Tuesday, June 19, 2007 - 2:35 PM
Ponderosa Pines (Boise Centre on the Grove)

Fertile Island Degradation Following Western Juniper Cutting

Chris Miwa, Oregon State University, Corvallis, OR and Ron Reuter, Oregon State University Cascade Campus, Bend, OR.

Western juniper (Juniperus occidentalis) cover has more than doubled within the last century and currently occupies over 9 million acres in the Intermountain West. Encroachment has altered the spatial distribution of soil nutrients and plants in these systems, forming nutrient enriched ‘fertile islands,' under tree canopies. The purpose of this study was to determine the persistence of fertile island characteristics after restoration treatment (tree removal). The study site was a BLM grazing allotment in Eastern Oregon where trees had been cut 1 ,8 and 15 years ago. In each age class juniper stumps were randomly selected for sampling. At each stump three radial transects, set at 120º 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 stump then combined to a single composite sample per distance class. Samples were analyzed for total C and N, soluble P, K, Ca, Fe, Si, Al and Na, inorganic NH4 and NO3 and moisture. Preliminary data show that fertile islands persisted to 15 years post canopy removal for total C and N while accumulations of Ca, P, K and NO3 degraded within 8 years. Soil moisture content did not vary between canopy and interspace zones. In semi-arid and arid systems where N availability is considered to be the most limiting plant nutrient, western juniper fertile islands can be a preferred safe spot for seedling establishment. The persistence of these fertile islands should be taken into account for restoration purposes, such as seeding of forbs and grasses. Further work is needed to determine if these resource islands encourage or inhibit regrowth of native forbs and grasses.