Plant Community Structure, Fire Disturbance, and Recovery in ...

Contributions to the Study of Biological Diversity Vol. 3
(L.) L. Shrubs included Conocarpus erectus L.
(a mangrove associate), Talipariti tiliaceum (L.)
Fryxell (= Hibiscus tiliaceusL.), Thespesia
populnea (L.) Sol. ex Corrêa, and Caesalpinia
bonduc (L.) Roxb. These were occasionally
interspersed with juveniles of mangrove species,
particularly Laguncularia racemosa (L.) C.F.
Gaertn. and Avicennia germinans (L.) Stearn.
Apparently the shallow water over mud flats,
the shell margins, or the high silt content of the
coastal water are not conducive to the
establishment of Rhizophora seedlings
immediately along the coast (Pons & Pons
1975), although Rhizophora propagules were
sometimes found stranded on the shell sand of
the forebeach.
During field work, the beach ridges of the
Waini coast ranged from a few meters to over
150 meters in width. Where these were
sufficiently wide, somewhat higher diversity of
shrubs and trees was found on the back beach
towards the mangrove swamps, with species
including Spondias mombin L., Annona glabra
L. and Morinda citrifolia L. Just below the
surface, the wider beach ridges contained lenses
of nearly fresh water with salinity as low as 1
psu (Hollowell, unpublished). Because of
available fresh water, the back beach was in
places a site of agricultural activities. The
dominant crop grown for trade was Cocos
nucifera L. (Coconut), which grows well in the
shell substrate over rich mud. Manihot esculenta
Crantz (Cassava) is also commonly cultivated
for community use, along with a variety of
garden vegetables and ornamentals. Naturalized
Carica papaya L. (Pawpaw, Papaya) was found
frequently on beach ridges, usually 10 or more
meters from the shore. Terminalia catappa L.
(East Indian Almond) is a naturalized tree found
on both beach ridges and higher cheniers farther
inland. The small tree or shrub Morinda
citrifolia L. (Noni), an Asian native widely
known for medicinal values, is scattered in the
back beach up to the margins of the mangrove
swamp.
- Coastal Mangrove Swamps
Mangrove swamps are common along
nearly all tropical shorelines where wave energy
is low. They are dominated by woody plants
with a tolerance to salt water (Tomlinson 1986).
While mangrove species belong to several plant
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families, they have all developed structural and
physiological adaptations to the salinity,
waterlogged soils, and dispersal and
establishment challenges of the coastal
environment (Ball 1988). Adaptations include
roots that function to exchange air and provide
support in waterlogged soils, a capacity to
exclude or secrete salt, and fruits that germinate
at least partially while on the parent or during
dispersal by water. The number of mangrove
species is several times higher in the Western
Pacific than the Atlantic region.
The Coastal Mangrove swamps were
divided into two subsets, Avicennia forest and
Mixed Mangrove forest (Figure 1.13). Swamp
areas nearest to the ocean were most often
dominated by Avicennia germinans (L.) Stearn
(Black Mangrove, Courida) which reached 30
meters in height (Figure 1.15). Where the
coastline has been accreting, Avicennia
Figure 1.15. A pure Avicennia Coastal Mangrove
swamp near Waini Point, showing the dense carpet
of pneumatophores. Trees in this area were measured
as up to about 50 cm diameter and 32 meters in
height. The pneumatophores allow gas exchange for
the roots. Most of these trees lean to the west due to
the soft soil and the prevailing trade winds.
germinans is usually the first species to colonize
a mudflat, and where monospecific stands of this
species are found near the ocean, the trees often
fell within a narrow range of intermediate
diameters, suggesting that they might be the first
generation on new land. A large area of this type
occurred at the northwest end of the Waini
Peninsula, including the swamp in the vicinity
of Almond Beach. In the Mixed Mangrove
swamp Avicennia was found with Rhizophora