Hilaria Mutica Research Articles

Changes in rodent community structure in the Chihuahuan Desert México: comparisons between two habitats

From 1996 to 2001, we conducted a study of two adjacent rodent communities in the Mapimi Basin of the Chihuahuan desert in Mexico. The objective was to test the resource level hypothesis in explaining differences in two contrasting but spatially close habitats: a tobosa grassland area (Hilaria mutica) and a mesquite (Prosopis glandulosa)–creosote (Larrea tridentata)–prickly pear (Opuntia rastrera) shrubland. Based on the inherent differences in the two habitats, we made the following predictions relative to the resource level hypothesis: (1) shrublands should have higher inherent density, diversity, and richness of small mammals than grasslands; (2) annual and seasonal changes in density, diversity, richness, and community composition should be more pronounced in grassland than in shrubland. Concerning the first set of predictions, rodent density was higher in the shrubland (17.7±1.1ind/ha) than the grassland (5.8±0.7ind/ha; F1,48=292.2, p⩽0.001). Overall species richness was equal in both habitats but the richness at any given time was significantly higher in shrubland (7.5±0.2 species vs. 5.6±0.3 species, F1,48=35.0, p⩽0.001). Species diversity, however, was equal in both habitats. Concerning the second set of predictions, rodent densities differed significantly in both areas annually (grassland: F5,24=10.9, p<0.001; shrubland F5,24=11.0, p<0.001) and seasonally (grassland: F1,24=27.2, p<0.001; shrubland: F1,24=15.3, p<0.001). However, the variability in the relative number of individuals captured per year was higher in the grassland compared to the shrubland. Also, rodent densities in grasslands responded directly to the amount of precipitation of the previous calendar year while those in shrubland did not respond until November. The composition of the rodent community, as expressed by the first principal component of a principal components analysis varied yearly and seasonally for both shrubland (annual: F5,24=14.6, p<0.001, seasonal: F1,34=12.1, p>0.001) and the grassland (annual: F5,24=3.01, p=0.03, seasonal: F1,24=13.5, p=0.001). However, we found changes in community structure in grasslands but not in shrubland were related to previous year precipitation levels. We suggest that differences between the two areas reflected the higher productivity and biomass stability in the shrubland compared to the grassland. Consequently, we concluded that the results in general supported the resource level hypothesis in explaining the structure and dynamics of rodent communities in the Chihuahuan desert.

Chromosome studies in the grass subfamily Chloridoideae. II. An analysis of polyploidy

Polyploidy is frequent among the grasses. This study indicates that it has a high frequency in the subfamily Chloridoideae, where more than 90% of the studied specimens are polyploids. These levels range from diploid (2n= 20 forx= 10 and 2n= 18 forx= 9) to 16‐ploid (2n= 160) forx= 10 inCtenium concinnumNees and 20‐ploid (2n= 180) forx= 9 inHilaria muticaBenth. This polyploid trend is seen in southern Africa, as well as worldwide. Analysis indicates that many polyploids are alloploids, suggesting extensive hybridization within this group. This is supported by the presence of apomixis in many members of the subfamily. Both polyploidy and apomixis are thought to be important evolutionary mechanisms in Chloridoideae as well as closely related Panicoideae, and have a high frequency in southern Africa. Due to the stable ecological, geographical and climatological history of Africa, the continent is ideally suited for the stabilization of hybrid complexes by means of apomixis and polyploidization.

Variability in soil redistribution in the northern Chihuahuan Desert based on 137Cesium measurements

