Mangroves in Taiwan: current status and restoration projectsbft.cirad.fr/cd/BFT_273_43-54.pdf · coastal fisheries. Mangroves are an ideal niche ecosystem for birds, crabs, and other

B O I S E T F O R Ê T S D E S T R O P I Q U E S , 2 0 0 2 , N ° 2 7 3 ( 3 ) 43TAIWAN / MANGROVES

DOSSIER

Mangroves in Taiwan:current status

and restoration projects

Photo 1. Arrested mangrove growth due to adverse environmental conditions in Chinglo, Penghu; exampleof a seven year-old Avicennia marina with a sapling height of only 35-70 cm. August 2001. Photo K.-C. Fan.

This paper presents an overview of Taiwan’s mangroves, including diversityand distribution, uses, major threats, conservation and other problems. The restorationof mangroves in Taiwan is also discussed, and five partially successful mangroverestoration projects are described, with particular reference to the Anping Harborrestoration project in Tainan City that successfully restored Rhizophora stylosaand Lumnitzera racemosa.

Kuei-Chu Fan

Department of ForestryNational Pingtung University of Science and Technology1 Hseuh Fu RoadNei Pu, PingtungTaiwan

RÉSUMÉ

LA MANGROVE DE TAIWAN : ÉTAT ACTUEL ET PROGRAMMES DE RESTAURATION

Taiwan a une ligne de côte longue de1 140 km, mais c’est seulement dansla partie ouest de l’île que la man-grove trouve un habitat favorable àson développement. Elle y occupeune surface de 287 ha, ce qui peutêtre considéré comme négligeable auregard de l’aire totale de cet écosys-tème dans le monde. Avicenniamarina, Lumnitzera racemosa,Kandelia candel et Rhizophora sty-losa sont les quatre espèces princi-pales de palétuviers de cette man-grove, considérées chacune pour lepays comme étant en voie d’extinc-tion. L’objectif de cet article est deprésenter les caractéristiques géné-rales de la mangrove taiwanaise,notamment sa distribution et sadiversité, l’utilisation du milieu, lesproblèmes de gestion et de protec-tion. Les questions de restaurationsont aussi discutées et cinq projets,ayant réussi au moins en partie, sontprésentés. Le programme d’AnpingHarbor (Tainan City) suit une méthodeoriginale (utilisation de tubes PVCpour protéger des plants de R. sty-losa et de L. racemosa) qui a permisde réhabiliter avec succès des sec-teurs inondés.

Mots-clés : mangrove, protection,restauration, Kandelia candel,Taiwan.

ABSTRACT

MANGROVES IN TAIWAN: CURRENT STATUS AND RESTORATION PROJECTS

Taiwan has a shoreline 1 140 km long,and the western coastal zone is asuitable habitat for mangroves. Thetotal mangrove area in Taiwan coversonly 287 ha, a tiny proportion of thetotal area of mangroves in the world.Four main mangrove species arefound in Taiwan, namely Avicenniamarina, Lumnitzera racemosa,Kandelia candel and Rhizophora sty-losa, all of which have been declaredas endangered. This paper aims pri-marily to present an overview ofTaiwan’s mangroves, including diver-sity and distribution, uses, majorthreats, conservation and other prob-lems. The restoration of mangroves inTaiwan is also discussed, and fivepartially successful mangroverestoration projects are described. Inparticular, the Anping Harbor restora-tion project in Tainan City used aplanting method that employedpolyvinyl chloride (PVC) pipes andsuccessfully restored R. stylosa andL. racemosa seedlings in floodedareas. Finally, the problems of man-grove restoration in Taiwan are dis-cussed.

Keywords: mangrove, Taiwan, preser-vation, restoration, Kandelia candel.

RESUMEN

MANGLARES DE TAIWÁN: ESTADO ACTUAL Y PROYECTOS DE RESTAURACIÓN

Taiwán tiene una línea costera de1 140 km de longitud y la costa occi-dental es un hábitat favorable paralos manglares. La superficie totalocupada por el manglar de Taiwán essólo de 287 ha, representando unaproporción insignificante de la super-ficie total de los manglares del pla-neta. En Taiwán se encuentran cuatroespecies principales de mangle:Avicennia marina, Lumnitzera race-mosa, Kandelia candel y Rhizophorastylosa. Especies que han sido decla-radas plantas amenazadas. Este artí-culo intenta, en primer lugar, presen-tar una visión global estos manglares,incluidas su diversidad y distribución,su utilización, características princi-pales, conservación y problemas.También se examina la restauraciónde los manglares en Taiwán y se des-criben cinco proyectos de restaura-ción del manglar que fueron, enparte, exitosos. En particular, el pro-yecto de Anping Harbor, en TainanCity, con un método de plantaciónque utiliza tubos de policloruro devinilo. Permitió restaurar R. stylosa yL. racemosa, a partir de siembra enzonas inundadas.

