Growth of winterfat following defoliation in Northern Mixed Prairie of Saskatchewan

Abstract

An observed increase in winterfat (Ceratoides lanata (Pursh) J.T. Howell) on ungrazed rangeland suggests that this shrub may potentially be an important forage resource in the Northern Mixed Prairie under improved grazing management. The objectives of this study were to: 1) compare density, frequency, and cover of winterfat in a grazed pasture and site that had been protected from grazing for about 30 years; and 2) evaluate regrowth of winterfat following defoliation during the growing season on a clayey range site in Saskatchewan. Density, frequency, canopy cover, and basal cover were significantly greater in the protected range than the grazed pasture. Density (1.1 SE +/- 0.01 plants m-2) and frequency (70% 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-fold 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 defoliated in late July or August current year production the following year was significantly lower than control and earlier defoliations. Current year production peaked in late July and August. Total standing crop was 2- to 4-fold greater in the control than the defoliation treatments because the biomass produced in previous years was removed from clipped plants. Because winterfat produces substantial amounts of new growth following defoliation in May, June, or July it is recommended that this shrub be grazed only once during the growing season to prevent grazing 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.