Grasslands Of South America Research Articles

The effect of livestock grazing on plant diversity and productivity of mountainous grasslands in South America - A meta-analysis.

Mountainous grasslands in South America, characterized by their high diversity, provide a wide range of contributions to people, including water regulation, soil erosion prevention, livestock feed provision, and preservation of cultural heritage. Prior research has highlighted the significant role of grazing in shaping the diversity and productivity of grassland ecosystems, especially in highly productive, eutrophic systems. In such environments, grazing has been demonstrated to restore grassland plant diversity by reducing primary productivity. However, it remains unclear whether these findings are applicable to South American mountainous grasslands, where plants are adapted to different environmental conditions. To address this uncertainty, we conducted a meta-analysis of experiments excluding livestock grazing to assess its impact on plant diversity and productivity across mountainous grasslands in South America. In alignment with studies in temperate grasslands, our findings indicated that herbivore exclusion resulted in increased aboveground biomass but reduced species richness and Shannon diversity. The effects of grazing exclusion became more pronounced with longer durations of exclusion; nevertheless, they remained resilient to various climatic conditions, including mean annual precipitation and mean annual temperature, as well as the evolutionary history of grazing. In contrast to results observed in temperate grasslands, the reduction in species richness due to herbivore exclusion was not associated with increased aboveground biomass. This suggests that the processes governing (sub)tropical grassland plant diversity may differ from those in temperate grasslands. Consequently, further research is necessary to better understand the specific factors influencing plant diversity and productivity in South American montane grasslands and to elucidate the ecological implications of herbivore exclusion in these unique ecosystems.

Pathways of glyphosate effects on litter decomposition in grasslands

AbstractGrasslands store a third of global terrestrial carbon but are vulnerable to carbon loss due to inappropriate livestock grazing. Grasslands management can be improved with a mechanistic understanding of biogeochemical processes that determine carbon storage, such as plant litter decomposition.Herbicides, such as glyphosate, are used to improve the quantity and quality of the forage. In the Flooding Pampa, the most extensive cattle grazed natural grassland and one of the few remnants' temperate grasslands in South America—glyphosate is applied to promoteLolium multiflorum, a forage grass associated with a fungal endophyte nontoxic for cattle.We studied five mechanistic pathways in which the application of glyphosate can alter litter decomposition. We grouped them into single application pathways, through effects on living plants (1), leaf litter (2) and bare soil (3), and repeated annual application pathways, through legacies on ecosystem properties (4) and through the growth of an annual forage grass with a fungal endophyte (5). Single application pathways were tested in a greenhouse experiment using leaf litter ofL. multiflorumand of a native dominant grass. Repeated annual application pathways were tested through a field experiment with 3‐year annual glyphosate application using leaf and root litter ofL. multiflorumwith and without endophyte association.Glyphosate application on living plants produced leaf litter with 70% higher nitrogen content and 140% higher decomposition constant than naturally senesced litter. In contrast, glyphosate application on naturally senesced leaf litter reduced decomposition constant by 20%. Glyphosate application on the soil did not affect the decomposition of naturally senesced leaf litter but accelerated the decomposition of the glyphosate‐killed plants even more.Legacies of repeated annual application of glyphosate resulted in a notable reduction in plant cover (45%) and potential soil respiration (57%), with a consistent acceleration of leaf (53%) and root (18%) litter decomposition. Furthermore, endophytes inL. multiflorumplants reduced leaf litter decomposition by 22%. On the contrary, endophytes did not alter root litter decomposition.Glyphosate application on living plants and legacies of repeated application on the ecosystem stimulate litter decomposition, which can result in a net carbon loss from grasslands. In other ecosystems, the net result on decomposition would depend on the relative cover of vegetation, above‐ground litter and bare soil. This study highlights that glyphosate application should be considered when evaluating sustainable management to preserve and enhance soil carbon storage in grasslands.Read the freePlain Language Summaryfor this article on the Journal blog.

