Effects of different management regimes on mangrove ecosystem services in Java, Indonesia

Abstract

Indonesia is home to the largest area of mangrove forests in the world. Urban expansion, aquaculture farms, oil-palm plantations and timber extraction have caused an estimated decline of about 1.2 million hectares of Indonesia’s mangroves since the 1980’s, and currently only 3 million hectares remain. The major cause of mangrove conversion is aquaculture expansion. Assessing global values of mangrove ecosystem services has been useful to draw attention to the value of mangroves for humans, but these values cannot simply be extrapolated to specific areas and as such cannot inform management. Most valuation studies of mangrove ecosystem services talk about ‘mangroves’ that are in reality subject to widely different management regimes and as such are difficult to compare. This is one of the explanations for the wide ranges in values. Making sound decisions on management of (former) mangrove systems requires knowledge on the impact of management on the provisioning of all relevant ecosystem services. However, mangrove ecosystem services provision is rarely directly linked to management. Our report intends to fill this gap. This report reviews the current state of mangrove ecosystem services and relates their provision to different mangrove management regimes in Java, Indonesia. Based on our findings, decision makers and managers should be able to explore the crucial elements of optimal coastal management, by considering which management purpose will result in the provision of which bundle of ecosystem services. More specifically, this report details which ecosystem properties underpin ecosystem service provision, and describes state and performance indicators for seven ecosystem services: food, raw materials, coastal protection, carbon sequestration, water purification, nursery for fish and shrimp, and nature-based recreation. Mangrove tree age (and related height, diameter, root length, species richness and structural complexity) were found crucial for all seven ecosystem services. This report’s typology of management regimes is new to science, in that it develops a full range of ten specific management characteristics and indicators, and eight ecological characteristics. The typology used the local variation in legislation and management activities. Moreover, the easily measurable ecological characteristics served to both verify management regimes on location and to quantify ecosystem services. A rapid field assessment was conducted to verify the management regimes. This study’s typology is firmly rooted in scientific literature and Javanese legislation, and enables a consistent indicator-based comparison of ecosystem service provision for multiple management regimes. A further novelty in the typology is the inclusion of silvo-fishery, eco-certified aquaculture and the comparison between natural and converted mangrove systems (i.e. aquaculture). Our review yielded nine different silvo-fishery models that vary widely in their management and ecological characteristics and, therefore, the ability to provide ecosystem services. Comparing mangrove management regimes to aquaculture regimes enables decision makers to compare trade-offs for the first time. Natural mangroves were found to score highest for all ecosystem services except food. Conversely, mangroves converted to aquaculture received the maximum score for food production, but this coincides with low or even negative provision of all other ecosystem services. Such disservices are high carbon emissions, wave height increase (increasing flood risk) and water pollution. Nevertheless, fishery yields in more natural mangrove systems compare in magnitude (in terms of kg/ha/yr) to aquaculture, while also providing additional benefits. However, this may entail a wide variety of species in the case of mangroves while aquaculture delivers specific target species. Mangrove plantations and silvo-fisheries, which combine rehabilitation with raw materials and shrimp provision, respectively, also outscore mangroves converted for aquaculture. This clearly indicates the merits of restoring mangroves formerly used for intensive land use.