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Prominence of the Sierra Madre Occidental in
the Biological Diversity of Mexico
Robert 8ye 1
Abstract.-The conifer-oak forests that cover the five mountainous
morphotectonic provinces of Mexico occupy about 21 % of Mexico
terrestrial surface and are the most diverse with the greatest richness
and degree of endemism of vascular plants. The Sierra Madre Occidental
is prominent in Mexico's biological diversity because it is the northern
most extension of the major Mexican mountain chains and the largest
morphotectonic province. As such, it serves biogeographically as a
barrier, a north-south corridor, a refuge and a center of adaptive radiation.
The benefits derived from the Madrean forests for humans can be
measured in terms of local and national values. Management for
non-timber forest products may provide greater economic benefit to
residents.
INTRODUCTION
Santa Maria, Conchos, and Nazas rivers. The few
geological studies recognize upper and lower volcanic complexes in the largest volcanic field of
Mexico and one of the largest in the world with
200 to 400 calderas, some up to 40 km in diameter.
The lower volcanic complex is adnesitic and was
formed between 100 to 45 Ma while the upper
volcanic complex i,s extensive silicic ignimbrite,
about 1000 m thick, and developed about 54 to 34
Ma. Local Tertiary and Quaternary sedimentary
clastic bodies are deposited in depressions.
Of the eleven morphotectonic provinces that
are defined by distinctive physiographic and geologie-tectonic features, five are mountainous and
covered with conifer-oak forests (Ferrusquia
1993). Even though these forests account for 21 %
of Mexico's territory, they are richest in vascular
plants species (ca. 7,000 species or 24% 9f the vas. cular flora) and have the greatest number of
endemics (ca. 4,000 species or 32% of the endemic
flora) (Rzedowski 1993).
The Sierra Madre Occidental Morphotectonic
Province is the largest of the Mexican provinces
and covers about 289,000 km 2 or 14.68% of Mexican land surface (Ferrusquia 1993). Covering parts
of the states of Sonora, Chihuahua, Durango, Sinaloa, Zacatecas, Nayarit and Jalisco, the Sierra
Madre Occidental ranges in altitude from 200 m to
over 3,000 m with 65% of the area between 20003000 m. The altitude rather than the 10° latitude
spread has a more significant effect on climate
which in general is temperate humid (Cfb, Cwa)
and tropical (Aw). The dominant land forms are
sierras and plateaus. The Pacifie drainages include the Yaqui, Mayo, Del Fuerte, Culiacan, San
Lerenzo, Mezquital, and Atengo rivers while the
eastern drainages include the Casas Grandes,
VEGETATION
The vegetation of the Sierra Madre Occidental
is dominated by the conifer-oak forests and
bounded on the east by the Chihuahua desert and
grasslands and on the west by the Sonoran desert
and the dry tropical forests (Rzedowski 1978). The
forests in higher altitudes consist of various species of Pinus while moist pockets harbor other
conifers of the genera Abies, Picea and Pseudotsuga.
In addition to several taxa of Quercus, other hardwoods of the mixed forests include Alnus, Arbutus
and Populus trees. The marginal forests on the east
slope have pifton pines and dryland oaks (e.g.,
Quercus emoryi Torr., Q. grisea Liebm.) while the
western transition zone in the canyons have barrancan oaks (e.g., Q. albocincta Trel., Q. tuberculata
Liebm.). The deep barrancas cut into the western
flank of the Sierra Madre Occidental and provide
1Jardin Botanico, /nstituto de Bio/ogis, Universidsd Nsciona/
Aut6noms de Mexico, DF, MEXICO.
19
botanists as the rugged mountains and barrancas
became more accessible (Knobloch 1979).
Although no systematic floristic surveys have
been completed for the region, selected local studies in Chihuahua and Durango suggest that the
vascular flora consists of between 2,200 and 3,000
species although estimates are as high as 3,5004,000 (Felger and Dahl no date). The three
characteristic trees of the flora are pines, oaks and
madrofios. The north temperate genus Pinus has
100 species worldwide of which 45.5% are native
to Mexico (Styles 1993). The Sierra Madre Occidental with about 18 species along with
Transvolcanic Mountains and the southern Sierras
are the richest areas in Mexico~- With 450 species
primarily in temperate and subtropical in the
northern latitudes, Quercus is represented in the
western hemisphere by 200-225 species (Nixon
1993). Mexico is home to 135 to 150 species of
which 86 are endemic. Although not as rich as
central and southern Mexico with 60-75 species,
northwestern Mexico has approximately 41 species. The United States with 87 species of oaks
shares 31 with Mexico along the northern border.