Nest‐site features influence nest survival of the Hellmayr's pipit in extensive cattle‐grazed grasslands

AbstractThe Pampas Grasslands in South America have been almost completely transformed by urbanization and agriculture. Many grassland birds persist only in extensive natural pasturelands, which are under constant pressure from fragmentation, cattle‐grazing, and exotic plant species. Identifying which habitat features affect bird breeding success is important for their conservation in altered habitats, although few studies have been conducted in the Pampas Grasslands. We analyzed the influence of habitat features on the daily nest survival rates (DSR) of the Hellmayr's pipit (Anthus hellmayri), a grassland passerine endemic to South America, in a cattle‐grazed grassland. We evaluated the effects of vegetation features at a nest‐site scale, proximity to habitat edges, cattle density, and temporal factors. During 3 breeding seasons (2017–2020), we confirmed the fate of 90 nests, 25 of which were successful (27.8%). Predation was the most common cause of failure (80%), followed by weather‐induced abandonment (10.8%). Average DSR was 0.9106, with a cumulative survival probability of only 7.4%. The best model indicated that DSR was higher in nests adjacent to grass clumps than in those placed in depressions and followed a quadratic trend with nest age. Clump nests may be better protected from aerial predators and rainfall; hence pipits could be more successful in areas with more grass clumps. The very low nest success raises concern regarding the value of these grazing fields as breeding habitats; we urge authorities and landowners to increase conservation efforts in the remaining natural grasslands in the Pampas.

<strong>Two new species of <em>Margyricarpus</em> (Rosaceae, Sanguisorbeae) from high-elevation grasslands in southern Brazil, and other notes on the genus <em>Margyricarpus</em></strong>

Margyricarpus pinnatus is a poorly understood entity from natural grasslands of South America that it better considered as a species complex. In this work we contribute to the advancement of the taxonomic knowledge of this challenging species complex by describing two new species of Margyricarpus from southern Brazil. We present field photographs, illustrations, a distribution map and ecologic and conservation notes on the new species.

Phosphorus fractionation in grasses with different resource-acquisition characteristics in natural grasslands of South America

AbstractThe natural grasslands in South America have soils with low phosphorus (P) availability (1.0 to 7.5 mg kg−1), possibly altering the absorption and accumulation of P in grasses. We evaluated the chemical fractionation of P in the leaves of the most important grasses present in these grasslands to better understand the mechanisms involved in the storage of P. The grasses studied wereAxonopus affinisandPaspalum notatum(fast tissue cycling and high nutrient demand) andAndropogon lateralisandAristida laevis(slow tissue cycling and low nutrient demand). They were grown in pots filled with an Ultisol with two levels of P: control, and addition of 50 mg P kg–1. The main P fractions were the inorganic soluble (44%) and P in RNA (26%). Addition of P increased the total P concentration, following the orderA. affinis(140%) >P. notatum(116%) >A. lateralis(81%) >A. laevis(21%). In conclusion, the speciesA.affinisandP.notatumresponded to P fertilization with high variation and accumulating P in less-structural chemical forms, such as inorganic P. The speciesA.lateralisandA.laevisshowed low variation in the concentration of P forms, with higher P concentrations in structural forms.

From pampa to puna: Biogeography and diversification of a group of Neotropical obligate grassland birds (Anthus:Motacillidae)

The evolution of Neotropical birds of open landscapes remains largely unstudied. We investigate the diversification and biogeography of a group of Neotropical obligate grassland birds (Anthus: Motacillidae). We use a multilocus phylogeny of 22 taxa of Anthus to test the hypothesis that these birds radiated contemporaneously with the development of grasslands in South America. We employ the R package DDD to analyze the dynamics of Anthus diversification across time in Neotropical grasslands, explicitly testing for shifts in dynamics associated with the Miocene development of grasslands, the putative Pleistocene expansion of arid lowland biomes, and Pleistocene sundering of Andean highland grasslands. A lineage-through-time plot revealed increases in the number of lineages, and DDD detected shifts to a higher clade-level carrying capacity during the late Miocene, indicating an early burst of diversification associated with grassland colonization. However, we could not corroborate the shift using power analysis, probably reflecting the small number of tips in our tree. We found evidence of a divergence at similar to 1 Mya between northern and southern Amazonian populations of Anthus lutescens, countering Haffer's idea of Pleistocene expansion of open biomes in the Amazon Basin. We used BioGeoBears to investigate ancestral areas and directionality of colonization of Neotropical grasslands. Members of the genus diversified into, out of, and within the Andes, within-Andean diversification being mostly Pleistocene in origin.

