Tips for planting Mangroves
Planting Mangroves is not difficult provided that one observes some basic guidelines.
The pre-condition for success is to conduct an initial survey of representative habitats in areas close to the chosen site that should focus on:
1. Mangrove species (number of trees of each species per hectare)
2. Type of substrate
3. Depth of water at high and low tides
4. Salinity of water trapped in mangrove mud at low tide
5. Ground vegetation and mangrove associate plants
It is evident that the best results will be achieved by replicating the exact species mix determined in those findings.
Since both Red and Black Mangroves are viviparous, it is recommended to start with those species first.
Suitable propagules of the target species can usually be easily collected in adjacent mangals or in areas that are highly representative of the chosen site. Whereas some publications advocate the establishment of nurseries where the seedlings can be germinated before being planted out after 8-9 months, this is quite cumbersome and really only necessary for very large projects. Although possible, we do also not advocate the collection of wildlings, i.e. small Mangroves that have already started growing elsewhere. Plant growth is highly influenced by local micro-conditions and therefore, re-planting to other sites carries a disproportionate rate of failure.
We have been highly successful in keeping propagules in black plastic bags in a shaded area and planting them out as soon as they start developing the first leaves and roots.
Of note, when keeping them damp, we have done so by using small amounts of brackish water which we have collected at the planting site. This has ensured that the plants were subjected to the exact salinity they would then have to withstand once planted out.
When planting, we have chosen to plant one seedling per sqm corresponding to 10,000 seedlings per hectare. Sites with substantial wave action may require denser planting. With an average success rate of 70%, it is recommended to collect approx 50% more propagules than indicated by the size and the conditions of the planting site.
The trees need to be regularly maintained for the first two years.
Maintenance consists in removing debris and dead plants, replacing dead and lost plants and removing algae and barnacles. After two years, the plants are generally self-sustaining and can be thinned out where required.
White Mangroves and other Mangrove associates like Beach Pandanus, Pandanus pyriformis, and Beach Hibiscus, Hibiscus tiliaceus, do not reproduce via propagules and must thus be grown conventionally from seeds or cuttings.
These plants grow on drier soil on the fringes of the Mangrove swamp and we strongly recommend having them germinate in plastic bags that contain the exact same soil of the target sites and that are ideally kept lightly shaded and adequately watered at, or in the immediate vicinity of the ultimate planting site.
Planting out should then be effected as soon as the plants appear sufficiently robust, this for them to adapt to the specific micro-conditions whilst they are still highly flexible.
We shall be happy to assist in any way possible but the ultimate responsibility of doing the work will reside with the planters themselves.
This is why they are being paid to do so.
We recommend that anybody requiring professional assistance, especially larger resorts, address themselves to Marine Ecology Consulting who are one of Fiji’s pioneers in Mangrove management and can contribute anything from mere advice to full-scale project management.
A list of selected Mangrove restoration papers can be found here.