- LATE-HOLOCENE FIRE HISTORY IN A FOREST-GRASSLAND MOSAIC IN SOUTHERN BRASIL - 81Applied Vegetation Science 10: 81-90, 2007© IAVS; Opulus Press Uppsala.

Abstract Question: Is the diverse mosaic of forest/grassland (Campos) vegetation on the hills in the Porto Alegre region natural or of anthropogenic origin? What are the best approaches to management and conservation of forest/grassland mosaics in southern Brazil?Location: 280 m a.s.l., Rio Grande do Sul State (30°04'32''S; 51°06'05''W, southern Brazil.Methods: A 50-cm long radiocarbon dated sediment core from a swamp on Morro Santana was analysed for pollen and charcoal, and multivariate data analysis was used to reconstruct past vegetation and fire dynamics.Results: The formation of swamp deposits is related to a change to wetter climatic conditions since 1230 cal yr BP. The diverse forest/grassland mosaic existed already at that time and can be seen as natural in origin as it has been also shown from other studies in southern Brazil. Since 580 cal yr BP, forests expanded continuously. The marked higher occurrence of the pioneer Myrsine during the last 70 years, indicates a change in the disturbance regime. In the past, vegetation has been influ-enced by mostly anthropogenic fire, set first by Amerindians and later by European settlers.Conclusions: Management for conservation of forest/grassland mosaics should take into account, first, that grasslands are remnants of earlier drier Holocene periods and not a result of deforestation and, second, the history of disturbance by grazing and fire. Suppression of grazing and burning has likely resulted in a trend towards more woody vegetation under modern wet climatic conditions. If management for conservation excludes fire, the present grassland patches will tend to disappear due to forest expansion under the modern humid climate. Maintaining or reintroducing cattle grazing in conservation areas could be an alternative to fire.

Keywords: Anthropogenic fire; Campos (grassland); Char-coal; Conservation management; Forest mosaic; Multivariate analysis; Natural fire; Palaeoclimatology; Palaeoecology; Palaeofire; Pollen analysis.

Abbreviations: AD = Anno Domini; AMS = Accelerator mass spectrometry; Cal yr BP = calibrated years before 1950; PCoA= Principal Coordinates Analysis.

Late-Holocene fire history in a forest-grassland mosaic in southern Brasil: Implications for conservation

Behling, Hermann1,*; Pillar, Valério D.2,4; Müller, Sandra C.2,5 & Overbeck, Gerhard E.3

1Albrecht-von-Haller-Institut für Pflanzenwissenschaften der Georg-August-Universität Göttingen, Abteilung für Palynologie und Klimadynamik, Untere Karspüle 2, DE-37073 Göttingen, Germany;

2Departamento de Ecologia, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil; 3Vegetation Ecology, Technische Universität München, Am Hochanger 6, DE-85350 Freising-Weihenstephan, Germany;

E-mail overbeck@wzw.tum.de; 4E-mail vpillar@ecologia.ufrgs.br; 5E-mail smuller@ecologia.ufrgs.br; *Corresponding author; E-mail hermann.behling@bio.uni-goettingen.de

Introduction

The presence of mosaics of grassland and forests in southern Brazil, under modern, wet climatic condi-tions favourable for forest development, has puzzled field biologists. Lindman (1906) observed that forests should be able to expand over grasslands, and attributed observed patterns to the transitional situation between tropical forests to the north and temperate grasslands to the south. Rambo (1954, 1956a, b), hypothesized, pri-marily on phytogeographical evidence, that grasslands were the older vegetation type, while forest expansion is a recent response to more humid climate conditions. Hueck (1966) also wondered why these grasslands can exist under the present humid conditions. More recently, palynological studies elucidated vegetation and climatic changes during the Quaternary on the southern Brazil-ian highland (Planalto Sul-Brasileiro) which is today characterized by mosaics of Campos (grassland) and Araucaria forest (Behling et al. 2004). In southern and southeastern Brazil, late glacial times were characterized by dominance of grasslands under a climate colder and drier than today (Behling 2001). In contrast to grasslands in southeastern Brazil, southern Brazilian grasslands were not replaced by forests until the Late Holocene, after about 4300 cal yr before present (BP), with expan-sion increasing in speed only ca. 1100 years ago at the Cambará do Sul site (Behling 1998, 2001; Behling et al. 2004). For the hilly lowland region around Porto Alegre, located south of the highland, no palynological studies have been conducted so far. Around Porto Alegre city tropical taxa find their southern limit (Waechter 2002), and modern vegetation is characterized by fragments of Atlantic rain forest and subtropical semi-deciduous forest in mosaics with Campos, in their distribution primarily related to an altitudinal gradient and exposure (Rambo 1954, 1956a; Teixeira et al. 1986). As a result of this situation, the

82 BEHLING, H. ET AL.

area supports an interesting mixture of floristic taxa from the coastal Atlantic rain forest, from seasonal deciduous forest of the upper Uruguay river, the Jacuí and Ibicuí river valleys and from Pampas grassland further to the south, continental taxa of the Gran Chaco to the west, and grassland species from central Brazil (Rambo 1961; Veloso & Góes-Filho 1982). However, the vegetation history is poorly known, and it is unclear whether these grasslands should be considered natural relicts stabilized by disturbances such as fire and grazing (Pillar & Quadros 1997), or whether they are a consequence of deforesta-tion in recent centuries, with subsequent reforestation impeded by fire or grazing. The origin of the grasslands is an important issue for nature conservation. If grasslands were a consequence of human induced deforestation, management would have to aim at re-establishment of the forest. However, if grasslands had prevailed in past climatic periods, it is desirable to conserve these relicts and their high biodi-versity. Management to sustain the modern mosaics of Campos and forest in the Porto Alegre region depends, in part, on understanding historical reference conditions for fire magnitude and frequency. In this study, we use a late Holocene pollen and charcoal record from a sediment core sampled at Morro Santana to analyse past vegeta-tion and fire dynamics in order to provide background information for management and conservation.

