Trees of the Northern Sierra Madre Occidental and Sky Islands of Southwestern North America

Transcription

1 This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Trees of the Northern Sierra Madre Occidental and Sky Islands of Southwestern North America Richard S. Felger 1 and Matthew B. Johnson 2 Abstract.-This report covers the naturally occurring montane tree flora of the northern Sierra Madre Occidental of eastern Sonora and western Chihuahua and the sky islands extending into southeastern Arizona and southwestern New Mexico. This flora is comprised of 233 species in 130 genera and 61 families, which represents approximately 5 percent of the total flora of the region. The region is a meeting place of the temperate North American and Neotropical tree floras with intrusions of Sonoran and Chihuahuan desert at lower elevations. The legume (Fabaceae), oak (Fagaceae), and pine (Pinaceae) families are the most diverse, and the oaks (Quercus) and pines (Pinus) are the largest genera. This is the first comprehensive listing of the trees of the northern Sierra Madre Occidental. Extensive areas of tropical deciduous forest (TDF) cover the lower elevations of the southern part of the region in Sonora and Chihuahua and harbor 60 percent of the regional tree flora. Oak woodland and pine-oak woodland occur at higher elevations and mixed conifer forest at the highest elevations, and support 43, 33, and 11 percent respectively of the regional tree flora, The Madrean forest once stretched unbroken into the American tropics but accelerating deforestation is leading to fragmentation of the keystone species populations, INTRODUCTION This publication covers the trees of the sky island mountains of southeastern~rizona, southwestern New Mexico, northeastern Sonora, and northwestern Chihuahua, and the contiguous northern Sierra Madre Occidental in western Chihuahua and eastern Sonora. The northern limit of this bioregion is mar ked by the Pinalefto Mountains (Mt. Graham) in Arizona. Out of practicality we have set the southern limit of this study at the Sonora-Sinaloa border and adjacent mountains of southwestern Chihuahua. The mountains just east of the Cascada de Basaseachic in southern Chihuahua form the southeastern point, and the Sierra de Alamos in southern Sonora marks the southwestern point. The sky island ranges in Arizona include the Chiricahua, Galiuro, Huachuca, Pinalefto, Rincon, Santa Catalina, Santa Rita mountains, and in New Mexico the Animas and southern Peloncillo mountains. A land of extremes, it is topographically and geologically complex. 1 Dry/ands Institute, Tucson, AZ. 2Desert Legume Program, University' of Arizona, Tucson, AZ. We are including all of the tree species known to us in the montane regions at elevations above the deserts and grassland in the north, and above tropical thornscrub in the south. The northern sky islands, especially at higher elevations, have a continental and temperate makeup. Many north temperate tree species penetrate far southward in the interior of Mexico at intermediate or higher elevations in areas such as the Central Plateau. Fourteen percent of the tree flora, or 33 tree taxa (species and a few subspecies or varieties) reach their southern limits in the region (Table 1, p ). Overall, the region is arid to semi-arid except at the highest elevations. The lower elevations in the northern part of the region are bounded by the Sonoran Desert on the western flanks and the Chihuahuan Desert and grassland on the eastern flanks. The southern mountains, especially at lower and intermediate elevations, support tropical and subtropical biota. This southern flora, in southeastern Sonora and southwestern Chihuahua, consists largely of a flora that is continuous with the American tropics. As one moves northward through our region, there is a tendency towards a reduction in stature and an attrition of tropical species and genera. Seventy-two percent 71

2 of the tree flora, or 164 species of southern or tropical origin reach their northern limits in the region (Table 1; also see Felger et al., this volume). Nine plant families represented by trees here do not extend farther north in western North America, i.e., Bombacaceae, Clethraceae, Cochlospermaceae, Erythroxylaceae, Magnoliaceae, Myrsinaceae, Myrtaceae, Olacaceae, and Opiliaceae. The total annual precipitation generally decreases from south to north, but increases with elevation. Precipitation is largely bi-seasonal. The monsoon-like, summer rainy season is most pronounced and dependable towards the south, while winter precipitation increases in importance northward. Soil moisture is the principal limiting factor in this dry region. The northward expansion of many of the more tropical or subtropical species is blocked by an invisible "frost-line" of freezing weather coupled with increasing aridity. Frosts are infrequent or virtually absent towards the southern part of the region at lower to intermediate elevations. Increasing aridity northward tends to raise the lower elevational limits of the tropical/subtropical trees while the frost-line descends in elevation. This results