Mapping invasion and eradication of feral goats in the Alcedo region of Isabela Island, Galapagos

We conducted a time series analysis using the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data product over the Alcedo volcano region of Isabela Island in the Galápagos to determine vegetation changes before, during, and after a feral goat invasion and eradication project. Enhanced vegetation index (EVI) values for the Alcedo region of Isabela Island were analysed from 2000 to 2010 with respect to the presence of a large population of goats that was eradicated between 2004 and 2006. This study finds large-scale, seasonal vegetation pattern changes between 2000 and 2005, and 2005 and 2010. Statistically significant EVI decreases prior to and during eradication in zones where goats were present in high numbers and increases following eradication in zones with lower goat density are found. EVI appears to have changed little over the entire study period, though earlier imagery would likely reveal stronger positive post-eradication trends. Because EVI primarily reveals greenness and little about vegetation composition and structure, we find that long-term in situ vegetation monitoring is also needed to obtain a meaningful assessment of the effects of invasion and eradication at the species level.