Restoring Zanzibar’s Shores with Screw Pine – Coastal erosion is becoming an increasingly serious challenge for Zanzibar. Shoreline retreat threatens not only coastal ecosystems, but also infrastructure, tourism, fisheries and the livelihoods of communities that depend directly on the sea.
Mangrove restoration is already widely used in sheltered estuarine environments. But exposed sandy beaches and rocky limestone shores present a very different challenge. Here, another native coastal plant may have an important role to play: screw pine (Pandanus spp.).
With its characteristic stilt roots, tolerance to salinity, drought and nutrient-poor soils, screw pine can help trap sediments, stabilise unstable substrates and reduce the effects of wind and wave energy. Yet its natural regeneration in Zanzibar is under pressure from trampling, livestock grazing, vegetation clearing and coastal development.
For the Zanzibar Environmental Conservation Organization (ZAVECO), screw pine therefore represents an opportunity not only for coastal restoration, but also for greater community participation in protecting Zanzibar’s shores.
ZAVECO recommends establishing community-based screw pine nurseries to increase the availability of seedlings for restoration while creating opportunities for local communities to participate directly in environmental conservation. The organisation also recommends including screw pine more systematically in coastal restoration programmes, monitoring seedlings after transplantation and continuing research into the factors that influence their survival and growth.
But making this approach sustainable raises a practical question.
If screw pine is to be propagated at larger scale to restore Zanzibar’s coastline, how should the seedlings be raised?
Traditionally, beach sand is used as a nursery growing medium. Taking sand from beaches, however, risks disturbing the same coastal environments that restoration projects are intended to protect.
To address this problem, ZAVECO carried out an applied nursery trial between June 2025 and May 2026 to test whether screw pine could be successfully raised using a humus-rich soil mixture instead.
The question behind the research was simple:
Can screw pine seedlings be successfully raised without taking sand from the very beaches restoration projects are trying to protect?
SEEDLING IN TWO DIFFERENT SUBSTRATES
ZAVECO established a comparative nursery experiment using 78 screw pine seedlings divided equally between two different growing media.
39 seedlings were grown in 100% beach sand, while another 39 seedlings were grown in a humus-rich mixture of humus and topsoil.
Both groups were maintained in the same nursery, with identical exposure to sunlight, temperature, relative humidity and watering schedules.
Every two weeks, researchers measured seedling height, number of leaves and survival.
The aim was not simply to identify which substrate produced the fastest growth. The more important question was whether seedlings raised without beach sand could develop into healthy planting stock suitable for future transplantation across Zanzibar’s diverse coastal environments.
HIGH SURVIVAL IN BOTH SUBSTRATES
After the monitoring period, seedlings showed high survival in both nursery treatments.
The humus-rich mixture recorded a survival rate of 87.18%, with 34 of the original 39 seedlings surviving.
In beach sand, survival reached 84.62%, with 33 of 39 seedlings surviving.
Across the whole experiment, 67 of the 78 seedlings survived, giving an overall survival rate of 85.90%.
The results also showed no significant differences in final height or leaf production between the two groups.
The humus-grown seedlings therefore recorded slightly higher survival, while screw pine showed high survival in both growing media.
WHY REPLACING BEACH SAND MATTERS
This is where a relatively small nursery experiment connects with a much larger environmental question.
Using beach sand to grow plants intended to restore beaches creates an obvious contradiction when that sand has to be extracted from coastal environments.
Large-scale dependence on beach sand for nursery production could contribute to local habitat disturbance and coastal erosion — precisely the pressures that restoration programmes are intended to reduce.
The ZAVECO trial found that the humus-rich mixture performed comparably across the measured growth and survival parameters. The study therefore concludes that humus-rich soil could provide a sustainable alternative to beach sand for screw pine nursery propagation.
FROM NURSERIES TO COMMUNITY-BASED COASTAL RESTORATION
The nursery trial is only one part of the process.
ZAVECO recommends that seedlings continue to be monitored after transplantation to understand their long-term survival and growth under real coastal conditions.
The study also calls for further research comparing the cost and effectiveness of different nursery media and examining other factors that can influence screw pine growth, including salinity, water availability and nutrient levels.
Community involvement is equally important.
Public awareness of the role of screw pine in controlling erosion and protecting shorelines could encourage greater participation in conservation activities, while community-based nurseries could connect restoration directly with the people living along Zanzibar’s coastline.
Ultimately, the study proposes considering screw pine as part of broader climate-change adaptation strategies for Zanzibar, particularly because of its potential role in shoreline protection in the face of sea-level rise and extreme weather events.
A BLUE LIFE HUB PERSPECTIVE
For Blue Life Hub, there is a broader lesson.
Nature-based coastal restoration does not begin when a seedling is planted on an eroding shoreline. It begins much earlier — with the choice of native species, nursery methods, local materials, scientific monitoring and the involvement of the communities that will ultimately live with and care for restored coastal ecosystems.
In an island environment such as Zanzibar, making that entire chain sustainable may be just as important as planting the trees themselves.
Scientific basis: “Assessing the Feasibility of Raising Screw Pine Seedlings in Humus Soil as an Alternative to Beach Sand for Coastal Restoration in Zanzibar”, Zanzibar Environmental Conservation Organization (ZAVECO), project period June 2025 – May 2026.
Restoring Zanzibar’s Shores with Screw Pine