Methods

Study area

Morro Santana (max. altitude 311 m) is a hill lo-cated in the eastern region of Porto Alegre (Fig. 1). The grasslands of Morro Santana are found mainly on the top and on the northern slopes, while forests dominate the southern, eastern and western slopes (Aguiar et al. 1986; Brack et al. 1998). The total area of Morro San-tana is ca. 1000 ha. A part is under heavy anthropogenic influence (e.g. urban settlements, quarries), 220 ha are grassland, 25 ha shrubland (locally known as capoeira), 339 ha native forest, and 42 ha are forest plantations (Pinus/Eucalyptus). Forests consist of a mixture of floristic elements, principally from seasonal deciduous forest and Atlantic rain forest. According to a local classification (Brack et al. 1998), four distinct forest types can be found on the hills of Porto Alegre: a sub-xerophilic forest (near the top); a hygrophilic forest (on southern moister slopes and valleys), a mesophilic forest (between these ex-tremes) and a riparian forest (along small creeks). The hygrophilic forest includes the greatest part of the pluvial tropical taxa, while species with wider ecological range dominate in areas near the top of the hill and in riparian forest in the northern slope. A list of the most important

Fig. 1. Map showing the location of the study site (arrows) in Porto Alegre, southern Brazil. The im-age in detail indicates land cover (dark grey: forest, light grey: grassland; white: urban and quarries). Detailed image source: http://www.ecologia.ufrgs.br/atlasdigital/diag_ambiental/index.php containing images Quickbird ©Digital Globe taken between March 2002 and March 2003.

- LATE-HOLOCENE FIRE HISTORY IN A FOREST-GRASSLAND MOSAIC IN SOUTHERN BRASIL - 83

species is given in Table 1. The grasslands, dominated by C4 grasses but with some C3 species, include a shrub component, with total cover of shrubs between 10 and 20%, depending on time since the last fire. In general, higher cover values of shrubs and pioneer tree species can be found close to rock outcrops, where woody plants probably are more protected from fire. Circular patches of woody vegetation are associated with some rock outcrops (Müller & Forneck 2004), suggesting forest encroachment in between-fire intervals. Usually occurring in dense patches with cover values locally above 50%, Eryngium horridum and E. pristis (Apiaceae) dominate in some grassland areas. In total, the grasslands on Morro Santana contain ca. 450 to 500 vascular plant species (Overbeck et al. 2006). Present-day burning frequency on Morro Santana is high: on average, all parts of the grassland burn ap-proximately every 3 to 5 years. Most fires are set by local inhabitants. Based on comparison of aerial pho-tographs from the past 20 years (Adelmann unpubl.), it was concluded that the forest-grassland border stayed almost constant under the impact of frequent burning. Recent research indicates that the grassland vegetation can return to pre-burn conditions shortly after the burning (Overbeck et al. 2003, 2005). The modern climate in the Porto Alegre region is subtropical humid (Cfa in the Köppen classification), with mean precipitation of 1348 mm.a–1 and average annual temperature of 19.5 ºC, average temperature of the hottest month 24.7 ºC, of the coldest months 14.3 ºC;

data from Porto Alegre meteorological station (Nimer 1990). Precipitation is well distributed throughout the year, but occasional dry spells may occur during the summer months. Human presence in the Porto Alegre region is re-corded since around 9000 yr BP, with successive occu-pations by different groups. Most recently, the Guarani, occupied the region from 1800 yr BP until the arrival of Europeans in the mid-17th Century, when the indigenous population was reduced after attacks by Portuguese slave dealers (Noelli et al. 1997; Schmitz 1991). The Guarani were farmers, cutting and subsequently burning forest areas, where soils were more fertile and easier workable than under grassland, but they did not have domesticated grazing animals. In AD 1732, the Porto Alegre area was first settled by cattle farmers, and in AD 1740 land rights were ceded for a sesmaria of ca. 130 km2, including the area of Morro Santana (Macedo 1999), where a farm house was constructed, indicating that at least a good part of the area must have been grassland. In recent decades, the lower parts of the flanks of the hill have been subject to irregular expansion of squatter settlements (Adelmann & Zellhuber 2004), but grassland and forest areas are not so used. Currently, ca. 60% of Morro Santana belong to the Federal University of Rio Grande do SUL (UFRGS) and is to be turned into a nature conservancy reserve.

