Executive Summary

A rapid assessment of mangrove restoration sites within the Shirazi–Funzi Mangrove Complex covered 107 sites across four village blocks—Shirazi, Munje, Bodo, and Funzi—spanning a total area of 127.25 hectares. Four mangrove species (Sonneratia alba, Rhizophora mucronata, Ceriops tagal, and Bruguiera gymnorrhiza) were recorded, with S. alba demonstrating the strongest growth performance (average DBH/DGL of 2.6 cm and height of 100.8 cm), followed by R. mucronata. Overall, 63 sites (63.35 ha) recorded survival rates above 50%, while a smaller subset of sites exhibited very low survival rates, reflecting significant variability in restoration outcomes. Salinity conditions were generally favorable in most sites, with 71 sites recording ≤40 ppt, although 10 sites experienced hypersaline conditions (>66 ppt), likely constraining mangrove establishment and growth.

The assessment highlights uneven restoration performance driven by species-site suitability, salinity, and hydrological conditions. Replanting emerged as the most immediate priority, complemented by hydrological remediation and strengthened protection and conservation measures. Additional recommendations include fisherfolk sensitization, improved livestock control, and, in extreme cases of persistent poor performance, relocation of restoration efforts to more suitable sites. These findings underscore the need for adaptive, site-specific restoration strategies to enhance the effectiveness and sustainability of mangrove restoration within the Shirazi–Funzi landscape.

1. Introduction

1.1 Background on Mangrove Restoration

Mangrove ecosystems play a critical role in climate change mitigation and adaptation, biodiversity conservation, and the livelihoods of coastal communities. They are among the most carbon-rich ecosystems globally, with significant potential for long-term carbon sequestration, while also providing essential ecosystem services such as shoreline protection, fisheries support, and improved coastal resilience.

In recent years, mangrove restoration efforts within the Shirazi–Funzi Mangrove Complex have been implemented to enhance ecosystem recovery, strengthen community livelihoods, and contribute to climate mitigation through nature-based solutions. These efforts form part of a broader strategy to generate high-quality blue carbon outcomes aligned with international carbon standards and methodologies.

As the project progresses toward verification and potential issuance of carbon credits, it is essential to assess the status of planted sites to understand restoration performance, identify challenges, and inform adaptive management actions.

1.2 Objectives of the Assessment

The primary objective of this assessment was to conduct a rapid, site-level review of mangrove planting efforts in preparation for the upcoming Validation and Verification Body (VVB) site visit, which is a critical step toward the issuance of carbon credits.

Specifically, the assessment aimed to:

  1. Evaluate the growth performance and survival of planted mangrove species across selected sites.

  2. Assess environmental conditions, particularly salinity, that may influence restoration outcomes.

  3. Examine spatial variation in site performance across the four village blocks of Shirazi, Munje, Bodo, and Funzi.

  4. Identify key constraints affecting mangrove establishment and growth.

  5. Generate evidence-based recommendations to strengthen restoration effectiveness and readiness for VVB verification.

Overall, the assessment provides a rapid diagnostic of restoration progress and supports informed decision-making to enhance project performance and credibility within the carbon certification process.

2. Methods

2.1 Study Sites and Sampling Design

The assessment was conducted across previously planted mangrove sites within the Shirazi–Funzi Mangrove Complex, spanning the four village blocks of Shirazi, Munje, Bodo, and Funzi. A subset of sites was randomly selected using a GIS-based algorithm in QGIS to ensure spatial representativeness across the planted landscape.

At each selected point, a 10 m × 10 m sampling plot was established within the planted polygon. In cases where site-specific conditions prevented measurement at the exact point, alternative locations within the same polygon were identified to maintain representativeness.

Data collection was carried out using Kobo Collect, which allowed for efficient digital capture of field measurements and observations.

2.2 Variables Measured

  • Field data were collected in accordance with VM0033 guidance for mangrove restoration projects, including:

– Forest Structure Metrics: Diameter at Ground Level (DGL)/Diameter at Breast Height (DBH) and tree height for all planted species.

– Survival Rate: Number of surviving seedlings per plot relative to total planted, expressed as a percentage.

– Salinity: Water samples were collected from holes dug to a maximum depth of 45 cm. If water was not encountered within this depth, an alternative location within the planted polygon was used.

– Drivers of Degradation and Threats: Observations were recorded on biotic and anthropogenic pressures affecting site performance, including grazing, cutting, or human disturbance.

