Discovering spatio-temporal dependencies in mangrove forest change: evidence from northwestern Asian communities

The Iranian southern intertidal ecosystems are colonized by mangrove forests (mostly Avicennia marina) and presented a notable mangrove area expansion over the past decades. To discover its spatio-temporal dependencies, five mangrove forests were studied along a coastline of more than 1,200 km. Cloud-free Landsat images were processed using a temporal median filter to produce one representative Landsat image for each year from 1988 to 2020. The images were categorized into mangrove and non-mangrove classes using an object-based algorithm and visual post-classification. A consistent mangrove area expansion was observed across all regions, which regressed linearly against time with an adjusted R-2 range of 0.914-0.955 (p < 0.01). The expansions were also found to be highly significantly similar (0.182 < p < 0.822) using the t-test applied on the slope of region-specific regression models. Three spatial metrics of infilling, edge-expansion, and outlying were developed to investigate the spatial pattern of expansions. Results showed the dominance of the edge-expansion pattern across all regions (53-78% of the expansions), which was attributed to the better establishment of propagules near and under the canopy of parent trees. The outlying pattern (11-22%) was related to mangrove colonization along the inland creeks.