Geology topics
W. L. Halvorson
Publications and source records attributed to W. L. Halvorson.
Commentary on the ESA's Public Policy responsibility
No abstract available.
Ecological studies of vesicular arbuscular mycorrhizae in a barrier sand dune
An ecological survey of the vegetation of a barrier dune on the south coast of Rhode Island showed Ammophila breviligulata , Solidago sempervirens , Lathyrus japonicus , and Myrica pensylvanica to be the dominant plant species. All plants were mycorrhizal. Six species of vesicular–arbuscular (VA) fungi occurred in association with these plants, with Gigaspora gigantea and Acaulospora scrobiculata the most abundant. Also present were Gigaspora calospora , Glomus etunicatus , Glomus fasciculatus , and an undescribed species of Gigaspora . Spore densities and frequencies were measured in a transect across the dune and were compared with plant cover and physical factors (pH, soil moisture, organic matter, soil nutrients, chlorides, and sand grain size). Areas on the dune with greatest vegetation cover by Ammophila were associated with greatest spore densities and fungal diversity in the rhizosphere. For most plant species, maximum spore density occurred in the front half of the plant's distribution range, nearest the dune crest. There was little correlation between spore populations in the soil and physical characteristics, with the exception of sand grain size. The importance of considering VA mycorrhizae in sand dune stabilization programs is discussed.
Growth responses of Spartina patens and Spartina alterniflora by means of a two dimensional factorial design
Growth of Spartina patens and Spartina alterniflora was compared under identical greenhouse conditions. Mature plants were grown in quartz sand and watered with the following solutions: (1) full Hoagland's solution; (2) Hoagland's minus iron; (3) Hoagland's minus nitrogen; (4) Hoagland's with NaCl added to 28 o/oo ; (5) sea water of 28 o/oo . S. patens showed improved growth in Hoagland's solution and Hoagland's minus iron, but showed significantly less growth in solutions 3, 4 and 5. S. alterniflora showed no significant difference in growth in the treatment cultures. General trends which were shown are: (1) S. patens grew better under low iron levels while S. alterniflora 's growth was only slightly enhanced under low iron conditions, and (2) growth of both species was reduced more due to saline conditions than to a lack of nitrogen.
Topographic influence on the pattern of plant communities, phenology, and water relations of a desert ecosystem
No abstract available at this time
Environmental influence on the pattern of plant communities along the North Rim of the Grand Canyon
No abstract available at this time
Environmental influence on the pattern of plant communities along the north rim of the Grand Canyon
No abstract available at this time
An introductory investigation of the toxicity of Larrea tridentata
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