Sonia L. Fontana

Glacial Survival of Boreal Trees in Northern Scandinavia

Tree Refugia Ideas of how and when boreal plants spread to the formerly glaciated parts of the world following the retreat of the glaciers 9000 years ago are long debated. Models of the postglacial spread of boreal plants argue for dispersal from southern refugia; however, Parducci et al. (p. 1083) have shown that both spruce and pine were present in small ice-free regions of Scandinavia much earlier than thought. DNA haplotyping confirmed that a remnant mitochondrial type of spruce, once unique to Scandinavia, now lives alongside the more common spruce originating from Eastern Europe. Evidence from lake cores collected from central and northern Norway indicated the survival of conifers as early as 22,000 years before the present, when apart from ice-free pockets, most of Scandinavia was covered by ice. DNA from modern and ancient spruce and pine indicate that both survived in ice-free areas during the last glaciations. It is commonly believed that trees were absent in Scandinavia during the last glaciation and first recolonized the Scandinavian Peninsula with the retreat of its ice sheet some 9000 years ago. Here, we show the presence of a rare mitochondrial DNA haplotype of spruce that appears unique to Scandinavia and with its highest frequency to the west—an area believed to sustain ice-free refugia during most of the last ice age. We further show the survival of DNA from this haplotype in lake sediments and pollen of Trøndelag in central Norway dating back ~10,300 years and chloroplast DNA of pine and spruce in lake sediments adjacent to the ice-free Andøya refugium in northwestern Norway as early as ~22,000 and 17,700 years ago, respectively. Our findings imply that conifer trees survived in ice-free refugia of Scandinavia during the last glaciation, challenging current views on survival and spread of trees as a response to climate changes.

Revisiting pollen accumulation rates from Swedish lake sediments

Early hope that the estimation of pollen accumulation-rates (PAR) from lake sediments would permit the quantitative reconstruction of past vegetational composition abated when results from several experiments uncovered the problems of the method. A review of monitoring experiments, mainly conducted between 1960 and 1980, shows that basin size, transport of pollen with flowing water and sediment redeposition and focusing are the most important factors influencing pollen deposition in lakes. With careful site selection most of these factors can be rendered unimportant or constant. It is shown that PAR estimates from three small lakes in a rather homogeneous forest region are very similar for the last 9000 years. Results from monitoring of pollen deposition in pollen traps provides important information in the interpretation of PAR. Monitoring experiments were conducted to explore the deposition of pollen on and in small lakes. Pollen deposition in pollen traps floating on small lakes was not different from pollen deposition observed on land. PAR estimates from lake sediments were comparable with the results of pollen monitoring obtained with Tauber-type traps. A proportion of airborne pollen deposited on a lake surface is lost during the transport to the lake sediment. The amount of pollen that is lost differs between pollen types.

Molecular‐ and pollen‐based vegetation analysis in lake sediments from central Scandinavia

Plant and animal biodiversity can be studied by obtaining DNA directly from the environment. This new approach in combination with the use of generic barcoding primers (metabarcoding) has been suggested as complementary or alternative to traditional biodiversity monitoring in ancient soil sediments. However, the extent to which metabarcoding truly reflects plant composition remains unclear, as does its power to identify species with no pollen or macrofossil evidence. Here, we compared pollen‐based and metabarcoding approaches to explore the Holocene plant composition around two lakes in central Scandinavia. At one site, we also compared barcoding results with those obtained in earlier studies with species‐specific primers. The pollen analyses revealed a larger number of taxa (46), of which the majority (78%) was not identified by metabarcoding. The metabarcoding identified 14 taxa (MTUs), but allowed identification to a lower taxonomical level. The combined analyses identified 52 taxa. The barcoding primers may favour amplification of certain taxa, as they did not detect taxa previously identified with species‐specific primers. Taphonomy and selectiveness of the primers are likely the major factors influencing these results. We conclude that metabarcoding from lake sediments provides a complementary, but not an alternative, tool to pollen analysis for investigating past flora. In the absence of other fossil evidence, metabarcoding gives a local and important signal from the vegetation, but the resulting assemblages show limited capacity to detect all taxa, regardless of their abundance around the lake. We suggest that metabarcoding is followed by pollen analysis and the use of species‐specific primers to provide the most comprehensive signal from the environment.

