Ecology of the Saguaro: II
NPS Scientific Monograph No. 8
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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 saguaros—and other warm-desert plant populations—at 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 events—recurring 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 interest—specifically 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 monument use.

1. Reevaluate programs relating to roads—their 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 nonmechanized environment.

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 first—and most important—step 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 elsewhere.

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 life.

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 factors.

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 communities—past, present, and future—provide 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.

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Last Updated: 21-Oct-2005