Rangelands Of Central Argentina Research Articles

Twenty-five Years of Fire Research in the Temperate Semi-arid Rangelands of Central Argentina: A Synthesis

Fire is a natural part in the semiarid zone of central Argentina (Caldenal). Historically, it had an important ecological role in this ecosystem on the species composition, vegetation structure and vegetation dynamics. Fire frequency decreased in the past 100 years as consequence of fine-fuel removal by domestic livestock grazing and active fire suppression. If intermittent fires do not occur the rangelands will be converted to savannas, shrublands or woodlands. The aim of this review was to explain the ecological role of fire in the southern Caldenal rangelands, the woody and grass species response to fire, and to discuss the effect of post-fire defoliation on forage grass species. Controlled fire could be used as a management tool for to reset the ecological balance among grass and woody species in the region. After controlled fire, for the recovery of desirable perennial grasses the burned rangelands may should not be grazed for at least one year. However, there is the need for further research to understand the effects of the controlled fire on soil seed bank, soil chemical, physical, and biotic properties, and use of controlled fire combined with other of woody species control strategies to prescribe sound and generalized management policies.

Reproductive traits in four spontaneous Pappophorum vaginatum populations in arid Argentina

Arid zones, where native rangelands are common, are essentials for millions of people livelihood. These areas support 50% of the world's livestock and are where 44% of the world's food is grown. In rangelands of Central Argentina, Pappophorum vaginatum is basically the unique, warm-season perennial grass species palatable to grazing livestock. Our major objective was to determine variability in reproductive characteristics among four spontaneous, overgrazed populations (i.e., P1, P2, P3, P4) of that species to identify promissory materials for domestication. Studies were conducted during three consecutive growing seasons within the southwestern part of the Phytogeographical Province of the Monte, in southwestern Buenos Aires, Argentina. Measured reproductive characteristics were related to flowering initiation, seed production and natural reseeding potential. Significant differences were found for flowering initiation and natural reseeding potential, but not for viable anthecia per plant among the four populations of P. vaginatum. This species fructified from the beginning to the end of the studied growing seasons with a great anthecia production per plant. The light weight of these anthecia and their awns would favor a great wind dispersal and most likely the establishment of new seedlings of P. vaginatum. This suggests that sexual reproduction might have a relatively greater importance than asexual reproduction (i.e., tillering) in the persistence of the overgrazed P. vaginatum in the plant communities of the studied region. Selection of plant materials with a late flowering initiation will allow to extend the forage production of a better quality. The variability among and within populations found on this study supports the idea that would be promissory to start selection programs to obtain improved germplasm to reincorporate to grasslands of the south of the Phytogeographical Region of the Monte (Argentina) not only to increase livestock production but also to recover and maintain biodiversity.

Correction: Summer habitat use and activity patterns of wild boar Sus scrofa in rangelands of central Argentina.

[This corrects the article DOI: 10.1371/journal.pone.0206513.].

Summer habitat use and activity patterns of wild boar Sus scrofa in rangelands of central Argentina.

Biological invasions are one of the main components of human-caused global change and their negative impact on invaded ecosystems have long been recognized. Invasive mammals, in particular, can threaten native biodiversity and cause economic impacts in the region where they are introduced, often through a wide range of conflicts with humans. Although the wild boar, Sus scrofa, is considered by the IUCN as one of the 100 invasive species most damaging to biodiversity in the world, in Argentina there have only been a few studies focused on its ecology with most of them conducted in protected areas. In this study, we evaluated the effect of several factors related with human disturbance, landscape composition, degree of fragmentation and the presence of a potential competitor and a predator on the habitat use of wild boar using data from camera traps and site-occupancy modeling. Additionally, we described the daily activity pattern of the species and we studied the level of overlap with both a potential competitor and a predator. The sampling effort totaled 7,054 camera trap days. Farm density, proportion of shrubland and proportion of grassland with bushes were the detection variables included in the most supported model whereas proportion of grassland and capture rate of the Pampas fox Lycalopex gymnocercus were the occupancy variables included in the most supported model. However, the proportion of grassland was the only variable that showed statistically significant support in the averaged model, indicating that habitat use of wild boar in this area was significantly negatively affected by the level of grass cover. Wild boars were mostly nocturnal, with more activity between 21:00 and 3:00 and a peak around midnight. Wild boars showed a high level of overlap with the activity pattern of the Pampas fox and a low overlap with the activity pattern of the puma Puma concolor. Despite wild boar being introduced in Argentina a few decades ago, this study is the first landscape-scale research carried out in an agricultural landscape in Argentina and the first one based on camera-trapping data. Our study contributes valuable information that could be used to design strategies to reduce wild boar population or to minimize the damage caused by this invasive species in Argentina.

