Biodiversity and management of the madrean archipelago: the sky

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Trees of the Northern Sierra Madre Occidental
and Sky Islands of Southwestern North America
1 2
Richard S. Felger and Matthew B. Johnson
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 We are including all of the tree species known
to us in the montane regions at elevations above
This publication covers the trees of the sky is the deserts and grassland in the north, and above
land mountains of southeastern~rizona, tropical thornscrub in the south. The northern sky
southwestern New Mexico, northeastern Sonora, islands, especially at higher elevations, have a
and northwestern Chihuahua, and the contiguous continental and temperate makeup. Many north
northern Sierra Madre Occidental in western Chi temperate tree species penetrate far southward in
huahua and eastern Sonora. The northern limit of the interior of Mexico at intermediate or higher
this bioregion is mark ed by the Pinalefto Moun elevations in areas such as the Central Plateau.
tains (Mt. Graham) in Arizona. Out of practicality Fourteen percent of the tree flora, or 33 tree taxa
we have set the southern limit of this study at the (species and a few subspecies or varieties) reach
Sonora-Sinaloa border and adjacent mountains of their southern limits in the region (Table 1, p. 78-
southwestern Chihuahua. The mountains just east 83).
of the Cascada de Basaseachic in southern Chi Overall, the region is arid to semi-arid except
huahua form the southeastern point, and the at the highest elevations. The lower elevations in
Sierra de Alamos in southern Sonora marks the the northern part of the region are bounded by the
southwestern point. The sky island ranges in Ari Sonoran Desert on the western flanks and the Chi
zona include the Chiricahua, Galiuro, Huachuca, huahuan Desert and grassland on the eastern
Pinalefto, Rincon, Santa Catalina, Santa Rita flanks. The southern mountains, especially at
mountains, and in New Mexico the Animas and lower and intermediate elevations, support tropi
southern Peloncillo mountains. A land of ex cal and subtropical biota. This southern flora, in
tremes, it is topographically and geologically southeastern Sonora and southwestern Chihua
complex. hua, consists largely of a flora that is continuous
with the American tropics. As one moves north
ward through our region, there is a tendency
towards a reduction in stature and an attrition of
1D ry/ands Institute, Tucson, AZ.
2Desert Legume Program, University' of Arizona, Tucson, AZ. tropical species and genera. Seventy-two percent
71
of the tree flora, or 164 species of southern or would not be surprising to find the flex and the
tropical origin reach their northern limits in the two Prunus species in northern Sinaloa. A number
region (Table 1; also see Felger et al., this volume). of others occur only in the southern part of our
Nine plant families represented by trees here do region and in northern Sinaloa, e.g., Albizia si
not extend farther north in western North Amer naloensis, Brongniartia alamosana, Diospyros
ica, i.e., Bombacaceae, Clethraceae, sonorae, Opuntia thurberi var. alamosenses, O.
Cochlospermaceae, Erythroxylaceae, Magno wilcoxii, Quercus albocincta, Q. tarahumara, and
liaceae, Myrsinaceae, Myrtaceae, Olacaceae, and Sabal uresana. In fact, the flora of northern Si
Opiliaceae. naloa flora is not separable from that of southern
The total annual precipitation generally de Sonora and southwestern Chihuahua (Gentry
creases from south to north, but increases with 1946a, 1946b, 1982).
