Tropical Rainforest Notes

5 Layers of Tropical Rainforest

• Tropical rainforests have 5 layers.

What is an Ecosystem?

• An ecosystem involves input, process, and output.

• An ecosystem is a system of complex interactions between all living organisms and their environment.

• It consists of two components:

  • Abiotic components: Non-living features and the physical environment.

  • Biotic components: All living organisms.

• Example:

  • Abiotic: Temperature, light, moisture.

  • Biotic: Plants, animals, microorganisms.

What are Tropical Rainforests?

• Tropical rainforests are mainly located in areas north and south of the Equator, mostly between 10°N and 10°S.

• In some cases, their geographical range extends between 23.5°N (Tropic of Cancer) and 23.5°S (Tropic of Capricorn).

Three Main Tropical Rainforest Areas:

• Amazon Basin in South America: The largest area of tropical rainforests.

• Central & South America > Africa > Southeast Asia & Oceania

• Congo Basin

• Australasia

Climatic Characteristics of Tropical Rainforests

• High annual rainfall: > $2000$ mm.

• High annual mean temperature.

• High relative humidity.

Significance

• The most productive and complex ecosystem on Earth.

Abiotic Components of a Tropical Rainforest Ecosystem

Climatic Conditions

• Tropical rainforests are affected by an equatorial or tropical maritime climate, which is hot and humid.

  • High annual mean temperatures (over $25.8°C$) with a small annual range of temperature of $2-4°C$.

  • No obvious seasonality; hot year-round.

  • High annual rainfall (over $2000$ mm) with no seasonal variation or distinct dry season; wet year-round.

  • Relative humidity is constantly above 90%.

  • Rain mostly falls in the afternoon as convection rain: short-lived, heavy downpours often accompanied by thunder and lightning.

Why is it Like That?

• Tropical rainforests are located at low latitudes where the angle of the sun is large throughout the year.

• Inputs of solar radiation are large.

• Tropical rainforests are located along the Intertropical Convergence Zone (ITCZ).

• A strong convection current is formed as winds from the Northern and Southern Hemispheres converge at the ITCZ.

Convection Rain Formation

1. During the daytime, intense sunlight heats up the ground surface.

2. Air temperature is high near the ground.

3. Air is heated, expands, and rises.

4. Strong vertical air currents form.

5. Excess water vapor in the air condenses and forms clouds.

6. Air temperature falls to the dew point and air becomes saturated.

7. Strong convection currents help water droplets develop into thick, heavy clouds.

8. Heavy convection rain forms.

9. Cooler air sinks to replace rising air.

Soil Characteristics

• Various soil types are found in tropical rainforests, typically reddish or yellowish oxisol.

• The unique characteristics of the soil are closely related to the climate and vegetation of rainforests.

  • Dense vegetation leads to a lot of litter.

  • Heavy rain.

  • High temperature and humidity.

  • Large biomass.

Soil Profile

• Thick soil profile ($30-50$ m), formed by intense weathering of bedrock.

• Water movement:

  • Infiltration and percolation.

  • Leaching of nutrients to streams/groundwater.

Soil Layers

• Thin humus layer: Quick decomposition due to hot and wet climate.

• Topsoil: Contains limited nutrients.

• Subsoil.

• Bedrock.

Characteristics

• Dense vegetation produces a lot of litter (dead organic matter).

• When litter decays, it forms a layer of humus (partially decomposed organic matter) in the topsoil.

• Under hot and wet climate, humus decomposes quickly.

• Heavy rain causes strong leaching (percolation of soluble minerals down the soil).

• Residual accumulation of insoluble minerals, e.g., iron and aluminum oxides, makes it acidic.

• Presence of iron oxides gives the soil its red color.

• Limited nutrients in the topsoil because they are absorbed quickly by plants or leached away by heavy rain.

Weathering

• Formed by intense weathering of bedrock.