Forests expand as livestock pressure declines in subtropical South America

Bernardi, R. E., M. Buddeberg, M. Arim, and M. Holmgren. 2019. Forests expand as livestock pressure declines in subtropical South America. Ecology and Society 24(2):19. https://doi.org/10.5751/ES-10688-240219

The Grass was Greener: Repeated Evolution of Specialized Morphologies and Habitat Shifts in Ghost Spiders Following Grassland Expansion in South America.

While grasslands, one of Earth's major biomes, are known for their close evolutionary ties with ungulate grazers, these habitats are also paramount to the origins and diversification of other animals. Within the primarily South American spider subfamily Amaurobioidinae (Anyphaenidae), several species are found living in the continent's grasslands, with some displaying putative morphological adaptations to dwelling unnoticed in the grass blades. Herein, a dated molecular phylogeny provides the backbone for analyses revealing the ecological and morphological processes behind these spiders' grassland adaptations. The multiple switches from Patagonian forests to open habitats coincide with the expansion of South America's grasslands during the Miocene, while the specialized morphology of several grass-dwelling spiders originated at least three independent times and is best described as the result of different selective regimes operating on macroevolutionary timescales. Although grass-adapted lineages evolved towards different peaks in adaptive landscape, they all share one characteristic: an anterior narrowing of the prosoma allowing spiders to extend the first two pairs of legs, thus maintaining a slender resting posture in the grass blade. By combining phylogenetic, morphological, and biogeographic perspectives we disentangle multiple factors determining the evolution of a clade of terrestrial invertebrate predators alongside their biomes.

Temporary grazing exclusion promotes rapid recovery of species richness and productivity in a long‐term overgrazed Campos grassland

Moderate grazing intensity is considered the basic requirement to enhance ecosystem function in grasslands. Yet, deterioration by overgrazing is common in many biomes, including Campos grasslands in South America. Understanding how grazing management can lead to recovery of ecosystem function is essential to design and implement effective strategies for sustainable use of this resource. In a long‐term field experiment carried out in Southern Brazil, we studied the effects of temporal grazing exclusions (spring or fall) at moderate and severe livestock grazing intensities (maintained by adjusting contrasting forage allowances) on the species richness, botanical composition, forage mass, sward height, and photosynthetic active radiation intercepted. The experiment was arranged in a completely randomized design with three replications of grazing exclusions, applied simultaneously at moderate and severe grazing intensities. Moderate grazing intensity showed a bimodal structure of shorter and taller canopies, and high species richness. Severe grazing created a shorter and homogeneous sward structure characterized by less standing biomass and species loss. In response to grazing exclusions, sward height, standing biomass, and light interception recovered almost to the levels of moderate grazing. Further, within 2 years grass species richness increased and botanical composition changed toward grasses with erect habit prevailing in moderate grazing intensity. Our study confirms that (1) moderate grazing intensities allow the coexistence of high number of species and (2) spring grazing exclusions of long‐term overgrazed grasslands can lead to a quick start to recover the grass species richness, primary productivity, and species composition like that prevailing in well‐managed grasslands.

Revision of Rhynchospora (Cyperaceae) sect. Luzuliformes

Rhynchospora sect. Luzuliformis is one of the 28 sections of the genus proposed by Kukenthal, the last taxonomist to have studied the section. It has three species and two varieties, and most species are found in open areas of the southern grasslands of South America. Species were studied in the field and in herbaria, and literature was reviewed. As main results we highlight the new specific status and new name, Rhynchospora boeckeleriana, the designation of two neotypes and three lectotypes, and a new record for Brazil, R. praecincta. Full descriptions of the four species are provided, as well as a key to distinguish the species of section Luzuliformes.

