ARTICLE IN PRESS Perspectives in Plant Ecology, Evolution and Systematics Perspectives in Plant Ecology, Evolution and Systematics 9 (2007) 101–116 www.elsevier.de/ppees

Brazil’s neglected biome: The South Brazilian Campos Gerhard E. Overbecka,, Sandra C. Mu¨llerb, Alessandra Fidelisa, Jo¨rg Pfadenhauera, Vale´rio D. Pillarb, Carolina C. Blancob, Ilsi I. Boldrinic, Rogerio Bothd, Eduardo D. Forneckd a

Chair of Vegetation Ecology, Department of Ecology, Technische Universita¨t Mu¨nchen, Am Hochanger 6, 85350 Freising, Germany b Laboratory of Quantitative Ecology, Department of Ecology, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonc¸alves 9500, Porto Alegre 91540-000, RS, Brazil c Department of Botany, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonc¸alves 9500, Porto Alegre 91540-000, RS, Brazil d Laboratory of Landscape Ecology, Department of Ecology, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonc¸alves 9500, Porto Alegre 91540-000, RS, Brazil Received 16 October 2006; accepted 20 July 2007

Abstract The South Brazilian grasslands occupy some 13.7 million ha and support very high levels of biodiversity. This paper reviews the current state of ecological knowledge on South Brazilian Campos and of threats and challenges associated with their conservation. The principal factors shaping grassland physiognomy and diversity are discussed, and information is presented on diversity of plant species; best estimates suggest that 3000–4000 phanerophytes occur in the South Brazilian grasslands. It is argued that, despite their high species richness, Campos vegetation is not adequately protected under current conservation policies. In the past three decades, approximately 25% of the grassland area has been lost due to land use changes, and this trend continues. However, representation of Campos grasslands in conservation units is extremely low (less than 0.5%), and the management in most of these is inadequate to preserve the grasslands, as grazing and fire are important factors for their persistence. In conclusion, the following urgent needs are identified: (1) to create more conservation units in different regions, including different grassland types throughout southern Brazil, (2) to develop proper management strategies where grasslands are subject to shrub encroachment and forest expansion, (3) to conduct research on biodiversity and ecological processes in the Campos region and (4) to raise public awareness of the value and vulnerability of this vegetation type. r 2007 Ru¨bel Foundation, ETH Zu¨rich. Published by Elsevier GmbH. All rights reserved. Keywords: Biodiversity; Conservation; Grassland; Land use change; Plant species; Preservation

Corresponding author. Academy of Spatial Research and Planning, Scientific Section III: Natural Resources, Environment, Ecology, Hohenzollernstraße 11, 30161 Hannover, Germany. Tel.: +49 511 3484 222. E-mail address: [email protected] (G.E. Overbeck).

Introduction Brazil is one of the world’s megadiverse countries (e.g. Barthlott et al., 1996; Lewinsohn and Prado, 2005), but

1433-8319/$ - see front matter r 2007 Ru¨bel Foundation, ETH Zu¨rich. Published by Elsevier GmbH. All rights reserved. doi:10.1016/j.ppees.2007.07.005

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the threats to its wildlife and natural landscapes are dramatic (e.g. Brandon et al., 2005; Mittermeier et al., 2005). In a recent special section in Conservation Biology (vol. 19(3); Lovejoy, 2005), a number of papers discussed biodiversity and nature conservation in Brazil. According to the current official classification of vegetation in Brazil by IBGE (2004), Brazil possesses six major continental biomes – Amazonia, the Atlantic Forest (with inserted discontinuous grassland areas, especially on plateau sites in its southern part), the Caatinga, the Cerrado, the Pantanal, the Pampa – and additionally the coastal areas (Fig. 1). The grassland vegetation in southern Brazil – referred to here as the Campos (grassland) region – is thus included in two separate biomes in the IBGE (2004) classification: the biome of the Pampa, in the southern half of Rio Grande do Sul state, and the Atlantic forest biome. The latter includes the grasslands of the South Brazilian Plateau that form a mosaic with forests in the northern half of Rio Grande do Sul and in the states of Santa Catarina and Parana´ (see Fig. 1). In the special section in Conservation Biology, the grasslands in southern Brazil were barely mentioned (see e.g. Brandon et al., 2005) and the grassland areas in the Atlantic Forest biome and the Pampa biome were not discussed in any detail. In this paper, we provide a review of the ecological characteristics of South Brazilian grasslands and of their present state of conservation. We briefly characterize the vegetation throughout the grassland region, identify the principal ecological factors responsible for grassland

biodiversity, and initiate a discussion on sustainable management and biodiversity conservation. Like other non-forest vegetation types in Brazil (e.g. Cerrado; see Cavalcanti and Joly 2002), the Campos region has not been treated as a conservation priority in the past: The current threats, successes and conservation challenges are presented in this paper. As most research has been conducted in Brazil’s southernmost state Rio Grande do Sul, and as this state contains approximately 75% of the grassland area, much of the available data is from this state.

Present-day vegetation in southern Brazil – an overview Due to its geographic position around the 301S parallel of latitude, at the limit for tropical vegetation types (Cabrera and Willink, 1980), and its position on the eastern side of South America, southern Brazil occupies a transitional zone between tropical and temperate climates, with hot summers and cool winters and no dry season. Variation in geological substrate and altitude further contribute to the diversity of vegetation types in the region (Waechter, 2002). The natural vegetation in South Brazil is a mosaic of grassland, shrubland and different forest types (Teixeira et al., 1986; Leite and Klein, 1990). Atlantic forest (Atlantic forest sensu stricto, Oliveira-Filho and Fontes, 2000)

Fig. 1. Location of South Brazilian grasslands: (a) overview, (b) official Brazilian classification of biomes (IBGE, 2004) and (c) distribution of grasslands in Brazil’s southern region (abbreviation of states: RS: Rio Grande do Sul; SC: Santa Catarina, PR: Parana´).

