Plant response to defoliation in a subalpine green fescue community

Abstract

This study was prompted by concerns that expansion of elk (Cervus canadensus) ranges upward into subalpine grasslands might be damaging green fescue (Festuca viridula Vasey) meadows in Mount Rainier National Park. Objectives of the study were to examine effects of season and intensity of defoliation on phytomass productivity and canopy cover of these subalpine dry meadows and to relate these observations to the degree of elk utilization actually occurring on 3 representative meadows. Grazing in all meadows was very light. Less than one half of the plants examined showed any evidence of having been grazed. Plants which were grazed typically had less than 15% of their tops removed. Only green fescue was grazed to any significant extent by elk. Defoliation treatments (0%, 25%, 50%, and 75% of aerial phytomass removed in either early-, mid-, or late-season 1986 and again in 1987) had little effect upon plant cover the following year. Total herbage production was greater for defoliated than for undefoliated control plots in 1987, but did not vary with season of defoliation. Reproduction of green fescue and Lupinus latifolius Agardh. tended to decline as defoliation intensity increased in 1987. Neither season nor intensity of defoliation affected any of the parameters measured in 1988, a year of very low plant production. Green fescue subalpine grasslands appear to be quite tolerant of defoliation. All treatment effects were small relative to yearly differences induced by climatic variation.