The Desert Laboratory Repeat Photography Collection - An Invaluable Archive Documenting Landscape Change

Photography Collection, the The Desert Laboratory Repeat largest collection of its kind in the world, is housed at the U.S. Geological Survey (USGS) in Tucson, Arizona. The collection preserves thousands of photos taken precisely in the same places but at different times. This archive of “repeat photographs” documents changes in the desert landscape and vegetation of the American Southwest, and also includes images from northwestern Mexico and Kenya. These images are an invaluable asset to help understand the effects of climate variation and land-use practices on arid and semiarid environments.

The U.S. Geological Survey (USGS) is the guardian of the largest archive of “repeat photographs” in the world—the Desert Laboratory Collection—which contains images not only from the American Southwest, but also from northwestern Mexico and Kenya. Repeat photographs are used to document landscape changes over time and are taken at precisely the same locations at specific sites at different times.

History of Repeat Photography and the Desert Laboratory Collection

The Desert Laboratory Repeat Photography Collection is rooted in the work of a Bavarian professor, Sebastian Finsterwalder, who pioneered the technique of repeat photography. Beginning in 1889, Finsterwalder compared older and newer photographs he had taken of mountain glaciers to estimate rates of glacial retreat (melting) in the Alps. Before the 1950s, only a few studies used repeat photography as a scientific tool in the United States. In 1956- 1957, Homer Shantz repeated images he had taken on 1919-20 and 1924 excursions from Cape Town to Cairo in Africa (Shantz and Turner, 1958). This publication, the first book-length report of landscape change relying entirely on repeat photography, was highly influential in the fledgling field.

In the late 1950s, Jim MacDonald from the University of Arizona in Tucson wanted to analyze vegetation change documented in repeat photographs as a proxy for climatological data. McDonald recruited James Rodney Hastings to conduct field work on repeat photography of the Sonoran Desert. Hastings’s project gained the attention of Raymond M. Turner, and in the summer of 1960, they began a long collaboration to systematically replicate historical photographs of the region. This effort culminated in the classic book The Changing Mile (Hastings and Turner, 1965), which documents long-term vegetation change in the vertical mile of elevation that encompasses the Sonoran Desert. This book was recently updated as The Changing Mile Revisited (Turner and others, 2003).

The Desert Laboratory Collection, established by Turner in 1960, greatly expanded as the applications for repeat photography increased. In the early 1980s, Robert Webb engaged Turner, by then a member of the USGS, to study ecosystem recovery at abandoned ghost towns in the Mojave Desert. In 1989, Turner retired from the USGS, and Webb became the guardian of the collection. Webb applied the repeat-photography technique to a wide variety of research questions ranging from long-term channel change of regional rivers—such as change along the Colorado River in Grand Canyon—to documentation of changes in permanent vegetation plots in the Mojave Desert. Turner, meanwhile, continued to use repeat photography in documenting the combined effects of climate variability and land-use practices, including an expansion of Shantz’s work in Kenya (Turner and others, 1995). The collection now includes matches of photographs that date to the 1860s.

In the early 1960s, Hastings and Turner used repeat photography to help in studying the biogeography of desert plants in Baja California, Mexico. In the mid-1990s, Stephen Bullock of Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), a Mexican government agency in Ensenada, Baja California, asked Turner and Webb to help assess landscape change on the Baja Peninsula, focusing on long-term change in columnar succulent plant species affected by land-use practices. This ongoing work has shown systematic changes in the populations of highly valued plant species on the peninsula (Bullock and others, 2005).

As of 2007, the Desert Laboratory Collection contains about 35,000 negatives and transparencies taken at 4,961 camera stations. A total of 6,766 original photographs taken at these camera stations were used to create 9,658 matches (many images have been matched multiple times). The largest number of matches was made in Grand Canyon, the site of ongoing studies related to the effects of Glen Canyon Dam on the Colorado River (Webb, 1996). The southern and northern Arizona regions have the most matches (1,904), followed by southern Utah (902). A total of 636 camera stations have been established in Baja California and another 150 in Kenya.

