Showing papers in "Journal of Range Management in 1990"

Measurements of Terrestrial Vegetation

Abstract: Units for Measurements. Statistical Concepts for Field Sampling. Frequency and Cover. Density. Biomass. Monitoring and Evaluation. Remote Sensing. Appendix. Index.

Differences in riparian vegetation structure between grazed areas and exclosures.

Abstract: The valuable role that healthy riparian ecosystems play in regional diversity of plant and wildlife communities is just beginning to be recognized. Resource managers need to know how degraded riparian areas respond to changes in management, such as reduction and elimination of grazing. Differences in vegetation structure were examined in a montane riparian zone in northcentral Colorado after 30 years of cattle exclusion and continued, but reduced, grazing pressure. In order to assess the changes in the riparian community, canopy coverage, density, and standing crop of important riparian species were measured in 1985 and 1986. Total vascular vegetation, shrub, and graminoid canopy cover was greater (P?0.05) in the exclosures as compared to grazed areas, while forb canopy cover was similar (P>0.05) between treatments. Exclosures had nearly 2 times the litter cover, while grazed areas had 4 times more bare ground. Willow canopy coverage was 8 1/2 times greater in protected areas than in grazed areas. Kentucky bluegrass (Poa pratensis L.) cover was 4 times greater in grazed areas than exclosures, while the cover of fowl bluegrass (Poa palustris L.) was 6 times greater in the protected sites. Canopy cover of other important riparian species, such as tufted hairgrass (Deschampsia caespitosa (L.) Beauv.), Nebraska sedge (Carex nebraskensis Dewey), and beaked sedge (C. rostrata Stokes), was similar (F>0.05) between treatments. Mean peak standing crop over the 2 years of the study ws 2,410 kg/ha in the exclosures and 1,217 kg/ha in caged plots within grazed areas. Cattle utilized approximately 65% of the current year's growth of vegetation during the 1985 and 1986 grazing seasons. Riparian areas provide habitat for wildlife and fish species, while providing forage for domestic livestock. These areas provide a diversity of foraging and breeding sites that permit coexistence of many wildlife species. Intact aquatic ecosystems with abundant streamside vegetation insure healthy fish populations (Kauffman and Kreuger 1984). Improper livestock use of riparian areas can increase erosion and reduce plant vigor, resulting in lowered forage production and altered plant age structure and species composition (Knopf and Cannon 1982, Kauffman and Krueger 1984, Skov

Overstory-understory relations in pinyon-juniper woodlands in New Mexico.

Abstract: Herbage biomass for blue grama (Boutdoua grdlis [H.B.K. Lag& pinyon ricegrass (Pfph&tu&un jimbriatum [H.B.K.] Hit&c.), New Mexico muhly (Muhihkgfa pcsrciflorcl Buckl.), other grasseq and forbs was estimated on 25 pinyon-juniper stands of varying overstory cover on the Fort Stanton Experimental Ranch insouthcentral New Mexico. Negative 2”d degree polynomial curvea best expressed the relationshipa between total understory and blue grama biomass and overstory canopy cover. Positive polynomial relationships were shown for cool-season graazs, New Mexico muhly, and pinyon ricegrass. Reducing pinyon-juniper canopy cover would likely increase blue grama production and reduce production of New Mexico mubly and pinyon ricegraas.

Estimates of critical thermal environments for mule deer

Abstract: Mule deer (Odocoikus hemlonus hemionus) can be thermally stressed under a wide range of ambient conditions. We developed a model that provides examples of the combinations of wind, solar radiation, and air temperature that may result in thermally critical environments for standing, full-fed adult mule deer during winter in snow-covered and snow-free, open habitats, and in meadows in summer. Critical thermal combinations of environmental variables are shown as 3-dimensional surfaces and tables. Animal size, age, pelage characteristics, and gound cover (height and albedo) further affect the energy costs for thermoregulation by mule deer. The need for habitat managers to consider the provision of thermal cover to reduce beat or cold stress in mule deer depends on the combinations of environmental variables in a particular habitat and geographic location. Implications, limitations, and management consideratiom of our estimates are discussed.

