Floristic groups and plant communities of southeastern Santa Fe,Argentina

This paper is a survey of the vegetation of the southeastern departments in the Province of Santa Fe (Argentina). The vegetation was analyzed following Braun-Blanquet's approach modified by Mueller-Dombois & Ellenberg (1974). The most relevant species of the region were placed in 25 groups according to their requirements or general behaviour. Most of the communities are herbaceous, and apart from the woody and some other miscellaneous ones they were grouped into three ecologically and floristically defined sets. The first set, the Stipa grasslands and related communities, which are characterized by the more or less abundant presence of Stipa hyalina, Stipa neesiana and Stipa papposa, comprises five different communities. The second, the halophilous communities, comprises five communities, the two Spartina ssp. grasslands, the halophilous prairies of Distichlis spicata, the short sedge Scirpus americanus communities and the ‘pela-dales’. The third, the hygrophilous communities, comprises nine communities which are not so well defined as the ones in the other sets. Besides, two further communities have been included, the Paspalum quadrifarium and the Melica macra tall grasslands.     

Anthropic modifications on megafauna bones in the paleontological collections of the Museum national d’Histoire naturelle de Paris: Historical aspects and implications for the Pampean Pleistocene peopling

The most abundant evidence of Pampean Pleistocene human presence are modified bones, as lithic procurement sites located farther than 300 km away. Therefore, we focused on the study of bone modifications, in particular cut and percussion marks. We studied Pampean paleontological collections of Argentine and European museums as an alternative resource of previously unnoticed human modification evidences. We compared marks characteristics with those of archaeological collections from diverse climatic and cultural adaptations, from middle Pleistocene sites (Vallonet, Atapuerca, Lazaret, Arago and Terra Amata) to terminal Pleistocene ones (Abri Pataud, Isturiz and La Vache). Marks typologies were defined, leading to the identification of a particular cutmark that we named double parallel considered as highly diagnostic of anthropic use of lithic artifacts. We also propose that hafted artifacts were used on carcass processing. Perimortem bone modifications are classified in relation with mark morphology (e.g., percussion striae), inferred gesture or action (e.g., breakage of diaphysis), and inferred objective of that action (e.g., marrow extraction). The megafauna specimens analyzed from the historical collections (d’Angelis-Vilardebó, 1847, Muñiz-Dupotet, 1842 and Breton-Bonnement, 1881) present modifications compatible with dismemberment, defleshing, tongue and masseter extraction, and utilization as anvils. The lack of contextual data (location, stratigraphy) and the loss due to museum selection/collecting of accompanying material prevent paleoenvironmental and paleoecological inferences. Regional geology indicates that most of the historical collections were exhumed in riverbank cuts with ages between 70 and 13 ky BP. Preliminary direct dating presents evidence of a Pampean human occupation, at least, since OIS 2.     

Success of active restoration in grasslands: a case study of birds in southern Brazil

Grasslands in southeastern South America have been extensively converted to various land uses such as agriculture, threatening regional biodiversity. Active restoration has been viewed as a management alternative for recovery of degraded areas worldwide, although most studies are conducted in forests and none has evaluated the effect of active restoration of grasslands in southeastern South America. From 2015 through 2017 we monitored a federally owned tract of grassland from the beginning of the active‐restoration process. We compared the bird community in this active‐restoration area (AR) with a reference area (NG) in Pampa grasslands in southern Brazil. We sampled birds by point counts and surveyed vegetation structure in plots. Over the 3 years of active restoration, bird species richness and abundance were higher in AR (30 species, 171 individuals) than NG (22 species, 154 individuals). The species composition also differed between the two habitats. Grassland bird species were present in both AR and NG. The vegetation structure differed between AR and NG in five attributes: height, short and tall grasses, herbs, and shrubs. Since it has been found that active restoration is useful in promoting species diversity, we encourage studies of the use of long‐term restoration efforts. Our study, even on a local scale, showed a rapid recovery of the bird community in the active‐restoration compared to native grassland, and suggests the potential for recovery of the degraded grasslands of the Brazilian Pampa biome.     

Post‐dispersal granivory in a tall‐tussock grassland: A positive feedback mechanism of dominance?

