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 juniper (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 distribution 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 collected beneath juniper trees of five size classes, and one area devoid of juniper 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 sub(org)), total nitrogen (N), total phosphorus (P) and total sulfur (S); mineral soil was analyzed for exchangeable calcium (Ca sub(ex)), magnesium (Mg sub(ex)) and potassium (K sub(ex)). Mass of the organic layer and amounts of organic layer nutrients increased with juniper size, and were higher under canopies than in intercanopy and no juniper areas. Concentrations of organic layer N, P, and S declined with distance from tree boles. Tree size, distance and soil layer interacted to affect concentrations of soil C sub(org), K sub(ex), Ca sub(ex) and Mg sub(ex). Concentrations of soil N and S increased with tree size. Amounts of soil nutrients, except C sub(org), were not significantly influenced by tree size, but amounts of all soil nutrients, except S and Ca sub(ex), were greater under juniper trees than intercanopy areas. Only Ca sub(ex) and Mg sub(ex) appeared to have been lost from intercanopy soils compared to no juniper soils.