Vegetation dynamics in the southern Brazilian highlands during the last millennia and the role of bogs in Araucaria forest formation

Quaternary International xxx (2014) 1e10

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Vegetation dynamics in the southern Brazilian highlands during the last millennia and the role of bogs in Araucaria forest formation Caroline Scherer, Maria Luisa Lorscheitter* Departamento de Botânica, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-970 Porto Alegre, RS, Brazil

a r t i c l e i n f o

a b s t r a c t

Article history: Available online xxx

For the first time in the highlands of southern Brazil, a palynological study was performed on sedimentary records from two Araucaria forests. Radiocarbon dates were used. The sites were Alpes de São Francisco (29
270 2600 S, 50
360 5700 W) and Banhado Amarelo (29
180 4800 S, 50
080 1300 W), located in the Eastern Plateau region of Rio Grande do Sul in São Francisco de Paula municipality. Between 13,000 and 10,800 BP, Alpes de São Francisco was cold and dry, and contained a shallow water reservoir surround by marsh, near sparse grassland, with forests probably in refuges. Between 10,800 and 9400 BP, the climate was warmer and the moisture increased. The reservoir began to be filled with herbaceous plants, regional grassland developed, and forests probably began to expand from the refuges. Between 9400 and 5600 BP, the climate was dry, grasslands decreased in size and forests became more isolated and were probably located in refuges. From 5600 BP onward the moisture increased, forming a local bog at 5000 BP. The bog was colonized by pioneer arboreal taxa and Araucaria forest that expanded until ca. 3300 BP. Between 4300 and 3300 BP, Banhado Amarelo consisted of an incipient herbaceous marsh with adjacent sparse grassland. A delay in the arrival of moisture at the site was probably due to geographic conditions. Between 3300 and 1600 BP, the humidity increased in Banhado Amarelo, forming a bog with forest cover. After 3300 BP in Alpes de São Francisco and after 1600 BP in Banhado Amarelo, the data suggest a reduction in the reproductive capacity of the forest taxa, probably due to temperature elevation. Therefore, these forests need urgent environmental conservation programs and the present-day bogs are very important as possible generators of Araucaria forest patches in Eastern Plateau depressions. Ó 2014 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction

influence comes from southern South America. Thus, this region is very suitable for the study of past regional changes. At a height of w1000 m, the Eastern Plateau is adjacent to the coastal plain, and receives large amounts of moisture from the ocean. Precipitation levels are between 1750 and 2500 mm, the highest in southern Brazil (IBGE, 1982; Nimer, 1989). The high oceanic humidity spreads to the Eastern Plateau with a gradual reduction extending w10 km inland, and no regular dry season occurs. The annual average temperature is w12e14
C, and January is the warmest month with an average temperature of w20
C. The coldest month of July has an average temperature of w6
C (Nimer, 1989). Pollen analyses from sedimentary records of bogs in the highlands of southern Brazil have advanced the understanding of palaeoenvironments in the last millennia. The results indicate a cold and semiarid environment at the end of the last glacial stage, a warmer and humid climate in the early Holocene, a drier environment in the mid-Holocene, and an increase in temperature and humidity in the late Holocene (Roth and Lorscheitter, 1993; Behling, 1995, 1997, 1998, 2002; Behling et al., 2001, 2004; Behling and Pillar, 2007; Leonhardt and Lorscheitter, 2010).

Despite major human impact, extensive preserved areas exist in the Eastern Plateau region of Rio Grande do Sul State in southern Brazil (IBGE, 1982). The plateau consists of a large undulating grassland: a relic of a drier past, unrelated to the moist modern environment, with patches of Araucaria forests. Today, these forests are expanding on the grasslands because of the increase in moisture in the last millennia (according to floristic studies by Rambo, 1953, 1956a; Veloso, 1962; Hueck, 1972; Klein, 1975). In the light depressions of the Eastern Plateau (small local basins located within an otherwise flat topography), bogs and, less frequently, Araucaria forest occur. Warmer advection climates from the northern areas of Brazil have an influence on the plateau region, but a cold climate

* Corresponding author. E-mail addresses: [email protected] (C. Scherer), [email protected] (M. L. Lorscheitter). 1040-6182/$ e see front matter Ó 2014 Elsevier Ltd and INQUA. All rights reserved. http://dx.doi.org/10.1016/j.quaint.2014.01.010

Please cite this article in press as: Scherer, C., Lorscheitter, M.L., Vegetation dynamics in the southern Brazilian highlands during the last millennia and the role of bogs in Araucaria forest formation, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.01.010

