Ecology of the Saguaro: II
NPS Scientific Monograph No. 8
The choice among alternatives for management of the
saguaro is contingent upon the questions of purpose and significance.
The available alternatives fall into two basic categories determined
either by (1) a commitment to an arbitrary and idyllic concept of nature
involving controlled environments and cultivated populations, or (2)
acceptance of the natural response of these populations to the
continuing climatic control of their numbers and distribution.
The first category of alternatives would create an
artificial environment inconsistent with the legislated purpose of the
National Park Service, and will be considered no further here. The
second category of alternatives, however, includes a powerful
opportunity for fulfillment of the National Park Service's obligation to
contribute to the understanding of basic ecological relationships.
Management recommendations offered here incorporate
and supplement the recommendations contained in our earlier (1976)
report, Ecology of the saguaro I: The role of freezing weather in a
warm-desert plant population. Although developed specifically for
National Park Service consideration for application to the management of
saguaro populations within Saguaro National Monument, these
recommendations and the findings upon which they are based have a much
broader applicability. Our recommendations apply in important degree to
the management of saguarosand other warm-desert plant
populationsat Casa Grande National Monument, Tonto National
Monument, and Organ Pipe Cactus National Monument.
At Organ Pipe Cactus National Monument, many of the
recommendations are specifically applicable to the management of the
senita (Cereus schotti) and organpipe (Cereus thurberi)
cacti, the two other species of large columnar cacti whose distribution
extends north of the United States-Mexico border.
At Organ Pipe Cactus National Monument, the organpipe
cactus, less cold-tolerant than the saguaro, closely approaches the
cold-limited northern and eastern boundaries of its geographic
distribution. The even more cold-sensitive senita reaches the absolute
limits of its northern distribution within the monument which contains
the entire United States population of approximately 500 plants.
In a manner similar in many ways to that of the
saguaro in slightly colder environments, the organpipe cactus and the
senita cactus are responding to the same climatic eventsrecurring
catastrophic freezes. At best, the future of these populations is
precarious, and the National Park Service should be concerned with the
present and future status of these populations, and as well, with the
status of other plant species that reach or closely approach the
northern limits of their distribution within Organ Pipe Cactus National
Monument. Their numbers should be carefully guarded, and their
continuing status closely observed.
Purpose, Significance, and Ecological Perspectives
Whereas a certain area within the Catalina
Division of the Coronado National Forest in the State of Arizona and
certain adjacent lands are of outstanding scientific interest because of
the exceptional growth thereon of various species of cacti, including
the so-called giant cactus, it appears that the public interest will be
promoted by reserving as much land as may be necessary for the proper
protection thereof as a national monument.Herbert Hoover,
Presidential Proclamation of 1 Mar. 1933.
Under the authority of the Antiquities Act of 8 June
1906, Saguaro National Monument was set aside because of its
scientific interestspecifically for the intrinsic interest
of the natural vegetation therein.
The primary significance of Saguaro National
Monument, therefore, lies in the natural associations of the vegetation
found within its boundaries. The monument includes the last remaining
example of an essentially undisturbed continuum of natural warm-desert
to mountain-forest biotic associations in the Southwestern United
States. The singular rarity of this resource clearly indicates the
importance of maintaining the integrity of the natural associations and
relationships within Saguaro National Monument.
It is upon consideration of (1) the legislated
purpose; (2) the intrinsic natural significance of the area; and (3) the
scientific and cultural values of the resources that our management
recommendations are based. The instability of saguaro populations at
Saguaro National Monument is a natural and primary characteristic of
those populations. There is little or nothing that can, or appropriately
should, be done to control that condition, for it is the expression of
the naturally evolved, genetically controlled response of the species to
natural fluctuations in the climatic environment. Our recommendations
are directed toward the development of a better understanding of the
evolution and function of natural ecological relationships, and to the
reduction or elimination of past and present human influences upon these
relationships. It is within the framework of the foregoing ecological
perspective and considerations of purpose and significance that we offer
the following management recommendations:
I. Exclude developments and associated intensive use
from highly responsive, uncommon, or rare habitats and natural
communities. All use causes some deterioration of saguaro and other
habitats. The question of what constitutes an acceptable level of
destruction must be answered with every decision to accomodate such
1. Reevaluate programs relating to roadstheir
locations, design, construction or reconstruction, maintenance
practices, and public use. The physical influence of the roads
themselves, road maintenance practices, and public activities associated
with road use destroy or degrade Saguaro habitat and contribute to the
death of adjacent saguaros and other vegetation.
