Chapter 3:

• Productivity

• Nutrient Cycling and

Soil Community

• Blackwater and

Whitewater Rivers

• Rainforest Gaps and

Tree Demographics

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

Productivity

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

Net Primary Productivity Comparison

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)

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

Tropical Rainforest Water and Nutrient Cycles

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)

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

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)

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)

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)

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)

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

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

Disturbance and Ecological

Succession in the Neotropics

• Process of vegetation replacement dynamics =

Ecological Succession

• Pioneer species are the first species to colonize