Palabras clave: manglar, preserva-ción, restauración, Kandelia candel,Taiwán.

44 B O I S E T F O R Ê T S D E S T R O P I Q U E S , 2 0 0 2 , N ° 2 7 3 ( 3 )

MANGROVES / TAIWANDOSSIER

Kuei-Chu Fan

Introduction

Taiwan is located at the westernedge of the Pacific Ocean, between21° 45’ 25” and 25° 37’ 53” N, and119° 18’ 13” and 122° 6’ 25” E (fig-ure 1). The Tropic of Cancer runsthrough Chiayi County, roughly divid-ing the island into the tropical south-ern and subtropical northern half(Hsueh, 1995). The current popula-tion of this island exceeds 21 million.With an area of only 36 000 km2, thepopulation density in Taiwan standsat over 580 persons per square kilo-meter today (Chiau, 1998). Taiwan’sclimate varies in each region becauseof the diverse terrain and the mon-soon season. The coastal lowlandsare subtropical to tropical, with a hot,windy climate and abundant rainfall.The average annual temperature inTaiwan is about 22-25 °C, and annualprecipitation averages 2 500 mm,with nearly 80 % falling during theMay-October typhoon season. The cli-mate is suitable for mangrove growth.

Mangrove forests are among themost productive ecosystems in theworld. They enrich coastal waters,supply commercial forest products,protect coastlines, and supportcoastal fisheries. Mangroves are anideal niche ecosystem for birds,crabs, and other animals, and offer anatural “classroom” for learning andleisure. The total area of mangrovesaround the world is between 181 077and 198 818 km2 (Spalding et al.,1997), with Taiwan’s mangroves onlyaccounting for 287 ha in 1995.Mangroves have therefore beendeclared as endangered speciesrequiring special care (Hsueh, 1995).

Because mangroves in Taiwanrepresent a negligible proportion ofthe total mangrove area in the world,very few authors have focused onmangrove research in this countryand only a small number of generalarticles have been published, mostlyin Chinese. International mangroveliterature therefore has little informa-tion on Taiwan’s mangroves. Thisreport provides an overview of

Taiwan’s mangroves (diversity, distri-bution, uses, major threats, conser-vation and current problems) anddescribes current mangrove restora-tion projects in Taiwan. Informationon this specific aspect of Taiwan’smangroves will hopefully provide adifferent perspective on mangroveecosystems around the world.

Diversity anddistr ibution of

species

Historical data suggest that theearliest record of collecting the man-grove species Kandelia candel (L.)Druce in the Tanshui area (figures 1and 2) could date from 1864, and thatit is likely to be a native Taiwanspecies (Liu, Lai, 1982). The othermangrove species were transplantedfrom Thailand and Malaysia duringthe 1940s (Yang, 1974).


DOSSIER

Figure 1. Geographical location of Taiwan (basedon Spalding et al., 1997).

Photo 2. The Tanshui River Mangrove NatureReserve protects an unusually purestand of Kandelia candel. December2001, at low tide. Photo K.-C. Fan.

Extinction andintroduction of species

According to Tomlinson’s (1994)classification, Taiwan once hosted sixmajor mangrove species (table I).However, harbor construction hadalready caused the extinction ofCeriops tagal C.B. Rob. and Bruguieragymnorhiza (L.) Lam. by the 1960s(Liu, 1982). Four species, namelyAvicennia marina (Forssk.) Vierh.,Lumnitzera racemosa Willd., K. candeland Rhizophora stylosa Griff. are cur-rently widespread along the western

coast of Taiwan. However, mangrovehabitats have rapidly diminished dueto intensive industrial and urbandevelopments, to the extent that R.stylosa and L. racemosa have recentlybecome rare species.

Three minor components andseven mangrove associates exist onthe island (table II). These trees andshrubs occupy peripheral tidal areasalong the western coastline. Theyinclude Excoecaria agallocha L.,Pemphis acidula J.R. Forst, Heritieralittoralis Dryand, Cerbera manghas L.,Terminalia catappa L., Barringtonia

racemosa (L.) Spreng., B. asiatica (L.)Kurz., Pongamia pinnata (L.) Pierre,Hibiscus tiliaceus L. and Thespesiapopulnea (L.) Sol. However, B. asiat-ica is found only in the Kenting andHenchuan areas in southern Taiwan,whereas B. racemosa grows only inthe Ilan area in north-east Taiwan.Pemphis acidula is not found in inter-tidal areas but grows on the dry coralrocks on Kenting and Lanyu Island.These three species have alsobecome rare because their habitatsare fairly restricted. The other man-grove associates such as C. manghas,P. pinnata and H. tiliaceus haverecently been widely planted in thecoastal windbreak and urban environ-ments. Clerodendrum inerme Gaertn.,Scaevola sericea L. and Myoporumbontioides also occur in the transi-tional habitats in southern Taiwan,and should be considered as man-grove associates.

