No abstract

Vegetation changes were evaluated over a 13 year period (1988-2000) on moderately grazed and lightly grazed rangelands in the Chihuahuan Desert of south central New Mexico. During the study period, grazing use of primary forage species averaged 49 and 26% on moderately and lightly grazed rangelands, respectively. Autumn total grass and black grama (Bouteloua eriopoda Torr.) standing crop were consistently higher on the lightly than moderately grazed rangeland throughout the study. Total grass standing crop declined on the moderately grazed rangeland when the last 3 years of study were compared to the first 3 years (10 versus 124 kg ha"1), but showed no change on the lightly grazed rangeland (320 versus 357 kg ha"1). Black grama, the primary perennial grass in the Chihuahuan Desert, increased in autumn standing crop on the lightly grazed rangeland, but decreased on the moderately grazed rangeland. Dropseed (Sporobolus spp.) autumn standing crop decreased on both rangelands during the study. However, this decrease was greater on the moderately grazed rangeland (97% decline) than on the lightly grazed rangeland (67% decline). Perennial grass survival following a 3-year period of below average precipitation was higher on the lightly grazed (51%) than the moderately grazed rangeland (11%). Severe grazing intensities on the moderately grazed rangeland during the dry period (1994-1996) appear to explain differences in grass survival between these 2 rangelands. Our study and several others show that light to conservative grazing intensities involving about 25-35% use of key forage species can promote improvement in rangeland ecological condition in the Chihuahuan Desert, even when accompanied by drought.

No abstract

In viva digdbiiity trials were conducted to evaiuate the infhtence of shrubs contafning low and high ieveis of soluble pbenoiic/tannins on dig-and nitrogen retention by Angora goats. Each of 6 shrubs and alfaG hay (M&ugo sutiva L.) were fed to goats at 30% (dry matter b&s) of the diet in 8 bariey straw-pr&ie bay mixture. Tbe mixture was reguiated so that ali diets contained about 8% crude protein. High soluble pl~enotic shrubs used included big sagebrush (Artemi.du-Nutt. ssp. &i&&da), gray oak (Querc~~ grireu Liebm.), true mountain mahogany (Cercocaqur montanus Raf.), and one-seed juniper (Juniperus ntonoqwma LEqdm.] Sug). Low-soluble pbenoiic species included common wfnterfat (CeruU&ftu lrurrrtr [pursh.], J.T. Howell), fourwfng saitbwh (A rr@fex cunescuw [purse.), Nutt.), and aifaifa. Nftrogen w of wfnterfat, gray oak, mount& mahogany and one-seed juniper dfets were iess QY.05) than the rifaifa controls, but big sagebrush did not differ (IP.05) compared with the rlfaifa control. Retafned nitrogen (g/d) differed (PC.05) only among aifaif8, juniper, 8nd mount8in mahogany die&t. Goats fed juniper had greater (IYO.05) retain4 nitrogen than the alfti control. Shrubs high in soluble phenolics, with the exception of bfg sagebrush, had elevated fecai nitrogen losses, but reduced urfnary nitrogen losses compared witb tbe aifalfa control. Forage organic matter intake (96 body weight) and nitrogen intake (g/d) were correlated more hfghiy with nitrogen retention thnn dietary crude protein (96) or dfgestibie protein (%). Present data indicate that protein found in paiatabie natfve shrubs is a&niiated with simiiar efficiency to that in aifalfa hay ff these shrubs are consumed at moderate ieveb.