Species Mangrove in Karimunjawa National Park
The composition of species, the number of trees, the average diameter at breast height and the average tree height of the mangrove ecosystem of Karimunjawa National Park are shown in Table 1. This study was divided into three stations focused on three islands, namely Karimunjawa Island, Kemujan Island, and Menjangan Island. Each island or observation station consists of three transects. It can be seen in Table 1 that at each research station there are mangrove species Rhizophora apiculate, Rhizophora mucronate, Ceriops tagal, Rhizophora stylosa and Xylocarpus moluccensis. The distribution is even because these species are natural mangrove species in the Karimunjawa National Park. The order of the total number of trees from the most to the least is station one (228 trees), station three (222 trees), station two (188 trees). The species that dominated the highest number of trees in all research locations was Rhizophora apiculata. According to Wetlands International, this species grows in silty, smooth, deep soil and is flooded during normal tides (Andradi et al. 2013). Prefers tidal waters that have a strong permanent influence of fresh water input. Rhizophora apiculate has a dominance level that reaches 90% of the vegetation that grows in a location. This is in accordance with the substrate conditions in the mangrove ecosystem of Karimunjawa National Park where many Rhizophora apiculate species grow and develop because their habitat is very suitable. The type and magnitude of the substrate percentage at each station can be seen in Fig. 2.
Table 1
Composition of Mangrove Species in Karimunjawa National Park
Station
|
Species
|
No. of trees
|
Mean DBH
|
Mean Height
|
1
|
Rhizophora apiculata
|
99
|
22,26
|
9,40
|
|
Rhizophora mucronata
|
38
|
22,46
|
7,70
|
|
Ceriops tagal
|
41
|
22,84
|
6,10
|
|
Rhizophora stylosa
|
36
|
13,83
|
6,80
|
|
Sonneratia caseolaris
|
9
|
13,36
|
6,50
|
|
Xylocarpus moluccensis
|
5
|
14,9
|
7,10
|
2
|
Rhizophora apiculata
|
59
|
15
|
8,20
|
|
Rhizophora mucronata
|
49
|
14,64
|
6,00
|
|
Ceriops tagal
|
34
|
10,23
|
6,40
|
|
Rhizophora stylosa
|
23
|
14
|
6,60
|
|
Xylocarpus moluccensis
|
12
|
11,87
|
6,80
|
|
Sonneratia caseolaris
|
11
|
15,53
|
5,50
|
3
|
Rhizophora apiculata
|
65
|
15,25
|
7,70
|
|
Rhizophora mucronata
|
52
|
15,1
|
7,20
|
|
Ceriops tagal
|
52
|
10,79
|
7,25
|
|
Rhizophora stylosa
|
33
|
15,35
|
7,00
|
|
Xylocarpus moluccensis
|
20
|
11,22
|
6,60
|
Sediment Characteristics
Based on Fig. 2 above, the type of sediment found in the three research sites is dominated by silt sediment, an average of 58%. Sediment conditions at a depth of 0-100 cm tend to be textured like sandy mud with a little clay. According to Komiyama et al (2005) the type of mangrove Rhizophora sp can grow well with a sandy loam texture. Because of the strong roots of Rhizpora and effective in sand traps. The condition of mangroves has a sandy loam substrate, this is because the location of the mangrove ecosystem is not too close to the beach which has high currents or waves. According to Indah et al (2008), which stated that the root forms of Rhizophora sp. anchoring and tight also causes the formation of a substrate. The formation of this substrate is strongly influenced by the presence of currents in tidal and ebb conditions which carry the particles deposited at low tide. Oceanographic factors that affect the distribution of sediments are currents and depth (Wickramasinghe et al. 2009). Waters that have relatively calm currents and shallow water depths between 16-20 cm so that the types of sediments distributed in the mangrove ecosystem are similar. This is due to the anchored and tight root forms of Rhizophora sp which also causes the formation of a substrate (Ortega et al. 2018). These roots make the process of capturing dust particles in Rhizophora sp stands run perfectly (Morton 2016). When there is a backflow, the dust particles are blocked by the roots. This shows the characteristics of the sediments that are suitable for the growth of mangroves in the Karimunjawa National Park which are dominated by Rhizophora sp.
