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here are many environmental and biological factors that can cause the
dying of mangrove trees. A concrete knowledge of these conditions is necessary
to save the trees. It is therefore essential that a comprehensive investigation
and diagnosis be conducted in the subject sites so that appropriate specific
prescriptions can be identified.
In general, these are the environmental and biological conditions that
can cause the dying of mangrove trees:
Poor/Absence of
Water Circulation
The mangrove forest may have poor water circulation, or there is a general
absence of water circulation due to some obstruction such as dikes, mud
accredition on waterways brought about by flood and/or typhoon-induced
strong waves. Poor water circulation reduces the generation of oxygen
by water as the tide rises and recedes. Mangroves grow in waterlogged
soil, which has no oxygen or air to sustain plant growth, and must depend
on oxygenated water to "breathe". As trees die, rotten plant
parts and other organic matter undergo decomposition and produce methane
gas that accelerates the suffocation of trees. Bad smell indicates this
stage of decomposition.
Under conditions of poor or absent water circulation, the trees may be
saved by allowing free circulation of tidal waters. Tidal action will
"aerate" the area and flush out all the harmful products of
biological decomposition.
Insect/Fungal Infestation
In some cases, mangroves die because of severe insect and fungal infestation.
Defoliation caused by the larvae of some insects, such as black moth and
some species of butterfly, is an indication of infestation. If the attack
is severe, massive defoliation can occur and fungi may have also attacked
the open parts of trees and thus affect the cambium layer. The cambium
layer is a channel where food is transported to all parts of the trees.
If this layer is infected, the whole tree will gradually die. Mechanical
breaking of trees caused by typhoons can also create entry points for
the attack of insects and fungi.
If this condition occurs, the trees may be saved through forest sanitation
activities such as intermediate treatments that will eliminate defective
trees and improve air circulation. Integrated pest control techniques
can also be applied.
Prolonged Dry Season
and Flash Floods
Prolonged dry season is another factor that cause the dying of mangrove
trees. The absence of the dilution functions of rain results in higher-than-normal
salinity levels of seawater. Indirectly, the reduction of freshwater inflow
from drying rivers during dry spells also contribute to this condition.
In addition, high ambient temperatures damage the breathing organs of
the trees.
Flash floods can also cause a sudden change in water salinity and temperature,
increased sedimentation in shorelines, damage to trees, and, ultimately,
the death of mangroves.
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