SOIL MORPHOLOGY OF CANOPY AND INTERCANOPY SITES IN A PINYON-JUNIPER WOODLAND

Pinon-juniper woodlands in the semiarid western USA have expanded as m uch as fivefold during the last 150 yr, often accompanied by Losses of understory vegetation and increasing soil erosion. We conducted this study to determine the differences in soil morphology between canopy a nd intercanopy locations within a pinon (Pinus edulis Engelm.)-juniper [Juniperus monosperma (Engelm.) Sarg.] woodland with uniform parent m aterial, topography, and climate. The woodland studied, located near L os Alamos, NM, has a mean tree age of 135 yr. We examined soil morphol ogy by augering 135 profiles in a square grid pattern and comparing so ils under pinon and juniper canopies with intercanopy soils. Only two of the 17 morphological properties compared showed significant differe nces. The B horizons make up a slightly greater proportion of total pr ofile thickness in intercanopy soils, and there are higher percentages of coarse fragments in the lower portions of canopy soil profiles. Ca nopy soils have lower mean PEI and higher mean organic C than intercan opy soils. Regression analysis showed that most soil properties did no t closely correspond with tree size, but total soil thickness and B ho rizon thickness are significantly greater under the largest pinon tree s, and soil reaction is lower under the largest juniper trees. Our fin dings suggest that during the period in which pinon-juniper woodlands have been expanding, the trees have had only minor effects on soil mor phology.