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occupies the eastern slopes and valleys of the South Brazilian Plateau from the northeast of Rio Grande do Sul to the coastal plain and highland slopes of Santa Catarina and Parana´. Araucaria forest, physiognomically dominated by Araucaria angustifolia (Bertol.) Kuntze in the upper stratum, is found mostly on the plateau in Parana´, Santa Catarina and Rio Grande do Sul states, forming mosaics with natural Campos, the area of the latter increasing towards the south. Seasonal deciduous forest, which together with Araucaria forest is included in Atlantic forest sensu lato (Oliveira-Filho and Fontes, 2000), can be found in western Santa Catarina and Parana´, along the upper Uruguai river and in the Ibicuı´ and Jacuı´ river basins in the central lowlands of Rio Grande do Sul. The northern section of Parana´ state likewise is characterized by seasonal semideciduous forest, and some Cerrado (Brazilian savanna) fragments. The same forest type occurs in the southeastern highlands (Serra do Sudeste) in Rio Grande do Sul. In the westernmost tip of Rio Grande do Sul state, an Acacia–Prosopis parkland vegetation provides a transition to the Chaco and Espinal formations further to the west (Waechter, 2002). The grasslands of the southern and western parts of Rio Grande do Sul often are included in the literature in the Rı´o de la Plata grasslands that extend into Argentina and Uruguay (Burkart, 1975; Soriano et al., 1992; Bilenca and Min˜arro, 2004). Phytogeographically, the South Brazilian Campos are in the Neotropical Region and are part of two biogeographical domains, Amazonian and Chacoan, represented by the Parana´ (Parana´ state, Santa Catarina state and the northern part of Rio Grande do Sul state) and Pampean (southern part of Rio Grande do Sul) provinces (Cabrera and Willink, 1980), respectively. The boundary between these provinces more or less corresponds to the 301S latitude line that separates the Mata Atlaˆntica and Pampa biomes in the Brazilian biome classification (IBGE 2004; more explanation further in this paper). In the Parana´ province, the relief is undulating (South Brazilian Plateau), precipitation is high (1500–2000 mm) without a dry season, and mean annual temperature ranges from 16 to 22 1C except at the highest elevations (reaching 1800 m in Santa Catarina state) where it is 10 1C (Nimer, 1990). While summers are warm, frosts can occur in winter, especially at higher elevations. The grassland vegetation, which cooccurs with subtropical and Araucaria forests, is considered as forming a separate zone within the Parana´ province, but geographically more or less interwoven with the flat southern Pampean province (Cabrera and Willink, 1980). In the Pampean province, i.e. the southern half of Rio Grande do Sul and adjacent areas of Uruguay and Argentina, annual precipitation (ca. 1200–1600 mm) and mean annual temperatures (13–17 1C) are both lower. Grass-dominated vegetation

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types prevail, with many herb, shrub and treelet species co-occurring within the grass matrix. Most of the flora stems from Chacoan domain, but there also are species from Andean–Patagonean and Amazon domains (Cabrera and Willink, 1980).

Past climate changes and vegetation history A century ago, Lindman (1906) noted the contradiction between the presence of grassland vegetation in southern Brazil and climatic conditions that allow forest to develop. Similarly, the presence of grasslands in the Rı´ o de la Plata region in areas where the climate is apparently capable of supporting forest vegetation has led to an intense debate of the so-called ‘‘Pampas problem’’ (e.g. Walter, 1967; Eriksen, 1978; Box, 1986). Palynological research clarified the climatic and vegetation history of southern and southeastern Brazil (e.g. Behling, 1998, 2002; Ledru et al., 1998; Behling et al., 2001, 2004, 2005; Behling and Pillar, 2007) and supported earlier theories by Rambo (1956a, b). In summary, four distinct climatic periods can be recognized from the late Pleistocene until today. Between about 42,000–10,000 years before present (BP), i.e. including the last glacial maximum, grasslands dominated in the region, indicating a cold and dry climate. Most of the region was probably treeless, with forest elements restricted to sites in deep river valleys and in the coastal lowlands. After 10,000 years BP, temperatures rose but Araucaria forest did not expand because the climate remained dry. However, Atlantic forest migrated southwards along the coast where conditions must have been wetter. From the beginning of the Holocene onwards, fire became more frequent, as indicated by the greater abundance of charcoal particles in peat profiles (Behling et al., 2004, 2005); this was probably related to the arrival of indigenous populations in the region coupled with a more seasonal climate. At roughly the same time, large grazing animals went extinct (Kern, 1994). Indigenous people most likely used fire for hunting and for land management (Kern, 1994; Schmitz, 1996), but no direct evidence exists. After the mid-Holocene, around 4000 years BP, the climate became moister, allowing for a slow expansion of forest, principally along rivers. The speed of expansion greatly increased after 1100 years BP, leading to a more pronounced substitution of grassland by forest vegetation, forming larger areas of continuous forest cover on the Plateau and riparian forests in the lowlands (Behling et al., 2004, 2005, 2007; Behling and Pillar, 2007). In the 17th century, Jesuit missionaries introduced horses and cattle into the region (Pillar and Quadros, 1997), and beef cattle production became an important land use in southern Brazil, and remains so today. As has been

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shown on other continents (e.g. Bond et al., 2003 for South Africa; Sauer, 1950; Vogl, 1974; Anderson, 1982 for North America), fire and/or grazing are probably the principal factors impeding forest expansion in grassland areas where climatic conditions are favourable for forest (see below).