Vegetation type / physiognomy

Forest: upper stratum(max. height: 12 to 20 m)

Forest: middle/lower strata

Grassland: lower stratum

Grassland: shrubs(cover between 10 and 20%, de-pending on time since last burn)Nuclei of woody vegetation at rock outcrops (protected from fire)

Important species

Trees: Alchornea triplinervia, Pachystroma longifolium (Euphorbiaceae), Eugenia rostrifolia (Myrtaceae), Cabralea canjerana (Meliaceae), Myrsine umbellata (Myrsinaceae), Cupania vernalis (Sapindaceae), Guapira opposita (Nyctagi-naceae), Ocotea spp. (Lauraceae), Ficus spp. (Moraceae).Trees: Sorocea bonplandii (Moraceae) Gymnanthes concolor, Sebastiania brasiliensis (Euphorbiaceae), Casearia decandra (Salicaceae), Trichilia elegans, T. claussenii (Meliaceae), Myrcianthes gigantea, Eugenia uniflora, E. uru-guayensis, Myrciaria cuspidata (Myrtaceae), Faramea marginata (Rubiaceae).Shrubs: Psychotria spp. (Rubiaceae); Mollinedia elegans (Monimiaceae).C4-grasses: Elionurus muticus, Aristida flaccida, Aristida laevis, Andropogon lateralis, Leptocoryphium lanatum, Schizachyrium tenerum, Trachypogon montufari.C3-grasses: Briza spp., Bromus spp., Melica spp. Herbs: Eryngium horridum, E. pristis (Apiaceae), Vernonia flexuosa, Aspilia montevidensis, Pterocaulon spp. Eupato-rium spp. (Asteraceae): Tibouchina gracilis (Melastomataceae), Richardia grandiflora, Relbunium hirtum (Rubiaceae); Aeschynomene elegans, Centrosema virginianum, Desmodium incanum, Crotolaria tweediana (Fabaceae)Cyperaceae: Rhynchospora spp. and Bulbostylis spp.Grassland shrubs: Baccharis spp., Eupatorium spp., Vernonia nudiflora, Heterothalamus psiadioides, (Asteraceae), Croton spp. (Euphorbiaceae).Forest border/pioneer species: Dodonaea viscosa (Sapindaceae); Agarista eucalyptoides (Ericaceae).Trees/pioneer species: Myrsine spp. (Myrsinaceae), Myrciaria cuspidata, Myrcia palustris, Eugenia spp. (Myrtaceae), Symplocos spp. (Symplocaceae), Maytenus cassineformis (Celastraceae), Matayba elaeagnoides (Sapindaceae), Styrax leprosum (Styracaceae), Casearia silvestris (Salicaceae), Lithraea brasiliensis (Anacardiaceae).

Table 1. Important species in forest and grassland on Morro Santana, Porto Alegre, RS, Brazil. Data for forests and woody species nuclei at rock outcrops from Brack et al. (1998), Müller & Forneck (2004), Müller (2005); data on grassland from Overbeck et al. (2006).

84 BEHLING, H. ET AL.

Data collection and analysis

The swamp on Morro Santana is ca. 100 m × 50 m in a shallow rocky basin on the hilltop. The core was taken from the deepest portion near the centre of the basin (30°04'32'' S; 51°06'05'' W, altitude 280 m) using a Rus-sian corer. Water depth was ca. 30 cm during the coring operation in March 2002. The recovered section of 50 cm length was extruded on-site, wrapped in plastic film and stored under refrigeration (+4 °C) after return from the field and before sampling. Three sediment subsamples of 1 cm thickness were taken from the core and dated by accelerator mass spectrometry (AMS) in the AMS laboratory at the University Erlangen/Nürnberg in Ger-many. The calibration of the radiocarbon dates has been carried out after CALPAL (Weninger et al. 2004). For pollen and charcoal analysis, 26 subsamples (0.5 cm3), taken in general at 2 cm intervals along the profile, were treated with hydrofluoric acid (HF), subjected to ac-etolysis, and mounted in a glycerin gelatin medium. Pol-len preparation included addition of exotic Lycopodium spores to determine pollen concentration (grains/cm3) and influx (grains/cm2.a). All subsamples were counted until a minimum of 300 pollen grains. This pollen sum includes herbs, shrubs and trees, but not aquatic taxa or fern and moss spores. Carbonized particles (5-150 µm) and algae colonies, including Botryococcus were counted and expressed as percentage of the total pollen sum. Pollen identification relied on the first author's reference collection (containing about 2000 Brazilian species) and pollen morphological descriptions in Behling (1993). For plotting of the pollen data, calculations and cluster analysis TILIA, TILIAGRAPH and CONISS software was used (Grimm 1987). Ordination by principal coor-dinates analysis (PCoA) was used for a synthetic view of community compositional changes (Orlóci et al. 2002), allowing the identification of phases of non-directional change and phase transitions as in Behling et al. (2004). PCoA was based on pairwise Euclidean distances between subsamples. Distances were computed from square root transformed pollen percentages in order to reduce the excessive weight of dominant pollen taxa. Indeterminate and spore-bearing taxa were not included in multivariate analysis. Rates of composition change (velocity) between time steps were computed by dividing the Euclidean distance by the time interval in calibrated years BP (see references above). Pearson correlation

coefficients were computed between pollen taxa counts and charcoal concentration, with P values obtained by randomization testing using 1000 random permutations. The analyses were performed by SYNCSA software (Pil-lar 2004). Calculated ages for each subsample were not rounded up when used as time frame for the multivariate data analysis results (Fig. 3).

Results

Stratigraphy

Sediments from Morro Santana were deposited on a rocky subsurface. From 50 to 19 cm core depth, sediments were mainly of dark grey, compact, almost completely decomposed organic material, with a few root and rootlets. From 19 to 0 cm core depth sediments were dark grey-brown, decomposed organic material, with abundant roots, rootlets and plant remains.

