastern boundaries roughly followed the base of the range, which varies from 5000-5200 feet (1524-1585 m) above sea level. The southern edge coincided with the International Boundary. The 5500-foot (1676 m) contour approximated the western boundary. We excluded most private lands at the base of the range, with the exception of the Ramsey Canyon Nature Preserve, Peterson Ranch in Scotia Canyon, and aquatic habitats at Beatty's Miller Canyon Orchard in Miller Canyon. The lower elevations of Fort Huachuca Military Reservation were also excluded from our study area.

Topography and Geology

The range is geologically diverse. Bolsa Quartzite, the basal sedimentary unit, rests uncon­formably on Precambrian granite. On the eastern slope, Paleozoic sedimentary rocks, mainly lime­stone but also some shales and siltstones, top the Bolsa quartzite. On the western slope, sedimen­tary rocks of Cretaceous age, including conglomerates and shales, interfinger with Trias­sic-Jurassic volcanic and sedimentary rocks (Keith and Wilt 1978).

Climate

Weather stations are maintained at Fort Huachuca at the northern end of the range and at Coronado National Memorial at the southern end. Annual precipitation at Fort Huachuca (4664 feet, 1422 m) is 14.6 inches (37.1 cm). About half falls in July and August as high-intensity "monsoonal" rains that originate as scattered convectional thunderstorms triggered and enhanced by surface heating and orographic effects. Winters at Fort Huachuca are rather dry. December and January, the wettest winter months, average 1.7~ inches (4.5 cm) of precipitation. About 10% of winter pre­cipitation falls as snow, which seldom stays on the ground more than a day or two. At higher eleva­tions, annual rainfall exceeds 25 inches (63.5 cm), and snow can remain on the ground all winter. Winter storms result from cyclonic storms and frontal systems associated with large-scale low pressure systems that typically originate off the coast of California and Baja California. They are less variable spatially and more variable tempo­rally than summer storms (Sellers and Hill 1974).

Summers and winters at Fort Huachuca are mild. The average January temperature is 46.3°F (7.9°C), with average daily maximum and mini­mum temperatures of 58.4 and 34.2°F (14.7 and 1.2°C). Summer temperatures are moderated by afternoon cloud cover. The average July tempera­ture is 77.5°P (25.3°C), with daily maximum and minimum temperatures of 88.6 and 66.4°P (31.4 and 19.1°C). At higher elevations, the average January temperature is 400 P (4.4°C), and the aver­age July temperature is 65°P (18.3°C) (Sellers and Hill 1974)0

137

THE FLORA

Plant Checklist

In winter 1990 and spring 1991, we searched the University of Arizona herbarium (ARIZ) and the herbarium at Fort Huachuca for specimens from the Huachuca Mountains. We critically evaluated all collections, and, if necessary, rede­termined them. Starting in August 1990 and continuing through June 1994, we made 41 trips into the range, mostly during the April-October growing season, and also in November and Janu­ary. We attempted to sample every habitat throughout the growing season with special em­phasis on discontinuous habitats such as cattle tanks, springs, peaks, and cliffs. Most of our effort was concentrated along trails and roads.

Between 1882 and 1989, collectors documented a total of 849 species in the Huachuca Mountains. During the course of our project, we found 137 species that were new to the flora. Another 7 spe­cies were added by other collectors between 1990 and 1993. The total flora comprises 993 species and infraspecific taxa in 467 genera and 101 fami­lies. Of these, 65 species are introduced. The native flora comprises 906 species and 27 infras­pecific taxa.

How Plant Checklists Grow

It is common for plant checklists to expand over several decades of collecting. The Mount Shasta, California, flora grew from 425 species and infra specific taxa in 1940 to 525 in 1963 (Cooke 1940, 1941, 1949, 1963), an increase of about 1 percent per year. The flora of Tumamoc Hill, Tucson Mountains, Arizona, increased 0.6 percent per year between 1909 and 1985, from 238 to 346 species (Thornber 1909, Bowers and Turner 1985). The flora of Organ Pipe Cactus National Monument grew from 522 species in 1980 (Bowers 1980) to 571 in 1992 (Pinkava et al. 1992), an in­crease of 0.8 percent per year. The flora of the White Mountains, California, increased 3 percent per year between 1973 and 1987, from 761 to 1078 species (Lloyd and Mitchell 1973, Morefield 1992). The small yearly increment in each case suggests that the initial floras were fairly complete. Linear regression of percent increase against final size of the flora suggests that, not surprisingly, the larger the flora, the more difficult it is to collect com­pletely (R2 = 0.95).

