Table Of ContentCOMPOSITION OF THE SAN DEL
FLORISTIC JOSE
MEXICO
CABO
CALIFORNIA
BAJA SUR,
OASIS,
RAYMUNDO DOMINGUEZ
LEON DE LA
JOSE LUIS LUZ,
DOMINGUEZ
CADENA, MIGUEL LEON,
NAVARRO
JUAN PEREZ
JOSE
and
Division de Biologta Terrestre
Centra de Investigaciones, Biologicas del Noroeste
La Paz
Apdo. Postal 128,
MEXICO
Baja Sur 23000,
California
beginning of century
the this
ited at
humedad
elevados niveles de se encuentran rodeados de territorios
ite
debido baja superficie que presentan exposicion a inundaciones
a la y la
,
ectado en los anos proximos debido a la sobreextraccion de agua para satisfacer
turismo de poblacion en expansion. El objetivo del presente estudio
idas del y la
mode como
de que
composicion actual en este oasis sirva referen^
lentar floristica
la
Baja California Sur the Mexican state with the least available freshwa-
is
ter. This is because of low rainfall and also the small number of permanent
waterways (spring, seeps, pools, rivers, lakes) and reservoirs, some of which
are locally called "pozas" or "oases" (Escurra 1988; Grismer and
et
al.
McGuire
1993). Additional causes of the aridity are the predominance of
-textured soils that favor water percolation, the high levels of evapo-
from
the soil, the lack of high mountains, and the narrowness of the
which Some
peninsula, provides
little surface area for hydrological basins.
Murphy
authors, such Axelrod and
as (1979) (1983), suggested an evolv-
climate on the peninsula. This change has allowed the climate vary
to
l
m
mesic subtropical environment through most
a of the Tertiary to the
xerophytic environment.
rrent If true, the oases could be interpreted
as
and disjunct mesic
ict habitats.
The
biological relevance of these small composi-
areas in their biotic
is
which
n, can be found only in places with constantly available water, in
mesic habitats outside the xeric peninsula, or on mountain tops where tem-
and
peratures are cooler precipitation greater than in the surrounding
is
The
desert. social and economical importance of these areas obvious.
is
Currently, there are dozens of oases in the peninsula, some of them
iso-
and Some known
lated others grouped. of the best are San Ignacio (27°25'N,
Comondu
112°52'W,elev. 150 m), (26°()2'N, 111°49'W, 400 m), La
elev.
Purisima(26°10'N,112°07'W,elev. 150m),Mulege(26°53'N,
112°02'W,
elev. 2 m). Las Pocitas system (around 24°30'N, 111°00'W, 100
elev. to
150 m), and San Cabo 109°4rW, Some
Jose del (23°03'N, m). of
elev.
1
these are close to the ocean; others are fed by water from the nearest moun-
tains or by springs. There are no geo-hydrological studies from which to
determine dynamics.
their
Other
wetlands, oases, or estuaries have vanished in the few decades,
last
some
because of water extraction in the hydrological basins to satisfy in-
demands
creasing of the local populations. possible that the disappear-
It
is
ance of wetlands has been exacerbated by combination
the of these de-
mands
with
the natural process of increased aridity in the region (Axelrod
1979; Spaulding and Graumlich 1986). Such wetlands include Todos Santos
(23°27'N, 110°18'W, 109M2'W,
elev. m), Santiago (23°28'N, 350
5 elev.
Agueda
m), and Santa (27° 18'N, 12°21'W, 230 Other may
m).
1 elev. areas
have been wetlands
centuries ago, El Carrizal (23°51'N, 110°10'W,
e.g.,
m)
elev. 150 and La Ribera (23°34'N, 109°35'W, 10 m).
elev.
