Major Changes in Grassland as a Result of Continued Drought

1. As a result of the great drought of 1934-37, the most important upland dominant, Andropogon scoparius, has suffered great destruction in the southern half of Nebraska. 2. The more deeply rooted Andropogon furcatus persisted during the early years of drought but has since suffered heavy losses. 3. Poa pratensis was nearly all killed in bluegrass pastures and only relatively small amounts remain in prairies. 4. Most species of forbs, including those very deeply rooted, have gradually succumbed to the continued drought, until they are only one-half to one-third of their former abundance. 5. Festuca octoflora, Bromus secalinus, and other annual grasses, which became extremely abundant after 1934, have now greatly decreased in quantity, filling the smaller interspaces rather than occupying large areas. 6. The scourge of the ruderal, Lepidium virginicum, so serious in 1936-37, has distinctly disappeared. Other annual weeds were extremely abundant only during one or two seasons. 7. The perennial, rhizomatous Aster multiflorus spread so widely into drought-bared areas as to ruin many prairies for production of hay. Erigeron ramosus was almost equally widespread. 8. A remarkable increase in abundance of Oxalis violacea, Allium mutabile, Tradescantia bracteata, and other species with thick roots or other storage organs has recently occurred. 9. Agropyron smithii, occurring sparsely at the beginning of the drought, has spread so widely as to cover one-half to three-fourths of the area of many former bluestem prairies. 10. Marked increases in territory dominated by Stipa spartea and Sporobolus heterolepis have appeared. Bouteloua gracilis and Buchloe dactyloides have greatly increased. Bouteloua curtipendula, a dominant, formerly of relatively low rank, has now become one of the most important prairie grasses. 11. Drought has reduced the basal cover in true prairie 50 to 66 per cent. The lower layer of grasses and forbs has been almost destroyed. Grassland types have been much modified.