A hypothesis for understanding the stability of northern Chihuahuan Desert landscapes is that the distribution of soil resources changes from spatially homogeneous in arid grasslands to spatially heterogeneous in invading shrublands. Since radioactive fallout 137Cesium ( 137Cs) was deposited uniformly across the landscape during the 1950s and 1960s and was quickly adsorbed to soil particles, any redistribution of 137Cs across the landscape would be due to soil redistribution or instability at either plant-interspaces or on a landscape scale. The concentration of 137Cs in soils collected from different vegetation communities (black grama grass, tarbush, tobosa grass, and mesquite) at the USDA-ARS Jornada Experimental Range in the Northern Chihuahuan Desert in New Mexico was determined. At the black grama grass and tobosa grass sites, 137Cs was uniformly distributed at the plant interspace scale. At the mesquite sites, 137Cs was concentrated in the dune area under mesquite shrubs with little to no 137Cs in the interdune areas. 137Cs data support the hypothesis that significant soil redistribution has occurred at dune sites created by invading mesquite. In the arid grassland-shrub sites with black grama grass, tobosa grass, and tarbush the 137Cs data support the hypothesis of spatially homogeneous distribution of soil resources. High concentrations of 137Cs in the biological soil crusts (0–5 mm) at the tarbush sites indicate that biological soil crusts can contribute to the stability of these sites.

Long-Term Impacts of Livestock Grazing on Chihuahuan Desert Rangelands

Rangeland ecological condition was monitored over a 48 year period on 41 sites on Bureau of Land Management rangelands scattered across 6 counties in southwestern New Mexico. All sites were grazed by livestock during the study period. Sampling occurred in 1952, 1962, 1982, 1992, 1997, 1998, and 1999. A modified Parker 3 step method in conjunction with Dyksterhuis quantitative climax procedures were used to determine rangeland ecological condition. At the end of the 48 year study period (1952-1999), the average rangeland ecological condition score across study sites was the same (P > 0.05) as the beginning of the study (39% versus 41% remaining climax vegetation, respectively). Major changes (P > 0.05) in rangeland condition occurred within the study period due to annual fluctuations in precipitation. Ecological condition scores increased in the 1980s and early 1990s due to above average precipitation. However, drought in the early to mid 1950's and again in the mid to late 1990's caused rangeland condition scores to decline. At the end of the study (1997-1999), 38% of the sites were in late seral ecological condition, compared to an average of 25% in the 1952 to 1982 period. The amount of rangeland in late seral ecological condition increased while the amount of rangeland in mid seral and early seral condition decreased in the 1990s compared to the 1952-1962 period. The average percent cover of black grama (Bouteloua eriopoda Torr.) and tobosa (Hilaria mutica Buckley), the primary forage grasses in the Chihuahuan Desert, were the same (P > 0.05) in 1952 and 1999. Over the 48 year study period, the average cover of shrubs including honey mesquite (Prosopis glandulosa Torr.) showed no change (P > 0.05). However major increases in honey mesquite basal cover occurred on 1 site and creosote-bush (Larria tridentata [Pursh] Nutt.) increased on another. Grazing intensity was evaluated during the last 3 years of study (1997, 1998, 1999). Overall grazing use of forage across sites and years averaged 34% or conservative. Our research shows controlled livestock grazing is sustainable on Chihuahuan Desert rangelands receiving from 26-35 cm annual precipitation. DOI:10.2458/azu_jrm_v55i4_navarro

Physiological impacts of biosolids application in desert grasses

Although some studies have demonstrated that application of biosolids enhances biomass production of desert grasses, there is a lack of information regarding the physiological mechanisms of this enhanced production. The main objective of this study was to evaluate how gas exchange and leaf area production of blue grama ( Bouteloua gracilis) and tobosagrass ( Hilaria mutica) are affected by different rates and seasons of biosolids application and irrigation regimes. Plants of both species were transplanted in pots and maintained under a rain-out shelter. Pots were treated either in the spring or summer with biosolids at rates of 0, 7, 18, 34 and 90 dry Mg ha −1 and irrigated at either 40 or 80% field capacity soil water content. The increase in biosolids rates produced increases in leaf area that did not always correspond with increases in photosynthetic rates ( P n ). This suggests that achieving a well-developed canopy was more important than increasing P n per se. However, plant responses to biosolids application varied with irrigation regimes and between species. A decrease in P n of blue grama treated with 34 Mg ha −1 of biosolids was, in part, due to stomatal closure to modulate water loss and possibly to relocation of N for root growth. Under 80% field capacity, tobosagrass seemed to have a less conservative strategy in regulating g s than blue grama. Spring application of biosolids resulted in higher P n than summer application. Photosynthetic rates of blue grama and tobosagrass were not always related to tissue N concentrations.

