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Have mangrove restoration projects worked? An in-depth study in Sri Lanka: Evaluation of mangrove restoration in Sri Lanka

Authors:

Abstract

This study investigated the effectiveness of mangrove planting initiatives in Sri Lanka. All the lagoons and estuaries in Sri Lanka were included in the study. We documented all agencies and locations, involved in mangrove planting efforts, along with the major drivers of these planting initiatives, their extents, and the possible causes of the success or failure of planting. An adapted three-step framework and a field survey consisting of vegetation and soil surveys and questionnaires were used to evaluate the objectives. We found that about 1,000–1,200 ha of mangroves, representing 23 project sites with 67 planting efforts, have been under restoration with the participation of several governmental and nongovernmental organizations. However, about 200–220 ha showed successful mangrove restoration. Nine out of 23 project sites (i.e. 36/67 planting efforts) showed no surviving plants. The level of survival of the restoration project sites ranged from 0 to 78% and only three sites, that is, Kalpitiya, Pambala, and Negombo, showed a level of survival higher than 50%. Survival rates were significantly correlated with post-care. Planting mangrove seedlings at the incorrect topography often entails inappropriate soil conditions for mangroves. Survival rates showed significant correlations with a range of soil parameters except soil pH. Disturbance and stress caused by cattle trampling, browsing, algal accumulation, and insect attacks, factors that may themselves relate to choosing sites with inappropriate topography and hydrology, were common to most sites. The findings are a stark illustration of the frequent mismatch between the purported aims of restoration initiatives and the realities on the ground.
Restoration Ecology (DOI: 10.1111/rec.12492)
Title: Have mangrove restoration projects worked? An in-depth study in Sri
Lanka
Running head: Evaluation of mangrove restoration in Sri Lanka
Authors and addresses:
Kodikara K.A.S.1,2*, Mukherjee N.3,4*, Jayatissa L.P.1, Dahdouh-Guebas F.2,4 **, Koedam N.2 **
1Department of Botany, University of Ruhuna, Wellamadama, Matara, Sri Lanka
2Laboratory of Plant Biology and Nature Management, Ecology and Biodiversity, Vrije Universiteit Brussel - VUB,
Pleinlaan 2, B-1050 Brussels, Belgium
3Conservation Science Group, Department of Zoology, University of Cambridge, Cambridge, CB23EJ, UK
4Laboratory of Systems Ecology and Resource Management, Department of Organism Biology, Faculty of Sciences,
Université Libre de Bruxelles - ULB, Av. F.D. Roosevelt 50, CPI 264/1, B-1050 Brussels, Belgium
Corresponding author: sunandaruh@gmail.com
*co first-authors
**co-last authors
Author contributions
KKAS, NK, FDG, LPJ designed the research; KKAS performed the fieldwork; NK, FDG, LPJ
supervised the research; NK, FDG, KKAS analyzed the data; NM, KKAS wrote the paper; NK,
LPJ, FDG edited the manuscript.
Abstract
The study aimed at investigating the effectiveness of mangrove planting initiatives in Sri Lanka.
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All the lagoons and estuaries in Sri Lanka were included in the study. We documented the all
agencies, locations, the extent, mangrove planting efforts, major drivers of the planting
initiatives, and the possible causes of success/failure of planting. An adapted three-step
framework and a field survey consisting of vegetation and soil surveys and questionnaires were
used to evaluate the objectives. We found that about 1000-1200 ha of mangroves, representing
twenty-three project sites with sixty-seven planting efforts, have been under restoration with the
participation of several governmental and non-governmental organizations. However, about 200-
220 ha showed successful mangrove restoration. Nine out of twenty-three project sites (i.e.,
36/67 planting efforts) showed no surviving plants. The level of survival of the restoration
project sites ranged from 0-78% and only three sites i.e., Kalpitiya, Pambala, and Negombo
showed a level of survival higher than 50%. Survival rate was significantly correlated with post-
care. Planting of mangrove seedlings at the incorrect topography often entails inappropriate soil
conditions for mangroves. Survival rates showed significant increase with soil parameters except
soil pH. Disturbance and stress caused by cattle trampling, browsing, algal accumulation, and
insect attacks, that may also find their origin in a choice of inappropriate site topography with
ecologically non suitable hydrology (for mangroves), were common to most sites. The findings
of this study are a sharp pointer to the mismatch between purported aims of restoration initiatives
and the realities on the ground.
Keywords: Climate zones, field survey, Indian Ocean tsunami, level of survival, mangrove
restoration, Sri Lanka
Implications
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This detailed study can be used as a baseline for future studies on mangrove restoration in
Sri Lanka and in the South East Asian region
The outcomes of the study provide a strong scientific basis and can easily be used as a
baseline for guiding future mangrove planting with special attention to appropriate site
topography with ecologically suitable hydrology
Findings of the study hold a key to identify the precious resources that need to be
divested in enhancing probability of planting success
Main text
Introduction
Mangrove ecosystems are primarily tropical, subtropical, and warm temperate (30°N to 37°S)
coastal wetlands occurring in 123 countries (Feller et al. 2010; Spalding et al. 2010; Mukherjee
et al. 2015). They are amongst the most productive ecosystems per unit area, having been
reported to contain up to 1023 Mg carbon.ha-1 (Donato et al. 2011). In addition, mangroves
continue to be widely used by coastal communities (e.g., for livelihood like food, fuel,
subsistence, shelter, and tourism) throughout most of their geographic distribution (Walters et al.
2008; Lee et al. 2014; Mukherjee et al. 2014).
In spite of their ecological and socio-economic importance, mangrove conservation has not been
able to match the rate of mangrove destruction and loss (Duke et al. 2007; Polidoro et al. 2010;
Richards & Friess 2016). In the last few decades, mangrove loss has been an issue of growing
concern, with several authors urging for stronger measures to stem this loss (Valiela et al. 2001;
Duke et al. 2007; Giri et al. 2011).
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Though calls for restoration and conservation of mangroves are not new and date back at least to
the 1970s (Teas 1977), the effect of mangrove loss on coastal protection was most widely noted
recently after several cyclonic and tsunami events in South and South East Asia (e.g., Cyclone
Haiyan in November 2013, Cyclone Aila in May 2009, and the Indian Ocean tsunami in
December 2004). The Indian Ocean tsunami forms a watershed in this context due to its massive
effect on human lives and property and the subsequent range of initiatives for mangrove
restoration which were launched as a consequence (Mukherjee et al. 2015). Projects of mangrove
restoration that had already been launched in some nations since the 1950s (e.g., China, India) or
1960s (e.g., Bangladesh) (FAO 2007) gained momentum after the Indian Ocean tsunami and
were replicated in several nations across the South Asian region after 2004 (ITTO/ISME 2008).
For the sake of clarity we will use the word ‘restoration’ irrespective of previous existence of
mangroves in particular sites, because the planting efforts usually claim that objective.
Given the considerable amount of funding and international attention that mangrove restoration
projects have received over the last decade (Primavera & Esteban 2008; Biswas et al. 2009;
Mukherjee et al. 2009), it is critical to evaluate the success (or failure) of restoration
interventions (Ellison 2000) for three main reasons: a) to document what proportion of planting
projects have led to establishment success of mature mangrove stands b) to understand the
restoration of ecosystem functions in restored planted sites and c) to serve as a guideline for
mangrove restoration projects in the future. Evaluating the success of mangrove restoration
projects is also critical from a financial and risk-assessment perspective since human lives may
depend on the coastal protection claimed to be offered by these planting initiatives.
