South America extends from 11°N to 62°S. Major boundaries such as the Andes on the western side of the continent and the land mass in the tropics create north-south and west-east variations in climate and ecosystems. Tropical forest covers 44% of the total land surface. Between 36 and 56°S, a temperate forest composed of high longevity trees dominates. The northern and central highlands are covered by small trees, shrubs and grasses. The central western part (Peru, Chile, the Andes, western Argentina and eastern Patagonia) is composed of deserts. These diverse climatic zones and ecosystems offer various potential sites for dendrochronological studies. The ideal conditions for paleoclimatic reconstructions using tree-rings are those that support the existence of long-living trees required to develop long chronologies, and/or the presence of subfossil woods. Over the last decade, the search for areas with some of these conditions has been one of the major goals of dendroclimatological studies in South America.Fil: Boninsegna, Jose Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Boninsegna, Jose Armando

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11Science HighlightsProgress in South American DendrochronologyJOSE A. BONINSEGNALaboratorio de Dendrocronologia, IANIGLA-CONICET, Mendoza, Argentina; pbonin@lab.cricyt.edu.arClimate and EcosystemsSouth America extends from 11°N to 62°S. Major boundaries such as the Andes on the western side of the continent and the land mass in the tropics create north-south and west-east variations in climate and ecosystems. Tropical forest covers 44% of the total land surface. Be-tween 36 and 56°S, a temperate forest composed of high longevity trees dominates. The northern and central highlands are covered by small trees, shrubs and grasses. The central western part (Peru, Chile, the Andes, western Argentina and eastern Patagonia) is composed of deserts. These diverse climatic zones and ecosystems offer various potential sites for dendrochronolog-ical studies. The ideal conditions for paleoclimatic reconstructions using tree-rings are those that sup-port the existence of long-living trees required to develop long chro-nologies, and/or the presence of subfossil woods. Over the last de-cade, the search for areas with some of these conditions has been one of the major goals of dendrocli-matological studies in South Amer-ica.Dendrochronological studies in South America started in the tem-perate region, where conifer and broad-leaf species with well marked annual rings grow (Boninsegna and Villalba 1996). Following this initial period, interest in tree-ring studies spread throughout the region and several scientific centers in Argen-tina, Brazil, Bolivia, Chile and Peru are now using dendrochronolog-ical techniques to assess ques-tions related to paleoclimate, forest ecology, biogeography, and forest production. Long Chronologies South American high longevity tress offer the possibility of recon-struction on long temporal scales. Long tree-ring chronologies have been developed in recent years us-ing Fitzroya cupressoides (Alerce). Fitzroya is a conifer growing be-tween 40° and 43°S and reaching ag-es of about 3,000 years. A network of 20 chronologies over 1,000 years long is already available in Argenti-na and Chile and a 5,100-year chro-nology is being developed in Chile (Wolodarsky, personal communica-tion). Austrocedrus chilensis is anoth-er long-lived conifer growing in north-western Patagonia (32 to 39 °S). It is possible to find living trees 900 – 1,000 years old. A network of 27 chronologies from Austrocedrus chilensis has been used to recon-struct past precipitation variations in northern Patagonia since A.D. 1600. Recently, a new set of millen-nial scale chronologies (using liv-ing trees and sub-fossils) have been produced. A combination of ring width, δ18O and density chronolo-gies is being used to study El Niño Southern Oscillation (ENSO) vari-ability in this sensitive region.Sub-fossil WoodOften, the acidity in peat bogs pro-vides conditions that permit the preservation of stumps. On Tierra del Fuego Island (51°-56°S), peat bogs are rather common. Samples extracted from different places yield radiocarbon dates ranging between 3,000 to 4,000 years. A floating chronology is now available and ex-tensive sampling is being carried out in order to fill the gap between the floating and the “living trees” chronologies (Roig 2002 personal communication).  Tree rings are routinely used to reconstruct Holocene climate varia-tions at high temporal resolution, but only rarely have they offered insight into climate variability dur-ing earlier periods. Roig et al. (2001) reported a floating 1,229-year chro-nology developed from sub-fossil stumps of Fitzroya cupressoides in southern Chile (41.4°S) dating to ca. 50,000 14C years B.P. They used this chronology to calculate the spectral characteristics of climate variabil-ity at that time, which was proba-bly an interstadial (relatively warm) period. A comparison with the pow-er spectra of chronologies derived from living F. cupressoides trees shows strong similarities with the 50,000-year-old chronology, indi-cating that similar growth forcing factors operated in this glacial inter-stadial phase, as during the current interglacial conditions.Chronology NetworkThe existing chronology