Distribution and surface areas

Taiwan has a shoreline of1 140 km (Chiau, 1998). The westerncoastal zone is characterized by tidalflats, offshore sandbars, lagoons andsand dunes, which form suitable habi-tats for mangroves. The eastern shore-line contains no mangroves becausethe coastal areas are rocky andsteeply sloping and thereforeunsuited to mangrove growth. The lit-erature does not give exact indica-tions as to the total area of mangrovesin Taiwan. According to the earliestestimate (Liu, 1982), economic devel-opment by that time had reduced themangrove area to only 120 ha. In anew survey, of mangrove distribution(figure 2) and areas (table II), Hsueh

(1995) estimated the total mangrovearea at 287 ha, an insignificant totalcompared with the world total.

Table II also shows that coldshocks below 15 °C are a constantfeature during December and Januaryin the areas north of Chiayi, includingTaipei, Taoyuan, Shingchu, andMiaolia County. The cold-tolerantspecies K. candel is dominant in theseareas, and Chuwei Nature Reserve is



Figure 2. Mangrove distribution in Taiwan (based on Hsueh, 1995).

Mangrove

the biggest mangrove area (50 ha) inTaiwan. On the other hand, the aver-age temperature in the Chiayi, Tainan,and Kaoshiung areas exceeds 22 °C inthe summer months. These areas areaffected by long periods of droughtfrom October to the followingFebruary. These conditions explainwhy A. marina is the dominant man-grove species in southern Taiwan. ThePeimen Coastal Reserve in TainanCounty is the biggest A. marina stand,but only covers 28 ha.

Uses of mangrovesin Taiwan

Traditional uses

Mangroves were used in thepast for many purposes in differentcountries, including for timber andfuelwood, food, pasture, salt andbioactive compounds for tanning andmedicinal purposes (Kovacs, 1999;

Ellison, 2000). Mangrove areas inTaiwan are very small, and the treesdo not grow large enough to beemployed as building materials forexample. Fuelwood is the mostimportant traditional use on thisisland. Fish farmers in the south-westcoastal areas of Yunlin, Chiayi andTainan County planted rows of man-groves to protect their ponds againstwind, waves and soil erosion in thedevelopment stage (Lee et al., 1977).

Current uses

Conservation of mangrove eco-systems around the world is currentlyreceiving a lot of attention. Mangrovehabitats in Taiwan also play a signifi-cant role in conservation and recre-ation, and in research programs onnature reserves and locally protectedareas. Since 1995, mangroves havethus been used as resources for eco-tourism or environmental education.

Major threats

In the last few decades, all ofTaiwan’s mangroves have been affectedby threats as severe as those in othercountries. As from the mid 1980s, manymangrove areas were lost to Taiwan’srapid economic growth; mangroveswamps were reclaimed for harbor con-struction, power plants, road buildingand industry. Some major threats tomangroves still exist and have in factbecome more serious, as described inthe following paragraphs.


DOSSIER

Table I. Major, minor mangrove and mangrove associates in Taiwan.

Family Species Life form Remarks

Major components Avicenniaceae Avicennia marina T

Combretaceae Lumnitzera racemosa S/T

Rhizophoraceae Bruguiera gymnorhiza T Recorded, but not found recently

Ceriops tagal T Recorded, but not found recently

Kandelia candel T

Rhizophora stylosa T

Minor components Euphorbiaceae Excoecaria agallocha T

Lythraceae Pemphis acidula S Grows on coral rock in Kenting and Lanyu Island

Sterculiaceae Heritiera littoralis T

Mangrove associates Apocynaceae Cerbera manghas T Used as a windbreak species

Combretaceae Terminalia catappa T Used as a windbreak and urban greening species

Lecythidaceae Barringtonia asiatica T

Barringtonia racemosa T

Leguminosae Pongamia pinnata S Used as a windbreak and urban greening species

Malvaceae Hibiscus tiliaceus S/T Used as a windbreak species

Thespesia populnea S/T

Other species Verbenaceae Clerodendrum inerme S

Goodeniaceae Scaevola sericea S Used as a windbreak species

Myoporaceae Myoporum bontioides S

Categories according to Tomlinson (1994); T: tree, S: shrub.

Photo 3. Four mangrove seedlingssuccessfully established in adegraded Casuarina stand at theShuangchun restoration project inTainan County. August 2001. Photo K.-C. Fan.

