Welcome to the Rangeland Ecology & Management archives. The journal Rangeland Ecology & Management (RE&M; v58, 2005-present) is the successor to the Journal of Range Management (JRM; v. 1-57, 1948-2004.) The archives provide public access, in a "rolling window" agreement with the Society for Range Management, to both titles (JRM and RE&M), from v.1 up to five years from the present year.

The most recent years of RE&M are available through membership in the Society for Range Management (SRM). Membership in SRM is a means to access current information and dialogue on rangeland management.

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Print ISSN: 0022-409x

Online ISSN: 1550-7424


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Recent Submissions

  • Range condition influences on Chihuahuan Desert cattle and jackrabbit diets

    Daniel, A.; Holechek, J. L.; Valdez, R.; Tembo, A.; Saiwana, L.; Rusco, M.; Cardenas, M. (Society for Range Management, 1993-07-01)
    Knowledge of comparative diet selection by cattle and black-tailed jackrabbits (Lepus californicus) would permit better estimation of grazing capacity on Chihuahuan desert ranges. Cattle and black-tailed jackrabbit diets were evaluated seasonally on good and fair condition ranges over a 2-year period. Fecal samples analyzed by the microhistological technique were used to determine diets of both animals. Key forage species in cattle diets were dropseeds (Sporobolus sp.), black grama (Bouteloua eriopoda Torr.), leatherweed croton (Croton pottsii Lam.), and bush muhly (Muhlenbergia porteri Scribn.). Key forage species in jackrabbit diets were honey mesquite (Prosopis glandulosa Torr.), cactus (Opuntia sp.), dropseed, broom snakeweed (Gutierrezia sarothrae Pursh.), and black grama. Overall diet botanical composition data showed cattle consumed 58% grass compared to 22% for jackrabbits (P < 0.05). Forb consumption was similar between the 2 animals and averaged about 31%. Shrub consumption averaged 47% and 12% for jackrabbits and cattle, respectively (P < 0.05). Range condition did not influence total grass consumption by either animal. Both animals, however, had lower forb and higher shrub consumption on fair compared to good condition range. Overall dietary overlaps between jackrabbits and cattle were 40 and 42% on good and fair condition ranges, respectively. Poisonous plants contributed up to 14 and 36% of cattle and jackrabbit diets, respectively. Data from this study show little forage competition occurs between cattle and jackrabbits when stocking rates and jackrabbit numbers are moderate. Several plants poisonous and unpalatable to cattle were important jackrabbit foods. These plants were more prevalent on the fair compared to the good condition range.
  • Mass-diameter regressions for moose browse on the Copper River Delta, Alaska

    MacCracken, J. G.; Van Ballenberghe, V. (Society for Range Management, 1993-07-01)
    Regression equations were developed to predict 3 mass components of 7 browse species important to moose (Alces gigas) on the Copper River Delta in southcentral Alaska. The accuracy of model predictions was the criterion for model selection. Model accuracy was evaluated using data splitting or jackknife procedures. Annual production of twigs and leaves and available twig mass on a stem were most accurately predicted from stem basal diameter with zero intercept models, zero intercept log-linear models, or log-log models. Twig mass eaten by moose was most accurately predicted from the diameter at the point of browsing of a twig with zero intercept or full linear models. Heteroskedasticity was significant (P < 0.05) in most of the data sets and could not be significantly reduced with log transformations or use of weighted least squares models. Heteroskedasticity appeared to have a relatively minor effect on model predictions. Most of the models gave mean predictions within +/- 20% of the actual values, particularly for the most ubiquitous species that were also the most important to moose. For each species, there were few differences (P < 0.05) in model coefficients between years and among habitat types. Differences in coefficient estimates appeared to be related to differences in stem morphology that were related to both site conditions and past browsing by moose.
  • Long-term effects of root plowing on vegetation in the eastern south Texas plains

