Journal of Biogeography (1997) 24, 197–204 Distribution of C3 and C4 grasses along an altitudinal gradient in Central Argentina M C∗, N A†, M E. A† and A M. A∗ ∗IMBIV, UNC-CONICET, CC 495, 5000 Córdoba, Argentina and †Facultad de Ciencias Agropecuarias, UNC. CC 509, 5000 Córdoba, Argentina Abstract. The distribution pattern of C3 and C4 grasses was studied in eight sites located between 350 m and 2100 m along an altitudinal gradient in Central Argentina. Of 139 taxa fifty-nine are C3 and eighty C4. Species of the C3 tribes (Stipeae, Poeae, Meliceae, Aveneae, Bromeae and Triticeae) and C3 Paniceae species increase in number at higher elevations; only one C3 species was found below 650 m. C4 Aristideae, Pappophoreae, Eragrostideae, Cynodonteae, Andropogoneae and Paniceae increase at lower altitudes. The floristic crossover point is at about 1500 m; the ground cover cross-over point is at about 1000 m. Analysis of the relationships between % C4 species along the gradient and INTRODUCTION Physiological differences of C3 and C4 grass species are reflected in their distribution patterns along environmental gradients or under varying climatic conditions. C4 grasses are generally represented more on warmer environments, while C3 grasses are represented more on cooler environments. These distribution patterns are remarkably consistent at a large range of spatial scales (Wentworth, 1983), and in all parts of the world where they have been investigated (Hattersley, 1992; Ehleringer & Monson, 1993). Usually temperature is the variable mostly correlated with the occurrence of C4 species in grass floras (Teeri & Stowe, 1976; Cavagnaro, 1988), even though some authors have stressed the importance of water availability and soil moisture indices (Chazdon, 1978; Tieszen et al., 1979). According to Hattersley (1983) generally both C3 and C4 grass species increase in number with increasing rainfall in their preferred temperature regime. The study reported here is one of the few examining the distribution of C3 and C4 grass species along an elevational gradient for grasslands in a temperate summer-rainfall region of the world (in Central Argentina). Our objective was to identify those climatic variables most correlated with C4 grass species composition. ∗ Corresponding author: Marcelo Cabido, IMBIV, Casilla de Correo 495, 5000 Córdoba, Argentina.  1997 Blackwell Science Ltd nine climatic and environmental variables showed the highest correlation with July mean temperature, but all temperature variables show highly significant correlations with % C4. Correlation with annual rainfall is lower but also significant. These results are consistent with previous research showing the relative importance of C4 grasses as temperature increases. C3 species make a high contribution to relative grass coverage below the C3/C4 floristic crossover point but are rare below 1000 m. Key words. C3 and C4 grasses, altitudinal gradient, climate, Argentina. METHODS The distribution of C3 and C4 grasses were obtained for eight sites along an altitudinal gradient ranging from 350 m to around 2100 m a.s.l. in the Córdoba Mountains (31°60′S and 65°50′W). Floristic surveys and Braun-Blanquet cover abundance data (Braun-Blanquet 1932), provided by Cabido (1985), Cabido & Acosta (1986), Cabido, Breimer & Vega (1987), Acosta et al. (1989) and Cabido et al. (1994), were used to assess the distribution of species. All the sites were open grasslands where grasses are the dominant species. Only the two lower sites had scattered trees. The climate is temperate with warm season rainfall (70% of the rain falls from November to March). A detailed description of the area is given by the authors cited above. Total number of