Pima County's Withdrawal from Its Past
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Pima County’s Withdrawal from Its Past Raymond M. Turner Reconstruction of Pima County’s past vegeta- 100 years when it was first used to document tion from the time of the first European intru- changes in glaciers.[1] It was not used for study- sion is an undertaking charged with obstacles. ing shifts in vegetation until 1957, when Homer Few detailed descriptions were made of the veg- L. Shantz, former president of the University of etation encountered by those early intruders. Arizona, traveled across Africa, matching land- These visitors often recorded the presence of con- scape photographs he had taken on a trip from spicuous plants found throughout the entire South Africa to the Belgian Congo in 1920.[2] region, but specifics were missing. Thus, we The vegetation of Pima County is as varied as find written references to saguaros, greasewood its topography, from peaks ascending to more (creosote bush), sagebrush (saltbush), and palo than 9,000 feet to desert valleys descending to verdes by travellers passing through the region, roughly 1,000 feet. At the higher elevations, quak- but these generalized references do little to re- ing aspen and corkbark fir mingle with other co- solve the mystery of where rough boundaries nifers and forest plants whose main distributional between various plant communities might have ranges extend far to the north; in the low val- been, nor do they offer a baseline for judging what leys, desert species such as creosotebush and changes might have occurred following those saguaros, with affinities to the south, dominate early days. the landscape. Photographs of Arizona’s varied Interest in the history of Pima County’s veg- landscape have been taken since 1867, although etation has increased in the wake of efforts to the first from Pima County were probably taken retain certain habitats as last-ditch refuges for later. By selecting a few of the several hundred waning populations of threatened organisms. In historic landscape views available from within addition, the rapidly expanding need for space Pima County and comparing those with exactly to accommodate the region’s growing human matched recent views, we can detect trends that population has made inroads into rural areas that may prove useful in making decisions about fu- were but slightly impacted by humans only a ture management and use of Pima County land. short time ago. Knowledge of a vegetation’s his- In this survey, we have obtained early pho- tory may aid in directing its destiny by provid- tographs from various archives, with dates rang- ing a hint of the ways in which we might steer ing from 1880 to 1942. We have attempted to the forces of change. What is the effect of fire, provide examples from the main vegetation livestock grazing, and climate on the vegeta- types that are represented in Pima County. This tion of our region? One method that provides survey of matched photographs will begin at partial access to vegetation history is the art of upper elevations and descend gradually to photographic matching or repeat photography. lower points across the landscape, except that Repeat photography as a tool for document- riparian habitat comparisons will be set aside ing landscape change has been with us for over and addressed separately.[3] [1] For a review of the use of repeat photography through the early 1980s, see Rogers et al. (1984). [2] See Shantz and Turner (1958). [3] One photograph (Figure 13) is presented without a pho- tographic match because that site has not been visited to obtain a more recent photograph. 1 2 113˚ 111˚ 32˚30' 9 7 8 Tucson 1 15 5 4 6 ree 11 ints 13 12 3 2 (Mexico) 4 nado National Forest 31˚3 aro National Park n Pipe Cactus National Monument 4 20 miles no O'odham Nation Figure Major road za Prieta National Wildlife Refuge Town Water course Map by Peter Griffiths. 3 Figure 1. Mica Mountain as seen from Man Head. Elevation: 8428 feet. Figure 1a. Lawrence M. Huey photograph. June 1932. Courtesy of the Desert Laboratory Archive. (1) Rincon Mountains Mica Mountain, with an elevation of 8666 tions above 6500 feet. Centuries-long tree-ring feet, is the highest point in the Rincon Moun- records show that the frequency of large fires on tains, on Tucson basin’s eastern rim. The peak’s Mica Mountain held at about one fire every six southern slope supports a forest of ponderosa years until the 1890s, after which the return in- pine, the dominant tree in forests at this eleva- terval lengthened due to fire suppression.