• Rock + water + humus under hot & wet conditions favor chemical weathering.

• Weathering at the same site.

• Erosion by wind, rain, water, river, sea moves material away.

Biotic Components of a Tropical Rainforest Ecosystem

Huge Biomass

• Biomass is the total amount of organic matter within an ecosystem.

• Tropical rainforest ecosystems have the largest biomass.

• Contain 315 billion tons of biomass, approximately 40% of total organic matter in plants on Earth.

• Average biomass: About 500 tons per hectare, the largest on Earth.

• The hot and humid climate throughout the year provides ideal growing conditions for plants and animals.

Evergreen Vegetation

• Year-round hot and humid climate results in insignificant seasonality, so plants are "evergreen."

• No distinct seasons in tropical rainforests.

• The climate allows plants to have buds, flower, and shed leaves at the same time during the year.

Stratified Vegetation

• Vegetation is usually stratified into five layers:

  • Emergent layer:

    • Height: 30-50 m.

    • Widely spaced.

    • Broad and umbrella-shaped crowns, high branches, thick and straight trunks, and buttress roots.

  • Canopy layer:

    • Height: 20-35 m.

    • Trees are closely spaced, forming a continuous layer of tree crowns.

    • Oval-shaped crowns, high branches, straight trunks, and buttress roots.

  • Young tree layer:

    • Height: 10-20 m.

    • Tree trunks are straight.

    • Short trees, sparsely spaced.

    • Conical crowns and slender trunks.

  • Shrub layer:

    • Height: 3-10 m.

    • Mainly shrubs, ferns, and tree seedlings.

    • Sparse vegetation of short shrubs, ferns, and other plants.

  • Undergrowth/Ground layer:

    • Height: 0-3 m.

    • Mosses, lichens, mushrooms, and giant fungi are found, sparsely spaced.

Microclimate

• Light intensity decreases down the rainforest.

• Temperature decreases down the rainforest.

• Wind speed decreases down the rainforest.

• Relative humidity increases down the rainforest.

High Biodiversity

• Tropical rainforests cover only 5% of the land area, but are home to 50% of Earth’s animal species.

• The stratified structure creates diverse habitats that attract a wide variety of species.

• Vegetation captures atmospheric carbon dioxide for photosynthesis.

• Tropical rainforests act as major carbon sinks, storing 62 billion tons of carbon dioxide and absorbing nearly 17% of the carbon dioxide released by combustion of fossil fuels.

Interaction Between Abiotic and Biotic Components

Vegetation Affects Climate

• Continuous tree crowns of the canopy layer and the stratified structure of vegetation influence wind speed, light intensity, temperature, and relative humidity.

• The canopy layer blocks most insolation, reduces wind speed, and traps moisture transpired from plants.

• Creates a unique microclimate.

Climate Affects Vegetation Growth

Adaptation Features in Woody Plants

• Woody plants have developed features to adapt to their respective habitats.

Growth of Climbers, Epiphytes, and Parasites

• Climbers grow up tree trunks for physical support and to compete for sunlight.

• Epiphytes grow on other plants to gain access to more direct sunlight and increase the possibility of wind pollination.

• Parasites grow on the host plant to absorb water and nutrients.

Growth of Shade-Loving Species

• The dark and humid environment at the ground level favors the growth of shade-loving species.

• The stratified structure creates different habitats with unique microclimates that favor the growth of a diverse range of species.

Adaptations

• Emergent/Canopy Layer:

  • Umbrella-shaped tree crowns: Extend widely to absorb sunlight.

  • Leaves have waxy surfaces and are light green: Reduce water loss from transpiration.

  • Tall trees with branches towards the top: Compete for sunlight.

  • Tall buttress roots (3-4 m height): Support trees against wind and weight.

• Below Canopy Layer:

  • Oval-shaped tree crowns: Maximize sunlight absorption in a less spacious environment.

