The impact of hurricanes Irma and Maria on the forest ecosystems of Saba and St. Eustatius, northern Caribbean

In September 2017, Irma became the first recorded category 5 hurricane to hit the Caribbean Windward Islands. The second category 5, Maria, followed two weeks later. In November 2017, we assessed the structural impact of this disturbance on highly valued Caribbean forest ecosystems. We recorded the status of 935 tree stems on Saba and St. Eustatius in stands at different elevations. Tree damage was substantial on both islands, with 93 percent of stems being defoliated, 84 percent having lost primary and/or secondary branches and 36 percent having structural stem damage. Average tree mortality was 18 percent, with mortality being nearly twice as high on St. Eustatius than on Saba. Surprisingly, we found that neither individual stem size nor community size distributions mediated the forests’response to the hurricanes. Our results show that these hurricanes comprised a density-independent disturbance, which may become more common as the frequency of strong hurricanes is projected to increase.

Key words: defoliation; density-independent disturbance; forest community structure; island ecology; tree mortality; tree size distribution; tropical cyclones.

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