Reldon F. Beck

Changes in grass basal area and forb densities over a 64-year period on grassland types of the Jornada Experimental Range.

Between 1915 and 1932, permanent 1 X 1-m quadrats were established on grasslands of the Jornada Experimental Range in southern New Mexico. Quadrat records accumulated from 1915 to 1979 on grasslands dominated by black grama [Bouteloua eriopoda (Torr.) Torr.], poverty threeawn (A ristida divaricata Willd.), tobosa [Hilaria mutica (Buckl.) Benth.], and burrograss (Scleropogon brevifolius Phil.) were used to examine changes in perennial grass basal area and forb densities. Quadrats originally dominated by black grama had large reductions in basal area during droughts, and basal area increased slowly following droughts. By 1979, black grama no longer occurred on 77% of the quadrats. Quadrats originally dominated by poverty threeawn changed to a mesquite (Prosopis glandulosa Torr. var. glandulosa) type. Perennial grass basal area on quadrats dominated by tobosa and burrograss decreased during droughts, but recovery was relatively rapid. Antecedent precipitation was associated with only 10 to 38% of the variation in perennial grass basal area. Perennial forb densities were low and fluctuated among years in all types. Annual forbs and grasses displayed large fluctuations in densities among years. The necessity of basing management of Chihuahuan Desert ranges on the perennial grass component is borne out by the low densities of palatable perennial forbs, and the extreme fluctuation and unpredictability in densities of annual forbs and grasses.

Cattle diets on semidesert grassland: botanical composition.

Highlight: Botanical composition of cattle diets on semidesert rangeland was studied by microhistological techniques. Cattle consumed 56% of all species available. Dietary portions of grasses, forbs, shrubs, and unidentifiable plants averaged 45, 32, 19, and 6%, respectively. Composition of diets changed with seasons. Grass contents of diets were highest in summer and lowest in spring. Mesa dropseed was the most common species in diets. Perennial grasses represented dependable sources of forage, but never comprised more than 50% of the steers’ diets in any season, and should not be used as the sole criterion for estimating forage production or determining stocking rates. Shrub portions were highest in spring when soaptree yucca was grazed almost exclusively. Forb fractions of diets varied little among seasons but were highest in winter. Forbs and shrubs comprised over one-half of the diets in certain seasons and should be grazed in these seasons if full benefit is to be derived from them. Preference ranking of forage plants evaluated selectivity and palatability but preference trends were inconsistent and most affected by species availability.

Some ecological relationships between creosotebush and bush muhly.

Highlight: Some ecological relations between creosotebush and bush muhly were observed and measured to determine the influence of bush muhly on creosotebush environment and vigor when the bush muhly is growing within the creosotebush canopy. Bush muhly growing within the creosotebush canopy significantly reduced the light intensity reaching the lower limbs of creosotebush. Shade screens used for simulating bush muhly shading did not significatly reduce the light reaching the creosotebushes but still appeared to influence the new growth of creosotebush leaves. Evidently, surface reflection under the screens still permitted sufficient light for some plant growth. No new basal stem growth was observed in creosotebushes where bush muhly was removed after occupying more than half of the aerial space of the creosotebush. There were more dead stems (50%) in creosotebushes growing with bush muhly present than in those without (20%). The amount of moisture in leaves and stems of creosotebush was significantly less when bush muhly was present.

Steer diets in southeastern Colorado.

Highlight: Hereford steers having continuous access to seeded, native, and old field pastures selected over 96% of their diet from six species of grasses and forbs. Changes in species preferences due to availability and maturation of plants caused shifts in summer grazing use made on the different pastures. A grazing proposal based on diets and the periods when steers preferred different forage species is to use old field pastures from mid-spring to early summer, seeded pastures in mid-summer, and native pastures in late summer through fall.

Range condition from an ecological perspective: modifications to recognize multiple use objectives.

Two changes in traditional range condition analyses are recommended: (1) to replace the terms excellent, good, fair, and poor with ecological equivalents of climax, late seral, mid-seral, and early seral in cases where this is practical; and (2) to develop relationships between products (e.g., livestock, wood products, water) or conditions (e.g., infiltration, site stability, erosion) and successional stage or state. Such information will allow the land manager to evaluate possible tradeoffs between managing for a particular successional stage or state and particular goods or

Increase in number of dominant plants and dominance-classes on a grassland in the northern Chihuahuan Desert.

