Bark-stripping of common buckthorn by goats during managed browsing on bur oak savannas

Abstract

Goats are being used increasingly to manage woody invasive plants in woodland habitats, but their specific impacts on those plants over a period of time during active, periodic browsing has not been documented. This study investigated bark-stripping by goats browsing on common buckthorn in savanna habitats (75 goats/hectare, 5 to 7 days), focusing on possible size-selective feeding and the cumulative effects of repeated, periodic browsing over a 3-year period. When surveyed after the first browsing period, bark was stripped selectively on buckthorn stems 20 to 60 mm in diameter. Approximately 60% of all stripped stems were completely girdled, but only 14–17% of stems were bark-stripped. After five browsing periods, 66% of standing stems displayed bark stripping and 39% were completely girdled. Buckthorn densities were reduced by 90% compared to the first browsing period, the decline resulting mostly from consumption of foliage and terminal shoots of small (< 20 mm) buckthorn and bark-stripping resulting in top-kill in intermediate-sized (20–60 mm) plants. Large buckthorn (> 60 mm) were largely unimpacted by goats. Relatively few (28%) seedling buckthorn were browsed by goats, although > 90% of 2nd-year plants were browsed. Buckthorn can be managed in part via goat browsing, but repeated, periodic browsing over 3 to 6 years may be necessary to produce a significant reduction in plant abundance, and other techniques will be needed to eliminate large, seed-producing plants.