Damage assessment in christmas tree plantations following vegetation control with sheep and geese

Abstract

Christmas tree farming in the Southern Appalachian Mountains is a potentially profitable but labor and chemical intensive enterprise. Control of competition from unwanted vegetation usually requires multiple applications of herbicides. Because geese and sheep have traditionally been used as "weeders" in orchards and cropland, the objective of this experiment was to evaluate the potential of these animals for herbaceous vegetation control in Christmas tree plantations. Three types of field trials were conducted at the Upper Mountain Research Station located near Laurel Springs, NC, during two growing seasons (1992 and 1993) to evaluate the natural browsing tendency displayed by sheep and different breeds of geese for different tree species. Food aversion training in a Fraser fir plantation was a special focus of the trials. Sheep and geese were managed to consume herbaceous vegetation through controlled, rotational grazing. Herbage mass of the residue was maintained between 693 and 2,000 kg/ha. Damage observed on four tree species (white pine, Fraser fir, Canadian hemlock, Colorado blue spruce) by "weeder" sheep and geese was dependent on animal species or breed. Untrained sheep and Pilgrim geese were most damaging to 1 yr old transplants (damage scores of 5.3 to 2.3). Trees with damage scores of less than 7 were judged to have reduced commercial potential. "Trainine" sheep to avoid browsing trees (using a gelatin capsule containing lithium chloride to affect feed selection) is a promising technique worthy of further research.