adapting to pacific island mangrove responses to sea level rise and climate change ·...

CLIMATE RESEARCHClim Res

Vol. 32: 161–176, 2006 Published October 26

1. INTRODUCTION

Accurate predictions of changes to coastal ecosystemarea and health, including in response to climate

change effects such as projected relative sea level rise,enables advanced planning appropriate for specificsections of coastline to minimize and offset anticipatedlosses, and reduce threats to coastal development and

© Inter-Research 2006 · www.int-res.com*Email: [email protected]

Adapting to Pacific Island mangrove responses tosea level rise and climate change

Eric L. Gilman1,15,*, Joanna Ellison1, Vainuupo Jungblut2, Hanneke Van Lavieren3, Lisette Wilson4, Francis Areki5, Genevieve Brighouse6, John Bungitak7, Eunice Dus8,

Marion Henry9, Mandes Kilman10, Elizabeth Matthews11, Ierupaala Sauni Jr.6, Nenenteiti Teariki-Ruatu12, Sione Tukia13, Kathy Yuknavage14

1University of Tasmania, School of Geography and Environmental Studies, Locked Bag 1-376 Launceston, Tasmania 7250, Australia2Secretariat of the Pacific Regional Environment Programme, PO Box 240, Apia, Samoa

3United Nations Environment Programme, Regional Seas Programme, PO Box 30552 Room T-232, Nairobi, Kenya4WWF-South Pacific, PO Box 8280, Boroko, NCD, Papua New Guinea

5WWF-Fiji, 4 Ma’afu Street, Private Mail Bag, Suva, Fiji6Coastal Management Program, Utulei Executive Office Building, Pago Pago, American Samoa 96799, USA

7Environmental Protection Authority, PO Box 1322, Majuro, MH 96960, Republic of the Marshall Islands8Wildlife Conservation Society, PO Box 277, Goroka, Eastern Highlands Province, Papua New Guinea

9Department of Economic Affairs, PO Box PS12, Palikir, Pohnpei, FM 96941, Federated States of Micronesia10Primary Resources Consulting Company, PO Box 1691, Port Vila, Vanuatu

11Palau Conservation Society, Box 1811, Koror, PW 96940, Palau12Ministry of Environment, Land, and Agricultural Development, PO Box 234, Bikenibeu, Tarawa, Kiribati

13Department of Environment, PO Box 917, Nuku’alofa, Tonga14Commonwealth of the Northern Mariana Islands Coastal Resources Management Office, Box 10007, Saipan MP 96950, USA

15Present address: 2718 Napuaa Place, Honolulu, Hawaii 96822, USA

ABSTRACT: Stresses associated with effects of climate change, including rise in relative mean sea level, pre-sent one set of threats to mangroves. Coastal development and ecosystems in the Pacific Islands region areparticularly vulnerable to climate change effects. We investigated the capacity of Pacific Island countries andterritories to assess mangrove vulnerability to the effects of climate change, and their capacity to adapt tomangrove responses to these forces. Technical and institutional capacity-building priorities include:(1) strengthening management frameworks to conduct site-specific assessment of mangrove vulnerabilityand incorporate resulting information into land-use plans to prepare for any landward mangrove migrationand offsetting anticipated losses; (2) reducing and eliminating stresses on and rehabilitating mangroves, inpart, to increase mangrove resilience to climate change effects; and (3) augmenting abilities to establishmangrove baselines, and monitor gradual changes using standardized techniques through a regional net-work to distinguish local and climate change effects on mangroves. Other priorities are to: (4) assess howmangrove margins have changed over recent decades; (5) determine projections of trends in mean relativesea level and trends in the frequency and elevation of extreme high water events; (6) measure trends inchanges in elevations of mangrove surfaces; and (7) incorporate this information into land-use planning pro-cesses. Also in (8) some locations require spatial imagery showing topography and locations of mangrovesand coastal development. Land-use planners can use information from assessments predicting shorelineresponses to projected sea level rise and other climate change effects to reduce risks to coastal development,human safety, and coastal ecosystems. This advanced planning enables coastal managers to minimize social disruption and cost, minimize losses of valued coastal ecosystems, and maximize available options.

KEY WORDS: Mangrove · Sea level rise · Climate change · Land-use planning · Pacific Islands

Resale or republication not permitted without written consent of the publisher

Clim Res 32: 161–176, 2006

human safety (Titus 1991, Mullane & Suzuki 1997, Elli-son 2004, Gilman et al. in press). Relative sea level riseis a major factor contributing to recent losses and pro-jected future reductions in the area of valued coastalhabitats, including mangroves and other tidal wet-lands, with concomitant increased threat to humansafety and shoreline development from coastal hazards(Gilman et al. in press). Global sea level rise is oneof the more certain outcomes of global warming; 10 to20 cm occurred during the last century, and several cli-mate models project an accelerated rate of sea levelrise over coming decades (Church et al. 2001, 2004a,Holgate & Woodworth 2004).

Over the past few decades, the 10 countries andterritories with native mangroves in the Pacific Islandsregion experienced an average rise in relative sealevel of 2 mm yr–1. Based on general estimates of man-grove sedimentation rates (Ellison & Stoddart 1991),and the possibility that subsurface sediment subsi-dence from organic matter decomposition, sedimentcompaction, and fluctuations in sediment water stor-age and water table levels may result in substantiallyhigher rates of sea level rise relative to the mangrovesurface (Krauss et al. 2003), island mangroves couldexperience serious problems due to rising sea level,and low island mangroves may already be understress. Gilman et al. (in press) determine that AmericanSamoa could experience a 50% loss in mangrove areaby the year 2100. A 12% reduction is possible in thePacific Islands region due to mangrove responses torelative sea level rise when employing the Intergovern-mental Panel on Climate Change’s upper projectionfor global sea level rise through the year 2100.

Shoreline development and coastal ecosystems areparticularly vulnerable to small increases in sea leveland other climate change effects in the Pacific Islandsregion. Many of the low islands do not exceed 4 mabove current mean sea level, and even on highislands, most development is located on narrow coastalplains. Small island states have limited capacity toadapt to relative sea level rise, including accommo-dating landward migration of mangroves and othercoastal ecosystems. This is a result of their small landmass, high population densities and population growthrates, limited funds, poorly developed infrastructure,and susceptibility to damage from natural disasters(Nurse et al. 2001). It may not be physically oreconomically feasible for many small island state com-munities to retreat from a landward-migrating man-grove and other coastal habitats, or to establish zoningsetbacks from coastal habitats for new development.

Pacific Island governments have recognized thevalue of mangroves and the need to augment conser-vation efforts (e.g. South Pacific Regional EnvironmentProgramme 1999a). The Pacific Islands contain roughly

3% of the world’s mangrove area, a small area inglobal terms, but each island group has a unique man-grove community structure (Ellison 2000) and man-groves provide site-specific functions and values (e.g.Lewis 1992, Gilman 1998). Reduced mangrove areaand health will increase the threat to human safety andshoreline development from coastal hazards such aserosion, flooding, and storm waves and surges. Man-grove loss will also reduce coastal water quality andbiodiversity, eliminate fish and crustacean nurseryhabitat, adversely affect adjacent coastal habitats, andeliminate a major resource for human communitiesthat traditionally rely on mangroves for numerousproducts and services (Ramsar Secretariat 2001). Man-grove destruction can also release large quantities ofstored carbon and exacerbate global warming trends(Ramsar Secretariat 2001).

