Protecting large animals such as elephants, rhinos and whales, and large trees like the sequoias, has a disproportionate positive impact on the health of the planet and resilience to climate change, finds new research.
Habitat loss, hunting, logging and climate change have put many of the world's most charismatic species at risk. A new study has found that not only are larger plants and animals at higher risk of extinction, but their loss would fundamentally degrade life on earth.
The paper, published in Nature Communications, develops a new ecological theory to explain why large animals and plants matter so much and why they are particularly vulnerable. It found that ecosystems with large plants and animals are generally more productive – meaning they grow faster and support more life. They also provide more vital services for human life, such as the removal of CO2 from the atmosphere. However, these large organisms are more susceptible to human pressures and climate change, and take longer to recover from shocks. Ecosystems that are missing large animals and trees are less resilient to change, less predictable and can collapse more easily.
The findings help to answer an ongoing debate about where to channel limited conservation resources. While charismatic species such as the tiger or redwood trees have historically been most appealing and therefore effective at pulling in donations, some scientists worried that this focus on a certain subset of plants and animals could be coming at the cost of protecting other, less well-loved species.
"This research shows there are fundamental scientific principles that explain why large animals and trees matter for the health and integrity of all life on Earth", said Prof Brian Enquist of the University of Arizona, lead author of the paper. "Protecting big, charismatic species does have an umbrella effect to protect the wider ecosystem and everything that lives in it."
The paper uses computer simulations to compare the state of the natural world in the Pleistocene period (before human-caused extinctions began), the present day, and a future world in which all large plants and animals had gone extinct. It found that the continued loss of large animals alone would lead to a 44% reduction in the total amount of wild animal biomass on the planet. It would also lead to a 92% reduction in soil fertility, which underpins the ability of the earth to grow plants and sustain life.
A key reason for these results lies with the transport of nutrients. When large animals eat in one location and defecate or urinate in another, they transport nutrients, often moving them from nutrient-rich areas to other, less fertile, parts of the land and oceans. The research also highlighted that forests with larger trees disproportionately store more biomass carbon and are more productive.
"For hundreds of millions of years, Earth has been a planet of giants. In the last few thousand years, these large animals and plants have been whittled away, and this process continues today," commented Prof Yadvinder Malhi, Leader of the Ecosystems Group at the Environmental Change Institute, University of Oxford. "Our paper shows why this loss of these giants matters for the very fabric of life on Earth, and why we must do everything possible to protect and restore them."
The research was carried out by researchers at the University of Arizona, the Santa Fe Institute, Northern Arizona University, the UN Environment Programme World Conservation Monitoring Centre and the University of Oxford.