Tropical Climates and Ecosystems

1. Tropical Climates and Ecosystems With Special Reference to the Neotropics, and Particular Reference to French Guiana Mihai Tomescu Neotropical Rainforest Ecology Seminar PBIO 693 Spring 2002

2. The questions I am trying to answer 1. What are the parameters that circumscribe tropical climates 2. How does El Nino function and what are its effects 3. What do we know about the recent climatic history of northern South America 4. What are the major types of neotropical ecosystems

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

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

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

6. 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

7. Earth’s axial tilt is also 2327’N I wonder why ? The Tropics are located at 2327’ latitude North and South Seasonality

8. Day/night length varies (even by over 35’) Heat patterns of air masses change, resulting in seasonality of rainfall. Wet seasonDry season. Sometimes two of each. Dry season: <100 mm rainfall/month many deciduous trees shed leaves most trees flower - insect pollinators more active Wet season: up to 1,000 mm rainfall/month or more seeds germinate at onset of rainy season, BUT... Most fruiting at peak of rainy season, BUT... Rainy north of the Equator Dry south of the Equator and viceversa. Seasonality Common misconception: there is no seasonality in the Tropics Animals et al. also respond to seasonality.

9. Normal conditions High pressure weather system stable over eastern Pacific Westward trade-winds and currents Upwelling and cold water along South American coast Warm waters in western Pacific Precipitations over Australia, Indonesia El Nino conditions High pressure weather system and westward circulation disrupted Upwelling shut down Warm oceanic waters and precipitations move westward Drought in Australia, Indonesia El Nino Southern Oscillation (ENSO)

10. Changes in weather patterns, with accompanying effects - forest fires, floods, mudslides etc. Catastrophic for ecosystems sensitive to seasonal variation Maybe even species extinctions ENSO effects Major disruptions to ecosystems, especially marine 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.

11. 0° 23°27’ 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  Precipitation is recycled within the Amazon basin Ecosystems on eastern and western slopes differ dramatically Eastern slopes very humid - rainforests Western slopes and coast extremely dry - deserts

12. A bit of climatic history Stute et al., 1995 Climatic history of northern SouthAmerica 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. Compare their reconstructions with previous results. Interpolating, for French Guiana the difference is of about 5-6C.

13. Weathering profiles from Bogota basin located at altitude of (A) 3150 m and (B) 2980 m, showing soil horizons, radiocarbon dates on charcoal, and distribution with depth of kaolinite oxygen (18O) and hydrogen (D) isotopic composition A bit of climatic history Mora and Pratt, 2001 Climatic history of northern SouthAmerica 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.

14. Mora and Pratt (continued) A bit of climatic history 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. 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.

15. The Tropical Rainforest Lush vegetation, many vines and epiphytes. The actual rainforest Essentially nonseasonal, dominated by broad-leaved, evergreen trees. The moist forest Annual precipitation >2,000 mm, spread evenly from month to month. More important participation of deciduous trees. In seasonally dry climates, precipitation >1,000 mm, mean annual temperature >24C. Tropical forests are among the most productive and extensive ecosystems on Earth. Debate going on whether their biomass has been increasing in response to atmospheric changes over the last century. Latest studies (Phillips et al., 2002) show that it has been increasing, providing a modest negative feedback to atmospheric CO2 accumulation. Major neotropical ecosystems

16. “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.

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

18. Low Quite high species diversity. Open woodlands with many deciduous trees. In areas with a pronounced dry season, often intermixed with savannas. Major neotropical ecosystems Savannas Grasslands scattered with trees and shrubs. Seasonal climate, occasional wildfires. May be relatively wet, or dry and sandy. Dry forests

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

20. 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

21. Average annual precipitation > 2,500mm > 3,000mm/year on most of the coast < 2,000mm/year in southern French Guiana Average temperatures 23C (73F) - 33C (91F) in Cayenne Around 27C in Saul Daily temperature fluctuations greater than annual fluctuations Seasonality of climate due to latitude and to the position of the InterTropical Convergence (ITC): Two Seasons Difference between longest and shortest days of the year 35’ August-October: ITC north of French Guiana – Dry Season December-June: ITC migrates south – Wet Season (May worst) French Guiana Climate Tropical – hot and humid

22. 18 kya 12 kya 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

23. Annual rainfall > 3,000mm Distributed over 280 days Seasonality: two dry seasons of unequal duration Main dry season – September-October “Little summer” – around March Small-scale zonation of vegetation Hyperhumid rainforest: mosaic of successional stages each initiated by treefalls Rock savanna: open vegetation on rocky outcrops and inselbergs cyanobacterial crusts – xerophytic herbs – shrubby thickets Low forest/Transition forest: between the two – low thickety vegetation adapted to xeric conditions Not a mere ecotone: harbors almost 200 characteristic species Liana forests & bamboo thickets: stagnant regeneration or relict patches French Guiana Charles-Dominique et al., 1998 Small-scale zonation of vegetation, vegetation and climate history Les Nouragues research station

24. Fire occurrences most frequent 10,000-8,000 BP 6,000-4,000 BP 2,000-0 BP Fires independent of human occuppation. Sometimes occur below human occuppation levels. Earliest anthropogenic remains in French Guiana around 2,000 BP. Not a local phenomenon. Charles-Dominique et al. (continued) French Guiana 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.

25. Charles-Dominique et al. (continued) French Guiana Climate history 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.

26. 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. Evidenced dry climatic phases between 2,200-1,200 BP. Suggest that the dry episodes reflect periods during which the climate mimicked present-day ENSO phenomena.

27. Leaf-fall periodicity is annual and seasonal is not correlated to rainfall or the dry season correlated to photoperiodical variations (exogenous) each tree has its own periodicity for leaf sheddding Leaf-fall periodicity thought to be unrelated to climate (endogenous) based on: wide spread taxonomic distribution of the character presence or absence among some taxa ancient origin of the character 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.

28. 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.

29. The answers to the questions 1. What are the parameters that circumscribe tropical climates ? Hot, often humid and seasonal Daily temperature fluctuations exceed average annual seasonal fluctuations Seasonality expressed principally in precipitation: dry season vs. rainy season

30. 2. How does El Nino function and what are its effects 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

31. 3. What do we know about the recent climatic history of northern South America 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

32. 4. What are the major types of neotropical ecosystems The answers to the questions Rainforest (jungle) Savannas and dry forests Riverine and floodplain Coastal

33. Bibliography • 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.