C3 and C4 grass species, % C4 species and % C3 and C4 grass cover were calculated for each elevational site. Cover values were obtained from BraunBlanquet data. The C4 photosynthetic pathway was identified by examination of Kranz anatomy in crosssections of fresh and herbarium specimens and from literature data (Smith & Epstein, 1971; Sánchez & Arriaga, 1990; Hattersley & Watson, 1992). Pearson’s correlation coefficients were calculated for the relationships between distribution parameters (% C4 and numbers of C3 and C4 species) and climatic variables obtained from the National Meteorological Service (Servicio Meterorológico Nacional 1958, 1962a, 1962b), from records of the Argentine Railways (unpublished data) and from stations located in private properties (Palacios & Zamar, 1986) (Table 1). 197 198 Marcelo Cabido et al. TABLE 1. Climatic parameters for the eight sites along an elevational gradient in Central Argentina. Altitude (m) 350 600 1000 1400 1600 1800 1900 2100 AAT ANF JANT JAMT JuANT JuAMT JMT JuMT AR SR 18.1 9.6 20.0 34.5 4.1 18.8 27.2 10.8 680 365 17.5 28.7 16.5 30.6 5.1 17.3 24.0 10.4 750 432 13.1 41.9 14.7 27.5 2.7 15.1 22.1 8.3 786 473 11.6 57.3 12.3 23.6 1.3 13.0 17.9 6.7 887 530 10.7 65.1 11.7 22.1 0.9 11.8 16.6 6.0 858 597 9.7 74.0 10.2 20.0 0.7 10.3 15.4 5.2 873 586 8.8 85.8 9.1 18.0 0.1 8.3 12.1 4.2 840 549 8.1 89.6 8.3 15.8 −2.0 8.8 13.3 4.1 891 644 ALT=altitude; AAT=annual average temperature; AR=annual rainfall; SR=summer rainfall; ANF=average number of days with frost; JANT=January average minimum temperature; JAMT=January average maximum temperature; JuANT=July average minimum temperature; JuAMT=July average maximum temperature; JMT=January mean temperature; JuMT=July mean temperature. FIG. 1. Frequency of occurrence of C3 and C4 grass species by tribe along an altitudinal gradient in Central Argentina. Light bars=C3 species; dark bars=C4 species.  Blackwell Science Ltd 1997, Journal of Biogeography, 24, 197–204 Distribution of C3 and C4 grasses in Argentina 199 more prevalent at lower altitudes. Andropogoneae species are more common at intermediate sites (between 1000 m and 1400 m). C3 and C4 grasses show a divergent distribution along the gradient (Fig. 2). The number of C3 species decreases from thirty-seven at 2100 m to four at 600 m, and only one (Stipa sanluisensis Speg.) at 350 m. C4 grasses are more numerous in the lower zone and less so above 1400 m (Table 2). Nevertheless, nine C4 grasses are still found at 2100 m where the January average maximum temperature is only 15.8°C. The floristic crossover point (equal numbers of C3 and C4 species) is at approximately 1500 m but the ground cover cross-over point is at 1000 m (Fig. 2). Although C3 species decrease considerably below 1600 m, their contribution to total grass coverage is well over 50% from above 1000 m (Table 2). Remarkably high positive correlation was found between both summer and winter temperature variables with % C4 species (Table 3). Correlation of % C4 with rainfall is negative and also is significant. Correlations between the number of C4 species and climatic variables are not significantly different (results are not presented). DISCUSSION FIG. 2. Relative C3/C4 grass species composition (%) and coverage (%) along an altitudinal gradient in Central Argentina. RESULTS Of the 139 grass taxa found along the elevational gradient, fifty-nine were C3 and eighty C4. Only the tribe Paniceae contains both C3 and C4 species. Most of the tribes show trends in their representation with increasing or decreasing altitude (Fig. 1). The C3 tribes Poeae, Aveneae, Bromeae and Arundineae and C3 Paniceae species are more represented at higher altitudes. In contrast, the C4 tribes