METHOD 1 Location RESULT AND DISCUSSION

Bogor, 21-22 October 2015 693 infiltration capacity of the soil. With the increased capacity of infiltration into the soil, the water storage in the soil increased so that can be streamed over time, especially during the dry season. Sustainable forest management is a necessity. One aspect to note is the preservation of the environmental aspects, in particular water system. Water system include water flood response, the base flow the dry season, and water quality. Aspects of the water system are an indicator of sustainable forest management. Low flows variability depend on drainage density, areal coverage of colluviums, slope, and percent of the channel network as first order stream Price et al.2011. Price 2011 mentioned that geomorphology, soil, land use, and climate change controls base flow. Many studies concluded that lower base flow associated with higher watershed forest cover, forests have high evapotranspiration rate. While other studies said that increased base flow with higher watershed forest cover due to higher infiltration rate Price, 2011. Beck et al. 2013 concluded that Base Flow Index BFI and Base Flow Recession Constant k were related to several climatic and physiographic characteristics, notably mean annual potential evaporation, mean snow water equivalent depth, and abundance of surface water bodies. Mazvimavi et al. 2004 mentioned that Base Flow Index has positive correlation with annual rainfall r=0.7. Stream water flows increase when transpiration decreases Schafer, 2014. Trees can reduce runoff at small catchment scale-at large scale, trees are more clearly linked to increased precipitation and water availability Ellison et al., 2011. The aim of the research is to investigate water yield of the forests during dry season. 2. METHOD 2.1 Location The study areas are located in Gombong for pine forest watershed and in Cepu for teak forest watershed. Administratively, Gombong is located in Kebumen district and Cepu area is located in Blora district. Both areas are located in Central Java Province. The parent material in pine forest is volvanic while in teak forest is limestone sedimen. 2.2 Method There are 8 eight sub watersheds with different area of pine forests in Gombong. The pine forest areas vary between 13 to 52 of sub watershed area. While in Cepu, there are 7 seven sub watersheds with different area of teak forest. The teak forest areas vary between 23 to 94 of sub watershed area. Each watershed was installed hydrological equipment for low flow measurements. 2.3 Data analysis Low flow data were measured during dry season, usually from July to September. Low flows were analyzed at every measurement. In order to make comparison with different watershed forest area, the low flows were measured at sub watershed area. The unit measurement of low flow is litresecondkm2 area of sub watershed. The low flows, both on pine and teak forest, were analyzed using trend line analysis with different forest cover area in sub watersheds.

3. RESULT AND DISCUSSION

3.1 Land cover of pine forest watershed

The area of pine forested watershed in Gombong is 3,795 ha consisting of 8 sub-watersheds, namely Silengkong, Watujali, Tapak Gajah, Pasuruan, Kedung Pane, Lowereng, Kali Kemit, Bogor, 21-22 October 2015 694 and Kedung Bulus sub watershed. Details of each sub-watershed and the land cover can be seen in Table 1, while their distribution in the watershed can be seen in Figure 1 below. Figure 1 shows that the pine forests in Kedung Bulus sub watershed not clustered but spread from the upstream, midstream, and downstream. Pine forests in the Kedung Bulus vary from the age of 5 five years to 30 thirty years. Dry land areas are located in the upper, middle, lower of the watershed. Table 1: The area and land cover of pine forest watershed Sub Watershed Area Forest Garden Dryland Paddy Settlement km2 Silengkong 1.17 52 23 25 Watujali 1.03 49 28 23 Tapakgajah 0.55 13 25 58 1 3 Pasuruan 0.80 20 32 44 2 2 Kedungpane 3.11 31 29 37 1 2 Lowereng 11.61 33 23 33 10 1 Kali Kemit 22.75 37 24 19 8 12 Kd.Bulus 37.95 35 28 24 5 8 Figure 1: Land Cover Map of Kedungbulus sub watershed