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Our study presents for the first time from southern Brazil the palynology of two sedimentary profiles from the plateau depressions covered by Araucaria forests. The objective was to contribute to a palaeoenvironmental regional reconstruction of the last millennia and to answer the following questions: 1. Can the analysis of palynomorphs preserved in these two Araucaria forest sediments provide comparable regional results to those of bog sedimentary profiles already studied in the southern Brazilian highlands? If this is possible, Araucaria forests profiles can also be used for this purpose. 2. What is the probable origin of the two selected forests? Could a preterit bog have been involved in their succession process? Bogs contain a high diversity of species in the region and play a relevant role as water reservoirs as they slowly release water to feed creeks, thereby exerting a regulatory action (Baptista et al., 2012). If Araucaria forests can originate from subtropical bogs, this is one more strong argument to preserve bogs in environmental conservation programs that aim to generate patches of Araucaria forest in Eastern Plateau depressions. 2. Materials and methods 2.1. Study sites The two subtropical Araucaria forest sites, Alpes de São Francisco forest (Profile 1) (29
270 2600 S, 50
360 5700 W; surface pH value 5.56; at 911 m elevation, near a canyon) and Banhado Amarelo forest (Profile 2) (29
180 4800 S, 50
080 1300 W; surface pH value 5.5; at 1003 m elevation, near a canyon), are situated in the São Francisco de Paula municipality, in the southernmost highland region of Serra Geral, southern Brazil, on the Rio Grande do Sul Eastern Plateau (Fig. 1). The two preserved forests were established on marshy plain soil and were contiguous with an extensive bog where soil water accumulated only by rain. Within each forest, a sedimentary profile was collected for pollen analyses. No rivers or streams occur in the two sites near the collected profiles. The most characteristic Araucaria forest species in the two sites are Araucaria angustifolia (Bertol.) Kuntze, Drimys brasiliensis Miers, Podocarpus lambertii Klotzsch ex Endl., Dicksonia sellowiana Hook, and Ilex paraguariensis A. St.Hil., with additional various Myrtaceae taxa and epiphytic species of Bromeliaceae, Orchidaceae, Hymenophyllaceae and bryophytes. At both sites, the contiguous bog (pH ¼ ca. 4.0) is extensive and well preserved, and consists of Sphagnum recurvum P. Beauvois and other typical species. Near the forest margin, a few P. lambertii and A. angustifolia individuals had invaded the bog, and a transitional shrub flora composed mainly of Asteraceae, were found on this margin. At Banhado Amarelo, an extensive Pinus plantation occurs near the Araucaria forest, which is a threat to the native ecosystem. A 123-cm-long sedimentary Profile 1, 20 samples (Alpes de São Francisco forest site) and a 95-cm-long sedimentary Profile 2, 13 samples (Banhado Amarelo forest site) were collected within the forests using a Hiller sampler. The profile lithology shows a homogeneous deposition of clay sediments, with small amounts of very fine sand. 2.2. Analysis Six 14C dates of sediments from the profiles were obtained from Beta Analytic Inc., Miami, Florida, U.S.A. The standard chemical treatment of the samples (one sample ¼ 8 cm3) was performed (Faegri and Iversen, 1989) by adding Lycopodium clavatum tablets (Stockmarr, 1971) to calculate the palynomorph concentration per cubic centimeter of fresh sediment, and using HCl, HF, KOH and acetolysis, as well as filtering through a 250-mm net. The slides were mounted in glycerol-jelly.

Fig. 1. I. Map of South America showing Rio Grande do Sul in southern Brazil; II. Location of Araucaria forests from Alpes de São Francisco (A) and Banhado Amarelo (B), Eastern Plateau; III. Detailed map of the Alpes de São Francisco forest (29
270 2600 S, 50
360 5700 W), profile point (arrow); IV. Detailed map of the Banhado Amarelo forest (29
180 4800 S, 50
080 1300 W), profile point (arrow).

Taxonomic identification was based on the reference collection of the Palynology Laboratory, Botany Department, Federal University of Rio Grande do Sul. The reference collection includes herbarium data of plant distributions. A minimum number of 500 pollen grains (grassland, forest, and indeterminate environments) and a minimum number of 100 exotic spores of L. clavatum were counted for each sample under a in light microscope, excluding all other palynomorphs, which were counted in parallel. The minimum number of pollen to count was determined by saturation curves. The percentage of each taxon of aquatic plants (excluding algae), herbaceous marsh plants, forest, grassland, and indeterminate environment plants was based on the total sum of these categories. The percentage of fungi was based on the total of fungi þ total of all categories, and the same approach was used for the percentage of algae. For the Banhado Amarelo profile, Di. sellowiana was excluded from the total of all categories due to the presence of a large number of its grains. Thus, the percentage of this species was calculated by its total plus the total of all categories. Tilia, Tilia Graph, and CONISS software (Grimm, 1987) were used to construct

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the percentage and concentration diagrams and the cluster analysis, which were the basis for paleoenvironmental interpretations. Although the analysis included all palynomorphs that offered palaeoenvironmental information (aquatic plants, herbaceous marsh plants, forest, grassland and fungi), only selected taxa were presented in percentage and concentration diagrams. In contrast, the diagram summing all of a group includes all their components. The three 14C dates of sediments from each profile were used to plot absolute and estimated ages in diagrams using Tilia Graph software.

