Impacts of human actions on ecosystems lie at the heart of the discussions of the Anthropocene. The unique biota of the Galápagos Islands is threatened by invasive species, habitat loss and shifted ecological baselines of what is ‘natural’. To investigate the trajectory of modern vegetation change relative to that induced by natural cycles, a paleoecological study was undertaken that compared desert and mesic settings. Sediment cores from the mesic highlands of the inhabited islands of Santa Cruz (Paul’s Bog, 800 m a.s.l.) and San Cristobal (El Junco Crater Lake, 679 m a.s.l.), as well as a core from the uninhabited arid island of Genovesa (Genovesa Crater Lake, 0 m a.s.l.) provided high-resolution fossil pollen records. Vegetation change was documented across periods of climatic extremes associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA), as well as the Last Glacial Maximum (LGM) and the Mid Holocene Dry Event (MHDE). These records provided a reference scale of natural ecosystem responses while the islands were uninhabited (effectively prior to the 1700s). Fossil pollen data during the period of human occupation were contrasted for inhabited and uninhabited islands and compared with modern pollen trap data.
Results/Conclusions
The presence of mesic plant types throughout the LGM, MHDE, MCA and LIA in the highlands supported the idea that high elevation slopes (>700 m) provided microrefugia during periods of drought stress. There were minor oscillations in plant assemblages at all sites in response to Holocene climate change prior to human arrival. Post-1930, upland (inhabited) communities diverged markedly from prior paths, while desertic (uninhabited) communities were unaffected. Comparison of ordinated results of fossil pollen with those from modern pollen traps, outlined the rapid change of the highland habitat to a no-analog system due to land clearing, agriculture and invasive exotic species. Projected increased ENSO intensity would not be unduly worrying for the survival of these terrestrial systems if it were not for the presence of invasive exotic species and human-induced habitat loss. The desertic systems will be stable in response to increasing aridity (La Niña intensification), but would be very vulnerable to invasion by invasive species if mesic conditions (El Niño intensification) predominate. Current eradication procedures, along with parkland preservation and restoration, are expensive, but are presently limited largely to the uplands. Extending those measures to the much greater area of lowlands will be a huge challenge.