Journal of
Arid
Environments
Journal of Arid Environments 61 (2005) 525-534
www.elsevier.com/locate/jnlabr/yjare
Distribution and density of maguey plants in the
arid Zacatecas Plateau, Mexico
M. ~ a r t i n e z - ~ a l v a d o rR.
~ . Valdez-Cepedac,
~,
H.R. ~ r i a s ~ ,
L.F. Beltrán-Moralesa, B. Murillo-Amadora,
E. Troyo-Diégueza, A. o r t e g a - ~ u b i o ~ . *
"Centro d<*ln~~estiyuciones
Bioloyiras del Noroeste., Mur Bermejo 195, Col. Pla,ya Palo de Stu. Ritu,
P. O. B0.r 128, La Paz, B. C.S. 23090, Mexico
h~nstitutoNacional de Investigaciones Forestales Ayricolas y Pecuarias, Av. Homero 3744,
Fracc. El Vergel, Chihuahua. Chih. 31100, Mexico
'Unrversidc~dAutonoma Choyingo, CRUCEN, Carretera Zucotecas-GuuclalajaraKm. 3.5,
El Oro, Zacatecas 98600, Mexico
Receivsd 5 August 2003; received in revised form 25 August 2004; accepted 21 October 2004
Available online 15 December 2004
Abstract
The dist~ibutionand density of Agave salmiuna ssp. crussispinu within the state of Zacatecas,
Mexico in {heperiod from May 2001 to October 2002 is reported here for the first time. A field
sampling aras conducted based on a stratified random design. The resulting sample size was
154 plots, which were distributed randomly in three strata: high, medium, and low density. In
each plot the following parameters were determined; latitude, longitude and number of agave
plants that were classified into the following stages: juvenile; pre-reproductive; reproductive;
and mature. The spatial data analysed using GIS showed that Agnve salmiana ssp. crassispina
is distribmed over approximately 59,905ha. Out of this total area, about 1142 ha were
classified 2s high density, 51,529ha as medium density, and 7234ha as low density. The
estimated density of agave plants in high-density strata was an average of 3125 individuals per
hectare in comparison with 788 and 652 individuals per hectare for medium. and low density,
respectively. It is recommended to protect the areas with higher density and to establish
*Correspnnding author. Tel.: + 52 112 536 33; fax: + 52 112 327 60.
E-mail address: aortega(@cibnor.mx( A . Ortega-Rubio).
0140-19631s -see front matter ((12004 Elsevier Ltd. Al1 rights reserved.
doi: 10.IO16,J.jaridenv.2004.10.002
526
M. Martínez-Salvador et al. / Journal of' Arid Environments 61 (2005) 525-534
plantations in those with low density, but with the necessary conditions for the development
and sustainability of this specie.
O 2004 Elsevier Ltd. Al1 rights reserved.
Keywords: Agave; Maguey; Distribution; Density; Agave sulmiana ssp. crassi.~pina;Zacatecas; Mexico
1. Introduction and literature
Al1 the species in the genus Agave are native to the south-western United States,
Mexico, Central America, and the Canary Islands (Saluson, 2000). About 75% of
these species live in Mexico, and 74% of them are endemic to this country (García,
1995; hlartínez-Palacios et al., 1999). Agave's greatest diversity is found in the
Mexicari Central Plateau (Gómez-Pompa, 1963; Saluson, 2000). Unfortunately,
protection provided to these species by the Mexican authorities has been limited;
hence, these ecosystems are being affected by destruction and changes to their
habitat as a result of human activities such as urbanization, agriculture, livestock
farming, road and dam construction, production of secondary products, as well as
collecting of seedlings and mature specimens for ornamental uses (Franco, 1995).
Some of the species of the Agavaceae and Nolinaceae families are preserved in 30%
of state-protected natural areas (Franco, 1995). However, the local populations of
many species in these families are endangered, among them Agave guiengola, A.
impressa, and A. nizandensis (García, 1995; Franco, 1995).
