High spatial resolution mapping identifies habitat characteristics of the invasive vine Antigonon leptopus on St. Eustatius (Lesser Antilles)

On the Caribbean island of St. Eustatius, Coralita (Antigonon leptopus) is
an aggressive invasive vine posing major biodiversity conservation
concerns.  The generation of distribution maps can address these
conservation concerns by helping to elucidate the drivers of invasion. We
test the use of support vector machines to map the distribution of
Coralita on St. Eustatius at high spatial resolution and use this map to
identify potential landscape and geomorphological factors associated with
Coralita presence. This latter step was performed by comparing
the actual distribution of Coralita patches to a random distribution of
patches. To train the support vector machine algorithm, we used three
vegetation indices and seven texture metrics derived from a 2014
WorldView-2 image. The resulting map shows that Coralita covered 3.18% of
the island in 2014, corresponding to an area of 64 ha. The mapped
distribution was highly accurate, with 93.2% overall accuracy (Coralita
class producer’s accuracy: 76.4%, user’s accuracy: 86.2%). Using this
classification map, we found that Coralita is not randomly distributed
across the landscape, occurring significantly closer to roads and drainage
channels, in areas with higher accumulated moisture, and on flatter
slopes. Coralita was found more often than expected in grasslands,
disturbed forest and urban areas, but was relatively rare in natural
forest. These results highlight the ability of high spatial resolution
data from sensors such as WorldView-2 to produce accurate invasive
species, providing valuable information for predicting current and future
spread risks and for early detection and removal plans.