3. Results The 14C sediment dates are given in Table 1 and all counted taxa are listed in Table 2. From the Alpes de São Francisco profile, the percentage diagrams and dendrogram are shown in Fig. 2 and the concentration diagrams in Fig. 3. The same information for the Banhado Amarelo profile is given in Figs. 4 and 5. The summary of climate and vegetation changes is displayed in Fig. 6. Table 1 Radiocarbon dates of sedimentary profiles of Araucaria forest in Alpes de São Francisco and Banhado Amarelo (according to Beta Analytic Inc.). Sample depth (cm)

Conventional ages (14C yr BP)a

Alpes de São Francisco 34 4120  40 100 10830  70 119 12650  70 Banhado Amarelo 49.5 2770  40 64 3860  40 89.5 4240  40 a b

13

C/12C

26.0& 19.0& 25.1& 23.7& 23.6& 24.1&

Calendar age (yr BC) (cal yr BP)b 2870 e 2570 13640 e 12360 1010 e 820 2460 e 2200

Lab. number

Beta 211189 Beta 204453 Beta 200630 Beta 233966 Beta 205843 Beta 233965

C-13 adjusted. 2 s, 95% probability, Beta Analytic, Miami, Florida.

3

Low percentages of aquatic plants (0e5%) compared to herbaceous marsh plants (14e30%), both with low concentrations; scarce forest taxa (2.5%) with rare amounts in concentrations; grassland taxa with high percentage (65%) and very low concentrations; rare fungi in percentages and concentrations (Figs. 2 and 3). ZONE II (98e27 cm depth, 10,800e3300 BP). Dark clayey organic sediments with small amounts of fine sand, friable, homogeneous color. 10,800e9400 BP: decrease in percentages and concentrations of aquatic plants; a little increase of herbaceous marsh plants in percentages (30e32%) and concentrations; forest taxa remain scarce (2.5%), rare in concentrations; percentages of grassland taxa remain high (65e60%), increasing a little in concentrations; trace amounts of fungi (Figs. 2 and 3). 9400e5600 BP: aquatic plants in low percentages (up to 4%) and concentrations; increased percentages of herbaceous marsh plants (32e50%), with lower concentrations between 8000 and 7000 BP; forest taxa remains at low levels (2.5e7.5%), rare in concentrations; great decrease of grassland taxa in percentages (60e35%), with low concentrations, mainly between 8000 and 7000 BP; fungi remain at trace amounts (Figs. 2 and 3). 5600e3300 BP: low percentages of aquatic plants (up to 4%), with distinct increase in algae concentrations; higher percentages of herbaceous marsh plants (50e55%), with great increase in concentrations. Maximum S. recurvum concentration at ca. 5000 BP; increase of forest taxa (7.5e15%), that are in very high concentrations during this phase; grassland taxa increase again (35e42%), with great increase in concentrations; fungi with percentage a little elevated (2%), their concentrations increase (Figs. 2 and 3). ZONE III (27e0 cm depth, 3300 BPepresent). Dark clay sediments rich in organic matter, friable, a small amount of fine sand and many small plant remains near the top. Trace amounts of aquatic plants; herbaceous marsh plants with lower percentages

Table 2 Palynomorphs found in the sedimentary profile counts from Alpes de São Francisco and Banhado Amarelo. Aquatic plants Herbaceous marsh plants Forest

