Why were mangroves degraded in Timbulsloko… and why is this worrying?

Timbulsloko is a small village in the north coast of the Indonesian island of Java (Demak), one hour away from the city of Semarang. There’s only one way to get to the village from land: a narrow road diverging from the national highway, that eventually enters a small community formed by brick houses and small stands selling nasi goreng and krupuk.

Picture of the road towards Timbulsloko. (c) Silke Tas.

As the trip continues, the landscape becomes clearer, and wide extensions of water surround the path on both sides, transforming the road into an artificial peninsula. Unfinished concrete houses line up along the margins of the road, which are the only emergent ground. Some of the buildings have been abandoned, but others have been rebuilt on concrete platforms that elevate the houses a meter from the ground.

Drone view of Timbulsloko. (c) Silke Tas.

Timbulsloko wasn’t always flooded by water. Over the last century, a large part of its mangrove forest was removed to build shrimp farming ponds. This means that the area was deforested and excavated to build large ponds where shrimps could grow.

Not only the soil has been excavated, but the whole coastal region is also sinking. Groundwater extraction in the nearby city of Semarang has caused the land to subside, meaning that the coastal region is sinking deeper with respect to mean sea level every year.

Effect of groundwater extraction over time. (c) Alejandra Gijón.

Road from Semarang to Timbulksloko. (c) Alejandra Gijón.

The mangrove loss does not help improve this situation. Mangrove forests behave like living wood fences, which shelter coastal areas from storms. Waves and currents slow down inside the mangrove forest. This means that any sand or mud particles being carried by the water can deposit and accumulate between the trees, in the same way that sugar deposits at the bottom of a still cup of coffee.


Sediment accumulation inside a mangrove forest. (c) Alejandra Gijón.

The accumulation of sediment can at least partly compensate for local subsidence, and sea level rise. By losing large part of its mangrove forest, Timbulsloko has thus lost a natural mechanism to protect itself against rising sea levels. But this also means that restoring the mangroves could be a way to improve the situation. This requires answering several questions:

  • What are the conditions that small mangroves need to grow healthy? Are those conditions satisfied in Timbulsloko? And if not, can we recreate them artificially?
  • Will the mangroves, once grown, be able to survive the subsidence rates in Timbulsloko?
  • And to what extent could the restored mangroves compensate subsidence, and protect the village?

Wetlands International started a mangrove restoration project in Timbulsloko in 2014, in collaboration with the local communities and Indonesian and Dutch institutions. The BioManCO research project builds on the knowledge collected during the pilot, and aims to help giving answers to the previous questions.

During the next posts we’ll explain the experiments we’ve done over the last years, and how they helped us build new knowledge for mangrove restoration. Keep checking our website if you want to read more 🙂

Related links:

Windows of opportunity: how do small mangroves find a spot to grow?

http://www.biomanco.org/uncategorized/windows-of-opportunity-what-are-the-conditions-needed-for-mangrove-colonisation/

How can we build a green belt in Demak?

http://www.biomanco.org/uncategorized/how-can-we-restore-the-abandoned-aquaculture-ponds/

Building with Nature Indonesia website:

https://buildingwithnatureindonesia.exposure.co/

Ecoshape website:

https://www.ecoshape.org/en/projects/building-with-nature-indonesia/