Aristida Purpurea Research Articles

Fire and Nitrogen Effects on Aristida purpurea Mineral Concentrations

Purple threeawn (Aristida purpurea Nutt.) is a perennial bunchgrass indigenous to much of North America that often dominates disturbed or previously overgrazed rangelands and is mostly avoided by herbivores as forage. Management of threeawn using fire and nitrogen addition can increase its forage quality and likelihood of selection by livestock. We assessed effects of fire, nitrogen fertilizer addition, and phenological stage on purple threeawn mineral concentrations the first growing season postfire on two similar sites in southeastern Montana. Fire (no fire, summer fire, fall fire) and rate of nitrogen fertilizer addition (0, 46, 80 kg N·ha−1) were arranged in a completely randomized, fully factorial design. Samples were collected at five phenological stages throughout each growing season. Minerals were evaluated using laboratory analysis of potassium (K), calcium (Ca), phosphorus (P), sulfur (S), magnesium (Mg), iron (Fe), zinc (Zn), manganese (Mn), and copper (Cu) concentrations. With no nitrogen addition, summer and fall fire increased Ca from 0.22% to 0.38% and 0.31%, respectively, S from 0.08% to 0.15% and 0.13%, and Mg from 0.06% to 0.14% and 0.12%, while fall fire decreased Fe from 289 to 176 ppm. In the vegetative stage, fire (fall and summer averaged) increased K from 0.38% to 1.08%, Ca from 0.22% to 0.35%, P from 0.10% to 0.23%, S from 0.08% to 0.16%, Mg from 0.05% to 0.13%, Zn from 19.2 ppm to 35.8 ppm and Cu from 2.8 ppm to 6.2 ppm. Increasing rate of nitrogen addition and advancing phenological stage had little to no effect on mineral concentrations relative to fire effects. Results indicate prescribed fire can increase mineral concentrations from deficient levels to exceeding requirements for growing cattle, providing more evidence supporting use of prescribed fire to increase forage quality and potential herbivore utilization of purple threeawn within 1 yr following fire.

Comparative and Phylogenetic Analysis of Complete Plastomes among Aristidoideae Species (Poaceae).

Simple SummaryAristidoideae is a subfamily of Poaceae, including three genera, Aristida, Stipagrostis, and Sartidia. In this study, the plastomes of Aristida adscensionis and Stipagrostis pennata were newly sequenced, and a total of 16 Aristidoideae plastomes were compared. All plastomes were conservative in genome size, gene number, structure, and IR boundary. Repeat sequence analysis showed that forward and palindrome repeats were the most common repeat types. The number of SSRs ranged from 30 (Sartidia isaloensis) to 54 (Aristida purpurea). Codon usage analysis showed that plastome genes preferred to use codons ending with A/T. A total of 12 highly variable regions were screened, including four protein coding sequences and eight non-coding sequences. All Maximum Likelihood and Bayesian Inference trees strongly support the monophyly of Aristidoideae and each of the three genera. Within Aristidoideae, Aristida is sister to the clade composed of Stipagrostis and Sartidia. The divergence between C4 Stipagrostis and C3 Sartidia was estimated at 11.04 Ma, which may be associated with the drought event in the Miocene period. Finally, the differences in carbon fixation patterns, geographical distributions, and ploidy may be related to the difference of species numbers among these three genera. This study provides insights into the phylogeny and evolution of the subfamily Aristidoideae.Aristidoideae is a subfamily in the PACMAD clade of family Poaceae, including three genera, Aristida, Stipagrostis, and Sartidia. In this study, the plastomes of Aristida adscensionis and Stipagrostis pennata were newly sequenced, and a total of 16 Aristidoideae plastomes were compared. All plastomes were conservative in genome size, gene number, structure, and IR boundary. Repeat sequence analysis showed that forward and palindrome repeats were the most common repeat types. The number of SSRs ranged from 30 (Sartidia isaloensis) to 54 (Aristida purpurea). Codon usage analysis showed that plastome genes preferred to use codons ending with A/T. A total of 12 highly variable regions were screened, including four protein coding sequences (matK, ndhF, infA, and rpl32) and eight non-coding sequences (rpl16-1-rpl16-2, ccsA-ndhD, trnY-GUA-trnD-GUC, ndhF-rpl32, petN-trnC-GCA, trnT-GGU-trnE-UUC, trnG-GCC-trnfM-CAU, and rpl32-trnL-UAG). Furthermore, the phylogenetic position of this subfamily and their intergeneric relationships need to be illuminated. All Maximum Likelihood and Bayesian Inference trees strongly support the monophyly of Aristidoideae and each of three genera, and the clade of Aristidoideae and Panicoideae was a sister to other subfamilies in the PACMAD clade. Within Aristidoideae, Aristida is a sister to the clade composed of Stipagrostis and Sartidia. The divergence between C4 Stipagrostis and C3 Sartidia was estimated at 11.04 Ma, which may be associated with the drought event in the Miocene period. Finally, the differences in carbon fixation patterns, geographical distributions, and ploidy may be related to the difference of species numbers among these three genera. This study provides insights into the phylogeny and evolution of the subfamily Aristidoideae.