Shoot and root biomass of desert grasses as affected by biosolids application

This research evaluated the effects of level and season of biosolids application and irrigation regime on shoot and root biomass production of blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Steud.) and tobosagrass (Hilaria mutica (Buckl.) Benth.), two perennial, warm season grasses of Chihuahuan Desert rangelands. Plants of both species were transplanted to pots and maintained under a rain-out shelter. The plants were treated either in the spring or summer with biosolids at levels of 0, 7, 18, 34, and 90 dry Mg ha−1 and irrigated at 40% or 80% field capacity soil water content. In general, biosolids increased shoot biomass of both species, which was partly a result of the increased soil NO3-N concentrations that followed biosolids application. More biomass was allocated to the roots of the grasses when biosolids and irrigation levels were low. In contrast, more biomass was allocated to the shoots when biosolids and irrigation levels were high. Shoot biomass production and soil NO3-N concentrations were enhanced more by the spring application of biosolids than by the summer application. The season of application influences the beneficial effect of biosolids on desert grasses.

Long-term impacts of livestock grazing on Chihuahuan Desert rangelands

Rangeland ecological condition was monitored over a 48 year period on 41 sites on Bureau of Land Management rangelands scattered across 6 counties in southwestern New Mexico. All sites were grazed by livestock during the study period. Sampling occurred in 1952, 1962, 1982, 1992, 1997, 1998, and 1999. A modified Parker 3 step method in conjunction with Dyksterhuis quantitative climax procedures were used to determine rangeland ecological condition. At the end of the 48 year study period (1952-1999), the average rangeland ecological condition score across study sites was the same (P &gt; 0.05) as the beginning of the study (39% versus 41% remaining climax vegetation, respectively). Major changes (P &gt; 0.05) in rangeland condition occurred within the study period due to annual fluctuations in precipitation. Ecological condition scores increased in the 1980s and early 1990s due to above average precipitation. However, drought in the early to mid 1950's and again in the mid to late 1990's caused rangeland condition scores to decline. At the end of the study (1997-1999), 38% of the sites were in late seral ecological condition, compared to an average of 25% in the 1952 to 1982 period. The amount of rangeland in late seral ecological condition increased while the amount of rangeland in mid seral and early seral condition decreased in the 1990s compared to the 1952-1962 period. The average percent cover of black grama (Bouteloua eriopoda Torr.) and tobosa (Hilaria mutica Buckley), the primary forage grasses in the Chihuahuan Desert, were the same (P &gt; 0.05) in 1952 and 1999. Over the 48 year study period, the average cover of shrubs including honey mesquite (Prosopis glandulosa Torr.) showed no change (P &gt; 0.05). However major increases in honey mesquite basal cover occurred on 1 site and creosote-bush (Larria tridentata [Pursh] Nutt.) increased on another. Grazing intensity was evaluated during the last 3 years of study (1997, 1998, 1999). Overall grazing use of forage across sites and years averaged 34% or conservative. Our research shows controlled livestock grazing is sustainable on Chihuahuan Desert rangelands receiving from 26-35 cm annual precipitation.

