Ecosystem collapse

An ecosystem is a collection of interacting organisms living within a biophysical environment. These systems are never static, meaning they are constantly changing. They rely on stabilizing processes to respond to perturbations, which are disturbances in ecological conditions. These processes help an ecosystem recover from degradation. However, if a disturbance becomes strong enough or fast enough, it can cross a critical threshold. Scientists often call this threshold a tipping point. When this happens, the ecosystem undergoes a collapse. This does not mean all life disappears from the area. Instead, the system loses its defining characteristics and its ecosystem services.

Ecosystem collapse is often described as a transformation of identity. The system loses its original biotic or abiotic features. Biotic features are the living parts, like plants and animals. Abiotic features are the non-living parts, like water or soil. When a collapse occurs, the system is replaced by a novel ecosystem. This new system may have a very different structure and function. In many cases, this change is effectively irreversible. Even if a reversal is possible, it is usually slow and difficult. A system with low resilience might collapse during stable times. It is then replaced by a more resilient system in the biosphere.

Many different drivers can trigger a collapse. Natural disturbances include fires, landslides, flooding, and severe weather. Disease and the invasion of new species can also cause problems. However, human activity has caused a noticeable increase in these disturbances over the last fifty years. Humans can change the chemical balance of environments through pollution. We also cause anthropogenic climate change, which modifies local weather patterns. Habitat destruction and fragmentation are major threats to land and sea systems. For example, overgrazing can cause land degradation. In Southern Europe, proper management of pastoral landscapes can help prevent desertification.

History shows us that these collapses have happened long before humans. During the Carboniferous period, great tropical wetlands called coal forests covered much of Euramerica. These forests featured towering lycopsids, which are a type of large plant. This ecosystem collapsed abruptly due to volcanism and climate change. The climate became cooler and drier, which was bad for the rainforests. This collapse caused many large vascular plants and giant arthropods to go extinct. It also allowed seed-bearing plants and amniotes to take over. We also see evidence of collapse in the fossil record from the Last Glacial Maximum. During this time, the ecosystems of Lake Baikal and Lake Hovsgol collapsed.

Specific historical examples illustrate the scale of these changes. The Aral Sea was once one of the largest lakes in the world. It sat between Kazakhstan and Uzbekistan. Since the 1960s, rivers were diverted for large-scale irrigation. By 1997, the lake had declined to only 10% of its original size. It split into smaller hypersaline lakes, which are lakes with very high salt levels. On Easter Island, the Rapa Nui subtropical broadleaf forests disappeared. This was caused by climate change, overexploitation, and introduced exotic rats. In the ocean, the Grand Banks cod fishery collapsed in the early 1990s. Overfishing reduced the fish populations to just 1% of their historical levels.

Many ecosystems are currently facing extreme risks. The Amazon rainforest is under threat from logging and climate change. Humans have already altered 87% of the oceans and 77% of the land surface. About 30% of global land area is now degraded. The Great Barrier Reef is also in decline due to pollution and climate change. As of 2023, roughly 50% of the coral has been lost. This impacts the 9,000 organisms that rely on the reef for survival. In Utah, the Great Salt Lake has lost over 73% of its water. It has also lost 60% of its surface area since 1850.

Scientists use specific tools to assess these risks. They use generic risk assessment protocols and stochastic simulation models. One important tool is the IUCN Red List of Ecosystems. This list has been in development since 2008. It helps track which ecosystems are at risk of losing their defining features. It is important to act before a species falls below viable population limits. If a population becomes too small, an extinction debt occurs. This means extinction will happen regardless of later actions. To prevent collapse, we must respond to early warning signals before the tipping point is crossed.