Himalaya Blackberry (Rubus armeniacus) Response to Goat Browsing and Mowing

Abstract

AbstractHimalaya blackberry is a nonnative shrub that has invaded sites throughout the Pacific Northwest. Its persistent canopy and large underground crowns create a competitive environment that prevents desirable species from germinating, establishing, or both. Cutleaf blackberry grows in association with Himalaya blackberry, and control efforts frequently target these two species. Control of Himalaya blackberry is complicated by vigorous vegetative regrowth after mechanical control, including mowing, and variable response to chemical methods. Recent interest in the use of goat browsing for invasive plant control has led land managers to use a variety of browsing regimes to control unwanted species through disturbance by herbivory. This study examined changes in functional group percent cover in a perennial grass pasture invaded by Himalaya blackberry and cutleaf blackberry in the southern Willamette Valley of Oregon. The appearance of species and their functional group membership after three treatment protocols are evaluated. Changes in the percentage of cover by Himalaya and cutleaf blackberries, annual grasses, perennial grasses, annual forbs, and perennial forbs were examined after two annual treatments with (1) high-intensity–short-duration goat browsing, (2) mowing, and (3) high-intensity–short-duration goat browsing followed by mowing. These data were then compiled by functional group to assess trends in the plants' revegetating the pasture after treatment. All treatments caused a significant decline in the percent cover of the invasive blackberries (P < 0.0001), but differences among treatments were not significant. The increase in the percent cover of perennial forbs for plots treated with goat browsing followed by mowing was significantly greater (P = 0.008) than it was in plots browsed only and those mowed only. Changes in percent cover of other functional groups were not significantly different with browsing or mowing treatments. Individual species within the perennial grass and perennial forb groups are discussed.