Coastal area reclamationmay destroy the most

sensitive mangrove habitats

Coastal zone management hasbecome one of the most importantissues in Taiwan in the last few years.The scarcity and high value of avail-able land have attracted both publicand private developers to the island’scoastal zones. Because coastal landsare generally perceived as suitablefor development, the coastal zonehas become a complex area of com-peting uses. Rapid urbanization, pol-lution, tideland reclamation, coastal

aquaculture and the development oftourism are exerting increasing pres-sure on Taiwan’s coastal zone. TheEnvironmental Protection Administra-tion (EPA) reports that more than 80industrial projects have been pro-posed or undertaken recently. Mostof these projects, developed on thewestern tideland, require areasexceeding 1 000 ha, and some ofthem even demand 10 000 ha (Chiau,1998). This situation reveals theincreasing negative impact on theenvironmental and ecological state ofmangrove habitats.

Land subsidence : one ofthe most serious problems

along the west coast

Overpumping of groundwater forcoastal aquaculture has caused landsubsidence. A recent report conductedby the Provincial Water ConservancyBureau revealed that an area of1 010 km2 – more than 10 % of Taiwan’sflat land – along Taiwan’s south-west-ern coastal zone was affected by landsubsidence (Chiau, 1998). This situa-tion has obviously exacerbated risksof excessive flooding in mangrovehabitats. For example, the coastal areain Chiayi County has sunk 90 cm since1987, causing flooding that killed offabout 10 ha of Avicennia stands in1993 (Chen, 1997).

Pest damage in mangroveecosystems is gradually

increasing in Taiwan

All mangrove ecosystems inTaiwan have been designated as pro-tected areas. This status restricts allhuman activity and management.However, the legislation does not pro-vide for proper management prac-tices to preserve mangrove growthand habitat. Excessive expansion ofmangroves causes drainage problemsand is also encouraging pests. Forexample, the larvae of Zeuzera cof-feae and Anoplophora maculata arethe primary wood borers of K. candelstands and have recently caused thedeath of mature trees.



Table II. Present status of major mangrove areas in Taiwan.

Location Species Habitat Area Protective measures (ha) (Management Agency)

Taipei County Watzuwei K. candel River bank 8.79 Watzuwei Nature Preserve

(30.00)* (Taipei County Government)

Taipei City Chuwei K. candel River bank 50.00 Chuwei Nature Preserve

(74.61)* (Taiwan Forestry Bureau)

Kuantu K. candel River bank 19.00 Kuantu Nature Preserve(55.00)* (Taipei Municipal Government)

Taoyuan County K. candel River bank 0.04

Hsingchu County A. marina River bank; 5.69 Hsinfeng mangrove reserveK. candel coastal plains (Hsingchu County Government)

Miaoli County K. candel River bank; 4.03 Chunan mangrove reservecoastal plains (Miaoli County Government)

Taichung County K. candel River bank 2.00

Changhua County K. candel River bank; 3.76coastal plains

Chiayi County A. marina River bank; 45.26 Chang-Yun-Cha, Haomeiliao K. candel coastal plains; Coastal ReserveR. stylosa lagoon (Chiayi County Government)

Tainan County A. marina Lagoon; river 75.27 Peimen Coastal ReserveK. candel bank; sand bar (Tainan County Government)L. racemosa

Tainan City A. marina Drainage bank; 14.92 Sutsa protected areaL. racemosa protected area (Tainan City Government)R. stylosa

Kaohsiung County A. marina River side; Salt 55.53 K. candel pan; R. stylosa Drainage bank

Pingtung County A. marina Drainage and 2.66 fishpond bank

Total 286.95

* Area of nature reserves.

Photo 4. Extremely strong growth of fiveyear-old Rhizophora stylosasaplings with abundant prop roots,in favorable fringe sites. June 2001. Photo K.-C. Fan.

Conservationproblems

The Tanshui River MangroveNature Reserve, the first mangrovereserve in Taiwan, was establishednear Taipei in 1986 to protect K. can-del. This species is found at the north-ern limit of global mangrove distribu-tion, at 31° 23’ N on the Kyushu Islandof Japan, and is able to withstandwinter chills with temperatures as lowas -4 - 5 °C . This species is generallyfound as an understory or subdomi-nant species within mixed mangrovestands in Thailand, Hong Kong, south-ern China, and the southern islandsof Japan (Maxwell et al., 1997).Therefore, the Tanshui reserve is notonly the biggest mangrove area inTaiwan, but is also one of the world’svery few pure stands of this species(photo 2). The Kuantu Reserve (pro-tecting waterfowl in particular) andWatzuwei Nature Reserve were estab-lished at a later stage, bringing thetotal national protected area to 78 haand covering 27% of existing man-groves (table II). However, mangroveconservation and protection are stillfraught with problems.