in narrowing elevational distributions or bands of tropical/ subtropical species northward and fragmentation of frost-sensitive and drought-intolerant populations into specific microhabitats. There is often somewhat of a paradox, because microhabitats with the most favorable moisture conditions (riparian bottomlands and north-facing slopes) tend to experience the most severe freezing temperatures (see Burquez et al., in press). The total flora for the region is estimated to include at least 4,000 species of vascular plants (Felger et al., this volume). Within this rich flora we have documented 233 species of trees (Table 1), which represent about 5 percent of the total flora. These tree species are distributed in 130 genera and 61 families (Table 2). In our opinion this tree flora is approximately 95 percent complete, with additional records likely to be found in the remote mountains and canyons in southwestern Chihuahua and adjacent Sonora. The largest families of trees are the legume (Fabaceae), oak (Fagaceae), and pine (Pinaceae) families, and the most diverse genera are the oaks (Quercus; fig. 1) and pines (Pinus) (Table 2). There are about seven tree species and one variety endemic to the region: Fraxinus gooddingii, flex rubra, Nolina matapensis, Opuntia th urberi var. thurberi, Prunus gentryi, P. zinggii, Yucca schottii, and Y. grandiflora (Table 1). However, it would not be surprising to find the flex and the two Prunus species in northern Sinaloa. A number of others occur only in the southern part of our region and in northern Sinaloa, e.g., Albizia sinaloensis, Brongniartia alamosana, Diospyros sonorae, Opuntia thurberi var. alamosenses, O. wilcoxii, Quercus albocincta, Q. tarahumara, and Sabal uresana. In fact, the flora of northern Sinaloa flora is not separable from that of southern Sonora and southwestern Chihuahua (Gentry 1946a, 1946b, 1982). The characters, including size, that constitute a "tree" are often highly subjective but useful for indicating trends, and important for considering keystone or habitat-modifying organisms. The demarcation between the larger shrubs and smaller trees is especially subjective. We have chosen a height of 5 m as the artificial limit between shrubs and trees, and when in doubt have favored including woody plants and excluding the more herbaceous species with seasonal die-back. We have also decided that if a plant is classified as a tree one should be able to climb up into it, or theoretically climb it if the spines are removed, without causing it to collapse. Many have a single trunk at least 10 cm in diameter at about 1 m above ground level. Some species included in this listing have multiple trunks arising at or near the ground and could be classified as shrubs rather than trees. In some cases a particular species may be a shrub across most of its distribution in the region, but in favorable habitats such as moist tropical canyons it may develop into a sizeable Table 2.-Summary of tree species of the northern Sierra Madre Occidental and the Sky Islands including the seven largest families and five largest genera. Gymnosperms Dicotyledons Monocotyledons Total Families: Fabaceae Fagaceae Pinaceae Moraceae Euphorbiaceae Cupressaceae Burseraceae Salicaceae Cactaceae Largest genera: QuerclJs Pinus Bursera Acacia Ficus Juniperus No. of No. of families genera No. of species

3 / v;. -I: ~~~,~....J.. ),~....-:.'.. ~ ~.. J,\-".'. " ~ " I I /' Figure 1.-leaves of nineteen species of Madrean and sky island oaks (Quercus): (a) Q. albocincta, cusi, encino roble, encino prieto, a Red (Black) Oak. (b) Q. arizonica, Arizona white oak, encino blanco. (c) Q. chihuahuensis, Chihuahua oak, encino blanco, encino chino, a White Oak. (d) Q. chryso/epis, canyon live oak, an intermediate Oak. (e> Q. coccolobifolia, encino negro, a Red Oak. (1) Q. durifolia, a Red Oak. (g) O. emoryi, Emory oak, blackjack oak, bel/ota, a Red Oak. (h) O. gambelll, Gambel oak, Rocky Mountain white oak. (I) Q. gr;sea, gray oak, a White Oak. (j) 0, hypo/eucoides, silverleaf oak, encino blanco, encino c%ra do, cusi, a Red Oak. (k) O. hypo/eucoides, the southern form, so,metimes known as Q. scytophylla Liebm. (I) O. mcvaughii, encino roble, a Red Oak. (m) O. oblongifol/a, Mexican blue oak, encino azul, a White Oak. en) O. rugosa, net-leaf oak, a Red Oak. (0) O. sideroxy/a, encino prieto, a Red Oak. (p) Q. subspathulata, a White Oak. (q)q. tarahumara, hand basin oak, encino cajete, a Red Oak. (r) Q. toumeyl, a White Oak. (s) Q. tubercu/afa, encino amarillo, a White Oak. (t) Q. vlminea, willow leaf oak, saudllo, a Red Oak. Drawings by MBJ. 73