Land-use planners can obtain information fromassessments predicting shoreline responses to pro-jected relative sea level rise and other climate changeeffects over coming decades to mitigate anticipatedlosses of coastal habitats and avoid and minimize dam-age to coastal development. In this study, we assessthe capacity of Pacific Island countries and territoriesto determine vulnerability and adapt to mangrove re-sponses to climate change effects. Results highlightpriority technical and institutional capacity-buildingneeds nationally and regionally.

1.1. Mangrove responses to relative sea level riseand other climate change effects

When relative sea level rise is the predominant forceshaping mangrove position, the landscape-level re-sponses of mangroves over decadal and longer periodscan be predicted based on reconstruction of the paleo-environmental response of mangroves to past sea levelfluctuations (Ellison & Stoddart 1991, Woodroffe 1995,Ellison 1993, 2000, Gilman 2004, Gilman et al. in press).Such predictions can be based on (1) the mean sea levelchange rate relative to the mangrove surface, (2) themangrove’s physiographic setting (slope of the land ad-jacent to the mangrove, slope of the mangrove, and pres-ence of obstacles to landward migration), and (3) erosionor progradation rate of the mangrove seaward margin(Ellison & Stoddart 1991, Ellison 1993, 2000, 2001,Woodroffe 1995, Alleng 1998, Gilman 2004, Gilman et al.in press). There are 3 general scenarios for mangroveresponse to relative sea level rise, given a landscape-level scale and time period of decades or longer (Fig. 1):

(A) No change in relative sea level: When sea levelis not changing relative to the mangrove surface, themangrove margins will remain in the same location(Fig. 1A).

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Gilman et al.: Adapting to mangrove responses to climate change effects

(B) Relative sea level drop: When sea level is drop-ping relative to the mangrove surface, this forcesthe mangrove seaward and landward boundaries tomigrate seaward (Fig. 1B). The mangrove may alsoexpand laterally if areas adjacent to the mangrove,which are currently at a lower elevation than the man-grove surface, develop hydrologic conditions (period,depth and frequency of inundation) suitable for man-grove establishment.

(C) Relative sea level rise: If sea level is rising rela-tive to the mangrove surface, the mangrove’s seawardand landward margins retreat landward where un-obstructed, as mangrove species zones migrate inlandin concert with migrating environmental conditions,such as period, frequency and depth of inundation andsalinity (Fig. 1C). The mangrove may also expandlaterally if areas adjacent to the mangrove, which are

currently at a higher elevation than the mangrove sur-face, develop a suitable hydrologic regime. Dependingon the ability of individual true mangrove species tocolonize newly available habitat at a rate that keepspace with the rate of relative sea level rise, the slope ofadjacent land and the presence of any obstacles tolandward migration of the landward boundary of themangrove, such as seawalls and other shoreline pro-tection structures, some sites will revert to a narrowmangrove fringe or experience extirpation of the man-grove community (Fig. 1D).

However, over small temporal and spatial scales, andwhere natural and anthropogenic forces other thanchanging relative sea level exert a larger influence onmangrove margin position, change in mangrove positionwill be variable (SCOR Working Group 1991, Woodroffe1995, Gilman et al. in press). For example, forces affect-

ing sediment-budget balances, includ-ing changes in sediment budgets fromrivers, variations in coastal currents,wind directions and strength, and con-struction of seawalls and other shorelineerosion control structures, can produceerosion or accretion of the mangroveseaward margin irrespective of anychange in sea level.

In addition to altered sedimentinputs, several other forces can affectmangrove margin position, as well astheir structure and health. Outcomes ofglobal climate change besides globalsea level rise, such as changes in pre-cipitation and resulting alterations tothe mangrove salinity gradient, in-creases in air and sea surface tempera-tures, changes in frequency and in-tensity of storms, changes in prevailingocean wave heights and direction, andchanges in tidal regimes may affectcoastal systems, including mangroves.For instance, Snedaker (1993) hypo-thesizes that the mangrove speciesRhizophora mangle will increase peatproduction with increased freshwaterinputs (for instance, if precipitationincreases or relative sea level is drop-ping), but will experience a net loss ofpeat if salinity increases (for instance,if relative sea level is rising or precipi-tation is decreasing), as the increasedavailability of sulfate in seawater wouldincrease anaerobic decomposition ofpeat, increasing the mangrove’s vul-nerability to any rise in relative sealevel. Areas with decreased precipita-

163

Fig. 1. Scenarios for generalized mangrove responses to relative sea level rise

Clim Res 32: 161–176, 2006

tion will have a smaller water input to groundwaterand less freshwater surface water input to mangroves,increasing salinity. Increased salinity decreases man-grove net primary productivity, growth, and seedlingsurvival, and may possibly change competition be-tween mangrove species (Ellison 2000, 2004). De-creased rainfall and increased evaporation will reducethe extent of mangrove areas, with a conversion oflandward zones to hypersaline flats, and there willbe a decrease in diversity of mangrove zones andgrowth (Ellison 2000). Mangrove areas experiencingincreased rainfall will experience an increase in area,with mangrove colonization of previously unvegetatedareas of the landward fringe, and there will be anincrease in diversity of mangrove zones and growthrates (Ellison 2000). Areas with higher rainfall havehigher mangrove diversity and productivity due tohigher supply of fluvial sediment and nutrients, aswell as reduced exposure to sulfate and reduced sal-inity (McKee 1993, Snedaker 1993, Ellison 2000, 2004).However, projected changes to these other global cli-mate parameters, including Pacific precipitation pat-terns, are less certain than global change in sea level,and the response of mangroves and other coastal sys-tems to these changes are not well understood (Ellison2000, Houghton et al. 2001, McLean et al. 2001).

Other forces that can affect mangroves includechanging nutrient, freshwater, and pollutant inputs,clearing of mangrove vegetation, filling, displacingnative species with alien invasive species, and vege-tation loss from insect infestations, fungal florapathogens, and other diseases (Ellison 1993, 1999,Gilman 1999, Saintilan & Wilton 2001). These pres-sures can also reduce mangrove resilience to the addi-tional stress of relative sea level rise and other climatechange effects. The projected increase in the fre-quency and elevations of extreme high water events inresponse to climate change (Church et al. 2001, 2004b,Woodworth & Blackman 2002, 2004, Gilman et al.2005) could also affect the position and health of man-groves by altering salinity, recruitment, and inunda-tion, in addition to changing the wetland sedimentbudget.

Also, degradation of adjacent coastal ecosystemsfrom relative sea level rise and climate change mayreduce mangrove health. Mangroves are functionallylinked to neighboring coastal ecosystems, includingseagrass beds, coral reefs, and upland habitat,although the functional links are not fully understood.For instance, mangroves of low islands and atolls,which receive a proportion of sediment supply fromcoral reefs, may experience lower sedimentation ratesand increased susceptibility to relative sea level rise ifcoral reefs become less productive due to climatechange effects.

1.2. National, regional and international initiatives

Due to anticipated effects of climate change in thePacific Islands region (Fig. 2), several international andregional initiatives discuss the severity of this threatand provide general guidelines for planning. However,there have been few site-based vulnerability assess-ments and few planning initiatives to manage man-groves responses to sea level rise and other climatechange effects.

