D4.2.1—Stability as a property of natural ecosystems

Key Points:

• Stability: An ecosystem is considered stable if it can persist indefinitely due to the mechanisms operating within it.
• Examples of Stable Ecosystems:
  • The Daintree Rainforest in Australia, estimated to be 180 million years old, contains species from ancient plant families, highlighting its long-term stability.
  • The Borneo Lowland Rainforest, though facing recent losses, has existed for about 140 million years.
  • The Namib Desert in Southern Africa, with its unique adaptations to arid conditions, has remained relatively intact and stable for an estimated 55-80 million years.

Fragility of Ecosystem Stability:

• While these examples demonstrate long-term stability, it’s crucial to remember that the mechanisms sustaining ecosystems are fragile.
• Even seemingly minor perturbations can disrupt the balance and cause changes within the ecosystem.

In essence, the image emphasizes that while some ecosystems have shown remarkable resilience over long periods, their stability is not guaranteed and can be easily compromised by various factors.

D4.2.2—Requirements for stability in ecosystems

There must be a steady supply of energy entering the system and nutrient cycles should not have significant leakages, meaning nutrients should remain within the ecosystem. Secondly, individual species, especially keystone species, must have high genetic diversity. This diversity allows populations to adapt and survive environmental selection pressures.

Several types of environmental change can disrupt ecosystem stability. Harvesting and removal of materials from the environment can disrupt nutrient cycles. Erosion can result in the loss of nutrients. Eutrophication, the nutrient enrichment of a body of water, can cause imbalances in the ecosystem. Selective removal of species, such as through epidemics or poaching, can also disrupt ecosystem structure, particularly if a keystone species is removed.

If the genetic diversity of a population drops below a certain threshold, it becomes less resilient. High biodiversity tends to be associated with stable ecosystems because it provides a robust community structure.

The relationship between climate and ecosystem type is crucial. For example, high rainfall allows for the development of forests, while moderate rainfall supports grasslands. Prolonged changes in precipitation due to climate change can cause ecosystem disruption. There are concerns that changes in rainfall patterns could lead to a tipping point in the Amazon rainforest, causing it to transition from forest to grassland.

D4.2.3—Deforestation of Amazon rainforest as an example of a possible tipping point in ecosystem stability

Key Points:

• Tipping Points: When an ecosystem experiences enough disturbance, it can reach a tipping point. This is a critical threshold where the system shifts abruptly and irreversibly from one state to another.
• Amazon Rainforest as an Example: The vast Amazon rainforest, despite its resilience, could be vulnerable to tipping points. Deforestation, caused by logging and other human activities, can lead to a decrease in forest cover. This reduction in forest cover decreases the amount of transpiration from plants, leading to a decrease in rainfall.
• Positive Feedback Loop: Lower rainfall further reduces forest cover, creating a positive feedback loop where one change amplifies another. This cycle can lead to a significant loss of forest and potentially trigger a shift from a stable forest ecosystem to a stable grassland ecosystem over large areas.

The table in the image shows the area of primary Amazon forest in three Brazilian states in 2001 and 2020. The calculation shows a significant percentage change in forest cover in Maranhão, highlighting the vulnerability of this ecosystem to deforestation.