– Hydrological Dynamics: Indicators of tidal flow, waterlogging, and drainage were documented to understand site-specific hydrological constraints.

These variables were integrated to derive a site-level performance index, reflecting the overall restoration status and ecosystem condition.

2.3 Data Analysis Approach

  • Data analysis combined field measurements with geospatial and statistical tools to produce a comprehensive evaluation of restoration outcomes.

  • R Programming Language: Used for statistical analysis, visualizations, calculation of growth metrics, survival rates, and performance indices.

  • QGIS and Google Earth: Utilized for spatial analysis, mapping of sampling locations, and visualization of site conditions.

  • Integration of Variables: Forest structure, survival rates, salinity, hydrology, and observed threats were synthesized to assign a composite performance index to each site, categorizing sites as poor, fair, or good in terms of restoration success.

  • This approach enabled a rapid but systematic assessment of site-level restoration outcomes and provided actionable insights to support verification under the VM0033 methodology.

3. Results

3.1 Survival and Growth Performance

Survival rate distribution by Block

Boxplot

The above box plot analysis reveals distinct differences in survival rate distributions across the four village blocks. Bodo and Shirazi exhibit notably higher median survival rates, with several outliers exceeding 200%, suggesting that certain sites within these blocks achieved exceptional restoration outcomes. In contrast, Funzi and Munje show lower and more consistent survival rates, indicating more modest performance. These variations may reflect differences in site conditions, species selection, or community engagement. The presence of high-performing outliers in Bodo and Shirazi points to localized success factors worth investigating further, such as microhabitat suitability or planting techniques. Overall, the results highlight the importance of tailoring restoration strategies to site-specific ecological and social contexts to optimize survival outcomes.

Average height and DBH

BoxPlot

Violin Plot

The distribution of average DBH/DGL across village blocks reveals modest variation in tree growth performance. Shirazi shows the highest median and the widest range, including an outlier exceeding 6 cm, suggesting that some sites within this block experienced accelerated growth. Bodo also presents an outlier above 2 cm, though its overall distribution remains tighter. Funzi and Munje display lower median values and narrower interquartile ranges, indicating more uniform but limited growth. These differences may reflect site-specific factors such as soil conditions, hydrology, or species composition. The presence of high-growth outliers in Shirazi and Bodo highlights the potential for targeted interventions or favorable microhabitats that could be replicated to enhance restoration outcomes elsewhere.

Height Distribution Table by Block

The box plot above illustrates variation in average height across village blocks, with Shirazi showing the highest median and widest spread, including an outlier approaching 175 cm. Bodo also presents relatively higher median values, while Funzi and Munje display lower and more tightly clustered height distributions. These differences suggest that tree growth performance may be influenced by site-specific ecological factors such as soil fertility, hydrology, or exposure. The exceptional height observed in Shirazi could reflect favorable microhabitats or species selection, while the more constrained growth in Funzi and Munje may point to environmental limitations or less optimal restoration conditions. These findings underscore the importance of tailoring restoration strategies to local contexts to enhance growth outcomes.

Combined Report

The combined box plot offers a comparative overview of survival rate, DBH/DGL, and height across village blocks, reinforcing patterns observed in individual analyses. While survival rates are highest in Bodo and Shirazi, growth metrics (DBH/DGL and height) show more nuanced variation, with Shirazi and Munje exhibiting stronger performance in certain dimensions. The juxtaposition of survival and growth data highlights that high survival does not always correlate with superior growth, suggesting that ecological conditions, species selection, or management practices may differently influence establishment versus development. This integrated view supports the need for site-specific strategies that balance both survival and long-term growth outcomes in restoration planning.

3.2 Environmental Conditions

Salinity patterns

(A) Salinity Distribution by Block (Boxplot)

The salinity distribution across village blocks shows notable spatial variability. Munje and Bodo exhibit the widest salinity ranges, with Munje displaying the highest variability and several elevated values approaching 100 ppt. In contrast, Funzi and Shirazi have narrower interquartile ranges and more consistent salinity levels. These patterns suggest that Munje and Bodo may be more exposed to tidal influxes, evaporation effects, or upstream saline intrusion, potentially influencing restoration outcomes. The relative stability in Funzi and Shirazi could reflect buffering by freshwater inputs or geomorphological protection. Understanding these salinity dynamics is essential for site selection, species matching, and long-term ecosystem resilience.