4 tree (e.g., Aralia humilis and Stemmadenia tomentosa). Other species are shrubs at higher elevations and in the northern part of the region (due to repeated freeze-damage or drought-stress) and trees in the more tropical southern regions (e.g., Erythrina flabelliformis, FOllquieria macdougalii, and Lysiloma watsonil). The summary of information in Table 1 calls for some comment. In reality the vegetation is not as simple as the classification presented. Many trees may extend into neighboring vegetation zones along riparian habitats or in other special situations. Extraordinary "shifts" in vegetation types occur on limestone (Whitaker & Niering 1965) and hydrothermically altered soils (Goldberg 1982, Burquez et al. 1992). The size-classes in Table 1 refer to the larger trees within any given taxon across the entire region. Fire and human mischief have eliminated most of the largest trees from many regions. In certain situations many common trees that are usually small or at most medium-sized may develop into large trees, e.g., Lysiloma watsonii and Vitex mollis along the Rio Guajaray north of Alamos, and Quercus tarahumara in the vicinity of Mulatos in east-central Sonora. Perhaps the large number of extraordinarily large trees in the Guarijio Indian region of the Guajaray is related to local conservation or management practices. There are, or were, trees virtually everywhere in the montane areas-most of the region is or was forested. But man is the enemy vf the tree. The forests are receding rapidly. Human population in the region remained low and major roads few until the middle or latter part of the twentieth century. Much diversity of near natural habitats remains, but assaults on trees are escalating. Major threats include dams, logging, firewood cutting, charcoal-making, dearing for agriculture, mining, urbanization, and replacement of the forests with buffelgrass (Pennisetum ciliare) at lower elevations in the southern part of the region. This summary is largely derived from our study of the trees of Sonora which will be treated in depth in a forthcoming book (Felger & Johnson in press). Selected references dealing with trees of our region or adjacent areas include Benson & Darrow (1981), Flora North America (1993), Gentry (1942), Hastings et al (1972), Kearney & Peebles (1960), Little (1950), Marshall (1957), Mearns (1907), Pennington & Sarukhan (1968), Powell (1988), Shreve (1951), Spellenberg et al. (in prep.), Standley ( ), Steinmann & Felger (in prep.), Turner et al. (in press), Vines (1960), Wiggins (1964), and White (1948). The nomencla- ture used here results from our interpretation of the taxonomic literature and our work on the flora of the region. The major vegetation types of the region and their tree floras are briefly summarized below. TROPICAL DECIDUOUS FOREST Tropical deciduous forest (TDF) is characteristic of the dry tropics worldwide. Increase in human population is leading to global devastation of this habitat. De-forestation and the resulting desertification has contributed to subtropical belts of misery circling the globe. TDF is the least studied of the major vegetation types of the world. Because it is hardly fashionable to save poorly-known, scrawny and often thorny trees in hot, uncomfortable climates, world conservation efforts have largely overlooked TDE The magnificent tropical deciduous forest of the northern Sierra Madre Occidental is seriously threatened. The TDF in Sonora and adjacent southwestern Chihuahua is the dry, northern arm of the great TDF swath which sweeps northward in western Mexico. Sonoran-Chihuahuan TDF is sandwiched between tropical thornscrub at lower elevations to the west and the oak zone at higher elevations to the east. Northward, along the east side of the Sonoran Desert, TDF merges into a kind of inland subtropical thornscrub (Felger & Lowe 1976, Burquez et al. in press) which in turn merges into desertscrub (Shreve 1951). Paul Martin and Chuck Bowden referred to TDF in Sonora as the Secret Forest (Bowden et al. 1993). Howard Scott Gentry (1942) called it the Short-tree Forest, and David Brown (1982) called it Sinaloan Deciduous Forest. Felger & Lowe (1976) and Burquez et al. (in press) call it tropical deciduous forest. In its natural condition in Sonora, Chihuahua, and northern Sinaloa, there is essentially 100 percent ground cover of forest often m tall made up of trees of tropical affinity. Summers are long and hot and winters short and mild. Freezing weather within the forest is rare and apparently most of the TDF species are highly frost-sensitive. May and June days grow hotter and hotter, building up to the beginning of the long-awaited summer rains. Afternoon douds increase day by day, and finally, when the violent thunderstorms begin, the leafless trees and vines and undergrowth burst forth in a blaze of green (Gentry 1942). The monsoon rains begin soon after summer solstice, celebrated on June 24 as El Dia de San Juan. The rains typically continue through August and into early September. Some 74