elevation. Precipitation is largely bi-seasonal. The The characters, including size, that constitute
monsoon-like, summer rainy season is most pro a "tree" are often highly subjective but useful for
nounced and dependable towards the south, indicating trends, and important for considering
while winter precipitation increases in importance keystone or habitat-modifying organisms. The de
northward. Soil moisture is the principal limiting marcation between the larger shrubs and smaller
factor in this dry region. The northward expan trees is especially subjective. We have chosen a
sion of many of the more tropical or subtropical height of 5 m as the artificial limit between shrubs
species is blocked by an invisible "frost-line" of and trees, and when in doubt have favored in
freezing weather coupled with increasing aridity. cluding woody plants and excluding the more
Frosts are infrequent or virtually absent towards herbaceous species with seasonal die-back. We
the southern part of the region at lower to inter have also decided that if a plant is classified as a
mediate elevations. Increasing aridity northward tree one should be able to climb up into it, or
tends to raise the lower elevational limits of the theoretically climb it if the spines are removed,
tropical/subtropical trees while the frost-line de without causing it to collapse. Many have a single
scends in elevation. This results in narrowing trunk at least 10 cm in diameter at about 1 m
elevational distributions or bands of tropical/ sub above ground level. Some species included in this
tropical species northward and fragmentation of listing have multiple trunks arising at or near the
frost-sensitive and drought-intolerant popUlations ground and could be classified as shrubs rather
into specific microhabitats. There is often some than trees. In some cases a particular species may
what of a paradox, because microhabitats with the be a shrub across most of its distribution in the
most favorable moisture conditions (riparian bot region, but in favorable habitats such as moist
tomlands and north-facing slopes) tend to tropical canyons it may develop into a sizeable
experience the most severe freezing temperatures
(see Burquez et al., in press). Table 2.-Summary of tree species of the northern Sierra
Madre Occidental and the Sky Islands including the seven
The total flora for the region is estimated to
largest families and five largest genera.
include at least 4,000 species of vascular plants
No. of No. of No. of
(Felger et al., this volume). Within this rich flora families genera species
we have documented 233 species of trees (Table Gymnosperms 2 7 26
1), which represent about 5 percent of the total Dicotyledons 56 119 198
Monocotyledons 3 4 9
flora. These tree species are distributed in 130 Total 61 130 233
genera and 61 families (Table 2). In our opinion
Families:
this tree flora is approximately 95 percent com
Fabaceae 23 36
plete, with additional records likely to be found in Fagaceae 1 21
the remote mountains and canyons in southwest Pinaceae 4 18
Moraceae 4 9
ern Chihuahua and adjacent Sonora. The largest
Euphorbiaceae 7 8
families of trees are the legume (Fabaceae), oak Cupressaceae 3 8
(Fagaceae), and pine (Pinaceae) families, and the Burseraceae 1 8
most diverse genera are the oaks (Quercus; fig. 1) Salicaceae 2 7
Cactaceae 4 6
and pines (Pinus) (Table 2).
There are about seven tree species and one va Largest genera:
riety endemic to the region: Fraxinus gooddingii, QuerclJs 21
Pinus 12
flex rubra, Nolina matapensis, Opuntia th urberi Bursera 8
var. thurberi, Prunus gentryi, P. zinggii, Yucca Acacia 6
schottii, and Y. grandiflora (Table 1). However, it Ficus 6
Juniperus 5
72
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
/
v~;. oak, encino blanco, encino c%ra do, cusi, a Red Oak.
,~~... -I: (k) O. hypo/eucoides, the southern form, sO,metimes
~...J..~ ~ J)..,. ..~......- :.' .. ~ 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
I Oak. (t) Q. vlminea, willow leaf oak, saudllo, a Red Oak.
I
/' Drawings by MBJ.
73
tree (e.g., Aralia humilis and Stemmadenia ture used here results from our interpretation of
tomentosa). Other species are shrubs at higher ele the taxonomic literature and our work on the flora
vations and in the northern part of the region (due of the region. The major vegetation types of the
to repeated freeze-damage or drought-stress) and region and their tree floras are briefly summa
trees in the more tropical southern regions (e.g., rized below.
Erythrina flabelliformis, FOllquieria macdougalii,
and Lysiloma watsonil).
TROPICAL DECIDUOUS FOREST
The summary of information in Table 1 calls
for some comment. In reality the vegetation is not Tropical deciduous forest (TDF) is charac
as simple as the classification presented. Many teristic of the dry tropics worldwide. Increase in
trees may extend into neighboring vegetation human population is leading to global devasta
zones along riparian habitats or in other special tion of this habitat. De-forestation and the
situations. Extraordinary "shifts" in vegetation resulting desertification has contributed to sub
types occur on limestone (Whitaker & Niering tropical belts of misery circling the globe. TDF is
1965) and hydrothermically altered soils (Gold the least studied of the major vegetation types of
berg 1982, Burquez et al. 1992). The size-classes in the world. Because it is hardly fashionable to save
Table 1 refer to the larger trees within any given poorly-known, scrawny and often thorny trees in
taxon across the entire region. Fire and human hot, uncomfortable climates, world conservation
mischief have eliminated most of the largest trees efforts have largely overlooked TDE The magnifi
from many regions. In certain situations many cent tropical deciduous forest of the northern
common trees that are usually small or at most Sierra Madre Occidental is seriously threatened.
