Influence of western juniper development on distribution of soil and organic layer nutrients

The purpose of this study was to determine effects of invading western juni per (Juniperus occidentalis Hook.) into big sagebrush (Artemisia tridentata Nutt.)/bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. and Smith [now Pseudoroegneria spicata]) ecosystems of central Oregon on spatial dist ribution of nutrients in organic and mineral soil layers. The organic layer and mineral soil from four layers (0-5, 5-15, 15-30, and 30+ cm), were col lected beneath juniper trees of five size classes, and one area devoid of j uniper on five replicated sites. Samples were taken at five distances (0 to 4 canopy radii) from tree boles into intercanopy areas. The organic layer and mineral soil were analyzed for organic carbon (C-org), total nitrogen ( N), total phosphorus (P) and total sulfur (S); mineral soil was analyzed fo r exchangeable calcium (Ca-ex), magnesium (Mg-ex) and potassium (K-ex). Mas s of the organic layer and amounts of organic layer nutrients increased wit h juniper size, and were higher under canopies than in intercanopy and no j uniper areas. Concentrations of organic layer N, P, and S declined with dis tance from tree boles. Tree size, distance and soil layer interacted to aff ect concentrations of soil C-org, K-ex, Ca-ex and Mg-ex. Concentrations of soil N and S increased with tree size. Amounts of soil nutrients, except C- org, were not significantly influenced by tree size, but amounts of all soi l nutrients, except S and Ca-ex, were greater under juniper trees than inte rcanopy areas. Only Ca-ex and Mg-ex appeared to have been lost from interca nopy soils compared to no juniper soils.