There have been several national or island-scalevulnerability assessments in Pacific Island countriesand territories that provide qualitative assessments todescribe the anticipated responses of coastal systemsto projected sea level and other climate change effectsand concomitant threats to developed portions of thecoastal zone. For example, Phillips (2000) describes thevulnerability of Vanuatu’s coastal villages to sea levelrise, referencing global sea level rise models producedby the Intergovernmental Panel on Climate Changeand other projected global climate change parameters(temperature and precipitation), as a basis for hypoth-esizing possible environmental, social, and economiceffects. Other vulnerability assessments have estab-lished the locations and elevations of coastal habitatsand development, and use global or relative sea levelchange projections to make rough predictions of thesections of coastline that will be affected. For example,Solomon et al. (1997) create a geographic informationsystem (GIS) of a developed stretch of the coastline ofViti Levu, Fiji using topographic maps to identify thelocations and elevations of coastal development,including sea walls, revetments, and other shorelineprotective structures. They then use this GIS to assessthe vulnerability of the coastline to inundation from 4sea level rise scenarios (a rise of 0, 0.25, 0.5 and 1 m)and storm surges. This approach to conducting a vul-nerability assessment does not incorporate naturalcoastal ecosystem response to changes in relative sealevel and other climate change effects.

All 12 Pacific Island countries with indigenous man-groves are Parties to United Nations Framework Con-vention on Climate Change (UNFCCC). Of these, 11countries (Kiribati, Marshall Islands, Federated Statesof Micronesia, Nauru, Palau, Papua New Guinea,Samoa, Solomon Islands, Tonga, Tuvalu, and Vanuatu)have submitted an initial National Communication tothe UNFCCC. Fiji has not yet submitted a NationalCommunication. The 11 initial National Communica-tions discuss general considerations and guidelinesrelated to coastal ecosystem vulnerability and adapta-tion to future sea level and climate change (FederatedStates of Micronesia 1997, Government of Samoa 1999,Government of Tuvalu 1999, Kiribati Government 1999,Republic of Nauru 1999, Republic of Vanuatu 1999,

164


Papua New Guinea Government 2000, Republic of theMarshall Islands Environmental Protection Authority2000, Republic of Palau Office of EnvironmentalResponse and Coordination 2002, Solomon IslandsGovernment 2004, Kingdom of Tonga 2005). A reviewof these reports highlights that there is a gap in infor-mation on anticipated site-specific responses of man-groves and other coastal ecosystems to climate changeeffects and site-specific strategies for adaptation.Examples of some of the general adaptation strategiesto manage mangrove and other coastal ecosystemresponses to climate change effects identified in sev-eral of these national communication reports include: • Establishing zoning rules for setbacks of new devel-

opment from mangroves • Retreating to higher ground or off-island for appro-

priate sections of coastline as a last resort • Identifying sections of coastal areas vulnerable to

flooding and inundation to guide future development • Fortifying relevant sections of developed coastline

These examples are representative of the level ofspecificity in the National Communication reports toassess the vulnerability of and adapt to coastal ecosys-

tem response to sea level and other climate changeeffects.

The South Pacific Sea Level and Climate MonitoringProject was initiated in 1991 to establish stations in11 Pacific Island countries to measure the relativemotions of land and sea at each station (South PacificSea Level and Climate Monitoring Project 2001). Theproject is managed by the National Tidal Facility ofFlinders University of South Australia. These data willassist in long-term calibration of satellite altimetry andprovide a measure of regional vertical control.

The Secretariat of the Pacific Regional EnvironmentProgram’s (SPREP) Pacific Islands Climate ChangeAssistance Programme was implemented from 1997–2000 to assist 10 Pacific Island countries that signedand ratified UNFCCC with their reporting, trainingand capacity-building responsibilities under the con-vention, including assessing their vulnerability to cli-mate change. Participants from 12 countries (PapuaNew Guinea was the one participating country withindigenous mangroves) received training on assessingclimate change vulnerability and adaptation require-ments during a 6 mo training course in 1998. Under

165

Fig. 2. Pacific Islands region and location of the 12 Pacific Island countries and 4 territories with indigenous mangroves (bold)

Clim Res 32: 161–176, 2006

this program, SPREP (2000) presents general guide-lines for Pacific Island governments to incorporateconsiderations of sea level and climate change intonew development planning.

The Regional Wetlands Action Plan for the PacificIslands (SPREP 1999a) specifies regional actions tomonitor mangroves. Action 3.3.1 calls for the develop-ment of a regional monitoring program to assess thestatus of mangroves in the region, evaluate the successof management and conservation actions, and developmore effective management practices. Furthermore,Action 3.3.5 identifies that mangrove swamps, particu-larly those of low islands, are likely to be sensitive torise in sea level. It promotes the development of a man-grove monitoring network for identification of changes,which has yet to be established.

SPREP implemented the project Capacity Buildingfor the Development of Adaptation Measures in PacificIsland Countries, in the Cook Islands, Fiji, Samoa, andVanuatu from 2002–2005. The project’s aim was tobuild capacity of communities in these 4 countries toadapt to climate change, including incorporation of cli-mate change adaptation considerations into nationaland local planning and budgeting. The project focusedon socioeconomic effects and policy development, anddid not address coastal ecosystem response to sea leveland climate change forces. For instance, SPREP con-ducted seminars for senior government officials fromthe 4 participating countries and produced and distri-buted briefing papers and educational materials toraise awareness of climate change effects and adapta-tion (Secretariat of the Pacific Regional EnvironmentProgramme 2003).

The South Pacific Applied Geoscience Commission(SOPAC) has developed an environmental vulnerabil-ity index for application at national scales to provide aquick and inexpensive method to characterize thevulnerability of natural systems at large scales. Itis not designed for site-based vulnerability assess-ments (SOPAC 2003).

2. CAPACITY-BUILDING PRIORITIES

We collected information from 10 of the 16 PacificIsland countries and territories with indigenousmangroves to identify capacity-building priorities toaddress mangrove responses to climate change effects(Fig. 2): American Samoa, Fiji Islands, Kiribati, Mar-shall Islands, Federated States of Micronesia, NorthernMariana Islands, Palau, Papua New Guinea, Tongaand Vanuatu. These 10 countries and territories con-tain 84% of the region’s indigenous mangroves (Gil-man et al. in press). Table 1 provides a synthesis of thecase study results. This section describes: (1) the tech-

nical resources needed for the best possible predictionof how a mangrove wetland will respond to projectedrelative sea level rise and climate change over comingdecades, (2) the institutional resources needed to man-age and adapt to these mangrove responses to climatechange effects, and (3) the technical and institutionalareas that are in urgent need of strengthening in thePacific Islands region.

Hawaii and Tahiti, where mangroves are human intro-ductions (Allen 1998, Ellison 1999), are not included inthe assessment, because management authorities inthese areas may actively control the alien invasive spe-cies (e.g. Smith 2005). While mangrove wetlands havebeen reported from Niue (Ellison 1999), a Niue gov-ernment focal point reported that there are no man-grove wetlands in Niue (F. Rex pers. comm.). While onetrue mangrove species, Excoecaria agallocha, is docu-mented in Niue (Yuncker 1943), this species is onlyfound in dry littoral forest.