In the Mexican state of Zacatecas, the most abundant agave subspecies is the
green maguey (Agave salmiana Otto Salm Dick ssp. Crassispina (Trel.) Gentry). It
includes wild plants with highly variable performance and phenotypes, but in general
terms they have a central spiny body, which range from 80 to 120cm high at
maturity. Their relatively few leaves are narrowly lanceolate, 60-90cm long,
16-25cm wide, green to grayish, concave, rigid and accuminate, tipped with a
subulade thorn 5-9cm long (Tello, 1983). Agave salmiana reproduces mainly
vegetatively by growing twigs or suckers around the mother plant, forming four to
seven young agave plants, which will eventually become new established plants
(Martínez-Morales and Meyer, 1985).
The wild populations of Agave in the study region occur on shallow soils derived
from igneous lithologies. Records of 25 years of precipitation data in the area show
that the mean annual precipitation is 450 mm and extreme temperatures may affect
their propagation (Aguirre et al., 2001) even though maguey plants are classified as
CAM plants and are able to withstand temperatures exceeding 55 "C (Nobel, 1996).
In addition, human pressure as well as intensive livestock grazing have resulted in a
remarkable decrease in the number of agaves. Therefore, it is evident that a rational
management system is needed to protect these populations and to prevent their
extinction (Aguirre et al., 2001). Moreover, the boom in tequila consumption and the
resulting shortage of blue agave fuelled a continued strong demand for Agave
salmialia ssp. Crassispina, an alternative/complementary source for producing this
M. Marthez-Salvatior et al. / Journnl o j Arid Environtnents 61 (2005) 525-334
527
alcoholic beverage. Consequently, harvesting of wild agave plants has considerably
increased in the region, a situation that could lead to major alterations in the region
ecosystem.
The present research is part of an ecological diagnosis of agave populations and
forest conimunities in the study region. Little or no information is available about
maguey distribution and density. The objective of this research was to evaluate
distribution and density of maguey. A second objective was to determine the type of
soils and landforms present in the area, using a spatial cartographic analysis. This
knowledgc may lead to a better understanding of the maguey ecosystems in the
Zacatecas plateau of Mexico.
Concerning the originality of the present work, we are certain that it is very
common LO use GIS to analyse population distributions; nevertheless, this is the very
first study, applying such techniques, analysing the ciirrent status of a coinmercial
native plant (the agave), in a very poor and arid Mexican State (Zacatecas).
2. Materials and methods
This study was conducted from May 2001 to October 2002 in the southeast of
Zacatecas, Mexico (Fig. 1). In this region Aguue salmiana ssp. crassi.~pinais naturally
distributed. Climate can be classified as BSIKW(w) which corresponds to the least
dry of the dry steppe type, with a mean annual temperature ranging between 12 and
18 "C, and an annual average precipitation of 450mm (UNAM, 1970; Garcia, 1981).
Most of l.he precipitation occurs from June to October, and fluctuations of wet and
dry years are not as dynamic as on other regions of Zacatecas with less than 300 mm
San Luis Potosi
Fig. 1. Localization of study area
528
M. Martínez-Salvador et al. / Journal o/ Arid Enuironments 61 (2005) 525-534
of annual precipitation. The dominant soils in the area are Eutric Lithosols and
Haplic Xerosols (according to the F A 0 soil classification system, modified by the
CETENAL (1972) for Mexico's local conditions). The dominant plants in the area
are xerophilous shrubs, which include severa1 species of the family Cactaceae, such as
Opuntiu species (nopal) as well as thorny shrubs and other microphyll species,
including Larrea divaricata, and Jutropha dioica (Rzedowski, 1978).