Conditioned Taste Aversion: Potential for Reducing Cattle Loss to Larkspur

Abstract: Barbey larkspur (Delphinium barbeyi L. Huth) is a palatable poisonous plant that causes a large number of cattle deaths on mountain rangelands. The objective of the study was to determine whether or not cattle could be conditioned to avoid eating larkspur. Five heifers were conditioned to avoid eating larkspur by intraruminal infusion of lithium chloride whenever they consumed larkspur in a pen feeding trial. Five control heifers were likewise infused with distilled water. Following the conditioning, the heifers were taken to mountain rangeland in central Utah and observed in 1986 and 1987. The non-averted heifers consumed larkspur throughout the 1986 field trial, while the averted heifers generally consumed little larkspur. The aversion from the previous summer persisted as the averted heifers refused to eat larkspur in the first grazing trial in 1987. During the second grazing trial in 1987, the averted heifers were placed in a pasture with non-averted heifers to determine if social influences would affect learned aversions. A rapid breakdown of the aversions was observed and the averted heifers continued consuming larkspur after being separated from non-averted heifers.

Nonstructural Carbohydrates and Spring Regrowth of Two Cool-season Grasses: Interaction of Drought and Clipping

Abstract: The role that 8ccumuiatcd carbohydratesplay in plant regrowth has been discussed for over 60 years. However, few quantitative studies have been published on the importance of carbohydrates for regrowth in early spring after plants have been exposed to periods of either drought or drought plus defoliation. We examined the relationship between total nonstructural carbohydrate (TNC) concentrations and pools (biomass X concentration) and spring regrowth for crested wheatgrass [Agropyron desertorm Fisch. ex Lll) Schult.] and bluebunch wheatgrass [Pseruforuegnericr spidta (Pursh) A. L&e ssp. @cata,Syn: A. spicatms (Pursh) !hibn. and Smith] with and without clipping under drought, natural, and irrigated conditions. In spring 1985 and early spring 1986, after 1 or 2 years of clipping, crown and root TNC concentrations an IT NC pools per tiller were generally similar for clipped and un ipped plants of both species. Nonstructural carbohydrate concentrations in crowns and roots did not relate to rate or totai production of dark regrowth in mid-spring 1985 and early spring 1986. In early spring 1986 following 2 years of repeated treatments, crown and root TNC pools were on average 7 times higher under drought, in both clipped and unclipped plants, than they were under the higher moisture-level treatments for both species. The large pools of TNC in drought-treated plants appeared to enhance the production of dark regrowth when meristematic limitations on growing tillers did not exist in early spring. These results suggest that plants exposed to prolonged periods of drought or drought plus defoliation may have rapid initial regrowth upon alleviation of these stresses because high amounts of TNC may have accumulated in their storage organs during stress. In addition, the results suggest that high TNC availability facilitates growth only when meristematic activity is high.

Plant biology of the basin and range

Abstract: In a very real sense, much of North American physiological plant ecol ogy began in the Basin and Range and has been researched there over the last four decades. However, we believe that this book may be the first attempt to bring together the full range of contemporary research into the fascinating plant biology of the Basin and Range Province. We have invited contributions from researchers presently working in and around the Province and asked them to review the major vegetation zones and distinctive environmental issues from a predominantly plant ecophysiological perspective. As researchers interested in plant physi ological and ecological processes, and in atmospheric processes affect ing vegetation, we have tended to emphasize the atmosphere, plant, soil continuum in structuring this book. After an introduction to the geography of the region, we deal with atmospheric processes and climates of the Great Basin, follow with chapters on the different vegetational zones, treated from ecophysiological perspectives, and then place emphasis on plant-soil relations. We have not treated plant animal interactions in the detail that the impacts of man and his domesticated animals on the desert ecosystem deserve. However we have included a review of a very promising technique (analysis of stable isotopes at natural abundance) for integration of these processes. We close with a compelling statement of the case for the Great Basin as a laboratory for climatic change research, prepared by a multidisciplinary team from the Desert Research Institute."

