For as long as humans have existed on the planet we have been impacting our surrounding environment. We began by chopping down trees to build homes and fires, foraging for plants, and hunting for animals within our landscape for food. We quickly advanced toward manipulating the land to serve our purposes through varying methods of agriculture, travel, and increased urbanization and commercial networks. At this point in Earth’s physical history, our impact on the environment is so substantial that many researchers believe “pristine nature,” or ecosystems untouched by human intervention, no longer exist. This era of human dominance has been coined the ‘Anthropocene Era’ by some scientists, who argue that Earth is being overwhelmingly defined by the actions of humans above natural processes. But how can we truly understand in what way and even if humans can impact nature in such a manner that creates irreversible changes, as nature, itself, is a resilient system?
The Importance of Island Ecosystems
To examine this question, an international team of researchers turned to our most remote oceanic islands. These islands were colonized within the past 3,000 years; therefore, they provide opportunities to analyze what an ecological transition from prehuman to human dominated ecosystems looked like and the degree in which human impacts can modify an ecological system long-term. Islands are preferred over continents since it’s harder to identify what a prehuman ecosystem may have looked on a continent, not only because humans first settled within these places a much longer time ago, but also that continents heavily vary by region.
The researchers utilized fossil pollen extracted from the sediment layers which was then dated and identified to investigate how the vegetation on 27 islands in different regions around the world have developed over the last 5,000 years. They found that almost everywhere they studied, the arrival of humans has triggered an accelerated rate of change in plant species composition. This change was observed on 24 of 27 islands independently of current and past island area, latitude, isolation, and elevation of the sampling site.
This dynamic was particularly pronounced on islands colonized within the last 1,500 years. In islands that were settled more recently, like the Poor Knights archipelago in New Zealand (13th century) and the Galápagos Islands (16th century), there was a steeper increase in the rate of change than on islands where humans arrived >1500 years ago, such as New Caledonia and Fiji. Researchers suggested that this most likely because introduced species, land use practices, and technology deployed by later settlers was more elaborate/transformative than those of earlier settlers.
Time Can Help Ecosystems Heal Somewhat
Additionally, they found that the ecological legacies of human arrival on islands may persist for centuries and are often irreversible. For example, the Tawhiti Rahi island within the Poor Knights archipelago is currently uninhabited. After initial arrival by Polynesians in the 13th century, the island’s forest cover was cleared by fire for human habitation and gardens. In 1820 the islands were declared protected, and humans were no longer permitted to settle there. The island became totally reforested within 150 years, but its current composition is completely different from that of the prehuman period.
These findings indicate that these human-affected ecosystems are neither similar to nor likely to return to the dynamic baselines observed before human arrival. Even though ecosystem change can also be driven by a number of natural factors such as earthquakes, volcanic eruptions, extreme weather and changing sea levels, this study shows that disturbance caused by humans surpasses all of these events and are long-lasting components of these systems. These disturbances are distinctive and produce different effects on the surrounding ecosystem than natural disturbances in the prehuman period, when island ecosystems often recovered rapidly to pre-disturbance states.
In our goals to protect and conserve biodiversity within our ecosystems and mitigate the risks posed by climate change, this study provides great insight on how to move forward. The researchers advise that conservation strategies must account for the long-term impact of humans and the degree to which ecological changes today differ from prehuman times. Our ecosystems are resilient, but with the current increased pressure we are putting on these systems, more ambitious changes to ensure the protection of ecosystem services and biodiversity is needed. These goals are still within reach, only if we can act on them before more irreversible harm is done.
article by Tatiana Eaves
- Galapagos Islands: Photo by Annie Spratt on Unsplash
- Poor Knights Archipelago: Peter Southwood, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Pollen: Photo by Alex Jones on Unsplash