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In this paper, we investigate the effectiveness of mangrove restoration initiatives in Sri Lanka,
which have almost all taken place in the wake of the 2004 Indian Ocean tsunami. Survival of
planted seedlings for at least five years was used as the proxy for success in this study. This
criterion was used for Rhizophora mucronata in studies that were carried out in Sri Lanka by
Ranasinghe (2012). Sri Lanka is an important study area to analyse restoration success rates for
the following reasons: a) Sri Lanka was severely affected by the 2004 tsunami. This was
followed by substantial investment, i.e., about 13 million USD, for planting of mangroves over
the past decade (IUCN 2009), b) compared to other tsunami-affected nations in south Asia, there
has been considerable research on mangroves in Sri Lanka. This provided a baseline for this
study (Pinto 1986; Amarasinghe 1996; Dahdouh-Guebas et al. 2002, 2005, 2006; Jayatissa et al.
2008; Kodikara & Jayatissa 2010; Dissanayake et al. 2014; Madarasinghe et al. 2015, 2016) c)
the geographical extent of Sri Lanka is conducive for an in-depth nation-wide survey of
restoration projects. Several studies on mangrove restoration and success have been reported in
Sri Lanka (IUCN 2011; Ratnayake et al. 2012). However, only 3-4 planting sites were subjected
for the study and no detailed data on total planting initiatives, the planted extent, the total
surviving area, planting agencies involved, and major drivers. Therefore we believe that the
causes for the failure and recommendations that have been given are not strong enough in
extrapolating to country level. Further, several similar investigations on the failure of mangrove
planting after the 2004 tsunami have been reported in different countries, such as in Aceh,
Indonesia, Philippine, and Thailand in the Asia, Brazil, and the USA. In these studies, different
aspects of mangrove restoration e.g., topography of mangrove planting (Primavera & Esteban
2008; Samson & Rollon 2008), causes for mangrove restoration failure (Samson & Rollon 2008;
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Brown et al. 2014a, 2014b), technical guidance and recommendations (Lewis 2000, 2005;
Primavera & Esteban 2008; Lewis & Brown 2014; Asaeda et al. 2016) and socio-economic
aspects of mangrove restoration (Stevenson et al. 1999) have been discussed. Many studies
discussed on mangrove restoration of such countries based on some selected dimensions.
Therefore, we intended to carry out our study to extensive extent covering many dimensions on
mangrove planting (e.g., agencies, the locations, the extent etc.), the major drivers of these
planting, the success of the planting projects as that gives higher validation for mangrove
planting on country level.
Hence the key objectives of this study were to: 1) document the agencies involved, the locations,
the extent, and number of mangrove planting initiatives along the Sri Lankan coastline; 2)
calculate the rate of survival of seedlings in these planting projects (as a measure of success of
planting effort); 3) identify the drivers of these planting projects. In addition, attention must be
paid to soil conditions since according to previous studies, mangrove plants are frequently
subjected to poor soil conditions as the result of planting at unsuitable topographical position
(Field 1996; Elster 2000; Lewis 2000, 2005; Samson & Rollon 2008; Brown et al. 2014a).
Therefore, investigating the causes of success/failure of planting initiatives including soil
parameters in planting sites was also included as one of the objectives.
Methods
Study site: Sri Lanka is located in the Indian Ocean between 05°55’ and 09°51’ N latitude, and
079°41’ and 081°53’ E longitude. Its area is approximately 65,610 km2 with a coastline of about
1,620 km. The country has been divided into four major climatic zones namely wet, dry,
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intermediate, and arid zones (Pemadasa 1996). The wet zone is mainly confined to the
southwestern region, the dry zone to the northern and the eastern part of the country. These two
zones are separated by the intermediate zone. The arid zone on the other hand is found in the
northwestern and the southern parts of the country and climatic conditions are very different in
the climatic zones (Table 1). According to CZMP (2003), 5009 ha of mangrove cover is found in
the dry and arid zones, 644 ha in intermediate zone and 430 ha in the wet zone. However,
mangrove cover between 2003 and 1983 was reduced by about 2450 ha in the dry and arid zones
(CZMP 2003).
Framework for evaluation: To address the objectives we use an adapted version of the
framework given in Mukherjee et al. (2015), (Figure 1). This framework consists of three parts
namely ecological (e.g., species planted), social (e.g., drivers of planting initiatives), and
economic (e.g., funding agency of the intervention). Though there is a plethora of frameworks
currently available in the literature (e.g., Costanza et al. 1997; Balmford et al. 2002) we chose
this framework owing to its ecocentric approach as opposed to an anthropocentric one (sensu
Binder et al. 2013).
Questionnaire survey: Using the above three-step framework, a preliminary field survey and
interviews, we designed a questionnaire to evaluate the mangrove restoration planting in Sri
Lanka (Appendix S1). The survey was conducted between October 2012 and February 2014. The
key stakeholders were identified through a combination of methods: expert knowledge elicitation
and preliminary field survey that was carried out before October 2012. We used the snowball
sampling technique (Atkinson & Flint 2001) to identify further resource persons engaged in
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mangrove planting. In total, 105 people including 16 community leaders participated in the
survey individually. Site-specific data such as regarding planting agencies, planting objectives,
age of planted trees, and major disturbances that occurred before and current experiences,
technical guidance and post-planting monitoring schemes, were collected through the
questionnaire (Appendix S1). In addition, data from the questionnaire were cross-checked with
secondary literature on restoration planting through an online search on government and donor
agency websites and field surveys.
Field survey: All brackish water body complexes including lagoons and estuaries along the Sri
Lankan coastline (1620 km) that have been described (Ranasinghe 2012) were surveyed between
2012 and February 2014 in order to evaluate survival of planted seedlings.
i) Vegetation survey: The degree of survival was estimated in two ways. When the number of
seedlings in planting sites was around 200 or less and sparsely distributed (non-homogeneous)
they were counted individually. If there were more than 200 plants, at least three vegetation plots
of 20×20 m² were monitored. Three more representative plots were used for the monitoring when
the total area of the planting site exceeded about 0.5 ha. Survival was recorded and afterwards
the findings were extrapolated to the total prevailing area of mangrove seedlings, saplings, or
shrubs. The number of mangrove species used in restoration, major detectable stress factors,
disturbances, and status of post-planting monitoring were recorded. The current total surviving
planted area was calculated only using those sites where survival was greater than 50%. For the
rest, due to poor survival, surviving plants were scattered sparsely and it was not possible to
estimate the area covered.
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In addition, the state and morphology of seedlings, saplings, and shrubs was inspected visually
for signs of departure from normal leaves (leaf yellowing, browning, wilting, dwarf growth,
deformation, and biotic invasion e.g., insect attacks). Above a 50% threshold of signs of seedling
damage (per seedling), seedlings were considered “dead” (Figure 2). These results were
aggregated at the site level based on the dead/alive criterion. The map that shows the mangrove
planting project sites was created with Arc GIS 10.1 software.
ii) Soil survey: Soil pH and redox potential were measured with a Multimeter (18.52.01.
Eijkelkamp). The pH was measured at 30 cm depth for the seedlings/saplings and 50 cm depth
for the shrubs of the project sites established beyond the intertidal zone by direct insertion of a
glass electrode through a wide-enough hole into the soil. Redox potential was also measured at
30 cm and 50 cm depth by immediate insertion of the electrode through a hole made by using a
hollow PVC (polyvinyl-chloride) pipe, into the soil. When the planting had been done in the
intertidal area, readings of soil slurries that were collected at 30 cm and 50 cm using scale-up
PVC pipe, were taken during the exposure of the soils at low tides. We used a plastic pipe to
collect soil samples under submerged conditions. Soil bulk density (SBD) was measured using
three inch diameter ring-drive method. A three inch diameter ring (7.62 cm), beveled edge down,
was driven into the soil to a depth of 8 cm by using a hand sledge. Three samples from each site
were collected. Soil samples were weighed and each sample was taken into a known-weight
ceramic crucible and it was dried until a constant weight was obtained by the oven-drying
method (temperature = 80 °C) until stable weight. Soil bulk density (g/cm³) was calculated using
the following equation (1). (NRCS, Department of Agriculture, USA, 2014). The average value
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of three soil samples was obtained for each site.
