Effects of tank tracking on range grasses

The Department of Defense (DoD) must constantly balance its military mission and its commitment to stewardship on large tracks of federal land. These military training lands are some of the most intensely used land in the United States, and training requires that vegetation, primarily grasses, be as resilient as possible. The objectives of this study were to evaluate (i) plant establishment and (ii) the effect of light to heavy tank traffic that ranged from zero to four passes on range grasses at the Yakima Training Center, Yakima, Washington. Characteristics measured include the number of 10-cm gaps without plant materials in seeded rows of the target (sown) species, the biomass of the target species, and the percentages of bluegrass colonization, bare ground, and cheatgrass encroachment in tracked and untracked areas. Both stand establishment and the ability to produce rhizomes are associated with the ability to recover after training. The wildryes did not establish well and subsequently had more 10-cm gaps and lower yields than the other introduced species tested. Among the natives, Snake River wheatgrass and western wheatgrass exhibited the most resilience across the different tracking intensities. The largest decline in percentage target species was observed between the two- and four-pass treatments. After five years, cheatgrass was not able to encroach on Snake River wheatgrass, Siberian wheatgrass, and bluebunch wheatgrass plots. Tracking generally reduced the stand of the target species and increased the amount of bare ground.