Suitability of mangroveconservation andprotection laws

National level The Watzuwei, Chuwei and

Kuantu Nature Reserves were estab-lished under the Cultural HeritagePreservation Law (CHPL). Their man-agement agencies are Taipei CountyGovernment, Taiwan Forestry Bureau,and Taipei Municipal Government,respectively (table II), but no oneagency co-ordinates the conservationof the three mangrove reserves. TheCHPL strictly enforces conservationlegislation, and entirely restricts anyinterference in nature preserves. Forexample, K. candel has recentlygrown well and thus enlarged thesand bar at the mouth of KellungRiver. A simulation of hydrologicalconditions up to 2006 has demon-

strated that mangrove growthincreases flow velocity, raises thewater level by approximately 18 cmduring floods and damages dikes(Hsu et al., 1999). However, govern-ment officials think the CHPL ispresently the best way to protectK. candel.

Local levelThe Executive Yuan established

Chang-Yun-Cha, Haomeiliao, andPeimen Coastal Reserve in 1984, inline with the Nature EnvironmentProtection Plan for Taiwan’s coastalareas. Hsingchu, Miaoli County andTainan City Governments have alsoestablished small mangrove reserves.These reserves do not enjoy the samelevel of protection as reserves underthe CHPL, as their management hasbeen desultory.

Lack of effectiveprotective management

Designating nature preservesand coastal protected areas is onlythe starting point for mangrove con-servation; the key issues include theensuing proposals, detailed plans,and concrete management practices,with reforms of any inappropriatepractices. However, no effective pro-tective management serves Taiwan’smangrove reserves. The present man-agement policy simply involves regu-lar patrols to prevent mangroves frombeing destroyed and to protect themfrom certain activities that are harm-ful to their habitats.

Lack of database forindividual mangrove

ecosystems

Many scientific efforts andinvestigations have focused on theecology of Tanshui Nature Preservesince the 1970s. However, baselinebackground data on local mangrovereserves or unprotected areas remains unavailable. An inventoryreport on each mangrove ecosystemshould therefore be prepared as soon

as possible to provide baseline infor-mation to integrate policies forTaiwan’s mangrove resources.

Lack of coordinationamong agencies

Coordination involves horizontaland vertical cooperation and consul-tation among government agenciesand between government and otherorganizations. Taiwan has so farlacked a national policy on mangroveprotection. Moreover, no particularagency manages and preserves man-groves. Various administrativedepartments handle mangrove affairsat local government level. For exam-ple, several different projects werefound to overlap in the same pro-tected areas due to poor coordinationamong agencies.

Photo 5. Development of numerous prop roots with superiorgrowth on three year-old Rhizophora stylosaseedling grown in 50 cm PVC pipes. August 2001. Photo K.-C. Fan.


DOSSIER

Restoration ofmangroves in

Taiwan

More recently, urban andaquatic development world-wide hasdiminished mangrove forests, andcaused concerns in every country forthe conservation of these naturalresources and their restoration.Mangrove forests have been restoredto achieve various objectives, includ-ing commercial uses (silviculture),protection of fisheries habitats andshorelines and restoration of bal-anced ecosystems (Kaly, Jones,

1998; Ellison, 2000). This sectionbriefly reviews the history and prob-lems of mangrove restoration inTaiwan.

The concept of restoration/rehabilitation for a

mangrove ecosystem

Some scientists have empha-sized the different meanings given toterms such as restoration and reha-bilitation. Field (1998) makes a dis-tinction between rehabilitating anecosystem, which he defines as thepartial or full replacement of theecosystem’s structural and functionalcharacteristics, and total restorationof an ecosystem, which aims to bringan ecosystem back to its original con-dition. According to this interpreta-tion, restoration is one possible resultof a successful rehabilitation effort.Non-scientific organizations generallyhave no clear definitions of restora-tion. Restoration managers havetherefore frequently emphasizedmangrove planting as the primaryapproach in restoration (Ellison,2000). Similarly, in Taiwan, scientists,government officials and conserva-tionists have carried out mangroverestoration projects that also involvedplanting mangrove propagules,seedlings, or even saplings inselected places. However, this reportemploys the term “restoration” toavoid confusion.

Mangrove restoration in Taiwan

The mangroves along the westcoastal line are all artificial planta-tions dating from 1945-1975 (Lee etal., 1977; Huang, Hsu, 1982), exceptK. candel, which is native to Taiwan(Liu, Lai, 1982).

1945-1975 Mangrove reforestation projects

were initiated in the 1940s, and mostprojects were carried out between1945 and 1975 by the Taiwan ForestryBureau, with funding from the Councilof Agriculture (table III). Governmentofficials employed labor to plantseedlings of K. candel, A. marina (themajor planting species) and R. sty-losa (in small quantities). Most plant-ing areas were very small; the largestcovered 25 ha at Chiku in TainanCounty in 1962. These projects aimedprimarily to protect the coast.However, unsuitable environmentalconditions and human impacts killedall planted mangrove seedlingsbefore 1980 (Huang, Hsu, 1982). Theonly exception was in Hungmaokangin Hsinchu County, where K. candeland A. marina grew well and therestored area expanded to 5.3 ha. In1988, the County government estab-lished a local mangrove reserve toprotect the mangrove ecosystem.