  • Leaves are dark green in color: To maximise the absorption of sunlight

• Climbers: Rely on tree trunks for physical support and sunlight competition.

• Epiphytes: Grow on trunks/branches for sunlight absorption.

• Parasites: Grow on host plants to absorb water and nutrients.

• Shade-loving Species:
  *Mosses, ferns found on the forest floor due to dark and humid conditions.

Unit 2: Energy Flow and Nutrient Cycling of a Tropical Rainforest Ecosystem

• Abiotic and biotic components are linked by energy flow and nutrient cycle.

Energy Flow

• Energy flows along the food chain.

• A species relies on other species for food, and itself serves as a food source for another.

Food Chain

• A food chain shows the one-way feeding relationship between different organisms in an ecosystem.

• A trophic level is the position of an organism in the food chain.

Four Principal Trophic Levels

1. Plants (Producers/Autotrophs):

   • Can produce their own food through photosynthesis.

   • First trophic level.

2. Animals (Primary Consumers/Herbivores):

   • Obtain energy by eating plants.

   • Second trophic level.

3. Secondary Consumers (Carnivores):

   • Obtain energy by eating herbivores.

   • Third trophic level.

4. Tertiary Consumers (Carnivores + Omnivores):

   • Obtain energy by eating animals and plants.

   • Fourth trophic level.

Food Web

• Food chains are too simple to describe actual energy flow.

• Organisms have various food sources, and are also food sources for other organisms.

• This forms a complex food web.

Energy Flow

• Transfer of solar energy from the sun to green plants through photosynthesis, then transferred to organisms at different trophic levels along the food chain.

• Energy is lost at all stages of the food chain.

Example

• Solar energy -> Plant -> Caterpillar -> Lizard -> Jaguar -> Decomposers (nutrients soil)

• Feeding relationships among organisms form a network of food chains known as a food web.

Energy Flow Efficiency: The Ten Percent Law

• Only about 10% of the energy from one trophic level can pass to the next higher trophic level.

• Some food parts are inedible, some cannot be digested, and energy is consumed to maintain life functions, growth, and repair.

Energy Flow Diagram

• Sun -> T1 (Producers) -> T2 (Primary Consumers) -> T3 (Secondary Consumers) -> T4 (Tertiary Consumers) -> Decomposers

• Energy loss at each level through respiration and excretion.

• Unused energy at each level.

Explanation

• The Sun is the primary source of energy; plants use it for photosynthesis.

• Some energy is lost as heat during plant respiration and transpiration.

• Some energy is stored in plants and used for growth and reproduction.

• Some energy is passed to primary consumers when they eat plants.

• Primary consumers use and lose some energy during respiration and excretion.

• Some energy is passed to secondary consumers when they eat primary consumers, and so on.

• When plants or animals die, some energy is passed to decomposers.

• There is also energy loss when decomposers carry out respiration and excretion.

Trophic Pyramid

• Fill in the amount of usable energy available for the next higher trophic level:

Questions

1. Do you think many trophic levels can be found in a food chain?

   • No, energy flow is inefficient. Only 10% of energy is passed to the next trophic level. Not enough energy to support many levels.

2. The number of organisms and biomass decreases with increasing trophic levels.

Nutrient Cycling

• Nutrients are inorganic substances like nitrogen (N), phosphorus (P), and potassium (K).

• Air, rainfall, and soil provide nutrients that plants use to grow.

• Plants turn inorganic substances into organic matter.

• When plants die, their organic matter is decomposed into inorganic nutrients.

  • These are taken up by other plants and reused.

Nutrient Cycling

• Nutrient cycling is the movement and exchange of nutrients in an ecosystem.

1. Plants absorb nutrients from the soil.

2. Nutrients are turned into organic matter (biomass) of the plants.

3. Dead leaves and other plant parts are decomposed into inorganic nutrients.

Nutrient Cycling in a Tropical Rainforest Ecosystem

• Consists of two parts: nutrient flow and nutrient storage.

