THE INFLUENCE OF SLOPE ON THE GROWTH OF
REHABILITATED MANGROVE VEGETATION
ON THE NORTH SHORE OF CENTRAL JAVA
(A Case Study on the North Shore of Brebes and Jepara)
by :
Erny Poedjirahajoe *)
INTRODUCTION
The creation of green belt width is highly determined by several factors, such as the shore topography [1]. The more even the shore is, the larger the rise and fall of tides green belt and the wider the mangrove which will be planted. Based on several researches and supported by theories concerning the influence of shore topography on habitat factor, which also influences the vegetation growth, then this research is conducted. The selection of research location was conducted based on the difference on the generated alluvial mainland (West and East area), as well as the green belt width which visually looks different. On the North Shore of Jepara, mangrove green belt is not very wide, so that the effective rise and fall tide zone for mangrove vegetation growth is also relatively narrow. On the other hand, on the North Shore of Brebes Regency, the green belt seems very wide so that the effective rise and fall tide zone is also very wide, in fact, the embankment which have been constructed by the community in mangrove area are within the effective rise and fall tide zone. It can be proved why in the mangrove area in Brebes Regency there are many embankments which use the embankment type, it is by planting mangrove in the middle of the embankment.
By knowing the approximate effective rise and fall tide zone (the green belt width) through slope, it is expected that the mortality percentage of the rehabilitated vegetation can be decreased, and on contrary it will increase the growth percentage. Therefore, this result can be used as a reference/indicator in managing mangrove area, especially concerning the rehabilitation activity. Planting can be syncronized activity will be more effective because it will be able to save the cost and the energy, as well as increasing the success of vegetation growth. Therefore, this research will play an important role in the country development, especially in forestry
.
MATERIALS AND METHODS
The research location is situated in mangrove rehabilitation area on the North Shore of Brebes and Jepara Regency. In each area, the same mangrove planting year is investigated. In mangrove rehabilitation area on the North Shore of Brebes and Jepara Regency, mangrove planting year was determined, which was planting year 2000. The width is 6.5 ha for Brebes Regency and 5 ha for Jepara Regency. The data sample was taken on the same width, 2 ha. In that area, measurement towards the slope was conducted, it was repeated several times along that area. And then, plot was developed and vegetation density and height were measured. The measurement was conducted by dividing the area into 3 zones. The interval with the next measurement was 100 m. In each zone, besides measuring the vegetation density and height, measurement towards pH, salinity, mud thickness, DO was also conducted, and soil sample was taken to analyze the organic substance of N, P, K element. The result analysis used was the multiple regression[2]
RESULTS AND DISCUSSION
Mangrove rehabilitation area on the North Shore of Brebes and Jepara Regency was planted with mangrove species R.mucronata with the same planting interval, 2 x 1 meter. Planting the same species was
conducted because R.mucronata is tolerant to the backup of water class on rise and fall tide zone [3]. Besides
that, based on the root structure, R.mucronata roots are stronger compared to that of the other dominant species.
The specific anchoring root structure is the manifestation of the function which mangrove possesses, among others it is capable of holding mud substrate and becomes the place for sea biota to lean on during the fall of the tides.
In both areas Brebes and Jepara, R.mucronata was used as the rehabilitation vegetation. Vegetations which
were planted in 2000 with planting interval 2 x 1 m turned out to visually show the different morphology. At a glance this difference is on the vegetation density and height.
The average slope in Brebes and Jepara is 1.45% and 4.27 %. At a glance, this difference is not significant. However, it influences the environment factor. In general, on the shore in which mangrove is planted, the slope is almost even. It is because on a shore which slopes slightly, mud substrate accumulation can be generated, besides that it is supported by the movement of rise and fall of the tides which tends to be subtle. It is different from the shore which slopes considerably (more than slopes slightly up to steep). On such shore, usually mud substrate accumulation cannot be found, because on a shore which slopes considerably, river mouth is hardly found so that this type of habitat is not suitable for mangrove. Steep shores have high rise and fall of the tides current, consequently mangrove is hardly found. X2 analysis which was used to differentiate slope rating in Brebes and Jepara area shows that there is significant difference between slope in Brebes and that of in Jepara. Although slope on the North Shore of Jepara is high, there is still mud accumulation from the river mouth. Of course the green belt of mangrove growth in Jepara is not as wide as that of in Brebes Regency. Therefore, although it was planted with the same vegetation quantity with the same planting interval, in the end the density of vegetation growth is different. A high slope means that the green belt width is smaller compared to that of a slight slope. The growth substrate which is effective for vegetation growth is also fewer.
