IB Biology Topic D4.2.3: Deforestation of Amazon Rainforest Notes

The Amazon Recycles Its Own Rainfall Through Transpiration

1. The Amazon rainforest regulates climate by producing oxygen, storing carbon, and recycling rainfall through transpiration.
2. Transpiration is the release of water vapor from plant leaves, which cools the air, forms clouds, and returns water as rain.
   1. Cooling: as water evaporates from leaves it takes heat with it, cooling the surrounding air.
   2. Cloud formation: the rising water vapor condenses into clouds that produce rain.
   3. Rainfall recycling: up to 50% of the Amazon's rainfall is recycled this way, keeping the forest wet enough to survive.

Deforestation Sets Off a Positive Feedback Loop

1. Cutting down trees reduces transpiration, which starts a positive feedback loop that drives further forest loss.
   1. Less transpiration: fewer trees release less water vapor, so less rain falls.
   2. Drier conditions: the drier forest catches fire more easily, killing more trees.
   3. Self-reinforcing cycle: each round of loss makes the next round more likely, speeding up the decline.

Losing 20 to 25% of the Forest Could Tip It Into Savanna

1. Scientists estimate that losing 20 to 25% of the Amazon could push it past a tipping point.
2. Past that point the forest would dry out and switch to savanna-like grassland, a change that would be effectively irreversible.

Deforestation Releases Carbon and Wipes Out Biodiversity

1. Releases stored carbon
   1. The Amazon holds about 120 billion tonnes of carbon.
   2. When trees are cut or burned this carbon is released as carbon dioxide, adding to global warming.
2. Drives biodiversity loss
   1. The Amazon is home to about 10% of all known species.
   2. Clearing land destroys habitats and breaks the links between species, pushing ecosystems toward collapse.
3. Harms Indigenous communities
   1. Local and Indigenous people rely on the forest for food, medicine, and cultural traditions.
   2. Deforestation removes their livelihoods and erodes practices built up over centuries.

Percentage Change Lets You Quantify Forest Loss

1. Deforestation over time can be measured with percentage change.

$$
\text{Percentage Change} = \frac{\text{Final Amount} - \text{Initial Amount}}{\text{Initial Amount}} \times 100
$$

The Amazon Is Close Enough to the Tipping Point to Matter Now

1. Because the loss is self-reinforcing, the forest could cross its tipping point before the damage is obvious.
2. That makes the Amazon a clear example of how a single ecosystem can lose stability once a threshold is passed.