Graduate Thesis Or Dissertation

 

Effects of soil surface shading, mulching and vegetation control on Douglas-fir seedling growth and microsite water partitioning Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/f1881r14h

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  • A two year study with 500 seedlings was conducted in the harsh, drought prone southwest Oregon environment to assess the effects of 12 soil surface shading, mulching and vegetation control techniques on soil temperature and moisture environments and seedling growth. Treatments modified, to various degrees, soil surface temperatures, reduced soil surface evaporation and reduced vegetative competition for water in the seedling root zone. These modified conditions affected seedlings by reducing soil water loss to increase water available for seedling use and adjusting the timing of seedling growth. Seedlings in treatments where competing vegetation was removed had significantly larger final shoot volumes and stem diameters. Soil water loss was significantly less in treatments where soil surface evaporation was controlled by mulching or controlling competing vegetation. Shaded and control treatments used the most water over the season. Soil water loss in treatments with vegetation controlled by herbicide was significantly less than those with vegetation control by scalping which disturbs the soil surface by removing the loose soil and duff layer. Therefore, seedlings grew the most with treatments that elicited the most efficient use of available microsite water either by reducing soil surface evaporation or vegetative competition. Transpiration data supported these conclusions by showing more than twice the water was transpired by competing vegetative species per unit leaf area than by seedlings. In addition, estimates of percent cover by seedlings and all vegetative species occupying the site showed competing vegetation to cover 78.6% of the site compared to 2.4% cover by the seedlings. This illustrates the degree of competition the vegetation gives to the seedling over the whole site even in an environment where water is a limiting resource.
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