SBD = oven dry weight of soil/ volume of soil of 7.62 cm diameter ring………………(1)
Salinity for each site was measured with the help of a hand-held refractometer (Atago S/Mill-E,
Japan) using 5 ml aqueous solutions under submerged conditions (soil slurry extracted with
interstitial water under non-submerged conditions) that were collected into a vial and mixed
thoroughly before taking the readings. Average salinity of six readings i.e., in both dry and rainy
seasons was calculated (Pers. communication GBM Ransara). Geo-coordinates were recorded
with a hand-held GPS (Garmin e TREX 10). Hydrological data (tidal amplitude and freshwater
input) were obtained from the National Aquatic Resources Research and Development Agency
(NARA), and the Irrigation Department (ID) respectively. The accuracy of demarcation of the
climate zones was cross-checked with the Department of Meteorology, Sri Lanka.
Statistical Analysis
Mean and standard deviation of the age of planting initiatives, planted trees, and soil parameters
were calculated and all statistical analyses were performed using R-3.2.2 statistical package.
Correlation and regression analyses were performed between survival rate and soil bulk density,
pH, redox at 30 cm, redox at 50 cm, technical guidance for planting and post-care. Normality
was tested using the Shapiro test. Data were not normally distributed. Therefore, Spearman
correlation test was conducted. Afterwards, non-linear transformation was performed and
multiple regression was conducted for the variables. Variation of rate of survival with respect to
post-care and technical guidance were illustrated using box and whisker plots.
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Results
1) Mangrove planting projects along the Sri Lankan coastline
Twenty three restoration/planting project sites were identified in this study (Figure 3, Table S2 &
S3). Since the Indian Ocean tsunami in 2004, approximately 1000-1200 ha of mangroves have
been planted. However, the current total surviving planted area is only about 200-220 ha. The
projects are situated in all four different climate zones i.e., wet, dry, intermediate, and arid zones.
However, the proportion of sites was different in these four zones: 52% of the planted sites were
situated in the dry and arid climatic zones, 30% in the wet zone and the rest, i.e., 18%, are in the
intermediate zone (Table 2). We observed multiple planting initiatives by different agencies in a
same site. Sixty seven planting initiatives were recorded within these 23 sites (Table 2). Many
planting attempts could be observed in tsunami-affected areas (Figure 4 & Table 3).
The key actors involved in planting initiatives can be broadly categorised as governmental
organisations or non-governmental organisation (national and international). The governmental
organisations include the Coastal Conservation Department, regional Forest Departments, the
University of Ruhuna, the National Aquatic Resources Research and Development Agency.
IUCN and Mericarp are the international NGOs, while Galle project, Sewalanka, Turtle
Conservation Project, Saviya Development Foundation, and Small Fishers Federation of Lanka
are local NGOs. In addition, there were five unidentified internationally affiliated NGOs that
have attempted mangrove restoration in Sri Lanka in the past decade.
2) Survival of seedlings and age of the planting projects
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The use of Rhizophora spp. for planting was significantly higher, i.e., 97%, of the total planted
propagules and seedlings (Figure 5 & Table S2), compared to nursery-maintained Bruguiera
spp., Excoecaria sp., and Sonneratia caseolaris (i.e., 3%). Thirty six (36) planting attempts out
of 67 (54% of the total), showed no surviving plants. Two-thirds of them (21) were recorded in
the dry and arid zones. In total, for all the project sites, the level of survival (based on the
dead/alive criterion) varied from 0–78% (Table S2). Even after several planting attempts 40% of
the sites had failed (9 out of 23 had no surviving plants). Further, the level of survival for 16 of
the project sites was lower than 10% (Table S2). Only three sites, i.e., Kalpitiya (arid zone),
Pambala (intermediate zone), and Negombo (wet zone), had a level of survival higher than 50%.
Mannar (arid zone) had the fourth highest survival level at 33%. Many failed mangrove
restoration project sites could be observed in the tsunami-affected areas (Figure 4). However, all
successful sites mentioned above are located in areas that were less affected by the 2004 tsunami
(Figure 4 & Table 3).
The average height of planted mangroves in Thambalangama, Rekawa, Galle, Negombo,
Pambala, and Kalpitiya was found to be 4-6 m (Figure 3) in eight to ten years. However, stunted
growth and crooked saplings were observed in the project sites situated in Panama, Panakala, and
Halawa (Figure 3 & 6).
Most of the restoration projects were initiated after the Indian Ocean tsunami of 2004. However,
some of the attempts like those of the University of Ruhuna in Galle and of the Small Fishers
Federation of Lanka in Pambala and Kalpitiya, were initiated in the 1990’s and are about 17-20
years old. The average time after planting was 9.5 (SD ±0.8) years as of 2016.
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Soil pH for the study sites ranged from 7.1 to 5.8 (Table S4). The sites in the wet zone showed
significantly lower pH values (P= 0.0003; sig. level 0.001) as compared to the rest. SBD ranged
from 1.22 to 1.89 g/cm³. The bulk densities were significantly lower (P=0.03; sig. level 0.05) in
the arid zone. Redox potential at 30 cm and 50 cm ranged from +6 to -146 mV and -43 to -171
mV respectively. Redox potential at 30 cm was relatively higher in the intermediate and wet
zones than in the dry and arid zones. Below a depth of 30 cm, redox potential varied between
-100 and -200 mV. However, there was no significant difference of redox potential at 30 and 50
cm between the different climate zones.
3) Drivers of these planting projects
According to the data obtained from the questionnaire survey, the main planting objective of 20
restoration sites that were established after the tsunami, 2004 was coastal protection and the rest
which were initiated before the tsunami was for mangrove regeneration (e.g., some planted sites
in Pambala, and Galle). We observed that the mixed planted sites which were established before
and after the tsunami 2004 were found in only five sites including Galle, Pambala,
Kaluwamodara, Maggona, and Kalpitiya, thus representing both the above objectives (Table S2).
4) Causes of success/failure of planting initiatives
The choice of topographic positioning for mangrove planting showed a remarkable variation.
Some planting efforts were established at the higher intertidal area and even beyond, like in
abandoned swamps, and meadows e.g., Komari, Palandi, Helawa, and Panakala while some were
at the low intertidal zone e.g., Rekawa, Medilla, Meegama, and Ittapana. Due to this
inappropriate topographic positioning, mangrove seedlings are subjected to several stress factors
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and disturbances. Indications of stress factors and disturbances (drought, smothering, high
irradiance, flooding, algal accumulation, infestation by barnacles, browsing, and cattle
trampling) (Figure 6) were observed in all restoration sites. Cattle trampling and browsing were
ubiquitous (Table S2). In addition, algal accumulation through flotsam collection (i.e., 77%) and
insect attacks (i.e., 95%) were also frequent for most of the sites (Table 2). The occurrence of
some stress factors and disturbances were further coupled with the climate zone. For instance,
mangrove seedlings/propagules planted at the low intertidal area exposed to long-term
submergence due to heavy rains in the wet zone while mangrove seedlings/propagules at the
higher intertidal area suffered due to drought and high irradiance (average 79524.48 (SD ±
1630.2) Lux between 11.45-14.30 hrs) in the dry and arid zones. Post-care has not been observed
for all the sites (Table S2). Even though technical guidance and consultation are one of the key
elements in mangrove restoration success, only for six sites (Kalpitiya, Pambala, Negombo,
Mannar, Galle, and Rekawa) restoration was reported by respondents to have followed some
restoration principles. There were 10 sites with a post-planting monitoring process while we
were unable to find any evidence from the respondents and on-site observations for the other
ones. Removing flotsam, debris, and attached barnacles, up-righting the fallen
seedlings/propagules, avoiding cattle trampling, and secured fencing and frequent site visits, and
replacing dead seedlings/propaguels were observed and identified as post-planting monitoring
processes. Survival rate was significantly correlated with post-planting care (Figure 7) and soil
parameters except soil pH.
