An evaluation of the invasion potential of Kochia prostrata (forage kochia) in southwestern Idaho, USA

Graduation date: 2011Purposeful introductions of exotic species for rehabilitation efforts following wildfire are common on rangelands in the western U.S., though potential ecological impacts of introduced species in novel environments are often poorly understood. One such introduced species, Kochia prostrata (L.) Schrad (forage kochia) has been seeded on over 200,000 ha throughout the Intermountain West to provide fuel breaks and forage, and to compete with invasive plants. Despite its potential benefits, it has been reported to spread from some seeded areas, and no studies have addressed its potential interactions with native species. A systematic investigation is needed to increase understanding of the extent to which K. prostrata spreads from seeded areas, the environmental conditions under which it spreads, and its potential interactions with the associated plant communities. I sampled 28 K. prostrata post-fire rehabilitation and greenstrip seedings in southwestern Idaho, which ranged from 3 to 24 yr since seeding. I analyzed cover of K. prostrata and the associated plant community in paired seeded and unseeded areas, and quantified extent of spread from seeded areas. Sites seeded with K. prostrata had lower species richness and Shannon-Wiener diversity than adjacent unseeded areas. Abundance of K. prostrata was negatively associated with that of most plant functional groups, including all native species, but was positively associated with abundance of exotic annual forbs. Kochia prostrata spread to unseeded areas on 89 % of sampled sites; distances of the farthest individual from the seeding boundary were greater than those previously reported, ranging from 0 to 710 m, with a mean distance of 208 m. Further, while spread increased with time since seeding, it was apparently independent of the composition of communities into which spread occurred. This study improves understanding of the ecological implications of seeding K. prostrata, demonstrating potential to spread from\ud seeded areas into native plant communities, and that K. prostrata does not seem to enhance native species diversity in seeded areas over time. These findings will enable land managers to make scientifically-based decisions regarding use of this species