GROWTH OF WINTERFAT FOLLOWING DEFOLIATION IN NORTHERN MIXED PRAIRIE OF SASKATCHEWAN

An observed increase in winterfat (Ceratoides lanata (Pursh) J.T. Howe ll) on ungrazed rangeland suggests that this shrub may potentially be an important forage resource in the Northern Mixed Prairie under impro ved grazing management. The objectives of this study were to: 1) compa re density, frequency, and cover of winterfat in a grazed pasture and site that had been protected from grazing for about 30 years; and 2) e valuate regrowth of winterfat following defoliation during the growing season on a clayey range site in Saskatchewan. Density, frequency, ca nopy cover, and basal cover were significantly greater in the protecte d range than the grazed pasture. Density (1.1 SE+/-0.01 plants m(-2)) and frequency (7.0% SE+/-3.6) were about 2-fold greater, while canopy cover (7.0% SE+/-1.4) and basal cover (1.7% SE+/-1.5) were 7- to 8-foI d greater, in the protected versus grazed range. When defoliated to a 5-cm stubble in May, June, or July plants produced significant amounts of regrowth but not when herbage was removed in August. When defoliat ed in late July or August current year production the following year w as significantly lower than control and earlier defoliations. Current year production peaked in late July and August. Total standing crop wa s 2- to 4-fold greater in the control than the defoliation treatments because the biomass produced in previous years was removed from clippe d plants. Because winterfat produces substantial amounts of new growth following defoliation in May, June, or July it is recommended that th is shrub be grazed only once during the growing season to prevent graz ing of this regrowth. Plants defoliated in May can potentially produce biomass equal to control the following year whereas plants defoliated in June, July, or August will likely require more than 1 year of rest to recover their annual productivity.