Soil and vegetation responses to sewage sludge on a degraded semiarid broom snakeweed/blue grama plant community

Abstract: Three rates of dried sewage sludge (22.5, 45.0, and 90.0 Mg (megagams) ha-t), were applied to a degraded semiarid grassland site on the Upper Rio Puerto Watershed in west-central New Mexico. Various soil and plant parameters were determined over 4 growing seasons. Most soil macronutrients, such as nitrogen (N), phosphorus (P), and potassium (K), and micronutrients, such as copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn), increased linearly with increasing sludge amendment rates. Heavy metals (cadium (Cd) and lead (Pb)) did not change as a result of sludge amendment in the first 3 growing seasons. However, concentrations of soil Cu, Mn, and Cd were just above maximum acceptable standards in the heaviest sludge treatment after 4 growing seasons. Plant density, specks richness, and diversity all decreased with increasing sludge rates. However, total plant foliar cover and herbaceous yields increased significantly with the application of sludge. Blue grama (Boutelouu grucilfs (H.B.K.) Lag.) cover and yields, in particular, increased 2 to 3 fold over the control as a result of sludge amendment, whereas broom snakeweed (Gutierrezia sarothrae (Pursh) Britt. + Rusby) density decreased over 4 growing seasons. The most favorable soil and vegetation results were from the 22.5 and the 45 Mg ha-’ sludge applkation rates.

Effect of honey mesquite on the water balance of Texas Rolling Plains rangeland.

Abstract: Understanding hydrologic processes on rangelands is essential to determine if water yield will increase through shrub management. Nine nonweighable lysimeters were monitored for 3 years to determine the water balance as hrfhrenced by vegetation. Cover types studied were honey mesquite (Prosopis glandulosa) plus herbaceous vegetation (M+H), mesquite removed leaving only herbaceous vegetation (H), and mesquite and herbaceous vegetation removed (BG). Throughout the study, BG lyshneters had greater soil water content than the vegetated sites but, regardless of cover type, only O&1.4% of precipitation drained below 3 m. Runoff and interrill erosion were closely associated with rainfall amount, peak short-term storm intensity, and amount of bare ground. Evapotranspiration accounted for over 95% of water leaving the vegetated sites. Herbaceous vegetation on the I-l lysimeters increased following mesquite removal. This increase offset any water yield benefit that may have accrued through shrub management. Results indicate that there is essentially no net change in deep drainage, evapotranspiration, or runoff on sites where the herbaceous component increases in response to shrub removal.

Spring burning Japanese brome in a western wheatgrass community

Abstract: Plots dominated by Japanese brome (Bromus japonicus) and western wheatgrass (Agropyron smithii) were burned in Badlands National Park, South Dakota, in April 1983 and/or 1984. Standing crop of all species and tiller densities of the 2 dominate species were determined for 4 years. Burning favored western wheatgrass and reduced Japanese brome tiller density and standing crop for at least 1 growing season. In years where no burning occurred, Japanese brome standing crop and tiller density were dependent on the presence of litter on the soil surface. Burning in April killed Japanese brome seedlings for 1 growing season and reduced subsequent generations by reducing surface litter accumulations, with the effect being greatest when autumn precipitation was below average. April burning reduced the standing crop of green needlegrass (Stipa viridula) for at least 3 growing seasons after burning but increased standing crop of buffalograss (Buchloe dactyloides) and sand dropseed (Sporobolus cryptandrus) for 3 to 4 years after burning. Threadleaf sedge (Carexfilifolia) standing crop was not significantly affected by burning.

Regeneration of woody species following burning and grazing in Aspen Parkland.

