Why Rhizophora-Dominated Mangrove Plantations May Not Save Our Coasts

Written by Cyril Mae Embalsado, Science Communication Officer

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Mangrove Forest in Puerto Princesa City, Palawan

Mangrove forests are a vital part of coastal ecosystems, particularly in tropical and subtropical regions, where they provide essential ecosystem services. Additionally, they play a significant role in climate change adaptation and disaster risk reduction by stabilizing coastlines against typhoons and storm surges. Mangroves also serve as breeding grounds for aquatic fauna and facilitate sediment accumulation essential for nutrient cycling. Furthermore, they support coastal livelihoods through provisioning services. Notably, mangroves are recognized for having greater carbon sequestration rates compared to their terrestrial counterparts, highlighting their role in climate change mitigation.

Despite their importance, mangrove loss has progressed over centuries due to coastal and urban development, pollution, and aquaculture expansion. In response, mangrove restoration has become the major conservation priority. Community-driven initiatives and large-scale planting campaigns aim to rapidly increase mangrove cover. But here’s the catch: most of these programs rely on planting only one mangrove species, Rhizophora. This approach has often resulted in limited ecological success, particularly in the Philippines.

Less Diversity, Less Life

Natural mangrove forests thrive on diversity. They consist of numerous species distribution in accordance to salinity, sediment characteristics, and tidal elevation. This species diversity generates complex habitats that support numerous organisms such as birds, fish, crabs, and other microorganisms as well as maintain ecological functions in an ecosystem; however, with Rhizophora monocultures, habitat complexity declines as this would simplify forest structures resulting in fewer species. Fewer species leads to reduction of ecological function.

Improper planting of Rhizophora propagules on seagrass beds and in the seaward zone in Perrelos, Carcar, Cebu

Planting the “Wrong” Trees in the “Wrong” Place

Successful restoration depends on matching the right species with the right environment. In the Philippines, Rhizophora species are often used for restoration efforts due to its rapid propagation. Rhizophora species exhibit vivipary, meaning their seeds germinate while still attached to the parent tree making propagules establish quickly after dispersal.  While this trait facilitates rapid coverage, zoning patterns are often overlooked. Normally, Rhizophora thrive in sheltered riverbanks and mid-ward zones where wave energy is low and sediments are fine and stable. Their stilt or prop roots are well-adapted for anchoring soft, muddy substrates, and for trapping sediments rich in organic matter. Since Rhizophora species propagules are easy to collect, they are frequently planted in seaward zones where conditions are unsuitable. In these areas, strong wave action, unstable substrates, and lower sediment accumulation hinder establishment and survival. In contrast, pioneer mangrove species namely Avicennia and Sonneratia are naturally adapted to this harsh environment. They tolerate high wave energy, possess specialized root systems (pneumatophores) that allow efficient gas exchange in anoxic soils, and colonize unstable sediments. These species typically establish first, stabilizing the substrate, and creating conditions that later allow Rhizophora to thrive further. Ignoring zonation mismatch leads to poor outcomes. When Rhizophora species are planted outside its suitable habitat, survival rates decline significantly (Primavera & Esteban, 2008).

Low Resiliency and High Mortality to Environmental Disturbances

Monoculture plantations lack functional diversity, which reduces resilience to environmental disturbances. Assessments following Supertyphoons Yolanda and Odette in the Philippines revealed that Rhizophora plantations suffered extensive damage and high mortality rates. Why? Unlike Avicennia and Sonneratia species, which can sprout new shoots either from the base or side branches, Rhizophora species mainly grow upward from the terminal bud. Damage to this growth path can easily disrupt survival. 

Mangrove zonation is not universal. It is region-specific. In the Philippines, pioneer mangroves species such as Avicennia and Sonneratia serve as frontlines due to their tolerance to strong wave action and unstable substrates. Their adaptations allow them to combat high environmental stress allowing them to reduce wave energy and stabilize sediments, preparing the environment for various species. On the contrary, in parts of America and Caribbean, Rhizophora species often occupy the seaward zone because of lower mangrove and species diversity.

Restoring Mangroves the Right Way!

Planting the right species in the right place promotes diverse mangrove forests and functional mangrove ecosystems. In this way, restoration programs can rebuild coastal ecosystems that are both productive and resilient. This reinforces an important lesson: Restoration should aim to rebuild ecosystems, not merely plant trees. This approach aligns with guidance from the Department of Environment and Natural Resources through MEMO-2024-54 (January 19, 2024), which emphasizes that mangrove restoration efforts should be grounded in science-based practices, adherence to natural zonation patterns, and species-site matching. The memo highlights the areas suitable and prohibited for enrichment planting, guidelines for nursery establishment and management, maintenance and protection, as well as capacity building and stakeholder collaboration. Furthermore, the memo clearly states that Rhizophora species are strictly prohibited in seaward zones, and instead promotes the use of appropriate pioneer species of mangroves such as Avicennia and Soneratia. 

Further, Rhizophora seedlings are best to be planted in abandoned ponds (in the midward zones), with the recommendation of Primavera of reverting Abandoned, Undeveloped, Underutilized (AUU) fish ponds to mangrove forests, in line with the 4:1 mangrove-pond ratio. Given these contexts, the government is urged to do their part in mangrove restoration, the correct way, to promote the ecological and socioeconomic benefits of this coastal habitat to the people and to the environment for a resilient future for all. 

Join the movement!

As mangrove ecosystems continue to decline, it is crucial that we turn awareness into action by supporting initiatives that value biodiversity, ecological suitability, and long-term resilience. Through Mangrove Matters Philippines (MMPH), we can ensure that mangroves continue to protect our coasts, sustain biodiversity, and fight climate change for generations to come. 

Small actions can grow into meaningful change as we work together. Mangroves have long protected our coast, now it is our turn to protect them–because caring for our mangroves means caring for our planet.