The attractive trees of the genus Arbutus have 20
species in world of which 9 are native to Mexico
(Gonzalez and Gonzalez 1992). Six of these grow
in the Sierra Madre Occidental. The madrofios are
the least studied of these major trees. None the
less they have complex relationships associated
organisms. For instance, a fungal anamorph of Sirosporium antenniforme (Berk. & Curtis) Bukak &
Serebrianikow grows in the foliar hairs of A. tessellata (Sorensen 1987) while the communal and
quasisocial butterfly with primitive morphology
and advanced behavior, Eucheira socialis Westwood, lives exclusively on the madrofios (Kevan
and Bye 1991). Hence Mexico is home to 30% to
45% of all the species of these three characteristic
Madrean tree genera. Within Mexico, the Sierra
Madre Occidental houses 66%, 30% and 33% of
the nation's madrofios, oaks and pines, respectively, that cover the five mountainous
morphotectonic provinces.
The Sierra Madre Occidental is a major center
for diversity of succulents and perennial herbs as
well. The 136 species of Agave on the American
continent are native to Mexico (Gentry 1982). The
three areas richest in species are the Sierra Madre
Occidental, the south-central Sierra Madre Oriental and the southern Tehuacan Valley of Puebla
(Reichenbacher 1985). The area richest in wild
beans (Phaseolus a genus of about 40 species) is the
western slope of the Sierra Madre Occidental
the opportunity for the growth of many tropical
elements in riparian habitats as well as on the dry,
steep slopes. Although the classifications of communities are not comparable, published
vegetation descriptions that cover the northern Sierra Madre Occidental are available for the
borderland of southwestern USA and adjacent
Mexico (Brown 1982, Muldavin and DeVelice
1987), the state of Sonora (COTECOCA 1974),
northeastern Sonora (White 1948), southern Sonora and adjacent Chihuahua (Gentry 1942),
northern Chihuahua (LeSueur 1945) and Durango
(Gonzalez 1983).
The flora of the Sierra Madre Occidental is one
of the poorest known in Mexico (Davila and
German 1991). The first botanical specimens
known from the sierras of Durango were obtained
by Martin de Sesse y Lacasta, Juan de Castillo,
Jose Mariano Mo cifio , Atanasio Echeverria and
Vicente de la Cerda of the royal Scientific
Expedition of New Spain. Between October 21,
1791, and January, 1792, they travelled between
Alamos, Sonora, and the city of Durango
(McVaugh 1972). The existence of specimens of
Fouquieria macdougalii Nash [Echeveria paniculata
Sesse & Mocmo] of the dry tropical forest of the
western slopes of the Sierra Madre and Gentianella
detonsa (Rothr.) G. Don subsp. superba (Greene)
J.M. Gillett [Gentiana ciliata Mocmo & Sesse] of the
pine-oak forests of northwestern Mexico and
adjacent Arizona (Gillett 1957) verify these
Spanish and Mexican explorers' initial botanical
work in the Sierra Madre Occidental. The next
major contribution to the floristic knowledge of
the area was made in 1846-1847 by the German
medical doctor F.A. Wislizenus (1848), who
collected plants at the base of the Sierra Madre
west of Chihuahua while a prisoner of war; many
new species were described by George
Engelmann of Missouri Botanical Garden.
Between November 23, 1849, and February 22,
1850, the British botanist Berthold Seemann
(1852-1857)
documented
plants
between
Mazatlan, Sinaloa, and the city of Durango. Later
in 1885, Edward Palmer made extensive plant
collections in the barrancas and sierras of
southwestern Chihuahua which were distributed
by the Harvard University and the Smithsonian
Institution (Gray 1886, Watson 1886). They were
followed by others at the end of the 19th century
such as C.G. Pringle, Carl Lumholtz, C.V.