medium-sized may develop into large trees, e.g., The TDF in Sonora and adjacent southwestern
Lysiloma watsonii and Vitex mollis along the Rio Chihuahua is the dry, northern arm of the great
Guajaray north of Alamos, and Quercus tarahu TDF swath which sweeps northward in western
mara in the vicinity of Mulatos in east-central Mexico. Sonoran-Chihuahuan TDF is sandwiched
Sonora. Perhaps the large number of extraordinar between tropical thornscrub at lower elevations to
ily large trees in the Guarijio Indian region of the the west and the oak zone at higher elevations to
Guajaray is related to local conservation or man the east. Northward, along the east side of the
agement practices. Sonoran Desert, TDF merges into a kind of inland
There are, or were, trees virtually everywhere subtropical thornscrub (Felger & Lowe 1976, Bur
in the montane areas-most of the region is or quez et al. in press) which in turn merges into
was forested. But man is the enemy vf the tree. desertscrub (Shreve 1951). Paul Martin and Chuck
The forests are receding rapidly. Human popula Bowden referred to TDF in Sonora as the Secret
tion in the region remained low and major roads Forest (Bowden et al. 1993). Howard Scott Gentry
few until the middle or latter part of the twentieth (1942) called it the Short-tree Forest, and David
century. Much diversity of near natural habitats Brown (1982) called it Sinaloan Deciduous Forest.
remains, but assaults on trees are escalating. Ma Felger & Lowe (1976) and Burquez et al. (in press)
jor threats include dams, logging, firewood call it tropical deciduous forest. In its natural con
cutting, charcoal-making, dearing for agriculture, dition in Sonora, Chihuahua, and northern
mining, urbanization, and replacement of the for Sinaloa, there is essentially 100 percent ground
ests with buffelgrass (Pennisetum ciliare) at lower cover of forest often 10-15 m tall made up of trees
elevations in the southern part of the region. of tropical affinity.
This summary is largely derived from our Summers are long and hot and winters short
study of the trees of Sonora which will be treated and mild. Freezing weather within the forest is
in depth in a forthcoming book (Felger & Johnson rare and apparently most of the TDF species are
in press). Selected references dealing with trees of highly frost-sensitive. May and June days grow
our region or adjacent areas include Benson & hotter and hotter, building up to the beginning of
Darrow (1981), Flora North America (1993), Gen the long-awaited summer rains. Afternoon douds
try (1942), Hastings et aL (1972), Kearney & increase day by day, and finally, when the violent
Peebles (1960), Little (1950), Marshall (1957), thunderstorms begin, the leafless trees and vines
Mearns (1907), Pennington & Sarukhan (1968), and undergrowth burst forth in a blaze of green
Powell (1988), Shreve (1951), Spellenberg et al. (in (Gentry 1942). The monsoon rains begin soon af
prep.), Standley (1920-1926), Steinmann & Felger ter summer solstice, celebrated on June 24 as El
(in prep.), Turner et al. (in press), Vines (1960), Dia de San Juan. The rains typically continue
Wiggins (1964), and White (1948). The nomencla- through August and into early September. Some
74
trees, such as Bursera spp., Cochlospermum, • Lysiloma microphyllum
Erythrina, Jatropha, Ipomoea, and Pseudobom • L. TIVatsonii
bax, defoliate very soon after the rains cease. • Pachycereus pecten-aboriginum
However, most of the trees defoliate more gradu • Pithecellobium leucospermum
ally. Midwinter rains may delay leaf-fall of certain • Senna atomaria
species. Drought-induced deciduating leaves pro • Stenocereus montanus
duce a virtually unique but ephemeral display of • S. thurberi
highly varied pastel colors (Bowden et aL 1993). • Tabebuia chrysantha
Spring drought brings on final defoliation to most • T. impetiginosa
of the TDF trees. As the weather turns hotter and • Wimmeria mexicana
dryer from March and April to June, even the tree
chollas (Opuntia thurben) and prickly pears (e.g.,
OAK WOODLAND
O. wilcoxiJ) become flaccid and droopy from
water loss. Cicadas call loudly and writers visiting Oak woodland vegetation is widely
the Sonoran TDF during the height of the pre distributed at elevations above desert, grassland,
summer drought tell of skeleton forests and the thornscrub, or tropical deciduous forest, but
lack of greenery. It is awesome to witness the sud below pine-oak woodland or pine forest. The
den transformation to luxuriant tropical green species composition and tree density in oak
with the start of the summer monsoon. woodland changes both with elevation and
Flowering trees can be found at virtually any latitude. Although these oak zones have been
time of the year but there are some significant called Madrean Evergreen Woodland (Brown
peaks of color display. Mid-winter brings the 1982), many of the oaks and associated species are
amapas (Tabebuia spp.), the palo santo (Ipomoea drought-decid uous during the late spring dry
arborescens), and then the echo (Pachycereus pec season. Autumn colors associated with falling
ten-aboriginum). Later in spring the cuajilote leaves in temperate regions are seen in our region
(Pseudobombax palmen) and rosa amarilla (Co during the pre-summer drought.