Mangrove Species Diversity
Important Value Index (INP) is an index that is calculated based on the amount obtained to determine the level of species dominance in a plant community (Pollisco and Simorangkir 2013). To determine the Important Value Index in mangrove vegetation trees can be obtained from the sum of the relative frequency, relative density, and relative dominance of a vegetation expressed in percent (%). From the results of calculations that have been carried out at the three observation stations, it can be seen that there are differences in the value of the Important Value Index for each type of mangrove, where Rhizophora apiculata found at station I has the highest Important Value Index, which is 113.25% while the lowest important value index is owned by vegetation. Xylocarpus moluccensis mangrove species found in station I amounted to 15.82%. The Important Value Index shows the range of the index that describes the community structure and distribution pattern of mangroves (Owuor et al. 2019). The difference in the index of the importance of mangrove vegetation is due to competition in each species to get nutrients and sunlight at the research site. Apart from nutrients and the sun, other factors that cause differences in the density of mangrove vegetation are the type of sediment and tides (Sarker et al. 2019).
The results of the analysis of the relative density of mangroves in Karimunjawa National Park presented in Table 2 shows that at the tree level the highest relative density is Rhizophora apiculata, which is 43.42% at station I, while the lowest relative density is Xylocarpus moluccensis, which is 2, 91% of which are at station I as well. The high relative density of Rhizophora apiculata is because this mangrove has a high ability to adapt so that it can develop well. The low density of Xylocarpus moluccensis is due to the fact that this species is not covered by the study area and is more commonly found near land.
Species frequency is one of the vegetation parameters that can show the distribution pattern or distribution of plant species in the ecosystem or show the distribution pattern of plants. The frequency value is influenced by the value of the plot where mangrove species are found. The more the number of squares found, the higher the frequency of the presence of mangrove species (Sidik et al. 2018). The results of the analysis of the relative frequency of mangroves that have been carried out in the mangrove ecosystem of Karimunjawa National Park at the highest tree level are at station III, which is the same as 20%. The species are Rhizophora apiculate, Rhizophora mucronate, Ceriops tagal, Rhizophora stylosa, and Xylocarpus moluccensis. Meanwhile, the lowest relative frequency at the tree level is Sonneratia caseolaris, which is 11.76% at station II. The large number of Rhizophora apiculate species is due to the condition of the sediment substrate at the study site in the form of sandy silt which is able to support mangrove growth so that this type of mangrove can survive and develop well. The silt substrate that is spread in almost all stations contains a lot of organic matter when compared to the type of sediment in the form of sand because it only contains minerals (Sarathchandra et al. 2018). Furthermore, the typical life cycle of Rhizophora with seeds that can germinate when they are still on the parent plant is very supportive of the wide distribution process of this species in the mangrove ecosystem (Thatoi et al. 2012).
At the tree level, the highest relative dominance value was occupied by Rhizophora apiculate with a dominance value of 51.08% at station I. This was because Rhizophora apiculate was able to compete to obtain more nutrients than other species due to the adaptation of its root system. Meanwhile, the dominance value which is relatively low is Xylocarpus moluccensis, which is 1.13%. This is due to the uneven distribution of Xylocarpus moluccensis and the level of habitat suitability, where the substrate type in the Karimunjawa mangrove ecosystem is mostly silt-sand type, while Xylocarpus moluccensis prefers a harder substrate.
Table 2
Value of Relative Frequency, Relative Dominance, Relative Density, Important Value Index, Diversity Index, and Evenness Index
St
|
Species
|
Total Individual
|
Relative values (%)
|
Importance value (%)
|
H’
|
E
|
IUCN
|
Frequency
|
Dominance
|
Density
|
1
|
Rhizophora apiculata
|
99
|
18,75
|
51,08
|
43,42
|
113,25
|
0,36
|
0,82
|
LC
|
|
Rhizophora mucronata
|
38
|
18,75
|
20,27
|
16,66
|
55,69
|
0,29
|
LC
|
|
Ceriops tagal
|
41
|
18,75
|
7,48
|
17,98
|
44,21
|
0,30
|
LC
|
|
Rhizophora stylosa
|
36
|
18,75
|
18,26
|
15,78
|
52,80
|
0,29
|
LC
|
|
Sonneratia caseolaris
|
9
|
12,5
|
1,76
|
3,94
|
18,20
|
0,12
|
LC
|
|
Xylocarpus moluccensis
|
5
|
12,5
|
1,13
|
2,19
|
15,82
|
0,08
|
LC
|
|
Total
|
228
|
100
|
100
|
100
|
300
|
1,47
|
|
2
|
Rhizophora apiculata
|
59
|
17,64
|
20,02
|
31,38
|
69,05
|
0,36
|
0.90
|
LC
|
|
Rhizophora mucronata
|
49
|
17,64
|
17,72
|
26,06
|
61,43
|
0,35
|
LC
|
|
Ceriops tagal
|
34
|
17,64
|
13,32
|
18,08
|
49,05
|
0,31
|
LC
|
|
Rhizophora stylosa
|
23
|
17,64
|
17,25
|
12,23
|
47,13
|
0,26
|
LC
|
|
Xylocarpus moluccensis
|
12
|
17,64
|
13,97
|
6,38
|
38,00
|
0,18
|
LC
|
|
Sonneratia caseolaris
|
11
|
11,76
|
17,72
|
5,85
|
35,33
|
0,17
|
LC
|
|
Total
|
188
|
100
|
100
|
100
|
300
|
1,62
|
|
3
|
Rhizophora apiculata
|
65
|
20