Hartman, F.E. Lloyd, E.A. Goldman, E.W. Nelson,
C.H.T. Townsend and C.M. Barber. The 20th
century saw more extensive collections by various
20
as Clethra mexicana DC., Ficus petiolaris HBK., and
Oreopanax peltatum Linden.
The Sierra Madre Occidental is the center of
species richness for many Mexican genera such as
Agastache, Dahlia, Oxalis, Psacalium, Tithonia. Often
these mountains not only host the widest ranging
species (e.g., Dahlia coccinea Cav.) but also endemic species (e.g., Dahlia sherffii Sorensen)
(Sorenson 1969). The Sierra Madre's western
drainages and adjacent coastal plain define biogeographic limits for species of Mexican genera
such as Datura lanosa Barlcay ex Bye (Bye et ale
1991) and Fouquieria macdougalii Nash (Henrickson 1972).
Not only are endemic species products of differentiation within the generic range but also
products of more dynamic biogeographic processes. Ceanothus ochraceus Suesseng., the species
with the most primitive characteristics of the genus and that grows in the semi-xeric mountains of
Chihuahua and Durango, probably represents the
ancestor that gave rise to the 55 species that radiated throughout North America to occupy more
xeric and more mesic habitats (Stebbins 1972).
Other endemics are relicts that have retreated due
to altered environmental conditions. The presence
of pollen of Picea in southern Veracruz during the
middle Pliocene (ca. 2.4 Ma) suggests that the continental climate of Mexico has warmed up
(Graham 1993). Today three species of spruce
grow in northern Mexico; P. chihuahuana Martinez
and P. mexicana Martinez are found in. the northern Sierra Madre Occidental (Taylor et al. 1994).
The 26 populations of P. chihuahuana are small
with an estimated total number of individuals of
17,000 (Sanchez and Narvaez unpubl.). The increased human pressures on the existing stands,
the lack of regenerative aggressiveness and pollen
flow corridors (Gordon 1968), and the 95% seed
mortality caused by larvae of predating moths
(Cydia phyllisi Miller) (Secretaria de Agricultura y
Recursos Hidraulicos 1993) suggest that this species may not survive in the near future.
Species with disjunct distribution or vicariant
species indicate evolutionary divergence in response to fragmentation and barriers in the past.
Pinus discolor Bailey & Hawksworth of the mountains of Chihuahua and Durango and adjacent
Arizona and New Mexico also grows at the southern end of the Sierra Madre Oriental in the states
of San Luis Potosi, Queretaro (Zavala and Campos
1993). In the pine-oak forests of northern Sierra
Madre Occidental, Ratibida latipalearis Richards is
a vicariant of R. coahuilensis B. Turner of the oak
woodlands of northern Sierra Madre Oriental
where 19 species grow (Delgado 1985, Nabhan
1990).
FLORA AND PHYTOGEOGRAPHIC
PATIERNS
The phytogeographic patterns of the flora of
the Sierra Madre Occidental are not well known.
The lack of adequate local floras in northwestern
Mexico does not permit a floristic analysis comparable to that for adjacent USA. The Apachian
Element could be centered in the mountains of
southeastern Arizona, southwestern New Mexico
and northeastern Sonora or it could be a northern
extension of the Sierra Madre Occidental
(McLaughlin 1986). This mountain chain serves as
a corridor, a barrier, as well as a refuge for endemics. The northwest-southeast orientation of
western Sierra Madre has served as a corridor for
southern migration of temperate plants as well as
the northern migration of tropical flora.
. The mountains of Chihuahua and Durango
host the southern most American extension of
northern temperate genera with such species as
Aquilegia skinneri Hook. (Munz 1946), Helianthella
quinquenervis (Hook.) A. Gray, Ligusticum porteri
C. & R. and Parnassia townsendii B.L. Robinson
(Bye and Soltis 1979). Certain species common in
eastern USA with extensions through Mexico and
into Guatemala have their western most range in
Sierra Madre Occidental; such examples"include
Ostrya virginiana (Mill.) K. Koch and Prunus serotina Ehrh. A similar eastern USA - Mexico pattern
is seen at the generic level with Tilia in which four
species are in the USA and one Mexican taxon, T.
mexicana Schlecht., the oldest living American species, which reaches its northwest limit in the
northern Sierra Madre Occidental (Jones 1968).