    Ruthven, D. C. III.; Fulbright, T. E.; Beasom, S. L.; Hellgren, E. C. (Society for Range Management, 1993-07-01)
    The long-term effects of root plowing in plant communities in south Texas are not clearly understood. Our objective was to compare plant species composition and diversity on root-plowed rangelands and untreated rangelands. Two rangeland sites that were root plowed during 1973-74 and 2 sites of native, untreated brush were selected on the Santa Gertrudis Division of the King Ranch, Kleberg and Jim Wells counties, Texas. Woody plant canopy cover was estimated with the line intercept method, and density was estimated with 20-X 1-m plots during 1990. Herbaceous canopy cover was estimated with 20 X 50-cm quadrats. Percent grass, lifter, and bare ground coverage were similar on root-plowed and untreated rangelands. Woody plant species and diversity averaged 19 +/- 2 species/ treatment (average +/- SE) and 2.56 +/- 0.15 on untreated areas compared to 7 +/- 1 species/treatment and 1.18 +/- 0.01 on root-plowed areas. Forb canopy coverage on root-plowed sites was about twice that of untreated sites. Huisache (Acacia smallii Ilsey) canopy cover and density were both more than 7-fold greater on root-plowed sites than on untreated sites. Browse species preferred by white-tailed deer (Odocoileus virginianus Raf.), such as colima [Zanthoxylum fagara (L.) Sarg.] and guajillo (Acacia berlandieri Benth.), were absent on root-plowed sites.
  • Livestock grazing impacts on infiltration rates in a temperate range of Pakistan

    Bari, F.; Wood, M. K.; Murray, L. (Society for Range Management, 1993-07-01)
    This study was conducted in a temperate range of northern Pakistan in 1987 and 1988. The main purpose of the experiment was to determine a suitable residual phytomass level for the moist temperate ranges of Pakistan. Data were collected for 2 consecutive growing seasons. A completely randomized design, with 4 treatments and 2 replications, was used. The treatments were 4 different residual phytomass levels. A rainfall simulator applied rainfall to 48 flexible circular plots (1m2). Analysis of variance and the LSD multiple mean comparisons determined treatment differences, and stepwise multiple regression identified the important vegetation and soil variables affecting infiltration. The control (no grazing) resulted in the highest infiltration while the treatment having the lowest residual phytomass had the lowest infiltration. Among the independent variables, standing phytomass was the most important variable affecting infiltration. Foliar and basal cover were also highly correlated to infiltration.
  • Influence of litter on herbage production in the mixed prairie

    Willms, W. D.; McGinn, S. M.; Dormaar, J. F. (Society for Range Management, 1993-07-01)
    Lifter (dead plant material) increases production in xeric environments but the nature of this effect is uncertain. The purpose of this study was to determine the relationship between liner quantity and herbage production over a 4-year period as well as to determine the effect of repeated removal of lifter on production. The study was made in a Stipa-Bouteloua-Agropyron faciation of the Mixed Prairie association, near Lethbridge, Alberta, Canada. Litter quantity was altered by mechanical removal before spring growth and the residue separated into coarse and fine components. In Experiment 1, the effect of lifter on herbage production was tested by removing lifter at 0, medium, and high levels that resulted in an average residue of coarse liner of 1,171, 787, and 377 kg ha-1. Coarse litter was related to an increase in herbage production (P < 0.05) in 3 of the 4 years studied. The effects of lifter were related to the growing conditions of each year. The linear regression coefficients describing the response (herbage production related to litter) ranged from 0.114 to 0.802 with the smallest effect under either very dry or very wet conditions. In Experiment 2, lifter was removed at high levels in either 0, 1, 2, or 3 successive years. These treatments resulted in an average residue of coarse litter of 1,300, 164, 149, and 188 kg ha-1. Herbage production was not affected by removing litter for more than 1 year but plant height, tiller weight, and herbage yield of some plant species were.
  • Improvement of dry tropical rangelands in Hainan Island, China: 2. Evaluation of pasture grasses

