Terry Ireland, Fish and Wildlife Biologist, U.S. Fish and Wildlife Service, 764 Horizon Drive, South Annex A, Grand Junction, CO 81506-3946
There are several federally threatened and endangered species that may be impacted by tamarisk and Russian olive. Piping plovers and least terns inhabit rivers east of the Rocky Mountains and require open sandbars for nesting, feeding and roosting. Whooping cranes use open sandbar habitat and adjacent fields and prairies for feeding and roosting during migration between Canada and southern States. Trees including Russian olives and some tamarisk have invaded what was historically open prairies and sandbars limiting nesting, feeding, and roosting sites for these species. Reduction of water flow by diversions and regulation of flows by dams may have allowed Russian olive and tamarisk to invade (at least to a greater extent) the sandbars and streambanks historically kept open by peak flows.
Bald eagles may be impacted by reduction or elimination of cottonwood nest and roost trees. Most bald eagles in the southwest, except some rock nesting eagles in Arizona, have been found nesting in cottonwood trees or pine trees.
Threatened, endangered, or rare fishes within the range of tamarisk and Russian olive could be impacted by these plants. The plants consume water where trees have not occurred previously or to a greater extent than native trees lowering water tables. The lowered water tables may make spring fed desert lakes unsuitable for rare fishes inhabiting them. Tamarisk and Russian olive also act to stabilize streambanks possibly reducing channel formation and flooding necessary for the Colorado squawfish and razorback sucker. Reductioin of flows from water diversions and regulation by dams has likely helped increase colonization of tamarisk and Russian olive. Russian olive seeds are eaten frequently by nonnative channel catfish possibly helping with their survival and, therefore, increased mortality of endangered fishes.
Southwestern willow flycatchers rely solely on riparian areas. Tamarisk may not provide adequate thermal cover in the southwest and may have reduced insect abundance that could lower reproductive success of flycatchers. Tamarisk and Russian olive, however, may provide nesting habitat where none existed historically or could exist currently. Prior to any tamarisk or Russian olive control within the range of the flycatcher the Fish and Wildlife Service should be consulted to discuss plans for control. If surveys have not been conducted in the project area surveys should be performed and the Service shold be informed of the results. If any tamarisk or Russian olive removal is allowed in occupied flycatcher habitat it should be done in small areas and replacement habitat should be developed prior to further control so that willow flycatcher nesting habitat is not eliminated for a period of years.
To what extent tamarisk and Russian olive impact threatened and endangered species is unknown. More research of specific impacts on threatened and endangered species is needed.