Abstract: The effect of short duration, heavy grazing by cattle was evaluated 3 and 6 years after burning and seeding of an aspen (Pop&s tremuloides Michx.) grove. Replicated paddocks of June grazed (early), August grazed (late), and ungrazed treatments were established. Regardless of treatment, density of all woody species was lower 6 years after burning than after 3 years. Early or late season grazing reduced the density of aspen and wild raspberry (Rubus strigosus Michx.). Late season grazing promoted a greater density of unpalatable western snowberry (Symphoricurpos occidentalis Hook.). Grazing reduced the height of aspen, preventing the development of a forest canopy. Herbage production averaged 1,700 kg ha-l, not differing between years 3 and 6: but the proportion of smooth brome (Bromus inermis Leyss.) increased while orchard grass (Ductylis gbmerutu C.\ declined, Burnine of asnen forest in I ---~~~~~ e --r--------~ ~~Central Alberta followed by forage seeding and short duration, heavy grazing is an effective, economical range improvement tool.

California's privately owned oak woodlands: owners, use, and management.

Abstract: Social science research is an important tool for guiding development of education programs for owners of private rangelands. California oak woodland, a productive and extensive range type in California that is undergoing rapid changes in use and management, is the focus of this study. Results indicate that landowners with different property size differ demographically, make different uses of their land, and have distinctly different attitudes toward oak management and living in the oak woodland. Owners of smaller properties, on the increase in rural California, do not earn their living from their land, and will respond best to resource education programs that they believe will contribute to bettering the quality of life they seek by residing in the oak woodland. Owners of larger properties, the traditional clientele of advisory agencies, will more likely respond to programs that protect and enhance earnings from their property. Still, even a third of the owners of the largest (over 5,000 acres) properties earn the majority of their income from sources other than their lands. To be effective, range-oriented education programs and policies must track the changing composition of rural populations, and the changes in attitudes, needs, and interests that accompany demographic shifts.

The effect of water stress on phenological and ecophysiological characteristics of cheatgrass and Sandberg's bluegrass

Abstract: Comparative field studies of cheatgrass (Bromus tectorum L.) with Sandberg’s bluegrass (PoasandbergiiVasey) were conducted to further our understanding of the plannt characteristics that contribute to success in habitats where water is a limiting factor. To evaluate the effect of soil water on phenological development, stomata1 conductance, and xylem pressure potential of these grasses, observations were made in the field for 2 growing seasons (1986 and 1987). Stomata1 conductance, transpiration, and xylem pressure potential data, gathered as soils dried during 1986, indicated that water stress developed earlier and to a greater degree in Sandberg’s bluegrass than in cheatgrass. Xylem pressure potential was lower in Sandberg’s bluegrass than in chedgrass, and the difference increased throughout the growing season. Stomata1 conductance and transpiration were greater for chedgrass than for Sandberg’s bluegrass. Maintenance of high soil water potentials by irrigating through the 1987 growing season retarded phenological development and delayed senescence by about 10 days for both species. Predawn xylem pressure potential for irrigated plants remained higher than for nonirrigated plants; however, as the plants senesced, xylem pressure potential also decreased in the nonstressed plants.

Comparative photosynthetic responses of big bluestem to clipping versus grazing.

Abstract: The gas exchange responses of big bluestem (Andropogon gerardii) were followed after defoliation by either cattle grazing or clipping and compared with the response of nondefoliated (control) plants Grazed plants had significantly higher rates of photosynthesis than either cUpped or control plants The photosynthesis/transpiration ratio as well as stomatal sensitivity to humidity indicate that leaves of grazed plants may have developed in a higher light and lower moisture environment than that of their clipped counterparts Although the experimental design could not preclude any indirect effects of animal activity (saliva, waste products, or trampling) on the grazed plants, the microenvironmental differences caused by grazing may be crucial in determining the responses of grasses to clipping versus grazing

Influence of grazing, vegetation life-form, and soil type on infiltration rates and interrill erosion on a Somalion rangeland.

