Pampean Vegetation

Plant Formations in the Pampean BioProvince

Peter Martin Rhind

Pampean Rolling Pampa These natural grasslands once covered large areas and were, for example, the characteristic vegetation in the Pergamino area (Buenos Aires Province), but their total area extents from the Rio de la Plata and Rio Parana in the northwest, to the Rio Salada in the southwest and the Rio Matanza in the southeast. The terrain over much of this area has a gently rolling relief with good drainage. The structure of these grasslands can be compared to prairie in humid years but are more like steppe during dry periods. However, except in the driest periods the foliage is usually dense with 90-100% cover and can reach heights of up to 100 cm. The species least affected by draught are the suffrutescent perennials (including species of Baccharis, Eupatorium, Heimia and Vernonia) and the bunch grasses Stipa brachychaeta and S. trichotoma. The dominant species, especially on fertile soils, are usually Aristida murina, Bothriochloa laguroides, Stipa neesiana, S. papposa and the endemic or near endemic Piptochaetium montevidense (Poaceae). Other frequent grasses are Briza brizoides, Melica brasiliana, Paspalum dilatatum and Piptochaetium bicolor, while less common species include several endemic or near endemic taxa such as Agrostis montevidensis, Danthonia montevidensis and Poa bonariensis (Poaceae). Shrubs and suffrutices are not common. Among the more frequent species are Baccharis articulata, Eupatorium buniifolium, Heimia salicifolia, Margyricarpus pinnatus, Vernonia rubricaulis and the endemic or near endemic Hedeoma multiflora (Lamiaceae). On the the other hand, there are numerous small herbs and sedges including Adesmia bicolor, Berroa gnaphaloides, Conyza blackei, Tragia geraniifolia and the endemic or near endemic Carex bonariensis (Cyperaceae) and Conyza bonariensis (Asteraceae). Some species, such as Chavreulia sarmentosa and the endemic or near endemic Facelis retusa (Asteraceae), Micropsis spathulata (Asteraceae) and Polygala australis (Polygalaceae) become much more conspicuous during spring. Where the soils are more alkaline there can be clear changes in species composition. Grasses such as Schedonnardus paniculatus, Sporobolus pyramidatus, Stipa papposa and the endemic or near endemic Bouteloua megapotamica (Poaceae) become more common together with broad-leaved herbs such as Solanum meloncilla and the endemic or near endemic Jaborosa runcinata (Solanaceae).

Pampean Flooding Pampa These wet or humid grasslands are located in the Laprida basin and the Rio Salada basin between the rolling and southern pampas. Some of the grasses, such as Bothriochloa laguroides and Briza subaristata, of these usually low and flat areas, are in fact, also found in rolling pampa but a number of others are characteristic. These include Chaetotropis elongata, Distichlis scoparia, Paspalidium paludivagum, Paspalum vaginatum, Sporobolus indicus, Stipa formicarum and Stenotaphrum secundatum, although composition can be significantly altered by domestic grazing, and there may be several introduced species. Where flooding tends to persist for long periods other species such as Agrostis jurgensii, Deyeuxia viridiflavescens, Leersia hexandra, Panicum milioides and Phalaris angusta become more conspicuous. Swamps and depressions that are more or less inundated all year round are typically dominated by one or two reed-like species. Among the common monodominants here are Typha dominguensis and the endemic or near endemic Zizaniopsis bonariensis (Poaceae), but in saline swamps either Spartina brasiliensis or endemic or near endemic Spartina montevidensis (Poaceae) usually predominate. Common broad-leaved herbs throughout the flooded pampa include Alternanthera philoxeroides, Eryngium ebracteatum, Heliotropium curassavicum, Petunia parviflora, Sida Copyright © 2010 Peter Martin Rhind leprosa, Vicia graminea and the endemic or near endemic Grindelia discoides (Asteraceae) and Pamphlalea bupleurifolia (family?).

