Mangrove forest encroachment by Nypa frutican, Derris trifoliata, and Acanthus spp. in Segara Anakan Lagoon

Abstract

Based on phytosociological methods and land cover change analysis, previous studies in Segara Anakan Lagoon (SAL) indicated the spreading of mangrove species living in the forest margin ecotone into the forest interior, encroaching the other mangrove communities. This current study aims to quantify the spreading pattern of those mangrove species, assess the effect of the spreading of those mangrove species to the other mangrove communities, and identify the location of the spreading pattern relative to the newly emerged islands. The spreading pattern can be demonstrated by analyzing landscape structures quantified by landscape metrics. It was done using multi-temporal mangrove maps, representing the changes in mangrove communities over four periods with a decade interval. The landscape metrics used were the aggregation index, the size of community patches, and the distance between the patches. These metrics were extracted by using landscape metrics, an R package. The changes in the metrics over time were compared namely 1990, 2000, 2010, and 2020. The results showed that the small patches of the forest margin species became more aggregated into a larger patch, while the mangrove forests became more fragmented. This condition occurred most in the west part of SAL where the new islands emerged.