Research has shed new light on the impact of humans on islands’ biodiversity. The findings show how human colonization altered forest across the islands of Macaronesia including the loss of landscape authenticity.
Oceanic island ecosystems are unique and often contain species that are limited to specific islands or island groups. They are also vulnerable to disturbance.
To provide a timeline of how humans changed these territories over the centuries, a team led by the University of Southampton, studied multiple indicators of landscape change buried in sediments deposited over periods of up to ten thousand years. The team examined samples including fossilised pollen, spores of dung-decomposing fungi that indicate the presence of sizable herbivores, fragments of charcoal indicating use of fires as well as the composition of the sediment itself.
Their findings, published in the journal PNAS, showed that while forests on the islands changed naturally over thousands of years, human arrival on the Canary Islands, around 2000 years ago, and Cabo Verde, 500 years ago, led to an increase in fires and rates of soil erosion, the latter associated with the introduction of non-native livestock such as goats and pigs. One particular type of forest typical of Macaronesia, known as thermophilous forest, and characterized by iconic species such as the dragon tree, was most impacted. In Cabo Verde, data suggest that island vegetation is suffering a process of homogenisation due to human pressures and the uniqueness of individual island ecosystems is being lost.
The team also found that the first use of Canarian forests by aboriginal settlers appeared to have limited impact on the native vegetation, such as the laurel forest of the island of la Gomera. This is possibly due to smaller populations, typically interacting and trading with other nearby islands. By contrast, colonial era settlers who arrived in the 15th Century, adopted much more aggressive acts of deforestation, change in land use, and introduction of non-native species due to much wider trading networks which had a much greater affect.
Dr Sandra Nogué Bosch, Lecturer in Palaeoenvironmental Science at the University of Southampton said, “Contrasting the long-term history of different ecosystems, such as island forests, helps put in perspective the transformative force that humankind is unleashing all around the world.”
