Treesearch

Abstract - Recent advances in our understanding of the origin and function of armouring in gravel-bed rivers have not addressed the role of non-uniformity and unsteadiness of flow. These flow attributes have important influences on both the surface and subsurface bed material size distributions which are observed at low flow, from which we commonly make inferences concerning bedload transport at high flow. Bed armouring, measured as the ratio of surface to subsurface bed material grain size, is highly variable spatially in a channel in which past and present bed aggradation indicates that...

Abstract - During waning flood flows in gravel-bed streams, fine-grained bedload sediment (sand and fine gravel) is commonly winnowed from zones of high shear stress, such as riffles, and deposited in pools, where it mantles an underlying coarse layer. As sediment load increases, more fine sediment becomes availabe to fill pools. The volume of fine sediment in pools can be measured by probing with a metal rod, and, when expressed as the fraction (V*) of scoured residual pool volume (residual pool volume with fine sediment removed), can be used as an index of the supply of mobile sediment...

We directly observed roost and nest site selection in a population of northern spotted owls (Strix occidentalis caurina) in northwestern California during 1985-89. Because of potential biases caused by use of radio telemetry in previous studies, we examined habitat use relative to habitat availability at a level not previously reported for spotted owls. Spotted owls selected coniferous forest characterized by trees >53.3 cm in diameter more often (P < 0.05) than it was available. Hardwood stands and coniferous forest dominated by smaller trees were used less than ((P < 0.05), or in...

Four of the 10 described species of Toxostoma thrasher breed in California-California thrasher (T. redivivum), Bendire's thrasher (T. bendirei), Crissal thrasher (T. crissale), and Le Conte's thrasher (T. fecontei). Urbanization, agricultural development, fire management, and livestock grazing are among the land uses that affect large tracts of the habitats occupied by these species. Other uses generally impact smaller areas. None of these species are likely to be eliminated from the California avifauna in the forseeable fiture. However, they are potentially susceptible, in varying...

Using data from two studies in the southern and central Sierra Nevada, we compared the presence and abundance of bird species breeding in mixedconifer forests during 1978-79 and 1983-85 to predictions &om the California Wildlife Habitat Relationships (WHR) System. Twelve percent of the species observed in either study were not predicted by the WHR database to occur in mixed-conifer vegetation (errors of omission). Twentyeight percent of the species predicted by the database were not observed in either study (errors of commission). We suggest several corrections to the WHR database and...

Interest in utilizing California's forest-zone hardwoods for lumber and wood products has waxed and waned for more than 140 years. In spite of many unsuccessful ventures, strong interest is once again evident from landowners, processors, consumers, and policy makers. Their interest suggests a need to know past pitfalls, to recognize some realities of hardwood properties and related processing needs, and to build on knowledge gained from the past. A critical analysis of past hardwood practices and problems leads to 22 reasons for the failure of a sustained hardwood industry to develop....