Ecosystem services of urban mangrovesMangrove forests have long been the victims of urbanisation. Yet they once covered more than three-quarters of the world’s tropical coastlines, and provide vital ecosystem services, including gigantic carbon storage. Against a global trend of rapid loss of mangrove forests, causing massive greenhouse gas emissions, Brisbane’s mangrove protection is a model of conservation, in a challenging setting of urbanisation.
Keywords: mangrove forests, ecosystem services, carbon storage, urbanisation, coastal development
Brisbane is located in a setting of extensive mangrove forests. These provide a large range of ecosystem services, including very high carbon storage. But the mangrove forests compete for space against urbanisation. To preserve ecosystem services and reduce ecological footprints, Brisbane and the Queensland region use multi-dimensional planning. Success has come by integrating environmental, social, economic and political perspectives (see also Berlin and Melbourne).
Urban Mangrove Management Strategies (UMMS) are the result of work by the Queensland Department of Primary Industries and Fisheries (DPI&F) and local governments. It has helped Queensland buck the global trend of rapid loss of mangrove forests. An estimated 30-50% of the total areal extent has been lost in just 50 years, due to coastal development, aquaculture and over-harvesting.
Mangroves' ecosystem services
Mangrove forests are extremely productive ecosystems located in the transition zone between terrestrial and marine ecosystems. They provide a large set of benefits: carbon storage, shoreline protection against erosion and storms, nutrient fixation, deltaic development, vital support for fisheries, timber and honey production, habitat for mammals, birds, reptiles, fish, epiphytes and invertebrates, and tourism (see also Abbotsford and New Orleans).
In view of climate change, possibly most important is the extremely large carbon storage of mangrove forests. Findings published in Nature Geoscience in 2011 by Donato et al. put mangroves among the most carbon-rich forests in the tropics, averaging 1,023 metric tons carbon per hectare. Deforestation of mangroves therefore may be generating 10% of all the emissions from deforestation globally while only accounting for 0.7% of tropical forest area.
Coastal kidneys and food sources
Mangrove forests are also described as “coastal kidneys”. They filter catchment runoff, particularly sediments and nutrients, thereby supporting clearer and cleaner water that is important for coral reef health and seagrass meadows. Pollution is also filtered, including heavy metals and agricultural chemicals.
Food production is another vital service. Three-quarters of all fish caught in Queensland directly use mangroves or depend on food chains that depend on mangrove forests. The contribution of mangrove habitats to the commercial fishery production is estimated at $250M annually. Their contribution to recreational fishing is about $50M per year.
Challenges and threats
Brisbane is Australia's third-largest city and marked by high population growth. This has brought development pressures primarily along the coast and waterways. There is popular demand for river views and pressure to develop maritime infrastructure, like marinas, ports, jetties and boat ramps. These put huge pressure on mangrove stands. Other pressures are associated with severe drought conditions in Queensland, and the wide-ranging effects of climate change, e.g. sea level rise. There is high concern over unprecedented root decomposition and sediment collapse observed in Queensland's mangrove areas.
Broader ecosystem approaches
The protection of mangroves and other marine ecosystems has moved from single-focus regulation to broader ecosystem approaches and strategic management. This has followed the broadening of community focus, from single issues like timber harvesting to whole ecosystem views. In response to the problem of diverging objectives, an Urban Mangrove Management Workshop was convened in 2004 by Queensland's DPI&F to bring together a diverse stakeholder and expert network, e.g. municipal councils, fisheries staff, mangrove/riparian experts. Out of this emerged Urban Mangrove Management Strategies (UMMS). There are a range of cited benefits from these strategic approaches. These include: creating shared understandings of the social, economic and environmental values, providing a consistent framework for planning, enabling innovative techniques, and reducing the costs of assessments and planning.
Strategic approaches adopted by the Bundaberg and Brisbane City Councils have involved:
- developing mangrove management categories
- bank vegetation mapping and auditing of bank condition
- key stakeholder consultation
- drafting an urban mangrove management strategy
- joint evaluation with DPI&F every 12 months.
Australian Government Department of Sustainability, Environment, Water, Population and Communities, 2006, “2004 Mangrove Mapping of Australia Brisbane”
John Beumer, Dawn Couchman, David Sully, Fisheries Queensland, DEEDI, Brisbane, Queensland, “Planning for uncertainty - Implications of SLR on marine plant communities on the east coast of Queensland”, Coastal Research Forum March 2011, Department of Employment, Economic Development and Innovation, http://www.seachangetaskforce.org.au/Conference2011/DrJohnBeumer.pdf
Dawn Couchman, Chris Lupton, John Beumer, John McDougall, Alan Barton, 2007, “Benefits of urban mangrove management strategies for riverine foreshores”, Queensland Coastal Conference,
Daniel C Donato, J Boone Kauffman, Daniel Murdiyarso, Sofyan Kurnianto, Melanie Stidham, Markku Kanninen, 2011, “Mangroves among the most carbon-rich forests in the tropics”, Nature Geoscience 4, 293-297
J.M. Knighta, P.E.R. Dalea, R.J.K. Dunnd, G.J. Broadbente, C.J. Lemckerta, ”Patterns of tidal flooding within a mangrove forest: Coombabah Lake, Southeast Queensland, Australia”, Estuarine, Coastal and Shelf Science, Volume 76, Issue 3, 10 February 2008, Pages 580-593
Mangrove Watch (Burnett-Mary Region), 2010, “Fact sheet & information”, http://www.mangrovewatch.org.au/images/brochure.pdf
State of Queensland Department of Environment and Resource Management, 2011, “Mangroves”, http://www.epa.qld.gov.au/wetlandinfo/site/factsfigures/FloraAndFauna/Flora/mangroves.html
WWF, n.d., “Blue Planet: Mangrove Forests”, http://wwf.panda.org/about_our_earth/blue_planet/coasts/mangroves/
WWF, n.d., “Mangrove Importance”, http://wwf.panda.org/about_our_earth/blue_planet/coasts/mangroves/mangrove_importance/
Key data are retrieved from the UN World Urbanization Prospects, the 2009 Revision, http://esa.un.org/unpd/wup/index.htm