2 sedimentation and infilling from the inlet rivers. Two options has been recommended to solve
this serious sedimentation threat i.e. inlet diversion, and lagoon dredging which now is on going.
The main purpose of this study were to describe mangrove vegetation and some of its ecological processes within Segara Anakan lagoon, Cilacap Specifically, the project aims
were: 1. to describe the mangrove floristically, including the structure and composition of the
vegetation and its regeneration; 2. to determine the small litter-fall production, quantify its nutrients, and
3. to estimate its rate of decomposition. Material and Methods
1. Forest structure and composition
There are three main locations on the study: Klaces area KLA representing the most impacted area and Sapuregel area SAP that is less impacted. Some study was also
set up in Motehan MOT area as the transition between the two locations. Three stations of 500 m length transect line was designated for each station. All study designed to be
comprehensively conducted on the same sites therefore its information obtained would be integrated and hopefully supporting one to another.
Figure 1. Study sites in Segara Anakan Cilacap.
All together the study were conducted in 6 transect lines of 500 m length and 20 m width, 3 transects were set up in Klaces area KLA1-3 and and 3 transects in Sapuregel
area SAP 1-3. The transect lines then divided into 20 x 20 m plots. Within each plots, all
3 trees with diameter
≥ 4 cm were measured diameter and height and identified to species. The number of saplings diameter
4 cm and height ≥ 1 m in each 20 x 20 m plot were recorded in one 5 x 5 m quadrat, and the number of seedlings diameter 1 cm and height
less than 1 m in one 1 x 1 m quadrat. The quadrats were placed in a certain corner of each 10 x 10 m plot. They are treated here as statistically independent samples. The
physiognomy of each representative site was determined by a series of profile diagrams. Each tree and sapling species present in these representative plots were plotted for their
position and measured for diameter, height bole and total height and canopy width. 2. Litter-fall and litter-layer
On each transect of 500 m were installed 5 litter traps for upper plants and 5 litter traps for lower plants Acanthus and Derris with a distance in between approximately 100 m. In
total 45 sets of trap of each category were installed. The upper-plant litter-fall were collected using traps which were made by attaching a conical-shape nylon mesh 2 mm to
a 1 m X 1 m wooden frame and hanged about 1.5 m above the mean high water level at spring tide. The lower plant litter-fall were collected using 1 m x 1 m x 1m open top and
bottom cages of nylon mesh 2 mm which encircled the target plants. The litter-fall collected from each trap on the 15th and on the last day of each month for a year period
then bulk by month before sorting into leaves, branches, fruits and flowers, and a miscellaneous fraction. The fractions were subsequently dried to a constant weight at 70 o
C for at least 72 h prior to weighing. A substantial number of samples were randomly picked from the batch for further chemical analysis N, P, K. The small litter-layer was
collected from 1 m x 1 m wooden frames that set up on the forest floor. The frames positioned in the same 20 m x 20 m plots as for the litter-fall collection, but they were only
collected on the last day of each month. Only leaf, stipule, reproductive part, and small wood litter-layer were collected. The litter-layer then cleaned, dried, sorted and weighed
using the same methods as for litter-fall. The litter-fall decomposition rate or, in the case of mangroves, litter-fall loss-rate, since there may be removal by the tide was calculated
as the ratio of annual litter-fall mass L to litter-layer or standing crop Xss, k = L Xss. Turnover rate, the rate of the amount of a substance released by or entering into a
compartment in a given time was defined as the inverse form of decomposition rate 1k. Half-lives t0.5 assuming an exponential model applies, were calculated as 0.693k
Olson 1963. 3. Leaf-litter decomposition
Decomposition was studied using freshly-fallen leaf-litter collected from the forest floor at low tide of Acanthus ilicifolius, Aegiceras corniculatum, Avicennia alba, Bruguiera
gymnorrhiza, Ceriops tagal, Derris trifoliata, Excoecaria agalocha, Finlaysonia sp., Rhizophora apiculata, Scyphyphora hydropillacea, Sonneratia alba
and Xylocarpus granatum
. Ten grams of this leaf-litter were enclosed separately in 30 cm X 30 cm 2-mm mesh nylon bags. The bags were left on the forest floor tied to plant roots or trunks in
sites that were dominated by the same species as the leaves that were used in the bags. Collections were made at 0, 2, 4, 8, 16 and 32 days. There were three replicate bags for
every collection. Litter remaining in the bags at every collection time was washed carefully with fresh water and air-dried. After the final collection the litter was oven-dried at 70°C
for 4 days and weighed. No chemical analyses were made for the litter because it was impossible to clear off the remnants of adhering mud without altering the chemical
composition of the sample.
4
Results and Discussion 1. Forest structure and composition
In total, there are 26 species of 15 mangrove families recorded in the area. Following Tomlinson’s functional classification Tomlinson, 1994 twelve species are
belongs to major mangrove component, while the rest either belongs to minor component 8 species or mangrove associate 6 species as it shown in the following table 1.