Radiocarbon dating

The results of the AMS radiocarbon dating indicate deposits of late Holocene age (Table 2). The sample taken near the base of the core is dated to 1191 ± 32 14C yr BP (48 cm core depth). The extrapolated and calibrated age for base of the core at 50 cm is 1230 cal yr BP. The sedimentation in the swamp was probably continuous. The sample at 19 cm core depth was dated to an age of –117 ± 52 14C yr BP. This sample appar-ently already contains post-atomic-bomb carbon and has therefore a modern age > AD 1945, possibly a result of contamination with young carbon of rootlets. However, the continuous representation of Pinus and Eucalyptus pollen (see description of the pollen record) since about 19 cm core depth suggests that the uppermost core part must have been deposited in the last 70 years, after the plantation of these exotic taxa in the region. An age of AD 1930 (20 cal yr BP) was therefore assigned to 19 cm core depth. The age model used is based on the two calibrated, older radiocarbon ages, 1180 and 580 cal yr BP (48 and 33 cm core depth), and the age of 20 cal yr BP (19 cm) for the age scale. Ages were calculated by interpolation for each pollen subsample and pollen zone.

Table 2. List of AMS radiocarbon dates for the Morro Santana core.Lab. number Depth (cm) 14C yr BP 13C/12C r. (p.mil) Calibrated Age (cal yr BP)

Erl-5810 19 -117 ± 52 –26.2 ModernErl-5811 33 548 ± 57 –23.8 579 ± 46 (cal AD 1371 ± 46)Erl- 48 1191 ± 32 –24.1 1180 ± 43 (cal AD 833 ± 43)

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Fig. 2. Pollen percentage diagram for Morro Santana, Porto Alegre, Brazil, depicting in (a) the diagram for the more abundant taxa and (b) the summary diagram, including the records of pollen concentration, pollen influx, concentration and influx of carbonized particles, and cluster analysis.

86 BEHLING, H. ET AL.

Description of pollen record Morro Santana

The pollen diagram from Morro Santana (Fig. 2a) shows the most abundant pollen and spore taxa out of 114 different types that have been identified and the pol-len sums of different groups (Fig. 2b). About 14 pollen types are still unknown. Marked changes in the pollen assemblages, assessed by cluster analysis (CONISS), allow for establishment of three pollen zones: zone MS-I, MS-II and MS-III. Pollen concentration and ac-cumulation rates range in the record between 50.000 and 250.000 grains/cm3 and between 2000 and 12500 grains/cm2/a, respectively. Values are higher at the end of zone MS-I and in zone MS-II. The pollen zones can also be identified in the ordina-tion diagram in Fig. 3, mapping the trajectory of pollen composition changes; the two ordination axes account for 38% of the total variation in the data set with 89 taxa (spores and indeterminate excluded). The main ordination axis separates pollen assemblages indicating herb-dominated Campos, on the right, from assemblages with more abundant woody taxa after 380 cal yr BP. Zone MS-I (50 - 33 cm, 1230 - 580 cal yr BP, nine subsamples, on the right in Fig. 3) is marked by abundant herb pollen (70-80%), dominated by Poaceae (26-36%), Cyperaceae (38-43%), Asteraceae (2-5%), Eryngium, Plantago australis-type, Eriocaulon and several other herb taxa. Two Zea mays grains were found in the mid-dle part of this zone. The group of trees and shrubs, consisting mainly of Myrsine, Moraceae/Urticaceae, Alchornea, Myrtaceae, Melastomataceae, Arecaceae, Sebastiana commersoniana (maybe S. serrata) and

some other taxa with lower percentages, shows pollen sums between only 5-15%. Percentages of pollen from aquatic plants such as Typha, Ludwigia, Myriophyllum and Hydrocotyle are less than 1% throughout the record. Fern spores are relatively scarce (5-10%) throughout all three zones. Several single spores of the tree fern Dick-sonia sellowiana were found. Sphagnum spores are rare. Colonies of the algae Botryococcus show percentages between 10-23%. Concentrations and influxes of charcoal particles are relatively high in the sediment of this zone, especially in the upper part of the zone MS-I. Zone MS-II (33 - 19 cm, 580 - 20 cal yr BP, seven subsamples, middle part in Fig. 3) is characterized by a continuous decrease of herb pollen (from 70 to 60%), while trees and shrubs (especially Myrsine) increase from 23 to 33%. In the Asteraceae (5-7%), Baccharis becomes and remains more abundant, while Eryngium pollen decreases from the previous zone. Two Zea mays pollen grains were also found in this zone. Isoetes spores increase markedly in this zone. Concentrations and influxes of charcoal particles decrease throughout Zone MS-II from a relatively high level at the beginning of the zone. Zone MS-III (19 - 0 cm, 20 cal yr BP - modern, 10 subsamples, left part in Fig. 3) is marked by the lowest representation of herbs (55-40%), especially Cyperaceae, and the highest representation of shrubs and trees (33-50%), in particular at the uppermost sample of the core. Myrsine pollen is quite frequent and pollen of the taxa Moraceae/Urticaceae, Myrtaceae, Dodonaea have the highest values in this zone. Several pollen grains of Pinus and Eucalyptus were found in this zone and Zea mays

