Tropical Rainforest Productivity and Nutrient Cycling


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Tropical Rainforest productivity, nutrient cycling, species adaptations to poor soils, forest gap dynamics, and whitewater and blackwater rivers

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Tropical Rainforest Productivity and Nutrient Cycling

  1. 1. Chapter 3: • Productivity • Nutrient Cycling and Soil Community • Blackwater and Whitewater Rivers • Rainforest Gaps and Tree Demographics
  2. 2. Productivity • Productivity = amount of solar radiation converted into sugars = amount of photosynthesis • Gross Primary Productivity (GPP) = total amount of photosynthesis accomplished • Respiration (R) = energy used for plant growth and maintenance • Net Primary Productivity (NPP) = biomass weight gain overtime • NPP= GPP - R
  3. 3. Productivity
  4. 4. Productivity examples • Tropical rainforest uses 50% of the GPP in maintenance • NPP of a tropical rainforest = 0.9 to 1.5 kg/m2/year • Clouds forests are less productive than rainforests because clouds intercept much of sun rays
  5. 5. Net Primary Productivity Comparison
  6. 6. Productivity Examples cont. • NPP is the capture of Carbon in tissue (no other ecosystem stores more carbon than the rainforest) • Growth in the tropics in not interrupted by winter • Productivity depends on adequate light moisture, and CO2, plus minerals from the soils (vitamins)
  7. 7. Nutrient Cycling and Soil Community • Decomposing and recycling is the mechanism how materials move from “living things” to “nonliving things” in an ecosystem • Temp and rainfall influences nutrient cycling – Heat = evaporation – moves nutrients – 50% of the rain that falls in the amazon is recycled via transpiration
  8. 8. Tropical Rainforest Water and Nutrient Cycles
  9. 9. Leaching • Heavy rainfall can wash the soils of minerals = leaching • In the tropical forest most of the minerals are in the living things, not in the soils • Adaptation: waxy leafs to avoid water loss (maintain nutrients and water)
  10. 10. Adaptations to poor soils • Mycorrhizae = fungi that live on the tree roots that help trees absorb nutrients • Rhizobium = bacteria association that grows on legume roots to help plants access Nitrogen • Lichens and termites can fixate Nitrogen • Tree adaptation = buttresses and upper layer roots
  11. 11. Tropical forest soils • Rapid Recycling, fast decomposing = no accumulation of organic mater on the forest floor • Soils vary, but usually old, washed, and poor in nutrients (70%) • If soils are young, (close to a volcano) rich • Removal of forests from white sandy soils (poor), can result in the regrowth of savanna rather than rainforest (due to the destruction of the tight nutrient cycling)
  12. 12. Blackwater and Whitewater Rivers • Blackwater rivers drain from poor nutrient soils (like a tea defense compounds in the vegetation) • Whitewater rivers drain from rich nutrient soils (new soils, good for agriculture)
  13. 13. Rainforest Gaps • Tree, or branches that fall create a canopy opening • A forest gap has a microclimate: more light, less humidity • Rainforests have many small gaps and several large gaps (4 to 6 % of total forest) • Tree falls connected to seasonality (peaking in rainy season)
  14. 14. Forest Gaps cont. • Vertical and horizontal heterogeneity increases with gaps (more biodiversity) • Solar radiation and light quantity is the single limiting growing factor for plants (gaps very important)
  15. 15. Forest Gaps cont. • Rainforest trees – Large gaps specialists – Small gaps specialist – Understory specialists • Pioneer species produce high amounts of seeds, and colonize open spaces created by gaps
  16. 16. Forest Demographics • How long does a rainforest tree survive? • How long does it take for a tree to grow from seedling to adult? • Does most of the growth happen in dry or rainy season? • In a forest with high rates of disturbance a forest turnover can be 118 +-27 years
  17. 17. Disturbance and Ecological Succession in the Neotropics • Process of vegetation replacement dynamics = Ecological Succession • Pioneer species are the first species to colonize