Tropical Rain Forests with notes on tropical savannas

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Tropical Rain Forests (with notes on tropical
savannas)

• Lecture
• J. Bockheim

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Location of Humid Tropical Region
Bailey, 1998
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Distribution of Tropical Rainforest
Tropical Rainforest
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Source http//soils.ag.uidaho.edu/soilorders/oxis
ols.htm
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Terminology

• Laterite generic term for Fe-enriched and
  cemented materials in inter-tropical regions
  also formerly used for Fe-enriched tropical soils
  (also ironstne and ferricrete)
• Bauxite an Al-rich (gibbsite/boehmite) formed
  from deep weathering in tropical regions
• Saprolite isovolumetric weathering especially
  in tropical and subtropical regions
• Oxisol a highly weathered soils of tropical
  regions containing an oxic horizon

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Nature of tropical forests/savannas

• 27 of land area 23.5 deg N-23.5 deg S central
  Africa, northern SA, Indonesia, coastal
  Australia, Central America
• Includes evergreen rain forest, moist dry
  deciduous forest savanna
• High biodiversity (up to 100 species/ha)
• Unique growth forms epiphytes, lianas, climbers,
  stranglers
• Tropical rainforests produce 40 of Earths
  oxygen
• Highest biomass, NPP, and N uptake of world
  eco-regions
• Accounts for 56 and 22 of world vegetation and
  soil C pool, respectively
• Climates
• Tropical rainforest Af, Am, 125-660 cm MAP
  25-30 C MAT
• Tropical savanna Aw, 50-150 cm MAP 25-30 C MAT
• High pedodiversity major soils Oxisols (35),
  Ultisols (28), Inceptisols (15), Entisols (14)

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Tropical Rainforest Ecosystem
Source http//www.digitalfrog.com/resources/raing
allery.html
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Tropical Rainforest
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Tropical Rainforest, cont.
Epiphytes
Buttressing
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Adaptations

• Epiphytes
• Lianas
• Epiphylls

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Adaptations

• Drip tips
• Bark
• Silicon metabolism
• Nutrient Storage in the biomass

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Tropical Savanna
Baobab tree
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Bailey, 1998
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Oxisol landscape
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Eutrustox landscape - Hawaii
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Rhodic Eutrustox (Molokai series) - Hawaii
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Key properties of Oxisols

• Low (lt10) weatherable minerals
• Abundant Fe, Al and Ti
• Ferricrete common
• Low Si
• Generally low base cations
• Often deep profiles 10-150 m
• High amounts of low-activity clay (kaolinite,
  gibbsite, goethite/hematite)
• Low CEC

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Soil Forming Process

• Desilication/Laterization
• Ferrolization
• Silica is released from primary silicates
• Al and Fe oxides remain
• Leaching of base cations
• Silica can recombine with Al to form clay
  minerals (kaolinite)

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Soil Forming Processes

• Plinthization
• Ability to harden once exposed to air
• Redistribution of the products of desilication
• Iron plays an important role
• Alternate reduction and oxidation
• Only possible with fluctuating groundwater
• Humification
• Litter humifies and mineralizes rapidly
• Produce organic acids

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Nutrient Cycling
Source Bruijnzeel, LA. (1991) Nutrient
Input-Output Budgets of Tropical Forest
Ecosystems A Review Journal of Tropical
Ecology, Vol. 7, (1) pp. 1-24.
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Uses of Oxisols

• Forest products
• Subsistence farming - shifting agriculture
• Low-intensity grazing
• Intensive plantation agriculture sugarcane,
  pineapples, bananas, coffee
• Medicinals ¼ from rainforest include curare
  (muscle relaxant), quinine (anti-malarial)
• Mining
• Tourism

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Deforestation In Amazonia
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Shifting Agriculture - southwestern Nigeria
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Grazing, Tropical Savanna
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Problems in managing Oxisols

• Low nutrients require liming, fertilization for
  intensive mgmt.
• Formation of ironstone
• Deforestation of tropical rainforest
• Loss of biodiversity
• Global change
• Poaching of large mammals
• Displacement of native populations

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Some References

• JCU Tropical Plant Science homepage
  http//www.jcu.edu.au/school/tbiol/Botany/
• Jordan, C.F. (1985) Nutrient cycling in tropical
  forest ecosystems - principles and their
  application in management and conservation.
  Wiley, NY
• Lal, R (1995) Sustainable management of soil
  resources in the humid tropics, United Nations
  University Press
• Whitmore, T.C. (1998) An Introduction to
  Tropical Rain Forests (2nd ed.), Clarendon Press,
  Oxford

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Conclusions