Eyes from the sky: Application of satellite-based indices to assess vegetation casualty on Grand Bahama Island one year post-Hurricane Dorian

Abstract

In the last two decades, major hurricanes have devastated the forest landscape of Grand Bahama. To capture the extent of the pine forest loss on Grand Bahama, we used satellite-based indices (NDVI, NDMI, and NBR) from Landsat and Sentinel-2 images and the support vector machine algorithm to estimate vegetation casualty pre- and post-Hurricane Dorian. We estimated that from 2004 to 2020, Grand Bahama lost 90.9% and 58.6% of its pine and mangrove forests, respectively. In the 15 years before Hurricane Dorian (2004–2019), stressors that included three major hurricanes (Hurricane Jeanne, Frances, and Wilma) resulted in a 44.5% (246.0 km2) loss of the pine forest vegetation on the island. Later, Hurricane Dorian, a Category 5 tropical cyclone, made landfall in Grand Bahama in 2019 and resulted in further loss of pine vegetation (46.3% of the original vegetation [256.1 km2]) and more than half of the mangrove forests after flooding 67.0% (919.3 km2) of the island. Although mean NDVI and NDMI began to exhibit pre-hurricane seasonal patterns half a year after Hurricane Dorian struck, their values remained abated one year following the storm.To account for the effects of seasonal fires, we evaluated pine vegetation for evidence of forest fires during the dry and wet cycles of the year from 2018 to 2020. We found that seasonal forest fires temporarily reduced the pine forest understory vegetation but minimally impacted the pine vegetation between the reported years. The total area of forest impacted by fires was 11.3%. These low-intensity fires burned 67.3 km2 (22.5%; 2018), 31.8 km2 (10.6%; 2019), and 21.3 km2 (7.1%; 2020) of the intact mature pine forest (299.5 km2) pre- and immediately post-Hurricane Dorian. Even though we were able to detect and map areas of pine regeneration in previously hurricane-killed pine forest, Hurricane Dorian eliminated these young pines. Overall, Grand Bahama experience a significant loss of its forest after the major hurricanes of 2004, 2005, and 2019. This research reports new findings on hurricane-related damage to the pine forest ecosystem in Grand Bahama, providing valuable information regarding the ecological consequences of severe hurricanes on these types of forests.