Characterization of puma–livestock conflicts in rangelands of central Argentina

Livestock predation is one of the major causes of conflicts between humans and pumas (Puma concolor). Using data from interviews with ranchers and kill-site inspections, we characterized puma–livestock conflicts in Villarino and Patagones counties of central Argentinean rangelands. Depredation was considered the major cause of livestock losses, and puma attacks were reported in 46.6% and 35.4% of ranches in Villarino and Patagones, respectively. The majority of ranches underwent losses smaller than 1000 USD. The proportion of livestock lost to predation (0.1–10.4%) and financial losses (5.3–1560.4 USD) per ranch/year varied across ranches, and small sheep ranches in Villarino were affected the most. Depredation was recorded only at night and preferentially in grassland with shrubs and cropland habitats. Although nocturnal enclosures appeared to decrease sheep losses, puma hunting was considered the most effective form of reducing depredation and was implemented by most ranchers. Mortality rates were 3.7 and 1.1–1.56 individuals/year × 100 km2 for sheep and pumas, respectively. Nocturnal fencing, shepherding and spatial separation from predators may efficiently reduce sheep losses. However, the poor association between the intensity of puma persecution and puma-related livestock losses suggests that conflict mitigation in central Argentina is not only about reducing damage but also about increasing tolerance.

Herbaceous vegetation response to controlled fire and postfire defoliation in a semiarid rangeland of Argentina

ABSTRACTSemiarid rangelands of central Argentina are shaped by fire and grazing. The aim of this study was to quantify the effect of controlled fire on aboveground biomass production of (1) herbaceous species as a whole group and (2) herbaceous species subclassified as desirable or undesirable perennial grasses and as herbaceous forbs at the end of two growing seasons after an experimental fire in a semiarid rangeland of central Argentina. The effect of the length of the resting period after fire on aboveground biomass production of desirable perennial grass species was also assessed; treatments consisted in defoliations at the end of the first and second postfire growing seasons, at the beginning and at the end of the second postfire growing season and only at the end of the second postfire growing season. Total biomass production of the burned treatments was higher than that of the control treatment, the difference being attributed to an increase in desirable perennial grass species biomass. This in turn was negatively affected by defoliation at the end of the first postfire growing season, suggesting that the beneficial effect of fire on biomass production might have been overridden by the stress imposed by an early defoliation. Overall, the results of the present study suggest that grazing should be held back for at least a whole year after the fire to achieve the pursued aim of increasing forage production by the use of controlled fire.

Influence of woody species on aerial growth of perennial grasses in semi-arid rangelands of central Argentina

Fil: Blazquez, Francisco Ruben. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Bahia Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida(i); Argentina. Universidad Nacional del Sur. Departamento de Agronomia; Argentina

Response of woody species to different fire frequencies in semiarid rangelands of central Argentina

The aim of the study was to assess the effect of different controlled fire frequencies on cover, density and mortality of the most common woody species in semiarid rangelands of the Caldenal district of central Argentina over a 20-year period. The study comprised three fire treatments: (1) high fire frequency (controlled burns every 3–4 years; HFF); (2) low fire frequency (controlled burns every 8 years; LFF); and (3) unburned control. Repeated burns of moderate intensity, regardless of frequency, reduced the cover and the individual height and canopy area of the most common woody species. Their density was barely affected and the mortality rates were negligible with woody species producing new sprouts after each burn. The woody species under study had a similar response to the high- and low fire frequency treatments. A controlled burn every 3–4 years, permitted the control of woody species cover, height and canopy area, which in turn may favour the production of desirable perennial grasses. The important managerial implication is that the repeated use of controlled fires of moderate intensities in the autumn, given appropriate grazing management, is likely to be essential to maintain these rangelands.

