Retinoic acid (RA) exerts important effects in the processes of vertebrate development, cellular growth and differentiation, and homeostasis. However, the mechanisms of action of RA in the control of cellular and developmental processes are incompletely understood, as the retinoid target genes have not been fully characterized. The goal of these...
Historical aerial photos were used to examine the early phase of forest succession after stand replacement disturbance, covering the Coast Ranges Province (CRP) and the western Cascades Province (WCP) of western Oregon. The study consisted of two components: characterizing the pattern of forest succession in western Oregon; analyzing the influence...
Ecosystems are highly heterogeneous systems subjected to important levels of environmental variability; however, it is common in terrestrial biogeochemical models to assume homogeneous properties of the elements of the system or constant environmental conditions. For some processes, heterogeneity in these models is treated very simplistically, but there is not much...
Arthropods are important food resources for birds. Forest management activities can influence shrub-dwelling arthropods by affecting the structure and composition of understory shrub communities. Changes in abundance and species composition of arthropod communities in turn may influence the distribution and abundance of insectivorous birds. I examined relationships among bird abundance,...
Tropical forest-to-agriculture conversions contribute to ~20% of contemporary global C emissions. Current global C flux estimates assume C is lost from vegetation and soils over time due to this conversion, and that C stocks in agricultural lands are fairly uniform across the tropics. Global C stock and flux estimates may...
A mechanistic simulation model of nitrogen fixation in dead wood was developed to help synthesize knowledge, develop hypotheses, and estimate rates of nitrogen fixation in the Pacific Northwest. In this model nitrogen fixation is directly controlled by log substrate, temperature, moisture, and oxygen content. Respiration and diffusion of
oxygen indirectly...
Litter nutrient dynamics contribute significantly to biogeochemical cycling in
forest ecosystems. These dynamics may be influenced by site attributes, litter nutrient concentrations, and soil nutrient availability either independently or synergistically. Litter nutrient dynamics were examined in two decomposition studies in temperate coniferous forests of Oregon. I used ¹⁵N-labelled litter of...
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MarkE. Harmon Steven S. Perakis
Litter nutrient dynamics contribute significantly to
Halogenated organic compounds have had widespread and massive applications in industry, agriculture, and private households, for example, as degreasing solvents, flame retardants and in polymer production. They are released to the environment through both anthropogenic and natural sources. The most common chlorinated solvents present as contaminants include tetrachloroethene (PCE, perchloroethene)...
Nutritional ecology of unhunted and sympatric populations of
Roosevelt elk, Cervus elaphus roosevelti, and Columbian black-tailed
deer, Odocoileus hemionus columbianus, was investigated in old-growth
forests of the Hoh Valley in Olympic National Park, Washington, from
September 1979 to November 1981. Seasonal diets of both cervids
generally were comprised of common...
An increment core-based, laboratory method was used to measure tissue-level respiration under controlled temperature (termed respiratory potential) of eleven tree species from three age classes. Respiratory potential was calculated on a basis of core dry-mass, volume, carbon, or nitrogen content and live bole volume. Methods tests suggested that core carbon...