Questions: Is post‐dispersal seed predation a factor contributing to a positive feedback mechanism for dominance of tall‐tussock grasslands? Do seeds dispersed into neighbouring microhabitats of contrasting dominance differ in their probabilities of being predated? Does predation rate vary among predator groups? Do seed eaters selectively forage among the available seeds? Location: The southern and flooding sub‐regions of the Argentinian Pampas. Methods: We examined seed predation by vertebrate and invertebrate predators within two microhabitats of grassland mosaics (highly dominated tall‐grass patches vs. scarcely dominated short‐grass matrix) for different seed species in semi‐natural grasslands. Proportion of seeds eaten by different predator groups was estimated through exclusion experiments and analysed using ANOVA for split‐split‐plot designs. Experiments were performed during the autumn of two consecutive years in both Pampa sub‐regions. Results: Removal of seeds after a five day trial was two to four times higher in the tall‐grass patches than in the short‐grass matrix. During the same period, vertebrate predation was six times higher than invertebrate predation in the tall‐grass phase of the Southern Pampa, but it did not differ in the short‐grass matrix. Relative predation among phases showed the same pattern in the Hooding Pampa, where preferences by seed species also varied according to phase. Conclusions: The highest predation intensity shown by vertebrates in the tall‐grass patches indicates that they are the main seed predators in these systems, possibly because this microhabitat grants them refuge against carnivorous predators. This could significantly reduce the available seeds for recruitment of subordinate species after different disturbance events (fires, trampling by large herbivores, burrowing), representing an active filter to the floristic composition of the patch and contributing with other mechanisms to the dominance of tall‐grass species.     

Fungal endophyte infection changes growth attributes in Lolium multiflorum Lam

Abstract Lolium multiflorum is a successful invader of postagricultural succession in the Inland Pampa grasslands in Argentina, becoming a dominant species in the plant community. Individual plants of this annual species are naturally highly infected with fungal endophytes (Neotyphodium sp.) from early successional stages. We assessed the effect of Neotyphodium infection on the biology of L. multiflorum. We evaluated growth attributes between endophyte infected (E+) and uninfected (E–) plants under non‐competitive conditions during the normal growing season. E+ plants produced significantly more vegetative tillers and allocated more biomass to roots and seeds. Although seed germination rates were greater in endophyte free plants, the rate of emergence and the final proportion of emerged seedlings were similar between the biotypes. The greater production of vegetative tillers, and the greater resource allocation to roots and seeds are likely to confer an ecological advantage to E+ plants, thus enabling their dominance over the E– individuals in natural grasslands.     

Soil arthropod composition differs between old-fields dominated by exotic plant species and remnant native grasslands

Secondary succession after agriculture abandonment (old-fields) is mostly dominated by exotic grass species. Non-native plant invasions may alter soil fauna, potentially inducing plant-soil feedbacks. Despite their importance in nutrient cycling and plant-soil interactions, meso and macrofauna received less attention than bacteria or fungi. Here we compared the composition of the soil arthropod community in native remnants and plant exotic-dominated old-fields grasslands in the Inland Pampa, Argentina. We sampled independent remnants and old-field grassland plots within a 100 km² agricultural landscape to test the hypothesis that the abundance of soil arthropod organisms is related to the quality of the plant biomass, whereas the diversity of the soil biota is related to plant species richness, resulting in a different soil biota composition because of differing plant communities. When compared to non-invaded remnant grasslands, soil activity and soil food-web characteristics of the old-fields sites included: 1. Higher total arthropod abundance, particularly of Isopoda, Pseudoescorpionida and Blattaria; 2. Lower abundance of Hymenoptera and Enthomobryomorpha (Collembola); 3. Lower diversity, and evenness, but similar richness of soil organisms orders; 4. Higher soil respiration rates and soil temperature; and 5. Higher total soil N and K⁺content, but lower soil P content. These results illustrate that soil arthropod composition can vary widely within grasslands patches depending on plant species composition. Also, the more diverse plant community of remnant grasslands supports a more diverse soil biota, although soil activity is slower. Our results support the strong linkage between plant community and soil arthropod composition and suggest that changes in soil biota composition might promote plant-soil feedback interactions inducing the persistence of these alternative grassland states in new agricultural human-modified landscapes.     

