Persistence of Western Juniper (Juniperus occidentalis) Resource Islands Following Canopy Removal

Western juniper (Juniperus occidentalis Hook.) encroachment has altered the spatial distribution of soil nutrients and plants in semi-arid systems of the northern Great Basin, forming nutrient enriched ‘resource islands’ under tree canopies. Our goal was to determine the persistence of resource island characteristics after restoration treatment (tree cutting). The study site was a privately owned grazing allotment in eastern Oregon where trees had been cut eight and fifteen years ago. In each age class and in uncut western juniper woodlands, juniper stumps or trees were randomly selected for sampling. At each bole three radial transects, set at 120° from each other, were marked and soil cores were collected to 5-cm depth at distances of 50, 100, 150 and 300-cm from the bole then combined to a single composite sample per distance class. Samples were analyzed for total C and N, soluble P, K, Ca, Fe, Al, Mg and Na and pH. Despite increases in shrub, forb and grass crops in the fifteen-year old cut treatment, western juniper resource island effects were still evident for most soil variables measured; tree island soils were significantly higher in Ctot, Ntot, P, K and Ca compared to inter-island soils. Resource island persistence was attributed to litter mats beneath relic canopies. Management efforts may be more successful at preventing establishment of undesired annuals by focusing on young juniper stands where resource islands are less developed.