2.1. Analyses of tide gauge data

A minimum of a 20 yr local tide gauge record isrequired to obtain an accurate trend in relative sealevel (Church et al. 2004a). Many Pacific islands expe-rience tectonic movements that result in substantialdifferences in local sea level relative to global eustatictrends. In addition to vertical land-level changes fromtectonics, change in relative mean sea level over timeas measured by a tide gauge can result from subsi-dence due to extraction of subsurface groundwater oroil, oceanographic processes such as El Niño phasesand changes in offshore currents, long-term changesin regional temperature, sediment consolidation, aswell as from global sea level change (Komar 1998,Church et al. 2001). The closer the tide gauge is tothe mangrove site, the more accurately it will reflectthe actual sea level changes that are affecting themangroves. For sites with a local tide gauge record of<20 yr or that are located far from the nearest tidegauge, sea level trends can be accurately calculatedusing the near global coverage of TOPEX/Poseidonsatellite altimetry data combined with historical globaltide gauge records (Church et al. 2004a). Pacific Islandcountries and territories also need the technical capac-ity to analyze available tide gauge data to determineprojected trends in mean sea level and extreme highwater events, and incorporate this information intoland-use planning.

Most (7 of 10) countries and territories have suffi-ciently long tide gauge records (≥ 20 yr) to determineaccurate trends in mean sea level and extreme highwater events (Fig. 3). However, tide gauges of 4 of the7 countries and territories with the long (≥ 20 yr) tide

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Gilman et al.: Adapting to mangrove responses to climate change effects 167

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gauge records are located several hundred kilometersfrom at least one mangrove site in that country. Threecountries with tide gauge records <20 yr require assis-tance to determine reconstructed sea level trends fromsatellite altimetry data combined with historical globaltide gauge records (Church et al. 2004a). Agenciesmanaging coastal land use and coastal ecosystems ofPacific Island countries and territories require assis-tance to determine trends in relative mean sea leveland trends in the frequency and elevations of extremehigh water events (Church et al. 2001, Woodworth &Blackman 2002, 2004, Gilman et al. 2005, in press), andassistance to interpret and incorporate this informationinto land-use planning.

2.2. Information on change in sea level relative tomangrove surfaces

Information on trends in the change in elevation ofthe mangrove surface is needed to determine howsea level has been changing in recent decades rela-tive to the mangrove surface. The most precisemethod to obtain information on sea level change isto install an array of tide gauges throughout a site,but this is expensive, laborious, and a minimum of a20 yr local tide gauge record is required to obtain anaccurate trend in relative sea level (Church et al.2004a). Measurement of 137Cs and excess 210Pb activ-ity in shallow sediment cores, observing sedimenta-tion stakes, and using soil horizon markers can pro-vide an accurate estimate of rates of change inmangrove surface elevation over recent decades (e.g.

DeLaune et al. 1978, Lee & Partridge 1983,Lynch et al. 1989, Krauss et al. 2003,Gilman et al. in press), which can then becompared to the relative sea level changerate as measured by the closest tide gauge.The measurement of radioisotope activityin mangrove sediment cores is expensive,especially if multiple cores are taken in anattempt to characterize an entire mangrovesite; this method does not account for sub-surface processes that affect the elevation ofthe mangrove surface that occur below thedepth of the cores, and there are severalpotential sources of error, including biotur-bation as well as abiotic processes. Alterna-tively, precision surveying from a bench-mark to points throughout a mangrove sitecould provide information on trends in ele-vation of the mangrove surface (Cahoon etal. 2002), which could then be compared tothe relative sea level change rate from anearby tide gauge.

American Samoa and the Federated States of Micro-nesia have some information on mangrove sedimenta-tion rates, obtained from monitoring the change indistance of the mangrove surface from the top of sedi-mentation stakes and from determining 137Cs andexcess 210Pb activity depth profiles from shallow sedi-ment cores (Krauss et al. 2003, Gilman et al. in press).Otherwise, regionally there is a lack of information onhow sea level is changing relative to mangrove sur-faces. The mangrove surface can change in elevationfrom sediment accretion or erosion and from subsur-face processes, such as organic matter decomposition,sediment compaction, fluctuations in sediment waterstorage and water table levels, and root production(Lynch et al. 1989, Krauss et al. 2003, Rogers et al.2005, Gilman et al. in press). Information on trends inchange in the elevation of the mangrove surface overrecent decades is needed.

2.3. Analysis of historical imagery to observechanges in mangrove margin positions

Analysis of a time series of recent historical aerialphotographs and satellite imagery, which show thepositions of mangrove seaward margins, can be usedto observe trends in movement of the mangrove mar-gins (erosion or seaward progression). This informa-tion can then be used to determine if the movementhas been correlated with the observed trend in relativemean sea level, and to predict the future position of theseaward margin. Extrapolation from observations ofhistorical shoreline movement is more accurate when

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gauge record <20 yr


the available imagery covers long time periods. Theextrapolation assumes that no new large forces, suchas human alterations to the coastline’s sediment bud-get, will substantially change the trend from the recentobservations.

Historical imagery ≥ 25 yr old is available for 8 coun-tries and territories (Fig. 4). Only American Samoa hasanalyzed available historical imagery to observe his-torical trends in changes in position of mangrove mar-gins (Gilman et al. in press). An effort to identify addi-tional historical aerial photographs, provide IKONOSand QuickBird space imaging to in-country GIS prac-titioners, and provide assistance to co-register avail-able historical imagery to the geo-referencedsatellite imagery is needed. Some countriesand territories may need assistance to estab-lish or augment capacity of a GIS program.

2.4. Mangrove boundary delineation

Periodic delineation of the mangrove land-ward margin using GPS or traditional surveytechniques is needed to observe any move-ment of the boundary, providing fundamentalinformation needed to determine trends inmangrove area. Interpretation of remotelysensed imagery (aerial photos and spaceimaging) generally can be used to delineatethe mangrove seaward margin (e.g. Gilman etal. in press), otherwise, delineation with GPSand survey equipment is needed. The worldatlas of mangroves (Spalding et al. 1997; a sec-

ond edition is due in 2007) includes informa-tion on the status and trends in mangrove area.

Five of 9 countries and territories havedelineated 80% or more of their mangroveboundaries (Fig. 5). Two countries have nomangrove boundary delineations. While PapuaNew Guinea has delineated mangrove bound-aries, the percent that has been delineated isnot known, and is not included in Fig. 5. Fourof the 10 countries and territories have de-lineated mangrove boundaries within the last10 yr. This highlights the need by some coun-tries and territories to delineate mangroveboundaries at regular intervals.

2.5. Map products

Topographic information is needed todetermine the mean slope of the land imme-diately adjacent to the landward mangrovemargins to estimate rates of landward man-

grove migration. This requires a recent delineation ofthe landward mangrove margin. Alternative scenariosfor projected change in sea level relative to the man-grove surface can then be used to estimate the dis-tance that the landward mangrove margin will move.If sea level is rising relative to the mangrove surface,then information on the current location of any obsta-cles to the landward migration of mangroves, such asseawalls, buildings, and roads, and the distance thatthese structures are from the current landward man-grove margin, is needed to determine how thesestructures may obstruct future landward mangrovemigration.

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Fig. 4. Age of oldest known historical image showing the location ofmangrove margins for 10 Pacific Island countries and territories with

indigenous mangroves

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Fig. 5. Percentage of total mangrove area with boundaries delineatedfor 9 Pacific Island countries and territories with indigenous mangroves

Clim Res 32: 161–176, 2006

Some countries identified a need for topographicmaps and maps showing the location of roads anddevelopment in the vicinity of mangroves. Support forin-country GIS programs may be needed to producethem. Seven of the countries and territories have>85% topographic map coverage of their mangroveislands (Fig. 6). Two lack any topographic map cover-age of their mangrove islands. Five countries and terri-tories have maps showing locations of developmentand roads in the vicinity of all mangroves (Fig. 7). Twocountries lack maps showing development and roadsnext to any of their mangroves.