Grassland

Indeterminate environment plants Fungi

Alismataceae, Botryococcus Kützing, Debarya (De Bary) Wittrock, Eichhornia Kunth, Isoëtes L., Mougeotia C. A. Agardh, Myriophyllum L., Pseudoschizaea rubina Rossignol ex Christopher, Salvinia Ség., Spirogyra Link, Zygnema C. A. Agardh Aspiromitus punctatus (L.) Schljakov, Blechnum L. type, Blechnum imperiale (Fée & Glaziou) H. Chr., Cyperaceae, Eriocaulaceae, Ludwigia L., Lycopodiella alopecuroides (L.) Cranfill, Lycopodium clavatum L. type, Osmunda L., Phaeoceros Prosk., Phaeoceros laevis (L.) Prosk., Polygala L., Selaginella marginata (Humb. & Bonpl. ex Willd.) Spring, Sphagnum recurvum P. Beauv., Typha L., Utricularia L. Senegalia C. S. Rafinesque 1 type, Senegalia C. S. Rafinesque 2 type, Alchornea triplinervia (Spreng.) Müll. Arg., Allophylus edulis (A. St.-Hil., Cambess. & A. Juss.) Radlk., Anacardiaceae, Araucaria angustifolia (Bertol.) Kuntze, Asplenium serra Langsd. & Fisch., Bauhinia forficata subsp. pruinosa (Vogel) Fortunato & Wunderlin, Bignoniaceae, Celtis L., Chrysophyllum L., Cyatheaceae, Dicksonia sellowiana Hook., Drimys brasiliensis Miers, Dryopteris Adans. type, Huperzia Bernh., Hymenophyllum Sm. type, Hypolepis Bernh., Ilex L., Marattia laevis Sm., Meliaceae type, Microgramma vacciniifolia (Langsd. & Fisch.) Copel. type, Mimosa scabrella Benth., Myrsine L., Myrtaceae, Pecluma pectinatiformis (Lindm.) M.G. Price, Phrygilanthus Eichler, Podocarpus lambertii Klotzsch ex Endl., Polypodium L. type, Polypodium hirsutissimum Raddi type, Roupala Aubl., Sapindaceae, Trema micrantha (L.) Blume, Urticales Amaranthus L. type, Baccharis L. type, Caryophyllaceae, Cuphea carunculata Koehne, Gnaphalium L. type, Iresine P. Browne type, Mutisieae 1, Mutisieae 2, Plantago L., Poaceae, Polygonum L., Scrophulariaceae type, Valeriana eichleriana (C. Muell.) Graebn., Verbena L.Vernonia Schreb. type, Vicia L. type Bryophyte, other bryophytes, Croton L. type, Cucurbitaceae, Eryngium L., Galium L. type, indeterminate angiosperms, Lamiaceae, Liliaceae 1 type, Liliaceae 2 type, Malvaceae, Melastomataceae, Mimosa L. 1, Mimosa L. 2, Mimosa ser. Lepidotae Benth., Richardia L. type, Rubiaceae, Valeriana L., stephanocolpate, other monoletes, other pteridophytes, other tricolpates, other tricolporate, other triletes, tricolporate 1, tricolporate 2, triporate verrucate Gelasinospora adjuncta Cain, Glomus Tul. & C. Tul., Athelia Pers. type, Helicoon pluriseptatum Beverw. type, Spore 1, Spore 2, Spore 3, Spore 4, other fungi, hifae

3.1. Alpes de São Francisco forest site: profile 1 ZONE I (125e98 cm depth, 13,000e10,800 BP). Clear gray, plastic clay sediments with little fine sand, changing in the upper part of the zone to dark gray plastic clay organic sediments with fine scattered sand.

(29e45%) and great decrease in concentrations. Trace amounts of S. recurvum after 3000 BP; very high increase of forest taxa (15e 45%) with a very great decline in concentrations toward the top; grassland taxa decrease drastically (42e15%), with scarce concentrations up the top; the percentages (2e50%) and concentrations of fungi have a great increase up the top (Figs. 2 and 3).

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Fig. 2. Palynological percentage diagrams for the sedimentary profile from Alpes de São Francisco forest, including chronology, depth, lithology, indicators of aquatic plants, herbaceous marsh plants, forest, grassland, composite diagram, fungi, zones, and dendrogram.

3.2. Banhado Amarelo forest site: profile 2 ZONE I (95e84 cm depth, 4300e4100 BP). Clear gray, plastic clay sediments with little fine sand content. Aquatic plants are rare in percentages and concentrations (not shown in diagrams); herbaceous marsh plants with large percentages of (60e40%) and trace amounts in concentrations; low percentage of forest taxa (7e22%), Di. sellowiana with the highest percentages of the profile (60e45%), trace amounts of forest taxa concentrations, including Di. sellowiana; grassland (20%) has trace amounts in concentrations; fungi with low percentages (2.5e5%), very scarce in concentrations (Figs. 4 and 5). ZONE II (84e29 cm depth, 4100e1600 BP). Clear gray, plastic clay sediments with little fine sand in the lower part, gradually becoming dark gray and rich in organic matter. Darker clay sediments at the end of the zone, with small amounts of fine sand, rich in organic matter and many plant remains.