Lugo
et al. (1988) pointed out, in a general classification of these areas,
that because of the catastrophic and
floods ecological limitations of such
1
60
Cabo
Di- La Luz, et al., Floristic composition of the San Jose del oasis
wetlands
pared to adjacent habitats. Because of the catastrophic floods, the
also have a relatively young structure. Moreover, they are influenced by
environmental seem regulate the structure and other
certain factors that to
Among
processes in the plant groups. these factors are the periodicity of
predominance
and droughts, the kinetic energy of the water, the of
floods
The
fundamental
the water flux, and the nutrient concentration in the soil.
niche for each species in the wetlands could be affected to a large degree by
dynamics and
water nutrient
factors.
Cowardin (1979) proposed a hierarchical system of classification
et
al.
wetlands that was based on water regimen, water chemistry, and soil
for
m
types. Each oasis can be considered ?Lpalustrine system if it is less than 2
we
deep, or system deeper, assume that the water flows
a lacustrine if if
Using same
slowly and has a small surface area. this classification, these
palms dominate physiogno-
must be designated as "forested wetlands" if
and
mically, or as "emergent wetlands" if cattails {Typha), reeds, forbs are
communities both
In addition to the desire to preserve these for ecologi-
composition
and socioeconomic reasons, the study of their plant basic
cal is
management.
and
to the proposal of legislation for their use
Vegetation around the San Jose del Cabo oasis, according the Mexican
(INEGI
chart of vegetation 1981), corresponds to the sarcocaulescent
official
Shreve and Wiggins (1964) and Wiggins (1980) recognized this
scrub.
area as a disjointed segment of the Sonoran Desert inside the Cape Region.
The physiognomically dominated by the sky-duster palm,
oasis
is
Washingtonia an endemic species occupying riverside and stream
robusta,
palm
probably
banks the southern half of the peninsula. In the past, this
in
was widespread inland where moisture in the was relatively high. To-
soil
day, these lands are occupied by abandoned or presently cultivated fields
and secondary vegetation. In natural conditions, the ground cover could
which
change dramatically according to the incidence of catastrophic floods,
seem occur once each decade.
to at least
Our was compile of the higher plants growing
objective to a floristic list
in the vicinity of the San Jose del Cabo oasis. This list can serve as a baseline
reference for additional studies seeking to record quality changes in the
The work
vegetation over time. was a part of a proposal for legislation to
made
community Such designation was
designate this as a protected area. a
by 1993.
state legislation in
by along edge
crossed foot river's
its
We
The
river consists of a strip of saturated soil of variable width. esti-
mated
a surface of about seven hectares for this area. About 16 hectares of
water were traversed by boat to collect aquatic plants.
Specimens
collected are housed in the herbarium of the Centro de
Investigaciones Biologicas (HCIB). References used were
for identification
Gould Moran
and Lot Shreve and Wiggins
(1981), et (1986), (1964),
al.
A
and Wiggins
(1980). checklist was devised beginning with our
first field
was considered complete when no
trip. It after the third trip additional
The
species were found. form of each species was noted based on the
life
references cited above. Relative abundance was determined by using
the
and shown
density distribution pattern Table because
in Finally, adja-
1.
cent land has been used for intensive agriculture, a proportion of the cur-
came
rent flora from weeds associated primarily with the Using
crops. in-
formation from the references and voucher specimens collected elsewhere
and we
in the state peninsula, classified each taxon of the flora as either
indigenous or non-indigenous.
The
San Cabo 23°04'N and 109°4l'W
Jose del oasis is at at the south-
Mexican
ern tip of the state of Baja California According Garcia
Sur. to
Koeppen
(1973), the climate formula BW(h')w(e). The climate very
is is
dry and very with mean annual 260
hot, a total precipitation (25 years) of
mm.