1976-1993After 1975 the government

directed no mangrove restorationprojects; all major work during thisperiod focused on protecting man-groves. During that time, some localpeople and fishermen planted man-grove seedlings to protect fish ponds,so that mangroves were planted spo-radically along the western coastalarea of Taiwan.

1994-presentIn 1994, former president Lee vis-

ited the mangroves of Indonesia andrealized the protection value of man-groves. He suggested that the govern-ment should establish mangroves on alarge scale along the coastal area.Since then, almost every county inwestern Taiwan has launched man-grove planting projects. In most cases,the four mangrove species wereplanted in an uncontrolled manner in asmall area (1-5 ha). Only a few man-grove restorations have been a partialsuccess, and some mangrove saplingshave survived and grown well up tonow. However, these projects arerarely documented. The following sec-tion (points ▪) gives limited informa-tion obtained from personal communi-cation with government officials andresearchers.



Table III. Mangrove afforestation projects during 1945-1975 in Taiwan.

Location Year Area (ha) Species Remarks

Hungmaokang, 1945 4 A. marina Spread to 5.3 ha Hsinchu County K. candel

Lungching, 1952 10 K. candel All died before 1980Taichung County

Hanpao, 1952-1954 12 A. marina All died before 1980Changhua County K. candel

Tungshiao, 1957-1960 5-6 K. candel All died before 1980 Miaoli County

Chinglo, 1958 2.9 A. marina All died before 1980Penghu County

Chiku, 1962 24.5 K. candel All died before 1980Tainan County R. stylosa

Chingshui, 1975 8 K. candel All died before 1980 Taichung County

Sources: Lee et al., 1977; Huang, Hsu, 1982; Hsueh, 1995.

▪ Haomeiliao restoration project inChiayi County (1993-1994; 3.0 ha).

Executive agency: Taiwan EndemicSpecies Research Institute.

Goal: increase biodiversity of themangrove ecosystem.

Planting methods: R. stylosa, L. race-mosa and K. candel propagulesand seedlings planted within mixedstand of Casuarina and A. marina.

Planters: paid workers planted allseedlings and propagules.

Current status: the mangrove isreported to have grown very well,especially R. stylosa and L. race-mosa, which have reached over 2 mafter four years. The current statusof this project is unknown.

▪ Kaoping River restoration project inKaohsiung County (1994-2000;4.5 ha).

Executive agency: Kaohsiung CountyGovernment.

Goal: establish a mangrove ecosys-tem park.

Planting methods: R. stylosa, L. race-mosa, K. candel and A. marina wereplanted in a new wetland along thebank of the Kaoping River.

Planters: mainly local students andmembers of the public.

Current status: a wetland was createdby constructing breaching dikesalong the river. Several petrochemi-cal plants are near the planting site.According to field observations inSeptember 2001, the mangrovegrowing area diminished to lessthan 2 ha, growth of the mangroveseedlings was disappointing, andmany creeping plants were encro-aching on mature A. marina trees.In such circumstances, the futurestatus of the project is uncertain.

▪ Shuangchun restoration project inTainan County (1995-present;3.5 ha, and the planting work iscontinuing).

Executive agency: Tainan CountyGovernment.

Goal: replace the degraded Casuarinawindbreak and create a coastalrecreation park including a planta-tion of mangrove species.

Planting methods: mixed planting offour mangrove species after remov-ing the degraded Casuarina stand.

Planters: employed workers for mostseedlings, with community familiesand children.

Current status: The author visited thesite in September 2001. The habi-tat, including favorable tidal inun-dation flows, is suitable for man-grove growth and canals within thewetland appear to have been dugto assist water flow. The venturehas successfully established75 000 mangrove seedlings in thedegraded Casuarina stand, and hasbecome the most successful man-grove restoration project in Taiwan(photo 3).

▪ Chinglo restoration project inPenghu County (1994-1995;1.5 ha).

Executive agency: National PingtungUniversity of Science andTechnology and Penghu CountyGovernment.

Goal: restore the mangrove ecosys-tem that was destroyed for aqua-culture in 1974.

Planting methods: R. stylosa,A. marina and K. candel weredirectly sowed with propagules,and L. racemosa were planted withone-year-old seedlings. The sitehas very high salinity and no freshwater.

Planters: employed workers.Current status: The survival rate and

growth of all four mangrove speciesprogressed very well during the first

two years of the project. However,growth was arrested by stressesfrom the harsh environment, includ-ing high salinity, heavy low-nutrientsoil (fish farmers removed the fer-tile silt), strong winds and heavysalt spray during the winter. Theauthor visited the site in August2001, when only 15 R. stylosasaplings had survived, and theK. candel samples also graduallydeclined and died. The salt tolerantA. marina is the dominant speciesbut a dwarf mangrove form (sevenyears old) is present, with a saplingheight of only 35-70 cm (photo 1).Most of the L. racemosa seedlingssurvived, but these have not grownsignificantly in height either.