4100e3300 BP: scarce aquatic plants in percentages and concentrations (not shown in diagrams); large percentages of herbaceous marsh plants (40e50%) and scarce concentrations; slight increase of forest taxa (15e25%), with low concentration. Di. sellowiana (45e50%) increases in concentrations; grassland taxa (20e27%) are very low in concentrations; fungi increase a little (4e8%) with rare in concentrations (Figs. 4 and 5). 3300e1600 BP: aquatic plants scarce in percentages and concentrations (not shown in diagrams); large percentages (35e50%) and great increase in concentrations of herbaceous marsh plants, including S. recurvum with the highest record concentrations; forest taxa decreases in percentages (30e15%), the same for Di. sellowiana (45e18%), both with great increase in concentrations, the highest of the record; grassland taxa increase in percentages (20e 48%) and concentrations; fungi increase in percentages (2.5e25%) and in concentrations (Figs. 4 and 5).

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Fig. 3. Palynological concentration diagrams for the sedimentary profile from Alpes de São Francisco forest, including chronology, depth, lithology, indicators of aquatic plants, herbaceous marsh plants, forest, grassland, fungi, and zones.

ZONE III (29e0 cm depth, 1600 BPepresent day). Dark clay sediments with little fine sand, friable, rich in organic matter and many plant remains. Scarce percentages and concentrations of aquatic plants (not shown in diagrams); herbaceous marsh plants with lower and uniform percentages (29e37%) and accentuated decrease in concentrations, including S. recurvum; increase in percentages (15e 30%) and great decline in concentration of forest taxa, the same to Di. sellowiana (18e30%); grassland taxa percentages (48e35%) present great decrease in concentrations; large increase in fungi percentage (25e60%) with high concentrations (Figs. 4 and 5). 4. Discussion: palaeoenvironmental interpretation 4.1. 13,000e10,800 BP The data for 13,000e10,800 BP indicate a shallow lake in the depression of the Alpes de São Francisco site where an Araucaria forest exists today (Isoëtes and Myriophyllum indicators; Fig. 2), with Cyperaceae on the marsh margin. Near the site, sparse grassland is indicated (very low concentrations of grassland; Fig. 3). The forest species were probably living in distant refuges (Rull, 2009; Mosblech et al., 2011; Correa-Metrio et al., 2013), with more favorable microclimates, such as the lower parts of valleys and river margins, or close to canyons (very low frequency of forest indicators; Fig. 3). At the end of the last glacial stage, the Eastern Plateau seems to have had a cold and dry climate, with an unforested landscape and sparse grassland. This semiarid condition agrees with other palynological analyses of bog profiles from this phase in the region (Roth and Lorscheitter, 1993; Behling et al., 2004; Leonhardt and Lorscheitter, 2010). For western Rio Grande do Sul, a distinct dry phase was indicated from 22,000 BP until the end of the last

glacial stage (Bombin, 1976; Behling et al., 2005). In the other highlands of southern Brazil, a dry cold climate has been indicated for 14,000e10,000 BP (Santa Catarina State, Behling, 1995), 12,500 BP and 14,880e12,950 BP (Paraná State, Behling, 1997, 2007), with grassland landscapes and Araucaria forest in valley refuges. In the same way, in this phase extensive areas of south and southeastern Brazil seem to have supported subtropical grassland landscapes, much lower temperatures than today and dry conditions, with greater moisture in the valleys where small forested areas occurred (Ab’Saber, 1977; Behling, 1998, 2002; Lichte and Behling, 1999). Near southern Brazil, in Buenos Aires Province, data from Quattrochio and Borromei (1998) and Prieto (2000) show a dry shrub grassland related to a cold and dry or subhumidedry to semiarid climate in this phase, which is similar to other Argentine regions such as Bariloche (Markgraf, 1984) and Tierra del Fuego (Quattrochio and Borromei, 1998). The main factor determining this adverse climate in the southern Brazilian highlands was probably the southwest cold winds (Bombin, 1976; Roth and Lorscheitter, 1993; Leonhardt and Lorscheitter, 2010) together with the strong activity of the Peru and Malvinas marine currents that reached lower intertropical latitudes compared to today (Kern, 1982). The marine regression (Kowsmann et al., 1977; Villwock and Tomazelli, 1998) was probably the other cause of the dry climate in the Rio Grande do Sul Eastern Plateau, with very low moisture arising from the ocean to result in limited precipitation. 4.2. 10,800e3300 BP The data from ca. 10,800 BP until 9400 BP suggest denser vegetation in the Alpes de São Francisco site (an increase in the concentration of herbaceous marsh plants, grassland, and some

