Casa Grande Ruins Administrative History

CHAPTER VII: THE ONLY BIT OF TYPICAL DESERT LAND (continued)

B. The Effect of Neighboring Agriculture on the Monument

Because of its small acreage, the monument land could never encompass a desert ecosystem. In the days before the development of modern agriculture, its desert vegetation blended with the surrounding area to provide an ecological niche for many birds and animals. Even the period of open-range cattle grazing did not seem to harm the wildlife. In 1924 George Boundey wrote that a faucet on the well pipe was allowed to drip water into a basin. The presence of water attracted all sorts of wildlife. He recounted that he had seen "ravens, hawks, mockingbirds, desert horned larks, hummingbirds, Sonora pigeons, ring necked pigeons, cactus wrens, yellow shafted flickers, thrashers, phainopeplas, cardinals, tanagers." Tracks near the basin indicated the presence of great horned owls, cottontails, jack and antelope jack rabbits, kangaroo rats and mice, fox, bobcats, and coyotes. He even saw a red racer snake and a gila monster drink the water. [8]

As a small piece of habitat, the monument was further hampered from serving any balanced natural function starting with the 1930s. Surrounding the monument with irrigated agricultural land destroyed the outside native vegetation and reduced the animals' natural habitat. To survive, smaller mammals were forced from the surrounding area onto the monument where overcrowding put pressure on the natural community. Enclosing the monument with a fence, as was done by 1934, prevented the free range of larger mammals. Thus somewhat protected, the smaller mammals multiplied. By the mid-1930s a serious rabbit overpopulation caused the destruction of young plants, especially mesquite. Without the benefit of natural checks and balances the monument vegetation cover suffered greatly. [9]

Starting in the 1930s destruction of the natural vegetation cover increased. This annihilation became especially noticeable with the death of the mesquite and diminished numbers of salt bush. In August 1936 monument personnel noticed that an infestation of bugs and worms had attacked mesquite trees. These insects were judged to be quite harmful. Without funds, however, the trees went untreated. Following circulated reports of this attack, two Park Service biologists came to Casa Grande in January 1937 to examine the mesquite. C. P. Russell and A. E. Borell concluded that soon no mesquite would exist on the monument. They judged that all of the existing mesquite were doomed because of their age combined with a mistletoe infestation and insect attacks. Russell and Borell also decided that the rapidly lowering water table could be responsible for the deterioration of the mesquite. Most important, however, there was a total lack of natural mesquite reproduction. An abnormally large rabbit population on the monument probably prevented new growth, but the lowered water table, they felt, could also be a cause. In the meantime, Russell and Borell thought that one of two courses of action could be used with the existing mesquite. Either the trees could be trimmed to keep them free of insects and other parasites during their remaining life or nature could be allowed to take its course. In any case, the removal of affected tree parts would not promote growth or reproduction. The solution to develop new mesquite trees involved a transplant program combined with irrigation. [10]

Dr. E. P. Meinecke came to the monument in the fall of 1937 to give a second opinion on the mesquite problem. He observed that while most mesquite were in decline, a few were sound and bright. The mesquite, Meinecke decided, had been in decline for a number of years. He listed three potential causes for mesquite deterioration. Part of the cause came from an infestation of mistletoe which hung heavy from the tree branches. A lowered water table, as the result of pumping for agricultural irrigation, aided the decline. Another consideration ascribed the damage to a flat-head borer (Chrysobothris octorola). Meinecke wrote that more had to be learned about the damage caused by the borer before any decision could be made on its effect. He observed that the borer only lived in the bark of dead or injured trees, so it possibly did not contribute to the death of the mesquite. In his judgement, Meinecke concluded that the lowered water table had the greatest impact on the mesquite. Another problem was the lack of mesquite reproduction, which he felt was mainly due to an overpopulation of rabbits that had found a safe haven on the monument. Another consideration came from the fact that the lower branches had been pruned from many of the trees. (Men involved with several depression-era programs had trimmed mesquite both as make work and at the recommendation of Russell and Borell.) Meinecke stated that mesquite needed to have lower branches because it was the shade from these lower branches that permitted mesquite seedlings to develop. Consequently, he recommended that pruning cease. [11]

Further studies were not undertaken on the mesquite problem and the trees slowly died. Superintendent Bicknell reported in January 1953 that conditions remained the same for the mesquite since he had first reported on them in 1936. Nearly all of these trees had died by the 1960s. An article in a 1971 issue of the Great Basin Naturalist concluded that, although data were incomplete, the mesquite decline resulted primarily from a lowered water table and a mistletoe infestation. Age, insect infestation, and lack of reproduction were considered secondary factors. All the mesquite, except for some around the visitor center/housing areas that are watered, have died. The death of the mesquite caused a change in soil moisture retention with the result that salt bush have also begun to decline. This same phenomenon created a favorable environment for the creosote bush and this vegetation moved into areas once occupied by the salt bush. Consequently, "the only bit of typical desert land" that Frank Pinkley thought the monument would support, has not occurred. The monument land no longer contains an area of "typical" desert. Because of the agricultural development around the monument's boundary, it has become an area on which some desert plants grow. [12]

Aside from a lowered water table, neighboring agriculture has potentially had other effects upon the monument flora and fauna. Beginning in the 1950s, farmers began to spray herbicides and pesticides on their fields from airplanes. By the late 1950s, just before harvest, cotton fields received an aerial spraying of a defoliant [Agent Orange?] to make it easier to pick the cotton. With each of these spray applications, planes undoubtedly flew over the monument releasing some spray. On other occasions spray would have drifted onto the monument as it was applied to neighboring fields. Some effects of these sprays on the monument's plants and animals have been determined, but a comprehensive study has yet to be conducted. [13]