Ecological strategies for managing tamarisk on the C.M. Russell National Wildlife Refuge, Montana, USA

Abstract

Tamarisk ( Tamarix ramosissima) is an introduced shrub or small tree associated with the loss of biological diversity in riparian habitat throughout much of western North America. Control measures are often expensive and ineffective, so land managers need site-specific information to guide cost-effective integrated management strategies. We sampled 12 randomly selected tamarisk-infested inlets on Fort Peck Reservoir on the C.M. Russell National Wildlife Refuge stratified by stream basin size. At each site we sampled 2–5 stands of riparian vegetation, recording plot elevation, canopy cover of vascular plants, density of woody species and age estimates for representative woody plants. Tamarisk plants 1–3 years old were abundant in the drawdown zone along the shore of Fort Peck Reservoir. The lack of plants older than three years indicates that tamarisk in the drawdown zone were destroyed during a recent two summers of inundation and suggests that three months of inundation will kill tamarisk plants. The oldest (17–22 years) and largest tamarisk plants in the study area were found in the full-pool zone and were recruited in periods of significant drawdown following high-water years. Tamarisk was uncommon in cottonwood and silver sagebrush stands on stream terraces above full pool. Only the largest streams in our study area appeared capable of supporting tamarisk and significant native riparian vegetation. Tamarisk plants at or above full pool level should be removed in these drainages to prevent upstream invasion and loss of native species. The level of the reservoir should be raised to the level of full pool for three consecutive months during the growing season every 3–5 years to prevent development of extensive stands of tamarisk in the drawdown zone capable of producing large quantities of seed.