María Virginia Mancini

Vegetational changes during the Holocene in Extra-Andean Patagonia, Santa Cruz Province, Argentina

Abstract Modern pollen-vegetation relationship was used in the interpretation of stratigraphical sequences from two archeological sites, La Martita cave (48°24′S, 69°15′W) and Alero Cardenas (47°18′S, 70°26′W) located in Extra-Andean Patagonia in the Santa Cruz Province. The modern pollen assemblages are related to vegetation units that extend from the Andes toward the Atlantic coast, reflecting the increase of aridity from west to east. The more humid areas in the west are represented by grass steppe with Festuca pallescens; in those areas of intermediate humidity shrub steppe can be found with a conspicuous stratum of Stipa (S. speciosa, S. humilis and S. chrysophylla) and shrubs (Nardophyllum obtusifolium, Berberis heterophylla, Senecio filaginoides, Mulinum spinosum) and in the most arid areas scrub steppe expands with Nassauvia glomerulosa and cushion plants such as Azorella caespitosa, Accantholippia seriphiodes, Chuquiraga aurea, Brachyclados caespitosus. A vegetational and paleoclimatic history is presented based on comparison with modern analogs and with other palynological records from southern Patagonia. Prior to 8000 yr B.P. a grass steppe extended indicating relatively high precipitation under cold conditions. Between 8000 and 6000 yr B.P. an increase of shrub-steppe taxa, dominated by Asteraceae tubuliflorae would relate to an increase in temperature, while precipitation remained in the previous range of about 200 mm. The mid-Holocene (5000 yr B.P.) is reflected in the La Martita sequence by a short-term return of steppe taxa, primarily grasses. This steppe could indicate cold conditions similar to those of the early Holocene, or an increase in precipitation. After 4500 yr B.P. the vegetation is represented by grass-shrub steppe. After 3500 yr B.P. the Alero Cardenas record shows a shrub steppe dominated by Asteraceae tubuliflorae. In records near the steppe-forest ecotone, at 47 and 50°S, the more extensive late Holocene forest suggests greater effective moisture, probably related to cooler temperatures. In Alero Cardenas grasses increase and shrubs are irregularly present. In Altiplanicie Central steppe vegetation is analogous to the present vegetation. In the present century taxa indicative of disturbance are present (Rumex acetosella and Brassicaceae).

Vegetation and climate during the Holocene in Southwest Patagonia, Argentina

Abstract Pollen analysis from archaeological sequences in the Lago Argentino area (Southwest Santa Cruz province, Argentina) are used to infer vegetation and climatic changes during the Holocene. These sequences are located in present-day grass and shrub steppes and in Andean desert. Comparison with modern pollen data and other fossil pollen sequences provides a regional analysis of Holocene vegetational changes and contributes to the understanding of the regional paleoclimatic history. The fossil records indicate that a grass steppe developed in the area at the beginning of the Holocene. According to the pollen spectra, a change to shrub steppe took place between 8500 and 3500 yr BP, suggesting drier conditions. The presence of grass steppe may relate to greater availability of moisture and decrease in temperature in the south of Lago Argentino from 3500 yr BP, and in the northern and eastern portions of the area from ca. 1000 yr BP onwards. In the high Andean zone a herbaceous-shrub steppe with Empetrum developed between 4500 and 3600 yr BP which indicates conditions colder than today. Towards 3600 yr BP an increase in Asteraceae, dominant up to 200 yr BP, indicates less availability of moisture. During the last 200 yr expansion of shrub steppe and decrease of the forest are documented. This period coincides with the increased European settlement of the region. The paleoenvironmental interpretation is related to human populations living in Southwest Patagonia since early Holocene times.

Late Quaternary Vegetation and Climate of Patagonia

Publisher Summary This chapter focuses on the existing pollen datasets from Patagonia, between 37 o and 52 o S covering the Late Quaternary and a comparison with selected pollen data from Chile. A continuous pollen record does not exist in Patagonia that link the Last Glacial Maximum (LGM) with previous interglacial–glacial periods. The only pollen record that probably represents interglacial conditions about 430 ka (MIS 11) is that from Canadon El Mosquito, in southern Patagonia. During the Mid Holocene, the westerlies brought higher humidity to both the Andean zone and the southern extreme of Patagonia. Semiarid conditions in extra-Andean region suggest that the westerlies were less intense than present. An increase of aridity and temperature at the northeast Patagonia led to an arid climate and to the establishment of the Arid Diagonal during this time. In Patagonia, postglacial times were characterized by high fire frequency. Human impact, volcanism, and climate have been proposed to explain spatial and temporal variations of this fire frequency throughout different intervals.