Proxy comparison in ancient peat sediments: pollen, macrofossil and plant DNA

We compared DNA, pollen and macrofossil data obtained from Weichselian interstadial (age more than 40 kyr) and Holocene (maximum age 8400 cal yr BP) peat sediments from northern Europe and used them to reconstruct contemporary floristic compositions at two sites. The majority of the samples provided plant DNA sequences of good quality with success amplification rates depending on age. DNA and sequencing analysis provided five plant taxa from the older site and nine taxa from the younger site, corresponding to 7% and 15% of the total number of taxa identified by the three proxies together. At both sites, pollen analysis detected the largest (54) and DNA the lowest (10) number of taxa, but five of the DNA taxa were not detected by pollen and macrofossils. The finding of a larger overlap between DNA and pollen than between DNA and macrofossils proxies seems to go against our previous suggestion based on lacustrine sediments that DNA originates principally from plant tissues and less from pollen. At both sites, we also detected Quercus spp. DNA, but few pollen grains were found in the record, and these are normally interpreted as long-distance dispersal. We confirm that in palaeoecological investigations, sedimentary DNA analysis is less comprehensive than classical morphological analysis, but is a complementary and important tool to obtain a more complete picture of past flora.

Holocene changes in trophic states of shallow lakes from the Pampa plain of Argentina

Changes in trophic status of shallow lakes from the southeastern Pampa plain of Argentina are evaluated based on the relative presence of submerged macrophytes and phytoplankton. The evolution of lake Lonkoy is reconstructed for the last 5000 years, using pollen, non-pollen palynomorphs (NPPs) and macrofossil remain analyses, revealing three main lake stages. A macrophyte-dominated clear lake prevailed until 670 cal yr BP. Afterwards, the lake changed to a turbid phytoplankton-dominated state. Recently, the lake has turned to a turbid phase, caused by resuspended sediment. These results are compared with two other paleolimnological records from the region, lakes Hinojales and Nahuel Rucá, revealing a similar late-Holocene evolution, with a shift from a macrophyte- to phytoplankton-dominated lake, occurring at broadly the same time. The shift of states may be attributed to a shift in climate after 1000 cal. yr BP towards wetter conditions during the Medieval Climate Anomaly.

Pollen deposition in coastal dunes, south Buenos Aires Province, Argentina

Modern pollen deposition and its relationship to the surrounding vegetation have been studied in order to help interpret vegetation change during the Holocene on the south coast of Buenos Aires, Argentina. Pollen has been monitored monthly with two Tauber

Coastal Dune Vegetation of the Southern Pampas (Buenos Aires, Argentina) and Its Value for Conservation