Aristideae, Pappophoreae, Cynodonteae and C4 Paniceae species, are  Blackwell Science Ltd 1997, Journal of Biogeography, 24, 197–204 There are clear differences in the distribution of C3 and C4 grasses along the altitudinal gradient studied. Lower altitude grasslands consist mainly of C4 grasses, whereas C3 grasses dominate at higher altitudes. Our findings are comparable with those reported for different regions of the world (Hattersley, 1992; Hattersley & Watson, 1992; Ehleringer & Monson, 1993). All temperature variables tested showed strong correlations with the relative abundance of C4 and C3 species, suggesting that the cooler the winter, the greater the relative success of C3 grasses, and the hotter the summer the greater the relative success of C4 grasses. An equally close relationship was found between % C4 and January average maximum temperature for Australia (Hattersley, 1983). While temperature and related variables are highly correlated with % C4 at continental scales (Hattersley, 1992), good correlations with rainfall are also reported along elevational gradients at more local scales, where precipitation increases with altitude (Chazdon, 1978; Rundel, 1980). In our study area rainfall also shows good correlation with % C4 and when only summer rainfall is correlated the coefficient is even higher. Our finding contrasts with that of Cavagnaro (1988) who reported non-significant correlation with rainfall for a close but climatically different region in Argentina. The cross-over point for the number of species occurs at 1500 m, and is characterized by a mean annual daily minimum temperature of approximately 7°C to 8°C. The cross-over point occurs at different elevations in other regions of the world but at similar mean minimum temperature ranges (Tieszen et al., 1979; Rundel, 1980). Several authors have found that mean minimum and mean maximum temperatures of the warmest month are the single best predictors of C3 and C4 species numbers (Wentworth, 1983). When our results are compared with those reported 200 Marcelo Cabido et al. TABLE 2. Number of species, % species and % cover of C3 and C4 grasses for eight locations along an altitudinal gradient in Central Argentina. Altitude (m) Number of C3 species % C3 species % C3 cover Number of C4 species % C4 species % C4 cover 350 600 1000 1400 1600 1800 1900 2100 1 4 19 20 20 21 27 37 2.3 0.03 10.0 0.04 35.8 51.8 39.2 65.4 60.6 63.3 65.6 63.0 69.2 71.4 80.0 72.1 43 36 34 31 13 11 12 9 97.7 99.7 90.0 99.9 64.2 48.2 60.8 34.6 38.2 36.7 34.4 37.0 30.8 28.6 20.0 27.9 TABLE 3. Correlation of % C4 grass species composition and environmental variables. Variables R ALT AAT ANF AR SR JANT JAMT JuANT JuAMT JMT JuMT −0.98∗∗ 0.97∗∗ −0.97∗∗ −0.86∗ −0.95∗∗ 0.96∗∗ 0.97∗∗ 0.94∗∗ 0.97∗∗ 0.96∗∗ 0.98∗∗ R=correlation coefficient; ∗∗=significant at P<0.01; ∗=significant at P<0.05. for lower latitudes (Chazdon, 1978 for Costa Rica; Tieszen et al., 1979 for Kenya; Rundel, 1980 for Hawaii), a pattern for the cross-over point emerges only for the mean maximum temperature of the warmest month, which ranges between 21°C and 22°C. However, when the mean minimum temperatures of the warmest month are compared for the cross-over point, our results are most comparable with those reported for temperate latitudes (Wentworth, 1983 for Arizona; Cavagnaro, 1988 for Argentina). This is in agreement with what has been suggested by Rundel (1980), and supported by Ehleringer (1978) and Cavagnaro (1988), that C4 grasses achieve floristic dominance at lower environmental temperatures in the tropics than in temperate regions. Teeri & Stowe (1976) and Long (1983) suggested that locations with a minimum temperature of the warmest month below 8°C appear to have