Annual Growth Bands in Hymenaea courbaril

One significant source of annual temperature and precipitation data arises from the regular annual secondary growth rings of trees. Several tropical tree species are observed to form regular growth bands that may or may not form annually. Such growth was observed in one stem disk of the tropical legume Hymenaea courbaril near the area of David, Panama. In comparison to annual reference {Delta}{sup 14}C values from wood and air, the {Delta}{sup 14}C values from the secondary growth rings formed by H. courbaril were determined to be annual in nature in this one stem disk specimen. During this study, H. courbaril was also observed to translocate recently produced photosynthate into older growth rings as sapwood is converted to heartwood. This process alters the overall {Delta}{sup 14}C values of these transitional growth rings as cellulose with a higher {Delta}{sup 14}C content is translocated into growth rings with a relatively lower {Delta}{sup 14}C content. Once the annual nature of these growth rings is established, further stable isotope analyses on H. courbaril material in other studies may help to complete gaps in the understanding of short and of long term global climate patterns

Two Late Quaternary Pollen Records from South-Central Alaska

Pollen records from Wonder and Ten Mile lakes, located at aititudinal treeline to the north and south of the Alaska Range respectively, document the vegetation history of a portion of the southern Alaskan boreal forest. The new pollen diagrams indicate a Betula shrub tundra, preceded at Wonder Lake by a sparse herb tundra, which characterized these two areas during latest Wisconsinan times. Populus was in the vicinity of Ten Mile Lake ca. 10,000 BP, but was apparently absent from Wonder Lake. Picea glauca grew at or near Ten Mile Lake by 9100 BP, with P. mariana becoming important ca. 7000 BP. The first forests at Wonder Lake were also dominated by P. glauca and followed by increased numbers of P. mariana. The timing of forest establishment at Wonder Lake is uncertain due to problematic radiocarbon dates. Alnus appears to be common in both regions by ca. 7000 BP. These records suggest that paleo-vegetational reconstructions are more difficult for the southern than northern boreal forests in Alaska because of greater topographic diversity, difficulties with over-representation of some pollen taxa, and problems with radiocarbon dating. Despite these concerns, available data from south-central Alaska suggest that southern and northern forests differ in their vegetational histories. Such differences, when related to temperature fluctuations that have been postulated for the Holocene, imply that the Alaskan boreal forest may not respond uniformly to future global warming.Les inventaires polliniques de Wonder Lake et de Ten Mile Lake, situés à la limite altitudinale des arbres au nord et au sud de la chaîne de l'Alaska permettent de reconstituer l'histoire de la végétation d'une portion de la forêt boréale du sud de l'Alaska. Les nouveaux diagrammes polliniques