Fig. 3. Ordination method is principal coordinates analysis based on Euclidean distances using pollen taxa percentages after square root transformation; taxa with the highest correlations with the ordination axes are shown in positions proportional to the correlation level. Taxa abbreviations = Alch = Alchornea, Apia = Apiaceae, Are1 = Arecaceae I, Are2 = Arecaceae II, Aste = Asteraceae-Asterioideae, Bacc = Baccharis, Conv = Convolvulaceae, Cype = Cyperaceae, Dodo = Dodonaea, Erio = Eriocaulon, Eryn = Eryngium, Euca = Eucalyptus, Irid = Iridaceae, Jung = Jungia-type, LaSc = Lithraea/Schinus-type, Meli = Meliaceae, MoUr = Mora-ceae/Urticaceae, Myrs = Myrsine, Myrt = Myrtaceae, Pamp = Pamphalea, Pinu = Pinus, Poac = Poaceae, Sebr = Sebastiana brasiliensis, Seco = Sebastiania commer-soniana, Syla = Symplocos lanceolata, Trem = Trema-type, Zant = Zanthoxylum, Zema = Zea mays.

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grains are more frequent than in the previous zones. Isoetes spores and the algae Botryococcus decrease over this zone. The concentration of charcoal particles is relatively low but the influx is highest in this zone. Pollen composition dynamics depicted by the ordina-tion analysis shows periods of non-directional changes and periods in which the changes were directional to-wards more abundant woody taxa. Directional jumps, characterizing phase transitions, were most evident from 620 to 540 cal yr BP, 380 to 300 cal yr BP and from 60 to 20 cal yr BP. Rates of pollen composition change between adjacent time points (velocity) were lower and rather constant between 1180 and 20 cal yr BP and much higher, 10 times faster, in the last 70 years (results not shown). Table 3 depicts correlations between charcoal concentration and pollen taxa; Dodonaea, Baccharis, Myrsine and Myrtaceae presented the highest negative, and Cyperaceae and Eriocaulon the highest positive correlations.

Discussion

The swamp formation in the shallow basin on the hill top of Morro Santana probably reflects a change to wetter conditions in this region at about 1230 cal yr BP. Very wet conditions have been also recorded in the nearby highland by data from the Cambará do Sul core, showing marked expansion of Araucaria forest after 1100 cal yr BP (Behling et al. 2004). Similarly, the São Francisco de Assis core in the lowland of western Rio Grande do Sul State, about 450 km further inland, records an expansion of gallery forests after 1550 cal yr BP. At about 540 cal yr BP the lower frequency of Eryngium in the Campos and the increase of Isoetes, may suggest a change to slightly wetter conditions and increased moisture availability in the shallow basin.

The results of the pollen and charcoal analysis indi-cate the occurrence of a mosaic of taxonomically highly diverse forest and Campos vegetation that were under the influence of fire during the late Holocene period. Between 1230 and 580 cal yr BP, Campos taxa were well represented on Morro Santana, while forest taxa were relatively less abundant. The Campos vegetation was pri-marily composed of species of the Poaceae, Cyperaceae and Asteraceae families, with the genera Eryngium and Eriocaulon also being important taxa. Some Cyperaceae may also originate from the studied swamp. Forest taxa, such as Moraceae/Urticaceae, Myrtaceae and Dodonaea, were rare. At about 580 cal yr BP, there is a change in the composition of the Campos vegetation by the increase of Baccharis and the decrease of Eryngium, among oth-ers. This trend is indicated by phase transitions in the vegetation composition around the same period and as well between 380 and 300 cal yr BP. This can be interpreted as an indicator of a decrease in fire frequency. Baccharis, which was negatively cor-related to charcoal concentration, is the most important genus of grassland shrub in the present-day vegetation, and its increase suggests development of shrubland in the absence of fire over longer periods (Müller 2005). Species of the genus Eryngium, positively correlated with charcoal concentration, have been characterized as disturbance specialists profiting from frequent fires in abundance and reproductive output (Fidelis et al. unpubl.), and thus should diminish in importance with greater fire intervals or with forest encroachment. During the subsequent period until the present, forests expanded continuously, especially by the increase of the pioneer Myrsine. The clearly higher representation of Myrsine, which was negatively correlated to charcoal concentra-tion, may indicate a change in the disturbance regime. Forest expansion in general can be considered as be-ing controlled by fire frequency. Grassland fires generally do not enter into the forest due to lack of sufficient flam-mable biomass (Overbeck et al. 2005). If fire intervals become longer, the forest margins may encroach on grassland by continuous recruitment of forest species and growth of lianas, leading to suppression of caespitose grasses and to reduction of fuel, thus limiting extent of the next fire. This process should be indirectly related to climate. Under wetter conditions and less frequent dry spells, fire frequency in general should be lower, and fires may be less intense, especially at the border with less flammable biomass. If this line of reasoning is true, this change in climate conditions seems to have started around 580 cal yr BP, evidenced by the sharp compositional change (Fig. 3) and by a reduction in charcoal concentration, leading to an overall shift towards more woody vegetation. However, sources of ignition may also be important

Table 3. Pollen taxa with the highest correlations with charcoal particles concentration recorded in the Morro Santana core. P-values were determined by randomization testing. Only taxa found in at least 50% of the subsamples are included.