Salinity Classes

Salinity classified into ecological classes:

  • Optimal: ≤ 40 ppt
  • High: 41–65 ppt
  • Hypersaline: > 66 ppt

Salinity Class distribution by Block

Percentage-Based Salinity Plot

The salinity class distribution presented in the above graphs reveal clear spatial patterns across village blocks. Shirazi has the highest number of sites overall, with a majority falling within the optimal salinity range (≤40 ppt), suggesting favorable conditions for restoration. Bodo and Munje show mixed salinity profiles, including several sites in both high (41–65 ppt) and hypersaline (>65 ppt) categories, indicating greater environmental variability and potential stress. Funzi has fewer sites and a relatively balanced distribution, though with limited hypersaline exposure. These patterns highlight the importance of localized salinity assessments when selecting sites and species for restoration, as salinity extremes may constrain survival and growth outcomes.

Hydrology and inundation classes

Hydrology Class by Block

The distribution of hydrology classes across village blocks reveals distinct spatial patterns in water access and tidal exposure. Shirazi has the highest number of sites overall, with a strong presence in Class 1 and Class 2 zones—areas bordering open ocean or secondary channels—suggesting consistent water flow and higher tidal influence. Bodo and Munje show more balanced distributions across all four classes, including several sites in Class 4 (dead-end creeks), which may experience limited water exchange and prolonged inundation stress. Funzi has fewer sites overall, with a concentration in intermediate hydrology classes. These findings underscore the importance of hydrological context in restoration planning, as water movement directly affects salinity, sedimentation, and seedling survival.

Similarly, the hydrology class distribution in the graph above reveals significant variation in water exchange conditions across village blocks. Shirazi stands out with the highest number of sites, most of which fall under the “good water exchange” category, indicating favorable hydrological conditions for restoration and growth. Bodo shows a more diverse hydrological profile, including several sites with blocked channels and poor hydrology, which may pose challenges for seedling survival and nutrient flow. Funzi and Munje have fewer sites and limited representation across hydrology classes, suggesting more uniform but potentially constrained water dynamics. These findings emphasize the need to factor in hydrological accessibility when selecting and managing restoration sites, as water movement directly influences salinity, sedimentation, and ecological resilience.

Linking Hydrology to performance

The box plot illustrates a clear relationship between hydrology condition and mangrove survival rate. Sites with good hydrology show consistently higher median survival rates, while those with poor hydrology exhibit lower and more variable outcomes. Interestingly, the moderate hydrology category includes outliers with survival rates exceeding 200%, suggesting that under certain conditions, even moderately flushed sites can support exceptional performance. These results reinforce the importance of water exchange in mangrove restoration, with good hydrology providing stable conditions for seedling establishment and growth. However, the presence of high-performing outliers in moderate zones also highlights the potential for localized success where other supportive factors may be present.

This performance breakdown complements earlier survival data by showing how hydrology influences overall site outcomes beyond survival alone. Sites with good hydrology not only dominate in number but also show a balanced distribution across high, moderate, and low performance classes, suggesting that favorable water exchange supports both establishment and sustained growth. In contrast, poor hydrology sites are fewer and skewed toward low performance, reinforcing the limiting effect of restricted water flow. Moderate hydrology sites show mixed outcomes, indicating that other factors—such as species selection or microhabitat features—may mediate performance under intermediate conditions. This layered view emphasizes the need for integrated site assessments when planning restoration interventions.

##                  Df Sum Sq Mean Sq F value Pr(>F)
## Hydrology_Class   2   2539    1269   1.089   0.34
## Residuals       107 124704    1166

Although sites with good water exchange tended to show higher survival rates, the differences across hydrological classes were not statistically significant (P > 0.05). This indicates that hydrology alone does not fully explain variations in restoration performance, and that multiple interacting factors such as salinity, anthropogenic pressures, and ecological stressors influence mangrove survival.

3.3 Drivers of Degradation

The analysis of degradation drivers reveals that illegal harvesting, siltation, and pest/disease outbreaks are the most widespread threats, affecting over 20 sites each. Hydrological cut-off and strong wave action also contribute significantly, while a notable number of sites report no active degradation. Less frequent but still relevant stressors include livestock browsing, prolonged flooding, and pollution. Rare occurrences such as parasitic plants, hypersalinity, and human trampling suggest localized impacts. These findings underscore the need for targeted interventions addressing both biophysical and anthropogenic pressures, with priority given to enforcement, hydrological restoration, and pest management in high-risk zones.