Notice of release of Menard Germplasm purple threeawn: a selected class of natural germplasm

Notice of release of Menard Germplasm purple threeawn: a selected class of natural germplasm

Germination and early establishment of dryland grasses and shrubs on intact and wind-eroded soils under greenhouse conditions

AimsGrassland-to-shrubland transition is a common form of land degradation in drylands worldwide. It is often attributed to changes in disturbance regimes, particularly overgrazing. A myriad of direct and indirect effects (e.g., accelerated soil erosion) of grazing may favor shrubs over grasses, but their relative importance is unclear. We tested the hypothesis that topsoil “winnowing” by wind erosion would differentially affect grass and shrub seedling establishment to promote shrub recruitment over that of grass.MethodsWe monitored germination and seedling growth of contrasting perennial grass (Bouteloua eriopoda, Sporobolus airoides, and Aristida purpurea) and shrub (Prosopis glandulosa, Atriplex canescens, and Larrea tridentata) functional groups on field-collected non-winnowed and winnowed soils under well-watered greenhouse conditions.ResultsNon-winnowed soils were finer-textured and had higher nutrient contents than winnowed soils, but based on desorption curves, winnowed soils had more plant-available moisture. Contrary to expectations, seed germination and seedling growth on winnowed and non-winnowed soils were comparable within a given species. The N2-fixing deciduous shrub P. glandulosa was first to emerge and complete germination, and had the greatest biomass accumulation of all species.ConclusionsGermination and early seedling growth of grasses and shrubs on winnowed soils were not adversely nor differentially affected comparing with that observed on non-winnowed soils under well-watered greenhouse conditions. Early germination and rapid growth may give P. glandulosa a competitive advantage over grasses and other shrub species at the establishment stage in grazed grasslands. Field establishment experiments are needed to confirm our findings in these controlled environment trials.

Caracterización del hábitat de Amoreuxia wrightii (Bixaceae), una especie en peligro de extinción en el noreste de México

