FIELD
EXPERIMENT
IMPACT AND RECOVERY OF PLANTS |
In the field study, we also studied the impact of oil and dispersed oil
treatments on trees and seedlings.
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Treatments caused significant mortality of mangrove
seedlings |
Oil treatments caused significant mortality
of mature Rhizophora stylosa trees within 2-7 months of application of
treatments. Treatments caused significant mortality of mangrove seedlings, both
naturally-occurring Rhizophora stylosa and planted Avicennia marina,
within 1-2 months. Mortality of Rhizophora stylosa trees and
seedlings was significantly lower in plots treated with dispersed oil compared
with plots treated with oil only, at each of the three sites. Variations in tree
mortality were not correlated with oil concentrations in sediments between
treated plots. Variations in tree mortality were also correlated with sediment
grain size.
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Oil treatments caused significant reduction in leaf biomass in
canopies of surviving trees between 2-22 months after oiling |
Oil treatments caused significant reduction in leaf biomass in
canopies of surviving trees between 2-22 months after oiling. The one surviving
oil plot had a 41% reduction in leaf standing stock at the completion of
monitoring, while the two dispersed oil plots had recovered at 22 months.
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Plate 8a. b, c, d. e. During field trials, plants were monitored for the impact
of oil treatments.
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A. Forest canopy growth and productivity was assessed
from litter fall collections made approximately monthly.
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B. Canopy and
density was measured using both litter fall and direct observations of tagged
leafy shoots. The number of leaves on these shoots was indicative of forest
canopy condition.
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C. Biomass of trees in plots was estimated using
allometric relationships determined by cutting down other trees and
systematically weighing the various parts (above-ground roots, trunk and stem,
branches and twigs, and leaves) of nine trees ranging from one to 12 metres
tall.
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D. Trees died in some plots as seen from above the canopy.
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E. Tree death in plots occurred 2-3 months after oiling, but depended on
prior tree condition, presence of infauna, as well as whether oil was dispersed
or not.
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