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Fig. 4. Palynological percentage diagrams for the sedimentary profile from Banhado Amarelo forest, including chronology, depth, lithology, indicators of aquatic plants, herbaceous marsh plants, forest, grassland, composite diagram, fungi, zones, and dendrogram.

forest indicators; Fig. 3). The increase of herbaceous marsh taxa in the site (mainly Cyperaceae, Phaeoceros laevis and S. recurvum) and the lower frequencies of aquatic indicators (Figs. 2 and 3) are probably due to the gradual filling of the local lake. Near the site, denser grassland is indicated (Fig. 3). A few pioneer forest indicators seem to begin the colonization of the marsh (Figs. 2 and 3). The changes in the site from 10,800 to 9400 BP probably also reflect regional events, with a denser grassland landscape, and the expansion of some arboreal taxa as a result of a climate with a little more moisture, rainfall, and an increase in the global temperature at the beginning of the Holocene.

The results are in accordance with other palynological sequences from bog profiles of the Eastern Plateau (Lorscheitter, 1992, 1997; Roth and Lorscheitter, 1993; Leonhardt and Lorscheitter, 2010) and those from coastal plain profiles (Lorscheitter, 2003), reflecting a large climatic event (clearly expressed in the concentration diagrams). The other southern Brazilian highlands, experienced similar vegetation changes with an expansion of the Atlantic pluvial forest and one of the Araucaria forest (Santa Catarina and Paraná states, Behling, 1995, 1997). However, this study indicates seasonal droughts in the Paraná highlands. Ybert et al. (2001) suggest a reinterpretation of the results of Behling (1995) because

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Fig. 5. Palynological concentration diagrams for the sedimentary profile from Banhado Amarelo forest, including chronology, depth, lithology, indicators of herbaceous marsh plants, forest, grassland, fungi, and zones.

he indicated a dry climate at the beginning of the Holocene that does not agree with the expansion of the Atlantic pluvial forest in this phase. Similarly, Leonhardt and Lorscheitter (2010) criticize some results that indicate dry conditions at the beginning of the Holocene in southern Brazil (Behling, 1995, 1998, 2007; Behling et al., 2004, 2005), suggesting that more information is needed from new records at additional sites, including a pollen concentration analysis, to clarify these results. In other parts of southern South America, various results have indicated the existence of a humid phase at the beginning of Holocene. The increase in temperature and moisture is related to conditions in Província de Buenos Aires and areas south of Tierra del Fuego (Quattrochio and Borromei, 1998). In the Pampas of eastern Argentina, a change from dry steppe to humid grasslands occurred in this phase followed by a rapid evolution of marsh environments, corresponding to a subhumid to humid climate (Prieto, 2000). The evidence also shows an increase in humidity in the northeast region of the Argentine Pampas (Prieto et al., 2004), the northeast region of temperate Nothofagus forests (Markgraf, 1984), southeast Patagonia (Mancine, 2002) and the sub-Antarctic zones (Markgraf, 1983). According to D’Antoni (1983), the increase in humidity at ca. 10,000 BP in South America is due to a change in the atmospheric circulation pattern at the beginning of the Holocene, with a greater expression of the South Atlantic Anticyclone compared to the South Pacific High. The environmental conditions in the Alpes de São Francisco site seem to become adverse, with moisture reduction from 9400 BP until 5600 BP (mid-Holocene), mainly between 8000 and 7000 BP; promoting a dry climate. The data indicate a vegetation retraction and an unforested depression, with fewer herbaceous marsh plants near the dry grassland (decreases in the concentration of algae, herbaceous marsh plants, and grassland, rare arboreal plants; Fig. 3). The same dry phase in the mid-Holocene was indicated by the palynology of bog profiles from the Eastern Plateau (Roth and Lorscheitter, 1993; Behling et al., 2001 at 7500e4000 BP; Leonhardt and Lorscheitter, 2010 at 9700e6500 BP). In adjacent low portions of the highlands, Leal and Lorscheitter (2007) show a