The spatial breakdown of degradation drivers reveals that Shirazi not only has the highest number of affected sites but also the widest diversity of stressors, indicating complex and overlapping pressures. Bodo and Munje show moderate levels of degradation with a mix of biophysical and anthropogenic drivers, while Funzi has fewer affected sites and a narrower range of threats. This spatial differentiation suggests that restoration strategies must be tailored not only to dominant drivers but also to the cumulative impact of multiple stressors within each block. Prioritizing multi-threat mitigation in Shirazi and targeted interventions in Bodo and Munje could enhance restoration effectiveness.

Socio-ecological threats Grouped Categories

Socio-Ecological Threat

The above word cloud highlights the range of site-level uses and pressures within mangrove areas. The prominence of “none” suggests that many sites are currently undisturbed or not actively exploited, offering potential for conservation or low-impact restoration. However, recurring terms like “pole-cutting,” “fishing,” and “firewood” indicate subsistence and livelihood-related activities that may contribute to degradation if unmanaged. Mentions of “cultural-spiritual” and “footpath” reflect non-extractive uses, underscoring the multifaceted value of mangrove landscapes. These insights reinforce the need for context-sensitive management that balances ecological integrity with community needs and cultural significance.

The Pareto chart above provides a prioritization lens for restoration recommendations, showing that a small number of categories account for the majority of site-level suggestions. “None” leads in frequency, indicating that many sites may not require immediate intervention or are already stable. However, the cumulative curve reveals that addressing just a few key categories—such as fishing, pole-cutting, and firewood—could resolve a significant portion of restoration needs. This insight supports a targeted management approach, where focusing on the most frequent and impactful recommendations can yield broad ecological benefits with efficient resource allocation.

Threats Vs Performance

Anthropogenic and environmental factors were the primary drivers of degradation across the assessed sites. Livestock grazing, mangrove cutting, and hydrological constraints were the most frequently recorded threats, with notable spatial variation across village blocks. Sites affected by hydrological limitations and elevated salinity generally exhibited lower survival rates and reduced growth performance, highlighting the importance of addressing both socio-economic pressures and ecological constraints in mangrove restoration planning.

Restoration Recommendations

The word cloud above highlights key restoration strategies prioritized across sites. “Replacement-planting” emerges as the most frequent recommendation, indicating widespread need to reintroduce mangrove cover where degradation has occurred. Other prominent strategies such as “protection-conservation” and “hydrological-remediation” reflect efforts to safeguard existing stands and restore ecological function. Mentions of “livestock-prevention” and “fisherfolk-sensitization” point to the importance of managing human and animal pressures through behavioral change and community engagement. The inclusion of “shift-site” suggests that in some cases, relocation may be necessary due to persistent environmental constraints. Together, these recommendations underscore the need for integrated, site-specific approaches that combine ecological restoration with social interventions.

The Pareto chart above provides a strategic lens for prioritizing restoration actions. “Replacement-planting” dominates the frequency distribution, followed by “protection-conservation” and “hydrological-remediation,” which together account for the majority of recommended interventions. The cumulative curve confirms that addressing these top three categories could resolve a significant portion of site-level restoration needs. Less frequent recommendations like “fisherfolk-sensitization,” “livestock-prevention,” and “shift-site” may be context-specific but still vital in targeted areas. This distribution supports a phased implementation strategy—starting with high-impact, widely applicable actions while allocating resources for localized solutions.

General Observations

Restoration recommendations varied across assessed sites, reflecting differences in ecological conditions and degradation drivers. Replanting emerged as the most frequently proposed intervention, followed by hydrological remediation and enhanced protection and conservation measures. Additional recommendations included fisherfolk sensitization, improved livestock control, and, in extreme cases of persistent poor performance, relocation of restoration activities to more suitable sites. The prioritization of interventions highlights the need for adaptive, site-specific restoration strategies to strengthen ecosystem recovery and reduce risks to long-term carbon permanence under the VM0033 framework.

Overall Performance Patterns

Performance by block (Bodo, Shirazi, Funzi, Munje)

The performance classification chart reveals spatial disparities in site outcomes across village blocks. Shirazi leads in total site count, with most sites rated as “Fair” or “Good,” indicating moderate success and potential for improvement. Bodo, though smaller in scale, includes a few “Excellent” sites, suggesting localized best practices or favorable conditions. Munje shows a balanced mix of “Poor,” “Fair,” and “Good” classifications, while Funzi has a higher proportion of “Poor” sites, pointing to persistent challenges. These patterns highlight the need for differentiated support—scaling up successful models in Bodo and Shirazi, while addressing limiting factors in Funzi and Munje to improve overall restoration performance.