Figure shows the geographic location of the
1 oasis.
m
The
oasis separated from the ocean (Gulf of California) by 40
is a
The
sandbar. water level in the oasis partially regulated by hydrostatic
is
forces of the tides, but intrusion of water small.
salt
is
The
borders of this oasis (and others of the Sonoran Desert) seem be
to
contracting with the gradual increasing aridity during recent millennia
(Van Devender
1990). In addition to depletion of the aquifer, occasional
from uplands sometimes
floods the are so violent that the oasis almost
is
swept
clean. After such floods, the flora recovers but the conformation of the
—
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Nelson 1905-1906,
(1921) noted, the existence of the "San Jose River,"
km
stream from
a that arose a spring about upland and flowed into
a
I
freshwater "lagoon" which
(the current supported
oasis), a flourishing agri-
cultural area of around 300 hectares. The human population, then, was
estimated to be 1600. Rice and sugarcane were some of the more promi-
nent crops because of their high water requirements.
Currently, one more
this oasis is in of the important tourist develop-
ments
in Mexico, Los Cabos. There are around 6000 hotel rooms, each
with a potential consumption of 400 500 when
to day'^ occupied.
liters
There consumption
also for domestic purpose by almost 35,000
is inhabit-
ants. Reuse of water highly recommended but not yet developed.
is
At demand
water came
first, to satisfy this entirely from wells, of
all
them
in the watershed of the In 1992 an aqueduct, which
oasis. gathers the
pumped
water by some
several wells, in agricultural upland, was
valleys
completed
to satisfy requirements of both tourists and inhabitants. has
It a
flow of 2000 3000 minute
to liters "^ This expenditure higher than
is re-
covery by the aquifer and
will inevitably drain
it.
We
did not recognize vegetation types based on physiognomic
criteria.
Palms, and
cattails, reeds have an irregular distribution along
the
river's
edge.
In the attached checklist, each entry followed by corresponding
is its life
form, abundance, and whether
it is native or non-indigenous. Table 2 sum-
marizes the life forms of the 109 taxa of vascular plants of Most
this oasis.
of them, 78 (71%), are annual or perennial 13(12%)
herbs; shrubs
are or
and 18 (16%) belong
trees, to other forms.
life
Table 3 gives the relative abundance of the species of the checklist. Only
four (3.6%) taxa have an abundance pattern of high density and regular
XXXX;
marked
distribution, in the catalog as these are Washmgtoma
ro-
Typha
busta, domingensis, Bacopa monnieri, and Phragmites Most
of
australis.
the species, 80 (73.4%), show a pattern of low density and regular
distri-
XX.
marked
bution,
There
is a notable difference between this oasis and the northern ones
in
the peninsula. This one has a low number of date palms, Phoenix
dactylifera,
a species introduced into the oases of the peninsula as a food resource by
Spanish
missionaries in the l6th and 17th centuries. This species survives
now
groves with minimal management.
as feral or
Our work
establishes the distribution of several taxa not known
before
on
for this latitude the peninsula, Echmodorus
i.e., berteroi, Kosteletzkia depressa
Phyla Rumex
incisa, Ruellia inundata, pulcher, and Xanthium strumarium,
all
known
wetlands from 4°
in to the north or in those tropical
areas.
De La
Luz,
e:
Tarle
2. Life
ft
Only 49 (44.9%) of the species natives (in the appendix
ii
The
narked N). remaining 60 digenous species indica-
(55.:
IW)
weeds (marked
ive of early successional stages or :ed
(
oming Amaranthus
from such
cultivated fields or irbed as
is,
fimbriatus, Argemone ochroleuca, Cynodon dactylon, Dactyloctenium aegypticum,
Datura inoxia, Pentyle califormca, and Sida xantii.