coverage of South America is patchy and largely concentrated in the temper-ate region of Argentina and Chile. In the last three years, an impor-tant number of new chronologies Year AD1880 1900 1920 1940 1960 1980 20000.00.51.01.52.0IndexPrecipitation (mm)050100150200250300Period 1953-1998 (46 years)r = 0.71Fig. 1: Polylepis tarapacana chronology developed by Argollo and Villalba in 2001 (personal communication) at Volcan Tunupa (19°S, 4600m. a.s.l.). The chronology is drawn in blue, while the dark red line correspond to precipitation data from Oruro (Bolivia).PAGES NEWS, VOL.10, N°1, APRIL 200212 Science Highlights(ca. 85) using the southern beech Nothofagus pumilio have been pro-duced in the southern part of Ar-gentina and Chile (Lara et al. 2001). An important product based on this network is a 400 years reconstruc-tion of meridional and zonal atmo-spheric circulation index over the Southern Ocean (50-60°S). The zon-al index shows dominant modes of variation at 4.4 – 5 year period, which may be associated with the Antarctic Circumpolar Wave. The meridional index shows that the 19th century was dominated by southerly flow; while during the 20th century northerly flow pre-vailed over the region. These results are consistent with the warming observed in the Southern Ocean in recent decades (Villalba et al. 2002 in prep.).An interesting number of chro-nologies developed from Cedrela lilloi and Juglans australis from the cloudy montane forest known as the “Yungas” (22-25°S) in the sub-tropical region of Argentina were successfully used in estimating past changes in precipitation (Villalba et al 1998). Additional chronologies in the same area are under develop-ment in an effort to extend the tem-poral scale. Tropical ChronologiesReconstruction of low latitude cli-mate variability has been hampered by the lack of suitable annually resolved proxy climate records. Several factors can be invoked to explain the unbalanced distribution of tree-ring records between trop-ical and temperate regions in the Americas.  Most tropical species do not form distinct rings and when rings are present, they are not an-nual. Some species show clearly visible rings but the circular unifor-mity is uncertain. Absence of sea-sonality appears to be the main reason for the lack of well-defined boundary rings in the tropics.  Nev-ertheless, there are tropical and subtropical regions that experience seasonal changes in precipitation or temperature that can induce the formation of defined growth rings. In order to fill the “tropical gap” between the presently available tree-ring chronology networks, sci-entist from Argentina and Bolivia are working together in the search of woody species suitable for den-drochronological research.High Altitude ChronologiesHighlands are climate-sensitive sites of particular interest to tree-ring re-search in tropical and subtropical regions.  In the South American subtropics (15°-25°S), the moder-ate seasonality of temperature may induce the formation of well-de-fined rings more effectively at cold-er treeline environments. At lower elevations in the Bolivian subtrop-ics, the presence of annual growth bands may be related to the occur-rence of dry-wet cycles and/or flood conditions. Because it is adapted to dry and cold conditions, Polyl-epis tarapacana reaches the high-est elevation (between 4100 and 5200m) of tree growth in the world. Some living P. tarapacana trees are known to reach ca. 600 years of age indicating the potential for long chronologies. One of these chronologies, at Tunupa (19°45’S), shows a remarkable correlation with precipitation as illustrated in Fig. 1. Presently, four chronologies are available at Volcan Sajama, Vol-can Tunupa, Soniquera and Volcan Granadas. The Soniquera chronolo-gy covers the interval AD 1411-2000. Bolivian chronologies are the high-est elevation tree-ring chronologies in the world.In Piura (Peru) Rodríguez and Córdova (2001, pers. comm.) suc-cessfully developed a tree-ring chro-nology using Bursera graveolens at Vicus Hill (5º9’S). The 38-year old series recorded the last two mega ENSO events (1982-83 and 1997-98). This important result suggests that dendroclimatological reconstruc-tion of El Niño-Southern Oscillation (ENSO) in Peruvian north coast is possible.Amazonian ChronologiesThe complex Amazonian forest is a true challenge for dendrochronolo-gy. Several attempts to explore the potential for new species to yield annual ring series have been car-ried out in different regions. Most of these studies were conducted in species of the Meliaceae family, in particular Sweitenia mycrophil-la and Cedrela odorata. In a recent work, C. odorata sampled at Pan-do, in Bolivia (11°S) showed vis-ible and circularly uniform rings, and reached ages of ca. 250 years (Roig pers. comm., Fig. 2). Strong variations in the width of the rings suggest high sensitivity to the vari-ations of a common factor in the stand, probably climate or a cli-mate-related phenomenon. C. od-orata has a wide latitudinal range, from the northern part of Mexico through the Amazonia basin as far as approximately 24°S, making the species a good candidate to devel-op a chronology network.Thanks partly to the efforts of the PAGES Focus I Pole-Equator-Pole Transect (PEP-I), and with the support of the Interamerican Insti-tute for Global Change Research (IAI), a