Abstract: Heavy communal graxhtg pressure and rapid phytomass decomposition reduce shrub interspace cover in Somalia from 100% at the end of the growing season to 5% at the end of the dormant season. Intense monsoonal rahw, characteristic of Somalia and other areas of subsaharan Africa, combined with sparse vegetative cover at the beginning of the rainy season, may result in overland flow and excessive erosion, even where sand content of the soil exceeds 9%. Little watershed research has been conducted in this region other than to document that the problem is extreme. The objectives of this study were to assess the seasonal hydrologic responses as influenced by 2 soils (sand vs. clay), grazing intensity (exclusion vs. heavy communal grazing), and cover types (shrub understory vs. interspace) in Somalia. Infiltration rate and interrill erosion on the sand site were significantly greater than on the clay site regardless of cover type or season. The clay site was dominated by annual forbs which rapidly decomposed. The sand site had greater annual and perennial grass cover which decomposed slower than forbs, providing longer and perhaps better protection from raindrop impact energy. Three growing seasons of livestock exclusion did not significantly increase soil cover on shrub hrterspaces; consequently, infiltration rates and interrill erosion remained similar to the communally grazed sites. Interspace cover left by livestock was instead removed by termites and other microorganisms. Restricted ability of livestock to graze beneath thorny shrubs and increased phytomass from shrub leaf-fall resulted in a greater accumulation of cover and litter beneath shrubs, which aided infiltration on clay sites, regardless of season.

Macro and trace mineral content of selected south Texas deer forages.

Abstract: White-tailed deer (Odocoileus virginianus) derive the majority of their dietary mineral intake from range forages which may be deficient in one or more essential minerals. We have described the macro and trace mineral concentration of 18 shrub, 26 forb, 7 grass, and 1 cactus species, known to occur in south Texas deer diets, collected from the Chaparral Wildlife Management Area in 1974 and 1975. Within each forage class, there were no seasonal differences in calcium (Ca), sodium (Na), potassium (K), or magnesium (Mg) concentrations. Phosphorus (P) concentrations in browse were higher (PI0 051 durinn the snrinn (0.20%) thnn dur_~ _~~~~ _ __e__, ______ _ _..-=_____ \\_ .__, “, ----__ -ing other seasons(O.U-0.16%). Forb P concentrations were greatest during the spring and winter periods (0.26 and 0.2970, respectively), and P levels in grasses (0.24-0.14%) decreased as the forage matured and reached senescence. Shrubs contained less P and K (p10.01) than either grasses or forbs; whereas, grasses contained lower concentrations of Ca and Mg (EO.01) than shrubs or forbs. Sodium concentrations did not diier among forage classes. Forbs contained greater (fiO.01) levels of copper (Cu) and zinc (Zn) than erasses or browsennd hr~wm c~n!ri~ed 1~9s ire” (Fe! m-----I ---(%0.01) than forbs or grasses. Manganese concentrations did not differ among forage classes. There were differences in mineral concentrations among species within forage class. Results suggest concentrations of all minerals except P met or exceeded minimum domestic animal requirements. Managers should provide a diversity of plant species and encourage practices that promote forb growth to provide optimum and nutritional benefits for deer.

Distribution of nitrogen fractions in grazed and ungrazed fescue grassland Ah horizons.

Abstract: AbStUCt Grazing affects the plant ecology and adds cxcreta, thereby lnfluenclng soll N relatlonshfps. Consequently, total N, mlnerallxable N, exchangeable N, hydrolyxable N, and urease activity were assessed at the Agriculture Canada Research Substation, Stavely, Albert8, in the Ah horizons on rough fescue (F&ucu scafueI& Ton.) grasslands stocked at either light (0.8 ha/AUM) or very heavy (0.2 ha/AUM) fixed rates for 38 years and in exclosurea located within each field for an equal period of time. Even though total N expressed as t/ha per Ah horizon remained the same, changes in various N fractions were nevertheless evident. Graxing resulted in more NH&N and NO&N in both fields at the time of sampling and each was greater at the higher stocking rate. Although soll N was less mfneralixable, it was more acidhydrolyxable at the nigher stocking rate. Urease activity also increased. The effect on soll N charrcteristics of increased excretr

Effect of grazing by sheep on the quantity and quality of forage available to big game in Oregon's Coast Range.