The physical-chemical aspects differ along with the vegetation growth. The higher the density is, DO, local temperature and mud thickness will increase. A high density refers to the increase of phytoplankton because of the increase of organic substance. Phytoplankton increases photosynthesis activity which generates oxygen. Therefore, the contents of dissolved oxygen in the water increase. The role of mangrove roots can increase mud substrate, so that the contents of organic elements especially N, P and K element will also increase [4].
Subsequently, the regression equation analysis shows that vegetation density and height are influenced by waters physical-chemical aspects. In Brebes, the regression analysis shows that density is determined by all waters physical aspects, except salinity. The regression equation formula is as follows:
Y = 368.3 - 5.28 X1– 12.2 X2 + 3.5 X3– 7.8 X4 + 0.7 X5 + 0.2 X6 + 0.7 X7 + 11.1 X8.. r value is 0.96
Y : Vegetation Density, X1: Slope, X2 : Temperature, X3 : Dissolved Oxygen, X4 : pH, X5 : Mud thickness, X6 : N element, X7: P element, X8 : K element, X9 : Salinity. The regression equation shows that vegetation density is influenced by slope (X1) and mud thickness (X5). Slope in Brebes on average is 1.45%. This slope is very slight so that the green belt becomes wide. At the beginning of mangrove planting, a fine planting media is available, consequently vegetation growth has a high life percentage. The result of regression equation on vegetation growth is not different from that of vegetation height. The equation of regression correlation between vegetation height and slope and waters physical-chemical aspects is as follows:
Y = 41.71 + 5.84X1– 17.51X2 + 4.73X3– 8.90X4 + 1.04X5 + 0.49X6 + 0.86X7 + 14.32X8. r value is 0.92
Although the result of regression equation between vegetation height and slope and waters physical-chemical aspect is the same as the regression equation between density and slope and waters physical-physical-chemical aspect, but vegetation height is not parallel with density. Mangrove vegetations which are growing high are accompanied with widening roots forming a strong stand. The wide of roots requires a wide space. Therefore, vegetations which are growing high are usually accompanied with a decrease on the density because there is a competition between individuals in the growth space.
In the waters in Jepara area, the regression equation analysis between vegetation density and height and slope and waters physical-chemical aspects shows the same result as that of in Brebes area. The regression correlation equation formula between vegetation density and slope and waters physical-chemical aspects is as follows:
Y = 12.22 + 0.42X1 + 1.41X2 + 0.91X3 + 0.69X4 + 3.41X5 + 0.01X6 + 0.01X7 + 58.49X8, r value is 0.98
Meanwhile, the regression correlation analysis between vegetation height and slope and waters physical-chemical aspects is:
Y = 971.80 + 4.72X1– 12.03X2 + 4.39X3 + 67.37X4 + 1.47X5 + 1.17X6 + 0.16X7 + 61.8X8 + 5.36X9. The analysis result and discussion shows that slope has significant influence on the growth of rehabilitated mangrove vegetation on the North Shore of Central Java.
REFERENCES
[1]. Anonimous, National Strategy for Indonesian Mangrove Ecosystem Management. Second Book Mangrove Ecosystem in Indonesia. Departement of Forestry. Departement of Fishery and Marine. Ministry of Environment. LIPI. JICA. Jakarta, 2003
[2]. Ludwig, JA and JF. Reynold, Statistical Ecology. John Wiley & Sons. New York. Chichester. Brisbane. Toronto. Singapore, 1988.
[3]. Poedjirahajoe E, Peran Faktor Fisik Kimia Habitat terhadap Pertumbuhan Mangrove di Delta Cisanggarung. DPP Fakultas Kehutanan UGM, 2002.