    Michalk, D. L.; Fu, N. P.; Zhu, C. M. (Society for Range Management, 1993-07-01)
    During 1981-83, we studied 19 grasses for potential improvement of dry tropical (1,001 mm annual rainfall) rangelands in Hainan Island, China. The productivity and persistence of the grasses were tested on sandy (< 5 mg/kg available P) and loam sods (12-25 mg/kg) under cutting in a randomized block design with plots split for sequential sowings in 1981, 1982, and 1983. Grass response to legume-fixed and nitrogen fertilizer was also assessed. Thirteen of the 19 grasses tested under cutting established satisfactorily (density > 5 plants/m2), but only 6 cultivars produced yields > 1.5 metric tonne (t)/ha. Melinis minutiflora Beauv., Brachiaria decumbens Stapf. and Chloris gayana Kunth. yielded more than 1.5 t/ha in 3-year-old swards on both soils, whereas Panicum maximum Jacq. and Setaria sphacelata (Schum.) Stapf. ex Massey only performed well on fertile loam soil. Grass establishment was superior on sandy soil, but plant density did not correlate well with production which was higher on red loam soil due to better waterholding capacity and nutrient status. Compatibility of these successful grasses with companion legumes was low with legumes contributing < 0 .4 t/ha to total yield of 3-year-old M. minutiflora, B. decumbens and P. maximum swards, and having minimal effect on soil nitrogen. Nitrogen fertilizer (50 kg N/ha/yr) more than doubled grass production, but was profitable only where grass response exceeded grass/legume swards > 4 t/ha. S. sphacelata was the only grass to form a stable mixture with companion legumes. [Macroptilium atropurpurem (D.C.) Urban and Stylosanthes guianensis (Aubl.) Sw.], which yielded more than 1.1 t/ha in 3-year-old swards on loam soil. This combination was recommended for improvement of loam soil rangelands. It is concluded from this study that range improvement with perennial grasses is confined to fertile soils, while direct broadcast of Stylosanthes legumes only into grazed native pastures is the practice recommended for improvement of infertile sandy soil until persistent low P tolerant grasses are found for the dry tropics.
  • Improvement of dry tropical rangelands in Hainan Island, China: 1. Evaluation of pasture legumes

    Michalk, D. L.; Fun, N. P.; Zhu, C. M. (Society for Range Management, 1993-07-01)
    During 1981-83, we studied some legumes for potential improvement of dry tropical (1,001 mm annual rainfall) rangelands in Hainan Island, China. The productivity and persistence of 16 pasture legumes were tested on sandy (< 5 mg/kg available P) and loam (12-25 mg/kg) soils under cutting in a randomized block design with plots split for sequential sowings in 1981, 1982, and 1983. Dry matter yield, sward composition, and legume density were measured at the end of the wet and dry seasons each year. Thirteen legumes established with density averaged over 3 sequential sowings > 1 plant/m2 on 1 or both soils, but only 5 perennial stylos (Stylosanthes), siratro [Macroptilium atropurpureum (D.C.) Urban], and centro (Centrosema pubescens Benth) (loam soil only) persisted through 2 dry seasons and yielded more than 0.5 metric tonne (t)/ha in 3-year-old swards. S. guianensis (Aubl.) Sw. cv Cook yielded best on both soils, but proved less tolerant to fire than cv Graham, which is the common stylo recommended by this study as a companion for siratro for improvement of loam soil rangeland. Siratro was the only non-stylo to produce > 2 t/ha and show relative stability with sward age, but careful grazing management and regular fertilization are needed to maintain siratro content above 40% in commercial sowings. Tolerance to fire, low P requirement, and high yield in 2- and 3-year-old stands makes S. scabra Vog. cv Seca the most suitable legume for sandy soil, but since it is slow to establish, a mixture of S. scabra and S. hamata (L.) Taub. cv Verano which is noted for its quick establishment and prolific seed production is recommended for range improvement of low P soils.
  • Habitat relationships of the pyrenean gray partridge

    Lescourret, F.; Génard, M. (Society for Range Management, 1993-07-01)
    Summer habitat relationships of the pyrenean gray partridge (Perdix peridix hispaniensis) were studied in the northern Pyrenees Mountains (France). Six available habitat types were defined, and those selected or avoided were identified. The only habitat type significantly (P < 0.05) selected was at intermediate altitudes, on fairly steep south-exposed slopes, with a moderate cover of woody plants. Two habitat types were significantly avoided. One occurred at low altitudes on mowed plateaus colonized by low woody plants, and the other was at high altitudes on slopes free of low woody plants. We suggest applications of the work in a model that should lead to valid habitat recommendations for restoring partridge populations.
  • Genotype and planting depth effects on seedling vigor in sericea lespedeza