5 trees, such as Bursera spp., Cochlospermum, Erythrina, Jatropha, Ipomoea, and Pseudobombax, defoliate very soon after the rains cease. However, most of the trees defoliate more gradually. Midwinter rains may delay leaf-fall of certain species. Drought-induced deciduating leaves produce a virtually unique but ephemeral display of highly varied pastel colors (Bowden et al 1993). Spring drought brings on final defoliation to most of the TDF trees. As the weather turns hotter and dryer from March and April to June, even the tree chollas (Opuntia thurben) and prickly pears (e.g., O. wilcoxij) become flaccid and droopy from water loss. Cicadas call loudly and writers visiting the Sonoran TDF during the height of the presummer drought tell of skeleton forests and the lack of greenery. It is awesome to witness the sudden transformation to luxuriant tropical green with the start of the summer monsoon. Flowering trees can be found at virtually any time of the year but there are some significant peaks of color display. Mid-winter brings the amapas (Tabebuia spp.), the palo santo (Ipomoea arborescens), and then the echo (Pachycereus pecten-aboriginum). Later in spring the cuajilote (Pseudobombax palmen) and rosa amarilla (Cochlospermum vitiiolium) bring forth floral displays. When fallen leaves are dry and crackling underfoot in the searing pre-monsoon heat the hillsides blaze with the dark blue of gauyacan (Guaiacum coulterl) and rose-purple of nesco (Lonchocarpus hermannii, = Willardia mexicana). These are just a few of the more conspicuous flowering trees. By and large the timing of fruit ripening and seed-fall coincides with the beginning of the summer rains. Sixty percent (140 species) of the tree species of the region occur in TDF. Legumes rule the tropical-derived TDF as well as the regional thornscrub and Sonoran desertscrub. The fast-growing mauto (Lysiloma microphyllum) and many other legumes account for the vast majority of the TDF vegetative cover. Biological diversity is high. No single species or small number of species dominates-the forest is shared by a horde of species. Prominent arborescent members of TDF in our region include the following: Bursera spp. Caesalpinia platyloba Ceiba aesculiiolia Conzattia m ultif]ora Fouquieria macdougalii Haematoxylum brasiletto Ipomoea arborescens Lonchocarpus hermmmii Lysiloma microphyllum L. TIVatsonii Pachycereus pecten-aboriginum Pithecellobium leucospermum Senna atomaria Stenocereus montanus S. thurberi Tabebuia chrysantha T. impetiginosa Wimmeria mexicana OAK WOODLAND Oak woodland vegetation is widely distributed at elevations above desert, grassland, thornscrub, or tropical deciduous forest, but below pine-oak woodland or pine forest. The species composition and tree density in oak woodland changes both with elevation and latitude. Although these oak zones have been called Madrean Evergreen Woodland (Brown 1982), many of the oaks and associated species are drought-decid uous during the late spring dry season. Autumn colors associated with falling leaves in temperate regions are seen in our region during the pre-summer drought. Extensive areas in the northern part of the region are dominated by open woodlands of Emory oak or bellota (Quercus emoryl). The acorns are harvested in considerable quantity in northern Sonora in early summer and sold locally. This is one of the few remaining comlnercial, wild food harvests in the region. The acorns are eaten fresh and are often consumed in cantinas-the floors becoming littered with the empty shells. Emory oak, Mexican blue oak (Q. oblongiiolia), and Arizona oak ( Q. arizonica) are the most common low-elevation oaks in the northern part of the our region. At lower elevations these oak zones border grassland or desertscrub. There is sometimes a broad ecotone between oak woodland and grassland where the oaks become widely spaced and grasses predominate, Such areas have been termed oak-grassland or oak-savanna. In mountains in southeastern and east-central Sonora oak woodland sometimes occurs as islands on acidic; hydrothermically altered soils within tropical deciduous forest, The ecotone between these two plant communities is often only a few meters. Oak woodland in southeastern Sonora and southwestern Chihuahua, called Oak Forest by Gentry (1942), shows considerable tropical affinity, At its lower limits it borders tropical 75

6 deciduous forest. Their boundaries are often remarkably well defined, apparently maintained by fire. Across the Rio Mayo and Rio Fuerte mountain drainages it is common to see low fires creeping almost harmlessly through dry grasses, forbs, and leaf litter among the barren oaks in May and June. These fires destroy small TDF trees and shrubs but not the oaks and their associated vegetation. The southern oak woodland is host to a rich array of subtropical or Mexican oak species. There is considerable elevational and habitat zonation among the diverse oaks. Many of the oaks in southeastern Sonora and nearby southwestern Chihuahua are strikingly large-leaved (e.g., the hand-basin oak, Q. tarahumara) as compared to those of the northern part of the region. The southern oaks often support tropical epiphytes such as bromeliads (Tillandsia spp.) and orchids (e.g., Encyclia microbulbon, LaeJia autumnalis, and Oncidium cebolleta). PINE-OAK WOODLAND Extensive areas of pine-oak woodland occur along the east side of the continental divide in western Chihuahua. Along the western slope of the Sierra Madre Occidental the climate is generally somewhat wetter, with presumably milder winter temperatures, resulting in a more diverse flora with more tropical elements.. inel uding Apache pine (Pinus engelmanmi), Durango pine (P. durangensis), egg-cone pine (P. oocarpa), pino chino (P. herrerae), and Mexican tropical-montane oaks. Towards southeastern Sonora and adjacent Chihuahua the pine-oak woodland is floristically and structurally akin to the Mexican pine-oak woodland of central and southern Mexico. Pine-oak woodland is continuous with oak woodland at lower elevations. In pine-oak woodland the pines form the overstory while the oaks generally form an understory. There are extensive areas of pine-oak woodland in the mountains of our region. Pine-oak woodland is included within the concept of Madrean Evergreen Woodland (Brown 1982), and the pine forest has been called Madrean Montane Conifer Forest (Brown 1982). For our purposes of this study it is not practical to distinguish pine-oak woodland from pine forest. Especially in the southern part of our region oaks are a major part of the forests containing pines. The abundance of oaks may be in part a consequence of overharvesting of pines. However, especially in the northern part of the region a distinctive pine forest is distinguishable" In these communities Douglas Fir (Pseudotsuga menziesij) is often locally common in an otherwise pinedominated forest, thus blurring the boundary with mixed conifer forest. At higher elevations within the pine-oak zones the pines become increasingly conspicuous and the tree density increases so that the vegetation could be called forest rather than woodland. Pine forest is characteristically dominated by one species of pine, usually Arizona pine (Pinus ponderosa var. arizonica), ponderosa pine (P ponderosa var. scopulorum), or white pine (P. strobi/ormis), with scattered individuals or small groups of oaks, especially Gambel oak (Q. gambe JiJ) and net-leaf oak (Q. rugosa). Gambel oak is the only winter-deciduous oak in our region. Pine for.. est is more widespread in Chihuahua and Durango than in Sonora. Ponderosa pine replaces Arizona pine at the higher elevations in Chihuahua and on the northernmost sky islands, These closely-related pines can be found intermixed in the Santa Catalina Mountains in southern Arizona. Mountains ranges to the south have only Arizona pine, while the ranges to the north have only ponderosa pine. MIXED CONIFER FOREST Mixed conifer forest is restricted to the highest mountain tops. Winters are cold and summers cool and moist. It is most extensive in the northern sky islands and at the highest elevations in Chihuahua. Southward in Sonora, mixed conifer forest occurs in extremely limited areas on northfacing slopes and riparian canyons on north slopes. Northeastern Sonora and adjacent Chihuahua support mixed conifer forests at elevations mostly above 2135 m (7000 ft). Mixed conifer forest barely extends into southeastern Sonora from Chihuahua above 2100 m (6890 ft) in the upper reaches of the Rio Mayo Drainage. Because there are more extensive areas of higher elevation in Chihuahua the mixed conifer forest is more common there. Three coniferous genera, Abies (fir), Pinus, and Pseudotsuga (Douglas fir), define this vegetation. These trees are colnmercially valuable for lumber, Most of the old growth forest has been logged, but in some places it is recovering from extensive logging in the mid-twentieth century, Most of the broadleaf (dieot) trees found here are winter-deciduous, e.g., Gambel oak (Quercus gambejij), capulin or wild cherry (Prunus serotina), ash (Fraxinus papillosa), aspen (Populus tremuloides), and New Mexico locust (Robinia 76

7 neomexicana). Riparian canyons are shaded with tall forests that may include big-tooth maple (Acer grandidentatum) and alder (Alnus oblongifolia) sometimes towering to 20 meters or more in height. The two highest sky island peaks, the Pinalefto and Chiricahua mountains in southeastern Arizona, support spruce-fir forest (Picea and Abies) as do a few localities on cold, north-facing slopes at the highest elevations in southwestern Chihuahua. ACKNOWLEDGMENTS We thank the Wallace Genetic Foundation for supporting our research on the trees of northwestern Mexico. We also thank Lucinda McDade and the staff at the University of Arizona Herbarium for their assistance, and Dennis Breedlove, Alberto Burquez, Mark A. Dinlmitt, Mark Fishbein, George Ferguson, James Henrickson, Phil Jenkins, Angelina Martinez-Yrizar, Stephanie Meyer, Andy Sanders, Richard Spellenberg, Victor Steinmann, Tom Van Devender, Michael Wilson, David Yetman, and many others for generous help with this tree flora. LITERATURE CITED Benson, L. & R.A. Darrow Trees and shrubs of the Southwestern deserts, 3rd. edition. The University of Arizona Press, Tucson, Arizona." Bowden, C., J.W. Dykinga, & P.S. Martin The secret forest. U ni versity of New Mexico Press. Albuq uerque. Brown, D.E. (ed.) Biotic communities of the American Southwest - United States and Mexico. Desert Plants 4: Burquez, A., A. Martlnez-Yrfzar, & R.s. Felger. in press. Biodiversity at the Southern Desert Edge in Sonora, Mexico. IN: R. Robichaux, ed. Ecology and Conservation of the Sonoran Desert Flora: a tribute to the desert laboratory. University of Arizona Press. Burquez,A.,A.Martinez-Yrizar, &PS.Martin From the high Sierra Madre to the