Statistical Analyses of Fluorometry Data from Chloroform Filtrate of Lamb Feces

Accurately identifying the botanical composition of free-ranging animal diets remains a challenge. Currently accepted procedures are time consuming, many requiring painstaking sample preparation while none produce data useful for real-time management. Automated procedures focusing on detection of chemical and/or physical plant properties using specific molecules called fluorophores offers possibilities for determining the species composition of herbivore diets. This study was designed to evaluate fluorometry techniques in herbivore diet determinations using fecal samples obtained from 13 lambs fed a basal diet of tobosa hay (Pleuraphis mutica Buckley), and containing 4 different levels (0, 10, 20, and 30%) of tarbush (Flourensia cernua D C.) leaf material. Chloroform (CHCl3) filtrate obtained from the lamb's feces was exposed to UV light from a xenon arc lamp. This caused fluorophore molecules in the filtrate to have their outer shell electrons move to a higher energy state as a result of UV light excitation. After excitation by UV light at 310, 320, 330, 340, 350, and 355 nm, the fluorophores returned to their ground state giving off light (fluorescence). This fluorescence intensity (counts) varied and when captured using appropriate electronics, produced 1,024 pairs of light intensities (counts) and fluorescent wavelengths between 175 and 818 nm in 0.63 nm increments. Previous research indicated differences among diets could be determined using distinct peaks in the red and blue regions of the visible light spectrum and a univariate (1 variable at a time) analysis. This research demonstrates the entire fluorescence data set can be used to determine differences among diets using multivariate statistics. Sequences of 5 increasingly complex statistical techniques were used to distinguish among diets: 2-dimensional plots, polynomial regression models, confidence interval plots, discriminant analysis, and 3-dimensional plots. Two-dimensional plots indicated 2 spectral fluorescence peaks, 1 in the blue-green (420-600 nm) and 1 in the red (640-720 nm) region of the visible spectrum. Because of the asymmetrical nature of these peaks, fifth-order polynomials were developed to differentiate among the 4 diets. Statistical reliability was high when discriminating between diets containing no tarbush leaf and the diets containing 30% tarbush leaf; however, it was not possible to statistically separate diets containing intermediate (10 and 20%) amounts of tarbush leaf material from each other or from the 2 extremes (0 and 30% tarbush leaf). These results suggest spectral signatures arising from fluorometry data may be useful for differentiating among botanical composition diets that differ in plant form, but that a multivariate approach may require large sample sizes. DOI:10.2458/azu_jrm_v54i4_mukherjee

Vegetación y flora de un ecotono entre las provincias del altilpano y de la planicie costera del noreste de México

Se estudió la vegetación y la flora vascular de un ecotono entre las provincias florísticas del Altiplano y de la Planicie Costera del Noreste de México. El área de estudio cubre una superficie de 2,526.25 km2 en el norte del estado de Nuevo León. Con base en 50 muestreos de vegetación, fotografías aéreas y colectas botánicas, se delimitaron y cartografiaron siete tipos de vegetación, mismos que se describen de acuerdo con su fisonomía, características ecológicas y componentes florísticos. Se determinaron 405 especies, incluyendo variedades y subespecies. La zona presentó afinidad geográfica con la vegetación del Desierto Chihuahuense en el Altiplano (pastizal de Hilaria mutica, matorral bajo inerme de Flourensia cernua y matorral mediano de Acacia-Prosopis-Flourensia-Larrea) y la Planicie Costera (matorral mediano subinerme de Leucophyllum frutescens y Acacia rigidula y matorral alto subinerme de Helietta parvifolia). Los matorrales de Prosopis-Acacia no mostraron afinidad geográfica definida. La coexistencia de vegetación arbustiva característica de las tierras bajas de la Planicie Costera, con la vegetación comúnmente encontrada en el Desierto Chihuahuense, podría explicarse en virtud del incremento en la aridez y el suave levantamiento de la superficie continental en sentido este-oeste y de la ausencia de accidentes topográficos notables en el sector nororiental de México.

Effects of biosolids on tobosagrass growth in the Chihuahuan desert

Little information is available about seasonal application and carry-over effects of biosolids application to semi-arid grasslands. Biosolids rates of 0 (control), 7, 18, or 34 Mg ha-1 were topically applied to tobosagrass (Hilaria mutica (Buckl.) Benth.) experimental plots in a Chihuahuan desert grassland in western Texas. Biosolids were applied twice in 1994, for one-year-only, either in winter-and-summer (WS), or spring-and-summer (SS) seasons. Half of the plots were irrigated every summer for 4 years (1994-1997). Tobosagrass standing crop (herbage yield) and total Kjeldahl nitrogen concentration (plant %TKN) were measured every year during the 4 years of the study (1994-1997). An increase in biosolids rate increased tobosagrass herbage yield linearly during the 4 growing seasons. Linear and quadratic responses to biosolids rates were observed in %TKN during the experiment. Irrigation increased tobosagrass herbage yield. Irrigation decreased %TKN in 1995 and 1996 and had no influence during the other years. Winter-and-summer applications increased herbage yield more than spring and summer applications in 3 out of 4 years. Spring-and-summer applications increased %TKN more than winter and summer applications only in 1996. Carry-over effects on tobosagrass herbage yield and %TKN were observed in the second, third, and fourth growing seasons after biosolids application. Twice-a-year application of biosolids for 1-year-only offers an excellent means to improve tobosagrass productivity and forage quality.