Abstract MONSERRAT, A.L.; CELSI, C.E., and FONTANA, S.L., 2012. Coastal dune vegetation of the Southern Pampas (Buenos Aires, Argentina) and its value for conservation. Vegetation structure and species composition of southern Pampas coastal dunes were studied to evaluate their significance for conservation. The vegetation was described in 41 plots of 100 m2 along four transects perpendicular to the coast. The floristic dataset was classified by two-way indicator species analysis. Vegetation distribution patterns were analysed in relation to the geomorphology and environmental factors. Fifty-one taxa (19 families) of vascular plants were recorded, with Asteraceae, Poaceae, and Fabaceae being the most abundant. The main vegetation groups obtained from the classification are related to distinctive geomorphology. (1) Upper beach and active dunes are habitats with extreme conditions, characterized by species-poor associations with low vegetation cover; group dominated by few shrubs and gramines like Panicum urvilleanum, Calycera crassifolia, and Senecio bergii. (2) Fixed/semifixed dunes are habitats with more stable substrate, characterized by dense vegetation, high species richness, and woody life forms; group dominated by Poa lanuginosa, Hyalis argentea var. latisquama, Oenothera mollissima, and Glycyrrhiza astragalina. (3) Hygrophilous communities are mostly associated with dune slacks with high herbaceous vegetation cover; group largely dominated by Cortaderia selloana, Typha sp., and Imperata brasiliensis. Detrended correspondence analysis shows that the major floristic variation follows a gradient from the beach inland. Also, there is a clear zonation pattern strongly associated with geomorphologic heterogeneity. The occurrence of threatened species (e.g., Adesmia filipes, Neosparton ephedroides) and endemic taxa (S. bergii and Baccharis divaricata) plus the high habitat diversity and plant species richness confers to the area special value for conservation. The ecological role of dune vegetation is discussed in conservation and management context. Resumen La estructura de la vegetación y la composición de especies de las dunas costeras australes de la Región Pampeana fueron estudiadas para evaluar su importancia para la conservación de la biodiversidad. La vegetación fue descrita en 41 cuadrantes de 100m2 cada uno, a lo largo de cuatro transectas lineales perpendiculares a la costa. El set florístico fue clasificado mediante un análisis de dos vías de especies indicadoras (TWINSPAN). Los patrones de la distribución de la vegetación fueron analizados en lo referente a la geomorfología y a los factores ambientales. Dentro de los cuadrantes, se registraron 51 taxa (19 familias) de plantas vasculares, con Asteraceae, Poaceae y Fabaceae siendo los más abundantes. Los grupos principales de vegetación obtenidos de la clasificación se relacionan con distintivas localizaciones geomorfológicas: (1) playa superior y dunas activas son ambientes con condiciones extremas, caracterizados por asociaciones pobres en especies con baja cobertura vegetal; el grupo es dominado por pocos arbustos y gramíneas, como Panicum urvilleanum, Calycera crassifolia y Senecio bergii; (2) dunas fijas/semifijas son ambientes con un substrato más estable, caracterizado por vegetación densa, alta riqueza de la especie y formas de vida leñosas; el grupo fue dominado por Poa lanuginosa, Hyalis argentea var. latisquama, Oenothera mollissima y Glycyrrhiza astragalina.; (3) comunidades higrófilas, asociadas principalmente a bajos interdunales con alta cobertura vegetal; el grupo está ampliamente dominado por Cortaderia selloana, Typha sp. y Imperata brasiliensis. El análisis de correspondencia muestra que la principal variación florística sigue un gradiente desde la playa hacia el interior del continente. También, hay un patrón claro de zonación fuertemente asociado a la heterogeneidad geomorfológica. La ocurrencia de especies amenazadas y de taxa endémicos, sumado a la alta diversidad de ambientes y riqueza de especies vegetales, confieren un valor especial al área para la conservación. El papel ecológico de la vegetación de las dunas se discute en el contexto de la conservación y manejo.

Radiocarbon Chronologies of Holocene Lacustrine Sediments from the Southern Coast of Buenos Aires Province, Argentina

Two lacustrine sediment sequences, La Olla 1 and Laguna del Sauce Grande, on the southern coast of Buenos Aires Province, Argentina, were investigated for carbon reservoir effects, which may influence age-depth chronologies. Fruits of the submerged macrophyte Ruppia cf. maritima from the La Olla 1 sequence, and gastropod shells of Heleobia parchappii from the Laguna del Sauce Grande core, were radiocarbon dated. In addition, terrestrial plant remains and shells of living specimens were dated to assess the presence and magnitude of a reservoir effect. A reservoir age of about 800 14C yr is estimated for the aquatic plant samples of La Olla 1 for the early Holocene. The reservoir effect is attributed to the inwash of 14C-deficient bicarbonate from the surrounding sand dunes. The decay of marine organisms and salt spray are likely the main sources of 14C-deficient carbon. The magnitude of the reservoir effect is consistent with marine reservoir offsets reported for the region. The 14C measurements on shells of living and fossil specimens of Heleobia parchappii indicate the absence of a reservoir effect at Laguna del Sauce Grande, which may be due to the large size and shallow nature of the lake. This study shows how the reservoir ages of 2 close-by lakes in very similar geological settings can be largely different. These results have significant implications for the interpretation of 14C dates from lacustrine deposits in the region.

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.

A new giant cypridid ostracod (Crustacea) from southern Buenos Aires Province, Argentina

Amphicypris argentinensis sp. nov., is described and illustrated from Laguna Caliba, an ephemeral fresh water lake from the southern coast of Buenos Aires Province, Argentina. Specimens were raised from dried sediment recovered from a bank of ostracod shells found at the edges of the lake. Deposition of progressively smaller ostracod valves stacked one into another (cup-in-cup structure) is documented. The geographical distribution and ecology of the genus is briefly discussed.