Fossil pollen from Los Toldos locality: A record of the Late-glacial transition in the Extra-Andean Patagonia

Abstract Paleoenvironmental changes during the Late-glacial transition are interpreted from a pollen record from two caves at Los Toldos (47°22′S; 68°58′W) in Extra-Andean Patagonia in Argentina. The paleoenvironmental interpretation is based on changes in the ratio between shrub and grass steppe taxa and on comparison with other pollen records from the region. Between 12,600 and 8750 yr BP two vegetational changes occurred thought to reflect the establishment of Holocene-type atmospheric circulation patterns. The first change is at ca. 11,000 yr BP expressed by replacement of shrub steppe with Ephedra by a grass steppe. The second change occurred ca. 10,000 yr BP when the grass steppe was replaced by a shrub steppe dominated by Asteraceae. Before ca. 11,000 yr BP the environmental conditions were extremely arid with precipitation lower than 200 mm. Between ca. 11,000 and ca. 10,000 yr BP effective moisture increased, probably related to an increase in precipitation to about 200 mm under cold conditions. A grass steppe extended through Patagonia and Tierra del Fuego, at least as far north as 47°S. It is difficult to find modern analogues for pollen associations south of 47°S older than 10,000 yr BP. Possibly at that time climate patterns were markedly different from today. At about this time of environmental changes Level 11 industry associated with extinct grazing herbivores developed. Starting at ca. 10,000 yr BP, with expansion of the shrub steppe of Asteraceae east of the Andes at 47° to 52°S and forest at 51°–54°S west of the Andes, temperature increased while water availability decreased. Precipitation probably was similar to the present, which suggests that the modern climate patterns were established at the beginning of the Holocene. The Toldense Industry, which is associated with remains of modern fauna as well as with the last remains of the Pleistocene fauna, developed in this period. The beginning of this development coincides with the extinction of Pleistocene fauna.

Insights into Holocene vegetation and climate changes at the southeast of the Andes: Nothofagus forest and Patagonian steppe fire records

Ecosystem fire regimes are a consequence of interactions among fuels and climate. The reconstruction of past fire regimes is of great importance for studying past climate changes and controls. The aim of this study is to compare two charcoal and pollen records from the Nothofagus forest-grass steppe ecotone (50°S) and the grass steppe (49°S). We compare fire regime responses to local vegetation changes, and inferred variation on climate conditions between 49° and 52°S during the Holocene. Cerro Frías and La Tercera charcoal records seem to be sensitive to centennial and millennial timescales of vegetation and climate variability inferred for southern Patagonia. During the Pleistocene–Holocene transition and during the middle Holocene, forest patchiness provided fuel vertical and horizontal continuity favoring fire activity. In contrast, in steppe environments high cover of shrubs favored grass patchiness, impeding fire spread. Higher pollen richness and variability through time seem to be related to higher vegetation patchiness. Past fire regime variability at the eastern side of the Andes has been closely related to westerly moisture influence between 52° and 48°S. Southern latitudes have been influenced by polar air mass intrusions to the continent during the last 5000 cal. yr BP.

Nothofagus forest dynamics and palaeoenvironmental variations during the mid and late Holocene, in southwest Patagonia

Southern Patagonia intersects the core of the Southern Westerlies, providing a unique opportunity for palaeo-reconstructions and the implication of past wind variations. There is a strong link between the strength of the westerlies and precipitation, which impacts vegetation communities. The palaeoenvironmental changes that occurred since the middle Holocene to present days are reconstructed from a peat record recovered in Peninsula Avellaneda (50°15′57″S; 72°50′33″W). Interpretations are based on pollen, charcoal and sediment analyses. Closed Nothofagus forest together with low fire activity characterized the region during the period c. 5500–3500 cal. yr BP, related to an increased in precipitation through an intensification of the westerlies. After 3500 cal. yr BP, shrub and grass communities became dominant at the expense of Nothofagus forest, suggesting a climatic shift to dry conditions, as a result of weaker westerlies. This patchy forest-steppe vegetation has favoured the occurrence of fire events. Subsequently, Nothofagus forest recovered for a short period between 2000 and 400 cal. yr BP. Then, major vegetation changes took place with the re-establishment of an open landscape. The calculated moisture balance index allowed us to hypothesize about the relationship between westerlies fluctuation and El Niño Southern Oscillation (ENSO) anomalies during the mid and late Holocene.

REGISTROS POLÍNICOS DE DEPÓSITOS DEL HOLOCENO EN EL SUDESTE DE PATAGONIA, ARGENTINA: SU APLICACIÓN EN LA RECONSTRUCCIÓN PALEOAMBIENTAL

Abstract. POLLEN RECORDS FROM HOLOCENE DEPOSITS IN SOUTHEASTERN PATAGONIA, ARGENTINA: THEIR APPLICATION ON PALEOENVIRONMENTAL RECONSTRUCTION. This work presents the pollen analysis of deposits from southeastern Patagonia (Argentina) aimed to reconstruct changes in vegetation and environmental conditions and its relationship to huntergatherer groups who inhabited the area. Pollen sequences from an archeological site (cave Cóndor 1) and an eolian-colluvial deposit with a pedogenesis process in the upper section corresponding to the late Holocene were analyzed. There is a change at the base of the sequence, from an Ephedra-dominated steppe to a grass-dominated steppe, indicating an increase in water availability. Both a lower humidity and a rise in temperature are suggested by increasing bushes during the early Holocene. The lack of pollen between 3250 and c. 1200 cal. yr BP may be related to the intensity of human activities. Pollen assemblages dated between c. 1050 and 600 cal. yr BP, suggest conditions in the area were drier than at present. Establishment a grass-dominated steppe and a soil layer at c. 600 cal. yr BP suggest more stable environmental conditions and an increased hydric availability. Increased erosion rates over the past few centuries produced an eolian deposit overlaying the soil, coeval with the European settlement.