Antecedentes y Objetivos: En México, Amoreuxia wrightii se encuentra en estatus de peligro de extinción de acuerdo a la NOM-059-SEMARNAT-2010. En este estudio se realizó la caracterización de poblaciones naturales de A. wrightii, mediante un análisis de la flora asociada y las propiedades físicas y químicas de los suelos donde se desarrollan en dos comunidades contrastadas desde el punto de vista de la cobertura del dosel en el matorral tamaulipeco en el noreste de México.Métodos: En 2014 se establecieron 10 sitios de muestreo en dos ambientes diferenciados por la estructura de la vegetación: cinco sitios en asociaciones vegetales con cobertura vegetal densa y cinco sitios en áreas perturbadas con suelo desnudo. En cada área se evaluó la estructura vegetal y variables edáficas y se realizó un Análisis de Correspondencia Canónica.Resultados clave: De acuerdo a la relación con otras especies, A. wrightii se asoció con especies pioneras, que emergen después de un disturbio, con el dominio de pastos como Aristida purpurea, Cenchrus ciliaris, Cynodon dactylon, Panicum obtusum, especies de herbáceas Gutierrezia sarothrae, Gymnosperma glutinosum y Parthenium hysterophorus, así como arbustos de porte bajo como Acacia amentacea, A. berlandieri y Eysenhardtia texana. De acuerdo con las variables edáficas, se observó que A. wrightii prefiere suelos arcillosos y limosos, con suelos con pH ligeramente alcalinos y con densidad aparente alta. Ningún individuo de A. wrightii fue registrado en sitios que presentaron suelos con altos contenidos de arena y altos contenidos de materia orgánica.Conclusiones: Amoreuxia wrightii fue más abundante en áreas con nula cobertura, desprovistas de vegetación, sobre suelos con bajo contenido de materia orgánica y altos contenidos de pH, limo, arcilla y densidad aparente. De acuerdo a la relación con otras especies, se asoció con especies pioneras, que emergen después de un disturbio.

Depleted Uranium Toxicity, Accumulation, and Uptake in Cynodon dactylon (Bermuda) and Aristida purpurea (Purple Threeawn).

Yuma Proving Grounds (YPG) in western Arizona is a testing range where Depleted uranium (DU) penetrators have been historically fired. A portion of the fired DU penetrators are being managed under controlled conditions by leaving them in place. The widespread use of DU in armor-penetrating weapons has raised environmental and human health concerns. The present study is focused on the onsite management approach and on the potential interactions with plants local to YPG. A 30day study was conducted to assess the toxicity of DU corrosion products (e.g., schoepite and meta-schoepite) in two grass species that are native to YPG, Bermuda (Cynodon dactylon) and Purple Threeawn (Aristida purpurea). In addition, the ability for plants to uptake DU was studied. The results of this study show a much lower threshold for biomass toxicity and higher plant concentrations, particularly in the roots than shoots, compared to previous studies.

Fire and Nitrogen Alter Axillary Bud Number and Activity in Purple Threeawn

Belowground accumulation of vegetative buds provides a reservoir of meristems that can be utilized following disturbance. Perennial grass bud banks are the primary source of nearly all tiller growth, yet understanding of fire and nitrogen effects on bud banks is limited. We tested effects of fire and nitrogen addition on bud banks of purple threeawn (Aristida purpurea Nutt.), a perennial C4 bunchgrass. Fire (no fire, summer fire, fall fire) and nitrogen addition (0, 46, 80 kg·ha-1) treatments were assigned in a completely randomized, fully factorial design and axillary buds were evaluated on two similar sites in southeastern Montana 1 and 2 years after fire. Permanently marked plants were assessed for live tiller production, and randomly selected tillers were sampled to determine active and dormant buds per tiller. Fire and nitrogen had opposite effects on axillary buds. Summer and fall fire reduced active buds by 42% relative to nonburned plots. Adding nitrogen at 46 or 80 kg·ha-1 increased active buds per tiller 60% compared with plots with no nitrogen addition. The number of dormant buds per tiller was similar across fire treatments and levels of nitrogen. Fire and nitrogen had interacting effects on total buds at the tiller level. Without nitrogen addition, fall and summer fire reduced total buds per tiller about 70%. Nitrogen had no effect on total buds per tiller for nonburned plants. However, total number of buds per tiller was greater with nitrogen addition following fall fire and increased with each increase in nitrogen following summer fire. Results indicate fire effectively controls purple threeawn through bud bank reduction and that nitrogen can stimulate bud production. Interacting effects of fire and nitrogen on buds reveal a potential source of inconsistency in nitrogen effects and a possible method of facilitating recovery of fire-sensitive bunchgrasses after fire.

