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Title: Studies of plant establishment limitations in wetlands of the Willamette Valley, Oregon
Authors: Oregon State University.
Wetlands Research Program (U.S.)
Wilson, Mark V.
Ingersoll, Cheryl A.
Davis, Mary M.
Wilson, Mark G.
Ingham, Elaine R.
Clark, Deborah L.
Keywords: Exotic plant species
Native collected stock
Nursery stock
Seed dormancy
Site preparation
Wetland restoration
Willamette Valley
Wetland conservation
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: The Willamette Valley was historically dominated by three types of wetlands: wet prairies, shrub/scrub, and forested. As a consequence of drainage for agriculture and urban development, most of these diverse wetlands have been lost. Restoration of native wetlands is limited by a lack of knowledge about native plant species growth and establishment requirements. This report presents results from four investigations of establishing wetland vegetation native to the Willamette Valley. In the first study, Pest Plant and Seed Bank Reduction (Chapter 2), three site preparation techniques were applied to a disturbed wet prairie that contained exotic species. The objectives of the study were to determine (A.) whether the treatments reduced pest plant abundances for more than 1 year, (B.) if treatments also reduced native plant species, and (C.) whether treatment effects were consistent among years. Tilling with fallowing and solarization (heating under plastic) were generally found to be more effective than burning at reducing existing plants. Native plants were affected by all treatments. Although each treatment was effective at reducing at least one exotic plant species, none of the treatments were generally effective at controlling pest plants. This may have been due to cool, dry weather conditions during the treatments that were not conducive to seed germination. The authors conclude that site treatments should be applied for more than 1 year, and native plant materials should be planted as soon as possible to outcompete the recovering exotic species. The second study, Seed Dormancy, Germination, and Establishment (Chapter 3), investigated native collected seed germination requirements, seed propagation under field conditions, and the performance of seeds in mixtures. Seed viabilities were found to vary greatly for the native species that were tested. This was due in part to a single collection date for each species that could not coincide with simultaneous ripening of all the seeds. Stratification with alternating temperatures sufficiently improved germination rates of the dormant species so that no further treatments were necessary. Poor seed germination rates in the field led the authors to recommend high seeding rates when native collected seeds are used. This helps offset the low germination rates of many species, but also increases the relative abundance of sowrt seeds to the seed bank. Differences in germination rates and times of different species in seed mixtures can be utilized in designing seed mixtures. The authors recommend a strategy to first establish rapidly germinating, short-lived species to compete with exotics, followed by more slowly germinating perennial species that will permanently occupy the site. Characterization of Mycorrhizae (Chapter 4) is an investigation of the potential for mycorrhizae to limit plant growth in restored wet prairies. The objectives of the study were to determine (A.) the mycorrhizal requirements of selected herbaceous species, (B.) if adequate mycorrhizal fungi were available for plant colonization at sites differing in levels of disturbance, and (C.) if there is a correlation between spore density in the soil and actual colonization of the plants. Mycorrhizae colonized surviving plants at all sites. Lack of germination or survival of some plants at some sites suggested a lack of required fungal species. A positive correlation between spore density and colonization further suggests that limited mycorrhizae may affect plant growth in wetland restoration areas with low fungal spore densities. Field Performance of Planted Nursery Stock and Stem Cuttings of Selected Woody Species (Chapter 5) further investigates the use of native plant materials for wetland restoration in the Willamette Valley. The objectives of this study were to (A.) compare survival and growth of stem cuttings and nursery stock of four selected woody species, (B.) determine growth of irrigated stem cuttings, and (C.) determine effects of fertilization on native plant nursery stock and stem cuttings. Results of the study were very species specific. Only stem cuttings from willow and poplar survived; Crataegus and Rosa cuttings died. Nursery stock had best survival rates for all species; however; height growth of stem cuttings was best. Fertilization had no significant effect on survival or growth of nursery stock or stem cuttings. Fertilization, however, stimulated growth of competing herbaceous species and may have been detrimental to growth of target species. NOTE: This file is large. Allow your browser several minutes to download the file.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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