    Qiu, J.; Mosjidis, J. A. (Society for Range Management, 1993-07-01)
    Sericea lespedeza [Lespedeza cuneata (Dumont de Courset) G. Don.] is a small-seeded forage legume that can improve forage quality and nitrogen content of interseeded pasturelands. Poor seedling vigor has caused interseeding failure. This study was conducted to determine the effects of genotype, planting depth, and their interaction on seeding vigor of services lespedeza in the field, and to determine if seedling traits measured in a growth chamber can be used to predict seedling growth in the field. Substantial variability was found among 54 sericea lespedeza genotypes for traits that can be used in a breeding program to improve seedling vigor. All seedling traits were correlated with each other, indicating a high proportionality existed among plant parts. Thus, any of the seedling traits measured could be used to represent seedling vigor. Genotypes 73-162-16, AU L2, AU L13, and 'Serala 76' outperformed other genotypes for most seedling traits under field and growth chamber conditions. Planting to a depth of 3 cm did not reduce seedling vigor, and therefore, may be recommended when there is insufficient moisture in the upper layer of sandy loam soils at planting. Although measurements taken in the growth chamber did not reliably predict field performance, information gathered in the growth chamber provides a good means of increasing the frequency of superior plants to be tested in the field.
  • Field stratification of antelope bitterbrush seeds

    Young, J. A.; Wight, J. R.; Mowbray, J. E. (Society for Range Management, 1993-07-01)
    The germination ecology of antelope bitterbrush [Purshia tridentata (Pursh) Nutt.] seed has probably been investigated more than any other range shrub. Seeds of this valuable browse species are known to require moist prechilling before they will germinate. Our purpose was to investigate the nature of this dormancy breaking by placing packages (2 X 2-mm mesh screen) of seeds on the surface and buried in the seedbed at several locations in Idaho and Nevada and to recover the seeds monthly through the winter. The seeds were categorized based on their being: (a) capable of germinating; (b) dormant; or (c) dead at each recovery. The seedbeds of the 2 sites in Nevada, during 2 years of drought, were not sufficiently wet to bring large amounts of the antelope bitterbrush seeds out of dormancy. The seeds did not rot in the field, and being protected from predation, they remained dormant in the seedbed. The highest elevation site in Idaho had as high as 80% of the seeds lose dormancy. If seedbed microenvironmental conditions were satisfactory, the inherent seed dormancy was lost by midwinter. Snow cover, as it influences seedbed moisture and temperatures, apparently is an important factor in the prechilling of antelope bitterbrush seeds.
  • Effects of sericea lespedeza root exudates on some perennial grasses

    Kalburtji, K. L.; Mosjidis, J. A. (Society for Range Management, 1993-07-01)
    Root exudates are substances released into the surrounding medium by healthy and intact plant roots. Research on root exudates has shown that root exudates can reduce seed germination and plant growth. There is no information on the effect of sericea lespedeza [Lespedeza cuneata (Dum. de Cours) G. Don.] root exudates on other plants. In a series of greenhouse experiments we studied (1) if sericea root exudates affect seed germination and seedling growth of the perennial grasses tall fescue (Festuca arundinacea Schreb.), bermudagrass [Cynodon dactylon (L.) Pers.], and bahiagrass (Paspalum notatum Flugge); and (2) if any such responses were cultivar dependent. The effects of the root exudates were measured in 2 experiments. In the first one, coarse perlite was used as a medium to measure seed germination and radicle and coleoptile growth. In the second experiment, soil was used as a medium to measure emergence and biomass. Root exudates from sericea lespedeza had no effect on germination and emergence of tall fescue and bahiagrass but reduced their radicle and coleoptile length and biomass. Germination, radicle, and coleoptile length, and emergence of bermudagrass decreased when exposed to the root exudates; however, biomass was not affected. Cultivars of the grass species differed in their response to the root exudates of sericea lespedeza. Thus, establishment of tall fescue in mixture with sericea lespedeza is not likely to be affected; however, its growth is likely to be decreased. Therefore, tall fescue contribution to total yield will be reduced. Conversely, establishment of bermudagrass is likely to be affected, but once established, its growth is expected to be similar to its grown alone.
  • Effects of sericea lespedeza residues on cool-season grasses