Nutrient Storage

• Dissolved nutrients from rain.

• Littering adds to litter stores.

• Nutrients stored in biomass, litter, and soil.

Nutrient Flow

• (a) Surface runoff washes litter away.

• (b) Leaching of nutrients from weathered rock.

• Biomass: Nutrients stored in plant and animal tissue, produced by photosynthesis, and uptaken by plant roots.

• Litter: Nutrients (organic matter) from dead plant materials, animal waste, and dead bodies.

• Soil: Nutrients (inorganic matter) broken down from decomposed litter and weathered rocks.

Characteristics of the Nutrient Cycle

Other Nutrient Sources for Plant Growth

• Weathering of bedrock.

• Rainfall.

• Dead animal parts.

Energy Flow vs. Nutrient Cycling

Ecological Equilibrium

• Abiotic and biotic components interact to achieve a stable balance.

• In the long term, an ecosystem can reach its climax state.

• However, this balance may be disturbed due to:
  *Natural hazards: Wildfires in TRF (climatic change T°C↑).
  *Man-made causes

Is the Tropical Rainforest a Complex but Fragile Ecosystem?

Complex Ecosystem

• High biodiversity, diverse habitats, and high density of species.

Fragile Ecosystem

• An ecosystem can withstand disturbances and return to ecological equilibrium if disturbances are small.

• The ability depends on:
  *Resistance stability.
  *Resilience stability.

Resistance Stability

• An ecosystem's ability to withstand disturbances and maintain its current status.

• Resistance stability increases with increasing complexity of the ecosystem.

• Rainforests have high resistance stability when disturbance is in small scale.

Fragility

• Ecosystem becomes very fragile when facing large-scale destructions like deforestation and fire.

• High resistance stability is limited to small-scale disturbances.

• Grassland ecosystems are simple, with fewer species that are widely spread, and are more resistant to disturbances and extinction.

Resilience Stability

• An ecosystem's ability to restore to its previous state after disturbance.

• Resilience stability decreases with increasing complexity of an ecosystem.

Restoration

• Complex forest ecosystems take centuries to be fully restored.

• Grassland ecosystems take only several years to recover.

Secondary Succession of Rainforests After Fire

• Pioneer species (lichens, ferns) -> Grass, shrubs, secondary forests -> Mature rainforest
  * 0 year -> 1-2 years -> 3-4 years -> 5-150 years -> 150+ years

Unit 3: Causes of Large-Scale Rainforest Deforestation

What is Deforestation?

• Deforestation: Human extraction of resources by cutting down trees.

Extent of Deforestation

• 12-15 million hectares of rainforest are lost each year = 36 football fields per minute (Source: WWF).

• Net annual losses of forest in the Amazon Basin, Congo Basin, and Southeast Asia ranged between 1.9 to 2.4 million hectares per year from 2010 to 2015.

• Deforestation rate: Amazon Basin > Southeast Asia > Congo Basin.

• Some experts predict all rainforests will disappear by 2030.

Inadequate Protection Efforts

• No significant reduction in deforestation in nearly all countries except Brazil.

Human Activities Causing Deforestation

Deforestation Drivers

• Agricultural development, resource extraction, and urban development.

Agricultural Development

Shifting Cultivation

• Subsistence farming practiced by indigenous people for generations.

• Different kinds of crops are grown.

• Farm produce are for own family use.

• Process:

  1. Open Small Piece of Land by Slash and Burn Method.

  2. Grow Different Types of Crops.

  3. Farmers Abandon Farmland After 2-3 Years.

  4. Regeneration of Secondary Forest When Field is Left fallow for 15-20 Years then cycle repeats

• Deforestation occurs due to rapid population growth forcing people to open up more land and shortening fallow periods.

Sedentary Farming

• Farming activity carried out by people settled in the same location for a long period of time.