Discussion
This study reports that 54% of planting attempts have resulted in complete failure and roughly
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40% of the sites chosen for planting had no success (survival rate of saplings after five years). Of
the 14 sites that had some recruitment, 50% (i.e., 7 sites) had survival rate of less than 10%.
These figures are of much concern given that 13 million USD were invested in such planting
efforts and the trend of investing in mangrove planting is still growing (Mukherjee et al. 2009).
Only three project sites (Negombo, Puttalam, and Kumana) had high survival rates (70%, 65% ,
and 53.5% respectively) and such survival rates are comparable to those of the other studies
carried out on mangrove species like Rhizophora mucronata (Toledo et al. 2001; Ratnayake et al.
2012). In this study, a minimum of 5-year survival rate was used in evaluating the success of the
mangrove restoration sites. We realize that a survey of vegetation structure including plant
diversity, density, biomass, and faunal recruitment as well as nutrient cycling as ecological
processes would add to the understanding of effective ecological restoration (Ruiz-Jaen & Aide
2005; Bosire et al. 2008). However, we intended to have a country-wide appraisal of survival
rates as a key indicator of success. Applying all criteria to evaluate ecological restoration in all
sites along the 1620 km coastal belt with more than sixty restoration initiatives demands
intensive scrutiny, for which more research is needed.
Several causes can be attributed to the failure which we observed. Firstly, the degree of damage
caused by the tsunami of 2004 was a major factor in selecting restoration project sites. More sites
were selected in the dry and arid zones than a careful scrutiny could have warranted (Feagin et
al. 2010). Not surprisingly, the restoration failure rates were proportionately higher in these two
zones especially along the east coast of the island. Most of the projects which sprang after the
2004 tsunami were largely donor-driven projects. The implementing parties had a mandate to
rapidly plant some vegetation, intended to lead to the establishment of a green belt in the
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tsunami-affected areas (IUCN 2009). This was further confirmed by some of the signboards that
denote “ghost planting initiatives” as no surviving mangrove saplings could be observed during
our field survey in the planting sites with such signboards. Due to this unscientific approach and
intervention, many failed mangrove restoration sites could be observed in the tsunami-affected
areas. From the ecological point of view, ignorance of the major ecological drivers of mangrove
health such as ecological requirements for salinity, hydrology, and appropriate species
composition were the main causes for mangrove restoration failure (Elster 2000; Primavera &
Esteban 2008; Ahmad 2012). In fact, inappropriate site selection that violates the basic technical
aspects, and lack of preliminary research on mangrove restoration can be highlighted as root
causes of failure. Further, the placement of plants at an inappropriate topography which subjects
them to too short or too long periods of depth, duration, and frequency of inundation, either from
local rainfall or local tides, or a combination of both, has been the key factor. In addition, crucial
factors for planting success such as awareness of the history of the sites including species
composition, hydrological requirements, optimum depth of substrate, and freshwater input
(Elster 2000; Bosire et al. 2008; IUCN 2009; Lewis 2009; Kathiresan 2011) were ignored in
most of our study sites. This was a direct consequence of selection of inappropriate topographic
positions for planting. Due to such situation, the mangrove seedlings, saplings were subjected to
severe stress conditions such as prolonged submergence, soil water deficit (Field, 1998; Hoppe-
Speer et al. 2011). Prolonged submergence and soil water deficit play a crucial role in reducing
the survival potential of mangrove seedlings and saplings especially in the dry and the arid
climate zones in Sri Lanka. Therefore, according to the data collected, such basic ecological
requirements and technical guidance have been ignored. The situation was similar along the Sri
Lankan context as we observed that in Thambalangama, Halawa, Panama, and Panakala project
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sites, mangroves were planted beyond the limits of the intertidal zone (i.e., at higher intertidal
zone) which caused restoration failure in such sites. Only 3 planting initiatives (established by
the University of Ruhuna in Galle and SFFL in Pambala and Kalpitiya) had followed technical
guidelines of mangrove restoration. These were also established in the neighbourhood of a
natural mangrove forest and were about 20 years old (in sharp contrast to the ad hoc planting
sites established after the tsunami of 2004). However, some technically guided project sites (e.g.,
Rekawa lagoon) also showed little evidence of survival due to lack of maintenance and
monitoring. Cattle trampling and browsing were the common disturbance factors for all the
project sites. The observed symptoms in the field could be due to the stress factors like prolonged
submergence, high irradiance etc., or nutrient deficiency/imbalance in soil (Bergmann 1992;
Vollenweider & Gunthardt-Goerg 2005). However, it is evident that mangrove seedlings
experience poor soil conditions due to improper positioning at the planting sites. Such conditions
directly affect nutrient availability, soil organic matter, and porosity (Boto & Wellington 1984;
Kidd & Proctor 2001; IPNI 2010; Tokarz & Urban 2015) which ultimately determines the
survival of mangrove plants.
Selection of unsuitable species like Bruguiera spp., Sonneratia caseolaris (as indicated by
species composition in respective reference forests nearby, e.g., in Meegama, Maggona, and
Kaluwamodara) was another cause of restoration failure. In contrast, planting organized by the
Small Fishers Federation of Lanka that has a Mangrove Re-plantation Advisory Board, had the
highest survival rates. Rhizophora mucronata has been used for restoration and the reasons for
the selection given by the practitioners were: ease of access, ease of handling both in nursery
condition (as nursery seedlings used for some sites e.g., Pambala, Kalpitiya, and Mannar) and
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planting, larger propagules hence higher survival rate, and better establishment at the lagoon
water edge. The planting agencies did not survey which species occur naturally in the area nor
did they use nearby natural forests as reference sites as recommended in restoration guides
(Bosire et al. 2008; Lewis 2009). In this case, actual topographic surveys combined with
hydrologic characterization of reference sites over a period of months during wet and dry seasons
is essential (Lewis 2000, 2005; Samson & Rollon 2008). However, such preparatory
investigation has not been recorded during our survey.
Secondly the governance structure of restoration projects was found to be of major concern.
Lack of coordination between institutions implementing restoration projects e.g., Forest
Department and Coastal Conservation Department, was observed in our study sites and is also
reportedly one of the major causes for mangrove restoration failure in Sri Lanka (Primavera &
Esteban 2008; IUCN 2009; Mangora 2011). For example, interviewed officials in the FD and
CCD had no awareness of the planting efforts established by them even though the government
records and our field observations stated otherwise.
Conversion of mangroves and potential planting sites to shrimp farming had been traced as the
major socio-economic issue in Sri Lanka (Dahdouh-Guebas et al. 2002). As far as we observed,
no political support for mangrove planting while shrimp farming extends under political
patronage.
Mangrove restoration projects in Sri Lanka have not been successful in restoring mangroves
despite the good intentions which fueled them in the first place. The findings of this study are a
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sharp pointer to the mismatch between purported aims of restoration initiatives and the realities
on the ground. The need to conserve and restore mangroves is critical and our results should not
be used as a motivation to stop investing in mangrove conservation. Well prepared and well
managed mangrove planting with post-care can lead to successful restoration, as has been amply
shown, e.g., in Kenya, East Africa (Bosire et al. 2008) to the benefit of multiple stakeholders.
Rather, our findings hold a key to identify where precious resources need to be divested such that
future projects have a higher probability of success. It might also be worthwhile to conduct
similar nationwide evaluations of planting initiatives in the South East Asian region, where the
bulk of global mangroves occur, and where most mangrove restoration has taken place to
compare the findings of this study. One such area is Matang Mangrove Forest Reserve, which
has been reafforested in 30-year cycles and managed since 1902 (Goessens et al. 2014).
