Technology Needs for Lake Management in Indonesia- Investigation of Rawa Danau and Rawa Pening


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<Technology Needs for Lake Management in Indonesia -
Investigation of Rawa Danau and Rawa Pening, Java>

D. Assessment of Resultant Ecosystem Changes within the Caldera

It is certain that the hydrological effects noted above would have had a significant impact on the ecology and biology of the original swamp forest, and on land use in the caldera. By its nature swamp forest can be assumed to be dependent on flooding of the land in which it grows. There is no information available on the basic needs of such flooding regimes which would ensure survival of swamp forest. It is not clear whether the area has to be flooded seasonally or only for a limited period each year. The biological information which would enable an interpretation of the hydrological data in a meaningful way is not available.

1. The area of the caldera covered by swamp forest

Although the area of the Cagar Alam is 2,500ha, the actual area of swamp forest is much less, and appears to be decreasing (PHPA/AWB, 1993). The swamp forest also appears to occur in scattered patches throughout the area of the caldera suggesting continuous loss of trees and forest area during recent years. It is noted in the 1993 Report that there is now no area of continuous canopy in the swamp forest which has become an open forest.

Though there have been few assessments of the area covered by swamp forest in the caldera, the assessments which have been made suggest a steady decline in the area of this forest type since records started. It appears that the swamp forest is not surviving well under the present conditions in the caldera. In the 1993 Report by PHPA/AWB this is attributed to the impact of human activity of various kinds on the swamp vegetation.

It is also probable that the area of swamp forest has been adversely affected by the lowering of the water level and the resultant drying out of the superficial soils in the Rawa. This drying process would have led to changes in the chemical composition of the soils (particularly the lower content of water and organic matter, as mentioned previously) which might also disadvantage some of the vegetation in the Rawa.

2. The present ecological system in the area formerly under water

The original exit from Rawa Danau was lowered to increase the area of land available for rice production. It is not surprising then to find that the original ecological system in a large area of the caldera has been replaced by sawah. This cultivation system leads to increased run-off from the land surface with much loss of clay, and to the creation of distinct padi fields at slightly different heights. The soil may have been fertilised, as rice crops normally receive additional fertiliser.

Some parts of the area, which were formerly cultivated, have been abandoned following the removal of the settlers as transmigrants to other islands. These abandoned areas remain as large areas of coarse grass and tough ferns with underground rhizomes. Small bushes grow among this vegetation, along with weeds.

The original area of swamp forest has probably been greatly reduced. It is uncertain to what extent the original ecological situation in the caldera resembled that which exists in some areas of fresh water swamp in Sumatra and Kalimantan at present. In particular it is quite uncertain to what extent the original swamp forest existed in conditions of permanent water cover.

3. Potential for natural re-generation of the swamp forest

It appears that this potential is not high at the present time. The presence of large areas of uncultivated land, as described above, has provided ample opportunity for regeneration of the swamp forest during the last six to eight years. None appears to have occurred, or none has been recorded and none is apparent to the casual observer.

Therefore one has to conclude that the environmental conditions at present are not favourable for natural re-growth of the swamp forest. This cannot be attributed in any obvious way to the activities of people, who have not used the abandoned sawah for cultivation for several years. The most likely cause of the failure of natural regeneration is the existence of unfavourable conditions of soil and water. This can be attributed directly to the lowering of the height of the exit from the caldera.

4. Conservation management of the Rawa

There is a clear case for positive, interventionist, management of the caldera. The evidence is that the swamp forest which is the justification for the existence of the Cagar Alam is decreasing in area and in conservation value with every year that passes. There are pressures for the use of the caldera as a water storage facility.

It would seem preferable to act positively to try to maintain and improve the conservation value of the caldera, rather than to let it deteriorate still further until in 40 years time one has to acknowledge that it has lost any conservation value and should be converted to a water storage facility.

5. Management strategies to ensure the survival of the swamp forest

The most obvious strategy at the present time and the most obvious priority is to restore the water level in the Rawa to something approaching the level of the water prior to the destruction of the rock lip at the exit from the Rawa.

The next most obvious tactic is to check on the reproductive success of the endemic species of plants and trees in the Rawa and to ensure that conditions for successful, re-generation of these species can be defined.

Should some of the tree species be shown to have a low rate of successful reproduction under the prevailing conditions, efforts should be made to collect seeds from several trees of the species in question. Seeds collected in this way should be germinated under controlled conditions to determine viability.

If necessary, additional samples should be taken from these threatened species for development of tissue culture techniques. By this means numerous seedlings may be able to be produced. Such tissue culture seedlings should be planted experimentally in the laboratory or in the field to determine the optimal conditions for successful growth in the swamp conditions. It may prove to be desirable to establish experimental plots within the area of the Cagar Alam in which seedlings can be planted for this purpose.

6. Need for coordination with conservation measures

These conservation oriented approaches will only be successful if implemented along with equivalent measures to protect the existing swamp forest remnants and to exclude local people more effectively from using the swamp forest for poisoning fish, cutting firewood, and illegally hunting and killing the wildlife. Soil erosion on hillsides has to be brought under control.

Therefore, these measures have to be implemented along with measures to increase understanding among local villagers of the consequences of their actions. The objectives of the management methods in use and of the Cagar Alam are poorly understood by many local people who simply ignore the regulations. Educational and information transfer objectives may best be achieved outside the present educational system, as the people to whom the information is aimed include most of the adults as well as the children.

Therefore, it maybe concluded that -

1 Two hundred years ago a much larger area of land in the caldera was permanently covered by swamp forest than is the case at present.

2 The lowering of the water level is likely to be one of the main causes of the decline in extent of the swamp forest.

3 The lowering of the water level may be adversely affecting the regeneration of some species of trees and other vegetation in the swamp forest.

4 The loss of water from soil in the caldera may be a continuous and on-going-long-term process.

5 Changes in the soil of the caldera following drainage and utilisation for rice production are likely to affect soil fertility and the growth of vegetation.

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