chlospermum vitiiolium) bring forth floral Extensive areas in the northern part of the
displays. When fallen leaves are dry and crackling region are dominated by open woodlands of
underfoot in the searing pre-monsoon heat the Emory oak or bellota (Quercus emorYl). The
hillsides blaze with the dark blue of gauyacan acorns are harvested in considerable quantity in
(Guaiacum coulterl) and rose-purple of nesco northern Sonora in early summer and sold
(Lonchocarpus hermannii, = Willardia mexicana). locally. This is one of the few remaining
These are just a few of the more conspicuous flow comlnercial, wild food harvests in the region.
ering trees. By and large the timing of fruit The acorns are eaten fresh and are often
ripening and seed-fall coincides with the begin consumed in cantinas-the floors becoming
ning of the summer rains. littered with the empty shells. Emory oak,
Sixty percent (140 species) of the tree species Mexican blue oak (Q. oblongiiolia), and Arizona
of the region occur in TDF. Legumes rule the oak ( Q. arizonica) are the most common
tropical-derived TDF as well as the regional low-elevation oaks in the northern part of the
thornscrub and Sonoran desertscrub. The our region. At lower elevations these oak zones
fast-growing mauto (Lysiloma microphyllum) and border grassland or desertscrub. There is
many other legumes account for the vast majority sometimes a broad ecotone between oak
of the TDF vegetative cover. Biological diversity is woodland and grassland where the oaks become
high. No single species or small number of species widely spaced and grasses predominate, Such
dominates-the forest is shared by a horde of areas have been termed oak-grassland or
species. Prominent arborescent members of TDF oak-savanna. In mountains in southeastern and
in our region include the following: east-central Sonora oak woodland sometimes
• Bursera spp. occurs as islands on acidic; hydrothermically·
• Caesalpinia platyloba altered soils within tropical deciduous forest,
• Ceiba aesculiiolia The ecotone between these two plant
• Conzattia m ultif]ora communities is often only a few meters.
• Fouquieria macdougalii Oak woodland in southeastern Sonora and
• Haematoxylum brasiletto southwestern Chihuahua, called Oak Forest by
• Ipomoea arborescens Gentry (1942), shows considerable tropical
• Lonchocarpus hermmmii affinity, At its lower limits it borders tropical
75
deciduous forest. Their boundaries are often communities Douglas Fir (Pseudotsuga menziesiJ)
remarkably well defined, apparently maintained is often locally common in an otherwise pine
by fire. Across the Rio Mayo and Rio Fuerte dominated forest, thus blurring the boundary
mountain drainages it is common to see low fires with mixed conifer forest.
creeping almost harmlessly through dry grasses, At higher elevations within the pine-oak zones
forbs, and leaf litter among the barren oaks in the pines become increasingly conspicuous and
May and June. These fires destroy small TDF trees the tree density increases so that the vegetation
and shrubs but not the oaks and their associated could be called forest rather than woodland. Pine
vegetation. forest is characteristically dominated by one spe
The southern oak woodland is host to a rich cies of pine, usually Arizona pine (Pinus
array of subtropical or Mexican oak species. There ponderosa var. arizonica), ponderosa pine (P pon
is considerable elevational and habitat zonation derosa var. scopulorum), or white pine (P.
