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

1. Chapter 3:
• Productivity
• Nutrient Cycling and
Soil Community
• Blackwater and
Whitewater Rivers
• Rainforest Gaps and
Tree Demographics

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. Productivity

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. Net Primary Productivity Comparison

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. 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. Tropical Rainforest Water and Nutrient Cycles

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. 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. 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. 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. 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)

15. 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)

16. 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

17. 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

18. Disturbance and Ecological
Succession in the Neotropics
• Process of vegetation replacement dynamics =
Ecological Succession
• Pioneer species are the first species to colonize