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R. M. Turner

Publications and source records attributed to R. M. Turner.

16 recordsLinked to original sources
USGS2004

Temporal and spatial patterns in emergence and early survival of perennial plants in the Sonoran Desert

Seedling emergence and survival of 15 perennial species were studied for six years in a 557-m2 permanent plot at Tumamoc Hill, Arizona, USA, an ungrazed site in the northern Sonoran Desert. The minimum rain required for germination and emergence ranged from 17.5 to 35.6 mm. Few species emerged in every year of the study. First-year survival averaged across all 15 species was 3.7%; only 0.1% of seedlings lived as long as four years. The odds of survival in the first year improved with increased rain. About three times as many seedlings died from predation as desiccation. In 2-m2 subplots, mortality of three woody species in the first 30 days after emergence appeared to be independent of seedling density. Short-, moderate-, and long-lived species displayed distinct survival strategies. Long-lived species compensated for generally poor seedling survival by frequent germination and emergence. Moderate-lived species exhibited highly episodic germination and emergence, a potentially risky behavior that might have been offset to some extent by relatively good long-term survival. Short-lived species had the highest seedling survival. Because these species can bloom in their first year, good early survival meant that some individuals were able to reproduce before they died.

Plant Ecology↗
USGS2004

Variance of size-age curves: Bootstrapping with autocorrelation

We modify a method of estimating size-age relations from a minimal set of individual increment data, recognizing that growth depends not only on size but also varies greatly among individuals and is consistent within an individual for several to many time intervals. The method is exemplified with data from a long-lived desert plant and a range of autocorrelation factors encompassing field-measured values. The results suggest that age estimates based on size and growth rates with only moderate autocorrelation are subject to large variation, which raises major problems for prediction or hindcasting for ecological analysis or management.

Ecology↗
USGS2001

Dieback and episodic mortality of Cercidium microphyllum (foothill paloverde), a dominant Sonoran Desert tree

Past and current dieback of Cercidium microphyllum , a dominant, drought-deciduous tree in the Sonoran Desert, was investigated at Tumamoc Hill, Tucson, Arizona, USA. Logistic regression predicted that the odds of a Cercidium plant being alive should decrease with increasing circumference, association with the columnar cactus Carnegiea gigantea, and occurrence on steep slopes. Slope azimuth, parasitization by Phoradendron californicum , and distance to nearest Cercidium within 5 m did not significantly affect the odds of survival. Carnegiea was a source of background mortality rather than a primary cause of dieback. Of the >1,000 living and dead plants sampled, 7.7% had died within the past 5 to 7 years. An additional 12.8% died in the more distant past. Diebacks tended to occur during severe deficits in annual, especially summer, rain. More than half of the dead plants in the sample were ≥ 50 cm in girth. In current and past diebacks on Tumamoc Hill, it seems likely that severe drought interacted with natural senescence of an aging population, weakening large, old trees and hastening their deaths.

Arizona↗
USGS1998

World conventional crude oil and natural gas: Identified reserves, undiscovered resources and futures

This report summarizes, at the petroleum basin level, the United States Geological Survey's World Energy Program 1993 assessment of world conventional oil and gas resources. The maps provided show boundaries of petroleum basins that are referenced by the assessment, as well as, future oil and gas potential. The 'Futures' or future potential of a basin is calculated as the the sum of the Identified Reserves and the modal value assigned to the conventional Undiscovered Resources.

Open-File Report↗
USGS1986

Palynological evidence for the historic expansion of juniper and desert shrubs in Arizona, U.S.A.

Analysis of the sediment of Pecks Lake, Yavapai County, Arizona, has permitted the first reported palynological evidence for the historic expansion of juniper and desert shrubs in the American Southwest. The palynological evidence is supported by the comparison of modern and historical photographs, which shows the regional expansion of pinyon-juniper woodland, and the local increase of mesquite and creosote bush. A gradual increase in juniper pollen percentages began over 2000 years ago, but the rate of increase abruptly accelerated after the historic introduction of grazing animals. In contrast, juniper percentages did not increase during a prehistoric interval of intense disturbance by humans, about A.D. 1200, and a different weed flora was present. Prehistorically, water depth was greatest at ca. 600 B.C. and was lowest just prior to the arrival of Europeans. Regional climate has gradually cooled since the beginning of the record at 2630 B.P. ?? 1986.

Review of Palaeobotany and Palynology↗
USGS1978

Management of flood-plain vegetation, 1967 to 1972, San Carlos Indian Reservation, Arizona

During 1967-71, 15,800 acres of flood-plain vegetation were cleared from a 26-mile reach of the Gila River valley and a 9-mile reach of the San Carlos River valley. Both areas are on the San Carlos Apache Indian Reservation, Arizona. The area cleared in the Gila River valley included the Gila River Phreatophyte Project and the clearing was conducted as prescribed by the experimental design of that research program. Establishment of replacement vegetation was attempted on the cleared areas with indifferent success. The report outlines methods used to remove the vegetation and to discourage its subsequent regrowth. Costs of the clearing operation are given by vegetation type, and descriptions of the procedures used for establishing new vegetation are given. Clearing and subsequent maintenance of parts of the flood plain were hampered by channel clogging and subsequent flooding of adjacent areas. Part of the area selected for clearing lies within the San Carlos Reservoir. The wide range of water level in the reservoir further aggravated maintenance of an inflow channel. Both draglines and a dredge were used to open a channel to the reservoir. Because the flow of the Gila River is intermittent, vegetation becomes established in the channel at the head of the reservoir during periods of no flow. The report concludes that the presence of the vegetation promotes silt deposition and further clogging. Inflow channel maintenance is a persistent problem that will require well-planned repetitive clearing of vegetation at the head of the reservoir.

Arizona↗