Msc

As species distribution along the sea-land interface to the land interior IS
attributed to gradients in soil electro-chemical properties and tidal frequency and
nutrient cycling in a system is dependent on litterfall and decay dynamics. Hence, the
study for estimating zonation pattern and regeneration status of species along the
ocean-land interior trans~cts, along with litter dynamics (literfall and litter decay) was
carried out at Puduvyppu mangrove forest. Zonation pattern of species was revealed
by carrying out phytosociological analysis along the land-ocean transect and
correlating with gradients in electro-chernical properties of soil. Litterfall was studied
by evaluating interzonal and monthly variations in litterfall between species for one
year. Leaf fall and production was inturn correlated with weather parameters. Decay
dynamics was studied by involving six predominant species of the forest namely,
Avicennia officinalis, Bruguiera cylindrica, Rhizophora mucronata, Sonneratia
caseolaris, Acanthus ilicifolius and Excoecaria agallocha and by estimating interzonal
and monthly variations in mass loss and nutrient concentrations of decomposing leaf
samples for 12 months.
Results show that the area can be divided into three zones (zone I: 0-300 m,
zone U: 301-800 m, zone Ill: 801-1200 m from the sea) based on species distribution
pattern. Species diversity along the zones decreased from zone I to zone I I, whereas,
phytosociological para~1eters of species increased. It was also observed that species
like R. mucronata and S. caseolaris were restricted in zone I, whereas, A. officinalis
and B. cylindrica were abundant towards the landward side, due to the tidal sorting of
the species.
Electrical conductivity and soil nutrient (N, K, Na) concentrations increased
towards the landward side, whereas, pH decreased. Furthermore, soil P concentrations
and in situ redox potential positively affected stand density and E. agallocha stand
density respectively.
Regeneration was profuse in the central zone of the forest (700-800 111 from the
sea) and decreased towards the landward side and the seaward side, implying that
monospecifity and tidal inundation affected regeneration. Among the species, A.
officinalis seedlings were abundant in the lower height class «50 cm) and B.

cvlindrica in upper height class (>50 cm), implying that shade tolerance of the species
decided its establishment potential.
Litterfall did not vary among the zones suggesting that the dominant A.
officinalis determined litterfall of the forest. Leaf fall peaked during winter season
(November-December), whereas, leaf production was initiated by rainfall, implying
that rainfall and temperature controlled phenological cycles in species.
Mass loss followed an exponential pattern in A. ilicifolius, A. officinalis. E.
agallocha and S. caseolaris, whereas, it followed a linear pattern in B. cylindrica and
R. mucronata. Similarly decay rates were inversely related with initial lignin and
lignin: nitrogen ratio of the decomposing leaves. And also, interzonal variations in
decay rates were observed, implying that site and species affected decay rates.
Nutrient concentrations decreased with Nand K concentrations decreasing and P
moderately increasing in the litter bags during the course of decomposition, implying
that tidal frequency and mineralization-immobilization frequencies decided nutrient
release patterns in these species. In general this is a low diversified, juvenile with an
efficient nutrient input-out put mechanism.