coast: changes in vegetation along highway 16, Maycobo-Hermosillo. Pp IN: K.F. Clark, J. Roldan-Quintana, & R. Schmidt (eds.). Northern Sierra Madre Occidental Province, Mexico, guidebook. EI Paso Geological Society.EI Paso, TX. Felger, RS. & C.H. Lowe The Island and Coastal Vegetation and Flora of the Gulf of California, Mexico. Natural History Museum of Los Angeles County, Contribu tions in Science pp. Felger, R.S. & M.B. Johnson. in press. Trees of Sonora, Mexico. Oxford University Press. New York. Flora of North America Editorial Committee Flora of North America 2. Oxford U niversi ty Press. New York. Gentry,H.s Rio Mayo plants - a study of the flora and vegetation of the valley of the Rio Mayo, Sonora. Carnegie Institution of Washington, Publication 527, Washington, D. C. Gentry, H.S. 1946a. Sierra Tacuichamona-a Sinaloa plant locale. Bulletin of the Torrey Botanical Club 73: Gentry, H.s.1946b. Notes on the vegetation of Sierra Surotato in northern Sinaloa. Bulletin of the Torrey Botanical Club 73(5): Gentry, H.S Sinaloan deciduous forest. Desert Plants 4: Goldberg, D.E :the distribution of evergreen and deciduous trees relative to soil type: an example from the Sierra Madre, Mexico, and a general model. Ecology 63: Hastings, J.R., R.M. Turner, & D.K. Warren An atlas of some plant distributions in the Sonoran Desert. Techni~ cal Reports on the meteorology and climatology of arid regions. University of Arizona, Institute of Atmosp heric Ph ysics. Kearney, T.H. & R.H. Peebles Arizona Flora. 2nd edition with supplement by J.T. Howell & E. McClintock. U ni versi ty of California Press. Berkeley. Little, E.L Southwestern trees - a guide to the native species of New Mexico and Arizona. Agricultural handbook no.9,govemmentprintingoffice,washington, D.C. Marshall, J.T., Jr Birds of Pine-Oak Woodland in Southern Arizona and Adjacent Mexico. Pacific Coast Avifauna Number 22. Mearns, EA Mammals of the Mexican Boundary of the United States.United States National Museum Bulletin56. Pennington, T.D. & J. Sarukhan Manual para la identificacion de campo de los principales arboles tropicales de Mexico. Instituto Nacional de Investigaciones Forestales, Secretaria de Agricultura y Ganaderia. Mexico, D.F. Powell, A.M Trees & Shrubs of Trans-Pecos Texas. Big Bend Natural History Association. Big Bend National Park, Texas. Shreve, F Vegetation of the Sonoran Desert. Carnegie Institution of Washington Publication no. 591, Vol. I of Shreve & I. L. Wiggins. Flora and Vegetation of the Sonoran Desert. Spellenberg, R., T. Lebgue, & R. Corral D. in prep. Annotated checklist of the plants of the Parque Nacional de la Cascada de Basaseachic, southwest Chihuahua, Mexico. Standley,P.C Trees and shrubsofmexico.contributionsfrom the United States National Herbarium 23. Steinmann, VW. & R.S. Felger. in prep. A synopsis of the E up horbiaceae in Sonora, Mexico. Turner, R.M., J.E. Bowers, & T.L. Burgess. In Press. Sonoran Desert plants: an ecological atlas. University of Arizona Press. Tucson. Vines, R.A Trees, shrubs, and woody vines of the Southwest. University of Texas Press. Austin. White, S.s The vegetation and flora of the region of the Rio de Bavispe in northeastern Sonora, Mexico" Lloydia 11: Whitaker, R.H. & W.A. Niering Vegetation of the Santa Catalina Mountains, Arizona: a gradient analysis ofthesouthslope.ecology46: Wiggins,I.L.1964.Floraofthe Sonoran Desert. p in: F. Shreve & I.L. Wiggins. Flora and Vegetation of the SonoranDesert,2vols.Stanford UniversityPress.Stanford. 77

8 Table 1.- Montane tree flora of the northern Sierra Madre Occidental and the Sky Islands. Geographic distributions: G = ''General'' distributions, found both north and south of the region; T = "Tropical" or "southern" taxa at the northern limits of their geographic ranges; N = "Northern" taxa at the southern limits of their ranges; R = occuring elsewhere within approximately the same latitudes as our region; E = endemic to our region. Tree size classes: S = small trees, 5-8 m tall; M = medium-sized trees, 9-18 m; L = large trees, 19 or more m. Habitats: TO = tropical deciduous forest; OK = oak woodland; PN = pine-oak woodland or forest; MX = mixed conifer forest. Non-native species are Indicated with an asterisk (*). GYMNOSPERMS (CONIFERAE - Conifers) G T N R E S M L TO OK: PN MX CUPRESSACEAE - CYPRESS FAMILY Cupressus arizonica Greene var. arizonica G M L OK PN C. lusitanica Mill. T L OK PN MX Juniperus coahuilensis (Martinez) R.P. Adams G S OK PN J. deppeana Steud. G OK PN J. durangensis Martinez T S OK PN J. flaccida Schldl. var. flaccida T S OK PN J. scopulorum Sarg. N S PN Taxodium mucronatum Ten. T L TD PINACEAE - PINE FAMILY Abies bifolia A. Murr. N L MX A. concolor (Gord. & Glend.) Hildebr. N L MX A. durangensis Martinez T L MX Picea chihuahuana Martinez T L MX P. engelmannii Engelm. var. engelmannii N L MX Pinus cembroides Zucco T S OK PN P. douglasiana Martinez T L PN P. durangensis Martinez T L OK PN P. edulis Engelm. N S OK PN P. engelmannii Carr. T L OK PN P. herrerae Martinez T L PN P. leiophylla Schiede & Deppe var. chihuahuana (Engelm.) Shaw T L OK PN P. lumholtzii Robins. & Fern. T L PN