Song‐based species discrimination in a rapid Neotropical radiation of grassland seedeaters

Acoustic signals among newly diverged taxa have the potential to convey species identity, information that is key to reducing hybridization. Capuchino seedeaters constitute a remarkable example of recently radiated endemic species from the grasslands of South America. They are sexually dimorphic and show striking differences in male plumage coloration and song. Contrasting with this divergence in phenotype most species show extremely low neutral genetic differentiation and lack of reciprocal monophyly, which is interpreted to be a product of recent common ancestry and hybridization. Here we use field‐based playback experiments to test for the first time if males of two species, Sporophila hypoxantha and S. palustris, discriminate between conspecific and heterospecific song. Using various measures of behavior we find that both species react more strongly to their own songs. The response to playback from another southern capuchino cannot be differentiated from that of a control song from a more distantly related Sporophila species. Additionally, we did not find evidence for reinforcement as the response of S. hypoxantha did not differ between individuals that co‐occur with S. palustris and those that do not. Our finding suggests that song, a culturally inherited trait, may help maintain reproductive isolation between species in the rapid and explosive capuchino radiation.

Spread in Trinidad of the South American Fire AntSolenopsis invicta(Hymenoptera, Formicidae)

Solenopsis invicta, a fire ant originally from the grasslands of South America, has become an important exotic pest in the USA, East Asia, and elsewhere. This species arrived by ship in Mobile, Alabama in the 1930s and has since spread across much of the southern USA. Beginning in 1981, S. invicta has been reported from a growing number of West Indian islands, including Puerto Rico (1981), the Virgin Islands (1988), the Bahamas (1993), Antigua (2000), Caicos Islands (2001), Anguilla (2006), St Martin (2006), Barbuda (2007), Montserrat (2007), Nevis (2007), St Kitts (2007), Aruba (2007), and Jamaica (2010). In the present study, we examined the status of S. invicta on the island of Trinidad.Although the first published record of S. invicta in Trinidad dates to 2000, we have reliable records of this species from sugarcane and rice growing areas of west-central Trinidad dating to 1991 and specimens collected in 1993. In 2003–2004, we surveyed ants at sites all over Trinidad to document the distribution of S. invicta and its congener, Solenopsis geminata. We collected S. invicta at 60 sites, all in west-central Trinidad. In contrast, we collected Solenopsis geminata at 158 sites spread across all 7 counties of Trinidad. The highest densities S. invicta populations occurred in County Caroni, with scattered populations extending into disturbed areas of County St. George to the north and east, and County Victoria to the south. As of 2004, S. invicta occupied ∼10% of the island, but we see no reason why this species will not spread throughout most open, disturbed sites in Trinidad, displacing S. geminata as the dominant fire ant on the island.

Does human influence on coastal grasslands habitats affect predation pressure on snakes?

The loss and modification of habitats by humans have been considered key factors in the decline of diversity of species worldwide. However, the real effect caused by these disturbances on the biota is still poorly understood. The assessment of the changes in the network of interspecific interactions, such as predation rates on the native fauna, can be an important tool to diagnose the functionality of disturbed ecosystems. In this study we evaluate the predation rate on snakes in coastal grasslands in South America under human influence. Predation rate of artificial snakes, unlike that obtained in other studies, was lower in human-altered areas than preserved ones. Our findings may be due to a reduction in the abundance and/or richness of species of native predators in more disturbed areas.

Shifts in soil organic carbon for plantation and pasture establishment in native forests and grasslands of South America.

The replacement of native vegetation by pastures or tree plantations is increasing worldwide. Contradictory effects of these land use transitions on the direction of changes in soil organic carbon (SOC) stocks, quality, and vertical distribution have been reported, which could be explained by the characteristics of the new or prior vegetation, time since vegetation replacement, and environmental conditions. We used a series of paired-field experiments and a literature synthesis to evaluate how these factors affect SOC contents in transitions between tree- and grass-dominated (grazed) ecosystems in South America. Both our field and literature approaches showed that SOC changes (0-20cm of depth) were independent of the initial native vegetation (forest, grassland, or savanna) but strongly dependent on the characteristics of the new vegetation (tree plantations or pastures), its age, and precipitation. Pasture establishment increased SOC contents across all our precipitation gradient and C gains were greater as pastures aged. In contrast, tree plantations increased SOC stocks in arid sites but decreased them in humid ones. However, SOC losses in humid sites were counterbalanced by the effect of plantation age, as plantations increased their SOC stocks as plantations aged. A multiple regression model including age and precipitation explained more than 50% (p<0.01) of SOC changes observed after sowing pastures or planting trees. The only clear shift observed in the vertical distribution of SOC occurred when pastures replaced native forests, with SOC gains in the surface soil but losses at greater depths. The changes in SOC stocks occurred mainly in the silt+clay soil size fraction (MAOM), while SOC stocks in labile (POM) fraction remained relatively constant. Our results can be considered in designing strategies to increase SOC storage and soil fertility and highlight the importance of precipitation, soil depth, and age in determining SOC changes across a range of environments and land-use transitions.

