climates

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Neotropical Rainforest Ecology Seminar PBIO 693 Spring 2002

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The Tropics The region that straddles the Equator, bounded by the two tropical circles 2327’N 2327’S 47-degree band of latitude Cancer Capricorn Climate: tropical, but also subtropical at the two latitudinal extremes

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Tropical climates Consistently warm, often hot temperatures High relative humidity High precipitations Seasonality Trade winds !

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Temperature and humidity 31C (88F) day 22C (72F) night Daily temperature fluctuation exceeds average annual seasonal fluctuation. Relative humidity is around 80%. Varies seasonally: 88% rainy season, 77% dry season Reaches 90-95% at ground level in tropical rainforests Seasonal fluctuation of temperature is extremely low: maximum 5C between mean temperatures of warmest and coldest month.

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Precipitations and winds Tropical areas fall within the trade-wind belts and encompass the InterTropical Convergence (ITC) Evapo(transpi)ration (very important!) Humid, warm air rises and is carried North and South away from the ITC Air cools down releasing precipitations and falling Backward flow toward the Equator Precipitations: 1,500 – 3,000 mm annually in the Amazon basin

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Seasonality The Tropics are located at 2327’ latitude North and South

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Seasonality Animals et al. also respond to seasonality. Common misconception: there is no seasonality in the Tropics

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El Nino Southern Oscillation (ENSO)

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ENSO effects A recent correlation analysis of past ENSO events and dengue epidemics in Indonesia and French Guiana (Gagnon et al., 2001) has demonstrated a significant correlation between the two. The two regions experience warmer temperatures and less rainfall during ENSO years. Major disruptions to ecosystems, especially marine

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The Andes and their effect on climate and vegetation The Andes are still rising, as we’re talking here! Act as a wall: prevent moisture-laden air in the Amazon basin from reaching the western coast Rain shadow effect Eastern slopes very humid - rainforests Western slopes and coast extremely dry - deserts  Precipitation is recycled within the Amazon basin Ecosystems on eastern and western slopes differ dramatically

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Stute et al., 1995 Climatic history of northern South America A bit of climatic history Reconstructed past temperatures (last 30 ky) based on concentrations of noble gases (Ne, Ar, Kr, Xe) in groundwaters (NE Brazil). Relative concentration of the gases reflect the temperature of the waters that incorporated them, which in turn reflect the mean annual ground temperature at the depth of the water table. Showed the differences in mean annual temperatures between the present interglacial and the last glacial period. Interpolating, for French Guiana the difference is of about 5-6C. Compare their reconstructions with previous results.

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A bit of climatic history Mora and Pratt, 2001 Climatic history of northern South America Reconstructed the climate of the last glacial stage based on O and H isotopic composition of minerals in weathering profiles of the Colombian Andes. There is a strong correlation between kaolinite isotope data (O and H) and surface temperature and rainfall.

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Mora and Pratt (continued) Isotope data from paleosols developed during the last glacial stage (LGS) suggest approximately 6C cooler temperatures. The data indicate higher isotope values of rainwater during the LGS, interpreted to reflect drier conditions. The temperatures match those cited by Stute et al. for the region, based on pollen spectra and tree line positions. A bit of climatic history Values of 18O vs. D for kaolinites in weathering profiles. Diamonds correspond to mean values in modern (Holocene) soils, and circles correspond to mean values in last glacial stage (LGS) paleosols. Discrete values within modern soils and paleosols are shown as small crosses.

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Major neotropical ecosystems

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“Major neotropical ecosystems” The Jungle – Disturbed Forest Areas Jungles actually represent early successional stages of the rainforest following disturbance. Fast-growing, shade-intolerant species. Thin-boled trees growing very close together. Palms, bamboos, vines abound. Even rainforests are mosaics of successional stages triggered by disturbance represented by tree-falls.

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Major neotropical ecosystems Riverine and Floodplain Ecosystems Gallery forests border rivers. Varzea floodplain forests run along whitewater rivers (sediment-rich) Igapo floodplain forests run along blackwater rivers (rich in humic matter) Rio Xingu

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Major neotropical ecosystems Savannas May be relatively wet, or dry and sandy. Seasonal climate, occasional wildfires. Dry forests Grasslands scattered with trees and shrubs.

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Major neotropical ecosystems Coastal ecosystems Mangal – the dominant vegetation along tropical coastlines. Formed by mangroves – salt-tolerant tree species. Seagrasses Coral reefs Mangroves and seagrasses contribute to the health of neighboring coral reefs Mangroves have an essential role in the ecology of coastal areas: habitat for animals, improve water quality prevent erosion.

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French Guiana Relief Located on the Guiana Shield Old rocks (Precambrian, 2.1-1.9 Gy), very stable Very eroded – flat relief (highest altitude 800m) Basalt dikes associated with the opening of the South Atlantic - form inselbergs

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French Guiana Climate Tropical – hot and humid

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French Guiana Vegetation All of the major ecosystems are present. Puig et al., 1981 Vegetation formations Climatic formations: Tropical ombrophilous lowland forest Precipitations >3,000 mm Precipitations >2,000 mm Edaphic formations: Mangrove Tall grassland with broad- leaved trees (savanna) Middle-altitude savanna + Gallery forest & Jungle

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French Guiana Charles-Dominique et al., 1998 Small-scale zonation of vegetation, vegetation and climate history Les Nouragues research station

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French Guiana Charles-Dominique et al. (continued) Vegetation history Found several charcoal layers in the soil – indicators of large-scale forest fires. Conclude that forest fires are the only type of major perturbation occurring at a moderate rate in the rainforest. Hypothesize that they could be favorable to the maintenance of a high species diversity by giving more or less periodical impulses to the dynamics of the ecosystem.