As a precautionary principle mangroves should be protected where they still occur. In addition,
mangroves can be replanted in areas where they have been degraded as far as the environmental
conditions (particularly the hydrography) are still conducive for hosting mangroves (Lewis 2005;
Lewis & Brown 2014). However, planting mangroves in areas that have undergone major
changes or in areas where mangroves were never reported should be preceded by a scientific
assessment of whether or not mangrove can grow there. For Sri Lanka, Feagin et al. (2010)
demonstrated that >90% of the Sri Lankan coastline is vulnerable to ocean surges (e.g., tsunami)
while mangroves can only grow along less than one-third of it. Unfortunately this has not been
respected as this study documented. Particular attention has to be given to identify alternative
bioshields or other means of coastal protection for the two-third of the coastline where
mangroves cannot grow.
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Acknowledgement
This work was supported by the VLIR-UOS-funded “Green Dyke project” (VLIR
Ref.ZEIN2008PR347, Flemish Interuniversity Council – University Development Cooperation),
University Grant commission, Sri Lanka (UGC/DRIC/UGC/DRIC/PG/2014AUG/RUH/02) and
Faculty of Science, University of Ruhuna, Matara, Sri Lanka (RU/SF/RP/2015/02). NM was
funded by the Fondation Wiener Anspach grant for her post-doctoral research.
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Tables, figure captions and figures
Table 1. Climate data and distribution of true mangrove and associate species with respect to
different climate zone. (Sources: Department of Meteorology, Sri Lanka; Jayatissa et al. 2002;
CZMP 2003; Pers. communication Ransara GBM)
Climate zone Mean annual
rainfall (mm)
Average annual
temperature
(˚C)
Tidal
amplitude
(m)
Average
salinity (ppt)
True
mangrove
species
Mangrove
associates
Dry <1750 31.5 0.4-0.6 13.8±0.7 11 12
Wet >2500 28.5 0.5 5.0±2.5 10 14
Intermediate 1750-2500 30.0 0.5 5.6±0.4 16 14
Arid <1250 32.5 0.4-0.6 13.2±1.9 11 12
Table 2. The number of sites and the number of planting attempts (plantations) in each site with
respect to different climate zones. Failed planting efforts in this table are defined as “zero
survival”.
Zone No. of sites Distribution of the
sites (%)
No. of planting attempts
(within 8 yrs)
No. of failed
planting initiatives
Wet 07 30.43 18 11
Dry 06 26.08 18 13
Arid 06 26.08 20 08
Intermediate 04 17.39 11 04
Total 23 67 36
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Table 3. The distribution of the replanted mangrove sites and their extent along the coastline
sectors affected and non-affected by the tsunami of 2004. Figure 4 gives further details on the
affected and non-affected coastline.
Coastline sector Approximate length
of the coastline
sector (km)
No. of
restoration
sites
Approx. coverage
replanted (ha)
Approx.
coverage of
surviving planted
area (ha)
Proportion of
replanted extent (ha)
km-1 of the coastline
Severely affected
by the 2004
tsunami*
1211.2 20 700-800 40-50 0.62
Less affected by
the 2004 tsunami*
512.1 03 300-400 150-200 0.68
Total 1722.4 23 1000-1200 200-220 0.64
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Figure 1. An interdisciplinary framework for evaluating coastal planting initiatives (source:
Mukherjee et al. 2015).
Figure 2. Scheme of the procedure for estimating the rate of survival using the dead/alive
criterion in the field.
Figure 3. Map showing the restoration project sites along the Sri Lankan coast line with respect
to major climate zones. Black circles show the actual locations of restoration project sites.
Different colours represent the level of success and a yellow triangle shows the status of post-
care in each site. Images refer to 1: Thambalangama; 2: Mannar; 3: Kalpitiya; 4: Rekawa; 5:
Batticaloa; 6: Halawa. (Photos were taken by K.A.S. Kodikara)
Figure 4. A map of Sri Lanka showing tsunami-affected Divisional Secretariat (DS) divisions in
Sri Lanka (Adopted from the official web site of the Department of Census and Statistics;
(http://www.statistics.gov.lk/tsunami/maps/Map_afftected%20DS%20division.htm )
Figure 5. Number of planted and surviving propagules and seedlings of Rhizophora spp. with
respect to the climate zones in Sri Lanka. Black bars: planted propagules and seedlings; Grey
bars: surviving plants
Figure 6. Disturbances and the common symptoms that were observed in the project sites. 1:
browsing (propagule tips grazed by cattle) and algal accumulation; 2: trampling; 3: growth
stunted and crooked stems; 4: insect attacks; 5: infestation by barnacles; 6: leaf yellowing and
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rust; 7: root rotting; 8: propagule tip die-back and stem browning. (Photos taken by K.A.S.
Kodikara)
Figure 7. Rate of survival (%) with respect to technical guidance and post-care. (Multiple regres-
sion, technical guidance significant at 0.01 level, P=0.0148 and Spearman rank correlation test,
post-care positively correlated at 0.05 level; P=0.0009). A thick black line indicates the second
quartile (median) and small circle data points indicate the outliers.
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Figure 1744
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Figure 2
A total of “X” surviving seedlings are observed in a restoration site out of “Y” planted seedlings. Basically X
number of plants survive and (Y-X) die. When considering X surviving plants
“a” of them are found to be healthy
(Visually free of signs of damage)
(X-a) of them show signs of damage
(E.g. crooked stem, dead leaves, severe chlorosis, necrosis)
Note: morphological signs of damage represent any symptom/s (mentioned under symptoms in the text), mechanical
damage to leaves and hypocotyls (seedling)/ stem (saplings/shrubs)
“p” of (X-a) show damages to leaves and stem (e.g. necrotic regions, chlorosis, etc.) which is below 50% overall
(>50%)
“q” of (X-a) remain and the level of damage to leaves and stem is above 50% (<50%)
These q seedlings were considered as “Dead” as they show damage greater than the level of 50%
Therefore, the total number of surviving seedlings/propagules/saplings = a+p
The level (or rate) of survival is therefore calculated as [(a+p)/Y] ∙ 100 = Survival %
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Numbe
r
Site
1Thambalanga
ma
2Batticaloa
3Komari
4Palandi
5Ureni
6Pottuvil
7Panama
8Panakala
9Halawa
10 Kumana
11 Kahadamodar
a
12 Rekawa
13 Medilla
14 Galle
15 Ittapana
16 Meegama
17 Yagirala
18 Kaluwamodara
19 Maggona
20 Negombo
21 Pambala
22 Kalpitiya
23 Mannar
Figure 11
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Tsunami
Less-affected area
Tsunami affected area
Figure 3
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Site Survival
level
0%
1-10%
11-25%
26-50%
51-75%
76-100%
Post care
present
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809
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Figure 4
Dry
Arid
Intermediate
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Wet
Planted seedlings
Surviving seedlings
Survived plants
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Figure 6
Figure 7Used
Used
Not used
Not used
(%)
(%)
-
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... The trends identified suggest that the survival of planted individuals can be influenced by decisions about what species to plant and where to plant them, as well as climate (at the global and macro-scale) and the coastal environmental setting, which has been successfully used to improve understanding on other aspects of mangrove forest ecology such as soil carbon storage [34]. These insights can help to identify some of the physiological limits (e.g., climate reflects temperature, tidal range reflects duration of immersion), that can result in the failure of restoration programs [40]. While some influences-such as climate-are beyond the control of practitioners working within a particular region, others, such as the species used and the minimum plant spacing adopted, can be readily adjusted to maximize survival and enhance project success [20,[41][42][43]. ...
... The failure of mangrove restoration projects is often related to the high susceptibility of propagules, seedlings and saplings to wind and wave erosion, as well as flooding and desiccation [21,40]. Repeated failures often occur when practitioners do not understand the physiological limits of different species, including planting them on bare mudflats or adjacent seagrass meadows where the soil characteristics are not compatible [20,21,40]. ...