Experimental control of Spanish broom (Spartium junceum) invading natural grasslands

A group of legumes generically known as brooms are among the most successful shrubs invading grasslands in South America and other regions. These species share a set of biological features that enhance their invasiveness, such as abundant and long-lasting seed banks, aggressive root systems and rapid growth, combined with their ability for re-sprouting after cutting or burning and for avoiding herbivores. They grow in dense stands that exclude native vegetation and are able to change ecological processes, increasing fire frequency and intensity, and fixing atmospheric nitrogen. The Spanish broom (Spartium junceum) is a shrub native form the Mediterranean that was introduced into the Argentine Pampas grasslands where it spreads over remnants of pristine ecosystems, threatening their biodiversity. This paper reports the results obtained after an adaptive management strategy aimed at controlling this species in a nature reserve, and compares the efficiency of different mechanical and chemical control techniques in terms of the number of plants killed and the effects on surrounding vegetation and on the recruitment of broom seedlings. Control was implemented in two phases, the first included three treatments: i) cut at the base of the plant, ii) cut followed by the immediate application of Togar (Picloram 3% + Triclopyr 6%, at a 5% dilution in diesel oil) on top of the cut stump, and iii) foliar spraying with Togar. The follow-up treatments, implemented one year later, consisted of spraying the re-sprouts with Togar (5% in diesel oil) or Glyphosate 36% (2% in water). The best option in terms of controlling Spanish broom was spraying the resprouts with Togar which gave 100% mortality of the treated plants, compared with values of 40% - 100% re-sprouting for the other options tested. None of the methods was associated with an increase in seedling recruitment, nor with significant changes in the vegetation in the immediate vicinity of the controlled brooms.

Poaceae pollen grain size as a tool to distinguish past grasslands in South America: a new methodological approach

Despite the dominance of grasslands during the last glacial period, especially in South America, the highly uniform morphology of Poaceae pollen grains has so far allowed only very few palynological studies based on Poaceae pollen. In our study we compare two methods of distinguishing between South American grassland ecosystems based on quantitative morphology of Poaceae pollen grains. We investigated data sets from Páramo in southern Ecuador, Campos de Altitude and Campos in south-eastern and southern Brazil as well as data sets from the Pampa in Argentina by measuring the pollen grain length, grain width, pore diameter and annulus width. Firstly we investigated the potential influence of chemical treatment of pollen grains on pollen grain size as well as the measurement setting for defining the boundary conditions for using Poaceae pollen grains in a palaeoecological investigation. Finally the measured pollen grain parameters were analyzed by comparison of average grain length using statistical tests. This approach reveals highly significant differences in average grain size between all grassland ecosystems. Assuming that a certain grain size range can be assigned to a certain Poaceae taxon, conclusions about differences and similarities in taxa composition can be derived. We used two methods of multivariate data analysis. One uses the pollen grain parameters directly for a Principle Component Analysis (PCA). The other is an already established method in grassland ecology which defines parameter based pollen grain types to investigate similarities between grassland ecosystems. Both approaches confirm the results of the grain length analysis. In this work we demonstrate that the method we developed has the potential to provide acquisition of so far inaccessible information on spatial and temporal patterns and dynamics of South American grasslands.