[4] The tion. This tree is well adapted to survive low in- forest on Mica Mountain as seen in 1932 from tensity ground fires once it becomes mature. One the top of Man Head Rock (Figure 1a) has there- set of records maintained by Saguaro National fore experienced roughly three decades of low fire Park shows that 411 lightning fires occurred in frequency. Figure 1b, taken in 1973, shows the the Rincon unit of the park between 1937 and fire lookout tower that stood on Mica Mountain 1986. Mostly small in extent, over 350 of these for several decades but has now been removed. fires occurred around Mica Mountain at eleva- The slope below the tower experienced a stand 4 Figure 1b. Martin A. Turner and Roger C. Wolf. April 15, 1973. Courtesy of the Desert Laboratory Archive. replacing fire in 1943 (the Manning Camp Fire) and a few new trees have become established during the 30 years since then. This 5,741 acre fire was the first large fire to occur following the beginning of fire suppression. Several trees grow- ing just below the camera station have died dur- ing the interval between photographs, making patches of the forest floor more visible in the later view. Many small trees in a fire-sensitive size range have become established. [4] See Baisin and Swetnam (1990). 5 Figure 2. Near the Helena Mine at the north end of the Santa Rita Mountains. View N40ºW. Elevation: 4600 feet. Figure 2a. F. C. Schrader photograph. 1909. Courtesy of the U.S. Geological Survey Photographic Library, Denver. (2) Helena Mine, Santa Rita Mountains The Santa Rita Mountains have been an area few evergreen oaks growing along minor north- of active mining since the late 1800s. In 1909, facing canyons. The low, dark shrubs at geologist Frank Schrader, working at the north- midground are fairyduster, a palatable plant that ern end of the mountain range, took photographs is closely cropped by livestock. in the vicinity of the Helena Mine (Figure 2a). At When visited in November 2002, the mes- an elevation of 4600 feet, this mountainous ter- quites had increased in density although the in- rain is well above the Sonoran Desert and sup- dividual plants were relatively small considering ported grassland, although incipient shrub inva- the century-long life of some (Figure 2b). Their sion was evident by the time of Schrader’s visit. small size is undoubtedly partly the result of cata- Scattered mesquites and ocotillos, leafless in this strophic freezes. The persistent dead branches on winter photograph, have attained a size consis- many of the mesquites is typical of plants frozen tent with the age of a decade or more. The cam- back by the severe freeze of December 1978.[5] era is aimed toward the northwest and captures a The live oaks are no longer present along the 6 Figure 2b. R. M. Turner photograph. November 5, 2002. Courtesy of the Desert Laboratory Photograph Archive. north-facing canyons. Since this site is within a few hundred feet of a former mine stamp mill which used many ricks of firewood during its mining heyday, we searched for signs that the oaks had been removed for stoking furnaces.[6] We found, lying on the ground where the oaks had stood, carcasses of large oaks that had fallen in place without signs of woodcutting activity. Death of these long-lived trees, which are resis- [5] For a description of the effect of the 1978 freeze on mes- tant to freezing temperatures and fire, is prob- quite in the nearby San Pedro Valley, see Glinski and Brown ably the result of the 1950’s drought.[7] The hills (1982). support many more ocotillos than earlier; the [6] By turning his camera to the right, Schrader took an- fairy duster has increased in number only slightly. other photograph that shows the stamp mill and ricks of firewood. (F. C. Schrader #1533, USGS Photograph Library, Denver). Also see Plate 37 in Turner et al. (2003). [7] See Swetnam and Betancourt (1998). 7 Figure 3. Gently sloping bajada of the Santa Rita Mountains as seen from Huerfano Butte. View northeast. Elevation: 3900 feet. Figure 3a. Photograph by David Griffiths. 1902. Courtesy of the National Archives. (3) Huerfano Butte Huerfano Butte is a conspicuous isolated His suspicion that the shrub population was likely prominence east of Sahuarita on the Santa Rita to grow was confirmed after seven more years of Experimental Range. David Griffiths climbed to observation when he asserted that “the time is the top in 1902 and took a series of panning pho- coming when these foothill grassy areas, which tographs. He wrote at the time that “close exami- now have only an occasional small shrub, will be nation of the broad, gentle, grassy slopes between as shrubby as the deserts and lower foothills . the arroyos. reveals a very scattering growth of if not more so.”[9] Burroweed, a small shrub, had mesquite (Prosopis velutina) which is in the form also “thickened and increased perceptibly during of twigs 2 to 3 feet high with an occasional larger the last five years.”[10] shrub in some of the more favorable localities.”[8] Figure 3a , one of the Griffiths panning pho- 8 Figure 3b.