Impact of herbivory on the dynamics of individual tillers of little bluestem (Schizachyrium scoparium) and brownseed paspalum (Paspalum plicatulum)

Abstract

The impact of herbivory (cattle) on dynamics of plant parts of individual tillers of little bluestem (Schizachyrium scoparium) and brownseed paspalum (Paspalum plicatulum) were studied in a simulated short-duration grazing system stocked at four different stocking rates. The research was conducted from April, 1983 to April, 1984 in a grassland of the Post Oak Savannah located at the Texas A&M University, Native Plant and Animal Conservancy near College Station, Texas. Responses of the individual tillers to defoliation were measured by using the marked tiller, marked leaf method. Response variables included lamina appearance; growth of lamina, sheath, stem, and inflorescence; senescence of lamina and sheath; disappearance of lamina, sheath, stem, and inflorescence; and tiller mortality. Variations in parameters studied were evalauated by soil series (Tabor and Axtell). Presence and level of herbivory did not impact rate of lamina appearance of both species. Lamina and sheath growth of little bluestem was not generally affected by levels of stocking. Responses of brownseed paspalum was similar to little bluestem, except when increasing herbivory level in late summer which reduced lamina growth. Lamina growth was high during spring for little bluestem and during fall for brownseed paspalum. Defoliation intensity did not impact relative growth rates of vegetative tillers of both species but absolute growth rate of brownseed paspalum increased as herbivory level increased in spring. Under the assumption that mortality corresponds to natality, herbivory apparently modified the pattern of mortality and recruitment of the tillers and increased rates of both variables for little bluestem and brownseed paspalum during the growing season. Herbivory reduced senescence and disappearance of lamina which was related to relative growth rates of both species. This study suggests that herbivory appears to alter mortality and by inference recruitment of a tiller population more so than regrowth potential of initiated tillers.