montrent une toundra arbustive à Betula, précédée au Wonder Lake par une toundra herbacée clairsemée, à la fin du Wisconsinien. Vers 10 000 BP, Populus était dans les environs du Ten Mile Lake, mais était apparamment absent du Wonder Lake. Picea glauca croissait autour du Ten Mile Lake à 9100 BP et P. mariana prenait de l'importance vers 7000 BP. Au Wonder Lake, les premières forêts ont également été dominées par P. glauca, puis par un nombre croissant de P. mariana. La chronologie de !'afforestation est incertaine en raison de datations au radiocarbone douteuses. Alnus semble être une espèce courante dans les deux régions vers 7000 BP. Les inventaires indiquent que la reconstitution de la paléovégétation est plus difficile à faire pour les forêts méridionales que septentrionales de l'Alaska, en raison de la plus grande diversité topographique, la sur-représentation de certains taxons et des problèmes de radio-datation. Les données indiquent tout de même que l'histoire de la végétation des forêts diffèrent au nord et au sud. Ces différences, mises en relation avec les fluctuations de températures présumées de l'Holocène, laissent croire que la forêt de l'Alaska ne répondra pas nécessairement de façon uniforme à un réchauffement climatique éventuel.DbiJibneBbie aiiarpa.viMbi ocaaKOB 03ep Baeae n TeHMaRJi, pacnojioxeHiibix B6JIII3H Bepxiiert rpaiiMUbi Jieca Ha ceBepe H wre A/iflCKiiHCKoro xpeôîa, OTpaacaioT ncropnio pacTHTejibHOCTH KOKIIOH lacr" Sopea/ibHoro jieca AJIBCKH. HoBbie ribiJibuebe anarpaMMbi iiOKaabiBaioT, HTO KycTapmiKOBOfi 6epr30B0fi TyHApe, xapaKTepiioft aJifl 3TMX aByx TeppiiTopufl B Teieime no3iuiero BiicKoiicmia, npemuecTBOBajia B oTaoaceiinnx 03. Banae 6emiaH TpaBHHUCTHa iyHapa. Populus iipopn3parra.n B otcpecruocnix 03. Teii.vianji 10000 /J.H., HO, JlO-BIUHMOMy, OTCyTCTBOBaa B pafione 03. BaHae. 9100 JI.H. B panoHe 03. Tenvianj] H.11I B iienocpeacrBeimoH 6/IH30CTH OT iiero npoH3pacTajia Picea glauca, KOTopan BMepTe c Picea mariana nrpaeT 3Ha'iiiTe/ibnyio pojib B codaBe pacTHTeJibHOCTM OKO/IO 7000 .i.n. B nepBbix Jiecax B paflone 03. BaHae TaKjKe aoMiiiuipoBajia Picea glauca, 110 3aTe,vi pojib Picea mariana iiaHimaeT B03pacacTaTb. Bpe.viH noflB/ieiiHfl jiecoB B panone 03. Banae uoKaiie ycraiiaBJiiiBaeTca iiaaeacHo paaiioyr-jiepoaiibiM McroaoM. Alnus o6pa3yer cooBiuecTBa B06011X pafioiiax OKOJIO 7000 JI.H. nojiyieiuibie aaiiHbie cBiiaeTejibCTByioT 0 TOM, HTO peKoiicTpyKniifl pacTiiTejibiiocTH 6yaer 6ojieecjio>KHon aJin lOîKHbix, ieM aJifl ceaepiibix 6opeajibiibix JiecoB AJIHCKH 1133a SHa'iinejibiioro TonorpafpimecKoro iiecxoacTBa,3aTpyaiieiii!Ji B iiHTepnpeTaumi neKOTopwx nbijibneitbix TaKCOHOB, npoGjieM c paanoyrjiepoaiibiM aaTHpBaiine.M. HeavioTpa tia 3TH npo6jieivibi, nojicpieHHbie aaHiibie noKa3biaiOT, HTO fjopeajibiibie Jieca 11a wre 11 ceBepe ioaciion iacni UetiTajibiion AJIHCKH wweioT pa3Jiiiiyio iiCTopnio. TaKiie pa3Jinmtfl, cBfl3xaiuibie c n3MeiieiijiflMii 3eMJiepaTyp B Teieiuie ro.'ioueiia, cBiiae-Te.TbCTByioT, HTO 6opeajibiibiri Jiec AJIHCKH ,vioxer ne OTBenaTb cienapnio rjio6aJibiioro noTen.ieiina u SyaymeM

