Land Suitability Analysis for Tropical Fruit Commodities as a Conservation Effort in Highlands Area, Indonesia

3.1 The weight of the criteria and characteristics of the study area

The weight distribution of each criterion on biophysical and social parameters for land suitability for fruit commodities in the highlands is presented in Table 1, while the spatial distribution is shown in Figure 2. The soil type in an area affects farm productivity, which directly or indirectly influences environmental sustainability [29]. Indonesia has a diversity of soil orders, which is indicated by the discovery of 10 out of the 12 orders in the world. The soil orders that are not in the country are Aridisols which characterize very dry climate areas, and Gelisols in areas of extreme cold conditions [30]. The study location with a total area of 93,550.60 hectares has 6 soil orders, which are Andisols, Inceptisols, Alfisols, Oxisols, Ultisols, and Entisols. The categories of soil great groups include Hapludands, Hapludalfs, Dystrudepts, Endoaqupets, Eutrudepts, Hapludults, Hapludoxs, and Udorthents. Meanwhile, the hapludands are the dominant group, with an area of 44.57% of the total highland area or approximately 41,880.12 hectares.

In the highland area, most of the soil types are fertile for the development of agricultural areas because they contain volcanic ash and good hydrological conditions. Therefore, the expert gave the highest score of 10 for the soil great group Hapludans, followed by Dystrudepts (19.56%) and Hapludoxs (15.27%). Dystrudepts belong to the order Inceptisols and Eutrudepts, with a weighted score of 8 for the suitability of fruit commodities with soil characteristics from albic materials and high fertility. The same score was also given to the soil great groups Endoaquents which were alluvial gleic and had the smallest area, while the lowest score of 3 was given to the soil great groups, Udorthents. This soil belongs to the order Entisols, which developed from young alluvium with a layered arrangement and an irregular organic C content [30].

Table 1. Distribution of sub-criteria weights and their extent in the Central Java highlands

Moreover, the altitude of the area affected other natural conditions such as temperature, humidity, light capture, and types of vegetation. Changes in light intensity in the highlands also caused a decrease in temperature and an increase in humidity. There is also a linear relationship between the altitude of the area and the level of fertility, where the extremely high areas have the quality of the land decreased sharply, causing difficulty in plants productivity [31]. The communities in the highlands also have local knowledge of using plant residues in form of weeds and crop residues in the soil. The residue is useful as organic fertilizer in conjunction with manure to increase soil fertility.

The results showed that 40.36% of the study area was at an altitude of 700-1000 masl with the majority of vegetable cultivation and was given a score of 10 for the development of fruit commodities. The height factor that affects the decrease in productivity of fruit plants caused a weight reduction. Approximately 26.68% of the study area is on a slope of more than 15 to 5%, which was included in the moderately steep category, while the next largest area was in steep and sloping conditions.

Generally, the development of agricultural areas is expected to be optimum in areas with flat to gentle slopes because the management of land with high slopes requires greater technical operational costs and mechanization. The efforts to plant landslide-resistant plants were also carried out, especially with Lamtoro or hedge plants, but in minimal quantities. Meanwhile, annual fruit crops can be recommended as landslide-resisting plants. Experts gave the highest score weight for the development of fruit in areas with a slope of less than 3%.

Indonesia is a tropical country with rainy and dry seasons which makes it suitable for developing endemic fruit commodities that are not grown in non-tropical countries. The characteristics of the highlands in tropical countries include high air humidity and rainfall. Since the study area has a rainfall intensity of 700 to 3,000 mm/year, which is ideal for the cultivation of horticultural commodities, it was given a score of 10. Meanwhile, rainfall with an intensity of more than 3000 mm/year was given a lower score of 5 because the plants require more intensive handling such as pesticide spraying.

The relatively steep slope with high rainfall caused the soil layer to be easily carried away by the flow of water, which has an impact on fertility. The temperature is a climatic factor that has an important effect on plant growth. The optimum temperature for the cultivation of fruit commodities is 16 to 18℃, which makes the expert give a score of 10. A score of 8 was also given for areas with temperatures over 18 to 20℃. Although lower or higher temperatures can still be tolerated by plants, their productivity and fruit size are likely to be smaller.

Wet climatic conditions in the highlands lead to a uniqueness that is not in other highlands in Indonesia. During the dry season around July and August, the air temperature reaches almost 0 to -8℃, and condensed ice crystals are discovered or in the local language called "embun upas". A previous study has shown that several efforts are needed on the management of soil nutrients due to the low temperature that inhibits metabolism and nutrient absorption [31]. In this study, the location has a homogeneous air humidity ranging from 82 to 83%, which is optimum for the development of fruit areas, therefore, a score of 10 was given. The climate change parameters with a significant effect on the decrease in plant productivity are the unpredictable changes in rainfall patterns and high temperatures. In some fruit commodities, humidity and air temperature that changes sharply affect the quality of pollen in the flowering process. The explosion of pest populations due to climate change and the adaptability of fruit crops has also affected the development of fruit areas [32, 33].

The most dominant area is dry land, where the main commodity is vegetables. Therefore, the annual fruit development area is an alternative to landslide prevention on land with high slopes. In this study, a score of 10 was given by the expert on real and mixed dry lands suitable for the cultivation of fruit commodities. This was followed by a score of 8 given to secondary dryland and plantation forests, open land, and shrubs that were not yet optimally covered with annual fruit plants as a landslide barrier. Since land with a high slope has a high erosion rate, plants with deep root systems are expected to be a solution for landslides that often occur.