Most additions to local floras are probably plants that have been previously overlooked. On occasion, however, movement of species onto a site increases the size of a local flora. New arrivals may be natives or exotics. In either case, careful observation is needed to distinguish newly ar­rived species from those that were simply overlooked. Especially in recent years, introduc­tion of exotics, either deliberately or accidentally, has expanded the size of many local floras. At Glacier National Park, Montana, exotics increased at an accelerating rate between 1920 and 1993 (Le­sica et al. 1993). Over 76 years, the number of introduced species in the Tumamoc Hill flora in­creased by an order of magnitude, from 2 to 52 (Bowers and Turner 1985, Burgess et al. 1991). Such examples could be multiplied many times. In the Huachuca Mountains flora, the 65 exotics include species seeded by the Forest Service to prevent erosion after fire (Dactylis glomerata/ Sanguisorba mino!; Melilotus spp.); escapes from cultivation (Pyracantha koidzumii Hedera helix/ Vinca majo!; Rubus procera); and naturalized ex-otics (Erodium cicutarium/ Bromus rubens/ Polypogon interruptus). About half of the exotic flora was first documented after 1962. The rapid vegetative growth and smothering habit of Rubus procera and Vinca major represent serious threats to the biodiversity of lower mesic canyons in the Huachuca Mountains.

The concentrated effort of compiling a plant checklist is another reason local floras increase in size. After 98 years of casual and infrequent col­lecting in the Rincon Mountains, the documented flora was 517 species (Bowers, unpublished data). The final checklist of 986 species (Bowers and McLaughlin 1987) represented an increase of 18 percent per year. McLaughlin (1993) doubled the known size of the Pinalefto Mountains flora, from 406 in 1988 (Johnson 1988) to 824 in 1993. In the Huachuca Mountains, collectors documented a to­tal of 849 species between 1882 and 1989. Between 1990 and 1994, 144 species were added to the flora, an increase of about 5 percent per year. This modest increment suggests that the flora was in­deed comparatively well known at the start of our project.

How local Floras Shrink

Loss of species from local floras has been noted infrequently in southeastern Arizona. Bow­ers and McLaughlin (1987) were unable to relocate 41 species in the Rincon Mountains; of these, 22

138

had originally been collected before 1909. Ron­deau (1991) did not find 55 species that had been collected in the Tucson Mountains between 1903 and 1988. In the Huachuca Mountains, 31 species may no longer belong to the flora, despite con­certed efforts to locate many of them. Inevitably, collectors of local floras seldom if ever relocate all the plant species documented from an area. Some are simply overlooked. Mislabeled vouchers might not have belonged to the flora in the first place. This is a particular problem for collectors in southeastern Arizona, where Lemmon's labels are notoriously unreliable (Kearney and Peebles 1960). Matelea balbisii/ Spirodela polyrhiza/ Woodsia scopulina and several other species re­ported from the Huachuca Mountains might well have been mislabeled as to location. Some species are "lost" as a result of taxonomic recombination; in our study area, Aquilegia longisissima/ Poly­gala piliophora and a few others might not prove to be good species.

Of greater biological interest are species that apparently no longer occur in an area. Some plants lost from the Huachuca Mountains flora are exotics that apparently failed to become estab­lished, including Coriandrum sativum/ Pastinaca sativa/ Lonicera japonica, and several others. A few native species may have been eliminated by development of the lower reaches of Carr, Miller, and Ramsey canyons. Odontrichum decomposi­tum, for example, was last seen at "James's resort" near the mouth of Ramsey Canyon (Jones 1930), now an area of houses, gardens, and pastures. Melica porteri "cannot exist in the presence of a cow" (Goodding 1950a) and may have been elimi­nated by grazing. Eventually, proliferation of exotic grasses such as Eragrostis lehmanniana and E curvula might have deleterious effects on the native flora. Both species dramatically decrease the diversity and productivity of native grasses (Cable 1971, Bock et al. 1986). Eragrostis lehman­nianil was introduced into Cochise County in the late 1940s; by 1951 it had spread onto Fort Huachuca, apparently from nearby highways (Goodding 1950a). Eragrostis curvula was intro­duced into the United States in 1928 (Crider 1945). These two exotics are now among the most com­mon plants at low to moderate elevations in the Huachuca Mountains.

