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Tropical forests

Tropical forests. Climate and distribution Forest characteristics and phenology Direct nutrient cycling Regeneration and gap dynamics Anthropogenic disturbance - shifting cultivation and pastures Forest fragmentation and conservation Late Quaternary climate change and conservation.

britanni-tillman
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Tropical forests

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  1. Tropical forests • Climate and distribution • Forest characteristics and phenology • Direct nutrient cycling • Regeneration and gap dynamics • Anthropogenic disturbance - shifting cultivation and pastures • Forest fragmentation and conservation • Late Quaternary climate change and conservation

  2. Tropical forest: regional climate

  3. Primary productivity (forests) [g m-2 yr-1]:Tropical: 1500 [1800] 2000 Temperate: 1000 [1300] 1500 Boreal: 500 [800] 1000 Diversity Malaysia Amazonas Africa Plants: 60 000 50 000 30 000 Birds: 127 270 150(3 km2)(3 km2)(50 km2) Bats: 81 98 115 Tropical forests:productivity and diversity

  4. Canopy stratification:(how many strata?)multiple strata facilitate high productivity and diversity

  5. Density variations in rainforest stands

  6. High stem density Diversity: majority of trees are rare - densities <1/ha. • Characters: • lots of small poles • ‘drip-tip’leaves • thin bark

  7. Leaf shape: acute (‘drip-tip’), entire margin ‘scratch and sniff’ taxonomy lichen growth on palm leaf

  8. Treefalls

  9. Tree stability on wet, clay-rich tropical soils

  10. Buttresses Stilts Plexus

  11. Cauliflory

  12. Lianas and vines

  13. Epiphytes:bromeliads and orchids

  14. Phenology: Malaysian rainforest % of trees Triggers: degree of water stress and photoperiod. Daylength variations of 15 minutes can trigger flowering in some tropical tree species.

  15. Biomass variations in rainforest stands

  16. Necromass variations in rainforest stands

  17. Nutrient storage: nitrogen

  18. Nutrient storage: phosphorus

  19. Nutrient storage: potassium

  20. Root distribution and the “direct nutrient cycle” • Dense root mats in surface soil exploit nutrients released by rapidly decaying organic matter on the forest floor. • Nutrient capture by tree roots facilitated by mycorrhizal associations (predominantly endomycorrhizal and vesicular-arbuscular).

  21. Nutrient shunts: leaf-cutter ants and termites

  22. Herbivore and insectivore mammals

  23. Seed/fruit eaters

  24. Herbivore resistance • mechanical: spines e.g. on climbing palms; • lactiferous: rubber (Hevea sp.) or • chemical: secondary chemicals in roots, stems, leaves or seed coats to dissuade herbivores from attacking tissue (see next slide).The tropical forest as a “pharmaceutical factory”. • biological: companion ants on Acacia shrubs in Central America ?

  25. Wapishan woman with cassava press, Guyana

  26. Regeneration and the maintenance of diversity

  27. Regeneration into gaps: intense competition for light

  28. Gap microclimates

  29. Antropogenic gaps and succession “milpas” Belize and Guyana

  30. Nutrient loss from shifting cultivation plot results from severance of direct nutrient cycle and changes in soil microclimate and hydrology

  31. Forest clearance: Rondonia, Brazil 1975 1992 100 km2

  32. Forest clearance for pasture, Guatemala[compare with size of milpa clearing]

  33. “Pasturization”:log, burn, seed in Amazonas

  34. Succession on abandoned pastures, Amazonia • 60,000 km2 land in pasture (mid-1980’s) • Generally abandoned after 4-8 years* • Pasture disturbances larger, more prolonged and more intense than slash and burn agriculture * abandonment as a result of soil infertility (especially phosphorus deficiency), insect attack, and weed competition Uhl et al., 1988. J. Ecology

  35. Pasture use history

  36. Biomass andnecromass

  37. “From green hell to red desert”?

  38. Abandoned pastures - nutrient stocks(NB: top 0.5m of soil only;N values / 5)

  39. Rates of species replacement in rainforest succession

  40. Biodiversity on abandoned pastures undergoing succession Heavy

  41. Recovery of tropical forests following disturbance Karen Holl (UC Santa Cruz) working on abandoned cattle pasture in Costa Rica has identified the following obstacles to TRF recovery: 1. Tree seeds have short viability 2. Tree seed dispersal is generally short (large seeds; commonly animal-dispersed) seedfall in pasture is only 1/10th that in the forest. 3. Heavy predation of seeds in pasture 4. Low survivorship of germinating seeds (severe microclimate, low mycorrhizal infection and high herbivory) 5. Competition from non-native pasture grasses (e.g. Imperata cylindrica)

  42. Seed dispersal into abandoned pasture, Costa Rica Mean no. seeds / m2 * *dispersal more effective when tree branches placed in pasture as perches for forest birds

  43. Rainforest fragments:Thomas Lovejoy’s experiments Forest species: survival? recruitment? dispersal? Patch: minimum size?

  44. LGM in the humid tropics: plant and animal responses Were tropical rain forests restricted to small refuges at LGM?

  45. The rise of refuge theory*:endemism in the Neo-tropical forest avifauna * Haffer (1969) Science, 165, 131-137. from: Prance and Lovejoy (1985) Amazonia, Oxford U.P.

  46. Caryocar ranges

  47. Ranges of related forest bird species and subspecies Trumpeters (Psophia) Jacamars (Galbula)

  48. Ranges of related forest bird species and subspecies Aracaris (Pteroglossus) Toucans (Rhamphastos)

  49. Species and subspecies ranges:Heliconius butterflies

  50. Inferred LGM forest refuges based on:1. birds2. lizards3. butterflies4. four tree families5. scorpions From: Nores (1999) J. Biogeography, 26, 475-485

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