Fire and nitrogen alter axillary bud number and activity in purple threeawn

Fire and nitrogen alter axillary bud number and activity in purple threeawn

Fire and Nitrogen Addition Increase Forage Quality of Aristida purpurea

Purple threeawn (Aristida purpurea Nutt.) is a native perennial bunchgrass with limited forage value that dominates sites with disturbed soils and persists with repeated severe grazing. Fire and nitrogen addition have been used to reduce threeawn and can increase grazing utilization of threeawn by livestock. We evaluated effects of fire, spring urea addition, and phenological stage on purple threeawn forage quality 1 yr postfire on two similar sites in southeastern Montana during the 2011 (site 1) and 2012 (site 2) growing seasons. Fire (no fire, summer fire, fall fire) and rate of nitrogen addition (0, 46, 80 kg N·ha-1) were arranged in a completely randomized, fully factorial design. Samples were collected at five phenological stages throughout each growing season. Forage quality was assessed using nutrient analyses of crude protein (CP), net energy (NEm), and total digestible nutrients; antiquality analyses of neutral detergent fiber (NDF), acid detergent fiber, and silica; in vitro fermentation for organic matter disappearance (IVOMD) and NDF disappearance; and gas production (asymptotic [maximum] gas production, fractional rate of gas production, lag time, and average fermentation rate). In vegetative stages, summer and fall fire increased CP from 6.2% to 12.1% and 13.0%, respectively, and NDF decreased from 72.1% to 69.4% and 68.2%, respectively. Summer and fall fire reduce silica content from 7.0% to 4.1% and 4.3%, respectively. Purple threeawn IVOMD increased by 14.0% and 13.0% following summer and fall fire, respectively, compared to nonburned plots. Nitrogen addition increased CP from 7.5% to 8.0% and 8.4%, respectively, with 46% and 80 kg N·ha-1, respectively. In vitro fermentation and gas production variables did not change due to nitrogen addition. Fire generally improved purple threeawn forage quality to a greater extent than did nitrogen addition. Results indicate fire can potentially improve the suitability of purple threeawn as a forage species.

Fire Effects on Basal Area, Tiller Production, and Mortality of the C4 Bunchgrass, Purple Threeawn

AbstractFire behavior associated with wild and prescribed fires is variable, but plays a vital role in how a plant responds to fire. Understanding the relationship between fire behavior and rangeland plant community response will help to improve the use of prescribed fire to achieve management objectives. Fire is an important ecological process in many rangeland ecosystems and can be used as a tool to maintain grassland plant communities and shift community composition. Purple threeawn (Aristida purpurea Nutt.) is a grass native to North America that has poor forage quality and the ability to form near monocultures. Therefore, the identification of tools to reduce purple threeawn abundance is desirable. We assessed the effects of summer and fall prescribed fire on purple threeawn plant basal area, tiller production, and plant mortality one growing season post fire in the northern Great Plains. Thermocouples and portable data loggers were used to measure the maximum temperature, heat duration, and heat dosage that individual purple threeawn plants experienced. Fire reduced basal area and tiller production 59 % and 57 %, respectively. Heat dosage (C-statistic = 0.69) and heat duration (C-statistic = 0.65) were good predictors of purple threeawn mortality. A restrospective analysis showed maximum temperatures were similar for fall and summer fires but heat duration and dosage were 44 % and 21 % greater for summer fires, respectively. Our results indicate that purple threeawn is a fire sensitive species. The ability to predict purple threeawn mortality could enhance the efficacy of prescribed fire as tool to restore purple threeawn and other Aristida-dominated plant communities.

Fire and Nitrogen Effects on Purple Threeawn (Aristida purpurea) Abundance in Northern Mixed-Grass Prairie Old Fields

