Mangrove
vegetation structure
dynamics and regeneration
Thesis
Philosophiae Doctor Scientiarum
Farid Dahdouh-GuebaS
General
Conclusions
·
Which are the features
that can be recognised from airborne remote sensing imagery
of mangrove areas ?
Identification of mangroves from airborne remote sensing has shown to
penetrate to the assemblage or genus level.
Species identification
is
a possibility if the local
species
composition is
known, but not if there are several genus members. The latter may be compromised if erroneous species lists are
provided, for instance for new mangrove areas.
A synthesis of all the sites studied indicates the plasticity of some
image attributes and the consistency of others.
·
What
is the spatio-temporal vegetation structure of
the mangroves ?
In our study sites the horizontal vegetation structure has been found to
comprise ‘zoned’ or ‘mosaic’ forest patches, depending on the tidal amplitude
. The
‘moving mosaic’, ‘growing mosaic’, ‘shifting zones’ or ‘growing zones’ dynamics, some of which associated to our study
sites, each comprise a particular evolution of the vegetation.
The floristic ‘accretion’, ‘invasion’ or ‘dominance/extinction’ describe the way in which
the floristic diversity is enriched or extinct as a result of the dynamics.
The vertical vegetation structure does not always comprise an adult,
young and juvenile vegetation layer, and the various combinations of
vegetation layers, on the species or assemblage level, can be an indication
for the future vegetation structure. The qualitative analysis of the vegetation structure using
remote sensing
and
GIS
combined with the quantitative analysis using ordinations, is
a complementary approach that allows predictions that can be used directly in
management or forestry plans.
·
What
is the mangrove regeneration
potential
and to which extent are propagule predators a constraint to regeneration ?
The short-term regeneration
potential (measured through e.g. rooting performance) has been found to differentiate between species
and forest patches. It
is under strong influence of differential propagule predation
in
our study sites (differences between species, between forest patches and
between sites), and was found to vary with the mangrove lagoon water level in
the non-tide dominated sites. A
model was proposed in which propagule predation is
presented as one link in the chain of events that leads to a particular
vegetation structure.
·
What
is the vegetation structure
of
a mangrove at its biogeographical
limit
?
The mangroves of the Parc National du Banc d’Arguin display four different
growth forms of the vegetation : high trees, wide trees, shrub formations and
sebkha formations comprising mangroves.
Although under stressful conditions, there was no decreased flowering
and only slightly decreased fruiting, the main problem being the fruits
falling in sites with unfavourable conditions.
·
Which
are the problems associated with the use of the PCQM for
the study of mangrove vegetation ?
The PCQ-Method may lead to an inconsistent over- or underestimation of the
density
and
the basal area
of
the mangrove, depending on the forest structure
(dense
/ sparse, aggregated / non aggregated), which can be partially solved by the
choice of a ‘transect’ or ‘at random’ PCQM approach.
Architecture of trees or colonies limits the applicability of the PCQM
by the book.
This page is maintained by
Farid Dahdouh-Guebas,
fdahdouh@vub.ac.be