2.6. Mangrove monitoring, assessment andregional network

Given uncertainties about future climatechange and the responses of mangroves andother coastal ecosystems, we need to manageadaptively and proactively. In-country staffwith training, experience, and motivation arerequired to conduct monitoring and assess-ment of relevant mangrove parameters, inpart, to facilitate adaptive management. Sealevel and climate changes are expected toalter mangrove position, area, structure, spe-cies composition, and health. Linking nationalmangrove monitoring efforts through a re-gional network using standardized techniqueswould enable the separation of site-basedinfluences from global changes to provide abetter understanding of mangrove responsesand alternatives for mitigating adverse effects(Ellison 2000, Nurse et al. 2001).

Four countries and territories identify a strong needfor training and capacity-building of in-country per-sonnel in mangrove assessment and monitoring: Vanu-atu, Kiribati, Northern Mariana Islands, and Palau.Other countries (American Samoa, Tonga, Fiji, Mar-shall Islands, Papua New Guinea, and the FederatedStates of Micronesia) have some in-country capacityalready, but identify information gaps. Fiji, FederatedStates of Micronesia and American Samoa conductsome monitoring of mangrove tree girth (diameter atbreast height or DBH), which allows quantitative assess-ment of mangrove ecosystem change in communitystructure and growth rates. Palau and Tonga have more

limited monitoring, such as of birds or humanimpacts.

There has also been no coordination in thelimited mangrove monitoring. The countriesand territories with a mangrove monitoringprogram do not employ standardized tech-niques to enable a meaningful comparisonof results from the different programs. Othercountries have no monitoring. There is noPacific Islands regional mangrove monitoringprogram in place. All countries indicate thatthey would be interested in participating in aregional network to monitor mangroves andassess mangrove response to sea level riseand climate change, if such a network wereestablished.

Establishing mangrove baselines and moni-toring gradual changes through regional net-works using standardized techniques willenable the separation of site-based influencesfrom global changes to provide a better

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mangroves

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Fig. 7. Percentage of islands containing mangroves with maps showingthe location of development and roads, for 10 Pacific Island countries and

territories with indigenous mangroves


understanding of mangrove responses to sea level andglobal climate change, and alternatives for mitigatingadverse effects (Ellison 2000, Nurse et al. 2001). Themonitoring system, while designed to distinguish cli-mate change effects on mangroves, would also there-fore show local effects, providing coastal managerswith information to abate these sources of degradation.

Establishing a regional wetland monitoring networkfor the Pacific Islands region has been proposed in theAction Strategy for Nature Conservation in the PacificIslands Region (SPREP 1999a), and the Regional Wet-lands Action Plan for the Pacific Islands (SPREP1999b). This has not been implemented to date.

2.7. Strengthening management frameworks

Governments need the institutional capacity to man-age a land-use permit or zoning program to ensurecoastal earthmoving and development activities aresustainable, including accounting for effects on man-groves, and to plan for any landward mangrove migra-tion. While existence of a coastal permit and zoningprogram does not necessarily mean that current legaland management frameworks and political will areadequately preventing mangrove degradation, it indi-cates that the institutional capacity needed to sus-tainably manage activities in mangroves and othersensitive coastal ecosystems exists. Given an existingcoastal development permit or zoning program, if thepolitical will exists, it could be possible to establishzoning setbacks for new coastal development adjacentto mangroves in certain sections of coastline, adoptrules on where hard versus soft engineering erosioncontrol structures can and cannot be constructed, anddetermine which sections of coastline would undergomanaged retreat versus fortification.

All 10 participating countries and territories reporthaving some form of coastal permit or zoning programthat regulates coastal activities such as earthmovingand development activities. The existence of a frame-work to manage coastal activities is part of the re-quisite institutional capacity to sustainably manageactivities in mangroves and other sensitive coastalecosystems. However, this does not necessarily meanthat current legal and management frameworks andpolitical will are adequately preventing mangrove de-gradation. There is a need to assess the efficacy ofnational management frameworks at preventing man-grove degradation to determine if this is an area inneed of attention. For instance, despite the existence ofa permit program for coastal development activities,the wetlands management framework in the USCommonwealth of the Northern Mariana Islands hasnot prevented site-specific, island-wide, or cumulative

losses of wetland functional performance or wetlandarea (Gilman 1998, 1999). Also, Palau’s state PublicLand Authorities have been leasing and allowingthe development of property containing mangroves(Republic of Palau Office of Environmental Responseand Coordination 2002).

Only American Samoa has assessed the site-specificvulnerability of mangroves to sea level and climatechange (Gilman et al. in press). Information from thecase studies and a review of National CommunicationReports to the United Nations Framework Conventionon Climate Change reveal that none of the 10 countriesand territories have developed a plan for adaptation tomangrove or other coastal ecosystem responses to cli-mate change effects. Technical assistance is needed tosupport conducting site-specific vulnerability assess-ments and to incorporate this information into land-useand master planning.

2.8. Mangrove rehabilitation

Capacity to rehabilitate (restore, enhance and cre-ate) mangroves will complement adaptation to man-grove response to sea level and climate change.Restoring areas where mangrove habitat previouslyexisted, enhancing degraded mangroves by removingstresses that caused their decline, and creating newmangrove habitat will help to offset anticipated reduc-tions in mangrove area and increase resilience to cli-mate change effects. If successful mangrove rehabili-tation has been achieved in the past, this indicates thatit may be possible to replicate this success at othersites. However, failure to provide adequate training tocoastal managers in the basics of successful mangroverehabilitation leads to project failures or projects thatonly partially achieve stated goals (Lewis 2005).

There has been limited activity in the region in reha-bilitation of mangroves, with small-scale successfulprojects only recorded from Kiribati, Northern Mari-ana Islands, Palau, and Tonga and 2 failed mangroverehabilitation efforts in American Samoa and PapuaNew Guinea. The results of 2 additional rehabilitationefforts in Palau and Fiji are not known. This highlightsthe need for improved staff training, capacity buildingand information sharing.

3. SITE PLANNING AND ADAPTATION STRATEGY

Management authorities, especially of small islandcountries and territories, are encouraged to assesssite-specific mangrove vulnerability to climate changeeffects now, and not wait for problems to becomeapparent, when options for adaptation will be rest-

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ricted. Managers can then incorporate the results ofthese vulnerability assessments into coastal land-usepolicies to provide adequate lead-time to minimizesocial disruption and cost, minimize losses of valuedcoastal habitats, and maximize available options. Thepolicy adopted to manage site-based shoreline responseto rising sea level will be made as part of a broadercoastal planning analysis. This analysis requiresbalancing multiple and often conflicting objectives ofmanagers and stakeholders to (1) sustain the provisionof ecological, economic, and cultural values; (2) addresspriority threats to natural ecosystem functioning;(3) maintain ecological processes and biodiversity;(4) achieve sustainable development; and (5) fulfillinstitutional, policy, and legal needs (Gilman 2002).