Taxa r P

Cyperaceae 0.57 0.003Eriocaulon 0.48 0.012Eryngium 0.39 0.054Poaceae 0.28 0.173Moraceae/Urticaceae -0.43 0.021Trema-type -0.44 0.022Myrtaceae -0.48 0.018Myrsine -0.52 0.007Baccharis -0.54 0.006Dodonaea -0.60 0.001

88 BEHLING, H. ET AL.

in determining fire frequency. Fire is considered to be a natural factor in Brazilian Cerrado (savanna) or in grass-land vegetation elsewhere (e.g. Kucera 1981; Coutinho 1990; Bredenkamp et al. 2002). Nevertheless, no direct evidence for this exists for southern Brazil: charcoal amounts found in peat cores (reaching back 42 000 14C yr BP and 22000 cal yr BP; Behling et al. 2004, 2005, respectively) increased considerably during the Holocene, from very low background levels during the Pleistocene, coinciding with increased human occupa-tion (Behling et al. 2004, 2005). Drier climatic periods probably encouraged the spread of fire. Even during the wet late Holocene period fire was quite frequent (Behling 2001). It is therefore reasonable to conclude that the charcoal evidence of the Morro Santana core indicates anthropogenic fire, caused first by Amerindians and later by European settlers. Furthermore, the significant cor-relation between charcoal concentration and pollen taxa, which were negative for taxa characterizing shrub and forest encroachment and positive for taxa characterizing the opposite, supports the conclusion that the charcoal originated mainly from grassland fires and not from fires after cutting and subsequently burning of forest areas for agriculture. If the latter were the case we would expect no correlation between charcoal and pollen taxa, since the areas burned for cultivation of forest soils were likely small. The high influx of charcoal particles during zone MS-III may suggest a higher fire frequency than during former periods. The increased human settlement in the surroundings during this period (Adelmann & Zellhuber 2004) may have contributed more ignition events, which combined with a shift in land use, with later abandonment of cattle grazing, led to more frequent fires. Our results indicate a general trend towards increase of woody vegetation cover in Morro Santana starting sometime between about 620 and 540 cal yr BP (AD 1330 and 1410), with faster ʻphase transition ̓changes between 380 and 300 cal yr BP (AD 1570 to 1650) and between about 60 and 20 cal yr BP (AD 1890 to 1930). What factors might have caused these changes? In the case of Morro Santana and the period described by the sediment core, climate and human induced disturbances cannot be disentangled. Interestingly, the early shifts coincide with vegetation and climate changes elsewhere (e.g. Eddy 1976). This climate driven process of woody vegetation expansion, was likely also affected by human induced changes in disturbance regimes, which may be linked to early Amerindian population displacement caused by the first Portuguese incursions in the territory and the intro-duction of cattle from the west during the 17th Century. Impact of the Guarani on the grasslands is unclear, but should not have been high, as they used forest areas,

not grassland, for agriculture. They may have caused occasional fires. Cattle grazing, the principal activity of European settlers in the region, affects vegetation directly by biomass removal and trampling, limiting plants unable to resprout, such as seedlings of forest woody species, and indirectly affecting fire intensity and frequency by changing flammable biomass ac-cumulation (Pillar & Quadros 1997; Fuhlendorf & Engle 2004). The lack of a clear signal in the pollen and charcoal record for the first officially established cattle farming settlements around AD 1740 indicates that this had minimal effect on vegetation and fire frequency, perhaps because feral cattle were affecting vegetation since much earlier, likely causing the phase transition in pollen composition that ended 300 cal yr BP (AD 1650). The sharp transition in pollen composition after about AD 1960 may indicate a change in land use coinciding with the ending of cattle grazing in the area due to the proximity to new urban settlements. In summary, the record from Morro Santana in the Porto Alegre area in southern Brazil provides insight in vegetation, climate, fire dynamics as well as human activities during the last 1230 years. The formation of a shallow swamp and the accumulation of sediments are related to a change to wetter conditions, as has been documented from the southern Brazilian highland at the same time. The palynological results document the existence of grassland vegetation at the study area since the late Holocene, suggesting that present-day patches of Campos surrounded by forest can be seen as natural vegetation, as relicts from drier climatic conditions from Pleistocene and early/mid Holocene periods, and did not develop as a consequence of deforestation and cat-tle introduction. Under the wet late Holocene climatic conditions, forests have expanded continuously since 580 cal yr BP. Natural fires in the Pleistocene or the early Holocene, before human occupation of the region, seem to have been very rare, if not nonexistent, in the South Brazilian grassland biome (Behling et al. 2004, 2005). Frequent fire, which occurred throughout the recorded late Holocene period, is mostly of anthropo-genic origin, and it is hard to tell whether fires would occur naturally under present climatic conditions, as on Cerrado sites protected from fire (Ramos-Neto & Pivello 2000). Nonetheless, independent of the origin of fires, the palaeoecological data from the Morro Santana core suggest that if grasslands were to be conserved and forest expansion impeded, fire should not be suppressed in ungrazed grasslands in southern Brazil. Our results suggest that management for conserva-tion of the mosaics of Campos (grassland) and forest in the Porto Alegre region, and elsewhere in southern Brazil, should take into account the history of distur-bance by grazing and fire. In the recent past decades,

- LATE-HOLOCENE FIRE HISTORY IN A FOREST-GRASSLAND MOSAIC IN SOUTHERN BRASIL - 89

suppression of grazing and the change in the dynamics of flammable biomass accumulation of Morro Santana grassland has likely resulted in a trend of increasing woodiness. If management for conservation continues to include fire suppression, the present grassland patches will tend to disappear, as forest expansion will not be impeded, with losses to plant and habitat diversity. The same is likely true for other areas in southern Brazil. Grasslands have a high biodiversity (ca. 3000 to 4000 grassland species in the Campos biome; Klein 1975; Boldrini 2002) but are currently subject to severe land-use changes and thus reductions in area due to expansion of agricultural production and silvicultural plantations by exotic forest species. In the few areas that are being protected (less than 0.5% of the biome; Anon. 2000), management currently aims at excluding all human influ-ence, including grazing and fire. This means that grass-land areas within conservation units will disappear as a consequence of shrub encroachment and forest expan-sion. In these areas, fire could be used as a management tool to preserve grasslands or forest-grassland mosaics. A decision not to suppress fire, however, would require changes in conservation policies and legislation, since the state legislation prohibits the use of fire as manage-ment tool. Maintaining or re-introducing cattle grazing in conservation areas could be an alternative to fire, likewise impeding forest expansion over grasslands.