▪ Anping Harbor restoration project atTainan City (1996-present; 4.6 ha).

Executive agency: National PingtungUniversity of Science and Techno-logy.

Goal: restore the R. stylosa andL. racemosa mangrove species,destroyed by harbor construction,using polyvinyl chloride (PVC)planting pipes to restore man-groves in flooded areas.

Planting methods: R. stylosa, L. race-mosa, K. candel, Myoporum bon-tioides and Thespesia populneapropagules and seedlings plantedin an urban wetland.

Planters: university students plantedmost seedlings, but employedworkers planted a few.


DOSSIER

Photo 6. Three year-old Rhizophora stylosa seedlings grown in 150 cm PVC pipes developedseveral prop roots but did not reach down to the bottom soil. March 2001. Photo K.-C. Fan.

Current status: A. marina trees alreadyoccupy the habitat, which is suitablefor mangrove growth (1.5 ha). Theremaining areas have unfavorablehydrodynamics or have been degra-ded by damaging environmentalimpacts. This project has involvedseveral mangrove replanting trials.Directly sowing R. stylosa propag-ules among Avicennia trees hasgiven a survival rate of only 30%.The high mortality rate is due to pol-luted soil, algal damage and heavywater turbulence. However, somesaplings have grown very strongly.With abundant prop roots on thefavorable fringe sites near the water-way, the plants reached a meanheight over 200 cm, with manypropagules emerging (photo 4). Tenmonth old L. racemosa seedlingsplanted in May 1998 had a survivalrate of 62.4% in the first year. Theseedlings grew to a height of 110 cmand flowered. However, three yearsafter planting, the sapling heightwas only 160 cm, mainly because theflourishing canopy of A. marina sup-pressed the saplings by limitingavailable sunlight.The author used PVC planting pipesto restore mangroves in a floodedarea of 1.0 ha. The PVC pipes hadan inside diameter of 10 cm, andwere cut to lengths of 150 and 50cm. Workers drilled five to ten smallholes along the whole length ofeach pipes to allow water

exchange. In July 1998, the 150 cmpipes were driven into the soil to adepth of 50 cm in the deepwaterarea. The 50 cm PVC pipes wereplaced (with 20 cm inserted intothe soil) in a small flood area wherethe highest flooding was approxi-mately 50 cm. Each pipe was filledwith muddy sediment from the sur-face, creating an artificial bottom,and the R. stylosa propagules withnew roots were then planted intothe top of the PVC pipes.Unfortunately, due to serious multi-ple stresses, the seedling survivalrate for this experiment was lessthan 5% after two months. The areawas replanted several times duringNovember 1998 and November1999 with R. stylosa propagules andL. racemosa seedlings. Recent fieldinvestigations show that some vig-orous R. stylosa seedlings grewextremely well in 50 cm PVC pipes,with a seedling height of 85-110 cm.The proliferating prop roots wereestablished in muddy soil, whichprovides stability and essentialnutrients, and the first propagulewas noted on the seedlings threeyears after planting (photo 5).The R. stylosa container seedlingsreplanted in the 150 cm PVC pipesin November 1998 also grew well,reaching a height of 75 cm andproducing several prop roots.However, they had not yet reachedthe bottom soil (photo 6).

The survival rate of L. racemosaseedlings grown in 150 cm PVCpipes was around 80%, and theseedlings produced fruits in the firstyear. However, the seedling heightwas only 60 cm throughout the firstthree years. These results are prima-rily explained by the seedlings’ shal-low root systems and lack of promi-nent aerial roots to adapt to floodstress. However, the view over theR. stylosa and L. racemosa seed-lings in the flooded area is magnifi-cent (photo 7).This research has shown that PVCpipes may be an effective, cheapand easy method for planting man-groves. However, there are stillmany problems. For example, inJune 2001, over 70% of theseedlings grown in the floodedarea were attacked and eaten byherbivorous caterpillars. Recently,many fish habitats have been in thetray circle (photo 8), affectingseedlings grown in PVC pipes.

Problems ofmangroverestoration

In Taiwan, most projects havebeen designed and implemented bygovernmental officials and organiza-tions. However, the lack of basic knowl-edge and experience in mangroverestoration have caused projects to failor only partially achieve their goals.

There are no reports or docu-mentation illustrating silviculturaltechniques for mangrove restorationin Taiwan. Although methods for plant-ing individual mangroves species arefamiliar and have been developed inmany countries (Fao, 1994; Field,1996), they may not be appropriate forthe small restoration area in Taiwan.

