Published on 6 November 2019
Forests between land and sea
Mangroves are plant formations that develop along the shallow, protected marine shores of the tropics and subtropics. The main vegetation in such an ecosystem are also called mangrove in English: they are amazing trees that have adapted to hostile coastal conditions; standing with their feet in salt water and breathing thanks to their aerial roots.
Mangroves are present in over 120 tropical countries. They are important reservoirs of food and raw materials and provide numerous ecosystem services:
- stabilization and protection of the coast against winds, waves and sea currents;
- carbon storage;
- supply of fuelwood and timber, and non-wood forest products such as medicinal plants;
- provision of habitat, breeding sites, spawning grounds for a very large number of animal species: mammals, reptiles, amphibians, birds, but especially fish and crustaceans.
Mangroves under threat
The steady increase of the human population in coastal areas puts considerable pressure on these fragile ecosystems. Many mangroves are threatened by human activities such as conversion to ponds for shrimp aquaculture, tourist resorts or urban areas, or simply by overexploitation. Mangroves are often exploited by coastal communities in a more or less controlled way.
In Peninsular Malaysia, the mangrove forest of the Matang Mangrove Forest Reserve covers more than 40,000 ha. Since the beginning of the last century, it has been developed and managed to ensure sustainable production of charcoal and timber. It is a world record for longevity in tropical forest management. The MMFR is divided into 4 types of zones: productive (74.8% of the total area of the reserve), restrictive productive (6.8%), protective (17.4%) and unproductive (1 %). Charcoal extraction and timber production can only take place in the first 2 types of zones. The silvicultural management consists of a 30-year rotation cycle with two thinnings at 15 and 20 years after plantation.
The Virgin Jungle Reserve (front) and other mangrove stands (back) in the Matang Reserve in Perak State, Peninsular Malaysia.
Photo credit: Farid Dahdouh-Guebas
Fieldwork in the intertidal mangroves consisted of measuring the diameters and heights of numerous trees.
Photo credit: Viviana Otero
Remote sensing to the rescue of management
To ensure sustainable management of mangroves against the backdrop of increasing external pressures, the development of methods for mapping and monitoring their biophysical properties is becoming increasingly important. This objective was pursued by the researchers of the STEREO project MAMAFOREST, using the Matang reserve as a study area. This has the advantage that it combines productive areas and protected areas.
To evaluate the viability and sustainability of logging within the reserve, they analyzed and integrated time series of optical and radar remote sensing data. After validation, they were able to extract biophysical parameters and quantify the yearly evolution of the structure, species and aboveground biomass of forest stands both in the production zones and in the protection zones.
Forest Age Maps (in years) for the following dates: April 29, 1996, April 16, 2008, July 23, 2010 and June 15, 2015 (from left to right).
Source: Publication in prep by Lucas et al.
In concrete terms, the project has led to the development of several products directly useful to managers:
- the establishment of the true age of the mangrove patches in the productive forest, which made it possible to draw up the very first correct age map of the reserve's stands;
- the development of a scientific protocol to generate up-to-date maps of forest age and biomass based on freely available imagery;
- the presentation of a mobile application that puts the scientific protocol into practice to generate up-to-date maps that the Forest Department can use to plan silviculture;
- the mid-term involvement and end-term training of Forest Department personnel to use the tools made availbale.