In order to determine the area of distribution of agave, the areas occupied by
desert crass scrub (CR) a species typical of the communities in which the target agave
populations occur, as well as their diverse associations, were identified using the
Thematic Maps on Use of Soils (scale 1:50,000) of the study region (F14: A61, A62,
A63, A71, A72, A73, A81, A82, A83) published by CETENAL (1970). The term F14
means tlie geographic region of UTM and the term A61 represents the specific place
of the thematic map. Having identified these communities, we conducted
photogrammetric analyses and field surveys to produce an updated map of the
area of distribution of Agaz~e salrniana ssp. crassispina. According with the
photogrammetric results, we decided to identify three environmental units where
agave is the main commercial species: high density when the observed vegetation
cover was greater than 40%; medium density when the vegetation cover was in a
range of 2 0 4 0 % , and low density when the vegetation cover was lower than 20%.
The collected data were mapped in a GIS system (ArcView), and a digital database
based o11 the area of distribution of agave was created using a UTM projection.
Using the soil and topographic maps (scale 1:50,000) developed by the CETENAL
(1972), two thematic maps of the distribution area of green maguey were digitized in
Arc View. The surface area of the main soils and landforms where its populations
occur wiis estimated based on these maps. Finally, we created a map of these areas
integrating the major soil and topographic features suitable for establishing agave
plantations in the regions with medium and low density.
With the specific objective of estimating the agave density in number of plantslha,
a field sampling was conducted based on a stratified-random design. The sample size
was calculated from the following equation (Freese, 1969):
where n is the sample size; L is the number of strata; Nh is the total size (number of
units) of each stratum h (1,2,. . . ,L); D is the desired standard error of the mean; Sh
is the stratum h standard error; and S: is the stratum h variance.
The appropriate sample size was determined using the variance in Agave salmiana
ssp. crassispina density, with a confidence leve1 of 95%. This calculation was
performzd after a preliminary survey in circular plots of 250 m2. With this size, the
number of species within the plots d o not vary when applying the methodology of
the nested sites (Franco, 1989). The resulting sample size was 154 plots (plots
sampled in the preliminary survey were not included), which were randomly
allocated in three strata or environmental units (high, medium, and low density). The
latitude and the longitude were considered at each plot to recognize each plot. In
M. Martinez-Salvador et al. / Journal of Arid Environrnents 61 (2005) 525-534
529
addition, agave plants were classified into one of the following stages, suggested for
Granados (1993): (1) juvenile, suckers that emerge from the roots of the mother
plant, establish themselves within a maximum radius of 2m, and will eventually
reach about 30cm in height; (2) pre-reproductive, agaves older than the juveniles,
independent from the mother plant, but that have not entered the clonal
reproduction stage; (3) reproductive, plants that have already initiated the vegetative
reproduction stage by producing suckers from their roots, they will eventually
produce seven descendants or more; this stage ends as soon as they initiate sexual
reproduction; and (4) mature, plants that have entered the sexual reproduction stage,
evidenced by the production of the floral stalk, which is an unquestionable sign of
the final stage of the plant life cycle.
With the specific objective for estimating the density of green maguey in each of
the study environmental units, the data obtained from the field sampling was entered
into a digital database, using Arc View software.
3. Results and discussion
According to the spatial data analysed using GIS and a mean comparison using
tukey's test (0.05 significance level), Agave salminana ssp. crassispina is distributed
over about 59,905 ha. Approximately 1142 ha, representing 1.91 % of the total area
was occupied by high-density populations. Medium, and low-density populations
were noted in 51,529 and 7234 ha, respectively (Fig. 2) coexisting with different plant
communities, such as nopal (Opuntia) groups, thornless and thorny shrubs. The
estimated density of agave plants was an average of 3125 individuals per hectare in
the high-density area (Table l), whereas in the other two areas, the estimated
numbers of individuals per hectare were considerably lower (Table 1). It was evident
that agake density gradually decreases with age, so the number of mature agaves was
much lower than that of the juveniles. This pattern was noted in the four categories
(Table 1). It would seem reasonable to suggest that this effect was due to different
disturbances such as frequent droughts or overgrazing that is a common practice in
the study region. Furthermore, the utilization of agave plants for commercial
purposes such as the sale of young plants, their exploitation as an alternative forage,
and for the production of mezcal and liquer beverages are additional factors
contribuhing in the decline in the number of individuals that eventually will reach
maturity.
