DROUGHT RESISTANCE IN RANGE AND PASTURE GRASSES

Rainfall is the limiting factor in the success of the livestock industry on the western range. Precipitation is especially critical in the southern Great Plains, the Southwest, and the semi-desert areas of the Intermountain Region. Here drought and its accompanying overgrazing constitute the major range problems and have been responsible for serious depletion of the forage resources of the region. Nelson (29) has shown that in years of drought basal area of black grama may fall as low as 10 or 11 per cent, of the maximum stand and 20 per cent, of a 13-year average. Craddock and Forsling (8) found in Southern Idaho that the volume of forage produced varied from 41 above to 33 per cent, below the nine-year average, largely as a result of winter and spring precipitation. Drought and overgrazing together result in much greater reduction than does drought alone or drought and moderate grazing (46, 47). Stewart (43) reported that Forest Service studies on western Utah winter ranges show that the drought from 1931 to 1934 caused a 20 per cent, decrease in available forage plants on ungrazed plots, but on overgrazed areas, depletion was approximately 60 per cent. Savage (36) and Savage and Jacobson (37), studying drought injury in the central and southern Great Plains, reported that as grazing was intensified all grasses decreased in all areas where drought was severe. Lantow and Flory (17), working on semi-desert grassland of New Mexico, concluded that permanent injury may be caused by drought on overgrazed range, but that on properly grazed range the recovery of the grass stand with increased precipitation is rapid. U. S. Forest Service workers (6, 7, 29, 33) have continuously stressed the injurious effect of drought on range plants. Boughman (3) showed that the root growth of several different range grasses is inhibited by clipping, the degree varying directly with the amount of clipping. Silker (41) found that drought survival of western wheat grass seedlings depended upon the formation of rhizomes.