This implies that the wetland has been changed from original struc-
its
The main
ture. sources of disturbances are the agricultural use of the adja-
cent land, the cutting down of the sky duster palm for support and roofing
of rustic "palapas," and the severe floods regularly affecting the oasis. All
An
these provide niches for species typical of early succesional stages. addi-
number
tional clue to support this statement the of species tied to high
is
humidity which
of (pointed out here "aquatics" [Aq], of there are
levels as
only seven [6.43%]).
might
Because of the proximity of the ocean to this wetland, one expect
the presence of any of the mangroves native to the Baja California
five
peninsula, but there are none. For Baja California Hastings et (1972)
al.
uncommon
and Wiggins (1980) identified Avicennia germinans, the
more Maytenus
Conocarpus Laguncularia racemosa, the inland
erecta,
phyllanthoides, and Rhizophora mangle, some of which occur even in higher
latitudes in the peninsula up to Bahia de los Angeles at 29°00'N.
A
possible explanation the absence of mangroves wetland
for in this
is
given by Alvarez-Lopez (1988) and Lugo et al.(1978). Mangroves grow in
warm
waters of low kinetic energy with highly predictable cycles. In tropi-
grow
cal latitudes, they in water with low salinity. In subtropical latitudes,
they are linked to highly saline water, a condition not prevailing here.
From
the types of freshwater vegetation in Mexico, Rzedowski (1978)
cited the "popal," "tular," and "carrizai" as those occurring in hot and tem-
These two
perature climates. last are poorly represented in this oasis
dominance
because of the Phragmites Typha
of, australis, Scirpus americanus,
domingensh and other monocotyledons. Floating and submersed
species are
,
dominant
not here. Potamogeton a widespread aquatic form in the penin-
is
but absent from the
sula, oasis.
it is
McGuire
Grismer and
(1993) studied 31 oases in the central Baja Cali-
own
fornia peninsula. Because each has physical and biological features,
its
own
each requires characterization. Ezcurra (1988) studied the
its et
al.
and phytogeography
flora of 17 oases in the hyper-arid zone of the Sonoran
They
Desert, almost in natural condition. reported only 26 species of
all
Most
vascular plants, none endemic. of these (31%) are taxa distributed in
Mexico The
northwestern and southwestern United hemicryp-
States.
tophytes (perennial herbs with perennating buds
their at the soil surface)
were the dominant forms (58%). Felger (1980) studied forms
life life in
Me 54%
several oases of the Sonoran Desert. found 145 taxa, of them annu-
The
form spectrum found
als. life in our checklist consistent with such
is
dominance
results, but of these probably a sign of disturbance, since 28
is
of our annuals (73.7%) are considered introduced weeds.
as
Rzedowski
(1978) indicated, in Mexico, that agricultural and industrial
demand
and water domestic have com-
activities for use affected aquatic
munities more than any other plant community type. The geographic po-
sition of San Jose del Cabo oasis, within the tropics, and the permanent
i.e.,
nature of the water would seem enough to allow a richer flora than that
human
Undoubtedly,
found. disturbance, clearing of channels, dredg-
e.g.,
down
ing, fumigation against mosquitoes, sewage and cutting
flow,
flres,
palms
have modified the original plant composition contribut-
drastically,
ing modification of both composition and
to structure.
Additional evidence of disturbance in this place the analysis of the
is
associated fauna. Nelson (1921) quoted for this oasis the endemic rice mouse
which
{Oryzomys coimi var. peninsidaris), Alvarez-Castafieda (1994) consid-
now
ered to be extinct.
in watershed and the water recycled after treatment for nonpotah
its is
O
use. Today, the oasis an informal park where tourists go for a stroll.
is
report represents one of the last opportunities for studying these spec
communities of the Baja California and the Sonoran Desert.
SEDESOL
This study was done with the funds of the former Delegacion
of Baja California Sur and the project "Estado Actual Potencial de
y
(SIMAC 94/MA-
Aprovechamiento de Oasis del Noroeste Mexicano"
los
CIBNOR.
The
001) granted to Dra. Laura Arriaga, authors are indebted to
Thomas Thanks
encouragement and
Daniel for editorial aid. also to Ellis
F.
Glazier for help with the English language text.
OTYLtDONLS
<
Dactyloctenium aegypticum
(L.)
