IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002 
  
(approximately 50 x 50 m) were isolated for field verification. 
Such exercise was necessary to separate the sparse and 
unhealthy within the monospecies. Classified final output was 
generated by supervised training sets using maximum 
likelihood classifiers. Landsat Thematic Mapper (TM) data 
and IRS 1D -LISS 3 data were used to map the land use and 
land cover during 1987 and 1998 respectively and compared 
with base information. The land use and land cover changes 
during these periods provided the change in coastal activities in 
the vicinity of Pichavaram mangrove and possible influence on 
the mangrove ecosystem. In order to map the mangrove 
zonation of Pichavaram mangroves, the area was divided as 
core, fringe and peripheral mangroves based on geomorphology 
(Fig. 3). 
Remote Sensing data basad Zonation Map of Pichavaram 
{IRS 1D = Jan, 1998) 
s 
    
    
pa, as M 
a; : A. 
1-Core Zone, 2-Fringe Zone and 3- Peripheral zone 
> 
vœu Rhizophora = Birch sand mes Sas 
: ‚ mes Wei C'eastal water 
mm Avicennia "9 esd lr 
sem Suaeda mm np Hm wwaler 
mm Plantation = Sandy suil mum Aquaculture 
Figure 3: IRS-1D, LISS Ill derived mangrove zonation 
The satellite data revealed that the Pichavaram mangroves were 
undergoing varieties of changes, namely, 1) dense mangrove 
area to sparse mangrove, 2) mud flat to mangrove, 3) 
mangroves to wetlands, 4) agriculture land to aquaculture 
ponds, etc. In general, the mudflats and sparse mangroves were 
improving and aquaculture developments did not affect the 
mangroves in this region. The GIS analysis of 1987 and 1998 
satellite derived land use/cover map showed an estimated area 
of 33 ha of healthy mangroves were degraded, around 58 ha of 
degraded mangroves became healthy mangrove, 29 ha of 
mangroves became mudflats and 24 ha mudflats became 
mangrove regions. Overall the extent of mangrove forests was 
estimated to be of 398 ha during 1987 and 411 ha during 1998 
(Anonymous, 2001). The substantial gain in the mangrove area 
in the mudflats was attributed to afforestation by Forest 
Department of Tamilnadu, MSSRF and CAS in Marine Biology 
Department. The regeneration of mangroves in degraded areas 
426 
might be due to improving the tidal flushing due to new 
channels created by Forest Department and MSSRF and 
afforestation measures. 
MANGROVE ZONATION 
Zonation of mangroves depends on factors like topography, 
estuarine morphology, frequency of tidal flooding, soil type, 
salinity, rainfall, water logging, evaporation, transpiration, and 
river discharge. In general complete zonation occurs only in 
areas, where considerable intertidal range, high rainfall and 
availability of silt in suspension exist, to ensure deposition of 
mud or soil surface enabling the mangrove to penetrate further 
Pichavaram has the soil composition of fine and coarse silt with 
20 to 30 % clay, 10-20% silt, 45% fine sand and 15 % coarse 
sand. The normal rainfall is upto 1500 mm in the nearest Port 
Nova rain gauge station. The tidal amplitude is only 1 — 1.5 
mts. (Anonymous, 1998). 
Though 10 species of mangroves from 6 families were 
identified, using satellite data they were found to occur in three 
zones, namely, (1) core zone dominated by Avicennia 
officinalis, Avicennia marina and other salt marsh species, (Fig. 
4), (2) fringe zone with Rhizophora and Suaeda (Fig. 5) and (3) 
peripheral zone with mixed mangroves and mangrove 
associates (Fig. 6) and halophytes including Avicennia marina, 
Arthrocnemum indicum, Salicornia brachiata, Suaeda 
maritima and Suaeda monoica. Avicennia marina found in the 
core region of Pichavaram is reported to have widest range of 
tolerance to salinity and found to occur in the high intertidal 
regions. In addition, Avicennia marina has smaller seeds and 
possibility to disperse the propagules to high intertidal regions 
was more. Whereas Rhizophora has larger seeds or propagules 
that are mostly confined to fringe regions of the creek due to 
insufficient tidal currents to disperse the larger seeds to high 
intertidal regions. But Suaeda monoica was found in 
succession in the fringe regions. In the peripheral zones a great 
number of species are present, where zonations are more 
complex and numerous, depending on the local conditions. 
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Figure 4. Core Mangrove zone showing Avicennia 
  
  
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