few or no C4 grass species. However, Schwartz & Redmann (1988) reported that C4 genera such as Muhlenbergia commonly occur at or below this temperature limit. In our study area such temperatures are found at the highest extreme of the gradient where nine C4 grass species are still found. They belong to the genera Muhlenbergia, Aristida, Eragrostis, Tripogon, Bouteloua, Bothriochloa, Schizachyrium and Sorghastrum. The C4 species at this altitude are restricted to sandy shallow soils with low indices of available soil moisture and water deficit at some time throughout the year (Cabido et al., 1987). The importance of soil moisture in determining C3/C4 species distribution has also been stressed by Tieszen et al. (1979). In our study area it seems to be related to at least the local C4 species distribution at higher elevation where soil moisture data are available (Cabido et al., 1987). In agreement with Teeri & Stowe (1976) C4 genera recognized as being particularly susceptible to low temperatures, such as Digitaria, Paspalum and Axonopus, were not found above 1900 m in our transect. The ground cover cross-over point found in this study is at approximately 1000 m, considerably lower than the floristic cross-over altitude. The high cover of C3 grasses below the floristic cross-over point results from the dominance effect exerted in grassland communities by big tussock grasses such as Stipa filiculmis Delile, S. tenuissima Trin. and Festuca hieronymi Hack. (Acosta et al., 1989). The mean maximum temperature of the warmest month at this elevation is about 27°C, which is similar to the value of 26°C reported by Wentworth (1983) for the cross-over point in Arizona, but substantially higher than the corresponding value of 22°C reported by Rundel (1980) for Hawaii. These results are consistent with the temperate versus tropical pattern of floristic cross-over temperatures discussed above. Below 1000 m the contribution of C3 species to total grass cover is negligible. By contrast C4 grasses still attain nearly 30% of total grass cover at higher elevations as a result of the dominance of some species in locally rocky or xeric sites, as mentioned before. The higher contribution of C3 grass species to total grass coverage below the floristic crossover point requires further explanation and research. Some possibilities are that it could reflect inertia of past plant communities widely distributed during the last glaciation, or the importance of other environmental constraints, such as edaphic factors. ACKNOWLEDGMENTS This study was supported by the National University of Córdoba through the Secretary of Science and Technology (SECyT) and the Research Council of Córdoba Province (CONICOR). Paul Hattersley made valuable improvements to a first draft of the manuscript. We are also indebted to Prof. D. Abal Solı́s who drew the figures. REFERENCES Acosta, A., Cabido, M., Dı́az, S. & Menghi, M. (1989) Local and regional variability in granite grasslands in the mountains of Central Argentina. Ber. Geobot. Inst. ETH. 55, 39–50.  Blackwell Science Ltd 1997, Journal of Biogeography, 24, 197–204 Distribution of C3 and C4 grasses in Argentina 201 Braun-Blanquet, J. (1932) Plant sociology, the study of plant communities, p. 438. New York, McGraw-Hill. Cabido, M. (1985) Las comunidades vegetales de la Pampa de Achala, Sierras de Córdoba, Argentina. Doc. Phytosociologiques, 9, 431–443. Cabido, M. & Acosta, A. (1986) Contribución al conocomiento fitosociológico del Sub-piso Superior de pastizales y bosquecillos de altura de las Sierras de Córdoba. Veroff. Geobot. Inst. ETH. 91, 118–140. Cabido, M., Breimer, R. & Vega, G. (1987) Plant communities and associated soil types in a high plateau of the Córdoba Mountains, Central Argentina. Mount. Res. Devel. 