tropical rainforest productivity and nutrient cycling
DESCRIPTION
Tropical Rainforest productivity, nutrient cycling, species adaptations to poor soils, forest gap dynamics, and whitewater and blackwater riversTRANSCRIPT
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Chapter 3:
• Productivity
• Nutrient Cycling and
Soil Community
• Blackwater and
Whitewater Rivers
• Rainforest Gaps and
Tree Demographics
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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
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Productivity
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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
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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)
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Nutrient Cycling and Soil Community
• Decomposing and recycling is the
mechanism how materials move
from “living things” to “non-
living 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
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Tropical Rainforest Water and Nutrient Cycles
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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)
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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
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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)
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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)
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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)
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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)
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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
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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
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Disturbance and Ecological
Succession in the Neotropics
• Process of vegetation replacement dynamics =
Ecological Succession
• Pioneer species are the first species to colonize