Wide ranging Rocky Mountain species such as
Pseudotsuga menziesii (Mirb.) Franco and Populus
tremuloides Michx. occur as isolated populations
with a few individuals in the sierra and extend
into central Mexico.
The western slopes of the Sierra Madre Occidental provide habitats for the northern extension
of many tropical elements. The dry tropical forests
have such northern limit endemic species of their
respective genera as Cocoloba goldmanii Standley,
Jarilla chocola Standley and Dioscorea remotifLora
Kunth, as well as northern limits of extensively
distributed plants to the south such as Tabebuia
chrysantha (Jacq.) Nicholson and Ceiba acuminata
(S. Wats.) Rose. The riparian habitats of the western canyons host plants with similar patterns such
21
the northern Sierra Madre Occidental during the
19th century. One example is the field exploration
of Edward Palmer in the Sierra Tarahumara in
1885 which was partially published by Gray
(1886) and Watson (1886). Of the 128 registers of
economic plants, 113 can be identified. When
these plants are compared to those employed currently, only 71 species (63% ) continue to be used
(Bye et al. in press). The remaining plants are not
known today for a given utility. Consequently,
370/0 of the ethnobotanical know ledge of the 19th
century Tarahumara has been lost in one hundred
years.
Present day use of plants by native peoples
and mestizos in the northern Sierra Madre Occidental is documented by few studies. Of the major
anthropocentric use category of plants, the most
frequent are those for remedial and alimentary
purposes. It is estimated that 400 native plant species are used as medicine while 300 are consumed
as food. Ethnobotanical data exist for the Mountain Pima of Chihuahua (Laferriere 1991,
Laferriere et al. 1991), the Tarahumara of Chihuahua (Bye 1979, 1981, 1985, Bye et al. 1975,
Cardena11993, Mares 1982, Pennington 1963), the
Tepehuan of Chihuahua (Pennington 1968), the
Warihio of Chihuahua-Sonora (Gentry 1963), the
Tepehuan of Durango (Gonzalez 1991), and the
Pima Bajo of Sonora (Pennington 1980).
The density of contemporary inhabitants of
the Sierra Madre Occidental is low. Current statistics show that in the Sierra Tarahumara there are
3.6 inhabitants per km2 and that the economic
measures indicate that the forest, cattle and mining is unilaterally extractive in the direction of the
major cities. Industries are to the east and to a
smaller degree to Sonora and Sinaloa (Enriquez
1988). The institutional economic pressures carried by mestizo residents and outside industries
who perceive the social space and natural resources differently than the Tarahumara have
created conflict between these cultures (Bassols et
al. 1986, Lartigue 1983, Vatant 1990).
(Richards 1968, Turner 1988). In the dry tropical
vegetation, closely related species of Parthenium
similar to the ancestral form are vicariants; on the
western slopes of the Sierra Madre Occidental of
Chihuahua and Sonora P. stramonium Greene
grows while in the states of Puebla and Oaxaca in
southeastern Mexico P. tomentosum OC. is found
(Rollins 1950). Although disjunct and vicarious
distributions are natural, the role of humans in
long distance dispersal should be considered as
well such as the case of Agave applanata Koch ex
Jacobi which is native to the highlands of central
Veracruz and adjacent Puebla and found growing
seemingly "wild" in the mountains of Chihuahua
and Durango (Gentry 1982).
CULTURAL ASPECTS
Indigenous residents of the Sierra Madre Occidental include speakers of such languages as
Pima, Tarahumara, Guarijio, Mayo, Yaqui, Tepehuan, Cora, and Huichol which represent minor
concentrations when compared to central and
southern Mexico (Olivera et al. 1987). Although
the absolute number of native speakers in Mexico
is on the increase, there is a decrease in the
number of individuals native speakers in the regions of the Sierra Madre (Valdes and Menendez
1987). The decline in the use of native languages is
often correlated with the decrease of knowledge
and use of native plants.
