Rough Fescue Response to Season and Intensity of Defoliation

Abstract

Rough fescue (Festuca scabrella Torr.) was subjected to 10 clipping regimes which varied in time or intensity of defoliation. The experiment was repeated at 2 sites for 3 consecutive years. Plant survival and vigor were evaluated the summer following defoliation. Clipping treatments involving weekly defoliation to a 5-cm stubble height from mid May to late June resulted in the greatest injury. Reduced injury occurred when clipping ceased in May or when 10 or 15 cm of herbage was retained. Season long defoliation to 20 cm or clipping only in the fall caused no apparent damage. Cutting in the fall plus spring resulted in greater injury than spring clipping alone on plants clipped from mid May to late June but a fall clipping effect was not observed consistently on plants clipped in May plus fall. Despite common observances of rapid decline of rough fescue (Festuca scabrella Torr.)' on overgrazed ranges, little work has examined defoliation response of this productive grass. Root and top growth yields were reduced by repeated monthly clipping to stubble heights of 4(1l/2), 7.5(3), or 12.5(5) cm (inches) in a greenhouse study (Johnston 1961). Magnitude of root yield reduction from the 12.5-cm treatment (comparable to 20% utilization) was much greater than reduction in herbage yield. Tiller production was depressed with the 2 most severe treatments but apparently was unaffected by the 12.5-cm stubble height treatment. The author advised caution in interpretation of clipping trials since 20% utilization on an Alberta fescue grassland indicated no depression of root or herbage yields. A long-term study (Johnston et al. 1971) showed that even light season-long grazing (0.8 ha/AUM) reduced rough fescue basal area after 16 years and the species was largely eliminated under very heavy grazing (0.2 ha/ AUM). Long-term consequences of a grazing trial could not be determined after 6 years on a central Albertan rough fescuewestern porcupine grass (Stipa spartea Trin.) rangeland (Bailey et al. 1980) but heavy (75%) utilization in either June or fall depressed grass production. Light (35%) utilization results were similar to the controls. Fescue yields the year following mowing in another Alberta study (Sinton and Bailey 1980) were greater than the control for the April 8 treatment; but cutting late in spring (April 27, June 1) or in fall (July 31, Oct. 18) resulted in production losses. Tiller density increased and leaf length decreased for all mowing treatments but the effects were most pronounced for the fall cuttings. Of the spring mowing treatments, leaf lengths were shortest and tiller stimulation was slightest for the June 1 mowing. In a previous paper, Stout et al. (1981) examined vegetative and reproductive growth of rough fescue. In the present study, response of rough fescue to a number of clipping regimes incorporating different times, frequencies and intensities of defoliation is compared.