The fossil record demonstrates dramatic al­teration of floras as a result of climatic change (Betancourt et al. 1990). Historical climatic change repeats this process on a briefer time-scale, espe­cially among small, local populations. Extirpation of 6 native perennials formerly found at high ele-

vations in the Rincon Mountains might have re­sulted from severe winter drought during 1920-1930 or 1942-1958 (Bowers and McLaughlin 1987). During the seasonally dry months of April, May and June, such species depend on soil mois­ture left by the winter snowpack. Severe winter drought could have eliminated their presumably small populations. A similar set of circumstances might have claimed some species in the Huachuca Mountains. High-elevation mesophytes not col­lected there since 1913 include Adiantum pedatum, Achillea mil1elolium, Dugaldia hoopesii, Macromeria viridillora, Sidalcea neomexicana, and Veronica serpyl1ilolia. Cur-. rently, Vaccinium myrtillus, Pyrola chlorantha, Mertensia Iranciscana, Pedicularis grayi, Actaea rubra, Hypericum lormosllm, Senecio huachu­canus and several others are known in the Huachuca Mountains only from small popula­tions at high elevations and may be similarly vulnerable.

Natural disasters, particular1'fire and flood,

may also have eliminated species from the flora. The Huachuca Mountains have experienced fre­quent severe fires in recent years (Taylor 1991, Wohl and Pearthree 1991). The southern end of the range has been particularly hard-hit, notably in 1977, 1988, and 1991 (Taylor 1991). The disap­pearance or retreat of several species can perhaps be ascribed to these or earlier fires. Rosa woodsii, collected in "moist draws" on Carr Peak in 1909, is now known only from upper Bear Canyon; Hy­pericum lormosum, collected on "moist slopes" of Carr Peak in 1909, is now known only from Bond and Sawmill springs. Valeriana edulis, which is no longer known from the flora, may have been eliminated by fire.

The most destructive fires may be followed by floods and debris flows, especially in steep drain­ages (Wohl and Pearthree 1991), with dire consequences for riparian herbs (Gori 1992). The small, scattered populations of Lilium parryi have experienced catastrophic declines in recent years as a result of flooding (Warren and Reichenbacher 1991, Wood 1992). Riparian plants that might have been eliminated from the Huachuca Mountains flora by floods or debris flows are Dryopteris filix-mas, Aster coerulescens, Monarda fistulosa, Oenothera kunthiana, Rubus arizonensis and Glyceria borealis. Small populations of riparian plants might have been eliminated during drought years, as well.

Clearly, a variety of natural and man-made disasters can eliminate species from local floras, particularly when populations are small and local.

139

Although our failure to relocate 31 species pro­vides only negative evidence, we find it suggestive that distinct patterns such as fire, flood, drought and development can be identi­fied. Some apparently extirpated species might well still occur in less accessible parts of the mountain range.

FLORISTIC ANALYSIS

All native species occurring in the Huachuca Mountains flora were classified into floristic ele­ments based on the system of floristic areas for the western United States developed by McLaughlin (1992). Methods for assigning species to floristic elements are given in McLaughlin and Bowers (1990) and McLaughlin (1994). For comparison, the floristic analysis of the Huachuca Mountains flora is presented along with those from the Rin­con and Pinalefto mountains (Bowers and McLaughlin 1987, McLaughlin 1993) (Table 1).

The system of floristic elements of McLaugh­lin (1992) is hierarchical. Five floristic provinces are recognized for the western United States: Cor­dilleran, Intermountain, Sonoran, Californian and Madrean. These provinces are subdivided into subprovinces, which are in turn subdivided into districts. Table 1 provides a breakdown of floristic elements for the Madrean Floristic Province. "Widespread" Madrean species are those that are (1) found in 20 or more of the local floras used by McLaughlin (1992) to develop the classification, and (2) centered on the Madrean Floristic Prov­ince. "Regional" Madrean species are ·those with more restricted distributions (found in 10 to 19 of 101 local floras from the western United States) that are centered within the Madrean Floristic Province. "Central Arizonan," "Chihuahuan," and "Apachian" species are narrowly distributed in

Table 1.-Florlstlc elements In the Huachuca, Rincon and Plnaleflo mountains. Values In the table are the percentage of the total native flora assigned to each floristic element.

