Eppinga, M.B.

Effective management strategies are needed to control expansion of invasive alien plant species and attenuate economic and ecological impacts. While previous theoretical studies have assessed optimal control strategies that balance economic costs and ecological benefits, less attention has been paid to the ways in which the spatial characteristics of individual patches may mediate the effectiveness of management strategies. We developed a spatially explicit cellular automaton model for invasive species spread, and compared the effectiveness of seven control strategies. These control strategies used different criteria to prioritize the removal of invasive species patches from the landscape. The different criteria were related to patch size, patch geometry, and patch position within the landscape. Effectiveness of strategies was assessed for both seed dispersing and clonally expanding plant species. We found that, for seed-dispersing species, removal of small patches and removal of patches that are isolated within the landscape comprised relatively effective control strategies. For clonally expanding species, removal of patches based on their degree of isolation and their geometrical properties comprised relatively effective control strategies. Subsequently, we parameterized the model to mimic the observed spatial distribution of the invasive species Antigonon leptopus on St. Eustatius (northern Caribbean). This species expands clonally and also disperses via seeds, and model simulations showed that removal strategies focusing on smaller patches that are more isolated in the landscape would be most effective and could increase the effectiveness of a 10-yr control strategy by 30–90%, as compared to random removal of patches. Our study emphasizes the potential for invasive plant species management to utilize recent advances in remote sensing, which enable mapping of invasive species at the high spatial resolution needed to quantify patch geometries. The presented results highlight how this spatial information can be used in the design of more effective invasive species control strategies

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.

Student Report

This research examined the current situation of pollution on the shores of Aruba, with a particular emphasis on plastic debris. It focused on the systematic comparison of litter concentration between the north coast and the south coast. Beach litter assessments were performed in order to address the following questions: What is the overall pollution level of Aruba’s shoreline? Is plastic the most abundant material found? If so is there a significant difference between plastic debris and other materials collected? Is there a significant difference in macro- and meso debris abundancy between the north coast (foreign origin) and the south coast (local origin)? Is there a difference in the trash abundancy found during the 2nd round of assessments from the amount of trash found in the 1st round of assessments? Is there a difference in trash abundancy in respect to distance from the waterfront? The main focus on this research is placed on macro-debris and meso-debris. A nice effect of this research has been that in the process of collecting data, all beaches studied were cleaned.

Research Aim

We compared the following two methods for creating a map of the current distribution of Coralita:

1) Observer/Expert-based ground survey map, and
2) Semi-automated vegetation classi cation using satellite imagery.