Abstract: Effects of sheep grazing in Douglas-fir (Pseudotsuga menziesii) plantations in Oregon's Coast Range were studied in 1981 through 1983 to determine the impact of grazing on big game habitat Biomass, dry matter digestibility, and crude protein content of forage present on grazed vs ungrazed areas were determined in October and March both years Sheep grazing reduced total current year's phytomass of browse and forbs (p<10) in October October phytomass of graminoids was not affected by grazing Forage from grazed areas in October generally had higher crude protein levels and dry matter digestibility than forage from ungrazed areas in October Few differences in either crude protein or dry matter digestibility of forage from grazed vs ungrazed areas were evident in March However, a greater quantity (p<10) of new, succulent forage was generally present in grazed areas compared to ungrazed areas These data suggest that sheep grazing can improve big game forage supply in Oregon's Coast Range by improving forage quality in the fall and by increasing the quantity of high quality forage in the spring

Effect of grazing and cultivation on some chemical properties of soils in the mixed prairie.

Abstract: Components of the organic matter were studied in soil under 3 Mixed Prairietypes: grasslnd dominated by needle-and-thread/blue grama (Stipa comata Trin. and Rupr./Bouteloua gracilis (HBK.) Lag. ex Steud.) in good range condition; grassland significantly modified by grazing, dominated by blue grama and in poor range condition; and grassland, dominated by needle-and-thread/blue grama in good range condition, but converted to cropland and under continuous wheat for 4 years. The soils were sampled on 13 April 1988. Concentrations of total organic carbon in the upper 2 cm were 1.39, 2.70, and 1.87%, respectively. The higher organic carbon under blue grama was caused by an active, ramified, fine rootmass which gave rise to most of the monosaccharides being of microbial origin. The monosaccharides in the lower Ap horizon in the cropland were generally of plant origin from incorporated

Effects of continuous grazing on habitat and density of ground-foraging birds in south Texas.

Abstract: We analyzed the response of the key habitat features and ground-foraging birds to 2 intensities of continuous grazing on sandy loam and clay soils in the Texas Coastal Bend during 1984-1985 Heavy continuous grazing increased the disperion but not necessarily the availability of bare ground in comparison with moderate continuous grazing Responses of habitat features (structure of ground cover, key food plants) depended on soil type Seasonal densities of eastern meadowlarks (Sturnella magna) were higher on clay than on sandy loam soils and higher under moderate than under heavy grazing Mourning doves (Zenaida macrowua) were more abundant on sandy loams than on clays and more abundant under heavy than under moderate grazing Northern bobwhite (Colinus viglnla=) abundance was uniformly low, regardless of grazing intensity and soil type

Vegetation response to increased stocking rates in short-duration grazing.

Abstract: Short-duration grazing (SDG) has been purported to increase forage production and utilization compared to other grazing systems, and thus can sustain higher stocking rates. This study was designed to determine if standing crop could be maintained as stocking rates increased. Four stocking rate treatments ranging from the recommended rate for moderate continuous grazing to 2.5 times the recommended rate were applied in a simulated 8-pasture SDG system. There was little change in frequency and composition of short-grasses over the study, but mid-grass frequency and composition both declined. Standing crop of all major forage classes declined as stocking rates increased. However, the rate of decline was less than proportional to the increase in stocking rate during the growing season. By fall, standing crop was inversely proportional to stocking rate, leading us to conclude that standing crop could not be maintained at the higher stocking rates. Low standing crop in the fall indicated a potential shortage of forage at the high stocking rates during the winter.

Root length leaf area, and biomass of crested wheatgrass and cheatgrass seedlings.