    Kalburtji, K. L.; Mosjidis, J. A. (Society for Range Management, 1993-07-01)
    Incorporation of crop residues into the soil prior to planting has been shown to reduce the growth of subsequent crops. Information is limited on the allelopathic effect of sericea lespedeza [Lespedeza cuneata (Dum. Cours) G. Don.] residues on multiple cropping and rotational systems. Experiments were conducted to determine (1) if sericea lespedeza residues affected seed germination and plant growth of rye (Secale cereale L.), ryegrass (Lolium multiflorum Lam.), and tall fescue (Festuca arundinacea Schreb.); (2) if cultivars of these species varied in response to phytotoxins from sericea lespedeza residues; and (3) if N fertilization nullified the effects of residues. Germination experiments were conducted by using water extracts from low- or high-tannin sericea lespedeza residues, distilled water (control), and topsoil and subsoil obtained from areas in which low- or high-tannin sericea lespedeza plants had grown for 4 years. Greenhouse experiments showed that germination, emergence, seedling growth, above-ground biomass, and N concentration of rye and tall fescue were reduced by sericea lespedeza residues. Although ryegrass germination was not affected by the residues, biomass and N concentration were reduced. Rye and tall fescue germination were not affected by soils where sericea lespedeza previously had grown, but ryegrass germination and seedling growth of all 3 species were reduced. Immobilized N was the main factor limiting plant growth. Fertilizer-N more than compensated for the negative effects of the residues on all species. Establishment of rye and tall fescue in a sericea lespedeza field is likely to require higher seeding rates than normal to compensate for reduced germination, whereas ryegrass would not be affected. Fertilizer-N may be needed to enhance growth of grasses that otherwise would be curtailed by sericea lespedeza residues.
  • Effects of mechanical treatments and climatic factors on the productivity of Northern Great Plains rangelands

    Haferkamp, M. R.; Volesky, J. D.; Borman, M. M.; Heitschmidt, R. K.; Currie, P. O. (Society for Range Management, 1993-07-01)
    Impacts of 7 range treatments and climate on late spring herbage standing crops (SC) were measured in rangelands near Miles City, Mont., from 1983 to 1990. Treatments, established in 8 pastures at 2 sites, were: (1) untreated control + season long grazing (SL); (2) soil tillage (ST) + SL; (3) ST + drill seeding legumes (DS) + SL; (4) brush control (BC) + ST + DS + switchback grazing (utilizing 2 pastures); (5) BC + ST + DS + SL; (6) ST + nitrogen fertilization + SL; and (7) contour furrowing (CF) + aerial seeding legumes + SL. Data were analyzed using years as a repeated measure. Treatments increased (p less than or equal to 0.05) total SC 320 kg/ha over controls, but did not affect species/species group composition. Treated pastures produced similar (p greater than or equal to 0.10) SC of 881 kg/ha. Total SC averaged 490 kg/ha more (p less than or equal to 0.05) in 1983, 1986, 1987, 1989, and 1990 than in 1984, 1985, and 1988. Perennial cool-season grass SC was greatest in 1986 (651 kg/ha). Peak annual grass SC (337-506 kg/ha) occurred in 1983 and 1984, the 2 years following ST or CF, and 1989 and 1990, the 2 years following severe drought. Although regression analyses showed fall, winter, and spring precipitation and temperature were closely related to spring SC, less than 50% of the variation in SC was accounted for when precipitation and temperature were summed on a 1-month, 2-month, or 3-month basis. Above-average fall and spring precipitation (September and April) resulted in the greatest total SC. Species composition varied temporally with changing weather conditions and management strategies.
  • Cattle avoidance of leafy spurge: A case of conditioned aversion

    Kronberg, S. L.; Muntifering, R. B.; Ayers, E. L.; Marlow, C. B. (Society for Range Management, 1993-07-01)
    Leafy spurge (Euphorbia esula L.) represents a serious threat to the productivity and profitability of many cattle ranches in the midwestern U.S. Sheep and goats will graze the weed, but cattle generally do not. We hypothesized that cattle avoid leafy spurge because it contains 1 or more chemicals that elicit a conditioned flavor aversion when consumed. First, we tested cattle to determine if they reduced their intake of a novel feed on subsequent days if we modestly increased rumen fill by introducing additional feed or additional feed plus an aversive agent (lithium chloride, LiCl) after they had consumed the novel feed. We observed that cattle became averted (P = .0001) to the novel feed only when LiCl was administered with additional feed. Simply increasing rumen fill by a small amount did not cause cattle to reduce their intake of the novel feed the following day. Secondly, we tested cattle to determine if they reduced their intake of a novel feed on subsequent days if we introduced leafy spurge into their rumina following consumption of the novel feed. We also tested cattle to determine if a spurge-induced aversion to a novel feed was preventable by inoculation with rumen microbes from sheep with spurge in their diets. We found that introducing spurge into cattle after their intake of novel feed reduced (P < .01) their intake of the novel feed on subsequent days. Cattle inoculated with rumen microbes from spurge-adapted sheep had similar (P > .40) aversions to a novel feed paired with spurge introductions. Apparently, cattle avoid leafy spurge partly or wholly because they develop a conditioned aversion after first ingesting some threshold amount of it.
  • Catastrophe Theory: A unified paradigm for rangeland ecosystem dynamics