Purple threeawn (Aristida purpurea Nutt. varieties) is a native grass capable of increasing on rangelands, forming near monocultures, and creating a stable state. Productive rangelands throughout the Great Plains and Intermountain West have experienced increases in purple threeawn abundance, reducing overall forage quality. Our objectives were to 1) reveal the effects of prescribed fire and nitrogen amendments on purple threeawn abundance and 2) assess nontarget plant response posttreatment. Season of fire (no fire, summer fire, fall fire) and nitrogen addition (0kg N · ha−1, 46kg N · ha−1, and 80kg N · ha−1) were factorially arranged in a completely randomized design and applied to two similar sites in southeastern Montana. We evaluated fire and nitrogen effects on purple threeawn basal cover, relative composition, and current-year biomass one growing season postfire at two sites treated during different years. Spring weather following fire treatments was very different between years and subsequently impacted community response. Initial purple threeawn biomass at both sites was 1 214 ± 46kg · ha−1 SEc. When postfire growing conditions were wet, current-year biomass of purple threeawn was reduced 90% and 73% with summer and fall fire, respectively. Under dry postfire growing conditions, purple threeawn current-year biomass was reduced 73% and 58% with summer and fall fire, respectively. Nitrogen additions had no effect on purple threeawn current-year biomass at either site. Current-year biomass of C3 perennial grass doubled with nitrogen additions and was not impacted by fire during a wet spring. Nitrogen additions and fire had no effect on C3 perennial grass current-year biomass following a dry spring. Prescribed fire appears to be a highly effective tool for reducing purple threeawn abundance on semiarid rangelands, with limited detrimental impacts to nontarget species.

Fire, Defoliation, and Competing Species Alter Aristida purpurea Biomass, Tiller, and Axillary Bud Production

Aristida purpurea (purple threeawn) is a competitive native perennial grass with monoculturistic tendencies and poor palatability. We examined effects of fire, defoliation, and interspecific/intraspecific planting for 1) threeawn responses in the presence of threeawn, Bouteloua gracilis, or Pascopyrum smithii, and 2) B. gracilis and P. smithii response with threeawn. Biomass, aboveground production, tillers, and axillary buds were analyzed following two fire and four clipping treatments applied to three species–pair combinations in a completely randomized factorial design with nine replications. Fire killed 36% of threeawn. Fire reduced surviving threeawn biomass 61% and reduced production 27%. Threeawn production was greatest when neither plant was clipped and least when competing species were moderately clipped, or when both plants were severely clipped. Tiller counts of burned threeawn were similar among clipping treatments, and less than non-clipped or moderately clipped plants not burned. Fire decreased threeawn axillary buds on average by 25%. Moderately clipped plants had greater production than those from other clipping treatments across species. Average threeawn percentage of pot biomass was greater with B. gracilis (46±3% SE) than P. smithii (38±3% SE). Fire reduced threeawn from 60±3% to 23±3% of pot biomass, indicating good potential for rapid reductions in threeawn dominance and restoration of plant diversity with fire.

A Nondestructive Method to Estimate Standing Crop of Purple Threeawn and Blue Grama

We used multiple regression analysis to develop models to predict standing crop of purple threeawn (Aristida purpurea Nutt.) and blue grama (Bouteloua gracilis [H.B.K.] Griffiths) nondestructively. Data were collected for 3 yr on the Texas Tech University Native Rangeland, Lubbock, TX, USA. Independent variables included plant length and area measurements (basal area and cross-sectional area at a 7.5-cm plant height and at 50% of total plant height). One hundred randomly selected plants of each species were measured in June 2008; 50 plants of each species were measured in June 2009 and 2010. Coefficients of determination exceeded 0.91 for both species in all 3 yr of measurement. For both species and years, cross-sectional area at 7.5 cm was the most important single predictor variable. For each species, models differed among years. Our regression models were successful at predicting mid- to late-season standing crop of purple threeawn and blue grama grass and provide an effective method for nondestructive monitoring of these species. This approach should be applicable to similar morphotypes of these species.

Fire in Chihuahuan Desert grassland: Short-term effects on vegetation, small mammal populations, and faunal pedoturbation

A prescribed burn resulted in significant decreases in canopy cover of the grasses: Bouteloua eriopoda, Sporobolus flexuosus, and Aristida purpurea. One year post-burn, basal cover of B. eriopoda remained significantly lower in burned patches than in unburned areas but there were no differences in basal cover of the other perennial grasses. Only one species of the 14 summer annual species occurred in both burned and unburned plots. There were six species of spring annuals in burned patches but no spring annuals in the unburned grassland ten months post-burn. Fire killed 100% of the snakeweed shrubs ( Gutierrezia sarothrae), 77% of the Ephedra torreyana shrubs, and 36% of the Yucca elata. All mesquite shrubs that were top-killed by fire, resprouted one month post-burn. Fire had no effect on abundance and species richness of rodents. There were fewer wolf spider, Geolycosa spp. burrows in burned areas than in unburned grassland. The area and volume of soil in termite galleries and sheeting were significantly larger in the unburned grassland than in the burned areas.