Huachuca Rincon Pinalerio EIQri§li~ Elemeo§ MQ!.mt~i[)§ MQUOtAio§ MQUOtAilJ§

Madrean Widespread 5.6 5.1 6;6 Regional 17.8 19.0 20.5 Central Arizonan 1.3 1.5 2.3 Chihuahuan 6.4 4.3 2.4 Apachian ~ at.6 2.M

Total Madrean 69.9 61.5 52.7

Sonoran 5.0 19.4 10.7 Cordilleran 18.0 10.6 27.2 Intermountain 3.5 2.9 4.6

~alifQ[[]ia[) 36 56 ~6

the western United States (found in 9 or fewer of the sample of 101 local floras) and are centered, respectively, within the Central Arizona, Chihua­huan and Apachian floristic districts.

The Huachuca, Rincon and Pinaleno moun­tains all lie within the Madrean Floristic Province, since the majority of their species belong to Ma­drean elements. All three floras are placed within the Apachian district, since the Apachian element is the largest narrow-species element in their re­spective floras. The Huachuca Mountains flora has the highest percentage of Apachian species, and all species with Madrean affinities constitute nearly 70% of the flora. The Cordilleran element accounts for 18% of the Huachuca Mountains flora; species with Sonoran and Californian affini­ties are better represented in the flora of the Rincon Mountains, and those with Cordilleran and Intermountain affinities are better repre­sented in the Pinaleno Mountains. The Chihuhuan element is somewhat better represented in the Huachuca Mountains than in the Rincon or Pi­naleno mountains.

The importance of Madrean floristic elements in the Huachuca Mountains is not unexpected. The Apachian element is particularly large. Gen­era notably rich in Apachian species (5 or more) in our study area include Asclepias/ Bidens/ Brickel­lia/ lpomoea/ Dalea/ Desmodium/ Cyperus, and Muhlenbergia. The Apachian element is most strongly associated with oak and pine-qak wood­lands, plant communities that are particularly well represented in the Huachuca Mountains.

The low percentage of Sonoran elements in the Huachuca Mountains contrasts with that of the Rincon Mountains. The base elevation of the Rin­con Mountains is 2000 feet (610 m) lower than that of the Huachuca Mountains, resulting in hotter summers, milder winters and lower rainfall, all conducive to a higher representation of species with Sonoran affinities. Those Sonoran species within the flora of the Huachuca Mountains are mostly species with widespread and regional dis­tributions. Some are spring-flowering annuals, a group that is not well represented in the Huachuca Mountains.

The Cordilleran elements are of much greater importance in the Pinaleno Mountains, especially above 9000 feet (2743 m) (McLaughlin 1993), than in the Huachuca Mountains (Table 1). Species with Cordilleran affinities are found mostly in the mixed-conifer and spruce-fir forests in the Pi­naleno Mountains, where moisture-loving, cold-tolerant plants thrive under high winter pre­cipitation and low winter temperatures. In the

140

Huachuca Mountains, where winters are neither as cold nor as wet, there is no spruce-fir forest, and the mixed-conifer forest is of limited extent. In the sky island region in general, and in the Huachuca Mountains in particular, the Cordille­ran elements include both many widespread taxa and many narrowly dis~ributed species with Mo­gollon affinities (centered in the Mogollon Rim of Arizona and the Mogollon highlands of New Mexico). In the Huachuca Mountains, species with Cordilleran and Mogollon affinities are found mostly at high elevations or in moist, shaded canyons.

SPECIES DIVERSITY

The plant species diversity of the Huachuca Mountains was evaluated in two ways. First, based on the elevational range of the study area and the collecting effort invested in compiling its flora, we compared the actual number of species observed with the number expected to occur (Bowers and McLaughlin 1982). The elevational range of our study area is 4466 feet (1361 m). For collecting time, we estimated low and high values based on the number of years in which 50 or more specimens were collected (22 years) and the number of years in which 75 or more specimens were collected (16 years). The results showed that, compared to other local floras from throughout Arizona, the Huachuca Mountains have 29-39% more species than would be predicted based on elevational range and collecting history.

We plotted number of species versus eleva­tional range for the Huachuca Mountains and 23 other local floras from Arizona and New Mexico (fig. 3). The regression line in figure 3 shows the relationship between elevational range and rich­ness in this sample of 24 floras [5 = 264 + 0.274(ilE), R2 = 0.502, P < .001)]. The flora for the Huachuca Mountains is the farthest above the re­gression line, that is, it has the highest residual value. Of the mountain ranges from the south­western United States whose floras have been investigated in detail, the Huachuca Mountains appear to be exceptional in their high species di­versity.