Pampean Inland Pampa Located to the west and southwest of the rolling pampa these grasslands cover a relatively flat terrain broken only by the ridges of fixed sand dunes. Most have now, however, been altered by domestic grazing but there is some original (climax) grassland in the San Luis Province. Here the foliage is less dense than in other pampas types with ground cover of just 60-80%. The dominant grasses are Elyonurus muticus and Sorghastrum pellitrum. Others include Aristida spegazzini, Bothriochloa springfieldii, Chloris retusa, Eragrostis lugens, Poa lanuginosa and Schizachyrium plumigerum. Perennial broad-leaved herbs are also characteristic with species such as Macrosiphonia petrae, Relbunium richardianum, Stevia satureiaefolia and the endemic Glandularia hookeriana (Verbenaceae) and Mitracarpus megapotamicus (Rubiaceae). Shrubs represent an occasional feature with the most frequent species being the spiny, endemic Prosopis alpataco (Fabaceae). Along the border between the provinces of Buenos Aires and La Pampa a slightly different assemblage occurs. Here the dominant grasses include Panicum urvilleanum, Poa ligularis, Stipa filiculmis, S. tenuissima and S. trichotoma. There are again numerous broad-leaved herbs with species such as Glandularia peruviana, Lathyrus pubescens, Oenothera longiflora, Pfaffia gnaphaloides and the endemic or near endemic Eryngium horridum (Apiaceae), Hypochoeris pampasica (Asteraceae) and Lathyrus subulatus (Fabaceae). Annual plants are also featured with common taxa including Cenchrus pauciflorus, Plantago patagonica, Vicia selloi and the endemic Conyza bonariensis (Asteraceae). Among the shrubby elements Baccharis appears to be the most common genus with species such as Baccharis coridifolia and the endemic Baccharis artemisioides (Asteraceae). Other common shrubs include the endemic or near endemic Hyalis argentea and Thelesperma megapotamicum (Asteraceae).

Pampean Southern Pampa This, the southernmost pampa, is situated in an area, which includes the pediments of Tandilia and Ventania mountains and the adjacent coastal plains. The remaining natural, unmodified areas are usually dominated by Piptochaetium lejopodum, P. napostaense, Poa ligularis, Stipa clarazii, S. neesiana, S. tenuis and S. trichotoma. Other common grasses include Briza subaristata, Melica macra, Piptochaetium cabrerae, Stipa ambiqua and the endemic or near endemic Bouteloua megapotamica and Piptochaetium montevidense (Poaceae). Many of the associated herbs and shrubs are also found in rolling pampa but there are also several southern endemic species such as Micropsis australis (Asteraceae) and Sphaeralcea australis (Malvaceae). In the more rocky, hilly areas the grass Paspalum quadrifarium and various broad-leaved herbaceous species of Eryngium (e.g. E. eburneum, E. elegans, E. horridum, E. paniculatum, E. serra) usually dominate, and where the soils are well-aerated the two shrubs Colletia paradoxa and Dodonea viscosa can become common forming thickets up to 2.5 m high in places. Other less common shrubs are Eupatorium buniifolium, Discaria longispina, Wedelia buphthalmiflora and the endemic Baccharis tandilensis (Asteraceae). At even high elevations above 500 m several local endemics become prominent including the grasses Festuca pampeana, F. ventanicola, Stipa juncoides (Poaceae) and the broad-leaved herbs Mimosa racae (Fabaceae), Plantago bismarkii (Plantaginaceae) and Senecio ventanensis (Asteraceae).

Pampean Mesopotamic Pampa Situated between Uruguay and the Parana rivers, this zone has both rolling and hilly aspects and in addition to grassland includes some remarkable gallery forests. The main

Copyright © 2010 Peter Martin Rhind distinguishing feature of the grasslands compared with other parts of the pampa is the abundance of subtropical grass genera such as Axonopus, Bothriochloa, Digitaria, Paspalum and Schizachyrium, and a reduction in the number of species of Piptochaetium, Poa and Stipa as compared with southern grasslands. On the other hand, the dominant species are Stipa neesiana and S. tenuissima together with Eragrostis cilianensis. Other abundant species include Aristida murina, Bothriochloa barbinodis, Briza subaristata, Bromus unioloides, Chloris ciliata, Deyeuxia viridiflavescens, Melica basiliana, Panicum bergii, Paspalum plicatulum, Schizachyrium intermedium, Setaria fiebrigii and Sporobolus indicus. The associated broad-leaved herbs and shrubs are more or less similar to those of rolling pampa.

Pampean Southern Campos Like the rolling pampas, these grasslands are also in areas of gently rolling terrain but these are Uruguayan grasslands and extend from the Rio Yi southwards to the Atlantic Ocean. In their natural state they are similar to rolling pampa and mesopotamic pampa. The dominant grasses include Agenium villosum, Bromus unioloides, Deyeuxia viridiflavescens, Leptocoryphium lanatum, Paspalum notatum, Poa lanigera, Stipa hyalina and the endemic or near endemic Poa bonariensis and Stipa megapotamica (Poaceae). However, before human intervention, Stipa charruana was probably the dominant grass especially on deep fertile soils and it still forms vigorous tall grass formations on soils of medium fertility. Associated shrubs are similar in species composition to the grasslands south of Rio de la Plata, but Paspalum quadrifarium was probably more frequent in pristine grasslands. In grazed areas the main dominants include Poa lanigera, Trifolium polymorpha and the endemic Carex bonariensis (Cyperaceae) together with a number of introduced species such as Lolium multiflorum. Broad-leaved herbs are again quite numerous and include the two umbilifers Diposis saniculaefolia and the endemic annual Notiosciadium pampicola (Apiaceae). In wet depressions species of Cyperus and Juncus predominate, and in hydromorphic soils the tall grass Cortaderia selloana becomes common. This species is now rare in the northern campos.