Using a diverse seed mix to establish native plants on a Sonoran Desert burn

Revegetating burns is a major challenge facing resource managers in the low- and unpredictable-precipitation deserts of the southwestern US. We monitored the effectiveness of using a diverse, 28-species seed mix for establishing native plants on a 1.5-ha (3.7-ac) burn in the northern Sonoran Desert. Our objective was to compare species performances, which we assessed by measuring species frequencies and cover on 5 sampling dates to capture variation during a 32-mo period following seeding. By 15 mo after seeding, desert senna ( Senna covesii (Gray) Irwin & Barneby [Fabaceae]) established best, with a frequency of 91% (based on 22, 10-m2 plots) and a relative cover of 19%. Four other seeded species also became established in ≥ 50% of plots by 32 mo after seeding. Several seeded species, including desert senna (which flowered only 7 wk after seeding) and purple threeawn ( Aristida purpurea Nutt. [Poaceae]), were observed with seed heads during one or more sampling periods. Although precipitation was only 67% of normal for 21 mo following seeding and 71% of species established in < 10% of plots, we consider the seeding to have met short-term management objectives because of the subset of highly successful species. Our results also illustrate the caution that should be used when evaluating seeding success: conclusions would have differed if the diversity of the seed mix had not included the successful species, and longer term monitoring was needed to detect some species in the seed mix that did not establish until 32 mo after seeding.

Ecophysiological responses of Chihuahuan desert grasses to fire

To better understand the effects of fire in the Chihuahuan desert, gas exchange characteristics of two dominant grass species, Bouteloua eriopoda and Aristida purpurea, and soil nitrogen availability were studied in response to prescribed fire at the Jornada Experimental Range in southern New Mexico. Burned and unburned plant individuals were measured before and after fire. Rates of net photosynthesis and stomatal conductance were highest in burned individuals, with those of A. purpurea exceeding B. eriopoda. Soil nitrogen supply rates increased compared to unburned controls. Similar to other grasslands where fire is common, physiological characteristics of vegetation responded positively. These adaptations indicate that fire may be beneficial in the preservation and restoration of native grasses.

Long-Term Effects of a Summer Fire on Desert Grassland Plant Demographics in New Mexico