In local floras from the western United States, elevational range is closely correlated with habitat diversity, since both temperature and precipita­tion vary with elevation, often over short distances. Habitat diversity in turn is a major de­terminant of species diversity. Thus local floras from areas spanning a large elevational range

(such as the Huachuca Mountains) tend to have higher species diversity (fig. 3). The Huachuca Mountains also have many aquatic habitats and much variation in gelogical substrates, and these factors probably also contribute to high species diversity in the range. The complex topography of the range, with its numerous deep canyons cut­ting nearly to the ridge lines, makes a topographically patchy landscape that may pro­mote high species diversity. Bennett and Kunzmann (1992) attempted to quantify topo­graphic "roughness" and found that their index was correlated with species diversity among a small set of floras from the sky island region. In some sky island floras, a pronounced biseasonal rainfall regime allows both a spring and a sum­mer flora to flourish (Bowers and McLaughlin 1987, McLaughlin and Bowers 1990). In the Huachuca Mountains, where winters are rather

1200

1000 U'l HUACHUCAS It RM w . U w 800 Q U'l

W > ~ 600 z L>-a

CNM NSR SA;R SC" • AM"· ". TM

OA ~M.

PM

.OP a:::

400 " FB w m

" " NHM CC ,,!M • AC

::l • PF z • WT • CW

• NM 200

0 0 500 1000 1500 2000 2500

ELEVATION RANGE (Meters)

figure 3.-Relationshlp between elevatlonal range (difference be­tween highest and lowest elevations) and species diversity among 24 local floras from Arizona and New Mexico. In addi­tion to the Huachucas, the floras plotted are: AC, Aravalpa Canyon, AZ (Warren and Anderson 1980); AM, Animas Moun­tains, NM (Wagner 1973); BA, Buenos Aires National Wildlife Refuge, AZ (McLaughlin 1992b); CC, Canyon de Chelly Na­tional Monument, AZ (Halse 1973); CNM, Chirlcahua National Monument, AZ (Reeves 1976); CR, Cooke's Range, NM (Co­lumbus 1988); CW, Chiricahua Wilderness, AZ (Leith liter 1980); OM, Datil Mountains, NM (Fletcher 1972); FB, Fort Bowie National Historic Site, AZ (Warren et al. 1992); MM, Mule Mountains, AZ (Wentworth 1982); NHM, Northern Huala­pai Mountains, AZ (Butterwick et al. 1991); NM, Navajo National Monument, AZ (Brotherson et al. 1978)j NSR, North­ern Santa Rita Mountains, AZ (McLaughlin and Bowers 1990); Op, Organ Pipe Cactus National Monument, AZ (Bowers 1980); PF, Petrified Forest National Park, AZ (Petrified Forest National Park 1976); PM, Pinaleno Mountains, AZ (McLaughlin 1993); RM, Rincon Mountains, AZ (Bowers and McLaughlin 1987); SC, Sycamore Canyon, AZ (Toolin et al. 1980); SA, Sierra Ancha, AZ (Pase and Johnson 1968); TM, Tucson Mountains, AZ (Rondeau 1991); WM, White Mountains, NM (Hutchins 1974); WT, White Tank Mountain Regional Park, AZ (Keil1973); WU, Wupatki National Monument, AZ (McDougall 1962).

141

dry, spring-flowering species are not well repre­sented.

Groombridge (1992) lists the" Apachian/ Ma­drean" region as one of 164 global centers of plant diversity. Floras from the sky island region are inherently richer than other floras from the west­ern United States (McLaughlin, this symposium). For example, the floras of the- Huachuca Moun­tains, Rincon Mountains, Sycamore Canyon, Chiricahua National Monument and Buenos Aires National Wildlife Refuge, all in the sky island re­gion, are farthest above the regression line in Figure 3. Much of the high species diversity of the Huachuca Mountains is due to the presence of a large Apachian component. Although it is clear that certain floristic elements and floristic areas are richer than others, the environmental, histori­cal and ecological factors that determine these inherent differences are not yet well understood.