Sporormiella as a tool for detecting the presence of large herbivores in the Neotropics

The reliability of using the abundance of Sporormiella spores as a proxy for the presence and abundance of megaherbivores was tested in southern Brazil. Mud-water interface samples from nine lakes, in which cattle-use was categorized as high, medium, or low, were assayed for Sporormiella representation. The sampling design allowed an analysis of both the influence of the number of animals using the shoreline and the distance of the sampling site from the nearest shoreline. Sporormiella was found to be a reliable proxy for the presence of large livestock. The concentration and abundance of spores declined from the edge of the lake toward the center, with the strongest response being in sites with high livestock use. Consistent with prior studies in temperate regions, we find that Sporormiella spores are a useful proxy to study the extinction of Pleistocene megafauna or the arrival of European livestock in Neotropical landscapes

Aquatic community response to volcanic eruptions on the Ecuadorian Andean flank: evidence from the palaeoecological record

Aquatic ecosystems in the tropical Andes are under increasing pressure from human modification of the landscape (deforestation and dams) and climatic change (increase of extreme events and 1.5 °C on average temperatures are projected for AD 2100). However, the resilience of these ecosystems to perturbations is poorly understood. Here we use a multi-proxy palaeoecological approach to assess the response of aquatic ecosystems to a major mechanism for natural disturbance, volcanic ash deposition. Specifically, we present data from two Neotropical lakes located on the eastern Andean flank of Ecuador. Laguna Pindo (1°27.132′S–78°04.847′W) is a tectonically formed closed basin surrounded by a dense mid-elevation forest, whereas Laguna Baños (0°19.328′S–78°09.175′W) is a glacially formed lake with an inflow and outflow in high Andean Páramo grasslands. In each lake we examined the dynamics of chironomids and other aquatic and semi-aquatic organisms to explore the effect of thick (> 5 cm) volcanic deposits on the aquatic communities in these two systems with different catchment features. In both lakes past volcanic ash deposition was evident from four large tephras dated to c.850 cal year BP (Pindo), and 4600, 3600 and 1500 cal year BP (Baños). Examination of the chironomid and aquatic assemblages before and after the ash depositions revealed no shift in composition at Pindo, but a major change at Baños occurred after the last event around 1500 cal year BP. Chironomids at Baños changed from an assemblage dominated by Pseudochironomus and Polypedilum nubifer-type to Cricotopus/Paratrichocladius type-II, and such a dominance lasted for approximately 380 years. We suggest that, despite potential changes in the water chemistry, the major effect on the chironomid community resulted from the thickness of the tephra being deposited, which acted to shallow the water body beyond a depth threshold. Changes in the aquatic flora and fauna at the base of the trophic chain can promote cascade effects that may deteriorate the ecosystem, especially when already influenced by human activities, such as deforestation and dams, which is frequent in the high Andes

Brazilian montane rainforest expansion induced by Heinrich Stadial 1 event

The origin of modern disjunct plant distributions in the Brazilian Highlands with strong floristic affinities to distant montane rainforests of isolated mountaintops in the northeast and northern Amazonia and the Guyana Shield remains unknown. We tested the hypothesis that these unexplained biogeographical patterns reflect former ecosystem rearrangements sustained by widespread plant migrations possibly due to climatic patterns that are very dissimilar from present-day conditions. To address this issue, we mapped the presence of the montane arboreal taxa Araucaria, Podocarpus, Drimys, Hedyosmum, Ilex, Myrsine, Symplocos, and Weinmannia, and cool-adapted plants in the families Myrtaceae, Ericaceae, and Arecaceae (palms) in 29 palynological records during Heinrich Stadial 1 Event, encompassing a latitudinal range of 30°S to 0°S. In addition, Principal Component Analysis and Species Distribution Modelling were used to represent past and modern habitat suitability for Podocarpus and Araucaria. The data reveals two long-distance patterns of plant migration connecting south/southeast to northeastern Brazil and Amazonia with a third short route extending from one of them. Their paleofloristic compositions suggest a climatic scenario of abundant rainfall and relative lower continental surface temperatures, possibly intensified by the effects of polar air incursions forming cold fronts into the Brazilian Highlands. Although these taxa are sensitive to changes in temperature, the combined pollen and speleothems proxy data indicate that this montane rainforest expansion during Heinrich Stadial 1 Event was triggered mainly by a less seasonal rainfall regime from the subtropics to the equatorial region.This work was funded by FAPESP research grant 2015/50683-2 to P.E. De Oliveira, VULPES Project, Belmount Forum

Paleodistributions and Comparative Molecular Phylogeography of Leafcutter Ants (Atta spp.) Provide New Insight into the Origins of Amazonian Diversity

The evolutionary basis for high species diversity in tropical regions of the world remains unresolved. Much research has focused on the biogeography of speciation in the Amazon Basin, which harbors the greatest diversity of terrestrial life. The leading hypotheses on allopatric diversification of Amazonian taxa are the Pleistocene refugia, marine incursion, and riverine barrier hypotheses. Recent advances in the fields of phylogeography and species-distribution modeling permit a modern re-evaluation of these hypotheses. Our approach combines comparative, molecular phylogeographic analyses using mitochondrial DNA sequence data with paleodistribution modeling of species ranges at the last glacial maximum (LGM) to test these hypotheses for three co-distributed species of leafcutter ants (Atta spp.). The cumulative results of all tests reject every prediction of the riverine barrier hypothesis, but are unable to reject several predictions of the Pleistocene refugia and marine incursion hypotheses. Coalescent dating analyses suggest that population structure formed recently (Pleistocene-Pliocene), but are unable to reject the possibility that Miocene events may be responsible for structuring populations in two of the three species examined. The available data therefore suggest that either marine incursions in the Miocene or climate changes during the Pleistocene—or both—have shaped the population structure of the three species examined. Our results also reconceptualize the traditional Pleistocene refugia hypothesis, and offer a novel framework for future research into the area