dry phase at 7000e5000 BP. For the other highlands of southern Brazil, a relatively dry climate has been indicated in the midHolocene, which would not allow forest expansion from the refuges (Behling, 1995, 1997, 2007; Behling et al., 2001, 2004), and is also the case in the western Rio Grande do Sul (Behling et al., 2005). To the southeast of the Andes, an arid climate has been indicated at 8000e6000 14C yr BP (Markgraf and Bradbury, 1982). In Bariloche, a return to steppe conditions was reported at 8500e 7000 BP, creating a landscape with sparse forests at 8000e6000 BP (Markgraf, 1984). To the south of Tierra del Fuego, Quattrochio and Borromei (1998) suggest a dry climate at 9500e5000 BP. These results reinforce the idea of a dry phase in other areas of southern South America during the mid-Holocene. The chronological differences in this dry phase are probably due to the geographical characteristics and their influence on the microclimate (Leonhardt and Lorscheitter, 2010). The data for the phase from ca. 5600 BP at Alpes de São Francisco indicate a substantial increase in moisture. Between 5600 and 3300 BP the local vegetation developed (the concentration of almost all taxa increased; Fig. 3). The herbaceous marsh plants expanded, with a distinct increase in algae typical of aqueous marsh soils. A bog developed and reached its climax ca. 5000 BP (the maximum concentration of S. recurvum was observed; Fig. 3). The data suggest denser regional grassland. Pioneer arboreal plants seemed to colonize the herbaceous marsh margin in this phase and expanded over the bog (Fig. 3). As a consequence of the forest appearance, the extent of the bog decreased from 5000 BP onward (a large reduction in the S. recurvum concentration; Fig. 3). Some grassland taxa could have invaded the bog (e.g. the Baccharis type that can also indicate shrub taxa and a transition to forest). After the pioneer taxa, Araucaria forest undertook its great expansion in the site until ca. 3300 BP (highest concentrations of A. angustifolia and Di. sellowiana; Fig. 3). At 5000 BP, the bog at the Alpes de São Francisco site was at its maximum stage of development, while the adjacent area (the actual bog) was still in its initial phase of expansion (Leonhardt and Lorscheitter, 2010). This suggests that the Araucaria forest

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Fig. 6. Summary of climatic and vegetation changes in the Eastern Plateau of Rio Grande do Sul, southern Brazil, according to the Alpes de São Francisco and Banhado Amarelo palynological profiles.

expanded and was covering the area of the bog from 5000 BP onward, and that today, the remainder of the bog will probably also be substituted by forest in this succession process. Some arboreal taxa invasions on the current adjacent bog, including A. angustifolia, occur according to this process. The data suggest that at ca. 5600e3300 BP the Alpes de São Francisco site was conditioned to higher regional moisture and the bog was replaced by Araucaria forest, near the denser grassland. Other Araucaria forest patches probably expanded in the same way on light depressions (on preterit bogs) on the Eastern Plateau in this phase. In southern Brazilian highlands, the beginning of the high regional moisture levels in the late Holocene has been confirmed by other palynological records of bog profiles (Roth and Lorscheitter, 1993; Behling, 1995, 1997; Behling et al., 2001, 2004; Leonhardt and Lorscheitter, 2010). On the lower northeast slope of Serra Geral in Rio Grande do Sul (Leal and Lorscheitter, 2007) and for the western areas of this state (Behling et al., 2005), the same humid phase is indicated. The great Holocene marine transgression

(Kowsmann et al., 1977; Villwock and Tomazelli, 1998) was an important factor in generating more humidity in the Eastern Plateau at ca. 5000 BP onward due to the proximity of the highland to the ocean (ascendant marine moisture, resulting in greater rainfall on the plateau). According to Martin et al. (1991) and Ybert et al. (2001), the probable El Niño-type events from 5000 BP onward also contributed toward the higher precipitation in southern Brazil. In contrast to the Alpes de São Francisco, the data for the phase from 4300 to 4100 BP indicate very little marsh vegetation at the Banhado Amarelo site. The area near grassland was poorly developed and the site was unforested (trace amounts in concentrations of forest and grassland taxa; Fig. 5). These conditions continued until 3300 BP. The general shortage of pollen at the Banhado Amarelo site probably reflects a delay in the arrival of the regional moisture due to a larger unprotected area of plains than at the Alpes de São Francisco site, which is surrounded by undulating elevated land, where it is easier to retain the environmental humidity. This would explain micro-regional climate differences in the chronology of distinct records from the southern Brazilian highlands.