among the diverse oaks. Many of the oaks in strobi/ormis), with scattered individuals or small
southeastern Sonora and nearby southwestern groups of oaks, especially Gambel oak (Q. gambe
Chihuahua are strikingly large-leaved (e.g., the JiJ) and net-leaf oak (Q. rugosa). Gambel oak is the
hand-basin oak, Q. tarahumara) as compared to only winter-deciduous oak in our region. Pine for. .
those of the northern part of the region. The est is more widespread in Chihuahua and
southern oaks often support tropical epiphytes Durango than in Sonora. Ponderosa pine replaces
such as bromeliads (Tillandsia spp.) and orchids Arizona pine at the higher elevations in Chihua
(e.g., Encyclia microbulbon, LaeJia autumnalis, hua and on the northernmost sky islands, These
and Oncidium cebolleta). closely-related pines can be found intermixed in
the Santa Catalina Mountains in southern Ari
zona. Mountains ranges to the south have only
PINE-OAK WOODLAND
Arizona pine, while the ranges to the north have
only ponderosa pine.
Extensive areas of pine-oak woodland occur
along the east side of the continental divide in
western Chihuahua. Along the western slope of MIXED CONIFER FOREST
the Sierra Madre Occidental the climate is gener
ally somewhat wetter, with presumably milder Mixed conifer forest is restricted to the highest
winter temperatures, resulting in a more diverse mountain tops. Winters are cold and summers
flora with more tropical elements .. inel uding cool and moist. It is most extensive in the north
Apache pine (Pinus engelmanmi), Durango pine ern sky islands and at the highest elevations in
(P. durangensis), egg-cone pine (P. oocarpa), pino Chihuahua. Southward in Sonora, mixed conifer
chino (P. herrerae), and Mexican tropical-montane forest occurs in extremely limited areas on north
oaks. Towards southeastern Sonora and adjacent facing slopes and riparian canyons on north
Chihuahua the pine-oak woodland is floristically slopes. Northeastern Sonora and adjacent Chihua
and structurally akin to the Mexican pine-oak hua support mixed conifer forests at elevations
woodland of central and southern Mexico. mostly above 2135 m (7000 ft). Mixed conifer for
Pine-oak woodland is continuous with oak est barely extends into southeastern Sonora from
woodland at lower elevations. In pine-oak wood Chihuahua above 2100 m (6890 ft) in the upper
land the pines form the overstory while the oaks reaches of the Rio Mayo Drainage. Because there
generally form an understory. There are extensive are more extensive areas of higher elevation in
areas of pine-oak woodland in the mountains of Chihuahua the mixed conifer forest is more com
our region. Pine-oak woodland is included within mon there.
the concept of Madrean Evergreen Woodland Three coniferous genera, Abies (fir), Pinus,
(Brown 1982), and the pine forest has been called and Pseudotsuga (Douglas fir), define this vegeta
Madrean Montane Conifer Forest (Brown 1982). tion. These trees are cOlnmercially valuable for
For our purposes of this study it is not practical to lumber, Most of the old growth forest has been
distinguish pine-oak woodland from pine forest. logged, but in some places it is recovering from
Especially in the southern part of our region oaks extensive logging in the mid-twentieth century,
are a major part of the forests containing pines. Most of the broadleaf (dieot) trees found here are
The abundance of oaks may be in part a conse winter-deciduous, e.g., Gambel oak (Quercus
quence of overharvesting of pines. However, gambeJiJ), capulin or wild cherry (Prunus serot
especially in the northern part of the region a dis ina), ash (Fraxinus papillosa), aspen (Populus
tinctive pine forest is distinguishable" In these tremuloides), and New Mexico locust (Robinia
76
neomexicana). Riparian canyons are shaded with Carnegie Institution of Washington, Publication 527,
tall forests that may include big-tooth maple (Acer Washington, D. C.