A classification of South Brazilian grasslands The national project of vegetation classification (RADAMBRASIL; Instituto Brasileiro de Geografia e Estatı´ stica (IBGE), 1986) divided the South Brazilian grasslands into two large phytoecological regions, the savannas and the steppes (Teixeira et al., 1986). This classification was based on vegetation physiognomy, with the term ‘steppes’ being used to characterize low, single-layer grasslands in the eastern part of Rio Grande do Sul, and ‘savannas’ to describe grassland composed of two layers. In the last edition of the official map of vegetation and biomes of Brazil (IBGE, 2004), building on work by Leite (2002) who used the term steppe for all grassland types in southern Brazil, the southern part of Rio Grande do Sul state was denoted Pampa Biome (IBGE, 2004), corresponding to 63% of the area of the state. The natural grassland vegetation that occurs on the Plateau of Rio Grande do Sul and Santa Catarina and to a smaller extent in Parana´, and that forms mosaics with forest formations, was considered as part of the Atlantic Forest Biome (IBGE, 2004), thus reflecting the phytogeographic provinces of Cabrera and Willink (1980). According to most vegetation classifications, steppe and savanna are inappropriate terms to describe the grasslands of southern Brazil. Steppes are usually considered to be semi-arid grasslands with a cool temperate climate, such as tall and short grass prairie in North America, or Eurasian grasslands from Ukraine to Mongolia (e.g. Breckle, 2002; Bredenkamp et al., 2002; Schultz, 2005). In all of these regions, low precipitation, generally less than 250 mm during the warm season, restricts the development of forest vegetation, but this is clearly not the case in southern Brazil. In South America, steppes can be found only in eastern Patagonia (Schultz, 2005). The term ‘‘Pampa’’ also seems unfortunate, because it usually is associated with the grasslands south of the Rı´ o de la Plata (Soriano et al., 1992). Savannas generally are defined as vegetation types possessing a mixture of woody and herbaceous life-forms in distinct strata that occur in tropical regions with strongly seasonal precipitation (Walker, 2001). In Brazil, the term savanna is applicable to Cerrado vegetation (Oliveira and Marquis, 2002); however, used more loosely (Cerrado sensu lato) the term Cerrado also includes the tropical grasslands

known as campo limpo or campo sujo (e.g. OliveiraFilho and Ratter, 2002). Describing the South Brazilian grasslands as savannas and steppes is thus in disagreement with the accepted international use of these terms (also see Marchiori, 2002). Classical botanical and phytogeographical studies (e.g. Lindman, 1906; Rambo, 1956a) and more recent works on grassland vegetation in southern Brazil (e.g. Boldrini, 1997; Pillar and Quadros, 1997; Overbeck and Pfadenhauer, 2007), although without classificatory objectives, prefer to refer to grassland formations in southern Brazil simply as Campos. However, terms as Campo limpo (clean grassland, i.e. without a woody component) and Campo sujo (dirty, i.e. shrubby grassland) have become commonly used. In trying to differentiate different types of grasslands within the Campos region, most studies reflect the two different biogeographical domains (see above; see Tables 1 and 2 for a compilation of characteristic species) and regional differences in Campos flora, with notably higher contribution of C3 grasses (e.g. from the genera Briza, Piptochaetium, Poa, Stipa) in the southern half of Rio Grande do Sul (Burkart, 1975; Valls, 1975). Boldrini (1997) describes six physiognomic regions of Campos vegetation in Rio Grande do Sul state, considering local floristic variations associated with climate, topographic variation and soil heterogeneity. However, a good portion of the variation in grassland physiognomy (e.g. distinction between campo limpo and campo sujo) and in the composition of the dominant species, irrespective of region, seems to be determined by grazing and fire regimes (Pillar and Quadros, 1997). Altogether, internal classification of the Campos grasslands is still in need of further research concerning floristic and structural differentiation and relative impacts of climate, substrate and management. Henceforth, when we refer to Campos or South Brazilian Grasslands, or Campos/ grassland region, without any further qualification, we mean both grasslands associated with Araucaria forest and the grasslands collectively considered as Pampa in the current classification of biomes by IBGE (2004) (see Fig. 4 for some impressions of Campos landscapes).

Main factors shaping grassland vegetation: grazing and fire Grazing – which is one of the main economic activities throughout the South Brazilian Campos (Nabinger et al., 2000) – is often considered the principal factor maintaining the ecological properties and physiognomic characteristics of the grasslands (Senft et al., 1987; Coughenour, 1991; Pillar and Quadros, 1997). After its introduction east of the Uruguay River in the 17th century, feral cattle rapidly spread over a large area of

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Table 1. Characteristic families and species of grasslands in the Atlantic Forest biome (grasslands in northern Rio Grande do Sul, Santa Catarina and Parana´) Amaryllidaceae Hippeastrum breviflorum Herb. Apiaceae Eryngium horridum Malme Eryngium pandanifolium Cham. & Schltdl. Eryngium urbanianum H. Wolffa Eryngium zozterifolium H. Wolffa Asteraceae Baccharis milleflora (Less.) DC. Baccharis sagittalis (Less.) DC. Baccharis uncinella DC.a Calea phyllolepis Baker Hypochaeris catharinensis Cabrera a Noticastrum decumbens (Baker) Cuatrec. Senecio juergensii Mattf . Senecio oleosus Vell.a Trichocline catharinensis Cabreraa Campanulaceae Lobelia camporum Pohl Cyperaceae Ascolepis brasiliensis (Kunth) Benth. ex C.B.Clarke Bulbostylis sphaerocephala (Boeck.) C.B. Clarke Carex brasiliensis A.St.-Hil. Carex longii Mack. var. meridionalis (Ku¨k.) G.A. Wheeler Eleocharis bonariensis Nees Lipocarpha humboldtiana Nees Pycreus niger (Ruiz & Pav.) Cufod. Rhynchospora barrosiana Guagl. Rhynchospora globosa (Kunth) Roem. & Schult. a

Fabaceae Adesmia ciliata Vogel Adesmia tristis Vogel Eriosema longifolium Benth. Galactia neesii DC. Lathyrus paranensis Burkart Lupinus reitzii M. Pinheiro & Miottoa Lupinus rubriflorus Planchueloa Lupinus uleanus C. P. Sm.a Macroptilium prostratum (Benth.) Urb. Rhynchosia corylifolia Mart. ex Benth. Trifolium riograndense Burkart a Poaceae Andropogon lateralis Nees Andropogon macrothrix Trin. Axonopus siccus (Nees) Kuhlm. Axonopus suffultus (Mikan ex Trin.) Parodi Bromus auleticus Trin. ex Nees Paspalum maculosum Trin. Paspalum pumilum Nees Schizachyrium tenerum Nees Stipa melanosperma J. Presl Stipa planaltina A. Zanin & Longhi-Wagnera Solanaceae Petunia altiplana Ando & Hashimoto Verbenaceae Glandularia megapotamica (Spreng.) Cabrera & Dawson Verbena strigosa Cham.

