Two New Factors Affecting Resistance of Grasses to Grazing

T HE question, Why do ranges deteriorate?, may seem to have an obvious answer or answers. Certainly, answers to the question are essential if degeneration of ranges is to be prevented. The causes of degeneration usually listed are too heavy stocking and preference of livestock for individual species. These two factors undoubtedly are basic, but the process deserves further consideration. During an investigation of the degeneration of range lands in the loess hills of central Nebraska, attention was given to the causes for the decrease of certain grasses and the corresponding increase in others. In addition to the causes usually listed, two new factors have been carefully studied. These are the height to which growing points (apical meristems) (Fig. 1) were elevated and the ratio of fertile to vegetative stems or culms. When the growing points are elevated to more than an inch above the soil they may be removed by grazing and no new leaves may be produced by those stems. A high ratio of fertile to vegetative stems has an effect similar to the elevation of growing points. When a grass stem enters the reproductive phase no new leaves are produced (Purvis and Gregory, 1937; Evans and Grover, 1940) and such flower stalks generally grow above the minimum grazing height (Fig. 2). Thus if either a growing point or a stem bearing a seed stalk is grazed, photosynthetic material may not be replaced. It is now well established that in the degeneration of native grasslands there is a decrease in desirable forage species and an increase in undesirable species. Recognition of range degeneration as the replacement of one plant population by another was pointed out in the early work of Sampson (1917). In 1941 Weaver and