The purpose of this study was to compare the effects of the invasive plant Russian olive (Elaeagnus angustifolia) and its native counterpart, plains cottonwood (Populus deltoides), on the primary food chain of Montana prairie streams. Russian olive is displacing plains cottonwood in riparian areas throughout eastern Montana and some expensive eradication efforts have been undergone to remove this invader. Research conducted to determine food web effects included: fat, protein, and energy content analysis of leaves both species; experiments on benthic macro-invertebrate utilization of the two species via leaf dry weight analysis; experiments on Fathead minnow (Pimephales promelas), a prairie stream fish, weight gain when fed diets of the two species; and scientific literature review. Russian olive leaves had higher concentrations of protein and energy than plains cottonwood and similar concentration of fat. However, the additional protein and energy from Russian olive leaf litter was found to provide no benefits to these ecosystems. One possible negative impact of Russian olive is the surplus of nitrogen released in stream corridors. Visual observations concluded that macro-invertebrates prefer larger leaves that form packs, such as cottonwood, for habitation but this showed no effect on disappearance rates; paired t-test data analysis indicated changes in leaf dry weight of both species were significant (p<.05). Data analysis on weight gains of Fathead minnows continues and preliminary results indicate that both species provide diets adequate enough to maintain fish weight and survival. This study shows there are minimal effects of Russian olive on the primary food chain of Montana prairie streams, which may have implications on future management and eradication efforts of this species.
RUSSIAN OLIVE (ELAEAGNUS ANGUSTIFOLIA) LEAF LITTER AS A FOOD SOURCE IN MONTANA'S PRAIRIE STREAM ECOSYSTEMS
Society for Range Management
SRM Sacramento, CA