Restoration of mangroves doesnot appear to be especially difficult– mangroves may in fact be among theeasiest marine systems to reconstruct(Kaly, Jones, 1998; Ellison, 2000). Aslong as habitats have the right hydro-logical conditions, mangroves can grow

Photo 7. A magnificent view of Rhizophora stylosa and Lummitzera racemosa seedlings in the flooded area. November 2001. Photo K.-C. Fan.



in a variety of coastal environments,approaching the biomass, stand struc-ture, and productivity of natural forestswithin two decades. Unfortunately,some conservation organizations inTaiwan have convinced the public thatmangrove seedlings seldom surviveand that a mangrove forest is difficult toestablish.

Furthermore, in the restorationprojects managed by County govern-ment and local organizations, volun-teer groups and school children areinvited to take part in planting. Theyusually enjoyed the job, but they alsodamaged planting stock or handled itimproperly, which lowered theseedling survival rate. In fact, mostTaiwanese people do not knowenough about mangrove ecology andecosystem restoration, and lack con-cepts for subsequent management,maintenance and remedial work. Forexample, when mangrove seedlingshave survived or grown moderatelywell for as little as 3-5 years, govern-ment officials and conservationistshave been too quick to introduce eco-tourism into the mangrove restorationareas, not realizing the need for con-tinuing silvicultural work such as thin-ning to control forest density, and pestand disease control to prevent defoli-ation or death of mangrove trees.

Otherwise, scientists themselvessometimes argue against restorationprojects in Taiwan’s coastal area forthe following reasons:

▪ Most restoration areas arelocated at the mouth of a river or onriver banks. Mangroves that prolifer-ate too vigorously, like Kandelia can-del at the Kellung and Tanshui River,can cause drainage problems in those

areas. Furthermore, mangrove spe-cies planted to protect coastal areasmay compete with native plantspecies and produce negative effectsin the near future.

▪ Excessive replanting of man-groves in western coastal areas grad-ually destroys the habitat of Uca for-mosensis (an endemic species inTaiwan). Excessive replanting of man-groves may drive this unique crab toextinction because its habitat is hardclay mud on spacious flatlands with-out mangroves (Shih, 1997).

Conclusion andprospects

Mangrove areas in Taiwan arevery small and attention is presentlyfocused on conserving mangrovehabitats. Conservation legislation,especially the Cultural HeritagePreservation Law (CHPL), prohibitsany interference or human activity inmangrove reserves. Accordingly, man-groves may proliferate excessively,causing serious flooding and pestproblems. Therefore, the efforts of dif-ferent institutions in various regionsshould be better coordinated, espe-cially those of ecologists and foresterswho have been disregarded until now.Firstly, the protective legislation mustbe revised again and strictly enforced,and secondly, appropriate and practi-cal management guidelines must bedeveloped for mangrove reserves, toensure sustainable development ofmangroves in Taiwan.

Almost every county in westernTaiwan has undertaken mangroverestoration since 1994. Unfortunately,many projects have failed because ofunsuitable habitats and participants’lack of basic knowledge and experi-ence in mangrove restoration. A fewmangrove restorations have beenpartially successful, and some man-grove saplings have survived andgrown well. This valuable experienceurgently needs to be integrated withtechnology to develop practicalguidelines for mangrove restorationin Taiwan. The Anping Harbor man-grove restoration project, in particu-lar, is the first attempt to restore amangrove ecosystem in an urbanarea. This restoration site is verysmall compared to the world’s otherrestoration sites, and the areasinvolved are affected by unfavorablehydrodynamic conditions and toomany negative environmentalimpacts. Nevertheless, this projecthas included several mangrovereplanting trials, which have beensuccessful in some places and unsuc-cessful in others. All of these experi-ences may be valuable for other man-grove restoration projects.

Acknowledgements

The author would particularly liketo thank Dr. François Fromard of theLaboratoire d’Ecologie Terrestre at thePaul Sabatier University in Toulouse,for his invitation to write this articleand his valuable suggestions and com-ments on the manuscript. The authoralso thanks Dr. Ching-Long Yeh for pro-viding useful papers, Mr. Gang Yang fordrawing the maps, the officials ofKaohsiung, Pingtung County Govern-ment for providing useful data, and Mr.Chiao-Tseng Chen and Mr. Kao-LiangChen at Penghu County Governmentand Mr. Yang at Tainan County Govern-ment for their assistance with fieldwork and their offer of valuable experi-ence. Finally, special thanks are alsodue to Ms. Mei-Ling Yang, Jung-ShengHsia and Mr. Der-Far Pan at the TaiwanForestry Bureau for providing manyuseful references.


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Photo 8. The deepwater area at low tide for numerous fish habitats. August 2001. Photo K.-C. Fan.



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Documents

Mangroves in Taiwan: current status and restoration projectsbft.cirad.fr/cd/BFT_273_43-54.pdf · coastal fisheries. Mangroves are an ideal niche ecosystem for birds, crabs, and other