GRAZING INFLUENCES ON WATERING POINT VEGETATION IN THE CHIHUAHUAN DESERT

Long-term influences of livestock grazing on vegetation around waterin g points was studied on 2 upland Chihuahuan desert ranges in southcent ral New Mexico using regression analysis. One range had been conservat ively stocked since the 1950's while the other was more heavily stocke d. About 45% of the climax vegetation occurred on the heavily stocked range compared to 70% on the conservatively stocked range. During 3 ye ars of study, both ranges were stocked conservatively so annual utiliz ation of the key forage grasses was 30-35%. Regression analyses showed black grama (Boueteloua eriopoda Torr.), mesa dropseed (Sporobolus fl exuosus Thurb, Rybd.), threeawn (Aristida sp.), and total perennial gr ass standing crop increased as distance from water increased on the go od condition range (P < 0.05). However, black grama and threeawn stand ing crop showed no association with distance from water on the fair co ndition range. Broom snakeweed (Xanthocephalum sarothrae Pursh.), the primary poisonous plant found on both ranges, was associated (r2 = 0.3 5) with distance from water only on the good condition range in April. Poisonous plants other than broom snakeweed decreased as distance fro m water increased with the exception of the fair condition range in Oc tober. No livestock losses from poisonous plants were noted on either range over the 3 years. We attribute this to the present conservative stocking rates. Our study supports the recommendation that downward st ocking rate adjustments be made for the zone more than 1,600 m from wa ter.