CONCLUSIONS

After 112 years of plant collection, the flora of the fIuachuca Mountains is well known. Local flo­ras can never be completely collected. Additional field work inevitably turns up species that had been overlooked. Ornamental and crop plants in­vade from nearby settlements, sometimes becoming naturalized. Native plants, too, may oc­cupy new territory. Natural disasters such as fire, flood, and drought may extirpate some species, especially those with small populations in limited habitats. Human-induced disasters such as graz­ing and plant introduction may also take a toll. Inevitably, some species will be overlooked by collectors and mistakenly assumed to be extir­pated. Between 1882 and 1994, additions (144) to the Huachuca Mountains greatly exceeded sub­tractions (31). Plant checklists serve as a baseline for assessing floristic change in future decades.

In a region known for its biological diversity, the I-Iuachuca Mountains are exceptionally rich in plant species. Contributing factors include a large Apachian floristic element, complex topography, a wide elevational range, and a diversity of geologi­cal substrates and aquatic habitats.

LITERATURE CITED

Benn(~tt, P. S. and M. R. Kunzmann.1992. Factors affecting plant species richness in the Madrean Archipelago north of Mexico. In A. M~ Barton and S. S. Sloane, Chiricahua Mountains Research Symposium, Proceed-

ings, Pine Canyon United Methodist Camp, Chirica­hua Mountains, Arizona, 16-17 March 1992, p. 23-26. Southwest Parks and Monuments Association, Tuc­son, Arizona.

Betancourt,J. L., T.R. VanDevender, and P.S.Martin. 1990. Packrat Middens: The Last 40,000 Years of Biotic Change. University of Arizona Press, Tucson.

Bock, C. E.,J. H. Bock, K. L.Jepson, and J. C. Ortega. 1986. Ecological effects of planting African lovegrasses in Arizona. National Geographic Research 2:456-463.

Bowers, J. E. 1980. Flora of Organ Pipe Cactus National Monument. Journal of the Arizona-Nevada Academy of Science 15:1-11,33-47.

Bowers, ]. E. and S. P. McLaughlin. 1982. Plant species diversity in Arizona. Madron029:227-233.

Bowers, J. E. and S. P. McLaughlin .1987. Flora and vegeta­tion of the Rincon Mountains, Pima County, Arizona. Desert Plants 8:51-94.

Bowers, J. E. and R. M. Turner. 1985. A revised vascular flora of Tumamoc Hill, Tucson, Arizona. Madrono 32:225-252.

Britton, N. L. and T. H. Kearney. 1894. An enumeration of the plants collected by Dr. Timothy E. Wilcox, U. S. A., and others in southeastern Arizona during the years 1892-1894. Transactions of the New York Academy of Sciences 14:21-43.

Brotherson, J. D., G. Nebeker, M. Skougard and J. Fairchild. 1978. Plants of Navajo National Monument. Grea t Basin Naturalist 38: 19-30"

Burgess, T. L.,J. E. Bowers, and R. M. Turner. 1991. Exotic plants at the Desert Laboratory, Tucson, Arizona. Ma­dron038:94-114.

Butterwick, M., B. D. Parfitt and D. Hillyar?1991. Vascu­lar plants of the northern Hualapai Mountains, Arizona. Journal of the Arizona-Nevada Academy of Science 24-25: 31-49.

Cable, D. R. 1971. Lehmann lovegrass on the Santa Rita Experimental Range, 1937-1968. Journal of Range Management 24:17-21.

Columbus, J. T., Ill. 1988. Flora of Cooke's Range, south­western New Mexico. M.S. thesis, University of New Mexico, Albuquerque.

Cooke, W. B. 1940. Flora of Mount Shasta. American Midland Naturalist 23:497-572.

Cooke, W. B.1941. First supplement to the flora of Mount Shasta. American Midland Naturalist 26:74-84.

Cooke, W. B. 1949. Second supplement to the flora of Mount Shasta. American Midland Naturalist 41:174-183.

Cooke, W. B.1963. Third supplement to the flora of Mount Shasta. American Midland Naturalist 70:386-395.

Crider, F. J. 1945. Three introduced lovegrasses for soil conservation. USDACircularno. 730.

Crosswhite, F. S. 1979. "J. G. Lemmon & wife," plant explorers in Arizona, California, and Nevada. Desert Plants 1:12-21.

Fletcher, R. A. 1972. A floristic assessment of the Datil Mountains. M.S. thesis, University of New Mexico, Albuquerque.