Repeat Photography in Action— Some Examples

The 10-year collaboration in Baja California between USGS and CICESE focuses on quantifying rates and directions of change in plant populations and communities over the last century in the Vizcaíno Region of the Sonoran Desert. This effort documents long-term trends in mortality and “recruitment” of different plant species, and the growth rates and ages of two species— the columnar succulents cirio (Fouquieria columnaris) and cardón (Pachycereus pringlei)—that are emblematic of this region. Factors that may affect changes in plant communities and individual plants include plant harvesting, livestock grazing, off-road vehicle use, soil properties, climatic fluctuations, and geomorphic (land-shaping) processes, such as floods and stream-channel change. The project’s long-term goal is to create and maintain a baseline photographic archive for the region by compiling historical data from many widely dispersed sources and adding data from new sites to fill some critical gaps in the coverage of amount and rate of landscape change.

Historically, the desert grassland of southeastern Arizona and southwestern New Mexico was relatively free of woody vegetation (Turner and others, 2003). Two factors associated with European settlement changed this ecosystem—(1) fires set by lightning strikes or by Native Americans were actively suppressed, and (2) livestock consumed the fine fuels that formerly carried fires across the landscape. In addition, a climatic variation that favored increased winter rainfall during much of the past century encouraged woody species, notably native mesquite (Prosopis velutina and P. glandulosa) to expand their distribution from wash habitats to uplands. Repeat photos in the Desert Laboratory Collection continue to document these changes and the resulting disappearance of the once-open grassland and the establishment of a thornscrub savannah dominated by woody leguminous trees, particularly mesquite.

Plant communities along river margins (“riparian” vegetation) in the southwestern United States are threatened by water development, particularly the excessive use of ground water. Repeat photographs in the Desert Laboratory Collection show that large changes in riparian vegetation have occurred throughout the region (Webb and others, 2007), ranging from total removal in areas where ground-water extraction is excessive to large increases in areas once either barren or too swampy to admit growth of woody species. Increases have occurred both in native and non-native riparian vegetation. Non-native tamarisk (Tamarix ramosissima) forms monospecific stands that appear to exclude native species along several river reaches, but the establishment of native stands dominated by cottonwood (Populus fremontii) has occurred along numerous smaller rivers in the region, notably the San Pedro River in southeastern Arizona (Webb and others, 2007).

Change in riparian vegetation is inextricably linked to both climatic and geomorphic processes. Opportunities for the establishment of woody riparian vegetation followed down-cutting of arroyos in the late 19th and early 20th centuries that drained waterlogged floodplains. Periods of high winter rainfall during the early and late 20th century led to large winter floods, which simultaneously eliminated riparian vegetation and promoted germination and establishment of native and non-native species. Establishment of woody vegetation within arroyo walls promotes sedimentation on low floodplains, which promotes additional vegetation growth.

Debris flows are a type of flash flood that occur periodically in the tributaries of the Colorado River in Grand Canyon and elsewhere in the region. They transport large boulders into the Colorado River and its tributaries, creating constrictions and rapids. The resulting interaction between debris flows and the river strongly influences the geomorphology. Because few tributaries are measured for flow and the region is so remote, knowledge of when debris flows occurred in the past and their effect on the river was not well known. Using repeat photography, Griffiths and others (2004) determined that on average five debris flows occur every year, based on occurrence at 160 tributaries in Grand Canyon (about 20% of the total number). They used the repeat-photography information as the basis of a statistical model of debris-flow frequency in Grand Canyon by comparing the tributaries that produced debris flows versus those that did not over a 100-year period.

The Role of USGS

The invaluable archive of repeat photographs maintained by the Desert Laboratory Collection provides data that is crucial to helping understand the effects of climate variation and land-use practices on desert environments. Serving as the guardian and repository of this collection is only one of the many important scientific roles that the USGS is playing to help administer lands under the protection of the Department of the Interior and other government agencies.

Where this page came from

This page was imported from U.S. Geological Survey. Published by the U.S. Geological Survey and, as a work of the United States government, in the public domain.

Nobody has written it yet — it is the source material at a new address, which is why search engines are asked to skip it and why no one earns from it. It is up for grabs: take it on, and it is yours to rewrite and to earn from.