    Lockwood, J. A.; Lockwood, D. R. (Society for Range Management, 1993-07-01)
    Rangeland ecologists have elucidated 2 apparently distinct processes underlying rangeland dynamics. In some cases, disturbed or recovering rangelands move through a gradual, continuous series of changes which has been termed succession. In other instances, rangeland dynamics are typified by sudden, discontinuous changes in the vegetation, and this has been cared state-and-transition. Catastrophe theory is a mathematical framework designed for the study of discontinuous phenomena, but it also generates models that permit continuous dynamics. Based on available literature, it appears that rangeland ecosystems conform to the mathematics of catastrophe theory. Rangelands exhibit the 5 essential symptoms of catastrophe systems: modality (distinct conditions or states of existence), inaccessibility (conditions which are very unstable), sudden changes (relatively rapid movement between states), hysteresis (processes associated with degradation or recovery are not readily reversible by simply inverting the sequence of events), and divergence (relatively small changes in initial conditions can result in dramatically different outcomes with time). Catastrophe theory has been successfully used to model rangeland grasshopper population dynamics, and it appears that many of the same control variables affecting insects (e.g., temperature and precipitation) may also underlie vegetative community dynamics. Application of catastrophe theory to empirical data sets will require relatively long-term but low-intensity research efforts.
  • Broom snakeweed responses to drought: II. Root growth, carbon allocation, and mortality

    Wan, C.; Sosebee, R. E.; McMichael, B. L. (Society for Range Management, 1993-07-01)
    The effects of soil water deficit on root growth, carbon allocation, and plant mortality of broom snakeweed (Gutierrezia sarothrae (Pursh) Britt and Rusby) were studied during the spring-summer growing season in plants subjected to different soil water regimes. As soil water deficit developed, root length density decreased, indicating that water deficit reduced root proliferation. Root/shoot ratio remained unchanged (p > 0.05) as soil water potential decreased from -0.023 Mpa to -2 MPa; but it became higher (P < 0.05) in extremely stressed plants (-3.4 MPa), indicating that root growth was favored over shoot growth. Root length density was more closely correlated with green tissue dry weight/-stem dry weight ratio (r = 0.82, p < 0 .0001) than with root/shoot ratio (r = 0.52, p < 0 .05). This suggests that (1) expansion of photosynthetic area was more sensitive than stem growth to water deficit and (2) carbon allocation within the shoot was more sensitive to water deficit than allocation between root and shoot. Plants died when gravimetric soil water decreased to around 0.03 g g-1 (equivalent to a soil water potential of -7.5 MPa). The leaf relative water content just before death was about 0.50. Soil water content in the top 20 or 30 cm of the profile is the single most important factor determining mortality of the snakeweed plant and can be used in making decisions in snakeweed control programs.
  • Broom snakeweed responses to drought: I. Photosynthesis, conductance, and water-use efficiency

    Wan, C.; Sosebee, R. E.; McMichael, B. L. (Society for Range Management, 1993-07-01)
    The effects of water deficit on photosynthesis, transpiration, stomatal conductance, canopy development, and water-use efficiency of broom snakeweed (Gutierrezia sarothrae (Pursh) Britt and Rusby) were studied during the spring-summer growing season in pot-grown plants subjected to 5 soil water regimes. Stomatal conductance was proportionately more reduced by a mild water stress (soil water potential = -0.2 MPa) than were canopy development and photosynthesis. However canopy development was most affected by moderate to severe soil water deficit (< -1.1 MPa), followed by photosynthesis; transpiration and leaf conductance were least affected. When subjected to severe water stress, broom snakeweed controlled its water loss mainly through reduced canopy development rather than stomatal closure. Photosynthesis was more limited by mesophyll conductance than by stomatal conductance. Water-use efficiency was not affected by mild water stress. As soil water deficit developed, water-use efficiency declined, which was a response to nonstomatal limitation to photosynthesis and less sensitive stomata to severe water deficit. Broom snakeweed maintained positive net photosynthesis at soil water potential as low as -3.4 MPa and leaf water potential of -8.19 MPa. Waterspending behavior (low water-use efficiency) and high degree of drought tolerance were the main physiological characteristics of broom snakeweed subjected to water stress.