A. Eliminate roads and associated developments from
high density saguaro stands in nonrocky habitats. Access to these stands
can be accomplished by the development of high standard walking trails
originating near the periphery of these stands. The users of such trails
could enjoy the benefit of the more intimate experience offered by a
B. Redesign to a low standard and, where necessary,
relocate and pave roadways for public use. The narrow, unobtrusive
Cactus Forest Drive, constructed with minimum disturbance to vegetation
and natural drainage patterns, provides an excellent model for the
design of ecologically compatible and aesthetically pleasing roadways.
The wide, intensively maintained roads of the Tucson Mountain section of
the monument, on the other hand, have grossly altered natural drainage
patterns, are increasingly deepening erosion channels, and their
presence, maintenance, and use contribute substantially to the
deterioration and death of adjacent vegetation.
C. Develop a program of minimal maintenance for
unpaved roads. With the application of a grader, motor vehicle trails
that have been used for decades without significant erosion channels now
require grading with ever-increasing frequency. Ditching to control
runoff further establishes erosion channels and damages the root systems
of adjacent shallow-rooted saguaros and other plants.
D. "De-construct" rather than "obliterate" abandoned
roadways. The firstand most importantstep in aiding the
natural regeneration of vegetation on abandoned roadways is the
restoration of natural microtopography and drainage patterns. In some
instances this will entail removal of berms and dikes, recovery of fill,
refilling of cuts, and replacement, in kind, of eroded soil. The
practice of scarifying, particularly where it follows the slope, can
contribute to further erosion and, at best, is a questionably beneficial
practice. "Pitting," used in preference to scarifying, effectively
reduces erosion and creates sites favorable for natural reestablishment
of perennial vegetation.
2. Eliminate picnic areas from saguaro habitats. Soil
compaction, destruction of vegetation, wood-gathering, vandalism, and
removal of young saguaros associated with these developments all
contribute to the degeneration of the site and adjacent habitat,
ultimately leading to the death of existing saguaros and precluding the
germination, establishment, and survival of young plants.
3. Limit further developments within saguaro habitats
to those that will not attract destructive use and cannot be located
II. Develop management programs to provide more
effective control of activities that are directly destructive to natural
populations, communities, and habitats.
1. Control uses that are destructive to saguaro
habitat such as off-pavement vehicle parking and off-trail foot and
horse travel. Where necessary, provide and direct the use of appropriate
facilities for such activities.
2. Intensify management programs to control
increasing vandalism and removal of saguaros. Old plants destroyed will
not be replaced in a human lifetime. Young plants destroyed are those
few that have survived the many hazards of the first critical years of
III. Continue programs to eliminate all
cattle-grazing. Continuing consumptive use by these exotic animals has a
devastating impact upon the biotic as well as the aesthetic environment.
Grazing intensifies detrimental actions of natural environmental
IV. Continue research designed to obtain basic
information on population and community dynamics and institute new
programs to facilitate related studies.
1. Continue on-going saguaro population studies and
institute additional studies on related communities. The response of
saguaro populations and the associated biotic communitiespast,
present, and futureprovide a valuable measure of climatic change
and the resulting effects.
2. Institute additional studies to inventory and
estimate the status and trend of saguaro populations and other key
species in characteristic and topographically dissimilar habitats.
3. Establish weather stations and maintain accurate
and consistent weather records, using standard calibrated instruments
and recognized procedures. Lack of reliable on-site climatic data has
been a major handicap in efforts to relate environmental factors to
saguaro population changes.
4. Map and identify all transplanted saguaros
surviving from previous research activities. The absence of such
identification precludes the obtaining of accurate information on
natural survival at those locations.
V. Encourage and facilitate nondestructive
independent scientific research activities appropriate to the purpose
and significance of the area.
VI. Incorporate research findings into the
interpretive program, stressing natural evolution and physical
environment in relation to natural populations and communities.
VII. Allow continuation of natural regenerative
processes in saguaro habitats from which adverse use has been
eliminated. Avoid interference with these processes by avoiding the
introduction of horticultural and other programs that will unbalance
on-going natural recovery of deteriorated habitats.
Last Updated: 21-Oct-2005