3.2 Land cover of teak forest watershed

Land cover in teak forest watershed consists of a teak plantation forests, shrubs, paddy fields and settlements as shown in Table 3. The teak plantation forest in the watershed is divided by Age Group KU from KU I to VII. To obtain varying forest area in a watershed then installed 7 seven hydrological stations namely Modang, Cemoro, Kejalen, Sambong, Kendilan, Gagakan, and Ngroto sub watershed. From Table 3 it appears that the percentage of forest area varies from 23 to 94.3 of the sub-watershed. The spread of land cover can be seen in Figure 2. Figure 2 appears that the teak forests clustered in the upper and middle sub-watershed. Paddy filed mostly located in the lower of the watershed. Shrubs are located in the middle and upper of the watershed. Bogor, 21-22 October 2015 695 Table 3: Land cover type of each sub watershed in teak forest watershed Sub watershed Area Forest Shrubs Paddy field Settlement Km2 Modang 3.38 94.3 2.3 0.19 3.21 Cemoro 13.47 91.1 6.6 0.2 2.1 Kejalen 20.14 80.9 7.9 1.3 9.9 Sambong 27.79 74.8 12 3.2 10 Kendilan 48.86 23 46.67 17.73 12.6 Gagakan 64.8 47.5 30.7 9.9 11.9 Ngroto 69.8 44.9 30.9 14.3 9.8 Figure 2: Land cover map of teak plantation forest sub watershed

3.3 Physical condition of pine forest watershed

One of the factors that determine the low flow is physical condition or watershed characteristics. The physical condition of the watershed, drainage density, slope, geomorphology, and geology are also affect the low flow.. Watershed physical conditions of each sub-watershed in Pine forest can be seen in Table 5. Bogor, 21-22 October 2015 696 Table 5: Physical condition of pine forest watershed Sub Watershed Area Dd Slope Topography km2 kmkm2 Silengkong 1.17 3.01 61 Mountainous Watujali 1.03 3.34 53 Mountainous Tapakgajah 0.55 2.81 46 Mountainous Pasuruan 0.80 3.21 34 Hilly Kedungpane 3.11 2.96 26 Hilly Lowereng 11.61 3.45 32 Hilly Kali Kemit 22.75 3.18 43 Mountainous Kd.Bulus 37.95 3.27 36 Hilly

3.4 Physical condition of teak forest watershed

Physical condition of teak plantation forest watershed consist of drainage density Dd, slope, and topography. Most of the watershed shape in the sub watersheds are elongated, the Dd vary from 1.62 to 2.18 kmkm 2, slope vary from 15 to 32 . The detail physical condition of teak forest can be seen in Table 6. Table 6: Physical condition of teak forest watershed Sub watershed Area Dd Slope Topography Km2 kmkm2 Modang 3.38 1.62 20 Hilly Cemoro 13.47 2.07 18 Hilly Kejalen 20.14 2.18 26 Hilly Sambong 27.79 1.98 32 Hilly Kendilan 48.86 1.65 15 Plain Gagakan 64.8 1.86 22 Hilly Ngroto 69.8 1.92 18 Plain

3.5 Monthly rainfall

Rainfall is a sources of water flows to river and other storages not only surface water but also ground water. Variation of the streamflow discharge depend on rainfall amount, ranfall intensity, rainfall duration Hadisusanto, 2010. Dry season is took place when rainfall is zero or almost zero during the month. In the case of pine forest the dry season started from June to September as can be seen in Figure 3. In case of teak forest the dry season started from July to September as seen in Figure 4. Figure 3: Monthly rainfall at Silengkong Pine forest in 2012. 200 400 600 800 1000 1 2 3 4 5 6 7 8 9 10 11 12 Bogor, 21-22 October 2015 697 Figure 4: Monthly Rainfall at Ngroto Watershed Teak forest in 2012, 2013, and 2014 Based on minthly rainfall data, low flow in pine occured during July to September and low flow in teak forest occured during August to September.

3.6 Low Flow in pine forest

In order to compare with different sub watershed area, the low flow discharge has been divide by the area of the sub watershed. Therefore the unit of low flow will be Litresecondsquare km. Low flows measurement in pine forest have been done in July and August. During September, the low flows have not measured due to some sub watershed has no stream flow. The relationship between low flow and pine forest area can be seen from determinat coeffisient R 2 . Based on the low flow measurement in July, R 2 various from 0.092 to 0.153 as seen in Figure 5. There is a trend that low flow increase when the forest area in the watershed increase. The relationship between low flow and forest area on August shows the same trend as on July but with determination coeffisien R 2 higher i.e 0.379 to 0.406 as seen in Figure 6. It means that forest cover more influence on low flow or the influence of forest cover increase following dry season. Based on Figure 5 and 6, the influence of pine forest on low flow was 13 in July and 40 in August. It means that there are others factor influenced low flow. It could be geological layer, soil depth, slope steepness in each sub watershed. Lacey and Grayson 1998 mentioned that there are direct and indirect influence of geological factor on base flow. The direct inluence on base flow includes groundwater flow will be stored in the rock. While indirect influence on base flow includes soil formation. The different rock will product different soil types and soil depth influencing their water balance. Delin et al. 2007 concluded that soil characteristic and climate are main factor to predict base flow in Minnesota. Furtheremore, Stukey 2006 made a regression between base flow and forest area, he also added others variable such as annual rainfall, percentage of basin and percentage of settlement in the city.