|
24,73
|
29,28
|
74,01
|
0,36
|
0,95
|
LC
|
|
Rhizophora mucronata
|
52
|
20
|
24,25
|
23,42
|
67,67
|
0,34
|
LC
|
|
Ceriops tagal
|
52
|
20
|
13,82
|
23,42
|
57,25
|
0,34
|
LC
|
|
Rhizophora stylosa
|
33
|
20
|
23,61
|
14,86
|
58,48
|
0,28
|
LC
|
|
Xylocarpus moluccensis
|
20
|
20
|
13,58
|
9,01
|
42,59
|
0,22
|
LC
|
|
Total
|
222
|
100
|
100
|
100
|
300
|
1,54
|
|
|
The diversity of mangrove species in the study area based on the Shannon-Wienner diversity index (H') was in the moderate category at all stations. The data in Table 2 shows that for tree growth rates, the diversity index (H') ranges from H' 1.47 to 1.62. This shows that the mangrove ecosystem has moderate diversity, the condition of the ecosystem is quite balanced, the water conditions are still stable, and the ecological pressure is moderate. The value of diversity in a community depends on the number of species and the number of individuals in the community. The species diversity of a community will be high if the community is composed of many species and no species dominates (Rahmila and Halim 2018). Conversely, a community has a low value of species diversity, if the community is composed of a few species and there is a dominant species. The mangrove vegetation found showed varying zoning at each station. These mangroves do not fully form zoning based on their tolerance to salinity and periods of inundation as suggested by many mangrove experts. In this study, mangroves grow from the edge of the sea to the mainland. The part near the sea is dominated by Rhizophora apiculata. This species is very dominant along the coastline of Karimunjawa Island, Kemujan Island, Menjangan Island. Sonneratia caseolaris, Ceriops tagal, Rhizophora stylosa and Rhizophora mucronata are at the rear, while Xylocarpus moluccensis and other minor component mangrove species fill the rear zone. This mangrove vegetation profile diagram shows that there are differences in mangrove zoning at each research station, especially for the rear zoning, while the front zoning tends to be uniform, dominated by Rhizophora apiculate. According to the conservation status of the IUCN red list, all mangrove species found in the study in Karimunjawa National Park are included in the least concern (LC) category. Although it is still classified as low risk, it is not impossible that in the next few years the number of species will be threatened along with the increase in anthropogenic activities in Karimunjawa National Park. So that conservation efforts need to be carried out
Furthermore, the evenness index value at each research station ranged from 0.82 - 0.95. Based on the evenness index criteria, this value is stable for all stations. This shows that the species found at each research station tend to have uniformity, meaning that no particular species dominates a station. If the value of the evenness index is small, then the species uniformity in the community is lacking, meaning that the number of individuals for each species is not the same, so there is a tendency to be dominated by certain species (Zhila et al. 2013). On the other hand, the higher the uniformity index value, the higher the distribution pattern in the community and no particular species is dominant.
Distribution patterns in clusters are generally found in nature, due to the need for the same environmental factors (Syahid et al. 2020). There are a number of reasons why plants show a clumped distribution (Mangora 2011). Most of the mangrove seeds/fruits are not consumed by animals, so the ripe fruit will fall near the parent tree and will grow into an adult tree. According to Santos et al (2014), that the formation of a clustered distribution pattern is related to the pattern or way of eating because in certain areas there are many food sources. In addition, external reproduction factors and the characteristics of the substrate that are suitable for mangrove growth are one of the factors for the formation of a group distribution pattern.
Biomass and C-Stock
Table 3 shows the stand biomass yield, stand carbon content, and sediment carbon content. The value of biomass and carbon in the stand is directly proportional because the larger the diameter of the stand and the greater the density, the greater the biomass and carbon content. It can be seen that station 1 has the highest carbon content among the other stations. This is because at station 1 the mangrove ecosystem is included in the national park area, so that the condition of the stands and the condition of the surrounding environment are still very natural. This case is different from what happened at station 2. The condition of mangroves located on the southern coast of Kemujan Island has been damaged a lot. This is presumably because there are residential residents around the mangrove area which causes the conversion of mangrove land to agricultural land. There is agricultural land for tropical crops such as rice and coconut plantations which can be seen in Fig. 1. Organic carbon in sediment is one of the constituents of organic compounds in the waters. Organic carbon is a priority for soil improvement and for carbon storage. The ability to store carbon is higher than the mangrove tree itself. There is a high potential for emissions due to disruption of large carbon stores. Table 4 shows the carbon content based on depth and total carbon content in the Karimunjawa mangrove ecosystem.