Acknowledgements. V.P. receives support from CNPq (Brazil), S.M. was supported by a CAPES (Brazil) PhD grant, G.O. by a PhD grant from the German National Academic Foundation and through a travel grant by DAAD/CAPES in a PROBRAL cooperation. We thank Dr. Gillson and two anonymous re-viewers for constructive and valuable comments on an earlier version of this manuscript.

References

Anon. (Ministério do Meio Ambiente). 2000. Avaliação e ações prioritárias para conservação da biodiversidade da Mata Atlântica e Campos Sulinos. Relatório técnico. Brasília, DF, BR.

Adelmann, W. & Zellhuber, A. 2004. Analysis of environmen-tal conflicts in areas of urban expansion using scenario methods (com versão em português). In: Porto, M.L. (org.) Workshop ʻProteção e manejo da vegetação natural da região de Porto Alegre com base em pesquisas de padrões e dinâmica da vegetaçãoʼ, pp. 60-64. PPG-Ecologia, UFRGS, Porto Alegre, BR.

Aguiar, L.W., Martau, L., Soares, Z.F., Bueno, O.L., Mari-ath, J.E. & Klein, R.M. 1986. Estudo preliminar da flora e vegetação de morros graníticos da Região da Grande Porto Alegre, Rio Grande do Sul, Brasil. Iheringia, Sér. Bot. 34: 3-34.

Behling, H. 1993. Untersuchungen zur spätpleistozänen und holozänen Vegetations- und Klimageschichte der tropi-schen Küstenwälder und der Araukarienwäldern in Santa Catarina (Südbrasilien). Diss. Bot. 206: 1-149.

Behling, H. 1998. Late Quaternary vegetational and climatic changes in Brazil. Rev. Palaeobot. Palynol. 99: 143-156.

Behling, H. 2002. South and southeast Brazilian grasslands during Late Quaternary times: a synthesis. Palaeogeogr. Palaeoclimateol. Palaeoecol. 177: 19-27.

Behling, H., Pillar, V.D., Orlóci, L. & Bauermann, S.G. 2004. Late Quaternary Araucaria forest, grassland (Campos), fire and climate dynamics, studied by high-resolution pollen, charcoal and multivariate analysis of the Cambará do Sul core in southern Brazil. Palaeogeogr. Palaeoclimateol. Palaeoecol. 203: 277-297.

Behling, H., Pillar, V.D., Orlóci, L. & Bauermann, S.G. 2005. Late Quaternary grassland (Campos), gallery forest, fire and climate dynamics, studied by pollen, charcoal and multivariate analysis of the São Francisco de Assis core in western Rio Grande do Sul (southern Brazil). Rev. Pal-aeobot. Palynol. 133: 235-248.

Boldrini, I.B. 2002. Campos sulinos: caracterização e biodi-versidade. In: Araújo, E.d.L., Noura, A.d.N., Sampaio, E.V.d.S.B., Gestinari, L.M.d.S. & Carneiro, J.d.M.T. (eds.) Biodiversidade, conservação e uso sustentável da flora do Brasil, pp. 95-97. Universidade Federal Rural de Pernambuco, BR.

Brack, P., Rodrigues, R.S., Sobral, M. & Leite, S.L.C. 1998. Ár-vores e arbustos na vegetação natural de Porto Alegre, Rio Grande do Sul, Brasil. Iheringia, Sér. Bot. 51: 139-166.

Bredenkamp, G.J., Spada, F. & Kazmiercżak, E. 2002. On the origin of northern and southern hemisphere grasslands. Plant Ecol. 16: 209-229.

Coutinho, L.M. 1990. Fire in the Ecology of the Brazilian Cerrado. In: Goldammer, J.G. (eds.) Fire in the Tropical biota – Ecosystem processes and global challenges, pp. 81-105. Springer-Verlag, Berlin, DE.

Eddy, J.A. 1976. The Maunder Minimum. Science 192: 1189-1202.

Fuhlendorf, S.D. & Engle, D.M. 2004. Application of the fire-grazing interaction to restore a shifting mosaic on tallgrass

90 BEHLING, H. ET AL.

prairie. J. Appl. Ecol. 41: 604-614.Grimm, E.C. 1987. CONISS: A Fortran 77 program for strati-

graphically constrained cluster analysis by the method of the incremental sum of squares. Computer Geosci. 13: 13-35.

Hueck, K. 1966. Die Wälder Südamerikas. Fischer, Stuttgart, DE.

Klein, R.M. 1975. Southern Brazilian phytogeographic features and the probable influence of upper quaternary climatic changes in the floristic distribution. Bol. Paranaense Geo-ciências 33: 67-88.