• Landlords and outside settlers grow food crops (e.g., rice) and cash crops (e.g., tobacco).

• Usually found in floodplains and river deltas.

• Chemical fertilizers and pesticides are used.

• Excessive Use of Chemical Fertilisers Can lead to Soil erosion and pollution

Plantations

• Large-scale farming activity that produces cash crops like cocoa, rubber, sugar cane, coffee, and tropical fruits.

• Crops are grown in large-scale monocultures.

• Farm produce is usually exported to earn foreign exchange.

• Forests are cleared for a single crop, depleting soil nutrients.

• In recent years, large-scale monocultures have expanded rapidly and use large amounts of fertilisers and pesticides. Excessive use of fertilisers will pollute water resources

Livestock Rearing (Cattle Ranching)

• Raising cattle to produce beef for human consumption.

• Main cause of deforestation in the Amazon region.

• Transnational corporations buy rainforest at a low cost and clear it to raise cattle for meat production.

• Soil fertility of Land declines in Several Years. This then causes the corporations to then buy new pieces to raise more cattle.

Resource Extraction

• People directly extract or utilize resources in the rainforests.

• Collection of firewood,

  • People are too poor to afford alternative energy.

  • Firewood and charcoal are the major source of energy.

• Commercial logging done when TNCS cut down valuable wood for profit.The value of the wood is burned.

• Construction of hydro-electric power plants for devleopment to attract investment.

  • Construction of dams, reservoirs and power stations removes large pieces of rainforests. and may also provide Improvement in navigation, flood prevention and water supply regulation

• Mining to extract precious materials underground by TNCS whom generally remove vegetation and clear the topsoil

Urban Development

• Trees at the fringe of rainforests are usually cleared for urban development.

• Two main types of urban development: transport networks and town development.

• Construction of transport networks for Accessibility. In addition roads attract exploit undisturbed forest land to earn a living.

• Many rainforest-rich countries encourage development of their rainforests and developing areas for urbanisation which includes re-settling Indonesians for population pressure in urban areas and to develop for Tourism.

Pros and COns to Tourism

• Good Source of income to the countries and channel through which the public can be educated on rainforest conservation.

• Development of tourist facilities modifies the environment and large visitors can disturb the plant and animal life.

Underlying Reasons for Rainforest Destruction

• Increase in demand for resources, Population Growth add to the burden on these resources.

• 1st Rural Areas are poor. They Have to open up rainforest an make money for a living.

• 2nd TRF Governments are underdeveloped. Thus They Rely on exploiting the rainforest for Economy. States gives incentives to encourage development.

• Shifting diets and Globalisation. As the Land is in Tropical areas is cheaper Multi National Enterprises develop livestock/agricultural industries. Products are exported to more developed contries.

Why Are Tropical Rainforests Disappearing At a Faster Rate today Than in The Past?

• Rapid population growth. Total world population reached 7.7 in 2018.

• Rising living standards and Increase consumption of products.

• Heavy forgin debt and Governments give incentives on exports.

• Poverty. Where One billion people live in poverty and uneven distribution of wealth is serious.

• Political instability.

Why do Rainforest Countries Destroy the Forests?

• Beef export is an important economy for many rainforest countries.

Impacts of Large-Scale Rainforest Deforestation

• Deforestation alters the biosphere, triggering changes to the local atmosphere, hydrosphere, and lithosphere.

• Deforestation has serious environmental and socio-economic impacts on a local and global scale.

Local Environmental Impacts on Local Areas

Atmosphere (Local Climate)

• The climate of deforested areas becomes hotter and drier due to increased reception of solar radiation and reduced precipitation.

• Hinders rainforest regeneration and increases the risk of forest fires.

Hydrosphere

• Transpiration plays an important role in rainfall formation in rainforests.

• Deforestation reduces moisture, increases evaporation, and reduces rainfall.

• Deforested areas suffer from reduced rainfall and increased risk of drought.