Endemic species.

the lowlands south and west of the Plateau. In the grassland islands of the Plateau, cattle were not introduced until the beginning of the 18th century (Porto, 1954). In 1996, Rio Grande do Sul state had 13.2 million animals, corresponding to 50% of the total number of cattle in South Brazil (IBGE, 2005). Cattle raising in southern Brazil generally occurs by continuous and extensive grazing, and natural grasslands remain the base for cattle farming (Nabinger et al., 2000). However, excessive grazing results in decreased soil cover and risk of erosion, and in the replacement of productive forage species by species that are less productive and of lower quality, or even in the complete loss of good forage species. On the other hand, extremely low grazing pressure can result in dominance of tall grasses of low nutritional value or of shrubs and other species of low forage quality, mainly from the genera Baccharis (Asteraceae) and Eryngium (Apiaceae) (Nabinger et al., 2000). For a sustainable grazing regime, the balance between forage production, grassland diversity and soil preservation needs to be identified. Creation of gaps and reduction of competition through grazing in general leads to an increase in plant diversity, in terms of species (Boldrini and Eggers,

1996) and plant functional types (‘functional diversity’). Under grazing, allocation of aerial biomass is concentrated closer to the ground, and prostrate plant types, e.g. Axonopus affinis Chase and Paspalum notatum Flugge (both Poaceae) with stolons or rhizomes are favoured over taller species (Dı´ az et al., 1992, 1999; Boldrini and Eggers, 1996; Landsberg et al., 1999; Lavorel et al., 1999). Usually, grazed grassland communities show two distinct layers – a short layer of prostrate species that are intensively grazed and a taller layer of plants with a more or less patchy distribution; the latter is often composed of caespitose grasses with low forage value species and other species that are unattractive for grazing animals (shrubs, thorny species such as Eryngium spp.). Grazing exclusion leads to a change in structure, with dominance of tall tussock grasses (Boldrini and Eggers, 1996; Quadros and Pillar, 2001; Rodrı´ guez et al., 2003) that are better competitors for light under exclusion of grazing and fire (Bullock, 1996). As grassland productivity varies greatly between the cool winter season and the hot, but usually sufficiently moist summers, ranchers adjust the stocking rate of their pastures according to the carrying capacity in winter.

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Table 2.

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Characteristic families and species of grasslands in the Pampa biome (grasslands in southern Rio Grande do Sul)

Apiaceae Eryngium elegans Cham. & Schltdl. Eryngium horridum Malme Eryngium sanguisorba Cham. & Schltdl. Asteraceae Acmella bellidioides (Sm.) R. K. Jansen Aspilia montevidensis (Spreng.) Kuntze Aster squamatus (Spreng.) Hieron. Baccharis coridifolia Spreng. Baccharis dracunculifolia DC. Baccharis trimera (Less.) DC. Chaptalia runcinata Kunth Eupatorium buniifolium Hook. et Arn. Gamochaeta spicata (Lam.) Cabrera Senecio brasiliensis (Spreng) Less. var. brasiliensis Senecio cisplatinus Cabrera Senecio oxyphyllus DC. Stenachenium campestre Baker Vernonia flexuosa Sims. Vernonia nudiflora Less. Cyperaceae Carex bonariensis Desf. ex Poir. Carex phalaroides Kunth Carex sororia Kunth Cyperus luzulae (L.) Retz Eleocharis bonariensis Nees Eleocharis dunensis Ku¨k.a Eleocharis sellowiana Kunth Kyllinga brevifolia Rottb. Pycreus polystachyos (Rottb.) P. Beauv. Rhynchospora holoschoenoides (Rich.) Herter Rhynchospora megapotamica (A. Spreng.) H. Pfeiff. Fabaceae Adesmia araujoi Burkarta Adesmia bicolor (Poir.) DC.a Adesmia latifolia (Spreng.) Vogel Arachis burkartii Handroa Clitoria nana Benth. Desmodium incanum DC. Lathyrus pubescens Hook.& Arn. Macroptilium prostratum (Benth.) Urb. Rhynchosia diversifolia M. Micheli Stylosanthes leiocarpa Vog. Trifolium polymorphum Poir.a Hypoxidaceae Hypoxis decumbens L. Iridaceae Herbertia pulchella Sweet Sisyrinchium micranthum Cav. a

Juncaceae Juncus capillaceus Lam. Juncus microcephalus Kunth Oxalidaceae Oxalis articulata Savigny Oxalis eriocarpa DC. Oxalis perdicaria (Molina) Bertero Poaceae Andropogon lateralis Nees Andropogon selloanus (Hack.) Hack. Andropogon ternatus (Spreng.) Nees Aristida filifolia (Arechav.) Herter Aristida jubata Arech. Aristida laevis (Nees) Kunth Aristida spegazzinii Arech. Axonopus affinis Chase Bothriochloa laguroides (DC.) Herter Bouteloua megapotamica (Spreng.) O. Kuntzea Briza subaristata Lam. Coelorachis selloana (Hack.) Camus Danthonia secundiflora Presl Dichanthelium sabulorum (Lam.) Gould & C.A. Clark Elyonurus candidus (Trin.) Hack. Ischaemum minus J. Presl Melica eremophila M.A. Torres Melica rigida Cav.a Panicum aquaticum Poir. Paspalum dilatatum Poir. Paspalum nicorae Parodi Paspalum notatum Fl. Paspalum pauciciliatum (Parodi) Herter Paspalum pumilum Nees Piptochaetium lasianthum Griseb. Piptochaetium ruprechtianum Desv. Piptochaetium stipoides (Trin. & Rupr.) Hack. Saccharum trinii (Hack.) Renvoize Stipa filifolia Neesa Stipa megapotamia Spreng. ex Trin. Stipa nutans Hack. Stipa philippii Steud.a Stipa setigera C. Presl Rubiaceae Borreria verticillata (L.) G.F.W. Meyer Richardia humistrata (Cham. et Schlecht.) Steud. Verbenaceae Glandularia subincana Tronc. Lippia asperrima Cham. Phylla canescens (H.B.K.) Greene