A phylogenetic analysis of the genus Paspalum (Poaceae) based on cpDNA and morphology

With about 350 species, Paspalum is one of the richest genera within the Poaceae. Its species inhabit ecologically diverse areas along the Americas and they are largely responsible for the biodiversity of grassland ecosystems in South America. Despite its size and relevance, no phylogeny of the genus as a whole is currently available and infrageneric relationships remain uncertain. Many Paspalum species consist of sexual-diploid and apomictic-polyploid cytotypes, and several have arisen through hybridization. In this paper we explore the phylogenetic structure of Paspalum using sequence data of four non-coding cpDNA fragments from a wide array of species which were combined with morphological data for a subset of diploid taxa. Our results confirmed the general monophyly of Paspalum if P. inaequivalve is excluded and the small genus Thrasyopsis is included. Only one of the four currently recognized subgenera was monophyletic but nested within the remainder of the genus. Some informal morphological groups were found to be polyphyletic. The placement of known allopolyploid groups is generally congruent with previously stated hypotheses although some species with shared genomic formulae formed paraphyletic arrangements. Other species formed a basal grade including mostly umbrophilous or hygrophilous species. It is hypothesized that the genus may have diversified as a consequence of the expansion of C4 grass-dominated grasslands in South America.

Dental microwear analysis of notoungulates (Mammalia) from Salla (Late Oligocene, Bolivia) and discussion on their precocious hypsodonty

The extinct endemic South American notoungulates are remarkable for their early evolution of hypsodonty in the Late Eocene/Early Oligocene. Due to this ‘precocious hypsodonty’ they have been considered to be the earliest grazers, suggesting an early spread of grassland in South America (at least 10 Myr earlier than in North America). This hypothesis is based on the idea that the abrasion of their hypsodont cheek teeth might have been caused by silica phytoliths which are abundant in a rich-in-grass diet. The analysis of the dental microwear pattern (using an optical stereomicroscope connected to a tri-CCD camera) of hypsodont notoungulates from the Late Oligocene Salla Beds of Bolivia revealed the preponderance of thin parallel scratches on the fossil teeth of most of the taxa analyzed, like extant grazers. This microwear pattern above all indicates predominant sub-horizontal jaw movements in the chewing behaviour of notoungulates with “precocious” hypsodonty. This signals shearing movements as in a diet rich in tough plants. This peculiar chewing pattern and/or a larger ingested proportion of grass phytoliths or exogenous grit are further discussed as hypothetical causes of increasing wear on notoungulate teeth during middle Cenozoic times. We particularly argue that the putative precocious spread of grasslands in South America traditionally linked with notoungulate hypsodonty is still far from being supported. Many questions arise concerning the development of hypsodonty within notoungulates and this case perfectly illustrates that the relations between high-crowned mammals and the source of tooth wear in the fossil record may not be straightforward.

Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) as a parasite of pampas deer (Ozoctoceros bezoarticus)

In the Pantanal, domestic and wild animals share the same habitats; their parasites and environment interact in a complex and dynamic way. The Rhipicephalus (Boophilus) microplus is the most important cattle tick in Brazil. In the past two decades, some traditional management practices are being replaced with the aim of intensifying cattle production. Forested areas are being replaced by exotic pasture and ranch owners are replacing Nelore for European breeds. The pampas deer (Ozoctoceros bezoarticus) is a medium-sized cervid that occurs in grasslands of South America. Between December 2005 and January 2007, we captured and collected ticks from 15 pampas deer and 172 bovines. The abundance, intensity, and prevalence of ticks found in cattle were lower than those in pampas deer (p < 0.05), indicating that pampas deer is more susceptible than cattle. The high number of engorged females collected from pampas deer, their capacity to lay eggs, and the percentage of eclosion indicates that the pampas deer population in the Pantanal wetlands is sufficient to maintain the R. (B.) microplus, thus playing a important role in the transmission of ticks and tick-borne diseases. The recent deforestation to introduce Brachiaria sp. and European cattle needs to be carefully evaluated to prevent economic losses to the cattle industry and damage to the wildlife in Pantanal.

Allergy due to Phytolacca dioica

Figura 1. The Phytolaccaceae (Pokeweed) family (Magnoliophyta division and Caryophyllales order) is constituted by trees, bushes and herbs and groups around 18 genera and almost 125 species widely distributed. Some species are used like foods and dyes, others have medicinal and ornamental properties. Phytolacca dioica (Ombu, Umbra tree, Elephant tree, Beautiful shade), a semideciduous tree native of the “Pampas” grasslands in South America, an specie cultivated into southern Europe, where it became adapted in regions with a Mediterranean climate.