University of Minnesota, Duluth
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Strength characteristics of fruit tree bark
No full textMechanical harvesting of fruit trees by shaking their primary limbs or trunks has sometimes been responsible for injury to the trees at the point where shaking equipment is attached. Such injuries often result in infection by the fungus Ceratocystis fimbriata. In the present study, research was conducted to determine the strength of tree bark so as to evaluate its ability to resist injury caused by forces applied radially, tangentially, or longitudinally to the limb. The maximum radial stress which could be exerted on the bark of trees tested without damage which can lead to Ceratocystis canker was found to be in the range of 500 to 1000 psi, whereas the maximum tangential and longitudinal stresses were only about one-third or one-fourth as strong. Low strengths were generally associated with high moisture conditions, young tree age, and growing cambium
An ecological comparison of spiders from urban and natural habitats in California
No full textA comparative study of spider communities in urban, native, and semi-native habitats was conducted in 1980 in northern California. Selected biotic and abiotic factors thought to be responsible for observed differences in spider-community composition among habitats were investigated
Transmission of California aster and celery-yellows virus by three species of leafhoppers
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