Gentry, H.S. 1946a. Sierra Tacuichamona-a Sinaloa plant
grandidentatum) and alder (Alnus oblongifolia)
locale. Bulletin of the Torrey Botanical Club 73:356-362.
sometimes towering to 20 meters or more in
Gentry, H.s.1946b. Notes on the vegetation of Sierra Suro
height. The two highest sky island peaks, the Pi
tato in northern Sinaloa. Bulletin of the Torrey Botanical
nalefto and Chiricahua mountains in southeastern
Club 73(5):451-462.
Arizona, support spruce-fir forest (Picea and Gentry, H.S. 1982. Sinaloan deciduous forest. Desert Plants
Abies) as do a few localities on cold, north-facing 4:73-77.
slopes at the highest elevations in southwestern Goldberg, D.E. 1982. :the distribution of evergreen and de
Chihuahua. ciduous trees relative to soil type: an example from the
Sierra Madre, Mexico, and a general model. Ecology
63:942-951.
ACKNOWLEDGMENTS Hastings, J .R., R.M. Turner, & D .K. Warren .1972. An atlas of
some plant distributions in the Sonoran Desert. Techni~
We thank the Wallace Genetic Foundation for cal Reports on the meteorology and climatology of arid
regions. University of Arizona, Institute of Atmos
supporting our research on the trees of northwest
p heric Ph ysics.
ern Mexico. We also thank Lucinda McDade and
Kearney, T.H. & R.H. Peebles. 1960. Arizona Flora. 2nd
the staff at the University of Arizona Herbarium
edition with supplement by J.T. Howell & E. McClin
for their assistance, and Dennis Breedlove, Al
tock. U ni versi ty of California Press. Berkeley.
berto Burquez, Mark A. Dinlmitt, Mark Fishbein, Little, E.L. 1950. Southwestern trees - a guide to the native
George Ferguson, James Henrickson, Phil Jenkins, species of New Mexico and Arizona. Agricultural hand
Angelina Martinez-Yrizar, Stephanie Meyer, Andy book no.9,GovemmentPrintingOffice,Washington, D.C.
Sanders, Richard Spellenberg, Victor Steinmann, Marshall, J.T., Jr. 1957. Birds of Pine-Oak Woodland in
Tom Van Devender, Michael Wilson, David Yet Southern Arizona and Adjacent Mexico. Pacific Coast
Avifauna Number 22.
man, and many others for generous help with this
Mearns, EA. 1907. Mammals of the Mexican Boundary of the
tree flora.
United States.United States National Museum Bulletin56.
Pennington, T.D. & J. Sarukhan. 1968. Manual para la
identificacion de campo de los principales arboles
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K.F. Clark, J. Roldan-Quintana, & R. Schmidt (eds.). Desert plants: an ecological atlas. University of Arizona
Northern Sierra Madre Occidental Province, Mexico, Press. Tucson.
guidebook. EI Paso Geological Society.EI Paso, TX. Vines, R.A. 1960. Trees, shrubs, and woody vines of the
Felger, RS. & C.H. Lowe. 1976. The Island and Coastal Southwest. University of Texas Press. Austin.
Vegetation and Flora of the Gulf of California, Mexico. White, S.s. 1948. The vegetation and flora of the region of
Natural History Museum of Los Angeles County, Con the Rio de Bavispe in northeastern Sonora, Mexico"
tribu tions in Science 285.59 pp . Lloydia 11:229-302.
Felger, R.S. & M.B. Johnson. in press. Trees of Sonora, Whitaker, R.H. & W.A. Niering. 1965. Vegetation of the
Mexico. Oxford University Press. New York. Santa Catalina Mountains, Arizona: a gradient analysis
Flora of North America Editorial Committee .1993. Flora of ofthesouthslope.Ecology46:429-452.
North America 2. Oxford U niversi ty Press. New York. Wiggins,I.L.1964.Floraofthe Sonoran Desert. p.189-1740.IN:
Gentry,H.s.1942. Rio Mayo plants -a study of the flora and F. Shreve & I.L. Wiggins. Flora and Vegetation of the Sono
vegetation of the valley of the Rio Mayo, Sonora. ranDesert,2vols.Stanford UniversityPress.Stanford.
77
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 (*).
G T N R E S M L TO OK: PN MX
GYMNOSPERMS (CONIFERAE -Conifers)
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
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
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