7, 25–42. Cabido, M., Manzur, A., Carranza, L. & González Albarricı́n, C. (1994) La vegetación y el medio fı́sico del Chaco Arido en la provincia de Córdoba, Argentina Central. Phytocoenologia, 24, 423–460. Cavagnaro, J.B. (1988) Distribution of C3 and C4 grasses at different altitudes in a temperature arid region of Argentina. Oecologia, 76, 273–277. Chazdon, R.L. (1978) Ecological aspects of the distribution of C4 grasses in selected habitats of Costa Rica. Biotropica, 10, 265–269. Ehleringer, J.R. (1978) Implications of quantum yield differences on the distributions of C3 and C4 grasses. Oecologia, 31, 255–267. Ehleringer, J.R. & Monson, R.K. (1993) Evolutionary and ecological aspects of photosynthetic pathway variation. Ann. Rev. Ecol. Syst. 24, 411–439. Hattersley, P.W. (1983) The distribution of C3 and C4 grasses in Australia in relation to climate. Oecologia, 57, 113–128. Hattersley, P.W. (1992) C4 photosynthetic pathway variation in grasses (Poaceae): its significance for arid and semi-arid lands. Desertified grasslands: their biology and management (ed. by G. Chapman), pp. 181–212. London, Academic Press. Hattersley, P.W. & Watson, L. (1992) Diversification of photosynthesis. Grass evolution and domestication (ed. by G. Chapman), pp. 38–116. Cambridge, Cambridge University Press. Long, S.P. (1983) C4 photosynthesis at low temperatures. Plant Cell Environ. 6, 345–363. Palacios, A.A. & Zamar, J.L. (1986) Erosión hı́drica. Volúmen de Sı́ntesis: Proyecto Pachón-Achala. MaB 6-UNEP-UNESCO 110577-01 (ed. by R. Luti), pp. 244–310. Montevideo, ROSTLACUNESCO. Rundel, P. (1980) The ecological distribution of C4 and C3 grasses in the Hawaiian Islands. Oecologia, 45, 354–359. Sánchez, E. & Arriaga, M. (1990) El sı́ndrome de Kranz en POACEAE de la flora Argentina. Parodiana, 6, 73–102. Schwarz, A.G. & Redman, R.E. (1988) C4 grasses from the boreal forest region on northwestern Canada. Can. J. Bot. 66, 2424–2430. Servicio Meteorológico Nacional, República Argentina (1958) Estadı́sticas climatológicas 1901–1950. Buenos Aires, Publ. B1, No. 1. Servicio Meteorológico Nacional, República Argentina (1962a) Datos pluviométricos 1921–1950. Buenos Aires, Publ. B1, No. 2. Servicio Meteorológico Nacional, República Argentina (1962b) Estadı́sticas climatológicas 1951–1960. Buenos Aires, Publ. B1, No. 6. Smith, B. & Epstein, S. (1971) Two categories of 13C/12C ratios for higher plants. Plant Physiol. 47, 380–384. Teeri, J.A. & Stowe, L.G. (1976) Climatic patterns and the distribution of C4 grasses in North America. Oecologia, 23, 1–12. Tieszen, L.L., Senyimba, M.M., Imbamba, S.K. & Troughton, J.H. (1979) The distribution of C3 and C4 grasses and carbon isotope discrimination along an altitudinal and moisture gradient in Kenya. Oecologia, 37, 337–350. Wentworth, T.R. (1983) Distributions of C4 plants along environmental and compositional gradients in southeastern Arizona. Vegetatio, 52, 21–34. APPENDIX 1 Presence (+) and absence (−) of C3 and C4 grass species for eight sites along an altitudinal gradient in Central Argentina Altitude (m) 350 600 1000 1400 1600 1800 1900 2100 C3 species 1 Tribe Stipeae Stipa amethystina Steud. Stipa cordobensis Speg. Stipa eriostachya Kunth Stipa filiculmis Delile Stipa hunzikeri Caro Stipa juncoides Speg. Stipa neesiana var. longiaristata Arechav. Stipa neesiana Trin. & Rupr. var. neesiana Stipa nidulans Mez Stipa niduloides Caro Stipa papposa Nees Stipa polyclada Hack. Stipa pseudopampagrandensis Caro Stipa sanluisensis Speg. Stipa stuckertii Hack. Stipa tenuissima Trin. Stipa trichotoma Nees Piptochaetium medium (Speg.) Torres Piptochaetium montevidense (Spreng.) Parodi Piptochaetium