Graduate Thesis Or Dissertation
 

Effect of elevation, aspect, canopy, and season on soil temperature measurements for soil classification

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  • The effects of aspect, canopy, elevation, and season both singly and in combination on soil temperatures at 50 cm depths were evaluated. The objectives of the study were (i) to develop a standard procedure for obtaining soil temperature data adequate to classify soils at the family and great group levels, (ii) to evaluate the effects which elevation, canopy, aspect, and season singly and in combination have on soil temperature, (iii) to evaluate the durability and consistency of selected instruments, and (iv) to test whether the months used by the Soil Survey Staff (1975) for calculating mean summer and winter temperatures are appropriate for this locality. Monitoring sites were established at seven elevations spanning soil temperature regimes from mesic to cryic. At each elevation, sites were located on both northerly and southerly aspects, and within each aspect under full forest canopy and in an opening or clearcut. Temperatures were read monthly using four different instruments. Marys Peak, in the Oregon Coast Range, was chosen as the general location for the study. A number of methods were used in analysis of the data. Graphs showing various temperature interactions among the main site factors were developed. The Sips statistical package (Rowe and Brenne, 1981) was used to develop analysis of variance tables for seasons as defined by Soil Taxonomy as well as an alternative set of seasons, which were based on the observation in the data that maximum summer and minimum winter temperatures lag behind the periods as defined in Soil Taxonomy. Analysis of variance tables were constructed for these seasons both with and without data from 610 meters, to evaluate data from an unusually warm site at this level. This statistical package was also used to develop a regression model utilizing Soil Taxonomy seasons without data from 610 meters. Using Soil Survey Staff's (1975) seasons but excluding data from 610 meters, elevation by canopy, aspect by canopy, elevation by season, canopy by season, and aspect by season were statistically significant at the .05 level. This was mostly attributed to the insulation effect provided by the closed canopy resulting in reduced direct solar radiation reaching the soil surface. There was evidence of possible iso-temperature regimes occurring under closed canopy conditions at all elevations on both aspects if seasons were defined according to Soil Survey Staff (1975) guidelines. However, if seasons are defined to truly represent the three consecutive coldest and warmest months, then only two sites remained iso. A regression model with an R² value of .98 was developed for the Marys Peak area. Variables included aspect, canopy, elevation, season, and two-way interactions; elevation by canopy, elevation by season, aspect by canopy, and canopy by season. There were no significant differences between selected instruments concerning consistency. However, the Soiltest instrument was found to be the most durable and least expensive.
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