Autumn-Olive as a Nurse Plant for Black Walnut

Autumn-olive, Elaeagnus umbellata Thunb., is a promising species for planting in mixture with black walnut, Juglans nigra L. In five plantations in Missouri, Illinois, and Indiana, walnut grown in mixture with autumn-olive averaged 82% taller after 9 yr than walnut grown in pure stands. Two southern Illinois plantings were selected for more detailed study, one in a well-drained bottomland and the other on a broad upland ridge. In both areas, interplanting with autumn-olive stimulated a 134% increase in walnut height compared with walnut grown alone. Increased height of the walnut trees in mixed plantations was first apparent about 4 yr after planting, and the best group of four plots averaged more than 6.8 m tall at age 9. During the growing season, the mixed plantings are characterized by greater soil nitrogen, lower soil and air temperature, and lower soil moisture than found in the pure walnut plantings.