At stations 1 – 3, the carbon content increases with increasing depth. The high organic matter in the surface layer (0 cm) is due to the high litter production from each station, where the mangrove density also affects the level of organic matter content. This is in accordance with Oliver et al (2012) opinion, which states that the decomposition process of litter (leaves/branches/twigs) only occurs on the surface of the soil, whereas at a depth of more than 20 cm the effect of this process is not significant (Moriizumi et al. 2010). The condition of the sustainability of subsurface carbon stocks in particular is still poorly understood, but evidence from this study shows that land clearing, drainage, and/or conversion to ponds/agriculture, in addition to having an impact on vegetation biomass, also significantly reduces the carbon content of mangrove soils.
Table 3
Value of Above-ground Biomass, C-stock, and Average C-stock at All Station
|
Transek
|
Above-ground Biomass (t ha −1)
|
C-Stock (t C ha −1)
|
Average C-Stock (t C ha −1)
|
St 1
|
1
|
638,79
|
300,23
|
243,73
|
2
|
427,8
|
201,07
|
3
|
489,13
|
229,89
|
St 2
|
4
|
240,29
|
112,93
|
94,01
|
5
|
177,75
|
83,54
|
6
|
182,04
|
85,56
|
St 3
|
7
|
244,27
|
114,80
|
100,92
|
8
|
193,37
|
90,88
|
9
|
206,58
|
97,09
|
Table 4
Value of Carbon Content by Depth
Station
|
Depth
|
Total Soil C-Stock
|
Total Soil C-Stock (t C ha −1)
|
1
|
Depth 0 - 33 cm
|
156,00
|
482
|
Depth 34 - 67 cm
|
165,00
|
Depth 68 - 100 cm
|
161,00
|
2
|
Depth 0 - 33 cm
|
64,00
|
199,75
|
Depth 34 - 67 cm
|
67,50
|
Depth 68 - 100 cm
|
68,25
|
3
|
Depth 0 - 33 cm
|
127,00
|
400,1
|
Depth 34 - 67 cm
|
137,10
|
Depth 68 - 100 cm
|
136,00
|
The results of measurements of carbon content at the three stations based on depth have different results of carbon storage (Fig. 3). The carbon storage value was measured vertically with five different depths while the measured depths were 0-33 cm, 34-67 cm, 68-100 cm. Where each depth has a different carbon storage value. The highest carbon storage on average is at a depth of 34-67 cm with values ranging from 67.5 to 165 t C ha−1. The lowest value was found in the upper layer (0-33cm) at station 2 with a value of 64 t C ha−1. This condition is thought to be because the surface layer is heavily affected by currents, waves, and tides which cause organic content including carbon to be carried along with the movement of water (Halim et al. 2018). While the layer below it has been in the form of solids that have fused over the years through the sedimentation process. From the sedimentation process, there is a biogeochemical process that causes the carbon content at the bottom to increase with increasing depth. The biogeochemical cycle is the transfer of elements/compounds involving organic and inorganic (Alongi 2020). The function of the biogeochemical cycle is to maintain life on earth. The total average value for the estimated carbon of mangrove stands is 146.22 t C ha−1 and for the estimated carbon stock in sediments it is around 360.61 t C ha−1. The estimated carbon of mangrove stands in Karimunjawa National Park is lower than the carbon content in the coastal village of Botoc Philippines (Abino et al. 2013). However, the estimated carbon content of sediments in Karimunjawa National Park is almost twice as high as 360.61 t C ha−1. On a national scale, the carbon content in the mangrove sediments of Karimunjawa National Park is higher than that of mangrove forests in Mangunharjo (Hadiyanto et al. 2021), Baturapa (Marbun et al. 2020), the northern part of the mangrove ecosystem of Bunaken National Park (Verisandria et al. 2018), Jembrana Bali (Mahasani et al., 2015). According to Komiyama et al. (2008) in a study of mangrove forest biomass in various countries that was carried out for several years, variations in biomass estimates did not only depend on species but also on ecological conditions and geographical locations. With a relatively high density value in the Karimunjawa mangrove ecosystem, the potential for litter fall is also expected to be very high. Different values of carbon content are influenced by the number and density of trees, tree species, environmental factors including sunlight, water content, temperature, and soil fertility that affect the rate of photosynthesis (Alongi 2002). The mangrove ecosystem is one of the most important ecosystems in the effort to maintain the stability of flora-fauna diversity and mitigate global warming, namely as the best carbon storage compared to all other forest types on earth.