Effects of Biosolids on Tobosagrass Growth in the Chihuahuan Desert

Little information is available about seasonal application and carry-over effects of biosolids application to semi-arid grasslands. Biosolids rates of 0 (control), 7, 18, or 34 Mg ha-1 were topically applied to tobosagrass (Hilaria mutica (Buckl.) Benth.) experimental plots in a Chihuahuan desert grassland in western Texas. Biosolids were applied twice in 1994, for one-year-only, either in winter-and-summer (WS), or spring-and-summer (SS) seasons. Half of the plots were irrigated every summer for 4 years (1994-1997). Tobosagrass standing crop (herbage yield) and total Kjeldahl nitrogen concentration (plant %TKN) were measured every year during the 4 years of the study (1994-1997). An increase in biosolids rate increased tobosagrass herbage yield linearly during the 4 growing seasons. Linear and quadratic responses to biosolids rates were observed in %TKN during the experiment. Irrigation increased tobosagrass herbage yield. Irrigation decreased %TKN in 1995 and 1996 and had no influence during the other years. Winter-and-summer applications increased herbage yield more than spring and summer applications in 3 out of 4 years. Spring-and-summer applications increased %TKN more than winter and summer applications only in 1996. Carry-over effects on tobosagrass herbage yield and %TKN were observed in the second, third, and fourth growing seasons after biosolids application. Twice-a-year application of biosolids for 1-year-only offers an excellent means to improve tobosagrass productivity and forage quality. DOI:10.2458/azu_jrm_v54i1_jurado

Mesquite and grass interference with establishing redberry juniper seedlings

Excessive cover of juniper (Juniperus pinchotii Sudw.) reduces forage production, interferes with livestock management, and diminishes the watershed and wildlife habitat values of rangelands. We studied whether juniper seedlings were differentially suppressed in the presence of different grass species, and to what extent established mesquite (Prosopis glandulosa Torr.) trees facilitated or competed with establishing juniper seedlings. Seedlings growing with any of the grasses (RGR = 0.23 to 0.43 cm cm(-1)) grew significantly less than those with no grass competition (RGR = 0.72 cm cm(-1))(P &lt; 0.01). Juniper seedlings grew significantly less in the presence of buffalograss (Buchloe dactyloides (Nutt.) Engelm.) (RGR = 0.23 cm cm(-1) than with either sideoats grama (Bouteloua curtipendula (Michx.) Torr.) (RGR = 0.43 cm cm(-1)) or tobosagrass (Hilaria mutica [Buckl.] Benth.) (RGR = 0.43 cm cm(-1))(P &lt; 0.01). In contrast, juniper seedlings grew larger under intact canopies of mesquite (RGR = 0.99 cm cm(-1)) than in open grassland (RGR = 0.65 cm cm(-1))(P &lt; 0.05) due in part to the greater nutrient availability (P &lt; 0.05) under mesquite canopies. Juniper growing in sub-canopy positions with mesquite trees removed grew less (RGR = 0.84 cm cm(-1)) than those growing under mesquite canopies with root competition (RGR = 0.99 cm cm(-1))(P &lt; 0.05). Juniper growing under intact mesquite canopies but without mesquite root competition, grew no better or worse (RGR = 0.93 cm cm(-1)) than those with mesquite root competition (RGR = 0.99 cm cm(-1))(P &gt; 0.05), indicating that mesquite root competition with juniper is probably inconsequential. Since junipers grow mainly in fall, winter and spring when mesquite trees are dormant and leafless, the lack of competition may largely be due to these 2 species using resources at different times of the year. Greater nutrient availability beneath mesquite canopies, reduction of summer temperatures, and temporal separation of resource use clearly benefit juniper seedlings growing in the presence of mesquite. Managing for a vigorous grass component with low densities and cover of mesquite is the best way to limit the rate of invasion by juniper.