Effects of fire frequency on survival,growth and fecundity of Paspalum quadrifarium (Lam.) in a grassland of the Flooding Pampa (Argentina)

Abstract Fire and grazing are important factors in the regulation of the grassland structure of the Flooding Pampa (Buenos Aires Province, Argentina dominated by Paspalum quadrifarium plants (henceforth ‘pajonal’)). Winter burning of pajonal is a practice that increases P. quadrifarium growth and its nutritious value for cattle. The objective of this work was to determine the responses of different demographic variables of P. quadrifarium growing in a grassland managed with different fire frequencies. The work was carried out in a pajonal situated in San Ignacio (Ayacucho county, Buenos Aires Province, Argentina). The treatments were: high fire frequency (0.8 fires per year) and low fire frequency (0.4 fires per year). The population of P. quadrifarium was affected by fire frequency. Biomass, number of tillers, and the relative production of tillers per plant did not change with fire frequency. Plant height was negatively affected by fire frequency. Whereas no plant mortality was observed in high fire frequency, 30% of the mature plants died at the end of the experiment in low fire frequency. In both treatments, plant mortality was size‐dependent and juvenile plants were more affected than mature ones. Burning had an immediate negative effect on mature and juvenile plants in terms of fecundity, survival of tillers and basal cover. Tiller survival and fecundity were significantly lower in burned plants than in unburned ones. In the high fire frequency treatment the number of ramets and/or genets and basal cover were greater than in the low fire frequency treatment.     

Adaptations and biomass production of two grasses in response to waterlogging and soil nutrient enrichment

We analysed the response of two grass species, Danthonia montevidensis and Paspalum dilatatum to waterlogging, soil-nutrient enrichment and the combination of both factors. Waterlogging did not affect total biomass of D. montevidensis, but it slightly promoted growth of P. dilatatum. Most analysed variables showed no significant interaction between fertilization and waterlogging. Therefore, waterlogging does not produce a detrimental effect either in the growth of these species or in their response capacity to stimulating growth factors, such as fertilization.     

Environmental variables for modeling wheat yields in the southwest pampa region of Argentina

Two types of time scales – 10-day intervals (D) and phenological phases (P) – were applied to environmental variables for the development of statistical regression models relating to the southwest pampa region of Argentina, with the aim of detecting the effects of weather on wheat yields for the period 1977–1999. The parameters were grouped as meteorological and processed variables and indices. The processed variables used were total soil water availability (SWA) and the ratio of actual evapotranspiration to potential evapotranspiration (), obtained from a water-balance model in which the moisture anomaly index (Z) and the Palmer drought severity index (PDSI) were calculated according to Palmers model. For these parameters it was possible to establish the times of year and the phenological phases with the best correlation to grain yield. The regression equation for meteorological variables on a 10-day scale provides one of the best fits. Using mixed parameters, the two models, D and P, give rise to a standard error of estimate of approximately 200 kg ha^–1. Truncated models perform better on a P scale than on a D scale. The use of phenological stages improved yield assessment, particularly for those years with extreme meteorological conditions. The optimum models were tested and root-mean-square errors (RMSE) of 440 kg ha^–1 and 470 kg ha^–1 were obtained for P and D scales respectively.     

Responses to flooding intensity in Leontodon taraxacoides

Natural flooding is one of the major factors affecting vegetation dynamics in many regions of the world. The Flooding Pampa Grasslands (Argentina) are frequently exposed to flooding events of diverse intensity and duration, some of which Leontodon taraxacoides , an exotic dicot. frequent in these grasslands, seems to survive. Its responses to four different water depths (0, 1, 7 and 13 cm) were studied. The results indicate that plants in conditions of total submergence (depth of 13 cm) did not survive. In less severe flood conditions, increases in the leaf insertion angle resulted in the maintenance of a large proportion of the total leaf area above the water. Differences in leaf length and a decrease in the width and the proportion of lobes per leaf were also found under partial submergence conditions (depth of 7 cm). Root and leaf aerenchyma, present in unflooded plants, showed a significant increase in flood conditions. In spite of the anatomical and morphological responses, total biomass and leaf area were severely affected by water depth. Control plants allocated more biomass to reproductive organs, while partly submerged plants allocated more to leaves and less to reproductive organs. Mature L. taraxacoides plants presented a wide range of plastic adjustment as a survival strategy in soil anaerobiosis, and appear to be able to survive short spring floods in a vegetative state; in contrast, they might not tolerate total submergence conditions imposed by more intense and long-lasting floods.