Performance vs Salinity

The chart above reveals a strong link between salinity levels and site performance. Sites within the optimal salinity range (≤40 ppt) dominate in number and are largely classified as “Good” or “Fair,” indicating that moderate salinity supports healthier mangrove outcomes. In contrast, hypersaline sites (>65 ppt) are few and show a more even spread across performance classes, suggesting unpredictable or constrained growth conditions. High salinity sites (41–65 ppt) present mixed results, with some achieving “Excellent” ratings, pointing to the influence of other mitigating factors. These findings affirm the importance of salinity management in restoration planning, while also highlighting the potential for success in non-optimal zones under supportive interventions.

Salinity Distribution By Block

The box plot above reveals marked differences in salinity profiles across village blocks. Munje exhibits the highest median salinity and widest variability, including several outliers, indicating exposure to more extreme or fluctuating saline conditions. Bodo also shows considerable variation, while Funzi and Shirazi maintain lower and more stable salinity levels. These spatial patterns suggest that Munje and Bodo may face greater ecological stress, which could influence mangrove survival and growth. The relative stability in Funzi and Shirazi supports their suitability for restoration, emphasizing the importance of salinity monitoring in site selection and adaptive management.

Survival Vs Salinity

The scatter plot above reveals a generally negative correlation between salinity and mangrove survival across all blocks, with survival rates tending to decline as salinity increases. While each block shows its own trend line, Munje and Bodo exhibit steeper declines, suggesting greater sensitivity to salinity stress. Shirazi and Funzi display more moderate slopes, indicating potential resilience or buffering factors. Notably, some data points exceed 200% survival even at elevated salinity levels, hinting at localized conditions or adaptive responses. These patterns underscore the complex interplay between salinity and survival, reinforcing the need for site-specific assessments and adaptive restoration strategies.

HeatMap

The heatmap reveals distinct hydrological profiles across village blocks, with Shirazi showing a strong concentration of sites with “Good water exchange,” reinforcing its suitability for restoration. Munje and Shirazi also register high counts of “No water channel,” which may signal areas of hydrological isolation or stress. Bodo displays a more even distribution across hydrology types, including notable presence of “Blocked channel” and “Poor hydrology,” suggesting mixed restoration potential. Funzi has fewer sites overall, with moderate representation across categories. These spatial patterns highlight the need for block-specific hydrological interventions, especially in areas with limited water flow or structural barriers.

Conclusion

This rapid assessment of mangrove restoration sites within the Shirazi–Funzi Mangrove Complex reveals a spatially and ecologically heterogeneous landscape, where restoration performance is shaped by species selection, biophysical conditions, and localized socio-ecological pressures. A majority of sites demonstrated moderate to good restoration outcomes, with Sonneratia alba and Rhizophora mucronata exhibiting comparatively robust growth. However, a subset of sites continues to experience low survival and poor structural development, pointing to persistent ecological constraints that warrant targeted remediation.

Salinity and hydrological dynamics emerged as primary determinants of restoration success. Sites situated within optimal salinity ranges (≤40 ppt) and benefiting from functional tidal exchange consistently recorded higher survival rates and better canopy development. In contrast, hypersaline conditions and hydrological isolation—particularly in blocked channels and dead-end creeks—were strongly associated with poor performance. These findings underscore the critical role of hydrological connectivity and site suitability in shaping restoration trajectories and influencing long-term carbon sequestration potential under the VM0033 methodology.

Anthropogenic pressures—including illegal harvesting, livestock browsing, and human disturbance—further compound ecological stress, especially in blocks like Shirazi and Bodo where multiple degradation drivers converge. The prioritization of replacement planting, hydrological remediation, and enhanced protection measures reflects a growing consensus on the need for adaptive, site-specific interventions. Complementary actions such as fisherfolk sensitization, livestock control, and strategic site relocation are essential to mitigate risks and improve restoration outcomes.

Overall, while restoration efforts across the Shirazi–Funzi landscape show encouraging progress, sustained impact will depend on integrating ecological diagnostics with participatory management and locally grounded stewardship. This evidence base supports the refinement of restoration strategies, enhances project readiness for third-party validation, and strengthens the credibility and permanence of blue carbon benefits under the VM0033 framework.