The GIS results indicate marked changes in the extent of the
Somone ecosystem morphological units from 1946 to 2006 (Fig. 4).
This study focuses mainly on the mangrove morphological unit, as
it has undergone the most striking spatial and temporal changes
(Fig. 5). Three key periods were identified for changes in the
mangrove forest surface area: (1) decrease from 1946 to 1978, (2)
stabilization from 1978 to 1992, and (3) an increase from 1992 to
2006 (Fig. 5). From 1946 to 1978 (32 years), the mangrove area
decreased by 1.4 km2 in two phases: a loss of 0.4 km2 from 1946 to
1970, followed by an accelerated loss of 1 km2 from 1970 to 1978. In
the estuarine area, the mangrove forests first disappeared from the
lagoon, where they were replaced by mudflats, which increased in
area from 0.7 km2 in 1974 to 1.2 km2 in 1978 (Fig. 4). The area
covered by the mangrove ecosystem and the mudflats thus was
inversely proportional during this period. From 1978 to 1992, the
area occupied by mangrove forest remained relatively stable with
only a small decrease, from 0.17 km2 in 1978 to 0.12 km2 in 1989
(0.05 km2 in 11 years; Fig. 5). Following this, a large increase in
mangrove area was recorded from 1992 (0.15 km2), through 1999
(0.6 km2) and continuing to 2006 (>1 km2) (an increase of about
0.9 km2; Fig. 5). The area occupied by the devegetated mudflats
decreased proportionately during this period from 1.2 km2 in 1978
to 0.3 km2 in 2006, as the mangroves recolonized those mudflat
areas previously occupied by mangrove forest (Fig. 4).