Demak district, Central Java, Indonesia

lat (N): -06°53'14.20"

lon (E): 110°30'27.15"

We studied the natural and assisted processes of mangrove expansion in Demak Regency, Indonesia. We studied expansion in both landward direction (i.e. the aquaculture pond zone) and seaward direction (i.e. the coastal zone) from the current coastline in the project area (the old coastal road). The pond zone in the study area is characterized by active traditional aquaculture ponds, and drowning abandoned aquaculture ponds towards the coast. The coastal zone in the study is defined as the area ranging from MHW to MLW (the maximum depth at which the EMR-dams are placed), which ranges roughly 0 to 600 meters from the shoreline. In order to shed light on best practices for mangrove recovery, we aimed to answer four research questions: : 1) how has mangrove expansion occurred in seaward and landward direction in the past, mainly through planting or mainly through natural expansion?; 2) Can hydrological EMR measures (e.g. sluice gate management) induce natural mangrove recovery in the pond zone (i.e. would enough propagules be available at landward sites if hydrological connectivity to target ponds was increased)?; 3) Can wave-reducing and sediment-trapping measures (EMR-dams) induce natural mangrove recovery at challenging sites in the coastal zone by increasing the chances of a) new seedling establishment or b) survival of established seedlings? and; 4) Can mangrove planting in combination with EMR-dams accelerate mangrove recovery at challenging coastal sites?

We addressed research questions 1-4 in the manuscript, using the following correspondingly numbered methods. 1) GIS monitoring of natural and planted mangrove vegetation in the coastal zone and pond zone using time series of satellite images (Q1_GIS_data & Q1_forest_structure). 2) A year-round propagule monitoring campaign seawards and landwards of the old coastal road (Q2_EMR-hydrology_propagules) to assess the potential for natural mangrove colonization in the active pond zone if maximal EMR-hydrology would be applied. 3) A field experiment at multiple coastal sites with different wave exposure conditions to understand the effect of EMR-dams on mangrove recruitment and seedling survival (Q3_EMR-dams_natural_seedling_establishment_mon & Q3_EMR-dams_seedling_survival_exp). Finally, 4) a field experiment to study the effect of mangrove planting in combination with EMR-dams on seedling growth and survival (Q4_EMR-and-planting)