Site planning for some sections of shoreline contain-ing mangroves that are not highly developed and thatare experiencing a rise in relative sea level may callfor abandonment and adaptation to manage long-termretreat (Dixon & Sherman 1990, Mullane & Suzuki1997, Gilman 2002). ‘Managed retreat’ involves imple-menting land-use planning mechanisms before theeffects of rising sea level become apparent, which canbe planned carefully with sufficient lead time to enableeconomically viable, socially acceptable, and environ-mentally sound management measures. Coastal devel-opment can remain in use until the eroding coastlinebecomes a safety hazard or begins to prevent land-ward migration of mangroves, at which time the devel-opment can be abandoned or moved inland. Adoptionof legal tools, such as rolling easements, can help makesuch eventual coastal abandonment more acceptableto coastal communities (Titus 1991). Zoning rules forbuilding setbacks and land use for new developmentcan be used to reserve zones behind current man-groves for future mangrove habitat. Managers candetermine adequate setbacks by assessing site-specificrates for landward migration of the mangrove land-ward margin (Gilman et al. in press). Constructioncodes can be instituted to account for relative sea levelrise rate projections to allow for the natural inlandmigration of mangroves based on a desired lifetime forthe coastal development (Mullane & Suzuki 1997). Anynew construction of minor coastal development struc-tures, such as sidewalks and boardwalks, should berequired to be expendable with a lifetime based on theassessed sites’ erosion rate and selected setback.Otherwise, the structure should be portable. Rulescould prohibit landowners of parcels along thesecoasts from constructing coastal engineering struc-tures to prevent coastal erosion and the natural inlandmigration of mangroves. This managed coastal retreatwill allow mangroves to migrate and retain theirnatural functional processes, including protecting thecoastline from wind and wave energy.

Employing shoreline erosion control measures, suchas surge breakers, dune fencing, and detached break-waters, can help reduce the rate of coastal erosion(Mullane & Suzuki, 1997). Use of hard engineeringtechnology, including groins, seawalls, revetments,and bulkheads, a traditional response to coastal ero-sion and flooding in small island states and worldwide,can increase coastal vulnerability (Fletcher et al. 1997,Mullane & Suzuki 1997, Mimura & Nunn 1998, Nurseet al. 2001). These coastal engineering structures usu-ally can effectively halt erosion as relative sea levelrises, but often lead to the loss of the coastal systemlocated in front of and immediately downstream in thedirection of longshore sediment transport from thestructure, converting the seaward coastal system intodeepwater habitat (Fletcher et al. 1997, Mullane &Suzuki 1997). For some sites, it may be less expensiveto avoid hard solutions to relative sea level rise andinstead allow coastal ecosystems to migrate inland.These ecosystems provide natural coastal protectionthat may be more expensive to replace with artificialstructures (Mimura & Nunn 1998, Ramsar Secretariat2001). However, results of site planning may justify useof hard engineering technology and shoreline erosioncontrol measures to prevent erosion for some sectionsof highly developed coastline adjacent to mangroves.As a result, the mangroves’ natural landward migra-tion will be prevented and the mangrove fronting thedevelopment will eventually be lost, along with itsvalued function of buffering the developed coastlinefrom wave and wind energy.

Most cost-benefit analyses included in site planningonly examine costs and benefits as measured by mar-ket prices, ignoring mangrove and other coastal sys-tem values not described by established monetaryindicators (Dixon & Sherman 1990, Ramsar Secretariat2001). Site planning and cost-benefit analyses em-ployed to determine if a section of coastline abutting amangrove should be fortified or undergo managedretreat should account for the benefits of allowingmangroves to undergo natural landward migrationunder a rise in relative sea level. These benefitsinclude the continued provision of valued services andproducts, including consumptive benefits, educationand research, aesthetic and cultural benefits, andfuture values such as a mangroves future potential fortourism (Dixon & Sherman 1990, Ramsar Secretariat2001).

Customary management systems, although weak-ened, still continue to function at some level through-out the Pacific Islands region (Johannes 1982, Gilman2002). Community-based approaches, which capitalizeon traditional knowledge and management systems,and catalyze stakeholder support for requisite conser-vation measures, are suitable in some regions. Stake-

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holders will be more likely to comply with restrictionson their traditional resource use activities if they un-derstand and support the rules, which can be accom-plished through direct community participation in moni-toring, planning, and management decision-making.The optimal approach will depend on the local context.At some sites the rural conditions, including relativelysmall population size, high dependence of local com-munities on coastal and marine resources, social cohe-sion, customary tenure and traditional use of coastaland marine areas and resources, existence of strongand intact traditional authority, and low conven-tional government management capacity, make localcommunity-based management through collaborationbetween local government and the local community(e.g. clans or individual villages) appropriate (White etal. 1994). In urban areas with a more heterogeneouslocal community, more complicated and numerousresource uses and users, more numerous externalthreats to the coastal and marine environment, and lessrecognition of customary tenure and traditional gover-nance, community-based management would be lesseffective and there will be a larger need for centralgovernment management.

4. CONCLUSIONS AND NEXT STEPS

To assess mangrove vulnerability to sea level riseand other climate change effects and to plan for adap-tation, Pacific Island countries and territories need tobuild their technical and institutional capacity to:

(1) Determine trends in relative mean sea level andtrends in the frequency and elevations of extreme highwater events, and incorporate this information intoland-use planning processes.

(2) Measure trends in the change in mangrove sur-face elevation to determine how sea level is changingrelative to the mangrove surface.

(3) Acquire and analyze historical remotely sensedimagery to observe historical trends in changes in posi-tion of mangrove margins.

(4) Produce topographic maps and maps of locationsof development and roads for land parcels adjacent toand containing mangroves, and establish or augmentGIS programs. The World Bank-funded InfrastructureAsset Management Project in progress in Samoa mightserve as a suitable model.

(5) Develop standardized mangrove monitoring pro-grams as part of a regional mangrove-monitoringnetwork. Provide training opportunities for in-countrypersonnel to manage the mangrove-monitoring pro-gram, coordinate with a regional hub, and conductmonitoring techniques. Monitoring methods wouldinclude periodic delineation of mangrove margins.

(6) Assess efficacy of mangrove management frame-works and provide assistance to manage coastal activ-ities to prevent unsustainable effects on mangrovesand other coastal habitats, in part, to increase resi-lience to climate change effects, and plan for any land-ward mangrove migration in response to relative sealevel rise.

(7) Augment regional capacity to rehabilitate man-groves.

Establishing a regional mangrove monitoring net-work may enable many of the identified capacity-building priorities to be fulfilled, and should be one ofthe highest regional priorities. Participating countriesand territories could share technical and financialresources to maximize monitoring and conservationbenefits through economy of scale.

Assessing the efficacy of management frameworksto avoid and minimize adverse affects on mangrovesand other valuable coastal ecosystems and plan for anylandward mangrove migration is also critical. Ensuringthat management frameworks are capable of eliminat-ing and minimizing stresses that degrade mangrovesis necessary to provide for mangrove resilience to anticipated stresses from sea level and other climatechange effects. And managers will need the institu-tional capacity to plan for site-specific mangroveresponse to climate change effects, such as institutingsetbacks from mangroves for new development forappropriate sections of coastline. However, manage-ment frameworks will only be effective if local commu-nities and management authorities recognize the valueof mangrove conservation. It is therefore also a priorityto continually develop and augment a mangrove con-servation ethic.

