Successional pressures resulting from fire suppression and reduced grazing have resulted in vegetation-type conversion in the open spaces surrounding the urbanized areas of the San Francisco bay ...area. Coverage of various vegetation types were sampled on seven sites using a chronosequence of remote images in order to measure change over time. Results suggest a significant conversion of grassland to shrubland dominated by
Baccharis pilularison five of the seven sites sampled. An increase in
Pseudotsuga menziesii coverage was also measured on the sites where it was present. Increases fuel and fire hazard were determined through field sampling and use of the FARSITE fire area simulator. A significant increase in biomass resulting from succession of grass-dominated to shrub-dominated communities was evident. In addition, results from the FARSITE simulations indicated significantly higher fire-line intensity, and flame length associated with shrublands over all other vegetation types sampled. These results indicate that the replacement of grass dominated with shrub-dominated landscapes has increased the probability of high intensity fires.
Factors related to the composition of riparian forest stands on three streams in the northern Sierra Nevada mixed conifer forest type were related to proximity to the water course and years since ...fire. Using a linear regression analysis 46 variables were correlated to the natural log of distance from the thalweg “ln(distance)” including a highly significant positive correlation to dominance and percent canopy cover of conifers, and a significant negative correlation to the same variables when applied to hardwoods. Twenty six variables were correlated to years since fire “years” including similar correlations to the dominance and cover of hardwood and conifer species. However, the significance of the correlation and the degree of sample variability described by fire age was relatively low in comparison to that found for distance from the thalweg. In addition the relative frequency of fire scars increased in a linear fashion with distance from the watercourse. The results of this study indicate that the importance of fire as a determining influence on forest composition declines in proximity to the riparian zone.
Data collected across timber harvest boundaries on nine sites within the Redwood National and State Park management area in California, USA, were used to estimate the effective size of old-growth ...coast redwood preserves. Fourteen variables related to stand structure and composition, wildlife habitat, and physical environment were significantly correlated to distance from the timber harvest boundary using multiple regression analysis. A maximum depth of edge influence of 200 m was determined for variables exhibiting a significant correlation to the distance from the harvest edge. A spatial analysis using ArcView indicated that 53% of the old growth preserved within the study area was influenced by edge conditions, leaving 47% as effective old-growth.PUBLICATION ABSTRACT
Regeneration of hardwood species on three streams in the northern Sierra Nevada was correlated with several environmental factors. The occurrence of seedlings of Salix lutea (yellow willow), Salix ...laevigata (red willow), and Alnus tenuifolia (mountain alder) were negatively correlated with canopy cover and litter depth, and positively correlated with solar radiation. All three species occurred more frequently on sandy soils where the stream channel was wide and the slope was relatively shallow. The occurrence of Populus fremontii (black cottonwood) seedlings was negatively correlated with canopy cover, and sandy soils, and positively correlated with distance from the watercourse and solar radiation. Acer macrophyllum (big leaf maple) and Cornus sericea (American dogwood) seedlings occurred under relatively dense canopy cover, in low light environments, but were limited to sandy soils and wide stream channels. Results indicate that the hardwood species that exist in riparian corridors within the Sierra Nevada mixed conifer forest type are variably reliant on conditions common to flood prone areas such as sandy mineral soils and a high light environment for regeneration.
Feeding damage to trees by black bears (Ursus americanus Pallas) was recorded in proximity to timber harvest edges in harvested and old-growth stands of ceast redwood (Sequoia sempervirens D.Don ...Endl.) in northern California, USA. Bears exhibited distinct preference in their feeding patterns related to stand structure and composition and to distance from the timber-harvest edge. Most damage was recorded within regenerating stands. Regression analysis indicated that density of damaged trees was negatively correlated with distance from timber harvest edges within old-growth stands. A significant negative correlation was also found between the density of trees damaged by bears and habitat diversity (H') as measured by the Shannon diversity index. In addition, bears exhibited preference for pole-size trees (dbh = 10-50 cm) over all other size classes, and coast redwood over other species. In general, damage by bears appeared to act as a natural thinning agent in even-aged stands. No damage was recorded in old-growth stands except in close proximity to the timber-harvest edge where subcanopy recruitment was high. Se registraron los daños a los árboles por osos negros (Ursus americanus Pallas) en proximidad a los límites de cosecha de madera y en bosques maduros de Sequoia sempervirens D.Don Endl. en el norte de California, USA. Los osos demostraron preferencias distintas en sus patrones de alimentación relacionado a la estructura y composición de los lotes y a la distancia de los límites de cosecha. La mayoría de los daños fue registrada dentro de los lotes de regeneración. El análisis de regresión indicó que la densidad de árboles dañados estuvo negativamente relacionada a la distancia de los límites de cosecha dentro de los lotes maduros. Una correlación negativa significativa también fue encontrada entre la densidad de árboles dañados por los osos y la diversidad del habitat (H') medida con el índice de diversidad de Shannon. Además, los osos mostraron preferencia por el grupo de árboles con dap entre 10 y 50 cm sobre cualquier otra clase de tamaño, y sobre S. sempervirens entre las demás especies. En general, los daños por osos parecen actuar como un agente natural de estrechamiento en lotes de igual edad. No se registraron daños en lotes maduros, excepto en proximidad a los límites de cosecha donde abundaba el subdocel.
Using a biaxial stress tester for stretched canvas, a canvas sample carrying a heavy paint film has been tested for changes in tension caused by fluctuations in temperature and relative humidity ...(RH). The paint and priming were then removed and the bare, sized canvas was exposed to the same fluctuations in temperature and RH as before. These tests provided first-hand measurements of the tension within the canvas and paint layer and of the shear forces between these layers. A comparison of results demonstrates that cracking and deterioration is caused primarily by the paint film, which deforms the canvas and generates stress, rather than by movements of the substrate, as previously believed. This experiment provided additional proof for earlier fundamental findings (that small temperature changes have a considerable effect on the stress in the tested samples and, therefore, on canvas paintings and other surfaces). This study also provided more evidence that high RH (above 90%) can be extremely dangerous for the preservation of canvas paintings, but does not imply that smaller changes in RH may not be damaging to the structure of a painting.
Thousands of stress measurements on canvas paintings have been collected over the past three years using an automated logging program. They confirmed the observation that paint needs a stiff ...substrate in order to be preserved undamaged. Considerable fluctuations in the tension of stretched fabrics in response to changes in temperature and RH were recorded. Such fluctuations lead to repeated overstretching of the canvas during stress peaks. With each overstretching, the canvas loses some of its initial tension. With time, the canvas becomes so slack as to be incapable of providing a firm support for the paint film. No longer restrained in its expansions and contractions, the paint film distorts, and pulls the canvas to which it is attached. Stress diagrams of canvas samples following stretching, sizing, priming and aging show distinctly different patterns which support the above findings. Accordingly, in order to maintain the canvas as an effective support for the paint film, preventive conservation must preserve its stiffness. This can be achieved by the following means used either separately or in combination: (1) reducing stress fluctuations by strictly controlled air-conditioning; (2) providing the paint film with a stiffer support, as by lining; (3) eliminating stress peaks and maintaining sufficient tension with springs or other devices.
Thesis (Ph. D.)--University of Wisconsin--Madison, 1953.
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