Abstract: Cheatgrass (Bromus tectorum L) dominates large tracts of rangeland in the western United States Previous research has demonstrated the competitive nature of this species; however, the mechanisms contributing to its dominance have not been well elucidated It is often suggested that cheatgrass outcompetes perennial seedlings because it germinates and grows at lower soil temperatures However, even in studies where temperatures are not limiting, cheatgrass outcompetes perennial seedlings Therefore, I conducted a study to compare accumulation of root length, leaf area, and biomass of cheatgrass and crested wheatgrass (Agropyron desertorum (Fisch ex Link) Schult cv Nordan) seedlings under non-limifting conditions Seedlings were grown in pots in the greenhouse for 60 days post-sowing There were 4 seedlings per pot, and sampling was conducted weekly at 24-60 days after sowing Maximum and minimum temperatures were 28? C and 40 C, respectively, and plants were watered twice a week Cheatgrass had greater root length density and leaf area than crested wheatgrass, especially during the later samplings For the last 2 samplings, cheatgrass averaged about 12% more root mass and 56% more shoot mass, yet had more than twice the root length and leaf area of crested wheatgrass Cheatgrass was more efficient (per unit of biomass) in producing leaf area and root length, which helps explain its ability to quickly become established and exploit soil nutrient and moisture reserves

Defoliation effects on production and morphological development of little bluestem

Abstract: Response of key warm-season grasses to time, frequency, and duration of defoliation is needed to develop grazing systems for the Nebraska Sandhills. A 3- year (1986 to 1988) study was conducted on a Valentine fine sand (mixed, mesic Typic Ustipsamments) at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska, to determine the effect of defoliation on little bluestem [Schu 2 defoliations on 10 June and 10 Aug.; and 3 defoliations on 10 June, 10 July, and 10 Aug. Control plants were huvested only at the end of the growing season (October). All plots receiving summer defoliation were harvested in October to obtain aftermath yield. Treatments were initiated in 1986,1987, and 1988 and the effects of l,2, and 3 years of defoliation on dry matter (DM) yield, bud and tiller numbers, and tiller weight were measured. Experimental design was a split block with 4 plants as replications. In the first yeu of treatment annual DM yield from control plants was 2 times greater than that from all defoliated plants, but bud and tiller numbers were similar. In the second year of treatment, all treatments reduced annual DM yield and morphological development below that of the control if precipitation was subnonnal, but not if precipitation was above normal. In the third year of defoliation, with above-nonnd precipitation, single June or July defoliations produced DM yields and morphological development similar to that of the control, but single August or multiple defoliations generally reduced yield md development. Little bluestem may not persist if exposed to multiple, close defolitions during the growing season.

Above-ground phytomass dynamics in a grassland steppe of Patagonia, Argentina

Abstract: Aerial phytomass and litter dynamics of a grassland steppe in Patagonia, Argentina, were studied at either monthly or bimonthly intervals for 2 years. This area is characterized by a cold and wet winter (June to September) and a warm and dry summer (December to March). The growing season extends from September to April, with moist spring and fall periods interrupted by a midsummer drought. Festuca pallescens (St. Yves) Parodi produced about 95% of the total annual phytomass. Peaks of green phytomass were recorded in spring-summer of the first growing season (33.6 +/- 2.9 g . m-2) and in early spring (35.0 +/- 2.4 g . m-2) and fall (32.7 +/- 2.7 g . m-2) of the second growing season. Less abundant forage grasses were Poa ligularis Nees ap Steudel, Bromus setifolius Presl., Hordeum comosum Presl., and Rytidosperma virescens (Desvaux) Nicors. Shrubs and forbs represented less than 2% of the total annual phytomass of this grassland. The relationships between phytomass production of the main species and some environmental variables are discussed. These results contribute to the knowledge of above-ground phytomass dynamics and forage availability throughout seasons of this grassland in Patagonia, and are part of the data necessary for proper range management planning. This information will permit the designing of appropriate grazing schedules by balancing the number of grazing animals to the forage resources available.