142

Goodding, L. N. 1950a. Grasses on the Fort Huachuc" Wildlife Area.InC.D. Wallmo, Fort Huachuca Wildlif Area Surveys 1950-1951, p. 3-11. Arizona Game anc.. Fish Commission, Phoenix.

Goodding, L. N. 1950b. Plants of the Huachuca Moun tains. In C. O. Wallmo, Fort Huachuca Wildlife Are; Surveys 1950-1951, p. 12-19. Arizona Game and Fish Commission, Phoenix.

Gori, D. 1992. Sensitive plant studies in the "sky island' mountain ranges of s. e. Arizona. In A. M. Barton and S S. Sloane, Chiricahua Mountains Research Sympo­sium, Proceedings, Pine Canyon United Methodist Camp, Chiricahua Mountains, Arizona, 16-17 Marcl'1 1992, p. 27-30. Sou thwest Parks and Monuments Asso·· ciation, Tucson,Arizona.

Groombridge, B.1992. Global Biodiversity. Chapman and Hall, London.

Halse, R. R. 1973. The flora of Canyon de Chelly National Monument. M. S. thesis. University of Arizona, Tuc­son.

Heald, W. F.1951. Sky Islands of Arizona . Natural History 60:56-63,95-96.

Hunt,C. B.1967.Physiographyofthe UnitedStates.W.H. Freeman, San Francisco.

Hutchins, C. R.1974. A flora of the White Mountains area, southern Lincoln and northern Otero counties, New Mexico.C.R. Hutchins, Albuquerque, NM.

Johnson, W. T. 1988. Flora of the Pinaleno Mountains, Graham County, Arizona . Desert Plants 8:147-162,175-191.

Jones, M. E. 1930. Botanizing in Arizona. Contribu tions to Western Botany 16:1-31.

Kearney, T. H. and R. H. Peebles. 1%0. Arizona Flora, 2nd ed. University of California Press, Berkeley. With sup­plement by J. T. Howell, E. McClintock and collaborators.

Keil, D. J. 1973. Vegetation and flora of the White Tank Mountain Regional Park, Maricopa County, Arizona. Nl. S. thesis, Arizona State University, Tempe.

Keith, S. B. and J. C. Wilt. 1978. Road log from Douglas to Tucson via Bisbee, Tombstone, Charleston, Fort Huachuca and Sonoita. In New Mexico Geological Society Guidebook, 29th Field Conference, Land of Cochise, p.31-61.

Leithliter,J.R.1980. Vegetation and flora oftheChiricahua Wilderness Area. M. S. thesis, Arizona State Univer­sity, Tempe.

Lesica, P., D. Ahlenslager, and J. Desanto. 1993. New vascular plant records and the increase of exotic plants in Glacier National Park, Montana. Madrono 40:126-131.

Lloyd, R. M. and R. S. Mitchell. 1973. A flora of the White Mountains, California and Nevada. University of Cali­fornia Press, Berkeley.

McDougall, W. B.1962. Seed plants ofWupatki and Sunset Crater National Monuments. Museum of Northern Arizona Bulletin no. 7. Museum of Northern Arizona, Flagstaff.

McLaughlin, S. P. 1992a. Are floristic areas hierarchically arranged? Journal of Biogeography 19:21-32.

McLaughlin, S. P. 1992b. Vascular flora of Buenos Aires National Wildlife Refuge (including Arivaca Cienega), Pima County, Arizona. Phytologia 73:353-377.

McLaughlin, S. P. 1993. Additions to the flora of the Pi­nalefto Mountains, Arizona. Journal of the Arizona-Nevada Academy of Science 27:5-32.

McLaughlin, S. P. 1994. Floristic plant geography: The classification of floristic areas and floristic elements. Progress in Physical Geography 18:185-208.

McLaughlin, S. P. and J. E. Bowers. 1990. A floristic analysis and checklist for the northern Santa Rita Mountains, Pima Co., Arizona. Southwestern Naturalist 35:61-75.

Morefield,J.D.1992. Spatial and ecologic segregationofphy­togeographic elements in the White Mountains of CalifomiaandNevada.JournalofBiogeography19:33-50.

Parfitt, B. D. and C. M. Christy. 1992. Coronado National Memorial plant checklist-a synonymized list of the vascular plants. Department of Botany, Arizona State University, Tempe.

