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The purpose of this study was to describe the structures of an arid urban forest. Two distinct and adjacent residential neighborhoods in Tucson, Arizona, Winterhaven and Richland Heights, were chosen as the study site. Landcover classes were identified through aerial photointerpretation and digitized using AutoCad. A field inventory gathered vegetative measures. Through an analysis, species composition, horizontal and vertical structure were described. Results were compared between each neighborhood stand and among findings of previous structural studies. Results describe Winterhaven as an uneven-aged stand with 55% available growing space, 37% canopy stocking, a pattern of strong dominance and mostly exotic species. Richland Heights is an even-aged stand with 78% available growing space, 11% canopy stocking, a pattern of codominance and mostly native species. These and other structural analyses have provided a descriptive study of two arid urban forest stands.

I estimated the risk of selenium toxicity to endangered Yuma clapper rail and other marsh birds of the lower Colorado River (LCR). I collected sediment, invertebrates, Virginia rails, and least bitterns from 4 locations within the LCR valley, in May-August 1990, and collected additional bird species from 1 of the sites in April 1991. I analyzed the samples for selenium and other trace elements. Selenium accumulated in the backwater marshes of the LCR and was uniformly distributed among the backwaters sampled. Selenium increased 1-16X between successive trophic levels, however, selenium levels did not differ significantly among species with different diets. Based on the selenium levels in bird tissues and prey species, marsh birds in the LCR valley are at low risk of adult mortality, but moderate to high risk of teratogenicity. The rate of selenium accumulation in the backwaters must be reduced to decrease the risk of toxicity.

Sprouting response of Quercus emoryi and Quercus arizonica was studied following a May, 1987 wildfire on the Audubon Society Research Ranch Preserve in Santa Cruz, Co., AZ. Sprouting response of oaks was measured as total number and density of sprouts by species and diameter class. Thirty-five of the 109 trees examined (32%) sprouted in response to the fire, including 30.5% of all Q. emoryi and 36.4% of all Q. arizonica. In both species, small diameter (10 cm) trees are more likely to sprout than those larger than 10 cm. Quercus emoryi trends toward producing more sprouts/tree than Q. arizonica (avg. of 14.03 sprouts to 6.87 sprouts). Among all sprouters, however, there is no difference in the number of sprouts produced by trees in the two size classes. Sprout density is greater in Q. emoryi at 3.58 sprouts/cm. Q. arizonica averages 0.89 sprouts/cm. In all sprouters, density is greater in smaller stems (4.17 sprouts/cm) compared with 0.71 sprouts/cm in the larger size class.

The Sonora chub (Gila ditaenia) is a small minnow that is federally-listed as threatened. My research objectives were to quantify characteristics and persistence of macrohabitats used by this species through critical summer periods, and to quantify microhabitat selection in Sycamore Creek, Arizona. By the end of the summer drought, macrohabitats containing adults were deeper, larger and decreased less rapidly than areas with only immature fish or unoccupied areas. Loss of surface area was highest in inundated unoccupied areas and areas with only immature fish. Loss of Sonora chub from drying pools was highest in pools with immature fish. Ephemeral and unoccupied areas had higher percentages of floating algae and coarser substrates than persistent, occupied areas. General microhabitat characteristics selected by Sonora chub were areas with bedrock or fine substrates near cover and zero velocity. Microhabitat use usually differed among life stages, and availability and selection varied among pools.

Bluehead sucker (Catostomus discobolus) and speckled dace (Rhinichthys osculus) were the only native species in Shinumo Creek above a waterfall located about 120 m upstream from the confluence of Shinumo Creek and the Colorado River. Rainbow trout (Oncorhynchus mykiss) was the only introduced species found upstream of the waterfall. I attribute the coexistence of the native and introduced species is attributed to differential use in resources and the similarly small size of bluehead sucker and rainbow trout. Mean total length of bluehead suckers was 160 mm and the largest fish captured was 230 mm (n = 77). Mean length of rainbow trout was 149 mm (maximum = 300 mm; n = 46). Bluehead suckers in Shinumo Creek were smaller than individuals observed in the mainstem Colorado River. Small size may be a response to the decreased size of the habitat available. The permanence of the waterfall barrier near the mouth of Shinumo Creek is a result of regulation of the Colorado River that prevents inundation of the waterfall.

During 1991 and 1992, I studied environmental contamination of the aquatic communities at Imperial National Wildlife Refuge on the lower Colorado River. I collected composite samples of sediment, detritus, aufwuchs, aquatic plants, invertebrates, and fishes from 2 river sites, 5 backwater lakes, and 2 seepage lakes. Selenium concentrations (μg/g, dry weight) were elevated in sediment (geometric mean = 0.93, range = none detected (ND) to 4.1); detritus (4.50, 0.4-27.4); aufwuchs (4.85, 2.6-10.2); Najas marina (5.66, ND-21.0); Corbicula spp. (10.54, 5.8-26.5); Procambarus clarkii (7.70, 1.5-35.8); whole fishes (6.70, 1.6-17.2); and fish fillets (9.72, 5.8-22.6). Ninety-four percent of whole fishes and invertebrates (n = 185) contained concentrations of selenium that exceeded 3 μg/g, a concentration recommended by the U.S. Fish and Wildlife Service to protect aquatic birds from chronic selenium toxicity. Biological samples from seepage lakes had significantly lower (p ≤ 0.05) selenium levels than similar samples from backwater lakes. Selenium is incorporated into plants in backwater lakes and enters consumers primarily through the detrital food web.

One hundred sixty two composite samples were analyzed for organochlorine compound residues and 19 trace elements and heavy metals. There was no evidence that flushing of washes in times of flood increases contaminant levels in the Bill Williams River, or that historical mining operations currently contributed to the element load. There was evidence that Colorado River water increased selenium levels in biota in the delta; one hundred percent of fish collected from the confluence of the Bill Williams River and the Colorado River contained elevated selenium concentration (geometric mean = 9.98, range 2.80-17.56 μg/g dry weight). These levels exceed standards set for the protection of predatory species of fish and wildlife.

Disastrous wildland-urban interface fires are an increasing problem throughout the United States. Local government is ultimately responsible for protection of property and life threatened by these fires. This study attempts to identify the factors that influence local policy-making in this arena. Information for this study was gathered from a review of the natural hazard and public policy literature as well as three case studies. The case study areas are Orange County, California; Oakland California; and Eastern Pima County, Arizona. Eight factors which influence local government policy-making were identified from the literature and confirmed through interviews. These factors include: acknowledgement; authority; participation; timing; cost; political influences; and liability. This study concluded that natural hazard research can be applied to wildland-urban interface fire. It also concluded that while there is increasing awareness of the wildland-urban interface fire problem there appears to be a need for a change of approach.

I surveyed songbirds and lizards adjacent to dry rivers throughout metropolitan Tucson and related species richness to recreational use and habitat using stepwise multiple regression. Habitat characteristics included vegetation structure and floristics in river-edge areas, adjacent land uses, and land uses of the surrounding landscape. Bank stabilization had a negative effect on species richness of all bird groups. Total vegetation cover, mesquite (Prosopis velutina) density, and natural open space had a positive effect on species richness of most bird groups. Tall vegetation was important for species richness of lizards. River corridors could function as conservation corridors for five bird species and two lizard species. However, habitat for many other species was not continuous across the metropolitan area. Recommendations include protecting mesquite bosques without bank stabilization, protecting wide areas of upland vegetation near large protected areas, and increasing structural diversity and use of native plants in river parkways.