Defoliation effects on the arbuscular mycorrhizas of ten perennial grass genotypes in arid Patagonia, Argentina

Pappophorum vaginatum is the most abundant C 4, warm-season perennial grass in rangelands of northeastern, arid Patagonia, which is often exposed to continuous grazing. Eragrostis curvula is the only naturalized, C 4 warm-season genotype that has successfully established from seed during moist years in the study region, that is characterized by a scarce forage availability to livestock during the spring and summer. Successful introduction of perennial forage genotypes is then critical in that region. No studies have yet been conducted to determine the greater abundance of P. vaginatum compared to that of other native C 4 grass genotypes ( Aristida subulata, A. spegazzinii, Sporobolus cryptandrus) in the study area. The effect of defoliation on arbuscular mycorrhizal colonization was investigated on the four native, one naturalized and five introduced, C 3 perennial grass genotypes ( Leymus cinereus cvs. “Magnar” and “Trailhead”, and Achnatherum hymenoides cvs. “Paloma”, “Rimrock” and “Nezpar”) growing at the field. We hypothesized that the magnitude of mycorrhizal colonization (1) is similar on defoliated than on undefoliated plants of the native and naturalized genotypes, (2) is greater in the native and naturalized than in the introduced genotypes, and (3) is greatest in P. vaginatum than in all remaining genotypes. Plants of all ten genotypes were either exposed or not to a severe defoliation twice in the growing seasons of 2007/2008 and 2008/2009. The results showed that all studied genotypes maintained arbuscular mycorrhizal colonization levels following defoliation similar to undefoliated controls. The greatest arbuscular mycorrhizal colonization was often found on both cultivars of L. cinereus among all genotypes. The greatest arbuscular mycorrhizal colonization in P. vaginatum than in the other native genotypes at the end of the study, parameter that contributes to defoliation tolerance, could help to explain its greater abundance in rangelands of central Argentina. The higher arbuscular mycorrhizal colonization in both cultivars of L. cinereus might contribute to their successful establishment and survival in rangelands of northeastern, arid Patagonia. Genotype introduction in these rangelands is likely to affect community dynamics because of variable effects of the mycorrhizal symbiosis on the various plant genotypes.

Grazing effect on NDVI across an aridity gradient in Argentina

Grazing effects on aboveground net primary production (ANPP) have ever been controversial. Certain plant communities are very sensitive to grazing and others are not. We analyzed the grazing effect on ANPP across a gradient of mean annual precipitation (MAP) in rangelands of Central Argentina. We focused not only on the regional patterns of the grazing effect on ANPP but also on the response of the inter-annual variability of ANPP to this disturbance. We used the seasonal dynamics of the Normalized Difference Vegetation Index (NDVI), a spectral index calculated from the reflectance in the red and infrared portion of the spectrum as recorded by the AVHRR/NOAA sensor as an estimator of ANPP. This variable was recorded at increasing distances from the watering point in large paddock distributed through the MAP gradient (250–600 mm) of the extensive plains Arid Chaco in Argentina. Grazing effect on NDVI decreased along the regional gradient of MAP. The grazing effect on NDVI varied among years, being greater in dry than in wet years. Regional patterns changed among years because the NDVI close to the watering points had high inter-annual variability at the driest extreme of the gradient. Our findings contribute a conceptual framework to grazing management in semi-arid rangeland. Considering that grazing effect on NDVI-I was higher in arid than in wet sites implicates that appropriate grazing management strategies would be different in sites with different precipitation levels.

