Treesearch

The sources and oxidation pathways of atmospheric nitric acid (HNO3) can be evaluated using the isotopic signatures of oxygen (O) and nitrogen (N). This study evaluated the ability of Nylasorb nylon filters to passively collect unbiased isotopologues of atmospheric HNO3 under controlled and field conditions. Filters contained in passive samplers were exposed in continuous stirred tank reactors (CSTRs) at high (16 μg/m3) and moderate (8 μg/m3) HNO3 concentrations during 1–4 week deployment times. Filters were concurrently exposed at high and low N deposition sites along a gradient in the...

Management of invasive species requires confidence in the detection methods used to assess expanding distributions, as well as an understanding of the dominant modes of spread. Lacking this basic biological information, during early stages of invasion management choices are often driven by available resources and the biology of closely related species. Such has been the case for the management of the phytopathogen, Phytophthora ramorum , causal agent of sudden oak death (SOD) of oaks and tanoaks. To detect P. ramorum , The Oregon SOD eradication program has relied upon the aerial observatio...

The Blacks Mountain Experimental Research Project created two distinct overstory structural classes (high structural diversity [HiD]; low-structural diversity [LoD]) across 12 stands and subsequently burned half of each stand. We analyzed stand-level growth 10 years after treatment and then modeled individual tree growth to forecast stand-level growth 10–20 years after treatment. Net stand growth was compared between treatments and with adjacent Research Natural Areas (RNAs). An analysis of variance of growth in total aboveground tree biomass suggested that growth was greatest in unburned...

An experiment designed to evaluate the treatment effects of salvaging merchantable fire-killed trees on surface fuels and regeneration was established after a wildfire in northeastern California. The study was then monitored for 10 years. Surface fuel accumulations were rapid, corresponding with a high rate of snag decay and subsequent breakage or windthrow. Pine snags retained exhibited the fastest rates of breakage and transition to surface fuels, while white fir and incense-cedar were much more stable for the duration of this study. Natural regeneration observed following salvage was...

The US Department of Agriculture (USDA) Forest Service Blacks Mountain Experimental Forest is a 4,000 ha, pine-dominated tract in northeastern California, in the Lassen National Forest. Between 1934 and 1960 research at Blacks Mountain focused on various methods of harvest and bark beetle activity. These studies demonstrated the effectiveness of harvesting on tree growth and reducing widespread mortality from bark beetles. After a period of inactivity, research efforts accelerated in the early 1990s when a large-scale interdisciplinary research program was initiated, building on the...

Interspecific killing is common among carnivores and can have population-level effects on imperiled species. The fisher (Pekania [Martes] pennant) is a rare forest carnivore in western North America and a candidate for listing under the United States Endangered Species Act. Interspecific killing and intraguild predation are poorly understood in fishers and potential threats to existing western populations. We studied the prevalence and patterns of interspecific killing of fishers in the southern Sierra Nevada and Coastal Range of California. We collected forensic evidence and samples from...

Many riverine organisms are well adapted to seasonally dynamic environments, but extreme changes in flow and thermal regimes can threaten sustainability of their populations in regulated rivers. Altered thermal regimes may limit recruitment to populations by shifting the timing of breeding activities and affecting the growth and development of early life stages. Stream-dwelling anurans such as the foothill yellow-legged frog (Rana boylii) in the Trinity River of northern California are model subjects for examining associations between water temperature and the timing of oviposition,...

Given the general pattern of invasions with severe ecological consequences commonly resulting from multiple introductions of large numbers of individuals on the intercontinental scale, we explored an example of a highly successful, ecologically significant invader introduced over a short distance, possibly via minimal propagule pressure. The Sacramento pikeminnow (Ptychocheilus grandis) has been introduced to two coastal rivers in northern California where it poses a risk to threatened and endangered fishes. We assayed variation in seven microsatellite loci and one mitochondrial DNA gene...

Resource managers commonly face the need to evaluate the ecological consequences of specific water diversions of small streams. We addressed this need by conducting 4 years of biophysical monitoring of stream reaches above and below a diversion and applying two individual-based models of salmonid fish that simulated different levels of behavioral complexity. The diversion of interest captured about 24% of streamflow between June and October but had little or no effect over the remainder of the year. The change in biomass of Rainbow Trout Oncorhynchus mykiss and steelhead (anadromous...

Drift-feeding models are essential components of broader models that link stream habitat to salmonid populations and community dynamics. But is an additional feeding mode needed for understanding and predicting salmonid population responses to streamflow and other environmental factors? We addressed this question by applying two versions of the individual-based model inSTREAM to a field experiment in which streamflow was varied in experimental units that each contained a stream pool and the adjacent upstream riffle. The two model versions differed only in the feeding options available to...