The value of wetlands conservation is often underes-timated, especially in less developed countries withhigh population growth and substantial developmentpressure, where short-term economic gains that resultfrom activities that adversely affect wetlands are oftenpreferred over the less-tangible long-term benefitsthat accrue from sustainably using wetlands. Man-grove wetlands are one of the most threatened naturalcommunities worldwide, and have lost roughly 50% oftheir global area since 1900 (Ramsar Secretariat 1999).Mangroves experiencing stress from other anthro-pogenic activities such as clearing trees and dumpingof pollutants will be less resilient to additional climate-related stresses. Local communities and leaders mustrecognize the long-term benefits of mangrove conser-vation to reverse historical trends in loss of mangrovearea, maximize mangrove resilience to climate change,and where sea level is projected to rise relative to man-grove surfaces, enable unobstructed natural landwardmigration wherever possible. Education and outreachprograms are an investment to bring about changes in

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behavior and attitudes by better informing communi-ties of the value of mangroves and other ecosystems.This increase in public knowledge of the importanceof mangroves can provide the local community withinformation to make informed decisions about the useof their mangrove resources, and can result in grass-roots support and increased political will for measuresto conserve and sustainably manage mangroves.

Acknowledgements. This project was made possible throughsupport to E.L.G. from the United Nations Environment Pro-gramme Regional Seas Programme and Western PacificRegional Fishery Management Council. The authors aregrateful for information provided by Taakena Redfern andAberee Bauro of the Republic of Kiribati Ministry of Environ-ment, Land, and Agricultural Development; Frank Dayton ofthe US Army Corps of Engineers; Laura Williams of the CNMIDivision of Fish and Wildlife; Dr. Leroy Heitz of the Universityof Guam Water and Environmental Research Institute; Kash-gar Rengulbai of the Palau Bureau of Agriculture; AlmaRidep-Morris of the Palau Bureau of Marine Resources; MikeAurelio of PALARIS; Tiare Holm and Anu Gupta of the PalauConservation Society; Yimnang Golbuu, Charlene Mersaiand Steven Victor of the Palau International Coral ReefCenter; Ann Kitalong of The Environment, Inc.; and UmiichSengebau of The Nature Conservancy. Professor RichardColeman and Dr. Werner Hennecke of the University of Tas-mania, Australia, assisted with case study designs and com-mented on drafts of this report. Serena Fortuna and MetteLoyche Wilkie, Forestry Department, Food and AgricultureOrganization of the United Nations, assisted with identifyingnational focal points. Neil White, Commonwealth Scientificand Industrial Research Organization, provided mean sealevel rates through reconstructed analysis and regressionanalysis of monthly mean sea levels with tidal constituentsremoved for some of the countries and territories included inthis assessment.

LITERATURE CITED

Allen JA (1998) Mangroves as alien species: the case ofHawaii. Glob Ecol Biogeogr Lett 7:61–71

Alleng G (1998) Historical development of the Port Royalmangrove wetland, Jamaica. J Coast Res 14:951–959

Cahoon DR, Lynch JC, Perez BC, Segura B, Holland R, StellyC, Stephenson G, Hensel P (2002) A device for high preci-sion measurement of wetland sediment elevation: II. Therod surface elevation table. J Sediment Res 72:734–739

Church J, Gregory J, Huybrechts P, Kuhn M, Lambeck K,Nhuan M, Qin D, Woodworth P (2001) Changes in sealevel. In: Houghton J, Ding Y, Griggs D, Noguer M, vander Linden P, Dai X, Maskell K, Johnson C (eds) Climatechange 2001: the scientific basis. Cambridge UniversityPress, Cambridge, p 639–693

Church J, White N, Coleman R, Lambeck K, Mitrovica J(2004a) Estimates of the regional distribution of sea levelrise over the 1950 to 2000 period. J Clim 17:2609–2625

Church J, Hunter J, McInnes K, White N (2004b) Sea levelrise and the frequency of extreme events around theAustralian coastline. In: Coast to Coast ‘04 – Conf Proc,p 16–24

DeLaune R, Patrick W Jr, Buresh R (1978) Sedimentation rates

determined by 137Cs dating in a rapidly accreting saltmarsh. Nature 275:532–533

Dixon JA, Sherman PB (1990) Economics of protected areas.A new look at benefits and costs. Island Press, Washing-ton, DC

Ellison J (1993) Mangrove retreat with rising sea level,Bermuda. Estuar Coast Shelf Sci 37:75–87

Ellison J (1999) Status report on Pacific island mangroves.In: Eldredge LG, Maragos JE, Holthus PL (eds) Marineand coastal biodiversity in the tropical island Pacificregion: Vol 2. Population, development and conservationpriorities. Pacific Science Association and East WestCenter, Honolulu, p 3–19

Ellison JC (2000) How South Pacific mangroves may respondto predicted climate change and sea level rise. In: Gille-spie A, Burns W (eds) Climate change in the South Pacific:impacts and responses in Australia, New Zealand, andsmall islands states. Kluwer Academic Publishers, Dor-drecht, p 289–301

Ellison J (2001) Possible impacts of predicted sea level rise onSouth Pacific mangroves. In: Noye B, Grzechnik M (eds)Sea level changes and their effects. World Scientific Pub-lishing, Singapore, p 289–301

Ellison J (2004) Vulnerability of Fiji’s mangroves and associ-ated coral reefs to climate change. University of Tasmania,Launceston

Ellison J, Stoddart D (1991) Mangrove ecosystem collapseduring predicted sea level rise: holocene analogues andimplications. J Coast Res 7:151–165

Federated States of Micronesia (1997) 1997 Climate ChangeNational Communication. FSM National Government,Climate Change Program, Palikir

Fletcher CH, Mullane RA, Richmond B (1997) Beach lossalong armored shorelines of Oahu, Hawaiian Islands.J Coast Res 13:209–215

Gilman EL (1998) Nationwide permit program: unknownadverse impacts on the Commonwealth of the NorthernMariana Islands’ wetlands. Coast Manag 26:253–277

Gilman EL (1999) Compensatory wetland mitigation in theCNMI: an incipient discipline. In: Streever W (ed)An international perspective on wetland rehabilitation.Kluwer Academic Publishers, New York, p 3–17

Gilman EL (2002) Guidelines for coastal and marine site-planning and examples of planning and managementintervention tools. Ocean Coast Manag 45:377–404

Gilman E (2004) Assessing and managing coastal ecosystemresponse to sea level and climate change. UNESCO WorldHeritage Centre Pacific Project Planning Workshop 5–9Oct. 2004, Kiritimati Island, Kiribati. Blue Ocean Institute,New York

Gilman E, Coleman R, Hunter J (2005) Trends in frequencyand elevation of extreme high water events and causes,American Samoa. University of Tasmania and AmericanSamoa Coastal Management Program, Hobart

Gilman E, Ellison J, Coleman R (in press) Assessment ofmangrove response to projected relative sea-level riseand recent historical reconstruction of shoreline position.Environ Monit Assess

Government of Samoa (1999) First National CommunicationReport to the UNFCCC. Department of Lands, Survey andEnvironment, Apia

Government of Tuvalu (1999) Tuvalu Initial National Com-munication Under the United Nations FrameworkConvention on Climate Change. Funafuti

Holgate SJ, Woodworth PL (2004) Evidence for enhancedcoastal sea level rise during the 1990s. Geophys Res Lett31:7305–7326

174


Houghton J, Ding Y, Griggs D, Noguer M, van der Linden P,Dai X, Maskell K, Johnson C (eds) (2001) Climate change2001: the scientific basis. Cambridge University Press,Cambridge

Johannes RE (1982) Traditional conservation methods andprotected marine areas in Oceania. Ambio 11:258–261