Endemic species.

As a result, a large part of the biomass produced by highly productive C4 grasses in summer is not consumed, and the grasslands are therefore burned approximately every 2 years (Vincent, 1935), usually at the end of winter (August), to facilitate sprouting of fresh biomass. Further, grassland fires are used to

reduce the shrub cover (Gonc¸alves et al., 1997). This could be achieved by mechanical removal as well, though at higher costs and work effort. The use of fire for land management is controversial, and reliable scientific studies on its impact on species or functional type composition and soil properties are scarce. Fires in

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Table 3. Diversity and vegetation structure in relation to time since last burn in 0.25 m2 grassland plots in Porto Alegre, RS, Brazil (data from Overbeck et al., 2005) Time since last fire

Diversity (Shannon) Number of species Open soil (% cover) Litter (% cover) Standing dead biomass (% cover)

3 months

1 year

2 years

3 years

2.72 a 28 a 46.6 a 3.2 a 6.7 a

2.4 b 22.50 b 31.2 b 7.8 b 8.2 a

2.43 b 21.75 b 5.1 c 13.1 c 18 b

1.84 c 15.07 c 1d 37.2 d 28 c

Columns indicate different time since the last burn (3 months, 1 year, 2 years, 3 years or more). For each variable (row), different letters behind data indicate significant differences between plots with different time since the last fire (po0.05), tested by randomization testing with analysis of variance.

winter or early spring are known to diminish the contribution of cool season C3 grasses at the expense of warm season C4 grasses (Llorens and Frank, 2004). The common burning practice can thus be considered counterproductive from an agronomic point of view because it favours C4 grasses and therefore decreases forage availability in the critical winter period (Nabinger et al., 2000). Furthermore, fires tend to favour caespitose over rhizomatous or stoloniferous grasses, which usually is not a desired effect due to the lower forage quality of the tussock grasses (Jacques, 2003). In general, however, the majority of grassland species seem to be adapted to frequent (i.e. annually or every few years) burning (Quadros and Pillar, 2001; Overbeck and Pfadenhauer, 2007), even though no studies exist on the effect of different burning seasons and differences between grassland types. For ungrazed grassland subject to regular anthropogenic fires near Porto Alegre, Overbeck et al. (2005) showed that burning led to an increase in species number and diversity at the plot scale as competitive dominance by caespitose C4 grasses was reduced and a large number of inter-tussock species, principally forbs, were able to establish. With increasing time since fire, many species – especially small forbs – were gradually outcompeted by dominant grasses or were unable to regenerate under the thick litter layer that developed: although some of these species were lost from aboveground vegetation, they persisted with their belowground organs (Overbeck and Pfadenhauer, 2007; see Table 3). Abandoned grassland, i.e. grasslands where neither grazing nor burning takes place, shows high dominance of usually few tussock grass species and low diversity of herbaceous species. In grasslands situated in mosaics with Araucaria forests in the highlands of northern Rio Grande do Sul, species richness in 0.25 m2 plots ranged from 3 to 13, compared to maxima of 28 species on recently burned grasslands in the Porto Alegre region (Overbeck et al., 2005). Species richness of abandoned grassland can only be maintained by fire, and in the long run the grassland vegetation itself may be lost due to shrub encroachment (Overbeck et al.,

2005, 2006; see below). If livestock grazing is to remain an economically sound activity, understanding the impact of fire on soil properties becomes important. It has been suggested that grassland burns, although leading to short-term increases of total N, K, Ca, Mg and pH values in the uppermost soil layer (Rheinheimer et al., 2003), have negative effects on soil fertility and thus forage production in the long run (Heringer et al., 2002; Jacques, 2003); however, there have been too few studies to allow for general conclusions, especially concerning different frequencies and seasons of fire.

Forest–grassland dynamics In the absence of fire and grazing, grasslands are subject to shrub encroachment and, when in the vicinity of forest vegetation, to forest expansion (Machado, 2004; Oliveira and Pillar, 2004; Mu¨ller et al., 2006); this has been found for the South Brazilian plateau and for the Central Depression, but there have been no studies from the southern part of Rio Grande do Sul. Similar results were found by Safford (2001) for highland grasslands of southeastern Brazil. Increased density of shrubs and trees in grassland and savanna vegetation has been observed throughout the world in the last three decades (e.g. Archer, 1990; van Auken, 2000; Roques et al., 2001; Cabral et al., 2003), with different hypotheses being proposed to explain these patterns (such as climatic shifts or elevated global CO2 levels; e.g. Longman and Jenı´ k, 1992; Bond and Midgley, 2000; Sternberg, 2001). As the climate in southern Brazil is conductive to the development of forests, changes in the disturbance regime, especially grazing and fire regimes, should be decisive factors for vegetation changes at forest–grassland boundaries (Pillar and Quadros, 1997; Scholes and Archer, 1997; Pillar, 2003; Langevelde et al., 2003; Bond, 2005). Modelling of vegetation development in South Africa has shown that areas above a certain precipitation limit (650 mm for South Africa)