• Recent studies show deforestation in the Amazon basin reduces precipitation by 21% in the dry season by 2050.

Lithosphere

• Soil erosion accelerates the loss of soil nutrients, affecting rainforest regeneration.

• Sediments may cause silting of rivers, increasing the risk of flooding.

• Soil without protection is vulnerable to landslides during heavy rainfall.

Biosphere

• Loss of wildlife habitats and high biodiversity.

• Some species may become extinct.

• Disrupted energy flows and nutrient uptake cycles.

Energy Flow disruption due to Deforestation

• Removal of primary producers (trees) reduces food supplies for higher trophic levels and decomposers.

• Complex food web is disrupted, and the food chain is shortened.

Nutrient Cycling Disruption Due to Deforestation

• Increased residue on the ground leads to fast decomposition.

• The initial nutrient content of the soil increases, however, the lack of supply in plant litter causes the nutrient to deplete.

• Sharp surface runoff washes away plant litter, discourages nutrient retention, and accelerates nutrient loss via leaching.

• Leads to a drop in soil fertility over the long run.

Global Environmental Impacts

Global Warming

• Deforestation contributes about 20% of man-made greenhouse gas emissions.

• Deforestation means fewer trees are available to absorb CO2 via photosynthesis.

• Large-scale deforestation affects the global environment by accelerating global warming, altering rainfall patterns, and inducing climate change.

By Enhancing Global Warming

• Releases carbon stores and increases emmisions of Methane.

• Deforestation -> Reduction of Carbon storages +Release of GHGs -> Enhance Global Warming.

By altering rainfall patterns

• Some places become drier.

• Other parts are threatened by flooding as rainfall increases.

• Deforestation in the Amazon alters Rainfall. Some places include Mexico, the USA and South East Asia.

By Inducing Climate Change

• More frequent extreme weather events (heat waves, cold spells, super storms, flooding, and drought).

• Deforestation -> Altered temperatures and rainfall + More Extreme Weather.

Local Socio-Economic Impacts of Deforestation

• Shortages of water and food supply.

• Droughts reduce fish/crop levels and river reduce.

Degradation of Living Environment

• Rainforests act as a shield to protect society from water and air pollution which is often the result of slashing rainforests.

Degradation Causes

Examples

• Burning of rainforests in the Amazon Basin causing Trans Boundary Water and Air Pollution on the islands of Singapore and Malaysia.

Loss of Homes and Cultures

• Deforestation destroys homes of native Tribes.

• Unique knowledge is lost due to indigenous tribes not spreading their traditions and Cultures.

Hindrance to Local Economic Development

• Loss of timber that contains many resources, such as medicine.

• Inefficient power production and navigation due to reduced Rainfall and Sedimentation of rivers.

• Loss of Tourism Due to Degradation of Culture and loss of animal/plant life.

Global Socio-Economic Impacts of Deforestation

• Result of deforestation Include:

Loss of Genetic Resources

• Causes daily the loss of genetic components.

• May result in hindering cure for AIDS and cancers. Can eliminate agricultural biodiversity.

Exhaustion of Timber Resources

• Causes logging, lack of growth in forests and a rise in price of timber and resources.

Spread of Diseases

• Aids the spread of disease to higher latitudes and to agriculture.

• Warmer climate expands the geographical range of disease-carrying organisms and microorganisms.

Questions

• Table A.
  *Solar Radiation: Increased from 0.40 MJ/m2/day to 10.40 MJ/m2/day = 2500% increase.
  *Relative Humidity: Decreased from 70% to 50% = 28.57% decrease.
  *Wind Velocity: Increased from 0.03 m/s to 0.55 m/s = 1733.33% increase.
  *Evaporation (Dry Season): Increased from 0.53 mm/day to 3.93 mm/day = 641.51% increase.

• Table B: Soil Analysis and organic matter in Virgin forest is diminished after cultivation due to leeching.