Statistical analyses of fluorometry data from chloroform filtrate of lamb feces

Accurately identifying the botanical composition of free-ranging animal diets remains a challenge. Currently accepted procedures are time consuming, many requiring painstaking sample preparation while none produce data useful for real-time management. Automated procedures focusing on detection of chemical and/or physical plant properties using specific molecules called fluorophores offers possibilities for determining the species composition of herbivore diets. This study was designed to evaluate fluorometry techniques in herbivore diet determinations using fecal samples obtained from 13 lambs fed a basal diet of tobosa hay (Pleuraphis mutica Buckley), and containing 4 different levels (0, 10, 20, and 30%) of tarbush (Flourensia cernua D C.) leaf material. Chloroform (CHCl3) filtrate obtained from the lamb's feces was exposed to UV light from a xenon arc lamp. This caused fluorophore molecules in the filtrate to have their outer shell electrons move to a higher energy state as a result of UV light excitation. After excitation by UV light at 310, 320, 330, 340, 350, and 355 nm, the fluorophores returned to their ground state giving off light (fluorescence). This fluorescence intensity (counts) varied and when captured using appropriate electronics, produced 1,024 pairs of light intensities (counts) and fluorescent wavelengths between 175 and 818 nm in 0.63 nm increments. Previous research indicated differences among diets could be determined using distinct peaks in the red and blue regions of the visible light spectrum and a univariate (1 variable at a time) analysis. This research demonstrates the entire fluorescence data set can be used to determine differences among diets using multivariate statistics. Sequences of 5 increasingly complex statistical techniques were used to distinguish among diets: 2-dimensional plots, polynomial regression models, confidence interval plots, discriminant analysis, and 3-dimensional plots. Two-dimensional plots indicated 2 spectral fluorescence peaks, 1 in the blue-green (420-600 nm) and 1 in the red (640-720 nm) region of the visible spectrum. Because of the asymmetrical nature of these peaks, fifth-order polynomials were developed to differentiate among the 4 diets. Statistical reliability was high when discriminating between diets containing no tarbush leaf and the diets containing 30% tarbush leaf; however, it was not possible to statistically separate diets containing intermediate (10 and 20%) amounts of tarbush leaf material from each other or from the 2 extremes (0 and 30% tarbush leaf). These results suggest spectral signatures arising from fluorometry data may be useful for differentiating among botanical composition diets that differ in plant form, but that a multivariate approach may require large sample sizes.

Competition intensity as a function of resource availability in a semiarid ecosystem.

Two field experiments were conducted using three dominant perennial species of the Chihuahuan Desert: Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a flat-stemmed succulent cactus). Two hypotheses concerning competition in arid plant communities were tested. (1) Marked resource partitioning with no interspecific competition could be expected since the three species belong to different life-forms, and that plant growth in deserts is basically limited by harsh environmental conditions. (2) Alternatively, resource scarcity (particularly water) will result in strong plant competition. In a 1-year removal experiment, water status and plant growth of the three species were monitored in twelve 10 m × 10 m plots randomized in three blocks and assigned to the following treatments: (a) removal of all species, except H. mutica; (b) removal of all species, except L. tridentata; (c) removal of all species, except O. rastrera, and (d) control without any manipulation. In a watering experiment, under two neighbourhood conditions (growing isolated or in associations of plants of the three species in plots of 20 m2), the water status of the three species and the growth of H.mutica and L.tridentata were studied for 32 days after an irrigation equivalent to 30 mm of rain, similar to a strong storm event at the site. In the removal experiment, where plants were free to capture water, no evidence of competition was observed. However, during the watering experiment, in which water was forced into the soil, competitive effects were observed. Associated individuals of L. tridentata had lower xylem water potentials and osmotic potentials (OPs) and produced shorter twigs and less leaves and nodes. Although less pronounced, neighbours also had a negative effect on the OP in O. rastrera. According to these results, the intensity of the interspecific competition for water seems to depend on the level of resource availability in the soil. Thus, the validity of the two hypotheses tested in this study also depends on the level of resources. Competition could be absent or very low in years of low precipitation, as in the year of this study (173 mm against a 25-year average of 264 mm). However, when soil water availability is high, e.g. following heavy rain, the negative interactions between species could be more intense.