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French Guiana Charles-Dominique et al. (continued) If fires are not anthropogenic, then they are triggered by climatic trends: repetition of abnormally long dry seasons over a number of years and consequent lowering of the water table. Found remains of alluvial terraces that could only be formed during periods of intensive erosion. Such erosion could be explained only by extensive deforestation, such as that generated by large-scale forest fires. In the last decades particularly dry years have been recorded in in correlation with high ENSO incidences. Hypothesize that such episodes could be at the origin of drought periods characterized by high forest fire frequency. Although drier periods were characterized by different composition of the rainforest (fossil pollen, seeds and charcoal), open landscapes were not present in the area during the last 3,000 years. Climate history

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French Guiana Pujos et al., 1996 Paleoceanography of French Guiana shelf and climate history Studied the mineralogy of fine sediments in several cores taken on the continental shelf off the French Guiana coast. Demonstrated that fluctuations in the relative participation of the different continental sources that supplied the sediments reflect fluctuations in water discharge and erosion related to climate fluctuations. Suggest that the dry episodes reflect periods during which the climate mimicked present-day ENSO phenomena. Evidenced dry climatic phases between 2,200-1,200 BP.

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French Guiana Loubry, 1994 Phenology of decidual trees Studied leaf-fall periodicity on 500 trees over a two-year period. The rainforest in French Guiana is evergreen but contains approximately 100 deciduous tree species. These finds refine earlier hypotheses and suggest the participation of both endogenous and exogenous components in the determination of leaf-fall periodicity.

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French Guiana Sarthou et al., 2001 Island effects in French Guiana inselberg vegetation Studied the genetic structure of Pitcairnia geyskesii (Bromeliaceae) on populations distributed on three inselbergs by analysis of 10 isozyme loci. Inselbergs – rock savanna habitats isolated by expanses of rainforest, therefore expected to see island effects in plants restricted to inselbergs such as Pitcairnia. Found high levels of genetic variation within each population – probably as a result of association of genet longevity (clonal replication) and recruitment of new genets by efficient sexual reproduction. Substantial genetic differentiation and low gene flow among inselbergs.

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Hot, often humid and seasonal Daily temperature fluctuations exceed average annual seasonal fluctuations Seasonality expressed principally in precipitation: dry season vs. rainy season

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The answers to the questions Disruption of westward oceanic and air circulation west of South America; upwelling along western coast of South America stops; hot surface waters move eastward Abnormal weather patterns Forest fires, floods Disruption of ecosystems Epidemics

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The answers to the questions Last glacial stage: Dryer, Mean annual temperatures 5-8C lower Mean sea surface temperatures 2C lower After last glacial: Warming of climate Alternation of wetter and dryer episodes; dry episodes related to high incidence of ENSO

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The answers to the questions Rainforest (jungle) Savannas and dry forests Riverine and floodplain Coastal

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Adams, J., 2002. South America during the last 150,000 years. http://www.esd.ornl.gov/projects/qen/ nercSOUTHAMERICA.html Alden, A., 2001. Geologic map of French Guiana. http://geology.about.com/library/bl/maps/ blfrenchguianamap.htm Charles-Dominique, P., Blanc, P., Larpin, D., Ledru, M.-P., Riéra, B., Sarthou, C., Servant, M., Tardy, C., 1998. Forest perturbations and biodiversity during the last ten thousand years in French Guiana. Acta Oecologica 19(3), 295-302. Gagnon, A,.S., Bush, A.B.G., Smoyer-Tomic, K.E., 1996. Dengue epidemics and the El Nino Southern Oscillation. Climate Research 19(1), 35-43. Kricher, J., 1997. A neotropical companion. Second edition. Princeton University Press. Loubry, D., 1994. Phenology of deciduous trees in a French-Guianan forest (5 degrees latitude North) - case of a determinism with endogenous and exogenous components. Canadian Journal of Botany 72(12), 1843-1857. Mora, G., Pratt, L.M., 2001. Isotopic evidence for cooler and drier conditions in the tropical Andes during the last glacial stage. Geology 29(6), 519-522. Phillips, O.L., Malhi, Y., Vinceti, B., Baker, T., Lewis, S.L., Higuchi, N., Laurance, W.F., Vargas, P.N., Martinez, R.V., Laurance, S., Ferreira, L.V., Stern, M., Brown, S., Grace, J., 2002. Changes in growth of tropical forests: evaluating potential biases. Ecological Applications 12(2), 576-587. Puig, H., Blasco, F., Bellam, M.P., 1981. Vegetation map of South America. Explanatory notes. UNESCO, Paris. Pujos, M., Latouche, C., Maillet, N., 1996. Late Quaternary paleoceanography of the French Guiana continental shelf: clay-mineral evidence. Oceanologica Acta 19(5), 477-487. Rudant, J.-P., 1994. French Guiana through the clouds: first complete satellite coverage. European Space Agency EOQ 44. http://esapub.esrin.esa.it/eoq/eoq44/rudant.htm Sarthou, C., Samadi, S., Boisselier-Dubayle, M.C., 2001. Genetic structure of the saxicole Pitcairnia geyskesii (Bromeliaceae) on inselsbergs in French Guiana. American Journal of Botany 88(5), 861-868. Shirah, G.W. et al., 1998. El Nino visualisations. 1997-98 Temperatures Beneath Sea. http://nsipp.gsfc. nasa.gov/enso/visualizations/index.html Stute, M., Forster, M., Frischkorn, H., Serejo, A., Clark, J.F., Schlosser, P., Broecker, W.S., Bonani, G., 1995. Cooling of tropical Brazil (5C) during the last glacial maximum. Science 269, 379-383. Bibliography