Agave populations in the study area occur mainly on Eutric Lithosols (61.18%),
Haplic Xerosols (20.34%), Eutric Fluvisols (7.30%) and Calcaric Fluvisols (7.26%);
the remaining populations were found on other soil types like Phaeozem, Haplic
castañozem, and luvic xerosol. Lithosols and Xerosols represents the type of soils
that are very shallow, but they have a superficial thin layer of organic matter, and a
calcareous phase (Fig. 3). These soils dominate the hills and the bottom of
mountains where the slopes are greater than 13%, as well as the erosive valleys.
Eutric 1,ithosols are better suited for growing agave with high sugar contents
(Aguirre et al., 2001). However, it is generally accepted that Xerosol offers the
M. Martinez-Salvador e/ al. / Journal of'drid Eni)ironttients61 (2005) 525-534
San Luis Potosi
r'-"+
w i e c
Agave density
u
Non &ave
High density
.2415"
[IIIIIIID]]Medlum denalty
Low density
7
&uscaiie\
1) Plnoa
23 Villa Hldalgo
$ Norla de Angeles
.22000"
Guanajuato
4 LO"t0
5) Vllla Garsia
F,g. 2. Distribution of Agave .salmicrna ssp. crcis.si.spina in southeast Zacatecas, Mexico
Table 1
Density of' Agavc salrniana ssp. oassispina in the southeast of Zacatecas, Mexico
Stages
Number of individuals per hectare
High density
Juvenile
Pre-reproductive
Reproduc~ive
Mature
Total
Medium density
Low density
Mean
Mean
Std. err.
Mean
Std. err.
993.30
828.30
696.70
606.70
3125
66.11
66.85
48.96
34.22
203.80
249.20
173.96
161.26
788.22
32.60
69.08
32.30
38.69
Std. err.
biological optimum for agave production and development. These areas represent a
viable option for the establishment of plantations designed to protect and preserve
agave populations, conserve and rehabilitate fragile soils, and protect biodiversity in
these ecosystems (Fig. 3).
Green maguey is found mainly at the bottom of mountains, on hillsides and
valleys with gentle slopes of less than 13% (Fig. 4). These landforms cover 72.5% of
the total distribution area. Agave density tends to decreases as the slopes increase, so
M. Martínez-Salvador et al. / Journal of Arid Environmorts 61 (2005) 525-534
53 1
m Phaeozcni
m Euhicfluvisol
m calcsrlc ~ u * ~ s o I
m Haplic castañozen
m
Luvlc ye,oro1
1. Pinos
2 . Vnin iildalgo
5. N o i h de Angeles
4. Loreto
5. Vnin Garcln
Fig. 3. Soil types in the Ayave salmiana ssp. crassispina area distribution.
102"16
102"OQ"
IOl"46"
lOI"90"
lOl"16
101"OO
2230"
1
<13%
San Lulr Potoai
22"16"
22"OO"
22"00"
101'00"
IOl"45"
>13%
]
vaiieys
l. Plnos
2. Wla Hldalgo
3. Noiia de Angeles
4. Loreto
5. Vüia Garcla
Aguascaliente
102"15
0
1OT9 0
l O l " l 6
lOl"O0"
Fig. 4. Slope types in the Agave salmiana ssp. crassispina area distribution
on hills and mountains with slopes greater than 13%, it accounts for 20.43% of the
total dis~ributionarea. Agave is also found, although at a lower density, on erosive
valleys. This landform account for only 7.02% of the total distribution area. It
532
M. Martinez-Salvudor el (11.
/ Journal of'Arid Environments 61 (2005) 525-534
represents the area where the main impacted area is due to human disturbances with
easy accessibility. The lower portions of the area, with gentle slopes, are suitable for
estab1ish:ng agave plantations on areas where this species has been displaced or on
those with low density of agaves.