Plant demographic responses to an experimental summer fire were monitored for 12 yr on the Sevilleta National Wildlife Refuge, New Mexico, to determine recovery rates of burned plants and evaluate fire effectiveness in preventing shrub invasion of desert grasslands. Fourteen common species of grasses, shrubs, yucca, and cacti were measured for mortality, resprouting, regrowth, herbivory, and reproduction. After the first postfire growing season, black grama (Bouteloua eriopoda [Torr.] Torr.) declined 80% in size, whereas blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. ex Griffiths) exhibited no decline. Linear regression indicated that B. eriopoda needed 11 yr to recover. Spike dropseed (Sporobolus contractus A.S. Hitchc.) and purple three-awn (Aristida purpurea Nutt.) showed postfire declines in plant sizes, requiring 4- and > 5-yr recovery times, respectively. Sand muhly (Muhlenbergia arenicola Buckl.) exhibited no fire impact. Snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby) sustained 61% fire mortality and reduction in regrowth canopy size. Creosotebush (Larrea tridentata [Sesse & Moc. ex DC.] Coville) had 12% mortality, but survivors recovered over 12 yr. Fourwing saltbush (Atriplex canescens [Pursh] Nutt.) sustained 62% mortality, but recovered plant size in 5–6 yr. Winterfat (Krascheninnikovia lanata [Pursh] A. D. J. Meeuse & Smit) suffered 7% mortality, but required 9+ yr to recover. Pale desert-thorn (Lycium pallidum Miers) survived fire, recovering prefire canopy size in 3 yr. Torrey joint-fir (Ephedra torreyana Watson) exhibited < 1% mortality, and recovered in 2–3 yr. Soapweed yucca (Yucca glauca Nutt.) had < 2% mortality, recovered plant sizes in 2 yr, and increased numbers of rosettes 17%. Chollas (Opuntia imbricata [Haw.] DC. and Opuntia clavata Engelm.) suffered high mortality rates and required > 12 yr recovery times. Results demonstrated that summer fire may counter some shrub and cacti invasion in central New Mexico, but once shrubs mature, fire is less effective in removing woody plants to restore southwestern grasslands. Las respuestas demográficas de vegetación a un fuego experimental de verano fue monitoreado por 12 años en el Refugio Nacional de Fauna Silvestre Sevilleta, Nuevo México, para determinar las tasas de recuperación de plantas quemadas y evaluar la eficacia del fuego para la prevención de invasiones de arbustos en los pastizales de desierto. Catorce especies comunes de pastos, arbustos, yuca y cactus fueron medidas para determinar la mortalidad, el rebrote, el crecimiento, la herbívoria y la reproducción. Después de la primera temporada de crecimiento posterior a la quema, el tamaño de la navajita negra (Bouteloua eriopoda [Torr.] Torr.) disminuyó en un 80%, mientras que la navajita azul (B. gracilis [Willd. ex Kunth] Lag. ex Griffiths) no mostró ninguna disminución. El modelo de regresión linear indica que B. eriopoda necesitó 11 años para recuperarse. El zacate espigado (Sporobolus contractus A.S. Hitchc.) y el zacate tres barbas (Aristida purpurea Nutt.) también mostraron una reducción en el tamaño de las plantas después del fuego, y necesitaron 4 y >5 años de recuperacion respectivamente. El mal forrage (Muhlenbergia arenicola Buckl.) no mostró ningún efecto al fuego. El romerito (Gutierrezia sarothrae [Pursh] Britt. & Rusby) sufrió una mortalidad de 61% y una reducción el rebrote del tamaño del dosel por el incendio. La gobernadora (Larrea tridentata [Sesse & Moc. ex DC.] Coville) tuvo una mortalidad de 12%, pero las plantas sobrevivientes se recobraron en 12 años. El chamiso (Atriplex canescens [Pursh] Nutt.) sufrió 62% de mortalidad, pero el tamaño de planta se recuperó en 5–6 años. EL senecio (Krascheninnikovia lanata [Pursh] A. D. J. Meeuse & Smit) sufrió una mortalidad de 7%, pero tomo 9+ años para recuperarse. La mora de lobo (Lycium pallidum Miers) sobrevivió el fuego, recuperando tamaño del dosel en 3 años. La caniatilla (Ephedra torreyana Watson) mostró <1% mortalidad y se recuperó en 2–3 años. La yuca (Yucca glauca Nutt.) tuvo una mortalidad menor al 2%, recobró su tamaño en 2 años y aumentó el número de panículas en 17%. Las chollas (Opuntia imbricata [Haw.] DC. y O. clavata Engelm.) mostraron altas tasas de mortalidad y requirieron >12 años para su recuperación. Los resultados demuestran que un incendio en verano podria contrarrestar la invasión de arbustos y cactus en el centro de Nuevo Mexico, pero una vez que los arbustos están establecidos, el fuego es menos efectivo para remover plantas leñosas y restaurar los pastos del suroeste.

