Most of the grasses that remained after the "Dust Bowl" of the 30's were buffalo grass and blue grama. The bluestems, Indiangrass, Stipa species and side-oats grama disappeared. Why?
Tall grasses such as bluestems, indiangrass, switchgrass, and needlegrass are commonly called "decreasers" when range pastures are overstocked. Overgrazing is a common problem during arid seasons. During the Dust Bowl era, considered by meterologists to be the most devastating climatic event of the century, the mid-grass prairies became short-grass prairies due to the intolerance of taller-growing species to close cropping.
Sensitivity of tall grasses to close grazing in mid- to late-summer is due chiefly to the vulnerability of two clearly separated meristematic zones in the vegetative, non-flowering, aftermath shoots. We will call them System I and System II.
System I is the apical meristem (growing point) of a single shoot. In a vegetative shoot, the growing point remains within, or near, the crown zone, safely below the grazing height. It is comprised of a vegetative bud, below which are several bands (layers) of intercalary meristem, each having the potential to produce a new leaf. It is important to realize that the blade portion of a grass leaf makes considerable growth before the associated sheath begins elongation. This is important in grazing management.
System II is the zone of intercalary meristem found in the collar zone at the base of the blade. Cells in this band of meristem divide rapidly and later expand causing the blade to elongate. When a relatively immature blade is severed above the collar zone, blade elongation continues for a short period due chiefly to cell expansion. This mechanism for grass recovery is vital for the production of landscape turf and it accounts for the persistence of short grasses (blue grama, buffalo grass, bermudagrass) under close grazing. Tall grasses often suffer from intensive grazing because sheath elongation raises the collar zones of the leaves to a vulnerable height. Thus a leaf blade may be severed below the collar, or there may be insufficient leaf blade area remaining to sustain metabolism. It is obvious that photsynthesis will be seriously disrupted thereby depriving cells in thee apical meristem of their energy source. But of equal importance, with minimal blade tissue, transpiration will likewise be diminished. Transpiration is vital not only for the benefits associated with a cool leaf temperature but also for the conduction of water from the roots into the apical meristem. In turf management, this ill effect is called scalping. The remaining stubble dessicates. With tall growing grasses the grass may perish. This supports the adage to "take half - leave half."