FAUNA AND FLORA O F MANGROVE SWAMPS
89
(b) a Barringtonia racemosa Association, or ( c ) a Saltwort
Association. The first two are diagnostic of areas under freshwater domination where evaporation and transpiration are
more than balanced by a high rainfall and/or supply of fresh
water from large rivers. The saltwort association occurs where
evaporation and transpiration are in excess of the supply of
fresh water.
11. ZONATION OF MANGROVES
Three schemes have been proposed in descriptions of the zonation
of mangroves, two of these base the zonation on physical features of
the environment while the third follows more recent practice and
names the zones from the genus dominant in each one.
1. Watson (1928) in a pioneering study of Malayan mangroves
recognized five classes based on frequency of inundation (Fig. 6).
(i) Species growing on land flooded at all high tides: no species
normally exists under these conditions but Rhizophora mucronata will do so exceptionally.
(ii) Species growing on land flooded by medium high tides: species
of Avicennia, A . alba, A . marina (Forst.) Vierh. (= A . intermedia Griff) and Xonneratia griflithii Kurz., and, bordering
rivers, R. mucronata.
(iii) Species growing where they are flooded by normal high tides:
the majority of mangroves thrive under these conditions but
the rhizophoras tend t o become dominant.
(iv) Species growing on land flooded by spring tides only: such areas
are a little too dry for the rhizophoras and suit Bruguiera
gymnorhiza and B. cylindrica (L.) B1. better.
(v) Species on land flooded by equinoctial or other exceptional
tides only : B. gymnorhiza dominant but Rhizophora apiculata
B1. and Xylocarpus granatus survive.
2 . De Haan (1931) introduced salinity of soil water as the factor
controlling distribution with tidal flooding as a subsidiary factor. His
scheme has two main divisions each with subdivisions.
A. A brackish to salt water zone with salinities a t flood tide of
between lo%, and 30%,.
A1. Areas flooded once or twice daily on each of 20 days per
month.
A2. Areas flooded ten to nineteen times per month.
A3. Areas flooded nine times or less in each month.
A4. Areas flooded on a few days only, in each year.
89
(b) a Barringtonia racemosa Association, or ( c ) a Saltwort
Association. The first two are diagnostic of areas under freshwater domination where evaporation and transpiration are
more than balanced by a high rainfall and/or supply of fresh
water from large rivers. The saltwort association occurs where
evaporation and transpiration are in excess of the supply of
fresh water.
11. ZONATION OF MANGROVES
Three schemes have been proposed in descriptions of the zonation
of mangroves, two of these base the zonation on physical features of
the environment while the third follows more recent practice and
names the zones from the genus dominant in each one.
1. Watson (1928) in a pioneering study of Malayan mangroves
recognized five classes based on frequency of inundation (Fig. 6).
(i) Species growing on land flooded at all high tides: no species
normally exists under these conditions but Rhizophora mucronata will do so exceptionally.
(ii) Species growing on land flooded by medium high tides: species
of Avicennia, A . alba, A . marina (Forst.) Vierh. (= A . intermedia Griff) and Xonneratia griflithii Kurz., and, bordering
rivers, R. mucronata.
(iii) Species growing where they are flooded by normal high tides:
the majority of mangroves thrive under these conditions but
the rhizophoras tend t o become dominant.
(iv) Species growing on land flooded by spring tides only: such areas
are a little too dry for the rhizophoras and suit Bruguiera
gymnorhiza and B. cylindrica (L.) B1. better.
(v) Species on land flooded by equinoctial or other exceptional
tides only : B. gymnorhiza dominant but Rhizophora apiculata
B1. and Xylocarpus granatus survive.
2 . De Haan (1931) introduced salinity of soil water as the factor
controlling distribution with tidal flooding as a subsidiary factor. His
scheme has two main divisions each with subdivisions.
A. A brackish to salt water zone with salinities a t flood tide of
between lo%, and 30%,.
A1. Areas flooded once or twice daily on each of 20 days per
month.
A2. Areas flooded ten to nineteen times per month.
A3. Areas flooded nine times or less in each month.
A4. Areas flooded on a few days only, in each year.