napostaense (Speg.) Hack. Piptochaetium stipoides var. chaetophorum (Griseb.) Parodi − − − − − − − − − − − − − + − − − − − − − − + + − − − − − − − − + − + − − − − − − − − − + + + − − + − − − − − − − + + + + + + + − + + + + − + − − − − − − − + + + + + − − − + + − − − + − − + − − − − + + − + − + − − − + − + + − − − − − − − − + + − + − − + − − + − + − + + + − − − − − + + − + − − − − + − − + − + + + − − − − + + − − + − − − − − − − − + − + − − + + − + + − + + + + − + + 2 Tribe Poeae Briza paleapilifera Parodi Briza rufa (J. Presl.) Steud. Briza subaristata Lam  Blackwell Science Ltd 1997, Journal of Biogeography, 24, 197–204 202 Marcelo Cabido et al. APPENDIX 1 (contd) Presence (+) and absence (−) of C3 and C4 grass species for eight sites along an altitudinal gradient in Central Argentina Altitude (m) 350 600 1000 1400 1600 1800 1900 2100 − − − − − − − − − − − − − − − − − − − − − − − + − + − − − − − − − − + − − − + − − − + − − − − + − + + − − + − − + + − − + − − + + + − + + + − − − + − + + + + + − + + + + + + − 3 Tribe Meliceae Melica macra Nees Melica stuckertii Hack. − − − − + + − + − − − − − − − − 4 Tribe Aveneae Agrostis breviculmis Hitchc. Agrostis glabra (J. Presl) Kunth var. glabra Agrostis montevidensis Spreng. Agrostis tolucensis Kunth Aira caryophyllea L. Chaetotropis elongata (Kunth) Björkman Deyeuxia colorata Beetle Deyeuxia eminens f. brevipila (Hack.) Türpe Deyeuxia eminens J. Presl Deyeuxia hieronymi (Hack.) Türpe Koeleria kurtzii Hack. − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − + − − − − − − − − − − + − − − − − − − − − − + − − − − − − + − − − + − − + − − − + − + + + + + + + + + + + 5 Tribe Bromeae Bromus auleticus Nees Bromus brevis Steud. Bromus catharticus Vahl Bromus commutatus Schrad. − − − − − − − − + − + − + − + − + + + − + − + − + + + − + + + + 6 Tribe Triticeae Hordeum stenostachys Godr. − − + − − − + − 7 Tribe Arundineae Cortaderia selloana (Schult. et Schult.f.) Asch. & Graebn. Danthonia cirrata Hack. & Arechav. Danthonia montevidensis Hack. & Arechav. Lamprothyrsus hieronymi (Kuntze) Pilg. − − − − − − − − − − − − − − − − − − − − − + − + − + + − + + + − 8 Tribe Paniceae Panicum hians Elliott Panicum sabulorum Lam. var. sabulorum − − − − − − + − + + + − − − − − C4 species 1 Tribe Aristideae Aristida achalensis Mez Aristida adscensionis var. modesta Hack. Aristida adscensionis var. scabriflora Hack. Aristida circinalis Lindm. Aristida flabellata var. flabellata Caro Aristida laevis (Nees) Kunth Aristida mendocina Phil. Aristida pallens Cav. var. pallens Aristida spegazzini Arechav. var. spegazzini − − + − − − + − − − + + − + − + − − − + − + − + − + + + − − + − + − + + − − − − − − − − − − − − − − − − − + − − − − − − − − + − − − − − − − − + 2 Tribe Pappophoreae Cottea pappophoroides Kunth Pappophorum caespitosum R.E.Fr. Pappophorum pappiferum (Lam.) Kuntze Pappophorum philippianum Parodi Pappophorum vaginatum Buckley + + + + + + + + + + − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − 3 Tribe Eragrostideae Diplachne dubia (Kunth) Scribn. + + − − − − − − Festuca circinata Griseb. Festuca hieronymi Hack. Festuca tucumanica E. B. Alexeev Lolium multiflorum Lam. Poa annua L. Poa hubbardiana Parodi Poa resinulosa Steud. Poa scaberula Hook. f. Poa stuckertii (Hack.) Parodi Vulpia myurus var. hirsuta Hack. Vulpia myurus var. megalura (Nutt.) Auquier  Blackwell Science Ltd 1997, Journal of Biogeography, 24, 197–204 Distribution of C3 and C4 grasses in Argentina 203 APPENDIX 1 (contd) Presence (+) and absence (−) of C3 and C4 grass species for eight sites along an altitudinal gradient in Central Argentina Altitude (m) Eleusine tristachya (Lam.) Lam. Eragrostis cilianensis (All.) Janch. Eragrostis lugens Nees var. lugens Eragrostis orthoclada