Mineral Composition of Medicago minima and Erodium cicutarium Under Various Water Regimes

Medicago minima and Erodium cicutarium are two annual, naturalized species in semi-arid, temperate rangelands of central Argentina. A field study was conducted to determine the effects of different levels of soil water availability on concentrations and partitioning of sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) in various organs in these species. Aboveground plant parts and roots showed lower or similar, but not higher, Na concentrations under water stress than under irrigated conditions in both species and years. Concentrations of K, Ca, and Mg of aboveground plant parts and roots in both years for E. cicutarium and of Ca in 1989 for M. minima were greater under water stress than under irrigated conditions. Aboveground plant parts of both species had in general a lower Na and a greater K concentration than roots. Leaves and roots had similar Mg concentrations in M. minima. However, concentrations of this nutrient were greater or similar in roots than in leaves in E. cicutarium, and those of Ca were greater in leaves than roots in both species. Leaves and/or stems had greater Ca concentrations than fruits in both species and years under all water levels. The lowest concentrations of Na, Ca, K, and Mg among plant parts in both species were generally found in flowers. Aboveground plant parts of M. minima and E. cicutarium exceeded the Na, K, Ca, and Mg concentrations recommended for a balanced beef cattle diet under all water levels. Both species contained more Na, K, Ca, and Mg in shoots (all aboveground organs) than in roots in both years. Differences between species in the proportional allocation of whole plant Na, K, Ca, and Mg to the various aboveground and belowground organs under water stress, rainfed, and irrigated conditions are discussed.

Direct assessment of competitive ability and defoliation tolerance in perennial grasses

Stipa clarazii is a dominant, late-seral perennial grass species under exclosure or lightly grazed rangelands in semiarid Argentina, whereas S. tenuis and S. ambigua are earlier-seral perennial tussock grasses. Recent studies have demonstrated that late-seral species are more competitive and can have either similar or greater herbivory tolerance than earlier-seral species. We hyphothesized that (1) tolerance to defoliation is greater on defoliated plants of S. clarazii than on those of S. tenuis and S. ambigua, (2) competitive ability is greater in S. clarazii than in S. tenuis and S. ambigua when plants remain undefoliated or are exposed to a comparable defoliation intensity, and (3) competitive ability decreases in S. clarazii when this species is selectively defoliated within a non-defoliated, nearby neighbourhood of S. tenuis or S. ambigua. The study objectives included obtaining a direct measure of competitive ability and defoliation tolerance in the three perennial grasses when they grew either in isolation or in different neighbourhoods and were exposed to various defoliation patterns in the field. In 1998, two parallel studies were conducted within a 2-yr-old field exclosure during one growing season. In one study, responses were evaluated on either defoliated or undefoliated plants of all three species without neighbours. In a second experiment, four types of neighborhoods were selected such that a central (target) plant of one species was surrounded by five neighboring plants of a different species. Three different defoliation patterns were imposed on each neighbourhood type. Results led to acceptance of the first and second and rejection of the third hypothesis. When plants grew without nearby neighbours, greater growth rates for height, dry matter production and end-of-season daughter tiller production per parent tiller in S. clarazii relative to S. tenuis and S. ambigua contributed to greater regrowth in S. clarazii. Amounts of 15N atom excess were always greater in S. clarazii than in S. tenuis and S. ambigua independently of neighbourhood type and pattern of defoliation. However, uptake of 15N was similar in S. clarazii to that in S. tenuis or S. ambigua when S. clarazii was selectively defoliated within a non-defoliated, nearby neighbourhood of any of the other two species. Selective herbivory of S. clarazii, rather than factors associated with its competitive ability and defoliation tolerance, were found to be the major determinant driving its replacement by earlier-seral, less desirable perennial grasses in rangelands of central Argentina. Key words: 15N, Argentina rangelands, biomass, nitrogen uptake, species replacement, Stipa