... The failure of mangrove restoration projects is often related to the high susceptibility of propagules, seedlings and saplings to wind and wave erosion, as well as flooding and desiccation [21,40]. Repeated failures often occur when practitioners do not understand the physiological limits of different species, including planting them on bare mudflats or adjacent seagrass meadows where the soil characteristics are not compatible [20,21,40]. The results of analyses suggest that pencil-rooted species which survive well in fringing, estuarine and lagoon environments, do not fare as well in more sheltered and sedimentary environments such as deltas. ...
Article
Full-text available
Mangrove planting has been employed for decades to achieve aims associated with restoration and afforestation. Often, survival of planted mangroves is low. Improving survival might be aided by augmenting the understanding of which planting methods and environmental variables most influence plant survival across a range of contexts. The aim of this study was to provide a global synthesis of the influence of planting methods and background environment on mangrove survival. This was achieved through a global meta-analysis, which compiled published survival rates for the period 1979–2021 and analyzed the influence of decisions about minimum spacing and which life stage to plant, and environmental contexts such as climate, tidal range and coastal setting on the reported survival of planted individuals, classified by species and root morphology. Generalized Additive Mixed Modeling (GAMM) revealed that planting larger mangrove saplings was associated with increased survival for pencil-rooted species such as Avicennia spp. and Sonneratia spp. (17% increase cf. seedlings), while greater plant spacing was associated with higher survival of stilt-rooted species in the family Rhizophoraceae (39% increase when doubling plant spacing from 1.5 to 3.0 m). Tidal range showed a nonlinear positive correlation with survival for pencil-rooted species, and the coastal environmental setting was associated with significant variation in survival for both pencil- and stilt-rooted species. The results suggest that improving decisions about which species to plant in different contexts, and intensive care after planting, is likely to improve the survival of planted mangroves.
... Despite government-led conservation efforts (Appendix 1) and nongovernmental interventions, Sri Lankan mangroves are continuously degrading due to natural and anthropogenic drivers (Dahdouh-Guebas et al., 2021). Even though mangroves are fully protected by law, mangrove co-management initiatives are still lacking in the country (Kodikara et al., 2017). Co-management refers to the distribution of authority and decision-making between multiple stakeholders such as local communities, government organizations, and non-governmental organizations (NGOs) (Berkes, 2010). ...
... The situation was exacerbated by the 2004 Indian Ocean tsunami which partly destroyed Sri Lankan mangrove forests (Dahdouh-Guebas et al., 2005). This was then followed by rapid mangrove restoration initiatives in all coastal provinces, most of which ended up in failure (Kodikara et al., 2017). ...
... A questionnaire survey was developed to identify the mangrove management stakeholders in Sri Lanka (Appendix 2). Initially, six government departments along with non-governmental organizations (NGO's) and academics/researchers (Kodikara et al., 2017) working on mangrove management were selected (refer to Appendix 2 for respondent selection). The governmental departments were selected according to jurisdiction/legislation related to their involvement in mangrove 2 Blue carbon-"atmospheric carbon (dioxide) captured and sequestered by marine and coastal vegetation and stored in their biomass or as recalcitrant organic matter in the water body or sediments" (Zimmer et al., 2022). ...
Article
Understanding the extent of collaboration among stakeholders is key to supporting mangrove management. Despite the existence of robust policies, collaboration among stakeholders of mangrove co-management remains largely unexplored in Sri Lanka. This was partly due to the civil war, natural disasters, and other socio-economic changes over the past 30 years. Our study aimed to identify the collaboration between stakeholders of mangrove management and their perceptions regarding mangrove co-management in Sri Lanka using social network analysis and content analysis. Surveys were conducted in all five coastal provinces of Sri Lanka. Stakeholders included in the study were from government departments, non-governmental organizations, and private institutes. Our results showed that there were differences between coastal provinces in the mangrove management networks, specifically in the number of stakeholders involved and their degree of collaboration. Some important stakeholders (for example the Land Use and Policy Planning Department) were excluded from the social networks in certain provinces (Eastern and Western provinces). There were various issues hampering effective mangrove management such as inefficient communication, inconsistencies between policies, and insufficient financial capacity of government stakeholders responsible for policy implementation. According to the stakeholders in our study, providing mangrove management initiatives with long-term collaboration, post-care, continuous monitoring, and funding may help to overcome these challenges. Additionally, we suggest the establishment of a common platform to coordinate stakeholders. We further encourage increasing the participation of academics, researchers, and students from national universities in the mangrove co-management of Sri Lanka. Insights from this island-wide survey can be adapted to mangrove and other natural resource management trajectories in other countries as well.
... Nevertheless, a number of mangrove reforestation and conservation activities by governmental and NGOs are in progress in the country. Conversely, the average success rate of these activities are considered as below 50% (Kodikara et al. 2017). The present study investigated the current status and recent changes in mangrove area coverage of one of the major mangrove areas in Sri Lanka using high resolution satellite images. ...
... However, survival rates of planted mangroves were reported to be low (e.g. Thavanayagam and Thangamuthu 2014;Kodikara et al. 2017). For instance, Kodikara et al. (2017) reported that only three mangrove planting sites (Kalpitiya, Pambala, and Negombo) showed survival rates above 50%. ...
... Thavanayagam and Thangamuthu 2014;Kodikara et al. 2017). For instance, Kodikara et al. (2017) reported that only three mangrove planting sites (Kalpitiya, Pambala, and Negombo) showed survival rates above 50%. Whereas Thavanayagam and Thangamuthu (2014) reported that, in Batticaloa Lagoon, survival rates of planted mangroves were below 10% by the end of 2010. ...
Article
Full-text available
Sporadic patches of mangrove vegetation are unevenly distributed along the coast, particularly in the lagoons, of Sri Lanka. Sri Lanka has become the first nation in the world who decided to protect its all its mangroves in 2015. Mangrove vegetation is considered as a cost-effective ecosystem-based tool for protecting the country from coastal disasters, such as erosion and tsunamis. Batticaloa Lagoon is one of the major mangrove areas in Sri Lanka. This region underwent degradation of mangroves due to a number of natural and anthropogenic factors, including the 2004 Indian Ocean tsunami. Mangrove reforestation was conducted after the 2004 tsunami event in this area. The present study investigated the outcome of such activities in this lagoon in eastern Sri Lanka. Spatiotemporal changes in mangroves in Batticaloa Lagoon was estimated using multi-temporal satellite (Landsat, Sentinel-2, RapidEye and PlanetScope) data. The latest mangrove vegetation coverage in Batticaloa Lagoon is estimated as 1567 ha (2022) which is 26% less than the estimated area in 1995. It is estimated that nearly 20% of the total mangrove loss occurred during the 2004 Indian Ocean tsunami and, despite the reforestation initiatives undertaken by various agencies in Batticaloa, the depletion in mangrove coverage and urbanization continued in this region.
... Mangrove restoration projects and programmes have been implemented in many countries, these including projects in the 1950s in China and India (Kodikara, Mukherjee, Jayatissa, Dahdouh-Guebas, & Koedam, 2017 (Kodikara et al., 2017) and the 2013 Haiyan typhoon (Barnuevo, Asaeda, Sanjaya, Kanesaka, & Fortes, 2017;Wolanski & Elliott, 2015). Vietnamese mangrove restoration projects commenced in 1975 following the end of the Second Indochina War (Hong, 2008), with considerable subsequent activity (around 0.2 million hectares) funded through both state and international programmes. ...
... Mangrove restoration projects and programmes have been implemented in many countries, these including projects in the 1950s in China and India (Kodikara, Mukherjee, Jayatissa, Dahdouh-Guebas, & Koedam, 2017 (Kodikara et al., 2017) and the 2013 Haiyan typhoon (Barnuevo, Asaeda, Sanjaya, Kanesaka, & Fortes, 2017;Wolanski & Elliott, 2015). Vietnamese mangrove restoration projects commenced in 1975 following the end of the Second Indochina War (Hong, 2008), with considerable subsequent activity (around 0.2 million hectares) funded through both state and international programmes. ...
