Mangrove
vegetation structure
dynamics
and regeneration
Thesis
Philosophiae Doctor Scientiarum
Farid Dahdouh-GuebaS
Epilogue
One
thousand years ago, the human world population counted less than 500 million
people. By 1650 this figure
doubled a first time, by 1850 a second time and by 1975 a third time (Fisher,
1980). Now, at the turn of the
second millennium, the world population numbers more than 6 billion people.
On one hand this implies that natural resources are under a threat of
over-exploitation and under the potential threat of depletion, unless the
people using them understand the need for a sustainable use.
Even under the latter circumstances, the population explosion may
(have) be(en) too big for any sustainable use to generate positive results.
On the other hand it becomes increasingly difficult and may even
constitute an ethical problem to restrict people from using resources.
As just one example, in mangrove forests local people may be dependent on the resources (Dahdouh-Guebas et al.,
2000b). Restricting access to
natural resources through changes in property rights has been shown to
increase poverty (Reddy
& Chakravarty, 1999) and increasing
inequality and conflict therefore undermine the conditions which are deemed to
be necessary for the sustainable management of a resource (Adger et
al, 1997). In Vietnam, a former centrally planned economy, the
inequality is the result of the effects of the economic liberalization process
(Adger,
1999). Agrawal &
Gibson (1999) state that an effective institutionalisation of community-based
natural resource management and conservation is essential. This
is corroborated by Aagesen (1998) reporting that self-determination and
territorial rights are important factors in the indigenous interests in and
commitment to conservation of certain plant species (Aagesen,
1998).
Duraiappah (1998) also emphasizes that groups that adopt unsustainable
activities must be given the incentives (compensation, rewards, taxes, and
information provision) to stop. Omodei-Zorini & Contini (2000) and
Omodei-Zorini et
al.
(2000)
showed for instance that people around a Kenyan mangrove forest would stop
exploiting the mangrove if they were given cattle.
It
is in our tradition to establish human settlements along waterways and
coastlines (Fig. 1). Whereas the
industrialised countries have been able to develop large cities away from the
coast, in developing countries the vicinity of water bodies for many cities is
still very pronounced. The
coastal zone of most tropical and subtropical developing countries also host
mangrove forests, which are important on different eco-socio-economic
levels. They constitute a place to live and a place to live from.
Many settlements are located within the mangrove and in some countries
such as Thailand or Tanzania entire villages may built on poles (Kajia, 2000).
The people use mangrove wood for construction (houses, boats,
furniture) and as fuel (charcoal, firewood), and other mangrove products range
from the making of ointments and dyes to the making of fishing gear (cf.
Stafford-Deitsch,
1996; Dahdouh-Guebas et al.,
2000b).
A majority of the people living along the coast live from fishing or at
least consume fish. Since
mangroves act as breeding, spawning, hatching and nursing grounds for many
marine animal species a direct link between the mangrove cover
on one hand and both the lagoon and offshore fishery on the
other hand has been found, and several areas have witnessed a decrease in
production from fisheries with more intense mangrove destruction (Baran &
Hambrey, 1998; Baran,
1999; Naylor et al.,
2000). One of the main reasons for destruction of these forests is
shrimp aquaculture, largely under influence
of the world’s more industrialised countries, but clearly at the expense of
poor people in developing countries. For
the sake of the livelihoods of the communities depending of the mangrove and
on fisheries it is therefore essential that the mangrove ecosystem be
protected worldwide.
Assessment
and understanding of mangrove extent, evolution, regeneration
and restoration
is done in a framework of development
cooperation (cf. Fig. 5 in Dahdouh-Guebas & Koedam,
in prep.). At this point it must
be emphasized that there is a clear difference between field- and
goal-oriented development cooperation on one hand and fundamental and applied
scientific research relevant in the framework of development cooperation on
the other hand. Field-orientation
generally focuses on those countries that are least developed or most in need
of international aid, while goal-orientation concentrates on a number of
actions that can easily be translated into direct benefits for local
people. Belgian
International Cooperation for example prioritises five sectors in its
development cooperation – basic health care, education and training,
agriculture and food security, basic infrastructure and community building –
and three crosscutting themes – promotion of equal opportunities for women
and men, environmental management, social economy – (BTC,
1999).
It is clear that the present research does not fit into any of the
sectors and can only be squeezed into the ‘environmental management’
theme. So, there is still a
missing link between the research aspect and the field- and goal-oriented
development cooperation. In the
same context, on one hand it is claimed that previous knowledge has been
ignored and that more and more obscure aspects of mangrove ecosystems are
being subjected to examination (Field,
1998b), whereas on the other hand
mangrove ecologists tend to be primarily concerned with the intrinsic nature
of their research rather than in initiating the use of their findings in the
management of mangrove rehabilitation projects (Field,
1999).
