Treesearch

Martínez spruce (Picea martínezii T.F. Patterson) is a conifer currently passing through a bottleneck, reduced to a few relict populations totaling less than 800 trees. We used isozyme markers to analyze the mating system and survey the level of genic diversity in two populations. The mating system was characterized by a high frequency of selfing. The multilocus outcrossing rates (tm) and 95% confidence intervals were only 0.399 (0.197 < tm < 0.601) for the smallest population and 0.589 (0.475 < tm < 0.703) or 0.685 (0.465 < tm < 0.905), depending on year, for the largest. these are among...

Inorganic nitrogen (N) and sulfur (S) deposition in bulk throughfall and fog were determined at two sites located at opposite ends (42 km apart) of a pollution gradient in the San Bernardino Mountains. Plot-level averages for total annual N and S deposition in throughfall in 1996 were 18.8 and 2.9 kg·ha–1, respectively, at Camp Paivika (CP) and 2.9 and 0.4 kg·ha–1, respectively, at Barton Flats (BF). Deposition of N in throughfall in the four transects at CP ranged from 12.1 to 31.7 kg·ha–1·year–1. Spatial variability was high because of heterogenous canopy cover and varying exposure to...

This effort was developed under a U.S. GeologicalSurvey (USGS) initiative to sponsor science workshops focusingon various of multidiscipline, multiprogram themes inthe arid Southwest. The intent was to use the workshopsto explore leading-edge questions, as well as to providebetter communication and collaboration between USGS andother organizations and agencies. The workshop topics fallwithin the broad areas of landscape science of the Southwest,ecosystem studies, climatic variation, land use associated withdegradation of habitat and soils, and surfi cial processes inrelation to the environment

Valued resources in and along stream channels are commonly many river miles downstream of large sediment inputs such as landslides. Evaluating and predicting the arrival, severity, and duration of sediment impacts thus requires an understanding of how river channels digest elevated sediment loads.

Abstract - Local variations in boundary shear stress acting on bed-surface particles control patterns of bed load transport and channel evolution during varying stream discharges. At the reach scale a channel adjusts to imposed water and sediment supply through mutual interactions among channel form, local grain size, and local flow dynamics that govern bed mobility.

The Nantucket pine tip moth, Rhyacionia frustrana (Comstock) (Lepidoptera: Tortricidae), is a common pest of Christmas tree and pine plantations throughout much of the Eastern United States. The moth completes two to five generations annually, and insecticide spray timing models are currently available for controlling populations where three or four generations occur. The thermal requirements for the Nantucket pine tip moth to complete a generation were obtained from published data and used along with historical temperature data to produce maps indicating the number of annual generations...

Watershed assessment or watershed analysis describes processes and interactions that influence ecosystems and resources in a watershed. Objectives and methods differ because issues and opportunities differ.