The e~timated area with the potential for establishing agave plantations is
28,185ha, which is distributed in the three municipalities where this study was
conducted (Fig. 5). As shown in Table 2, the largest area (27,026 ha) corresponds to
the present moderate density populations. And finally, the area with the lowest
density covers 1159ha. This is the area where new plantations are urgently needed
for re-establishing agave species in the study area.
In Zacatecas, Mexico Agave salmiana ssp. crassispina occupies a total area of
59,905 ha, distributed in the municipalities of Pinos, Villa Hidalgo and Noria de
Angeles; however, high-density populations occur in only 1142 ha. Hence, harvesting
and use of this resource in the study area should be planned and performed using the
appropriate methods, including thinning and selective harvesting of young plants for
transplanting on the low density environmental units with appropriate characteristics (Fig. 5). In al1 the environmental units, it is advisable to harvest a maximum of
70% of the mature individuals, and to protect the remaining 30% so that they
continue to reproduce, which will preserve the species. The survival of juvenile, prereproductive and reproductive individuals should be ensured through promotion and
support of agave plantations and re-establishment programs for the regions with the
lowest density but with adequate characteristics.
San Luls Potosl
22"30"~
-22"30"
=
Yedium dsnsity
Be
22"15"-
22"OO"-
22"16"
Agumscalientes
-22"OO"
M
dmnsity
1). Plnos
2). Vllla Hidalgo
3). Noria de Angeles
4). Loreto
5). Villa Gamia
Fig. 5. Potential area for Agave salmiana ssp, crassispina plantations, in southeast Zacatecas, Mexico.
M. Murtrizez-Sulvudor et ul. / .lournul of Arid Environtrirnt.~61 (2005) 52.5-534
533
Table 2
Potential area for Agave salmiuna ssp. crassispinu plantation establishment, in the southeast of Zacatecas,
Mexico
Municipalii.ies
--
Pinos
Villa Hidalgo
N. Angeles
Total
Average of annual
precipitation
(mm)"
-
375
400
400
Average of annual
temperature ("C)"
Surface ha
-
Medium density
Low density
Total
23,067
3805
154
27,026
1159
0.00
0.00
1159
24.226
3805
154
28,185
-
16
16
16
"Source: INEGl (2002). Anuario Estadístico del eblado de Zacatecas
In 98% of its distribution area in Zacatecas, agave occurs at medium and low
densities (788 and 652 individuals per ha, on average), hence, it is critica1 to develop
and implement more efficient programs and actions to facilitate the establishment of
new agave planlations that Inay constitute the foundation of environmentally sound
systeins for the commercial production of agaves. In this work, we determined which
are the optimal areas for establishing agave plantations. Most of the appropriate
areas exhibit low densities, which are caused by the current over-exploitation of this
arid plant.
In the studied zone, certainly it is not possible to analyse the history of the hulnan
disturbances on the Agave populations. There are no any kinds of records. There are
no special licenses to exploit natural populations in the field. You can understand it,
because it is a very poor and chaotic Mexican State. Indeed the statc of Zacatecas is
the poorest in Mexico. Despite such lack of records of human disturbances on agave
populations, we can infer, through the ecological information presented in this
paper, which zones currently classified as Low Density zones- have the propitious
conditions as to be considered as High-Density zones. According with our ecological
and plant population analysis we can then conclude that these currently Low Density
zones, llave been suffered a high historic human disturbance.
Acknowledgments
This study was supported by the Centro de Investigaciones Biologicas del
Noroeste and by the Universidad Autónoma Chapingo. Project 2002-UAC023. We
thank irhe Integradora de Magueyeros del sureste Zacatecano. We whish to thank
two anonymous Reviewers and Professors C. Hutchinson and D. Ravetta, for al1 the
time and effort devoted to improve an earlier version of our manuscript. Special
thanks to Ing. José Luis Medina who professionally assisted us during the field work.
We wish to acknowledge Dr. Karl Wood and Dr. Kevin Mickus for revising the
Englisli language of our manuscript.
534
M. Martinez-Salt~udoret a l / .lournul of' Arid Enoironments 61 (2005) 525-534
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