Question

When parts of the Amazonian forest are clear-cut: a. True/False: Nutrient export is likely to decline. b. True/False: Atmospheric \(\mathrm{CO}_{2}\) is likely to decline. c. True/False: Soil moisture is likely to decline. d. True/False: Species diversity is likely to decline. Explain your reasoning for each of your answers.

Short answer

a. False. Nutrient export is likely to increase due to the reduction in the amount of nutrients being absorbed by plants and an increase in nutrient wash-off into nearby rivers and streams. b. False. Atmospheric \(\mathrm{CO}_{2}\) is likely to increase because of the decrease in the number of trees that can absorb it and the release of stored carbon due to decomposing plant matter and soil disturbance. c. True. Soil moisture is likely to decline because clear-cutting reduces the rate of transpiration and increases surface runoff. d. True. Species diversity is likely to decline due to the loss of habitat and the inability of some species to relocate or find necessary resources and shelter.

Step-by-step solution

Answer (a)

Nutrient export is likely to decline. False. When parts of the Amazonian forest are clear-cut, the trees, plants, and other organic matter are removed. This leads to the reduction in the amount of nutrients, such as nitrogen and phosphorus, being absorbed by the plants. As a result, these nutrients may be washed away into nearby rivers and streams, increasing the nutrient export.

Answer (b)

Atmospheric \(\mathrm{CO}_{2}\) is likely to decline. False. Trees and plants absorb \(\mathrm{CO}_{2}\) through photosynthesis and release oxygen as a byproduct. When trees are removed through clear-cutting, there is a decrease in the number of trees and plants that can take in \(\mathrm{CO}_{2}\). Additionally, the decomposing plant matter and increased soil disturbance can release stored carbon back into the atmosphere. Consequently, atmospheric \(\mathrm{CO}_{2}\) levels are likely to increase, not decline.

Answer (c)

Soil moisture is likely to decline. True. Trees and plants in the Amazonian forest play an essential role in maintaining soil moisture, as they absorb water from the soil and release it back into the atmosphere through a process called transpiration. Clear-cutting removes a significant number of trees and plants, reducing the rate of transpiration. This results in an increase in surface runoff, leading to a decrease in soil moisture.

Answer (d)

Species diversity is likely to decline. True. The Amazonian forest is known for its high species diversity, providing habitats for various plants, animals, insects, and microorganisms. Clear-cutting leads to the loss of habitat, causing many species to either relocate or face extinction due to the lack of available resources and shelter. As a result, species diversity is likely to decline in the clear-cut areas.

Key concepts

Nutrient Export in Ecosystems

Clear-cutting of forests has a significant impact on nutrient cycles within ecosystems. Typically, forests like the Amazon act as nutrient sinks, with plants and trees absorbing elements such as nitrogen and phosphorus from the soil to sustain their growth. When trees are cut down, these nutrients are no longer utilized by the forest vegetation and can be leached out of the soil by rainfall.

• The root systems of trees and plants, which bind soil and nutrients, are lost.
• Without uptake by vegetation, nutrients can be more easily washed away into waterways, leading to an increase in nutrient export.
• This process can lead to nutrient depletion in the soil and negatively affect water quality in adjacent ecosystems.

Rather than declining, the nutrient export from such ecosystems may actually increase with deforestation, affecting the fertility of the land and the health of nearby aquatic environments.

Atmospheric CO2 Levels

Forests, and particularly the vast Amazonian forests, are vital in regulating the amount of carbon dioxide (CO2) in the atmosphere. Trees and plants absorb CO2 during photosynthesis and store carbon in their biomass. This process reduces the amount of greenhouse gases in the atmosphere and mitigates climate change.

• Clear-cutting interrupts this carbon uptake by reducing the number of trees.
• Decomposition of felled trees and disturbance of soil releases stored carbon, further increasing atmospheric CO2 levels.
• With fewer trees to absorb CO2, the greenhouse effect can intensify, leading to a warming of the Earth's climate.

Therefore, deforestation contributes to an increase in atmospheric CO2 levels, which has major implications for global warming and climate patterns.

Soil Moisture and Transpiration

Trees and plants are integral to the water cycle within forest ecosystems due to their role in transpiration. Transpiration is the process by which moisture is carried from the soil through the plants and released into the atmosphere. It contributes significantly to the humidity of the air and helps to maintain soil moisture. Areas without sufficient tree cover often see a radical change in this balance.

• Clear-cut areas have reduced transpiration, leading to lower soil moisture levels.
• Increased surface runoff can occur as a result, meaning more water flows away rather than infiltrating the soil.
• The change in soil moisture can have cascading effects on the local microclimate and the survivability of remaining vegetation.

As trees are removed, the forest's ability to maintain soil moisture diminishes, potentially leading to drier soils and altering the local climate.

Species Diversity and Habitat Loss

The Amazonian forest is one of the most biodiverse regions on Earth, supporting countless species of flora and fauna. When areas of this forest are cleared, the effects on biodiversity are devastating.

• Habitats are destroyed, leading to loss of shelter and resources for countless species.
• Species may become endangered or extinct if they cannot adapt to the changes or relocate to new habitats.
• Clear-cutting disrupts the ecological balance, often favoring invasive species over native ones, further reducing biodiversity.

The decline in species diversity that comes with habitat loss from deforestation goes beyond the loss of individual species; it represents the loss of complex interactions within an ecosystem that are essential for its health and resilience.