P. maximinoi H.E. Moore T L PN P. oocarpa Schiede var. oocarpa T L PN P. ponderosa Laws. & C. Laws. var. arizonica (Englm.) Shaw T L PN MX P. ponderosa var. scopulorum Engelm. N L PN MX P. strobiformis Engelm. G L PN MX Pseudotsuga menziesii (Mirb.) Franco var. glauca (Mayr) Franco G L PN MX MONOCOTYLEDO NS AGAVACEAE - AGAVE FAMILY Yucca arizonica McKelv. N S OK Y. grandiflora Gentry E S OK Y. schottii Engelm. E S OK PN ARECACEAE (PALMAE) - PALM FAMILY Brahea aculeata (Brandeg.) H.E. Moore T S TD OK B. dulcis (H.B.K.) Mart. T S (M) TD OK PN B. elegans (Becc.) H.E. Moore T S (M) TD B. nitida Andre T S (M) TD OK Sabal uresana Trel. T M TD OK NOLINACEAE ~ BEAR-GRASS FAMILY Nolina matapensis Wiggins E S TD OK DICOTYLEDONS ACERACEAE - MAPLE FAMILY Acer glabrum Torr. N S MX A. grandidentatum Nutt. N L OK PN MX A. negundo l. N M PN MX 78

9 APOCYNACEAE - DOGBANE FAMILY Plumeria rubra L. T S TD Stemmadenia tomentosa Greenm. var. palmeri (Rose & StandI.) Woodson T S (M) TD Vallesia glabra (Cav.) Link T S TD AQUIFOLIACEAE - HOLLY FAMILY liex rubra S. Wats. E M OK PN MX I. tolucana Hemsl. T M PN MX ARALIACEAE - GINSENG FAMILY Aralia humilis Cav. T S (M) TD OK PN Oreopanax peltatum Linden T S (M) TD OK PN ASTERACEAE (COMPOSITAE) - ASTER OR COMPOSITE FAMILY Montanoa rosei Robins. & Greenm. T S TD Parthenium tomentosum DC. var. stramonium (Greene) Rollins T S TD OK BETULACEAE - BIRCH FAMILY Alnus incana (L.) Moench ssp. tenuifolia (Nutt.) Breit. N M MX A. oblongifolia Torr. N L OK PN MX Ostrya virginiana (P. MilL) C. Koch G L OK PN MX BIGNONIACEAE - BIGNONIA FAMILY Chilopsis linearis (Cav.) Sweet ssp. arcuata (Fosberg) Henricks. N S OK Tabebuia chrysantha (Jacq.) Nichols. ssp. chrysantha T M (L) TO T. impetiginosa (A. DC.) Standi. T M (L) TO BOMBACACEAE - SILK-COTION FAMILY Celba aesculifolia (H.B.K.) Britt. & Baker T M TO Pseudobombax palmeri (S. Wats.) Dugand T M TO BORAGINACEAE - BORAGE FAMILY Cordia sonorae Rose T S TO BUDDLEJACEAE - BUTIERFLY-BUSH FAMILY Buddleja cordata H.B.K. var. cordata T S (M) PN B. parviflora H.B.K. T S OK PN BURSERACEAE - FRANKINCENSE FAMILY Bursera arborea (Rose) Riley T L TO B. fagaroides (H.B.K.) EngL var. elongata McVaugh T S TO B. grandifolia (SchldL) Engl. T M TO B. lancifolia (Schldl.) Engl. T S TO B. laxiflora S. Wats. T S TO B. penicillata (DC.) Engl. T M TO B. simaruba (L.) Sarg. T L TO B. stenophylla Sprauge & Riley T M TO CACTACEAE - CACTUS FAMILY Opuntia thurberi Engelm. var. thurberi E S TO O. thurberi var. alamosenses (Britt. & Rose) Bravo T S TO O. wilcoxii Britt. & Rose T S TD Pachycereus pecten-aboriginum (Engelm.) Britt. & Rose T S (M) TO Pilosocereus alensis Weber T S TO Stenocereus montanus (Britt. & Rose) Buxb. T S (M) TO S. thurberi (Engelm.) Buxb. T S (M) TO CAPRIFOLIACEAE - HONEYSUCKLE FAMILY Sambucus mexican a Presl N S OK PN CELASTRACEAE - STAFF-TREE FAMILY Wimmeria mexicana (DC.) Lundell T S TO 79

10 CLETHRACEAE - CLETHRA FAMILY Clethra mexicana DC. T M OK PN COCHLOSPERMACEAE - COCHLOSPERMUM FAMILY Cochlospermum vitifolium (Willd.) K. Spreng. T M TD CONVOLVULACEAE - MORNING-GLORY FAMILY Ipomoea arborescens (Humb. & Bonpl.) G. Don var. pachyleuta Gentry T S (M) TD (OK) CORNACEAE ~ DOGWOOD FAMILY Cornus disciflora DC. T S OK PN EBENACEAE - PERSIMMON FAMILY Diospyros sonorae StandI. T M TD ERICACEAE - HEATH FAMILY Arbutus arizonica (A. Gray) Sarg. T M (L) OK PN MX A. xalapensis Sarg. T M PN ERYTHROXYLACEAE - COCA FAMILY Erythroxylum mexicanum H.B.K. T S TD EUPHORBIACEAE - SPURGE FAMILY Croton ct. niveus Jacq. T S TD Drypetes gentryi Monach. T L TD Jatropha cordata (Ort.) Mull. Arg. T S TD Manihot aesculifolia (H.B.K.) Pohl T S TD Manihot sp. T S TD *Ricinus communis L. G S TD Sapium appendiculatum (Mull. Arg.) Pax & K. Hoffm. T S TD Sebastiana pavoniana (Mull. Arg.) Mull. Arg. T M TD FABACEAE (LEGUMINOSAE) - LEGUME OR BEAN FAMILY: CAESALPINIOIDEAE - SENNA SUBFAMILY Bauhinia pringlei S. Wats. T S TO Caesalpinia caladenia StandI. T S TD C. palmeri S. Wats. T S TD C. platyloba S. Wats. T S TD Cercidium praecox (Ruiz & Pav.) Harms ssp. praecox T S TD Conzattia multiflora B.L. Robins. T L TO Haematoxylum brasiletto Karst. T S (M) TD *Parkinsonia aculeata L. T M TD Senna atomaria (L.) Irwin & Barneby T S TD MIMOSOIDEAE - MIMOSA SUBFAMILY Acacia pringlei Rose ssp. californica (Brandeg.) Lee, Seigler & Ebinger T S TD A. cochliacantha Wi lid. T S TO A. coulteri Benth. T S TO A. farnesiana (L.) Willd. T S TD A. occidentalis Rose T M TO A. pennatula (Cham. & Schldl.) Benth. T S OK PN Albizia sinaloensis Britt. & Rose T L TO Leucaena lanceolata S. Wats. T M TO *L. leucocephala (Lam.) de Wit T S TO Lysiloma microphyllum Benth. T M (L) TO L. watsonii Rose T M (L) TO OK Mimosa palmeri Rose T S TO *Pithecellobium dulce (Roxb.) Benth. T L TO P. leucospermum Brandeg. T S TO P. mexicanum Rose T M TO Prosopis glandulosa Torr. var. torreyana (l.d. Bens.) M.C. Johnst. G M TO P. velutina Woot. N M OK 80