The employment of native plants to satisfy
daily needs of the inhabitants of the Sierra Madre
Occidental was complemented by the cultivation
of introduced cultivars. The documentation of the
changes in the plant exploitation over time is difficult due to the few studies carried out in
archaeological and historical contexts. Few botanical materials have been identified from
excavations in the sierras of Chihuahua (Ascher
and Clune 1960, Clune 1960, Miller 1987, Montufar 1992) and Durango (Brooks et al. 1962). The
entrance of the Sierra Madre Occidental by the
Catholic Church permitted the Spanish government to systematically register various facts about
the missions through "Relaciones Geograficas"
and "Relaciones Topograficas de los Pueblos". Although no detailed study has been carried out on
the plants contained in the reports for the 18th
century, Pennington (1963, 1969, ·1980) correlated
the plants mentioned in these unpublished documents with those used by contemporary native
peoples in Chihuahua and adjacent Sonora. There
are few documented studies of useful plants in
FOREST RESOURCE EXPLOITATION
Official Mexican government statistics take
into account those forest products that are exported from the region. For example in the state of
Chihuahua for the year 1990 (anon. 1992), the timber products of the Sierra Madre Occidental
(1,578,701 m 3 or 350,176,260,000 old pesos) greatly
out weighed the non-timber products (candelilla,
palmilla, oregano) mostly from the foothills and
22
substitute, P. peltatum (HBK.) Casso of the Transvolcanic Mountains of central Mexico, began to
replace the dominant form in the market.
As with the case of "matarique", the prices of
"chuchupate" at the suppliers, wholesale and retail levels rose similarly. The market price per kilo
of dry roots of "chuchupate" (which is used to
treat gastrointestinal ailments and pains), increased US$1.S0 to US$8.00, US$2.50 to US$12.50
and US$3.S0 to US$18.00, respectively. "Chuchupate" (Ligusticum porteri) grows in the shaded
pine-oak forests of northern Sierra Madre Occidental but has rapidly declined due to
overcollecting to satisfy national and international
demands and to destruction of the forest habitat.
Tarahumara collectors in 1987 received US$0.33
per kg of dried root or 22% of the suppliers price
or 1.8% of the crude retail value. In addition to the
crude drug, it is one of two major ingredients of a
commercial product called "Copangel" which is
sold in the health food stores and pharmacies to
treat dyspepsia, gastritis and stomach ulcers.
Clinical trails in a Mexico City hospital confirmed
the effectiveness of the herbal remedy (Mundo et
aL unpubL).
The undisturbed "chuchupate" forest habitat
has on the average 60 adult gIants equivalent to
7.S kg of dried roots per 100m. Using the general
figures of natural plants densities in the forest, the
price paid to indigenous collectors and the retail
value of the finished product (US$5 per 100 capsules), the value of the "chuchupate" ~ine-oak
forest habitat can be estimated. A 100m plot of
this habitat in terms of "chuchupate" is worth
US$2.47 in direct gain by a Tarahumara collector
or, in terms of the retail product "Copangel",
US$749.93. If only 10% of the population is harvested and the regeneration cycle is 10 years long,
one hectare of chuchupate" has an annual worth
of US$24.70 to the collector. That hectare of forest
would be valued at $74,993 based upon the retail
product.
Using timber profits to which the Tarahumara
have a right to collect, Enriquez (1988) calculated
that each year a Tarahumara family receives
US$4.30 per hectare for harvested timber and
pulp. That hectare of forest would have a value of
$5,000 based upon the timber and pulp sales.
Although "chuchupate" seldom occupies uniformly a hectare, does not have an insatiable
market and is not the sole non-timber forest product in that plot, these general figures suggest that
integrative non-timber resource management of
critical habitats within the forest mosaic would return more financial benefit to the local residents
desert (890,S97 kg or 1,983,368,000 old pesos). This
pattern for the pine-oak forests is the same in
Durango but is strikingly different in the central
and southern Mexico states where non-timber
prod ucts such as resins and medicinal roots balance the timber products (Vargas and Terrazas
1990).
