The ecological impact of oceanic island colonization – a palaeoecological perspective from the Azores
Aim In many cases, human colonization drastically modified the ecosystems of remote oceanic islands before scientists arrived to document the changes. Palaeoecological records before and after human colonization provide insights into the original ecosystems and an assessment of subsequent human impact. We used pollen analysis to compare the impact of 15th century colonization of the Azores with that of natural disturbances such as volcanic eruptions and climate changes.
Location Azores archipelago, Atlantic Ocean.
Methods Sediment records from three highland sites in the Azores (on the islands of Pico and Flores) were dated radiometrically and analysed palynologically. Pollen taxa were classified as native, endemic or introduced based on comparison with flora lists. Data were statistically zoned and temporal trends identified using detrended correspondence analysis.
Results Human colonization of the Azores resulted in rapid, widespread, persistent vegetation changes on a scale unprecedented in the last 2700 years, detectable through the decline of dominant trees, the spread of grasses and fire‐tolerant species, the introduction of exotic plants, evidence for grazing and fire, and changes to soils and moisture availability. During the same period, volcanic eruptions appear to have had more localized impacts on the vegetation, lasting 500–1000 years and favouring endemic taxa. The effect of late Holocene climatic changes on the highland vegetation of the Azores seems to have been minor. Palaeoecological data indicate that at least two plant species went extinct on Pico after human colonization and that some plants regarded as introduced were almost certainly part of the original flora of the islands. Despite a consistent signal of human impact, compositional differences between Juniperus brevifolia communities on Pico and Flores remained after colonization.
Main conclusions Human colonization had a greater impact on the pristine vegetation of Pico and Flores than climatic changes and volcanic activity during recent millennia. The similarity between post‐colonization changes on the Azores and other oceanic islands suggests a consistent pattern and scale to historical‐era human impact on otherwise pristine ecosystems. These characteristics could be used to further elaborate biogeographical theory and direct conservation efforts towards species that appear most susceptible to human activity.
Document Type: Research Article
Affiliations: 1: Centre for Marine and Environmental Research, University of the Algarve, 8005-139 Faro, Portugal 2: Institute for Plant Sciences and Oeschger Centre for Climate Change Research, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland 3: Department of Geology, Utah State University, 4505 Old Main Hill, Logan, UT 84322, USA 4: Department of Earth and Ecosystem Sciences, Division of Geology – Quaternary Sciences, Lund University, Sölvegatan 12, 223-62 Lund, Sweden
Publication date: 01 June 2012