Pampean Northern Campos These grasslands, which extent from Uruguay to southern Brazil, are generally flat but with occasional rocky outcrops. However, there are hilly areas near to the sources of the Rio Negro and near the Rio Camaqua. The rivers and streams typically support gallery forests. The grasslands have many similarities with southern campos and pampas in general. They are mainly distinguished by the fact that species of Andropogoneae and Paniceae are more numerous, while species of Aristida, Piptochaetium and Stipa decrease in importance. The most important species are Andropogon lateralis, Axonopus compressus, Paspalum notatum and Schizachyrium condensatum, while other typical grasses are Agenium villosum, Leptocoryphium lanatum, Trachypogon montufari and Tridens brasiliensis. The associated broad-leaved herbs typically comprise Euphorbia papillosa, E. selloi, Gomphrena celosioides and the endemic or near endemic Mitracarpus megapotamicus (Rubiaceae). On knolls where lateritic soils predominate grasses such as Aristida jubata, Axonopus suffultus, Elyonurus muticus, Eragrostis airoides and Hypogynium virgatum occur, whereas in the humid valleys tall grass associations of Paspalum quadrifarum predominate. In the latter the associated grasses include Eragrostis babiensis, Eriochloa punctata, Rottboellia selloana, Stipa philippii and the endemic or near Phalaris platensis (Poaceae), while the most important herbs include Eryngium echinatum and Verbena littoralis. Some of the endemic species found in northern campos include Adesmia araujoi, A. bicolor, Arachis burkartii, Trifolium polymorphum (Fabaceae), Bouteloua megapotamica, Melica rigida, Stipa filifolia, S. philippii (Poaceae) and Eleocharis dunensis (Cyperaceae).

Pampean Sierras Pampeanas (Córdoba Mountains) Granite Shrub Formations On the granite outcrops of the Córdoba Mountains (central Argentina) two types of shrub formations can be distinguished - one is dominated by Satureja odora and the endemic Berberis hieronymi (Berberidaceae), the other by the two endemic or near endemic shrubs Croton argentinus (Euphorbiaceae) and Heterothalamus alienus (Asteraceae). The first of the formations occupies relatively large outcrops with deep crevices. Common associates include Asplenium gilliesii, Baccharis myrtilloides, Bowlesia lobata, Calceolaria losseni, Chenopodium chilense, Deyeuxia hieronymi, Dunalia brachyacantha, Thalictrum decipiens and the endemic or near endemic Blumenbachia insignis (Loasaceae) and Senecio pampeanus (Asteraceae). Shrub vegetation dominated by Croton argentinus and Heterothalamus alienus is usually confined to smaller outcrops in drier more exposed situations. Consequently most of the species are draught adapted (xerophytic). They generally include Borreria eryngioides and the endemic or near endemic Eryngium horridum (Apiaceae). Other endemic or near endemic species include Agrostis montevidense (Poaceae) and various composites such as Conyza burkartii, Hieracium giganteum and Stevia achalensis (Asteraceae). Throughout both of these shrub formations are various ferns such as Polypodium argentinum, Polystichum montevidense and Woodsia montevidense, some of which have interesting distributions. Several occur along the Andes, some from as far north as Central and North America, to the Córdoba Mountains and then reappear in the Buenos Aires Mountains – a distribution that has been described as the “pampean-andean” arch.

Pampean Sierras Pampeanas (Córdoba Mountains) Granite Herb Formations On the granite uplands of Córdoba in central Argentina two types of herb formations can be distinguished. One dominated by Sorghastrum pellitum and Stipa flexibarbata and the other by Crassula peduncularis and Limosella lineata. The first type occurs on shallow soils between loose rocks and shallow depressions. Most of the characteristic species are xerophytes and typically include Botrychium australe, Bromus auleticus, Gamochaeta spicata, Paronychia chilensis, Poa resinulosa, Stenandrium dulce and the endemic or near endemic Facelis retusa (Asteraceae), Hypochoeris caespitosa (Asteraceae) and Plantago brasiliensis var. cordobensis (Plantaginaceae). Many of the other endemic species found here are also associated with the Satureja odora - Berberis hieronymi shrub formations (see above), but there may also be various endemic or near endemic composites such as Conyza bonariensis and Gamochaeta calviceps (Asteraceae). Herb formations dominated by the dwarf plants Crassula peduncularis and Limosella lineata are mainly found in granitic depressions often surrounded by turf. These often dry out causing severe restrictions on plant growth. Consequently species diversity tends to be low and most of the associated plants are annuals such as Lilaea scilloides, Ranunculus flagelliformis and the endemic Soliva trinifolia (Astereaceae). The only perennial species are the endemic or near endemic Juncus achalensis and J. uruguensis (Juncaceae).