Runoff and erosion from a mosaic tobosagrass and burrograss community in the northern Chihuahuan Desert grassland

A mosaic plant community pattern was studied in the northern Chihuahuan Desert grassland region of sourthern New Mexico. The principal plant species of the mosaic were tobosagrass (Hilaria mutica(Buckl.) Benth.) and burrograss (Scleropogon brevifoliusPhil.). Water runoff, sediment concentration, incremental sediment, and plant and soil properties of both species aggregations were measured. The study site was a large aggregation of burrograss plants in a tobosagrass matrix. Water runoff was three times greater from the burrograss aggregation than from the tobosagrass aggregation both before and after the growing season. Sediment concentration and cumulative sediment loss were also greater from the burrograss than the tobosagrass, except under wet conditions in the early autumn when sediment concentrations were similar. Differences are attributed to greater cover, phytomass, and surface roughness in the tobosagrass aggregation.

Biosolids Effects on Tobosagrass and Alkali Sacaton in a Chihuahuan Desert Grassland

AbstractEnvironmentally responsible use of anaerobically digested biosolids (municipal sewage sludge) is an increasingly urgent ecological and societal concern. There is relatively little information available on effects of biosolids in arid and semiarid rangelands. The purpose of this research was to evaluate effects of rate, season, and number of consecutive years of biosolids application on tobosagrass (Hilaria mutica) and alkali sacaton (Sporobolus airoides), two commonly occurring native grasses in the Chihuahuan desert grassland. Biosolids were topically applied at rates of 0, 7, 18, 34, or 90 Mg ha−1 either during the dormant season or just prior to the onset of the growing season for 1 yr only, or for 2, 3, or 4 consecutive years; one‐half of the experimental plots were provided supplemental irrigation. In general, biosolids increased plant length and aboveground standing crop of these species. Plants responded more to dormant season application than to growing season application in the first year of the study. Carry‐over effects from earlier applications on current year's growth were species‐specific and depended on growing conditions.

Observations of White-Tailed Deer and Cattle Diets in Mexico

Most rangelands in northern Nuevo Leon, Mexico, have been grazed intensely for more than 10 years simultaneously by cattle and white-tailed deer (Odocoileus virginianus texanus). There is a lack of information concerning diet selection of white-tailed deer and cattle in this region. We observed the dietary preferences of these ungulates in northeastern Nuevo Leon for a 6 month period. Two adjacent areas were subjected to rotational grazing (RG) and continuous cattle grazing (CG). Fecal analysis was used to determine dietary overlap of these 2 sympatric ruminants. Cattle diets averaged 70% grasses, 23% browse, and 4% forbs. Deer diets were 63% browse, 24% forbs and 12% grasses in both areas. The preferred species for cattle in both areas were grasses. Deer preferred fortes on the continuous grazed area and grasses on rotational grazed area. Zacate toboso [Hilaria mutica (Buckl.] Benth.) was the most preferred species by both ruminants in both management systems. Differences between cattle and deer diets were significant (P < 0.05). The similarity index was higher on the rotational grazed (23%) than on the continuous grazed area (15%) (P < 0.05). The higher similarity index in RG area may have been a result of the altered forage preferences of deer. Zacate toboso under RG could be an important feed resource in those areas where white-tailed deer and cattle graze in common.