Article
Full-text available
Mangroves can play a major role in efforts to mitigate climate change through two pathways. These are (1) carbon sequestration following reforestation of areas where mangroves previously existed, and (2) protection of existing carbon stores in intact mangrove forests. There is considerable international interest in carbon mitigation by governments and businesses as a way of meeting emissions reduction targets, and this could result in significant investment in mangrove restoration and protection. This is likely to have positive benefits in terms of coastal protection, biodiversity protection and new economic activity. This project examined three aspects of mangroves related to the emerging carbon economy. There has been considerable (0.2 million hectares) mangrove restoration in Vietnam and this activity provides insights into the causes of project success or failure. A review of this restoration concluded that the failure of several past restoration projects in Vietnam could be attributed to poor species and site selection and lack of incentives to engage residents in long-term management. The economic, environmental and social aspects of mangrove-shrimp farming or aquaculture (MAS) systems in Ca Mau Province, Vietnam, were examined, and it was concluded that this approach allows the achievement of these multiple objectives. Whereas, most of the discussion around mangroves and their role in carbon management is at the international and national levels, implementation occurs at the local level. It was found that whereas local stakeholders had a reasonable understanding of climate change, they were less clear about carbon markets and the role that mangroves can play. This points to the need for new educational programmes. The study concluded that monitoring and verification systems for both carbon and biodiversity are essential to allow the resultant multiple benefits of carbon mitigation projects to be realised.
... Over the last 20 years, the number of mangrove restorations and rehabilitations projects globally has nearly tripled with the majority of those projects have been in the Southeast Asia and Brazil [10]. The failure rate of mangrove restoration and rehabilitations remains unacceptably high [11]. In the Philippines, for example, less than 20% of the planted sapling survives [12]. ...
... This is still far from the target of 600,000 hectares by 2025 [15]. This is exacerbated by the fact that mangrove rehabilitation and restoration projects almost always are perceived as one-off projects with minimum attention to providing evidence or information about previous successes, failures, or technical knowledge to guide successful projects [11,18]. Follow-up monitoring has been sporadic and shortterm [19]. ...
Article
Full-text available
Mangrove is an essential ecosystem for climate change mitigation and adaptation. Yet, mangrove rehabilitation and restoration remain a huge challenge indicated by the unacceptably high failure rate particularly during the early stage after planting. Long-term monitoring and evaluation is one of the key factors to improve success rate. Hence, study on the seedlings’ performance is essential. This study analyzes mangrove seedlings’ health by assessing survival rate and leaf morphometrics in silvofishery sites in Buer Village, Sumbawa District, Indonesia. One-hectare plot of Rhizophora mucronata planted on January 2020 and one-hectare plot of Rhizophora stylosa planted on February 2020 were selected. To analyze leaf morphometrics variations, forty leaves were collected from each plot. The seedlings of R. mucronata (CV 15%) have bigger competition and lower adaptation ability compared to R. stylosa ( CV 6%). Water quality parameters supports the growth of Rhizophora, sp . The species selected is appropriate for the location (middle to upper intertidal level). The success rate is high, around 95% and 80% for R. stylosa plot and R. mucronata , respectively. Factors attributed to the high success rate are (i) hydrological intervention, (ii) ownership and buy-in, (iii) international partnership, (iv) land tenure security, and (v) regular monitoring.
... Rendahnya keberhasilan penanaman mangrove ini disebabkan oleh pemilihan lokasi penanaman yang kurang tepat dari segi aspek topografi dan hidrologi yang kurang mendukung pertumbuhan mangrove. Lebih lanjut diuraikan faktor kegagalan program penanaman mangrove tersebut karena perencanaan yang kurang matang, tidak adanya petunjuk teknis penanaman, pemilihan spesies mangrove yang dominan hanya satu spesies (97% Rhizophora sp.), pemilihan spesies yang tidak sesuai dengan kondisi hidrologi lokal dan kadar garam lokasi penanaman, pemilihan lokasi penanaman yang terlalu kering, tidak adanya pemeliharaan pasca-penanaman, dan kurangnya koordinasi antara lembaga pelaksana program dengan pemerintah daerah dan masyarakat lokal (Kodikara et al. 2017). Permasalahan yang sama juga dialami oleh berbagai proyek rehabilitasi/restorasi mangrove di Indonesia (Brown, 2017 Dalam rangka mendukung pelaksanaan tugas pokok dan fungsi Kementerian/Lembaga serta memperkuat kolaborasinya dalam pengelolaan kawasan pesisir dan ekosistem mangrove, perlu dilakukan sinkronisasi dan harmonisasi program/kegiatan dan anggaran sehingga pencapaian target akan lebih efektif, efisien, kredibel, dan akuntabel. ...
... Mangrove forests provide numerous goods and services, inclusive of protecting our coastal resources against such weather events, therefore they must be preserved and protected [12]. Restoration projects such as mangrove planting campaigns at both the governmental and non-governmental levels must be encouraged [72]. Additionally, legislation involving the preservation of mangrove ecosystems should be enforced, including laws prohibiting the cutting down and destruction of mangrove trees for industrialisation and urbanisation [73]. ...
Article
Full-text available
Mangrove forests provide a wide range of ecosystem services and socio-economic benefits globally; however, climatic and anthropogenic forces have negatively affected this unique vegetation type. Information on observed changes is useful in the development of mangrove conservation strategies. Geospatial mapping techniques can provide such information, which is key for the sustainable management of this critical resource. In Trinidad and Tobago, mangrove forests have suffered losses within recent years. This study utilized remote sensing and geographic information systems (GIS)techniques to update an existing 2007 mangrove baseline map of Trinidad and Tobago to 2014 and identify significant changes in mangrove coverage for the 7-year period. Mangrove forest boundaries were delineated using ArcGIS 10.4.1 software through an integrated approach involving visual interpretation of2014 high-resolution, coloured aerial photography and classification of Sentinel-2 Multi-Spectral Instrument(MSI) satellite imagery. Resultant maps were verified using ground data collected between 2017 and 2019.Spatial analysis techniques were used to isolate and quantify areas of mangrove change. Results revealed that total mangrove coverage for both islands decreased from 9369.3 ha in 2007 to 9077.2 ha in 2014, a loss of292.1 ha for the 7-year period. Solid waste pollution and land cleared for development were both observed within mangrove areas. A mangrove species map generated for the Buccoo-Bon Accord region of southwest Tobago showed that the area is dominated by red mangroves. The outputs of this study can be used in mangrove forest conservation and management strategies to promote more sustainable development practices in Trinidad and Tobago and the wider Caribbean. The geospatial approach can be implemented when developing monitoring plans. Keywords: Mangrove mapping; Remote Sensing; Sentinel-2; Aerial photography; Trinidad and Tobago.
... Despite these global efforts, the success rate of restoration projects is often much lower than initial expectations, and efforts have even failed on occasion Lewis 2005;Primavera and Esteban 2008;Thompson 2018). For example, some reforestation programs in Vietnam had only 40% success (2011) and in Sri Lanka, 20% success was recorded, where 9 out of 23 plantations had completely disappeared (Kodikara et al. 2017). Furthermore, success rates in Columbia were as low as 20% (Elster 2000). ...