3.7 Low flow on teak forest

The relationships between forest area and low flow on teak forest were similar pattern with those on pine forest. In the beginning of the dry season, the determinan coefficient R² was lower than in the following months. During July 2012 the relationships between forest area and low flow have no pattern. The magnitude of low flow was almost same at different forest area as seen in Figure 7. During September 2013, there is a trend that the low flow increase when forest area increase but the determinan coefficient is low, only 0.133 and 0.155. Bogor, 21-22 October 2015 698 Figure 5: The relationship between forest area of pine and low flow a 17 July 2012, b 18 July 2012, c 19 July 2012, d 20 July 2012, c Figure 6: The relationship between low flow and forest area of pine a 7 August 2012, b 8 August 2012, and c 9 August 2012. There is a trend that more dry season period, the realtionship between forest area and low flow has higher in determinat coefficient R². In July 2012, R² for pine forest is 0.092 while in August 2012, R² increase become 0.406. For teak forest, R² is 0.397 to 0.539 for July 2012 and 0.133 to 0.155 for September 2013 and 0.639 for Oct 2014. . a b c d a b Bogor, 21-22 October 2015 699 Figure 7: The relationship between low flow and forest area of teak a 17 July 2012, b 18 July 2012, c 19 July 2012, and d 20 July 2012 Figure 8: The relationship between low flow and forest area of teak a 11 September 2013, and b 12 September 2013 Figure 9: The relationship between low flow and forest area of teak a 27 Augst 2014, b 16 Oct 2014. a b a b a b c d Bogor, 21-22 October 2015 700 Based on Figure 5 to 9 show that the more forest area in the watershed, the low flow will increase both for pine and teak forest. The water produce in pine forest is higher than in teak forest. The magnitute of increasing low flow on that forests are depend on their geologic structure, soil depth, slope steepness, litter thickness and annual rainfall. Low flow in pine forest vary from 0.5 litreseckm2 20 of forest area in the watershed to 1.5 litreseckm2 95 of forest area, while low flow in teak forest vary from 0.2 litreseckm2 20 forest area to 1 litreseckm2 90 forest area. There are some reason that pine forest produce more water than teak forest. First, annual rainfall in pine forest was higher than those in teak forest 2747 mm and 1309 mm. Second, parent materail in pine forest is volkanic while in teak forest is limestone sedimen. Third, the slope is more stepness in pine forest than those in teak forest. Johnson 1998 in his review of low flows mentioned that the low flow are sustained in very dry summer mainly by supplies from the drift and solid geology so are only affected by land use if the forest prevent sufficient winter recharge to there sources. Furtheremore, Robinson et al.2003 said that soil water under forest is drier than under grass. This reduce the soil moisture reserves to sustain base flows in dry weather periods. Forest area still influence the magnitute of low flow. Furthermore, Krakauer Temimi 2011 predict low flow by using stepwise multiple regression analysis. There are six predicted variable of low flow i.e.: 1 longitude, 2 soil infiltration capacity, 3 latitude, 4 channel length, 5 forest cover, and 6 precipitation. Low flow generation processes are complex and vary naturally in time and space. Forest management is only one of a number human activities that can potentially affect a regime of watershed hydrology Pike Scherer, 2003. For future research, factors influencing low flow since the beginning dry season until the end of dry season should be investigated in order to get the role of forest on generating low flow. Forests can have an important role in supplying fresh water, but their management must complement water management. There are some potential ways which forest and water can be supportive.First, mountainous forested watersheds require special attention as the highest fresh water producing area. Second, forest can be managed to enhance fresh water supllies. Third, the potential exist to mitigate the economic damage caused by flood through forest management, Fourth, a watershed perspective should be incorporated into the planning and mangement of forests, water, urban, and agriculture landuse. Fifth, incentives must be provided through forest and other land use management policies and institutions from local watershed to the river basin level Hofer, 2003

4. CONCLUSION AND RECOMMENDATION