Kucera, C.L. 1981. Grasslands and fire. In: Mooney, H.A., Bonnicksen, T.M., Christensen, N.L., Lotan, J.E. & Reiners, W.A. (eds.) Proceedings of the conference: Fire regimes and ecosystem properties, Dec. 11-15, Honolulu, HI, pp. 90-111. Gen. Tech. Rep. WO-26, Dept. of Agricult., Wash-ington, DC, US, Honolulu, HI, US.

Lindman, C.A.M. 1906. A Vegetação no Rio Grande do Sul. EDUSP/Itatiaia, São Paulo/Belo Horizonte, BR.

Macedo, F.R.d. 1999. História de Porto Alegre. Ed. da Univer-sidade/UFRGS, Porto Alegre, BR.

Müller, S.C. 2005. Padrões de espécies e tipos funcionais de plantas lenhosas em bordas de floresta e campo sob influência do fogo. Ph.D. Thesis, Universidade Federal do Rio Grande do Sul, Porto Alegre, BR.

Müller, S.C. & Forneck, E.D. 2004. Forest-grassland mosaics in the hills of Porto Alegre city: a study case of forest expan-sion patterns in Santana hill, Rio Grande do Sul, Brazil. In: Porto, M.L. (org.) Workshop Proteção e manejo da vegetação natural da região de Porto Alegre, com base em pesquisas de padrões e dinâmica da vegetação, pp. 29-37. PPG-Ecologia, UFRGS, Porto Alegre, BR.

Nimer, E. 1990. Clima. In: Anon. (ed.) Geografia do Brasil: Região Sul, pp. 151-187. IBGE, Rio de Janeiro, BR.

Noelli, F.S., Silva, F.A., Tocchetto, F.B., Vietta, K., Cappelletti, A., Costa, J.F.G., Soares, A.L.R. & Marques, K.J. 1997. O mapa arqueológico parcial e a revisão historiográfica a respeito das ocupações indígenas pré-históricas no mu-nicípio de Porto alegre, Rio Grande do Sul. Rev. Hist. Reg. 2(1): 209-221.

Orlóci, L., Pillar, V.D., Anand, M. & Behling, H. 2002. Some interesting characteristics of the vegetation process. Comm. Ecol. 3: 125-146.

Overbeck, G.E., Müller, S.C., Pfadenhauer, J. & Pillar, V.D. 2003. Are subtropical grasslands resilient to fire? In: Claudino-Sales,V. Tonini, I.M. & Correia Dantas, E.W. (eds.) Anais do VI Congresso de Ecologia do Brasil, pp. 623-624. Editora da Universidade Federal do Ceará, Fortaleza, BR.

Overbeck, G.E., Müller, S.C., Pillar, V.D. & Pfadenhauer, J. 2005. Fine-scale post-fire dynamics in southern Brazilian subtropical grassland. J. Veg. Sci. 16: 655-664.

Overbeck, G.E., Müller, S.C., Pfadenhauer, J. & Pillar, V.D. 2006. Floristic composition, environmental variation and species distribution patterns in burned grassland in southern Brazil. Braz. J. Biol. 66: 1073-1090.

Pillar, V.D. 2004. SYNCSA software for character-based community analysis, v. 2.2.4. Departamento de Ecologia, UFRGS, Porto Alegre, BR.

Pillar, V.D. & Quadros, F.L.F. 1997. Grassland-forest bounda-ries in southern Brazil. Coenoses 12: 119-126.

Rambo, B. 1954. Análise histórica da flora de Porto Alegre. Sellowia 6: 9-111.

Rambo, B. 1956a. A fisionomia do Rio Grande do Sul. Selbach, Porto Alegre, BR.

Rambo, B. 1956b. A flora fanerogâmica dos aparados ri-ograndenses. Sellowia 7: 235-298.

Rambo, B. 1961. Migration routes of the South Brazilian rain forest. Pesq. Sér. Bot. 5: 1-54.

Ramos-Neto, M.B. & Pivello, V.R. 2000. Lightning fires in a Brazilian Savanna National Park: rethinking management strategies. Environ. Manage. 26: 675-684.

Schmitz, P.I. 1991. Migrantes da Amazônia: a tradição Tupi-guarani. In: Kern, A.A., Jacobus, A. & Ribeiro, P. (eds.) Arqueologia pré-histórica do Rio Grande do Sul, pp. 295-330. Mercado Aberto, Porto Alegre, BR.

Teixeira, M.B., Coura-Neto, A.B., Pastore, U. & Rangel Filho, A.L.R. 1986. Vegetação. In: Anon. (ed.) Levantamento de recursos naturais, Vol. 33, pp. 541-632. Instituto Brasileiro de Geografia e Estatística, Rio de Janeiro, BR.

Veloso, H.P. & Góes-Filho, L. 1982. Fitogeografia brasileira - classificação fisionômico-ecológica da vegetação neo-tropical. Boletim Técnico do Projeto RADAMBRASIL, Série Vegetação 1: 1-80.

Waechter, J.L. 2002. Padrões geográficos na flora atual do Rio Grande do Sul. Ciência & Ambiente 24: 93-108.

Weninger, B., Jöris, O. & Danzeglocke, U. 2004. Calpal – The Cologne radiocarbon CALibration and PALaeoclimate research package. URL: http://www.calpal.de

Received 23 July 2005;Accepted 21 April 2006;

Co-ordinating Editor: K. Woods.