Kingdom of Tonga (2005) Initial National Communication inResponse to its Commitment under the United NationsFramework Convention on Climate Change. Kingdom ofTonga

Kiribati Government (1999) Initial Communication Under theConvention. Ministry of Environment and Social Devel-opment, Tarawa

Komar P (1998) Beach processes and sedimentation, 2nd edn.Prentice Hall, Upper Saddle River, NJ

Krauss KW, Allen JA, Cahoon DR (2003) Differential rates ofvertical accretion and elevation changes among aerial roottypes in Micronesian mangrove forests. Estuar Coast ShelfSci 54:251–259

Lee W, Partridge T (1983) Rates of spread of Spartina anglicaand sediment accretion in the New River estuary, Inver-cargill, New Zealand. NZ J Bot 21:231–236

Lewis RR III (2005) Ecological engineering for successfulmanagement and restoration of mangrove forests. EcolEng 24(4 SI):403–418

Lewis RR III (1992) Scientific perspectives on on-site/off-site,in-kind/out-of-kind mitigation. In: Kusler JA, Lassonde C(eds) Effective mitigation: mitigation banks and jointprojects in the context of wetland management plans.Proc Natl Wetland Symp, Palm Beach Gardens, FL,p 101–106

Lynch J, Meriwether J, McKee B, Vera-Herrera F, Twilley R(1989) Recent accretion in mangrove ecosystems basedon 137Cs and 210Pb. Estuaries 12:284–299

McLean R, Tsyban A, Burkett V, Codignotto J, Forbes D,Mimura N, Beamish R, Ittekkot V (2001) Coastal zones andmarine ecosystems. In: McCarthy J, Canziani O, Leary N,Dokken D, White K (eds) Climate change 2001: im-pacts, adaptation, and vulnerability. Cambridge Univer-sity Press, Cambridge, p 343–378

Mimura N, Nunn P (1998) Trends of beach erosion and shore-line protection in rural Fiji. J Coast Res 14:37–46

Mullane R, Suzuki D (1997) Beach Management Plan forMaui. University of Hawaii Sea Grant Extension Serviceand County of Maui Planning Department, Maui

Nurse L, Sem G, Hay J, Suarez A, Wong P, Briguglio L,Ragoonaden S (2001) Small island states. In: McCarthy J,Canziani O, Leary N, Dokken D, White K (eds) Climatechange 2001: impacts, adaptation, and vulnerability. Cam-bridge University Press, Cambridge, p 843–875

Papua New Guinea Government (2000) Initial NationalCommunication Under the United Nations FrameworkConvention on Climate Change. Government of PapuaNew Guinea

Phillips B (2000) Vanuatu vulnerability assessment: anapproach to integrated regional assessment. In: MimuraN, Yokoki H (eds) Proc APN/SURVAS/LOICZ Joint ConfCoastal Impacts of Climate Change and Adaption in theAsia-Pacific Region, Kobe

Ramsar Secretariat (1999) Global review of wetland resourcesand priorities for wetland inventory. Meeting of the Con-ference of the Contracting Parties to the Convention onWetlands, Ramsar COP7 DOC.19.3, Gland

Ramsar Secretariat (2001) Wetland values and functions:climate change mitigation. Gland

Republic of the Marshall Islands Environmental ProtectionAuthority (2000) Initial Communication Under the United

Nations Framework Convention on Climate Change.Majuro

Republic of Nauru (1999) Climate Change Response. FirstNational Communication under the United NationsFramework Convention on Climate Change. Yaren

Republic of Palau Office of Environmental Response andCoordination (2002) First Communication to the UnitedNations Framework Convention on Climate Change.Koror

Republic of Vanuatu (1999) Vanuatu National Communica-tion to the Conference of the Parties to the United NationsFramework Convention on Climate Change. Port Vila

Rogers K, Saintilan N, Heijnis H (2005) Mangrove encroach-ment of salt marsh in Western Port Bay, Victoria: the roleof sedimentation, subsidence, and sea level rise. Estuaries28:551–559

Saintilan N, Wilton K (2001) Changes in the distributionof mangroves and saltmarshes in Jervis Bay, Australia.Wetlands Ecol Manag 9:409–420

SCOR Working Group (1991) The response of beaches to sealevel changes: a review of predictive models. J Coast Res7:895–921

Secretariat of the Pacific Regional Environment Programme(2003) Capacity building for the development of adapta-tion measures in Pacific Island countries project. Biannualreport covering the period April 1st 2003–September 30th2003, Apia

Smith CR (2005) Recolonization and succession of wetlandcommunities following mangrove removal. University ofHawaii Department of Oceanography, Honolulu

Snedaker S (1993) Impact on mangroves. In: Maul GA (ed)Climate change in the Intra-American Seas: implicationsof future climate change on the ecosystems and socio-economic structure of the marine and coastal regimesof the Caribbean Sea, Gulf of Mexico, Bahamas andN.E. Coast of South America. Edward Arnold, London,p 282–305

Solomon Islands Government (2004) Initial National Commu-nications Under the United Nations Framework Conven-tion on Climate Change. Solomon Islands Government

Solomon S, Kruger J, Forbes D (1997) An approach to theanalysis of storm-surge and sea level vulnerability usingGIS: Suva, Fiji, South Pacific. In: Proc 1997 Can CoastConf. Canadian Coastal Science and Engineering Associ-ation, Ottawa

SOPAC (South Pacific Applied Geoscience Commission)(2003) Future directions for the environmental vulnerabil-ity index (EVI) project. SOPAC Secretariat, Suva

SPREP (1999a) Regional wetlands action plan for the PacificIslands. South Pacific Regional Environment Programme,Apia

SPREP (1999b) Action strategy for nature conservation in thePacific Islands region 1999–2002. South Pacific RegionalEnvironment Programme, Apia

SPREP (2000) Adapting to climate change: incorporating cli-mate change adaptation into development activities inPacific Island countries: a set of guidelines for policy-makers and development planners. South Pacific RegionalEnvironment Programme, Apia

South Pacific Sea Level and Climate Monitoring Project(2001) Precision monitoring with the continuous globalpositioning system (CGPS). Australian Marine Science &Technology, Curtin

Spalding MD, Blasco F, Field CD (1997) World mangroveatlas. International Society for Mangrove Ecosystems,Okinawa

Titus JG (1991) Greenhouse effect and coastal wetland policy:

175

Clim Res 32: 161–176, 2006

how Americans could abandon an area the size of Massa-chusetts at minimum cost. Environ Manag 15:39–58

White A, Hale L, Renard Y, Cortesi L (eds) (1994) Collaborativeand community-based management of coral reefs: lessonsfrom experience. Kumarian Press, West Hartford, CT

Woodroffe CD (1995) Response of tide-dominated mangroveshorelines in northern Australia to anticipated sea levelrise. Earth Surface Processes Landforms 20:65–85

Woodworth PL, Blackman DL (2002) Changes in extremehigh water at Liverpool since 1768. Int J Climatol 22:697–714

Woodworth PL, Blackman DL (2004) Evidence for systematicchanges in extreme high waters since the mid-1970s.J Clim 17:1190–1197

Yuncker TG (1943) The flora of Niue Island. Bernice P. BishopMuseum Bulletin 178:1–126

176

Editorial responsibility: Joan Kleypas, Boulder, Colorado, USA

Submitted: March 21, 2006; Accepted: June 19, 2006Proofs received from author(s): September 19, 2006

adapting to pacific island mangrove responses to sea level rise and climate change ·...

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