Even though there are no economic evaluations of the value of local plant resources in local
economy of the Sierra Madre Occidental, local and
regional trade of certain non-timber forest products has been recognized as important. The
Tarahumara Indians of the barrancas and sierras
exchange such items as food plants and products
(Agave spp., Coursetia glandulosa A. Gray), dye
plants (Haematoxylon brasiletto Karst., Indigofera
suffruticosa Mill., Erythrina flabelliformis Kearney),
chiltipin (Capsicum annuum var. glabriusculum
(Dunal) Heiser & Pickersgill), fibers (Yucca spp.,
Dasyliron spp., Nalina spp.) and medicinal plants
(Buddleia spp., Litsea glaucescens HBK., Hintonia latiflora (Sesse & Mocifto ex DC.) Bullock, Jatropha
platanifolia Standley) (Bennett and Zingg 1935).
Of the 300 plants used medicinal by the Tarahumara, about SO enter the local markets. In a
study of 47 plants that originate from the western
mountains of Chihuahua, 30 of these are used in a
similar fashion by both the Tarahumara and the
mainstream Mexicans (Bye 1986). The continued
employment by both cultural groups assumes that
the vegetal remedies are effective in the s~me human physiological system and could indicate the
potential for economic development. The current
condition of such plants as matarique", "chuchupate", and "te de milagro" suggest that careful
integration of a sustainable forest management
plan with the socioeconomic development of the
residents of the Sierra Madre Occidental is needed
urgently. Between 1978 and 1987, the prices at the
suppliers, wholesale and retail levels rose dramatically. In the case of "matarique" (which is
used to treat diabetes and arthritis), the price per
kilo of dry roots increased US$4.50 to US$7.50,
US$6.S0 to US$11.00 and US$9.00 to US$16.2S, respectively. During the period this dominant
element of the matarique" medicinal plant complex (defined as a group of taxonomically distinct
plants that share common names, uses and morphochemical traits; Linares and Bye 1987) was
Psacalium decompositum (Gray) H. Robins. & Brett.
of the pine-oak forests of northern Sierra Madre
Occidental and was commercialized throughout
Mexico and adjacent USA. The rising prices were
attributed to scarcity of the most effective form.
Even though not considered as efficacious, the
II
II
II
23
ment tool in the pine-oak forests of Chihuahua
(Sanchez and Dieterich 1983).
than exploitive cutting. Also, increasing the profit
margin for the collectors could make forest habitat
management more attractive to the inhabitants of
the Sierra Madre Occidental.
"Te de milagro" or "chucaca" (Packera candidissima (Greene) Weber & Love) is a massive
ground cover that invades clear cut areas in the
pine-oak forests of Chihuahua. The leaves are
drunk as a tea for alleviating kidney pain and are
prepared as a wash or salve to treat skin ailments.
"Hierbamil" is a commercial product sold as a
syrup or a cream in Mexican pharmacies. At first
glance, this plant has commercial potential as part
of a clear cut forest management plan. Unfortunately, the plant has one of the highest
concentrations of hepatotoxic pyrrolizidine alkaloids (Bah et al. 1994). Development of non-timber
forest products, in addition to considering
cost/benefit analyses, must consider the toxicology of the products to the consumers.
CONCLUSIONS
The Sierra Madre Occidental is prominent in
the biological diversity of Mexico, one of the
mega diversity countries of the world. It is the
largest morphotectonic province in Mexico with a
great range of altitude. Its northwest-southeast
orientation has allowed it to function as a barrier
to east-west migration as well as a corridor for
movement of northern elements south and vice
versa. The conifer-oak forest that covers the
mountains is the most diverse in Mexico in terms
of species richness of vascular plants as well as
degree of endemism.
Various ethnic groups live diffusely in the sierras and the associated western barrancas. The
non-timber forest products playa role in the local
and national economies even though they are not
registered in the official surveys. Some plants
have the potential to develop into viable economic
enterprises. The changes in land use affect, often
negatively, the abundance and survival of some
plants in the region.