Hack. Gouinia paraguayensis (Kuntze) Parodi Muhlenbergia ligularis (Hack.) Hitchc. Muhlenbergia peruviana (P. Beauv.) Steud. Sporobolus indicus (L.) R. Br. Sporobolus phleoides Hack. Sporobolus pyramidatus (Lam.) Hitchc. Sporobolus rigens (Trin.) Desv. Tripogon spicatus (Nees) Ekman 4 Tribe Cynodonteae Bouteloua aristidoides (Kunth) Griseb. Bouteloua curtipendula var. caespitosa Gould & Kapadia Bouteloua megapotamica (Spreng.) Kuntze Chloris virgata Sw. Chondrosum simplex (Lag.) Kunth Cynodon dactylon (L.) Pers.var. dactylon Cynodon hirsutus Stent var. hirsutus Eustachys distichophylla (Lag.) Nees Eustachys retusa (Lag.) Kunth Gymnopogon spicatus (Spreng.) Kuntze Microchloa indica (L.f.) P. Beauv. var. indica Neobouteloua lophostachya (Griseb.) Gould Tragus berteronianus Schult. Trichloris crinita (Lag.) Parodi Trichloris pluriflora E. Foum. 350 600 1000 1400 1600 1800 1900 2100 − + − + + − − − + + + + − + + + + − − − − + − − + + + − − − − + − − − + − − + − − − + + − − − + + − + − − − + + − − − − − − + − − − + + − − − + − − + − − + + + − − − + − − + − − + + − − − − + + + − + − + − + − − − + + + + + + − + − + − + − − − + + + + − + + − − + + − + + + − − − − − + + − − − + − + + + − − − − − − − − − − + − + − + − − − − − − − − − − + − − − − − − − − − − + − − − − − − − − − − − − − − − + − − − − − − − − − − − 5 Tribe Paniceae Axonopus fissifolius (Raddi) Kuhlm. Cenchrus myosuroides Kunth var. myosuroides Cenchrus pauciflorus Benth. var. pauciflorus Digitaria aequiglumis (Hack. & Arechav.) Parodi var. aequiglumis Digitaria californica (Benth.) Henrard var. californica Digitaria ciliaris (Retz.) Koeler Digitaria insularis (L.) Fedde Digitaria sanguinalis (L.) Scop. Digitaria swalleniana Henrard Echinochloa colona (L.) Link Panicum bergii Arechav. var. bergii Paspalum dilatatum Poir. subsp. dilatatum Paspalum humboldtianum Flügge var. humboldtianum Paspalum malacophyllum Trin. Paspalum nicorae Parodi Paspalum notatum var. latiflorum Döll Paspalum plicatulum Michx. var. plicatulum Paspalum quadrifarium Lam. Setaria hunzikeri Anton Setaria lachnea (Nees) Kunth Setaria leucopila (Scribn. & Merr.) K. Schum. Setaria macrostachya Kunth Setaria pampeana Nicora Setaria parviflora (Poir.) Kerguélen var. parviflora Setaria setosa (Sw.) P. Beauv. Setaria vaginata Spreng. var. vaginata Urochloa lorentziana (Mez) Morrone & Zuloaga − + + − − − − − + − − − + − − − − − − − − − − − − − − + − − − − + + + + + + − − − − − − − − + + + + + + + + + + − + − − − + − − − − − − − − + + + + + + − − − − − − − − − + + + − + + + − − − − − + − − − − − − − − − − + + + − + + − − − − − − + − − − − − − − − − − − − − + + − − − − − − − + − − − − − − − − − − − − − − − − − − − − − − + − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − 6 Tribe Andropogoneae Andropogon ternatus (Spreng.) Nees Bothriochloa barbinodis (Lag.) Herter Bothriochloa laguroides (DC.) Herter subsp. laguroides Bothriochloa saccharoides (Sw.) Rydb. Bothriochloa springfieldii (Gould) Parodi − − − − − − − − − + + + + + − + + + + − − − + + − − + + − − − − + + − − − − + −  Blackwell Science Ltd 1997, Journal of Biogeography, 24, 197–204 204 Marcelo Cabido et al. APPENDIX 1 (contd) Presence (+) and absence (−) of C3 and C4 grass species for eight sites along an altitudinal gradient in Central Argentina Altitude (m) Elionurus muticus (Spring.) Kuntze Heteropogon contortus (L.) Roem. & Schult. Schizachyrium condensatum (Kunth) Nees Schizachyrium salzmannii (Steud.) Nash Schizachyrium spicatum (Spreng.) Herter Sorghastrum pellitum (Hack.) Parodi 350 600 1000 1400 1600 1800 1900 2100 + + − − − − − + − − + − + − + + + + + − + + + + − − − − + − − − − − + + − − − − + + − − − − + +  Blackwell Science Ltd 1997, Journal of Biogeography, 24, 197–204