Article
Full-text available
Approximately half of the world’s mangroves are concentrated in Asia, but they have been logged at an alarming rate. To compensate for this, mangrove plantations are being attempted at various sites but with many failures. In this study, we investigated the role of a small portable reef in protecting young mangrove plants from hydrodynamic disturbances caused by short-period waves. To investigate the effectiveness of such a small reef, an experiment using a large wave flume was conducted with two types of real-sized portable reefs (stone and block reefs). A numerical wave model was also constructed to analyze in detail the turbulence around the reef. Our previous study showed that short-period waves can cause resonant oscillations in young mangrove plants. To confirm whether this occurs even behind a reef system, a young mangrove model made of flexible olefin resin was tested with a small wave flume placed behind porous and non-porous reefs, and its oscillation was precisely measured using a high-speed camera. These experiments yielded several new findings. If appropriately designed, small porous reefs can minimize oscillations with adverse effects and provide a favorable environment for the initial growth of mangroves at restoration sites.
... Further, invasive species such as Dillenia suffruticosa and Annona glabra are rapidly invading the mangrove ecosystem in some areas of the main river and the Meegama tributary. The past attempts to restore mangroves in the Kaluwamodara and the Meegama areas have become a failure due to ad-hoc decisions on species and location selection (Kodikara et al., 2017). Hence, Figure 6: Livelihood of people depended on the Bentota river mangrove (A: collected mangrove ferns-Acrostichum aureum, B: Aponogeton spp., C: Collected Kirala fruits-Sonneratia caseoloris, D: A fisherman is leaving for fishing in the Bentota mangrove. ...
Article
Full-text available
Being a tropical country located close to the equator, Sri Lanka is blessed with diverse mangrove ecosystems. However, most of its mangroves have not been studied in detail particularly in the northern areas. Although the Bentota river is located in one of the highly populated districts, mangroves along its banks have not been studied in detail for species composition and diversity. Hence, the present study focused on determining the diversity and abundance of true mangrove species associated with the Bentota river. Mangrove vegetation was sampled using 5 m wide belt transects laid perpendicular to the shoreline. True mangrove species in each transect were identified and gbh (Girth at Breast Height) and height were measured in all individuals. Shannon diversity (H’), Shannon Evenness (E), and Sampson index (D) were used to calculate and compare the diversity between sites. A total of ten true mangroves and 13 associates were recorded for the first time from the Bentota River. Nine (9) true mangrove species from the estuary area and eight from Kaluwamodara tributary were recorded whereas the least number of species (5) were recorded from the Meegama tributary. The highest Shannon diversity value (H’ =1.83) was recorded in the Kaluwamodara tributary followed by the estuary area (H’ =1.47). Approximately half of the true mangrove species (10) that have been recorded from Sri Lanka occur in the Bentota river mangrove. As some threatened mangrove species and numerous anthropogenic threats were recorded during the present study, immediate actions should be taken by the government to conserve mangroves in Bentota river.
Article
Reforestation is an eco-friendly strategy for countering rising carbon dioxide concentrations in the atmosphere and the negative effects of forest loss and degradation. China, with one of the world’s most considerable afforestation rates, has increased its forest cover from 16.6% 20 years ago to 23.0% by 2020. However, the maximum potential forest coverage achieved via tree planting and restoration is uncertain. To map potential tree coverage across China, we developed a random forest regression model relating environmental factors and appropriate forest types. We estimate 67.2 million hectares of land currently available for tree restoration after excluding existing forested areas, urban areas, and agriculture land covers/uses, which is 50% higher than the current understanding. Converting these lands to the forest would generate 3.99 gigatons of new above- and belowground carbon stocks, representing an important contribution to achieving carbon neutrality. This potential is spatially imbalanced, with the largest restorable carbon potential being located in the southwest (29.5%), followed by the northeast (17.2%) and northwest (16.8%). Our study highlights the need to align tree restoration areas with the uneven distribution of carbon sequestration potential. In addition to being a biological mitigation strategy to partially offset carbon dioxide emissions from fossil fuel burning, reforestation should provide other environmental services such as the restoration of degraded soils, conservation of biological diversity, revitalization of hydrological integrity, localized cooling, and improvement in air quality. Because of the collective benefits of forest restoration, we encourage that such activities be ecosystem focused as opposed to solely focusing on tree planting.
Conference Paper
Full-text available
Sri Lanka is one of the global biodiversity hotspots but the biodiversity of the country is highly affected by various factors. Based on the preliminary observations, Acacia auriculiformis has invaded in Rekawa lagoon region (06º03´N–80º50´E). Therefore, the main objective was to study the distribution and the abundance of A. auriculiformis at the periphery of the mangrove belt of Rekawa lagoon. The recent (2015) Google Earth imagery combined with field based observations were used for the initial survey and then randomly selected eight quadrates (40x40m2) were fully studied in 5 km stretch in Rekawa lagoon to get the species composition, their abundance and size classes. Simpson diversity index and Dominance Index were calculated for each sampling site. The total area that has been invaded by A. auriculiformis was 0.256 km2 (i.e. 4.91% to total land cover of Rekawa lagoon region). The results revealed that, seaward side of the lagoon is at high risk of further invasion. Moreover, A. auriculiformis dominated at the periphery of the mangrove belt while co-occurring with the true mangrove species, and replacing conventional mangrove associates like Acrostichum aureum. About 65% of the Acacia plants were grown up to tree level (10-12m in height, 25cm GBH) and about 20% was in sapling stage and the rest was seedlings. Simpson’s Index of Diversity for sampled area was 0.76 (SD+/- 0.06) though Dominance Index for A. auriculiformis in the seaward side plots was 0.421 (SD+/- 0.3).These results revealed that A. auriculiformis has already become a serious threat, compared to non-invaded plots, particularly to mangrove associates as it dominates at the landward margin of the mangrove belt. Therefore, this should be considered as an alarm to take necessary action to protect the mangrove ecosystem in Rekawa lagoon which is considered as prominent life support systems for coastal livelihood.
Article
Full-text available
Early life of viviparous mangroves merely depends on the propagule and it can be assumed that the period and the degree of dependency could depend on the size and the intrinsic factors of the propagule as well as on the edaphic and environmental factors in which the seedlings are growing. However scientific studies on the propagule dependency of mangrove seedlings is poorly studied, irrespective to the fact that such information is vital particularly in mangrove restoration programs. This study carried out to investigate the growth performances of seedlings and the variations in the content of carbohydrate foods (starch content) in the propagule during the first 20 weeks period of the seedling growth of two viviparous species, Rhizophora apiculata and Rhizophora mucronata, which are having larger propagules and commonly used in replanting programs. The experiment was conducted, under three salinity regimes (i.e. 5psu; 15psu; 30psu) in a planthouse. A separate set of propagules were planted within the mangrove forest of Pambala lagoon under natural conditions and subjected to the same investigation as above. Growth performances of both species grown under high salinity regime were significantly lower than those grown in low and moderate salinity regimes. Total leaf area of the seedlings of R. mucronata increased in higher order compared to that of the R. apiculata during the study period. After an initial drop in the content of starch in the propagules of both species, it started to increase slowly in the propagule of R. mucronata seedlings whilst the reduction was continued in R. apiculata propagules during the study period. However, the initial starch concentration of R. apiculata was remarkably higher than that of R. mucronata and hence, the starch content in R. apiculata, even after continued decreasing, was higher at the end of the study period. It can be hypothesized that the higher concentration of the stored food in smaller propagule of R. apiculata compared to lower concentration of the stored food in propagules of R. mucronata might lead to a similar longevity of viviparous mangrove seedlings of the two species allowing more or less same chance to survive and establish in the same habitat as observed in many mangrove ecosystems.
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The production of shrimp (Penaeus spp.) by means of coastal pond systems has been a traditional practice in Asia for hundreds of years. However, advances in technology coupled with an increased international market demand for shrimp led to the development of intensive aquaculture systems that departed from traditional sustainable systems. In many instances these intensive systems were poorly planned and/or managed and have since proven to be unsustainable, with the result that large areas of “land, ”much of it former coastal wetlands, now lie idle and unproductive, and new sites are being developed in an effort to maintain production output (Stevenson 1997).
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