11 PAPILIONOIOEAE - BEAN SUBFAMILY Brongniartia alamosana Rydb. T S TO Coursetia glandulosa A. Gray T S TO OK Oiphysa occidental is Rose T S TO O. suberosa S. Wats. T S TO OK Erythrina flabelliform is Kearney T S TO OK Eysenhardtia orthocarpa (A. Gray) S. Wats. G S TO OK Lonchocarpus hermannii Sousa T S TO Piscidia mollis Rose T M TO Platymiscium trifoliolata Benth. T M TO Robinia neomexicana A. Gray var. neomexicana N S OK PN MX FAGACEAE - BEECH FAMILY Quercus albocincta Trel. T M OK PN Q. arizonica Sarg. G M OK PN Q. chihuahuensis Trel. T M OK PN Q. chrysolepis Liebm. N S OK Q. coccolobifolia Trel. T M OK PN Q. crassifolia Humb. & Bonpl. T M OK PN Q. durifolia Seemen T L OK PN Q. emoryi Torr. R M OK PN Q. gambelii Nutt N M PN MX Q. grisea Liebm. G M OK Q. hypoleucoides A. Camus T M (L) OK PN Q. mcvaughii Spellenb. M (L) OK PN MX Q. oblongifolia Torr. R M OK Q. perpallida Trel. T M OK Q. rugosa Nee G M OK PN Q. sideroxyla Humb. & Bonpl. T M OK PN Q. subspathulata Trel. T M PN Q. tarahumara Spellenb. o Bacon & Breedl. T L PN Q. toumeyi Sarg. N S OK PN Q. tuberculata Liebm. T M (TO) OK PN Q. viminea Trel. T M (L) OK PN FOUQUIERIACEAE - OCOTILLO FAMILY Fouquieria macdougalii Nash T S TO F. splendens Engelm. ssp. splendens G S OK JUGLANOACEAE - WALNUT FAMILY Juglans major (Torr.) Heller G M OK PN LAURACEAE-LAURELFAMILY Cinnamomum sp. T L TO OK Persea podadenia Blake T L OK PN MAGNOLIACEAE - MAGNOLIA FAMILY Magnolia pacifica Vazq. ssp. tarahumara Vazq. T L OK PN MALPIGHIACEAE - MALPIGHIA FAMILY Bunchosia sonorensis Rose T S TO Malpighia umbellata Rose T S TO MELIACEAE - CHINABERRY FAMILY Cedrela odorata L. T L TO Trichilia americana (Ses. & Mog.) T.O. Penn. T S TO T. hirta L. T S TO MORACEAE - MULBERRY FAMILY Chlorophora tinctoria (L.) Benth. & Hook. f. T L TO Ficus cotinifolia H.B.K. T l TD F. insipida Willd. T l TO F. maxima Mill. T L TO F. pertusa L. 1, T L TO F. petiolaris H.B.K. T L TD (OK) F. trigonata L. T L TO Morus microphylla Bucki. N S OK PN Trophis racemosa (L.) Urban T l TO 81

12 MYRSINACEAE - MYRSINE FAMILY Ardisia revoluta H.B.K. T M TD Myrsine coriacea (Sw.) Roem. & Schult. T M OK PN MYRTACEAE - MYRTLE FAMILY *Psidium guajava L. T S TD OK P. sartorianum (0. Berg) Ndzu. T M TD NYCTAGINACEAE - FOUR-O'CLOCK FAMILY Pisonia capitata (S. Wats.) StandI. T S (M) (L) TD OLACACEAE - OLAX FAMILY Schoepfia schreberi J.F. Gmelin T S TD OLEACEAE - OLIVE FAMILY Fraxinus gooddingii Little E S OK F. papillosa Lingelsh. R M OK PN MX F. velutina Torr. G L OK PN OPILIACEAE - OPILIA FAMILY Agonandra racemosa (DC.) StandI. T S TD PLATANACEAE - PLANE-TREE FAMILY Platanus wrightii S. Wats. G L TD OK PN POLYGONACEAE - BUCKWHEAT FAMILY Coccoloba goldmanii StandI. T S TD RHAMNACEAE - BUCKTHORN FAMILY Colubrina triflora Brongn. T M TD Karwinskia humboldtiana (Zucc.) Roem. & Schult. T S TD Rhamnus crocea Nutt. N S OK R. cf. mucronata Schldl. T S OK PN Ziziphus amole (Ses. & Mo~.) M.C. Johnst. T S TD ROSACEAE - ROSE FAMILY Prunus emarginata (Dougl.) D. Dietr. N S (M) PN MX P. gentryi StandI. E S PN P. serotina Ehrh. ssp. capuli (Cav.) McVaugh T M OK PN MX P. serotina ssp. virens (Woot. & StandI.) McVaugh N M OK PN P. zinggii StandI. E L TD OK Vauquelinia californica (Torr.) Sarg. ssp. pauciflora (StandI.) Hess & Henricks. T S OK V. californica spp. californica N S OK RUBIACEAE - MADDER FAMILY Cephalanthus salicifolius Humb. & Bonpl. G S TO OK Hamelia xorullensis H.B.K. T S TO Hintonia latiflora (Ses. & Mo~.) Bullock T S TO Randia echinocarpa Ses. & Mo~. T S (M) TO RUTACEAE - RUE FAMILY *Casimiroa edulis Llave & Lex. T M TO Esenbeckia hartmanii Robins. & Fern. R S TO Ptelea augustifolia Benth. G S OK SALICACEAE - WILLOW FAMILY Populus angustifolia James N L PN P. brandegeei Schneid. R L TO OK P. fremontii S. Wats. ssp. fremontii N L OK P. trem uloides Michx. N M PN MX Salix bondplandiana H.B.K. L TO OK S. gooddingii Ball N M (L) TO OK PN S. taxifolia H.B.K. T S OK SAPINOACEAE - SOAPBERRY FAMILY Oodonaea viscosa Jacq. G S TO OK Sapindus drummondii Hook. & Arn. N S (M) OK S. saponaria L T M TO Thouinia acuminata S. Wats. T S TO T. villosa OC. T S TO 82

13 SAPOTACEAE - SAPOTE FAMILY Sideroxylon capiri (OC.) Pitt. ssp. tempisque (Pitt.) T.O. Penn. T L TO S. lanuginosum Michx. ssp. rigidum (A. Gray) T.O. Penn. N S OK S. persimile (Hemsl.) T.O. Penn. ssp. subsessiliflorum (Hemsl.) T.O. Penn. T L TO OK S. tepicense (StandI.) T.O. Penn. T L TO SIMAROUBACEAE - SIMAROUBA FAMILY Alvaradoa amorphoides Liebm. T S TO OK SOLANACEAE - NIGHTSHAOE FAMILY Cestrum lanatum Mart. & Gal. T S TO OK *Nicotiana glauca Graham G S TO OK PN Solanum erianthum O. Oon T S TO STERCULIACEAE - STERCULIA FAMILY Guazuma ulmifolia Lam. T M TO TAMARICACEAE - TAMARISK FAMILY *Tamarix ramosissima Ladeb G S TO TILIACEAE - LlNOEN FAMILY Heliocarpus attenuatus S. Wats. T S TO OK H. palmeri S. Wats. T S TO OK Tilia floridana Small G M PN THEOPHRASTACEAE - THEOPHRASTA FAMILY Jacquinia macrocarpa Cav. ssp. pungens (A. Gray) Stahl T S TO ULMACEAE - ELM FAMILY Aphananthe monoica (Hemsl.) Leroy T L TO Celtis iguanea (Jacq.) Sarg. T S (M) TO C. reticulata Torr. N M TO OK *Ulmus pumila L. N S OK URTICACEAE - NETTLE FAMILY Urera caracasana (Jacq.) Griseb. T S (M) TO OK VERBENACEAE - VERVAIN FAMILY Lippia umbellata Cav. T S TO OK Vitex mollis H.B.K. T S (M) (L) TO V. pyramidata Robins. T S TO OK ZYGOPHYLLACEAE - CALTROP FAMILY Guaiacum coulteri A. Gray T S TO