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DIVISION S-7-FOREST & RANGE SOILS

Soil Microclimate and Chemistry of Spruce–Fir Tree Islands in Northern Utah

Dep. of Forest Resources, Utah State Univ., Logan, UT 84322-5215 USA

helgavm{at}cc.usu.edu

The objective was to investigate differences in soil properties in high-elevation tree islands composed of subalpine fir [Abies lasiocarpa (Hook.) Nutt.] and Engelmann spruce [Picea engelmannii Parry ex Engelm.] relative to semiarid meadows in Northern Utah. We compared snow depths, surface soil temperature and moisture, and soil chemical properties (0–30 cm) between tree islands and the surrounding meadow. Snow accumulated evenly around the tree islands. Snow depth differences developed during snowmelt when shaded areas to the north of the islands retained snow longer. Less snow accumulated inside and at the edge of the tree islands. In summer, canopy shading inside the islands slowed soil moisture loss and decreased the magnitude and fluctuation of soil temperatures relative to the exposed meadow. Tree islands affected O horizon mass and chemistry: 6 to 10 kg m^-2 of O material, with higher macronutrient concentrations and lower C/N ratio, had accumulated under tree canopies; 3 kg m^-2 in the island interior; and <1 kg m^-2 in the meadow. Surface soils inside the tree islands had significantly higher C and N soil concentrations and higher C/N ratio. The pH of meadow soils was constant with depth (6.22–5.95). Below the trees, the pH in the upper soil was 0.1 to 0.3 units higher than in the meadow and decreased 0.8 to 0.9 pH units with depth. The presence of tree islands significantly modified the soil microclimate and nutrient distribution relative to the surrounding meadows.

Abbreviations: ANOVA, analysis of variance