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under appropriate conditions such as the absence of severe fires or the presence of safe sites, e.g. rock outcrops (Mu¨ller, 2005). Seed dispersal by animals also plays an important role in this process (Forneck et al., 2003; Duarte et al., 2006a, b). As long as there is a (possibly discontinuous) disturbance regime that prevents the grasslands from turning into forests, high floristic and structural diversity is promoted, since woody species from grassland and forest can be found in close proximity. In grasslands that are ungrazed but regularly burned, shrub and tree species richness and density tends to be higher close to the forest border,

should be covered by woody vegetation types in the absence of fire (Higgins et al., 2000; Bond et al., 2003). In Brazilian Cerrado, protection from fire leads to shifts in vegetation physiognomies to more closed forms (Hoffmann and Moreira, 2002; Miranda et al., 2002). In southern Brazil, colonization by forest species leads to a gradual but clear shift of forest–grassland boundaries or to the development of woody thickets within the grassland (Forneck et al., 2003; Machado, 2004; Oliveira and Pillar, 2004). In forest–grassland mosaics, many species common in local forests play the role of pioneer woody trees, expanding forest vegetation

number of tree individuals

26 24 22 20 18 16 14 12 10 8 6 4 2 0 24 22 20 18 16 14 12 10 8 6 4 2 0 44 40 36

(a) last fire in grassland: >3 years > 80cm > 30cm to < 80cm < 30cm

(b) last fire in grassland: 2 years ago

(c) last fire in grassland: 1 year ago

32 28 24 20 16 12

presence of rock outcrops

8 4 0 31 28 25 22 19 16 13 10 grassland

7 -

4 border

1

2 -

5

8

11 14 17 20 23 26

forest (m)

Fig. 2. Number of tree individuals along the forest–grassland gradient according to size class intervals (height) in a natural forest–grassland mosaic under the influence of fire in South Brazil (data from Mu¨ller, 2005). Grassland areas in (a) have not burned for more than 3 years, in (b) were burned 2 years ago and in (c) 1 year ago. Please note different scales on the y-axes.

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where fires are less severe. Farther away from the border, with typically higher frequency and severity of fires, grassland shrubs manage to increase their density significantly after a period of 2 years without fire (Fig. 2). Absence of fire leads to shrubby grassland with increasing densities of trees and shrubs, either as solitary individuals or clumped together, usually associated with rock outcrops (safe sites) (Mu¨ller, 2005). Further studies on the ecology of shrubs and forest pioneer trees are currently under way; as of now, exact determinants and likely vectors of successional processes at the forest– grassland interface are still not clear.

Campos biodiversity Information on plant biodiversity of the Campos is far from complete. Boldrini (1997) estimated a total number of 3000 grassland plant species in Rio Grande do Sul state alone, and Klein (1975, 1984) estimated approximately 4000 species. While this is lower than the number proposed for Brazil’s Cerrado region (6000 vascular species; Furley, 1999), it should be noted that Cerrado (total area 2 million km2) covers a much larger area than South Brazilian Campos, and therefore also includes a wider range of climatic and edaphic conditions (Furley, 1999) than the comparatively uniform Campos region (Ministe´rio do Meio Ambiente (MMA), 2000); thus it also includes a greater diversity of vegetation types from grassland to forest physiognomies (e.g. Oliveira-Filho and Ratter, 2002 for an overview). The federal government’s ‘‘Project of Conservation and Sustainable Use of Brazilian Diversity’’ (PROBIO; MMA, 1996) sponsored workshops that identified approximately 900 priority areas to be conserved throughout the country (MMA, 2002; Silva, 2005) and led to floristic and faunistic inventories in areas previously unstudied in southern Brazil as well. Grasslands on the South Brazilian plateau, i.e. grasslands within the Atlantic forest biome (totalling 1,374,000 ha, i.e. 1/10 of total Campos area), in Rio Grande do Sul and Santa Catarina where included in this project: 1082 species, 95 of them endemics and 35 endangered by extinction, could be listed in the course of these studies, taking into account the available literature, herbarium records and field investigations (Boldrini, 2007). No exhaustive compilations exists for grasslands in the southern or more western parts of Rio Grande do Sul. Despite these recent advances, the South Brazilian grasslands remain one of the regions for which large portions are still ‘‘insufficiently known’’ (Giulietti et al., 2005). A thorough analysis of the flora of the entire grassland region is still not possible (as is probably the case in other Brazilian biomes as well), but some broad patterns are clear. The most species-rich plant families

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throughout the Campos region are Asteraceae (ca. 600 species), Poaceae (ca. 400–500), Leguminosae (ca. 250) and Cyperaceae (ca. 200; numbers based on Boldrini, 1997, 2002; Arau´jo, 2003; Longhi-Wagner, 2003; Matzenbacher, 2003; Miotto and Waechter, 2003). Many species, especially of the C4 grasses, also occur in the Cerrado biome (where few C3 species are present), whereas many of the C3 species occur in the temperate grasslands further south, in the Rı´ o de la Plata region. This co-existence of C3 and C4 species is one of the distinct characteristics of the South Brazilian grasslands. Floristic and phytosociological surveys throughout the entire grassland region are needed in order to obtain more realistic estimates of the species richness. Only this will allow for meaningful floristic classification of the grasslands and for comparison with other grassland and savanna regions in South America, including studies on floristic connections. And only this will provide information on the diversity and endangerment status of different community types, thus serving as a basis for conservation efforts in the grassland biome. These studies should include investigations about the spatial aspects of diversity such species–area relationships or information on diversity at the plot level. Overbeck et al. (2005) found that a grassland area near Porto Alegre (burned grassland in a forest–grassland mosaic) had a very high fine-scale diversity with an average of 34 species on a plot of 0.75 m2. In total, approximately 450 vascular plant species can be found in the 220 ha of grassland at the study site (Overbeck et al. 2006), placing these grasslands among the most species-rich grassland communities in the world.

