Agriculture Reference
In-Depth Information
4.4 Hurricanes and Storms
According to the International Panel on Climate Change, there have been no reported
trends observed in tropical storms and no evidence of changes in the frequency or
areas of storm formation, but it is predicted that wind intensities will likely increase
by 5-10 % (Houghton et al.
2001
). However, the assessment made by Trenberth
(
2005
) indicates that tropical storms will indeed increase in frequency and/or inten-
sity due to climate change, posing an additional threat to mangroves. Large storm
impacts have resulted in mass mortality in ten Caribbean mangrove forests in the
last 50 years (Jimenez et al.
1985
; Armentano et al.
1995
). Cahoon et al. (
2003
)
and Ning et al. (
2003
) have demonstrated mass mangrove mortality due to hur-
ricanes. Roth (
1997
) suggests that species proportions may shift because they have
different rates of regeneration. Storm surges can also flood mangroves and, when
combined with sea-level rise, lead to mangrove destruction. Ellison (
2000
) suggests
that flooding caused by increased precipitation, storms or relative sea-level rise may
result in decreased productivity, photosynthesis and survival. Due to inundation of
lenticels in the aerial roots, the oxygen concentration in the mangroves is likely to
decrease, resulting in death (Ellison
2004
). It may also decrease the ability of man-
grove leaves to conduct water and thereby reduce photosynthesis (Naidoo
1983
).
4.5 Effects of Changes in Sea Level
Thermal expansion of the oceans and melting of glacial ice caused by global warm-
ing have been primarily responsible for eustatic sea level by 10-20 cm in the last
century (Church et al.
2001
). Several climate models project an accelerated rate
of sea-level rise over coming decades (Church et al.
2001
). Tectonic and isostatic
adjustments (i.e. ocean basin deformation and land subsidence or emergence) have
also influenced the sea-level rise (Kennish
2002
). During the twenty-first century,
mean sea-level projections range from 0.09 to 0.88 m (Houghton et al.
2001
). The
greatest climate change challenge that mangrove ecosystems will face is the sea-
level rise (Field
1995
). Mangroves can adapt to sea-level rise provided it occurs
slowly enough (Ellison and Stoddart
1991
), if adequate expansion space exists, and
if other environmental conditions are met.
4.6 Mangrove Adaptations that help them Survive Sea-Level Rise
Mangroves have adapted special aerial roots, support roots, and buttresses to live
in muddy, shifting, and saline conditions. Mangroves may adapt to changes in
sea level by growing upwards in place, or by expanding landwards or seawards.
Mangroves produce peat from decaying litter fall and root growth and by trapping
