Shaney Rockerfeller

ABSTRACT

Forest soils in northern Idaho often develop perched water tables during the winter and spring. Many of these soils have been cleared for agricultural production over the past 100 years. Research has determined that forest canopy removal increases catchment water yields, thereby raising concerns about the response of the perched water tables to forest clearing. This study was conducted to compare the duration and quantity of episaturation for two years on adjacent forested and cleared soils located on fragipan soil-landscape units. These soils support Abies grandis and Thuja plicata forest types in the eastern Palouse and Weippe Prairie of northern Idaho. Each soil was sampled to characterize the physical and hydraulic properties, and wells were installed on a forested and adjacent cleared treatment at each site to monitor seasonal perched water tables. Significant physical and hydraulic differences were not detected between the forested and cleared treatments. Development of seasonal perched water tables was related to antecedent soil moisture prior to fall-winter precipitation. Seasonal perched water tables developed in the cleared treatments during the end of November at the drier sites and during the middle of November at the wetter sites. Perched water tables developed in the forested treatments 1 to 2 weeks later than in the cleared treatments. After a 4- to 6-week lag, perched water tables in the forested and cleared treatments were approximately equal and responded similarly to precipitation. Dry-down of perched water tables in the spring was simultaneous. Seasonal perched water tables were present in the forested treatments for 21 to 30 weeks and in the cleared treatments for 22 to 36 weeks. Forest canopy removal results in the cleared treatments being episaturated for 10 % longer than the forested treatments. The cleared treatment had significantly greater quantities of water for 16 % of the period when both treatments contained perched water. Seasonal perched water table data indicate that forest clearing increases episaturation in cleared soils. Due to the rolling hill topography of the regions, increased episaturation can contribute to greater subsurface flow and erosion.