Canopy-tree influences along a soil parent material gradient in Pinus ponderosa-Quercus gambelii forests, northern Arizona

Abstract The distribution of canopy trees can impose within-site patterns of soil properties and understory plant composition. At ten sites spanning a soil parent material gradient in northern Arizona Pinus ponderosa-Quercus gambelii forests, we compared soils and plant composition among five canopy types: openings, Pinus ponderosa single trees, Quercus gambelii single stems, dispersed clumps, and thickets. Soil texture on average did not differ significantly among canopy types, whereas Oi horizon thickness and weight, 0–15 cm soil loss-on-ignition, and gravimetric soil moisture differed significantly among three or more canopy types. Understory plant richness per 4 m2 ranged from five species below P. ponderosa to 12 species in openings, with richness below Q. gambelii single stems significantly greater than below Q. gambelii thickets. C4 graminoids (e.g., Aristida purpurea) inhabited openings, while C3 species like Poa fendleriana also occurred below trees. The forbs Thalictrum fendleri and Lathyrus lae...

Uptake of Munitions-Derived Depleted Uranium by Three Grass Species

Uptake of depleted uranium (DU, 238U) derived from weathered munitions was assessed in a greenhouse experiment utilizing three common grass species, Schizachyrium scoparium (little bluestem), Buchloe dactyloides (buffalograss), and Aristida purpurea (purple threeawn). Both aboveground and belowground uptake was dependent on the soil DU concentration, and on the experimental moisture regime utilized during the experimental duration. Uptake was enhanced under higher moisture regimes, suggesting a greater degree of DU solubility and concomitant plant availability. Concentration ratios (calculated by dividing plant tissue DU concentrations by soil DU concentrations) decreased with increasing soil DU concentrations, but increased as more moisture was applied. The toxicity level of DU in root tissue was estimated to 270 mg kg−1.

Vegetation response of a mesquite-mixed brush community to aeration

Responses of plant communities to mechanical treatments such as aeration on semiarid rangelands are not clearly understood. Our objective was to compare woody and herbaceous plant cover, density, and diversity on aerated and nontreated rangelands. Five rangeland sites that were aerated with a double/tandem drum aerator during summer 1998 and 5 sites of nontreated rangeland were selected for study on the Chaparral Wildlife Management Area, La Salle County, Tex. Woody plant cover was estimated using the line-intercept method, and stem density was estimated in 30 × 1.5 m plots in 1999 and 2000. Forb and grass cover and density were estimated in 20 × 50 cm quadrats during spring and fall 1999. Woody and herbaceous plant diversity did not differ between treatments. On aerated sites percent woody plant cover was 4-fold less 1-year after aeration and increased 89% from the first to the second growing-season post treatment. Canopy cover of honey mesquite (Prosopis glandulosa Torr.), twisted acacia (Acacia schaffneri S. Wats.), and Texas pricklypear (Opuntia lindheimeri Engelm.) was greater on non-treated sites. By the second growing season after aeration, density of honey mesquite was greater on aerated sites, whereas Texas pricklypear had declined on aerated sites. Density of spiny hackberry (Celtis pallida Torr.) and Texas persimmon (Diospyros texana Scheele) was greater on aerated sites during the first growing-season post treatment. Cover and stem density of hog-plum (Colubrina texana T. G.), coma (Bumelia celastrina Kunth), and whitebrush [Aloysia gratissima (Gill. Hook.) Tron.] did not differ among aerated and nontreated sites by the first growing season after aeration. Forb cover was greater on aerated sites in spring 1999. Fringed signalgrass [Brachiaria ciliatissima (Buckl.) Chase], fall witchgrass [Digitaria cognata (Schult.) Pilger], and bristlegrass (Setaria spp. Beauv.) cover was greater on aerated sites in spring and fall 1999, whereas purple threeawn (Aristida purpurea Nutt.) was greater on nontreated sites. It is unclear to what degree environmental factors such as pre- and post-treatment climatic conditions and herbivory may have influenced vegetation response to aeration. The rapid regrowth of many woody plants following aeration may require the application of maintenance treatments within a relatively short time period to maintain treatment benefits. Aeration reduced total woody plant cover, increased the density of desirable woody plants, maintained woody plant diversity, increased grass cover, and may be a useful tool in managing South Texas rangelands for white-tailed deer (Odocoileus virginianus Boddaert) and cattle.