Land use and transformation of South Brazilian grasslands Expansion of agri- and silvicultural production Up to now, land use changes in southern Brazil have been poorly documented compared to other regions of Brazil (e.g. Cerrado; Klink and Moreira, 2002; or Amazonia; Fearnside, 2005), and the socio-economic causes and consequences of these changes have scarcely been investigated (see Naumov, 2005, for an overview for Brazil). As no analyses are available, here we mostly refer to data from the Brazilian agricultural census from 1996 (IBGE, 2005). In 1970, the total grassland area in Brazil’s southern region was 18.0 million ha (Nabinger et al., 2000) while in 1996 it was 13.7 million ha (i.e. 23.7% of the total land area in this region), with 10.5 million ha in Rio Grande do Sul (total area: 28.2 million ha), 1.8 million ha in Santa Catarina (9.6 million ha) and 1.4 million ha in Parana´ (20.0 million ha): thus, a decrease of 25% in the total area of natural grasslands

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has occurred in the past 30 years due to a strong expansion of agricultural activities. Production of corn (Zea mays), for example, has increased from 1.4 to 11.8 million tons from 1940 to 1996, production of soybeans from 1530 ton in 1940 to 10.7 million tons in 1996, and production of wheat from 95 thousand tons to 1.4 million tons during the same period (agricultural census from 1996; data from IBGE), with increases in area primarily at the expense of natural grasslands. In Rio Grande do Sul alone, in 2000/2001 7.0 million ha were used for production of soybeans (Bisotto and Farias, 2001). The three southern states of Brazil currently produce 60% of the rice in Brazil (50% in Rio Grande do Sul alone), totalling 6.5 million ha in area (EMBRAPA, 2005). The cultivation of exotic trees has received many incentives from both private industries and the government, e.g. for pulp production. The present area of tree cultivation in southern Brazil is about 1.9 million ha (IBGE, 2005; data for 1996) and new projects will increase this area in the near future. Particularly in the grasslands on the South Brazilian Plateau, former cattle production areas have been transformed into plantations of Pinus sp. over large areas. Since economic returns are higher for plantations than for cattle production, areas planted with Pinus sp. are increasing rapidly every year. Plantations are usually not sylvipastoral systems where at least part of the original species composition remains but dense monocultures that due to lack of light do not allow for any understory plants to grow. Nearby grassland areas are often being invaded by Pinus sp. because of its effective seed dispersal and germination capacity in open vegetation types (Bustamante and Simonetti, 2005), easily observable throughout the region. In the southern part of Rio Grande do Sul, plantations of Eucalyptus sp. (and to a lesser extent Acacia sp.) are rapidly increasing in area, also leading to loss of grassland species (Pillar et al., 2002). More specific data on the impact of these plantations on flora and fauna are missing thus far for southern Brazil, as are reliable and recent data on the spatial expansion of tree plantations.

Cultivated pastures The intensification of farming systems has led to increases in the area of cultivated pastures. Despite the high productivity and forage potential of many native species, they are not commercially exploited, and cultivated pastures are mainly formed using exotic species (Nabinger et al., 2000). In 1996, 7.0 million ha in the southern region of Brazil were covered by sown pastures, mainly with non-native species. Important cultivated grass species are e.g. Axonopus jesuiticus (Araujo) Valls, P. notatum var. saurae Parodi, both

native species, and the exotics Pennisetum americanum K. Schum. or Urochloa P. Beauv. spp. (syn. Brachiaria (Trin.) Griseb. spp.) (summer species), Lolium multiflorum Lam. and Avena strigosa Schreb. (winter species), along with some exotic Leguminosae (e.g. Nabinger et al., 2000). While these species have high forage value, their large-scale introduction leads to losses of natural grasslands. Not all introduced exotic forage species have positive economic effects. Eragostis plana Nees (Poaceae), an African species introduced in the 1950s, proved to be of low palatability and did not satisfy the nutritional demands of cattle; however, it spread rapidly throughout the region because of high seed production along with allelopathic effects. At present, it is estimated that about 400,000 ha in Rio Grande do Sul state have already been invaded by this species, with negative impacts on grassland diversity and forage quality (Medeiros et al., 2004).

Overgrazing and erosion Currently, the low productivity of pastures in southern Brazil reflects unsuitable management (Maraschin, 2001). Limited herbage production over the winter results in overgrazing during this period, with heavy weight losses of cattle under inappropriate management. Overgrazing has negative consequences for soil cover, facilitating degradation in regions with vulnerable soil conditions. The most drastic example of this comes from the southwestern part of Rio Grande do Sul where severe erosion and desertification has occurred, forming extensive sand patches on unconsolidated arenitic substrates (Trindade, 2003). In 2002, this region was included as a ‘‘Special Attention Area’’ in Brazil’s desertification diagnosis map, with the affected total area reaching 37 km2 (Suertegaray et al., 2001). Where edaphic conditions were susceptible to erosion, overgrazing accelerated these processes greatly. Trindade (2003) showed that temporary cattle exclusion may be effective in permitting the colonization of eroded areas by plant species from the surrounding communities; of these species, the grasses Elionurus sp. and Axonopus pressus (Nees) Parodi proved to be the most tolerant of sand burial. Adequate grassland management, directed towards maintenance of the vegetation cover and thus protection of soil from hydric and aeolic erosion would prevent these problems of degradation in the future.