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References

Altesor, A., Di Landro, E., May, H. & Ezcurra, E. 1998. Long-term species change in an Uruguayan grassland. Journal of Vegetation Science, 9: 173-180.

Altesor, A., Piñeiro, G., Lezama, F., Jackson, R. B., Sarasola, M. & Paruelo, J. M. 2006. Ecosystem changes associated with grazing in subhumid South American grasslands. Journal of Vegetation Science, 17: 323-332.

Anon. 1996. Habitats of South America. Institute of Terrestrial Ecology and Intitut Royal Des Sciences Naturelles De Belgique.

Burkart, A. 1975. Evolution of grasses and grasslands in South America. Taxon, 24: 53-66.

Burkart, S. E., León, R. J. C., Perelman, S. B. & Agnusdei, M. 1998. The grasslands of the flooding pampa (Argentina): floristic heterogeneity of natural communities of the southern Rio Salado Basin. Coenoses, 13: 17-27.

Cabido, M., Acosta, A. & Diaz, S. 1990. The vascular flora and vegetation of granitic outcrops in the upper Córdoba Mountains, Argentina. Phytocoenologia, 19: 267-281.

Facelli, J. M., Leon, R. J. C. & Deregibus, V. A. 1989. Community structure in grazed and ungrazed grassland sites in the flooding Pampa, Argentina. American Midland Naturalist, 121: 125-133.

Faggi, A. M., Krellenberg, K., Castro, R., Arriaga, M. & Endlicher, W. 2008. Biodiversity in the Argentinean Rolling Pampa Ecoregion: Changes Caused by Agriculture and Urbanization. Urban Ecology, pp. 377-389.

Feldman, S. R. & Refi, R. O. 2006. Changes in the floristic composition in a pampean native grassland under different management practices. Ciencia e Investigación Agraria, 33: 89-96.

Fontana, S. L. 2005. Coastal dune vegetation and pollen representation in south Buenos Aires Province, Argentina. Journal of Biogeography, 32: 719-735.

Overbeck, G. E., Müller, S. C., Fidelis, A., Pfadenhauer, J., Pillar, V. D., Blanco, C. C., Boldrini, I. I., Both, R. & Forneck, D. 2007. Brazil’s neglected biome: The South Brazilian Campos. Perspectives in Plant Ecology, Evolution and Systematics, 9: 101-116. ScienceDirect. Elsevier.

Parodi, L. R. 1947. La Estepa Pampean. Geografia de la Republica Argentina, 8: 143-207.

Perelman, S. B., León, R. J. C. & Oesterheld, M. 2001. Cross-scale vegetation patterns of flooding pampa grasslands. Journal of Ecology, 89: 562-577.

Prieto, A. R. 1996. Late Quaternary vegetation and climatic changes in the pampa grassland of Argentina. Quaternary Research, 45: 73-88.

Ragonese, A. E. & Castiglioni, J. C. 1970. La vegetacion del Parque Chaqueno. Boletin de la Sociedad Argentina de Botánica, 11: 133-160.

Rodríguez, C., Leoni, E., Lezama, F. & Altesor, A. 2003. Temporal trends in species composition and plant traits in natural grasslands of Uruguay. Journal of Vegetation Science, 14: 433-440.

Rusch, G. M. & Oesterheld, M. 1997. Relationship between productivity and species and functional group diversity in grazed and non-grazed Pampas grassland. Oikos, 78: 519- 526.

Sluijs, D. H. van der. 1971. Native grasslands of the Mesopotamia region of Argentina. Netherlands Journal of Agricultural Science, 19: 3-22.

Zuloaga, F. O. & Morrone, O. 1996. Catálogo de las Plantas Vasculares de le República Argentina. I. Pteridophyta, Gymnospermae y Angiospermae (Monocotyledoneae). Monographs in Systematic Botany from the Missouri Botanical Garden Press. Volume 60.

Zuloaga, F. O. & Morrone, O. 1999. Catálogo de las Plantas Vasculares de le República Argentina. II. Acanthaceae – Euphorbiaceae. Monographs in Systematic Botany from the Missouri Botanical Garden Press. Volume 74.

Zuloaga, F. O. & Morrone, O. 1999. Catálogo de las Plantas Vasculares de le República Argentina. II. Fabaceae – Zygophyllaceae. Monographs in Systematic Botany from the Missouri Botanical Garden Press. Volume 74.