Effects of Flourensia Cernua Ingestion on Intake, Digesta Kinetics, and Ruminal Fermentation of Sheep Consuming Tobosa

Tarbush (Flourensia cernua DC.) contributes substantially to the Chihuahuan Desert shrub biomass, but is browsed sparingly by livestock. This study was designed to assess nutritional benefits and/or toxicosis of ingestion of pre-bloom tarbush leaves by sheep fed a low quality native grass diet. Sixteen ruminally cannulated sheep (46 kg) housed in individual pens were randomly assigned to 1 of 4 treatments for 28 days. Treatments were ground tobosa grass (Pleuraphis mutica Buckl.) substituted with 0, 10, 20, or 30% (dry matter basis) whole tarbush leaves (19% CP). At 20 and 30% of the diet, tarbush increased (P = 0.0049) dry matter intake during week 3, and sheep consuming 30% tarbush tended to increase dry matter intake during week 2 (P = 0.0559). Dietary tarbush did not affect any variable associated with ruminal fluid kinetics, particulate digesta kinetics, or in situ degradation rates of tobosa dry matter or neutral detergent fiber (P > 0.05). Molar butyrate proportions (P = 0.0032) and total volatile fatty acid concentrations (P = 0.0064) were greater for the 30% tarbush treatments. Ruminal ammonia was greater (P < 0.0029) at 6, 8, and 12 hours postfeeding for the 30% tarbrush treatment. Sheep lost body weight regardless of treatment; however, sheep not fed tarbush boded (P = 0.0945) to lose more weight. &rum clinical profiles (day 0, 7, 15, and 21) confirmed nutritional stress but did not suggest toxicosis.

Effects of Flourensia Cernua Ingestion on Nitrogen Balance of Sheep Consuming Tobosa

Flourensia cernua DC. (tarbush) is a deciduous shrub with potential as a high-protein forage source for livestock. Twenty-four Polypay X Rambouillet wethers housed in metabolism crabs were used to evaluate tarbush as a N source for sheep fed a low quality grass diet. Treatments were 100% ground tobosa grass (Pleuraphis mutica BuckL) or tobosa substituted with 10, 20, or 30% whole pre-bloom tarbush leaves (n = 5) or 26% ground alfalfa (n = 4, Medicago sativa L.) on a dry matter basis (dmb). Sheep were fed ad libitum for 11 days, after which feed was restricted to 1% (dmb) of body weight for 11 days to reduce sorting and maintain uniform intake. Apparent dry matter digestibility was not improved (P = 0.2646) with tarbush or alfalfa. Fecal N was similar (P = 0.1626), but urinary N varied (P = 0.0008) among treatments. Apparent N digestibility differed (P = 0.0042) among treatments (43, 46, 50, 56, and 63% for sheep consuming 0,10, 20, or 30% tarbush or alfalfa, respectively). All treatments resulted in similar (P = 0.1569) but negative N retentions (-2.4, -2.2, -2.8, -2.0, and -1.5 g day-1 for sheep consuming 0, 10, 20, or 30% tarbush or alfalfa, respectively). Serum clinical profiles (day 22) confirmed all sheep were nutritionally stressed, but did not indicate toxicosis. Although neither tarbush nor alfalfa N compensated for the low quality basal diet, N from 30% tarbush was utilized with similar efficiency to alfalfa N. The major impediment for using tarbush as a N source appeared to be low palatability.

Competition between three Chihuahuan desert species: evidence from plant size‐distance relations and root distribution

Abstract. Using size‐distance data we tested the intensity and importance of competition between Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a succulent) in the Chihuahuan desert. We also compared the vertical and horizontal distribution of roots to assess the potential degree of overlap in the use of soil resources. The relationships between sizes and distances of nearest‐neighbour plants suggested that intraspecific competition is generally more important than interspecific competition. However, evidence of stronger inter than intraspecific competition was found in some cases. Species combinations showing significant interspecific competition involved always Opuntia, whereas Larrea and Hilaria did not influence each other. The analysis of the symmetry of competition showed that Opuntia was adversely affected by the presence of Hilaria or Larrea.Although differences were found in the distribution of roots, the results of the size‐distance study support the idea that, (particularly) Opuntia, below‐ground niche differentiation is not sufficiently important to totally avoid the negative effects of plant competition.