Root proliferation in perennial grasses of low and high palatability

Root proliferation of desirable (Stipa clarazii andS. tenuis) and undesirable (S.ambigua)perennial grasses was studied in semiarid rangelands of Central Argentina(40°39′S, 62°54′W) in 1998. On 17 September, soil coreswereremoved from the edge of the plant, metal structures lined with screen mesh(hereafter called bags) were buried in the holes, and root-free soil was placedinto these structures. Numbers of green tillers and circumference per plant hadpreviously been determined. Since plants were of unequal size among species,root length and root dry weight data are reported on a per green tiller basis.Half of the plants was defoliated to 5 cm stubble height on 17September and/or 12 October, while the other half remained undefoliated(controls). Bags were destructively harvested either 20 days after the firstdefoliation (first sampling) or 56 days after the second defoliation (secondsampling) by digging out soil very carefully around each bag. Roots were washedfrom soil, root length estimated by the line intercept method, root dry weightdetermined after oven-drying, and root length per unit root dry weightcalculated from the two measured variables. Root length and dry weight weremorethan 96% greater on defoliated and undefoliated plants ofS. clarazii than on those of S.tenuisor S. ambigua for both sampling dates. Root length perunitroot dry weight, however, was more than 43% greater (p < 0.05) inS. tenuis than in S. clarazii andS. ambigua during the second sampling. Defoliated plantshada similar root length and root dry weight than undefoliated plants in all threespecies, although plants of S. tenuis defoliated twiceshowed a greater (p < 0.05) root length than undefoliated controls. Rootlength and root dry weight were similar between sampling periods, except onundefoliated plants of S. tenuis which had a greater (p<0.05) root length and root dry weight at the first than at the second sampling.Although root length per unit root dry weight may be greater inS. tenuis than in S. clarazii andS. ambigua, greater root length and dry weight increasesinS. clarazii after defoliation appear determinant incontributing to explain its greater competitive ability and defoliationtolerance when compared with the other two species.Nomenclature of taxa followed.

Effects of Defoliation at Varying Soil Water Regimes on Aboveground Biomass of Perennial Grasses

We evaluated the effects of defoliation under varying soil water regimes on aboveground biomass of perennial grasses native to semiarid rangelands of central Argentina. The palatable species Stipa tenuis and S. clarazii were either defoliated or not for two years within a uniform competitive background of S. gynerioides, an unpalatable species which remained nondefoliated until the end of the study in 1997. Stipa gynerioides increased biomass when soil water was plentiful compared to water stress conditions. This species showed a greater percentage of medium- to large-size plants under rainfed and irrigated conditions than under water stress conditions. Greater shading of S. gynerioides as soil water content increased may have contributed to determine a greater proportion of small-size plants in S. clarazii and of dead plants in S. tenuis in the irrigated than in the water stress treatment. Results suggested that grazing of perennial forage grasses under high soil water contents speeded rather than slowed their degradation when they were competing within a matrix of ungrazed, unpalatable perennial tussock grasses.

Soil nitrogen availability under grasses of different palatability in a temperate semi‐arid rangeland of central Argentina

Abstract Grazing by domestic livestock is frequently associated with the replacement of high‐nutrient palatable species with low‐nutrient unpalatable species, which may have a substantial effect on nutrient cycling. The objective of the present study was to compare soil N availability and net N mineralization in soils under Poa ligularis (palatable grass) with those in soils under Stipa tenuissima (unpalatable grass) in a temperate semi‐arid rangeland of central Argentina. Nitrogen availability and net mineralization under laboratory and field conditions were measured. Soil N availability under P. ligularis was higher than or similar to soil N availability under S. tenuissima. In situ net N mineralization in the soil under P. ligularis was lower than or similar to net N mineralization in the soil under S. tenuissima. Potential net N mineralization was greater in the soil under P. ligularis than in the soil under S. tenuissima. Our results suggest that the replacement of palatable grasses by unpalatable grasses in the temperate semi‐arid rangelands of central Argentina may imply a reduction in the rate of nutrient cycling.

Dry Weight Production and Partitioning inMedicago minimaandErodium cicutariumUnder Water Stress

Medicago minimaandErodium cicutariumare two naturalized annual species in extensive semi-arid, temperate rangelands of central Argentina. A field study was conducted during 1989 and 1990 to evaluate the effects of different levels of soil water availability on above- and below-ground dry weight production and partitioning in these species. Dry weight production byM. minimawas more sensitive to water stress than that byE. cicutarium. Although the response was more marked inM. minima, both species allocated a larger proportion of total plant dry weight to fruits under water stress than under irrigated conditions during early spring. Percentage allocation of total plant dry weight into reproductive organs in both species, and stems and peduncles inE. cicutarium, was correlated with total dry weight of these organs; this might indicate a correlation between sink size and strength. Persistence of both species in the local flora appears to be associated with their capacity to colonize open, degraded areas and grow in association with native perennial grasses, as well as to tolerate severe drought periods.