Pase, C. P. and R. R. Johnson. 1968. Flora and vegetation of the Sierra Ancha Experimental Forest, Arizona. USDA Forest Service Research Paper RM-41.

Petrified Forest National Park. 1976. Seed plant checklist of Petrified Forest National Park. Petrified Forest National Park, Holbrook, AZ.

Pinkava, D.J., M. A. Baker, R. A.Johnson, N. Trushell, G.A. Ruffner, R. S. Felger and R. K. Van Devender. 1992. Additions, notes and chromosome numbers for the flora of vascular plants of Organ Pipe Cactus National Monument, Arizona. Journal of the Arizona-Nevada Academy of Science 24-25:13-18.

Pratt, J. J. 1963. Fort Huachuca Check List of Flora and Fauna. U. S. Army Electronic Proving "Ground, Fort Huachuca, Arizona.

Reeves, T. 1976. Vegetation and flora of Chiricahua Na­tional Monument, Cochise County, Arizona. M. S. thesis,ArizonaState University, Tempe.

Rondeau, R. 1991. Flora and vegetation of the Tucson Mountains, Pima County, Arizona.M. S. thesis, Univer­sityof Arizona, Tucson.

Ruffner, G. A. and R. A. Johnson. 1991. Plant ecology and vegetation mapping at Coronado National Memorial, Cochise Sounty, Arizona. Technical Report no. 41, Co­operative National Park Resources Studies Unit, School of Renewable Resources, University of Arizona, Tuc­son.

Sellers, W. D.and R.H.Hill.1974.ArizonaClimate. Univer­sity of Arizona Press, Tucson.

143

Taylor, L.1991. Hiker's Guide to the Huachuca Mountains. Thunder Peak Productions, Sierra Vista, Arizona.

Thomber,J.J.1909.VegetationgroupsoftheDesertLabora­tory domain. In V. M. Spalding, Distribution and Movements of Desert Plants, p.103-112. Carnegie Insti­tutionofWashington Publication no .113;

Toolin, L. J. 1980. Final report on the flora of Ramsey Canyon. Report submitted to the Arizona Nature Con­servancy, Tucson, Arizona.

Toolin, L.J., T. R. Van Devender, andJ. M. Kaiser. 1980. The flora of Sycamore Canyon, Pajarito Mountains, Santa Cruz County, Arizona. Journal of the Arizona-Nevada Academy of Science 14:66-74.

Wagner, W. L. 1973. Floristic affinities of Animas Mountain, southwestern New Mexico. MS. thesis, University of New Mexico, Albuquerque.

Wallmo, C. 0.1955. Vegetation of the Huachuca Moun­tains, Arizona. American Midland Naturalist 54:466-480.

Warren, P. L. and L. S. Anderson. 1980 . Annotated checklist of the plants of George Whittell Wildlife Preserve. In T. B.Johnson, ed., 1980 Progress Report for the Biological Survey of the George Whittell Wildlife Preserve, Gra­ham and Pinal Counties, Arizona, p. 80-124. Arizona Natural Heritage Program, Tucson.

Warren, P. L. and F. W. Reichenbacher.1991. Sensitive plant survey of Fort Huachuca, Arizona. Report submitted to U.S.Army,FortHuachuca,Arizona.

Warren, P. L., M.S. Hoy and W. E. Hoy. 1992. Vegetation and flora of Fort Bowie National Historic Site,· Arizona. Technical Report NPS/WRUA/NRTR-92/43. Coop­erative National Park Resource Studies Unit, Tucson, AZ.

Wentworth, T. R. 1982. Vegetation and flora of the Mule Mountains, Cochise County, Arizona. Journal of the Arizona-Nevada Academy of Science 17:29-44.

Wohl. E. E. and P. P. Pearthree. 1991. Debris flows as geomorphic agents in the Huachuca Mountains of southeastern Arizona. Geomorphology 4:273-292.

Wood, T. 1992. Management of a rare lily, Lilium parryi, at Ramsey Canyon Preserve. In A. M. Barton and S. S. Sloane, Chiricahua Mountains Research Symposium, Proceedings, Pine Canyon United Methodist Camp, Chiricahua Mountains, Arizona, 16-17 March 1992, p. 50-52. Southwest Parks and Monuments Association, Tucson,Arizona.

Yatskievych, G. A. 1980-81. Ferns and fern allies of the Garden Canyon area of the Huachuca Mountains, Co­chise County, Arizona. Desert Plants 2:237-243.