collaborative project involv-ing 15 investigators from 15 institu-tions in Argentina, Bolivia, Canada, Chile, Mexico, Peru and the USA aims to develop a comprehensive geographical coverage of  tree-ring treeline chronologies. It is expect-Fig. 2: Cedrela odorata tree growing at Pando, Bolivia (11°S 200m a.s.l.) in the southwest-ern part of the Amazon basin. The climate presents a mean annual temperature of 27°C and 1800 mm of precipitation with a marked dry period during the months of May to Sep-tember. The diameters of the dominant trees reach 1.0 – 1.5 meters (Photo: F. Roig).PAGES NEWS, VOL.10, N°1, APRIL 200213Science Highlightsed that they will allow the recon-struction of global-scale spatial and temporal patterns of temperature and precipitation along this tran-sect over the last several hundred years and to encourage the train-ing of scientist and the application of dendrochronology and paleoen-vironmental science within Latin America (Luckman and Boninseg-na, 2002). ACKNOWLEDGMENTSI thank J. Argollo and R. Villaba for providing the data used in figure 1.REFERENCESBoninsegna, J. A. and Villalba, R., 1996, Dendro-climatology in the Southern Hemisphere: Review and Prospects. In: Tree Rings, Environments and Humanity. Ed. J.S. Dean; D.M.Meko and T. W- Swetnam. Radiocarbon 1996, pp 127-141Lara, A; Aravena J.C., Villalba, R., Wolodarsky-Franke, A., Luckman, B. and Wilson, R., 2001, Dendro-climatology of high-elevation Nothofagus pumilio forest at their northern distribution limit in the Central Andes of Chile. Can. J. of For. Res., 31, 925-936.Luckman, B. and Boninsegna, J.A., 2001, The Assess-ment of Present, Past and Future of Climatic Vari-ability in the Americas from Tree-Line Environ-ments, PAGES News 9(3), 17-19Roig, F. A, Le-Quesne, C.; Boninsegna, J. A; Briffa, K. R., Lara, A., Gruddk, H., Jones, P.D. and Villagran, C., 2001, Climate variability 50,000 years ago in mid-latitude Chile as reconstructed from tree rings, Nature ,410, 567-570.Villalba, R, Grau, H.R., Boninsegna, J.A., Jacoby, G. and Ripalta, A., 1998, Tree-ring evidence for long term precipitation changes in subtropical South America, International Journal of Climatology, 18, 1463-1478.Post-fire Vegetation Dynamics in Southern Switzerland MARCO CONEDERA1 AND WILLY TINNER21 WSL Sottostazione Sud delle Alpi, CH-6504 Bellinzona; marco.condera@wsl.ch2 Institut für Pflanzenwissenschaften der Universität Bern, Altenbergrain 21, CH-3013 Bern; willy.tinner@ips.chIntroductionBecause forest fires in central Eu-rope are rare compared to North America, knowledge about the post-fire behavior of native European species is scanty. The expected cli-mate change for the next century could influence fire regimes in cen-tral Europe thereby leading to more frequent forest fires. Thus, knowl-edge about post-fire behaviour and fire-sensitivities of central-Europe-an plant species may become more important for understanding and managing forest ecosystems.In Switzerland most fires occur in the region south of the Alps during the early spring season (March to April). During this period the deciduous forest belt is threat-ened by fast spreading surface fires that, in certain cases, represent a very important disturbance factor (Conedera et al. 1996). It is well known that the vegetation shows different reaction patterns to fire depending on the life strategy of the species and the fire regime (Bond and van Wilgen 1996, Hof-mann et al. 1998), but because fire affects species composition at tim-escales of years to centuries, di-rect observation of the full range of post-fire vegetational change is not possible. To overcome this diffi-culty, we combine paleoecological, dendroecological and phytosocio-logical methods in order to (1) deter-mine vegetation response patterns during different historical periods and fire regimes and (2) provide in-formation on related long-term eco-system dynamics.PaleoecologySediment analyses of two small lakes (Lago di Origlio and Lago di Muzzano) were used to reconstruct vegetation history and fire ecol-ogy of the last 15,000 years (Tin-ner et al. 1999). A comparison of the recent sedimentary record with the wildfire database of southern Switzerland indicates that charcoal concentration and influx estimat-ed from pollen slides correlate well with the number of forest fires oc-curring within a distance of 20 to 50 km from the coring site (Tinner et al. 1998). In order to determine post-fire vegetation responses, we com-puted cross-correlations for pairs of pollen types and charcoal concen-A B CD E+0.5-230+0.5+0.5+0.5+0.5-0.5 -0.5 -0.5-0.5 -0.5-230 -230-230 -230+230+230+230+230+230Fig. 1: Correlograms of charcoal influx, pollen percentages and diversity from Lago di Origlio (5,100-3,100 BC cal.). Horizontal axis shows lag in years (one lag = 11.6 years). Vertical axis shows correlation coefficient – those outside the lines are significant at p = 0.05. A: decreasing taxa (charcoal vs. Ulmus spp.); B: increasing taxa (charcoal vs. Alnus glutinosa t.); C: opportun-ists (charcoal vs. Cichorioideae); D: fire precursors (charcoal vs. Pteridium aquilinum); E: plant diversity (charcoal vs. pollen diversity).PAGES NEWS, VOL.10, N°1, APRIL 2002

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Progress in South America Dendrochronology

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