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4.3. 3300 BPepresent-day In the Alpes de São Francisco site, the large forest expansion until ca. 3300 BP accentuated the decline of the bog, which disappeared at 2500 BP (very few spores of S. recurvum were found after this time; Fig. 5). From 3300 BP onward, almost all forest indicators were in decline (up to the profile top), including A. angustifolia (clearly indicated in the concentration diagrams; Fig. 5). As the profile was collected in a present-day preserved Araucaria forest related to a humid environment, this pollen decrease clearly is not due to forest retreat, but is probably due to the gradual temperature increase in the Eastern Plateau region in the last millennia that diminished pollen production, resulting in lower reproductive activity. The natural expansion of Araucaria forest in the region (Rambo, 1956b; Reitz and Klein, 1966; Van Auken, 2000; Cabral et al., 2003; Duarte et al., 2006) then probably became slower than in the humid phase before 3300 BP (the increase in concentration of fungal spores near the top of the profile agree with this moisture and temperature elevation). Similar results were indicated for the first time by Leonhardt and Lorscheitter (2010), who revealed lower pollen production in the Eastern Plateau from 2000 BP onward (according to the concentration diagrams). The increase in temperature does not permit a cold physiological drought, which promotes the A. angustifolia reproductive cycle (Backes, 1988), thus diminishing their pollen sacs to result in less seed production (Leonhardt and Lorscheitter, 2010). This allows the slow invasion of the more competitive neighboring tropical taxa, with smaller and lighter seeds, into Araucaria forest (Reitz and Klein, 1966), which is a serious danger for the preservation of this ecosystem. At the Alpes de São Francisco site, the large decrease in the concentration of grassland indicators after 3300 BP is probably the result of forest implantation over the bog, which made the arrival of pollen from open areas difficult, and the natural reduction of the grassland due to the rise in regional moisture levels (Rambo, 1956b; Leonhardt and Lorscheitter, 2010). From 3300 to 1600 BP the Banhado Amarelo site experienced a large expansion of herbaceous marsh plants, forming a bog, with algae in the aqueous areas. The forest colonized this bog immediately. The concentration of typical Araucaria forest indicators also increased (e.g., A. angustifolia and Di. sellowiana; Fig. 5). Grassland plants expanded in this phase, and some of them, such as the Baccharis type, are indicative of an intermediary stage of forest succession. From 1600 BP onward, bog plants decrease at the Banhado Amarelo site but, as in the Alpes de São Francisco site, the forest pollen was also greatly reduced in concentration (e.g., A. angustifolia and especially Di. sellowiana; Fig. 5), probably because of the same regional temperature increase, thus diminishing the pollen production until the present-day. Similar to the Alpes de São Francisco site, the decline in the concentration of grassland plants (Fig. 5) was probably caused by the occurrence of forest and by the moisture increase from 1600 BP onward. The possibility exists that part of the decrease in palynomorph concentration in the last millennia in both the Alpes de São Francisco and Banhado Amarelo was also due to some human influence, but this was not considered to be relevant because of the well preserved condition of the sites. 5. Conclusions For the first time, palynomorphs of profiles of the Araucaria forest in the highlands of southern Brazil were studied, providing consistent records of the vegetation and climate at the end of the last glacial stage and throughout the Holocene. The study reinforces previous palynological results from bog profiles: a semiarid phase at the end of the last glacial stage (sparse grasslands and Araucaria

9

forest in the refuges), the increase in temperature and moisture at the early Holocene (denser grassland and a little Araucaria forest expansion), a dry phase at the mid-Holocene (retraction of grassland and Araucaria forest), and a new moist phase in the late Holocene, with bog formation and the last expansion of Araucaria forest patches on grassland. In this humid phase, the posterior increase in the temperature was the main factor that slowed the expansion of Araucaria forest in the last millennia by influencing its reproductive cycle and permitting some invasion of adjacent tropical forest taxa. At this time of higher temperatures, the increase in humidity probably resulted in a lower expression of grassland components. Parallel to the expansion of Araucaria forest on the grasslands in the late Holocene, the present results show, for the first time, the expansion of this forest also on the bogs at the two studied sites. This confirms the assumption that Araucaria forests originate from bogs on the slight depressions of the Eastern Plateau. Some A. angustifolia plants and other arboreal taxa that have invaded the present-day margin bogs in Alpes de São Francisco, Banhado Amarelo, and other bogs on the Eastern Plateau provide evidence. These vegetation and climatic changes are more clearly visible in the concentration diagrams than in the percentage diagrams. Therefore, some results based only on percentage diagrams require reevaluation. However, small chronological differences in the climatic phases of distinct localities in the highlands of southern Brazil are probably due to micro-regional conditions and geographical characteristics. The results demonstrate the fragility of the Araucaria forest in southern Brazil in relation to climatic changes and the urgent need to preserve this unique ecosystem. In this context, the present-day bogs also need require preservation because of their importance and potential role as possible generators of Araucaria forests in the southern Brazilian highlands. Therefore, our results have showed that the palynology of forest profiles offers one more promising line in the study of palaeoenvironments from the southern Brazilian highlands.

Acknowledgments The authors are grateful to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the financial aid and scholarships received.

Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.quaint.2014.01.010.

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Please cite this article in press as: Scherer, C., Lorscheitter, M.L., Vegetation dynamics in the southern Brazilian highlands during the last millennia and the role of bogs in Araucaria forest formation, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.01.010