Access roads to tourist areas in the northern Dieng Plateau are relatively good and adequate. In this study, a score of 10 was given by the expert for village road and market access, which is closest and can be passed by transport vehicles. The perishable nature of horticultural products required fast handling, therefore, adequate access is expected to reduce transportation costs for marketing [34]. A total of 74.44% of agricultural land in the highlands has a distance of 0-500 meters from road access. The distance from the land to the market was also relatively close, with 66.35% located less than five kilometers to the nearest sub-district market. Farmers preferred to rent agricultural land with close access to roads, even though it is the highest transaction cost in their farming business.

3.2 Comparison of the importance of criteria elements

The Consistency Ratio (CR) value from the pairwise comparisons as shown in Table 2 is 0.089. This value showed the consistency of the expert's answers and the validity of the results because it has a value of 0.1. Furthermore, soil great groups have the highest weight since they are related to land productivity and as a determinant of erosion rate besides height and slope. This is supported by the previous study which stated that land in the Andisols order is more easily degraded and has an effect on methanogenesis [35, 36].

Meanwhile, the land height and slope are the criteria with the next highest weight. Local knowledge of farmers to overcome the relatively high slope contributes more to the manufacturing of terraces.

At the study location, at least 5 types of terraces were discovered, these include permanent and non-permanent bench terraces, drain, strip weed, and ridges Farmers carry out conservation efforts to remove the excess water that inundates the land during the rainy season.According to Sen et al. [37], the majority of farmers use ground cover mulch as the most popular form of adaptation to climate change. Meanwhile, limited farming capital and knowledge of small and medium-scale farmers were also obstacles to the implementation of climate change adaptation [38].

Rainfall is the fourth important factor and was included in the high category with an intensity of 230 rainy days per year. Highland areas with steep slopes, high rainfall, and dominant vegetables as vegetation require conservation efforts by planting annual fruit commodities to withstand the rainwater rate and minimize the soil movement that triggers landslides.

Climate change affects the inconsistency of the vegetation response caused by each climate parameter. Although there are very sensitive vegetations against extreme rainfall and humidity, some were still sensitive to temperature and the length of the dry season [39]. The rainfall and humidity in the study area which is a plateau of more than 700 masl are homogeneous. Environmental factors related to soil fertility, rainfall, temperature, humidity, and physical form of land are difficult for humans to change in a short time, however, soil quality can be gradually improved by changing plant habitats and building terraces [40].

Land use, distance to market, and access to the road are the three lowest elements because the study area is mostly dryland agriculture and mixed dry land as a cultivation area. The northern part is a tourism and cultural conservation area, therefore, access to roads and markets is adequate. At several points, problems with the quality of road infrastructure were encountered due to extreme rainfall. Improvements and construction of farm road infrastructure, apart from receiving financial assistance from the government, are often carried out in cooperation with the community.

3.3 Land suitability and availability for the development of highland fruit commodities

The results of the land suitability map overlay for highland fruit commodities with the availability of land from the spatial planning map of the Banjarnegara and Wonosobo Regencies are shown in Figure 3 and clarified by Table 3. The majority of land in the study area is in the S2 category (moderately suitable) for fruit area development by 42.26%, which showed that the land has severe limiting factors for sustainable land use. The limiting factor encountered is the hazard of erosion due to the high slope level and the undulating to the hilly topography. The development of annual fruit commodities in locations are is of the efforts to minimize erosion, however, these limiting factors can reduce productivity because it requires additional farming inputs.

Furthermore, marginally suitable (S3) and highly suitable (S1) classes were 25.57% and 18.17% of the total area, respectively. Most of the highlands are also at temperatures above 18℃, while the most suitable temperature for the growth of annual fruit plants in tropical climates is 16-18℃. A previous study has shown that perennial species are more resistant to climate change [41]. The characteristics of climate change indicated by extreme rainfall often damage plants that are more susceptible to high humidity and long droughts. Meanwhile, the inappropriate of the land is due to its location in a conservation area with an altitude of more than 2,000 meters above sea level and a slope of more than 40%. Water bodies and rock outcrops were also included in the constraints that are not in the development potential analysis.

Based on Table 3, a total of 63.76% of the land is not available for fruit area development. The unavailable land includes forest, plantation, and built-up areas that cannot be converted. The results showed that the land conditions are in various categories with the majority 17.48% of land in the S2 (moderately suitable) category were suitable and available for fruit area development. The forests in the north of the study area which are included in the Dieng Plateau have not been fully converted into conservation forests. In regulations, forests located at an altitude of more than 1000 masl are used for water storage and erosion prevention [42]. However, only part of the upper reaches of the Serayu River, the Telaga Warna area, and the Hindu Temple area is designated as nature and cultural reserves.

According to Mucharam et al. [43], the implementation of sustainable regional development requires the collaboration of local and central government authorities. Site-specific planning can be developed to a wider level with adaptation, especially to the characteristics of areas that have similarities. Meanwhile, several studies on economic aspects of conservation efforts in sustainable land management suggested the provision of incentives to farming households [35, 44]. This is used as a stimulus to replace the decrease in income at the beginning of adaptation to changes in farming behavior.

Table 2. The results of pairwise comparisons of land suitability criteria for fruit commodities in the highlands

SGG: soil great groups; ALT: altitude; SLP: slope; RF: rain fall; TEM: temperature; RH: relative humidity; LU: land use;

MD: markets’ distance; RD: roads’ distance

MD: markets’ distance; RD: roads’ distance

Consistency vector (p): 10.029

Consistency index (CI): (p-n) / (n-1) = (10,029 - 9) / 8 = 0.129

Random index (RI): 1.45

Consistency ratio (CR): CI / RI = 0.089≤ 0.10

Table 3. Land suitability and availability for the development of tropical fruit commodities