Between 1915 and 1932,194 permanent 1 X l-m quadrats were established on grasslands of the Jornada Experimental Range in southern New Mexico. Primaryand secondary-dominant species were determined from the first quadrat records and each quadrat was reevaluated in 1981 to determine current dominants. The first records showed that 13 species of perennial grasses occupied all primaryand secondarydominant positions on all quadrats. In 1981, there were 12 perennial grass species as primaryor secondary-dominants. Six shrub species occurred as primaryor secondary-dominants on 47% of the quadrat sites in 1981. Dominance-classes, i.e., single-species dominance or two-species dominant combinations, increased from 24 to 43. Thus, vegetation on this range has become more diverse and this diversity must be considered in grazing management.

Cattle diets on semidesert grassland: nutritive content.

Highlight: A study of chemical composition and organic Four esophageal fistwlated Hereford steers were used to matter digestibility of cattle diets was conducted on sample diets from a southern New Mexico semidesert range. semidesert grassland in southern New Mexico during different Diets were sampled during lo-day periods at five different seasons. Forage quality was highest in the spring. Fall diets seasons. Steers grazed study pastures 14 to 21 days prior to were lower in digestibility, contained less crude protein and collection periods for all but October collections. During each the least estimated digestible energy. Level of protein in fall period forage was collected from a continuously grazed diets was greater than requirements for dry co& but was iess than recommended levels for lactating cows or growing calves. Table 1. Average chemical composition, in vitro organic matter diA stepwise regression equation showed that protein accounted gestl%ility, and estimated digestible energy in cattle diets.’ for more variation in in vitro digestibility than did other components. Year and season

Comparing techniques for determining steer diets in northern Chihuahuan Desert.

Diets determined by bite count and microhistological analysis of esophageal extrusa and feces were compared for steers grazing on grass-shrublands in the northern Chihuahuan Desert. The study was conducted on the Chihuahuan Desert Rangeland Research Center near Las Cruces, New Mexico. The purpose was to determine the similarity of 3 dietary techniques on arid, heterogeneous rangeland. It was proposed that the number of bites of each species eaten was directly proportional to the weight eaten as determined by the 2 microhistological techniques. Samples of diets were collected in 4 seasons from 2 steers grazing in a continuous yearlong pasture and in season-long rotation pastures. The 3 dietary techniques did not give similar (p<O.10) estimates of the diets eaten by the steers. Mean similarity indices were highest (77%) comparing diets from analysis of esophageal and fecal material. Lowest mean similarity indices (57%) were from comparing diets from bite count and fecal analysis. Much of the discrepancy between techniques was because of different size plants being eaten and heterogeneity of plant distribution. An importance ranking of dietary species using the 3 techniques showed that the top 3 species comprised over 68% of the total diets. Any of the 3 techniques can be used to determine the common species in the diets which may be all that is necessary for some management and analysis needs.

Estimating Plains Pocket Gopher Abundance on Adjacent Soil Types by A Revised Technique

A measuring wheel proved useful as an aid for counting signs of the plains pocket gopher (Geomys bursar&s) on adjacent soil types in Washington County, Colorado. Signs of pocket gophers were about twice as frequent on the Haxfon Sandy Loam type as were signs on fhe Dune Sand type. There were progressively more signs from spring until autumn. Aboui 7.5 times more signs were observed on each area in Sepfember than in May.

Utilization of linear prediction procedures to evaluate animal response to grazing systems

Best linear unbiased prediction (BLUP) procedures were used to separate genetic merit from environment8i effects on 205&y weight (205-d wt) of calves produced by cows grazing 2 pasture systems. Phenotypic measures of 205-d wt were statistically partitioned into genetic effects (breeding value) and environmental effects. Means were regressed on year of birth of c?lf. Analysis of covariance was used to test difference in slope and elevation (means) of the regression lines. The continuously grazed pasture (CC) produced higher 205-d wt than did the rotationally grazed pastures (RG) (P<.lO). Rate of change in 205-d wt was similar in the 2 grazing systems. Genetic merit was similar among the animals in the 2 grazing systems. The rate of change per year in genetic merit (genetic trend) was also similar. Means tended to vary sharply from year to year, indicating inequality of genetic merit should be taken into account in this type of data. Mean environmental effects resulted in greater (PC.10) 205-d weight in CG than in RG. Rate of change of environmental quality was similar in the 2 systems. These results indicate, from the animals perspective, the RG system did not improve productivity when compared to CG. The CG system was of higher nutritional quality, but the rate of change was similar to that of the RG system.