This ‘missing link’ can best be established within a holistic forum
(e.g. human ecology) that is understandable by decision-makers (cf. Rönnbäck,
1999). The filling of this
missing link requires a separate investigation that integrates the finding in
management plans and is beyond the scope of this thesis.
However, underneath an attempt will be made to situate the different
research aspects better in the framework of development cooperation and local
and global management.
The
results of scientific research fall apart into different case studies, each of
which is an important piece in the whole research framework that has a
development
relevance. However,
it is difficult to present this relevance for every single manuscript
presented as a separate study. Therefore
the relevance of the key manuscripts presented in the present dissertation,
complemented with some of the manuscripts prepared in the same research
framework but not included in this work (Appendix 2), is summarised briefly
underneath.
[
‘Utilization of mangrove
wood products around Mida
Creek
(Kenya) amongst subsistence and commercial users’ (Chapter
II) :
relevant in assessing the local utilization patterns and establishing the degree of dependence of local people on the
mangrove resource;
[
‘High resolution
vegetation data for mangrove research as obtained from aerial
photography’ (Chapter IV), ‘A note on the
identification
of
mangroves from aerial photography in Kenya and Sri Lanka’ (Chapter
V) and
‘Remote sensing and zonation
of
seagrasses and algae along the Kenyan coast (Dahdouh-Guebas et al.,
1999a) :
relevant in assessing the possible tools which can be used to monitor
coastal ecosystems and the levels at which this can be done, as well as
the actual distributionand
composition of these ecosystems;
[
‘Conservation of
mangroves vs. development
of
shrimp farming :
investigation of the recent evolution of Pambala (Chilaw Lagoon,
Sri Lanka) using remote sensing
and
GIS
’ (Dahdouh-Guebas et al.,
2000c; Dahdouh-Guebas et al.,
subm.c)
:
relevant in highlighting the rate of mangrove destruction and the ecological
footprint of shrimp farming, and therefore the carrying capacity of the
environment;
[
‘Four decade vegetation
dynamics
in
Sri Lankan mangroves as detected from sequential aerial photography
:
a case study in Galle
’ (Chapter VI), ‘Two decade
vegetation dynamics in Kenyan mangroves as detected from sequential aerial
photography : a case study in Gazi
Bay’
(Chapter VII) and ‘An ordination study to view past, present and future
vegetation structure
dynamics in disturbed and undisturbed mangroves forests in
Kenya and Sri Lanka’ (Chapter VIII) :
relevant in understanding the evolution of mangrove vegetation structure
dynamics and to make predictions for the future to anticipate
artificial restoration
;
[
‘Propagule predators in
Kenyan mangroves and their possible effect on regeneration
’ (Chapter X), ‘Food preferences in Neosarmatium
meinerti de Man (Decapoda : Sesarminae) and its possible effect on the
regeneration of mangroves’ (Dahdouh-Guebas et al.,
1997) and
‘Propagule predation in Sri Lankan mangroves and
its effect on vegetation structure’ (Chapter XI) :
relevant in the framework of mangrove regeneration for finding the crab
species and mangrove areas that are most likely to display
propagule predation
and
for finding the mangrove species that is most likely to be adversely
affected by propagule predation;
[
‘Regeneration status of
mangroves under natural and nursery conditions in Galle
and
Pambala, Sri Lanka’ (Chapter XII) and ‘Natural regeneration
status
of mangrove forests in Mida
Creek,
Kenya’ (Kairo et al., in prep.) :
relevant in the framework of mangrove regeneration for monitoring
the
status of mangrove regeneration in natural and nursery conditions on a short and a long term;
[
‘Recovery process of a
restored mangrove system in Kenya : a floral perspective’ (Bosire et al.,
subm. b) and ‘Macrofaunal recruitment in a restored mangrove system in
Kenya’ (Bosire et al.,
subm. a) :
relevant in the evaluation of how similar the functions and services of
a restored mangrove forest are as compared to the natural mangrove;
[
Are the northernmost
mangroves of West Africa viable ? - a case study in the Parc National du Banc
d’Arguin, Mauritania – (Chapter XIII) :
relevant in understanding factors that limit the distribution
of
mangroves.
References
See Bibliography
This page is maintained by
Farid Dahdouh-Guebas,
fdahdouh@vub.ac.be