During the past decade, Swiss needle cast (SNC) damage has intensified in many Douglas-fir plantations in the Coast Range of Oregon, particularly along the immediate north coast. In plantations with severe symptoms, growth losses and reduced tree vigor are evident, but the magnitude of growth losses associated with varying intensities of damage is not known. A growth impact study was conducted in 1997 to quantify retrospectively the relationship between growth losses and visual symptoms in 10- to 30-yr-old Douglas-fir plantations in coastal northwestern Oregon, a population totaling 75,700 ha. A random sample of 70 Douglas-fir plantations was selected from the population and evaluated for Swiss needle cast severity. One 0.02 ha plot was destructively sampled in each plantation to reconstruct past height and basal area growth trends and to characterize foliage loss and distribution. The SNC “effect” was assessed by comparing growth of plantations with varying degrees of Swiss needle cast to growth of those that retained maximal amounts of foliage, after correcting for initial stand density, Douglas-fir growing stock, age, and site index. Of numerous possible SNC indices, mean needle retention (yr) explained the largest amount of variation in both basal area and top height growth. Prior to 1990, top height growth was similar across all plantations after correcting for site quality and plantation age; but, by 1992, top height growth losses appeared and were proportional to apparent foliage losses. In 1996, top height growth was reduced by up to 25% relative to plantations with little or no SNC. Basal area growth reductions began to appear around 1990, and in 1996 basal area growth of the most heavily damaged plantations was 35% less than the growth that would be expected in absence of SNC damage. The inferred volume growth loss for 1996 averaged 23% for the 75,700 ha target population, but this loss averaged as high as 52% for the most severely impacted plantations. West. J. Appl. For. 17(2):86ߝ95.
ABSRACT. An instrument is described which rapidly determines both numbers and volume distributions of dielectric particles suspended in a conducting solution. The volume distributions are shown to be independent of the suspending solution conductivity over a large range, and they can be repeated at about 10 sec intervals with sample volumes of 0.05 m]. Data are presented showing the linearity of the system, the effects of counting rate on the volume distributions, and a comparison of the absolute modal volumes of two different mammalian cells grown in tissue culture and two different pollens, as determined by this instrument, with the modal volumes measured by optical methods. I t is concluded that the instrument can be used to determine the absolute volumes of tissue culture cells to within 20% and may provide the only way to determine the actual volumes of such irregular objects as pollen.
A spiral path mechanical scintiscanning system has been used in conjunction with variously arranged sources of monoenergetic gamma -ray photons to generate three different modes of tomographic imagining. One mode images the absorption of the photons in a thick slice in the object; the second images the density of the tissue in the slice via Compton scattered photons. The third images the planar distribution of an internally deposited emitter. While all three modes utilize the laminographic properties of focusing collimators, the first two also use specially collimated sources. System parameters such as MTF and S/N were given along with results of phantom and clinical studies for several photon energies. Comparisons were made with conventional X-ray tomography and/or imaging wherever appropriate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.