Treesearch

Various Phytophthora species were recovered from tanoak trees, tanoak canopy drip, soils, and streams, which were sampled as part of a larger survey and management effort aimed at limiting the spread of Phytophthora ramorum Werres, De Cock & Man in't Veld (the causal agent of sudden oak death) in an epidemic area encompassing native forest and urbanised forest areas in south-western Oregon. Environmental samples were analysed by baiting with either green pear fruits or rhododendron and tanoak leaves. Tanoak bark samples and baits from environmental samples were plated on media semi-selectiv...

Phytophthora ramorum is a recently introduced pathogen in Europe and North America consisting of three clonal lineages. Due to the limited intralineage genetic variation, only a few polymorphic markers are available for use in studies involving the epidemiology and evolution of P. ramorum. A total of 159 primer pairs for candidate polymorphic SSR loci were tested with universal labeling. Four polymorphicmicrosatellite loci were identified within the NA1 lineage and one within the NA2 lineage, demonstrating the power and flexibility of the screening technique. The markers may significantly...

Empirical evidence suggests that biodiversity loss can increase disease transmission, yet our understanding of the diversity-disease hypothesis for generalist pathogens in natural ecosystems is limited. We used a landscape epidemiological approach to examine two scenarios regarding diversity effects on the emerging plant pathogen Phytophthora ramorum across a broad, heterogeneous ecoregion: (1) an amplification effect exists where disease risk is greater in areas with higher plant diversity due to the pathogen's wide host range, or (2) a dilution effect where risk is reduced with increasing...

Forests characterized by mixed-severity fires occupy a broad moisture gradient between lower elevation forests typified by low-severity fires and higher elevation forests in which high-severity, stand replacing fires are the norm. Mixed-severity forest types are poorly documented and little understood but likely occupy significant areas in the western United States. By definition, mixed-severity types have high beta diversity at meso-scales, encompassing patches of both high and low severity and gradients in between. Studies of mixed-severity types reveal complex landscapes in which patch...

Comparisons based on pretreatment calibrations between summer flows and antecedent precipitation indices (APIs) at the Caspar Creek Experimental Watersheds show increased dry-season flow for 8 yr after selective logging, followed by at least 27 yr of depressed flow. In contrast, summer flow in a partially clearcut watershed remained higher than expected for 18 yr after logging. The API-based models were used to evaluate the effects of selected climate change scenarios when combined with logging-related hydrologic changes, with the effects assumed to act independently. Changes in rainfall...

High severity wildfire can make watersheds susceptible to accelerated erosion, which impedes resource recovery and threatens life, property, and infrastructure in downstream human communities. Land managers often use mitigation measures on the burned hillside slopes to reduce postfire sediment fluxes. Hydromulch, a slurry of paper or wood fiber that dries to a permeable crust, is a relatively new erosion control treatment. Delivered by helicopter, aerial hydromulch has not been rigorously field tested in wildland settings. Concerns have been raised over its ability to reduce watershed...

Erosion on roads is an important source of fine-grained sediment in streams draining logged basins of the Pacific Northwest. Runoff rates and sediment concentrations from 10 road segments subject to a variety of traffic levels were monitored to produce sediment rating curves and unit hydrographs for different use levels and types of surfaces. These relationships are combined with a continuous rainfall record to calculate mean annual sediment yields from road segments of each use level. A heavily used road segment in the field area contributes 130 times as much sediment as an abandoned...

Mid-summer haying is a common management practice for prairies; plant species could differ in the effect of haying on subsequent growth and reproduction. We examined the effect of haying on prairie species by performing a clipping experiment. For each of seven species, sixteen plants were chosen and half were randomly assigned to a clipping treatment and half to a control treatment. Experimental plants (and surrounding vegetation) in the clipped treatment were cut to a 10-cm height in summer for two years. Measurements of plant height and the number of inflorescences were taken on all...

The dynamics of sediment transport capacity in gravel-bed rivers is critical to understanding the formation and preservation of fluvial landforms and formulating sediment-routing models in drainage systems. We examine transport-storage relations during cycles of aggradation and degradation by augmenting observations of three events of channel aggradation and degradation in Cuneo Creek, a steep (3%) gravel-bed channel in northern California, with measurements from a series of flume runs modeling those events. An armored, single-thread channel was formed before feed rates were increased in...

Market and policy incentives that encourage agricultural intensification, such as incentives for bioenergy, may contribute to biodiversity decline when they encourage a large-scale conversion of native and seminatural ecosystems to production fields. In order to appreciate the impact of these incentives on biodiversity, it is imperative to better understand how native and semi-natural ecosystems contribute to plant diversity and composition. We studied the five most common types of managed grasslands in Northeastern Kansas, a region undergoing agricultural intensification. We analyzed...