Neotropical Rainforest Ecology Seminar

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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
Cancer
23?27N
47-degree band of latitude
23?27S
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
Trade winds
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Seasonality
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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
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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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The Tropics are located at 23?27 latitude North
and South
Seasonality
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Seasonality
Common misconception there is no seasonality in
the Tropics
Animals et al. also respond to seasonality.
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El Nino Southern Oscillation (ENSO)
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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.
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The Andes and their effect on climate and
vegetation
The Andes are still rising, as were 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
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A bit of climatic history
Stute et al., 1995 Climatic history of northern
South America
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.
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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)
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.
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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.
Rio Xingu
Varzea floodplain forests run along whitewater
rivers (sediment-rich)
Igapo floodplain forests run along blackwater
rivers (rich in humic matter)
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Major neotropical ecosystems
Savannas
Grasslands scattered with trees and shrubs.
Seasonal climate, occasional wildfires.
May be relatively wet, or dry and sandy.
Dry forests
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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
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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 gt3,000 mm
Precipitations gt2,000 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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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.
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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.
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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.
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.
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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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Bibliography
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150,000 years. http//www.esd.ornl.gov/projects/qe
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