FOREST DAMAGE AND FOREST
MANAGEMENT
As mentioned above, overcollecting of certain
plants and the destruction of habitat has altered
the biological diversity of the Sierra Madre Occidental. Clear cutting and overgrazing are major
factors in the alteration of certain forest communities. Inappropriate land use such as the plowing
of the high wet "llanos" (which naturally do not
have tall trees) for afforestation plantings has lead
to the extinction of the endemic Taushia allioides
Bye & Const. (Bye and Cosntance 1979). Fire is
considered to be an important element altering
the forests of Chihuahua and Sonora (Garda 1983,
Dieterich 1983). Preliminary observations on certain plants suggest that the flora is adaptive to
periodic, light fires and/or long dry spells. Thick
scales, concentrated needles and dense bark protect the young seedlings of Pinus engelmannii
Carr. Perenial herbs with tuberous tap roots (e.g.,
Cologama spp.) or thick rhizomes with radiating
roots below (e.g., Psacaliulll spp., Roldana spp.)
survive surface fires. Shrubs (e.g. Ceanothus spp.)
and grasses (e.g., Muhlenbergia spp.) sprout vigorously after fires. Upon firing, Arctostaphylos
pungens HBK., which forms a dense chaparral
and prevents the establishment of seedlings under
the crown through light competition and deposit
of allelopathic substances in the soil, dies back
without sprouting, thus opening the habitat for
colonization by a more diverse flora. Controlled
burning is now being considered as a manage-
LITERATURE CITED
Anon. 1992. Anuario Estadfstico del Estado de Chihuahua. Instituto Nacional de Estadistica, Geograffa e
Informatica; Gobierno del Estado de Chihuahua, Chihuahua.
Ascher, R., and F.J. Clune. 1960. Waterfall Cave, southern
Chihuahua, Mexico. American Antiquity 26:270-274.
Bah, M., R. Bye and R. Pereda-Miranda. 1994. Hepatotoxic
pyrrolizidine alkaloids in the Mexican medicinal plant
Packera candidissima (Asteraceae: Senecioneae). Journal of Ethnop ~armacology 43: 19-30.
Bassols Batalla, A., C. Bustamente LelTIUS, M.R. Hernandez A., R. Garda, M.L. Perez Villegas. 1986. Lucha por
el Espacio Social. Regiones del Norte y Noreste de
Mexico. Universidad Nacional Aut6noma de Mexico
Nlexico.
Bennett, W.C., and R.M.Zingg. 1935. The Tarahumara, An
Indian Tribe of Northern Mexico. University of Chicago Press, Chicago.
Brooks, R.H., L. Kaplan, H.C. Cutler, and T.W., Whitaker.
1962. Plant material from a cave on the Rio Zape
Durango, Mexico. American Antiqui ty 27:356-369,
Brown, D.E. (ed.).1982. Biotic Communities of the American Southwest-United States and Mexico. Desert
Plants 4: 1-341.
Bye R. 1979. Hallucinogenic plants of the Tarahumara.
Journal of Ethnopharmacology 1:23-48.
l
p
l
24
Garcia Villafan, E.R.1983. Chihuahua y los incendios forestales. SARH-INIF Centro de Investigaciones del Norte
Nota Tecnicono.4.
Gentry, Howard Scott. 1942. Rio Mayo Plants. A Study of
the Flora and Vegetation of the Valley of the Rio Mayo,
Sonora. Washington, DC: Carnegie Institution of Washington, Publication no. 527.
Gentry, HS. 1963. The Warihio Indians of Sonora-Chihuahua: an ethnographic survey. Smithsonian Institution,
Bureau of American Ethnology Bulletin 186:61-144.
Gentry, H.S. 1982. Agaves of Continental North America.
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operative in our market surveys. Students and
colleagues at the University of Colorado and Universidad Nacional Autonoma de Mexico have
been very helpful during field work. A special
thanks goes to William A. Weber who has been
instrumental in the processing and identification
of my botanical specimens over many years. Consultation of the herbarium specimens at the
Mexico's National Herbarium (ME XU) was functional because of the excellent work of the
curators and staff. Financial assistance for field
and museum work was provided by Harvard University, National Science Foundation, National
Geographic Society, Palmer Study Fund, University of Colorado, Universidad Nacional
Autonoma de Mexico, CONACyT, and US-AID.
ACKNOWLEDGEM ENTS
Raramuri and chobochi residents of the Sierra
Tarahumara shared their knowledge with me
about the local plants. Vendors of medicinal
plants of Mexico and southwestern USA were co-
27