Treesearch

Female and male cervids often use different habitats, and patterns of habitat selection and space use by the sexes may be influenced in part by selection of different forage resources. We tested the hypothesis that female and male ruminants select habitats that differ with respect to quality and abundance of forage by evaluating sex-specific responses of North American elk (Cervus elaphus) to an experimental fuels-reduction program at the Starkey Experimental Forest and Range (Starkey) in northeastern Oregon. From 2001 to 2003, 26 stands of true fir (Abies) and Douglas-fir (Pseudotsuga...

The purpose of this paper is to quantify climatic controls on the area burned by fire in different vegetation types in the Western United States. We demonstrate that wildfire area burned (WFAB) in the American West was controlled by climate during the 20th century (1916-2003). Persistent ecosystem-specific correlations between climate and WFAB are grouped by vegetation type (ecoprovinces). Most mountainous ecoprovinces exhibit strong year-of-fire relationships with low precipitation, low Palmer drought severity index (PDSI), and high temperature. Grass- and shrub-dominated ecoprovinces had...

Planting with mixtures of tree species rather than single species is often considered during reforestation because of the potential increased productivity and other benefits. We examined tree growth at the stand and individual tree scales in two experiments contrasting monocultures with a 1:1 mixture of tree species: (1) Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) with a conifer of similar shade tolerance (western white pine (Pinus monticola Dougl. ex D. Don)) and (2) Douglas-fir with a more shade-tolerant conifer (western hemlock (Tsuga heterophylla (Raf.) Sarg.)). There was no...

Although dispersal is an important attribute of animal population ecology, knowledge of dispersal rates or distances for many wide-ranging species is lacking. Current methods require capturing and restraining animals, which can be cost prohibitive, fail to collect sufficient samples, or change animal ranging behaviors. Herein, we describe a novel, cost-effective and non-invasive method, using bait enriched with stable isotopes to mark the hair of American martens Martes americana. Captive martens that consumed isotopically labeled glycine exhibited significant and progressive enrichment in...

We reconstructed a 10,500-yr fire and vegetation history of a montane site in the North Cascade Range, Washington State based on lake sediment charcoal, macrofossil, and pollen records. High-resolution sampling and abundant macrofossils made it possible to analyze relationships between fire and vegetation. During the early Holocene (> 10,500 to ca. 8000 cal yr BP) forests were subalpine woodlands dominated by Pinus contorta. Around 8000 cal yr BP, P.contorta sharply declined in the macrofossil record. Shade tolerant, mesic species first appeared ca. 4500 cal yr BP. Cupressus nootkatensis...

Genetic structure of phytophagous insects has been widely studied; however, relative influence of the effect of geographic isolation, the host plant, or both have been the subject of considerable debate. Several studies carried out on bark beetles in the genus Dendroctonus evaluated these factors; nonetheless, recent evidence has shown that genetic structuring is a more complex process. Our goal was to examine the effect of geographic isolation on genetic structure of the Douglas-fir beetle Dendroctonus pseudotsugae. We used mtDNA cytochrome oxidase I (COI) sequences and RAPD markers. One...

The cohesion-tension theory of water transport states that hydrogen bonds hold water molecules together and that they are pulled through the xylem under tension. This tension could cause transport failure in at least two ways: collapse of the conduit walls (implosion), or rupture of the water column through air-seeding. The objective of this research was to elucidate the functional significance of variations in tracheid anatomical features, earlywood to latewood ratios and wood densities with position in young and old Douglas-fir and ponderosa pine trees in terms of their consequences for...

Tropical savannas including those of central Brazil (Cerrado) serve as an important regulator of energy and mass exchange with the atmosphere. However, the effects of interactions between grasses and deeply rooted trees and shrubs on energy and water fluxes of savannas are not well understood. In this study, eddy-covariance measurements were used to observe and compare the energy balance and evapotranspiration at two adjacent Cerrado sites differing in woody plant density. At both sites, ET reached a minimum at near the end of the dry season, indicating that reduced water availability...

Fossil, archaeological, and morphometric data suggest that indigenous red foxes in North America were derived from vicariance in two disjunct refugia during the last glaciation: one in Beringia and one in the contiguous USA. To test this hypothesis, we conducted a phylogeographical analysis of the North American red fox within its presettlement range. We sequenced portions of the mitochondrial cytochrome b (354 bp) gene and D-Ioop (342 bp) from 220 historical red fox specimens. Phylogenetic analysis of the cytochrome b gene produced two clades that diverged c. 400,000 years before present...

Growth and mortality of coast Douglas-fir (Pseudotsuga menziesii var. menziesii) were studied for 25 years after planting seedlings at 1- to 6-m spacings on a site of moderate quality in the western Cascade Mountains of Washington. Responses were compared to those from two other studies representing high and low site qualities. Third-year height did not differ among spacings (P = 0.80), providing no evidence that close spacing stimulated early growth. Piecewise regression identified the onset of competition-induced mortality when stand density index (SDI) exceeded 52% (S.E. = 4.6) of the...