Effects of Autumn Olive (Elaeagnus umbellata Thunb.) Density on the Growth of Mature White Oak Trees (Quercus alab L.)

Abstract

Invasive alien plants threaten forest ecosystems by employing numerous survival strategies including nitrogen fixation. Autumn olive (Elaeagnus umbellata L.), in associate with the symbiont Frankia, may alter forest soil chemistry, species composition and diversity and increase vegetative growth. This study examined the effects of autumn olive density on mature white oak (Quercus alba L.) growth in a second growth Michigan Forest. Three forest plots were selected showing increasing gradation of autumn olive density. White oak height, stem diameter, annual radial growth, leaf nitrogen content and leaf area were measured. Soil profiles were analyzed focusing on nitrogen concentrations. Tree seedlings and saplings were also sampled in each plot. Oaks grew significantly more per year and had significantly larger leaves in the high density and intermediate plots compared to the control plot. Tree juvenile abundance was highest in the control, whereas juvenile diversity was lowest in the high density plot. Chronic autumn olive nitrogen deposition may be increasing white oak vegetative growth and inhibiting juvenile tree growth.