Table 1. Species mangrove
Component Family Species
Major component
Avicenniaceae Rhizophoraceae
Sonneratiaceae
Palmae Avicennia alba
Avicennia officinalis Bruguiera cylindrica
Bruguiera gymnorrhiza Ceriops tagal
Ceriops decandra Rhizophora apiculata
Rhizophora mucronata Rhizophora stylosa
Sonneratia alba Sonneratia caseolaris
Nypa fruticans
Minor component Pteridaceae
Myrsinaceae Euphorbiaceae
Sterculiaceae Meliaceae
Acrostichum aureum Aegiceras corniculatum
Aegiceras floridum Excoecaria agallocha
Heritiera littoralis Scyphiphora hydropyllacea
Xylocarpus granatum Xylocarpus moluccensis
Mangrove associate Acanthaceae
Guttiferae Leguminosae
Asclepiadaceae Malvaceae
Rutaceae Acanthus ilicifolius
Calophylum inophylum Derris trifoliata
Finlaysonia obovata Hibiscus tiliaceus
Merope angulata
The number of mangroves found in Segara Anakan, 26 species in total, is somewhat comparable to the rest of Malesian and Australian mangroves “Old World”
mangroves such as Papua New Guinea 31 species; Johnstone and Frodin, 1982, Bintuni Bay, Papua 31 species; Pribadi, 1998, Sarawak 40 species; Chai, 1975, Quezon, The
Philippine 29 species; Fortes et al., 1989, Ranong, Thailand 24 species; Aksornkoae et al
., 1991, or Northern Australia 33 species; Wells 1983, and much higher compared to the mangroves from the “Atlantic” areas “New World” mangroves such as Eastern Coast
of United States of America 4 species; Reimold 1977, West Africa 6 species; Chapman 1977 and the South American mangroves 4 species; West 1977. This condition reflected
that Segara Anakan once was favorable place for mangroves development. The lagoon was more or less has a similar conditions to what Johnstone and Frodin 1982 mentioned, on
their review of Papuan Subregion mangroves, as the most favorable conditions to mangroves development i.e. deltaic area, embayment and deep estuary that is sheltered
5 from excessive wave action and where mud and silt accumulation are taking place,
together with high rainfall and no or only a feeble dry season. However, due to illegal cutting and conversion to other uses, presently forest condition has undergone serious
degradation and it is clearly shown in the forest structure.
Klaces area was dominated by Avicennia alba mean Important Value, IV; 139.85, Sonneratia caseolaris
IV; 36.39 and Sonneratia alba IV; 15.51, while Rhizophora apiculata
IV; 104.58, Aegiceras corniculatum IV; 31.41, Scyphiphora hydropyllacea IV; 22.30 and Aegiceras floridum IV; 16.57 were more dominant in Sapuregel area. In
term of tree density Sapuregel area with 3,140 ind.ha almost doubled than Klaces area 1,818 ind.ha, but tree size in Klaces mean trunk diameter 6.98 cm; height 4.79 m
slightly bigger than Sapuregel 5.39 cm and 3.38 m, respectively. The results shown that Klaces area was “younger” in term of vegetation colonization, characterized by the
domination of pioneer species such as Avicennia alba, Sonneratia caseolaris and Sonneratia alba
. The area, consist of several deltaic islands, only created in the past few years due to the high sedimentation in the lagoon. Sapuregel, located further to the east
from lagoon see Figure 1, even though dominated by smaller trees but denser and consist of Rhizophora apiculata, Aegiceras corniculatum, Scyphiphora hydropyllacea and
Aegiceras floridum
which normally found in more mature forest with more stable substrat. The similar species was also dominated the sapling stage in both locations and its
density in Sapuregel 5,075 indha way much higher than in Klaces area 2,125 ind.ha. However, Acanthus and Derris shrubs were dominating the seedling stage in Klaces area
with mean density of 6,733 indha and 2,200 indha, respectively. In Sapuregel area the seedling stage dominated by Rhizophora apiculata, Bruguiera gymnorrhiza, Ceriops tagal
and Ceriops decandra with mean density of 5,200 indha. The availability of sapling and seedling of the same tree species, for some extent, reflecting that the natural regeneration is
assured. It should be noted, however, the total number of sapling and seedling in Segara Anakan were way much lower compared to some other areas such as Bintuni Bay with
sapling density of 3,935.7ha and seedling of 60,938.7ha Pribadi, 1998 or Bungin River, South Sumatera with 929.7ha for sapling and 35,485.7ha for seedling Sukarjo et al.,
1984. There is no further information why Acanthus and Derris becomes so abundant in Klaces area but possibly due to the change of water salinity in the lagoon and uncontrolled
logging of other mangrove species in which, in normal condition, limited the growth of those both shrubs species.
On each transect of 500 m were installed 5 litter traps for upper plants and 5 litter traps for lower plants Acanthus and Derris with a distance in between approximately 100
m. In total, 45 sets of trap of each category were installed. The upper-plant litter-fall were collected using traps which were made by attaching a conical-shape nylon mesh 2 mm to
a 1 X 1 m wooden frame and hanged about 1.5 m above the mean high water level at spring tide. The lower plant litter-fall were collected using 1 x 1 x 1 m open top and
bottom cages of nylon mesh 2 mm which encircled the target plants. The litter-fall collected from each trap on the 15
th
and on the last day of each month for a year period then bulk by month before sorting into leaves, branches, fruits and flowers, and a
miscellaneous fraction. The fractions were subsequently dried to a constant weight at 70
o
C for at least 72 h prior to weighing. A substantial number of samples were randomly picked
from the batch for further chemical analysis N, P, K. The small litter-layer was collected from 1 x 1 m wooden frames that set up on the forest floor. The frames positioned in the
same 20 x 20 m plots as for the litter-fall collection, but they were only collected on the last day of each month. Only leaf, stipule, reproductive part, and small wood litter-layer
were collected. The litter-layer then cleaned, dried, sorted and weighed using the same methods as for litter-fall. The litter-fall decomposition rate or, in the case of mangroves,
6 litter fall loss-rate,
since there may be removal by the tide was calculated as the ratio of annual litter-fall mass L to litter-layer or standing crop X
ss
, k = L X
ss
. Turnover rate, the rate of the amount of a substance released by or entering into a compartment in a given time
was defined as the inverse form of decomposition rate 1k. Half-lives t
0.5
assuming an exponential model applies, were calculated as 0.693k Olson, 1963.
2. Litter-fall and litter-layer