Conservation in the Campos region Only 453 km2, i.e. less than 0.5% of the South Brazilian grasslands, are currently under legal protection in conservation units without direct land use (Ministe´rio do Meio Ambiente (MMA), 2000), the

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26°S

30°

Gap Status Level 1 2 3 4 5 water 34° 58°

54°

50°W

Fig. 3. Levels of representativeness (gap status levels) in conservation units larger than 1,000 ha of the different phytoecological regions in Rio Grande do Sul state. The levels range from 0% (1) to 7.1% (5). The ranges of each level of representativeness are not equal neither are levels continuous. See text for exact values for the different vegetation types.

largest part being in mosaics of Campos and Araucaria forest in the National Parks of Aparados da Serra, Serra Geral and Sa˜o Joaquim (northern Rio Grande do Sul and Santa Catarina). In order to identify which vegetation types in Rio Grande do Sul were underrepresented or not represented at all in the existing network of protected areas, we conducted a regional gap analysis (Jennings, 2000) for the whole of Rio Grande do Sul (both forest and grassland), including areas over 1000 ha protected under the categories I, II, III and IV of the World Conservation Union (IUCN; Olson and Dinerstein, 1998). The status categories used in the analysis were adopted from Stoms (2000). The result of the analysis were five different gap status levels (Fig. 3), all below the 10% minimum cover for effective biodiversity conservation as suggested by the IV World Congress on National Parks and Protected Areas (McNeeley, 1993) which has been adopted by the Brazilian government. The levels range from 0% to 7.1% of representativeness (Seasonal semideciduous forest (0%, i.e. no protected areas 41000 ha at all):

first level; Campos (0.14%): second level; Araucaria forest (0.36%) and seasonal deciduous forest (0.41%): third level; pioneer formations (2.62%) and Atlantic Forest (3.61%): fourth level; Acacia–Prosopis parkland (7.09%): fifth level). Thus, despite their high species richness and the threat from changing land use, the Campos is almost unrepresented in the conservation units. Further, no protected areas under categories I to IV at all exist in what the IBGE (2004) recognises as the Pampa biome i.e. the southern half of Rio Grande do Sul. Only legal protection can effectively prohibit transformation of natural grassland in the region into agricultural or silvicultural area and thus prevent complete loss of Campos vegetation. However, at least in the regions where most of the studies have been conducted, grasslands cannot be maintained in areas of integral protection, i.e. with a conservation status that does not allow for human interference, in the long run. Under the Brazilian system of conservation units, conservation in National Parks excludes all

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anthropogenic interference and ‘‘disturbances’’ such as grazing and fire. As discussed above, grasslands without management with grazing and/or fire in many areas are subject to shrub encroachment and subsequently will change into forests, even though this may take decades depending on the local situation and the proximity to forest borders. In mosaics of forest and grassland, as in the existing conservation units on the South Brazilian Plateau, this process seems to be quite fast (Oliveira and Pillar, 2004). Grasslands currently protected in conservation areas with integral protection (IUCN

categories I–III; see Rylands and Brandon, 2005), such as the National Parks, thus seem to be doomed to extinction if no management can be applied. No data exists on whether sufficiently frequent natural burns would occur in these areas to preserve the grasslands under today’s climatic conditions, as it is the case, for example, for protected Cerrado areas (e.g. Ramos-Neto and Pivello, 2000; Medeiros and Fiedler, 2004). Fire thus should be considered as a legal tool for conservation in South Brazilian grasslands, at least in areas where grazing is not feasible. Nonetheless, the fire regime applied (e.g. period and frequency of burns) should be carefully evaluated, as current knowledge is insufficient to be able to assure desired management results. Perhaps more importantly, continuation of extensive cattle grazing over wide areas should be supported and promoted by governmental institutions (Pillar et al., 2006). The aim should be to reconcile economic purposes and sustainable grazing practices, encouraging the reintroduction of native forage grasses and stimulating regular resting of pastures via rotational grazing (e.g. Gonc¸alves et al., 1999). Protection areas under IUCN categories IV, V or VI, i.e. less strict conservation that allows for certain kinds of land use, thus should be more adequate and successful than higher-level conservation areas: management is essential for grassland conservation. Nonetheless, Campos areas inside conservation units under integral protection provide a invaluable opportunity for research into vegetation dynamics and successional processes that are not currently well understood. For example, in the absence of fire and grazing will grassland turn into forest vegetation in all parts of the grassland region? How long will this process take, and what are the intermediate stages? These apparently simple questions are far from being answered in many parts of the Campos region. Particularly in what is referred to as the Pampa biome in the IBGE (2004) classification, i.e. the southern half of

Fig. 4. South Brazilian Campos landscapes, Top: Grazed grassland in mosaic with Araucaria Forest. Bom Jesus, highlands in northern Rio Grande do Sul (RS). The dominant grass species is Andropogon lateralis Nees. Forests are often found in small valleys or along escarpments. Photo: I. Boldrini. Middle: Baccharis uncinella DC. (Asteraceae) shrubs invading grassland areas abandoned for almost 15 years. Sa˜o Francisco de Paula, highlands in northern RS. Dominant grasses are Sorghastrum setosum (Arechav.) Herter and Andropogon lateralis Nees. Photo: V. Pillar. Bottom: Remnants of grazed Aristida jubata (Arechav.) Herter (Poaceae) grassland near Passo Fundo, northwestern RS. Most of the region has been transformed into intense agricultural lands (soy bean and wheat production). Baccharis trimera (Less.) DC. (Asteraceae) and Eryngium horridum Malme (Apiaceae), in the foreground, are usually rejected by cattle. Photo: V. Pillar.

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Rio Grande do Sul, grasslands may be quite stable even in the absence of management, in contrast to the grasslands in close contact with forest vegetation on the Plateau discussed above, but long-term studies are not available for these regions. The results from successional studies would provide an essential basis for developing strategies for the sustainable management of South Brazilian grasslands. Conservation action is urgent if losses of grassland area are to be stopped and extinction processes to be avoided – but conservation of grassland biodiversity must reflect ecological properties and successional processes and therefore allow for adequate management practices.

Acknowledgements The research leading to this paper was part of cooperation projects supported by CAPES (Brazil), the German Academic Exchange Service (DAAD), the German Research Foundation (DFG) and the State of Bavaria (Germany). V.P. received support from CNPq (Brazil). Our thanks go to Peter J. Edwards and to Catherine Burns for checking the manuscript.

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