Erosion in Ngrancah sub-watershed (DAS), Kulonprogo has caused sedimentation, causing land degradation and wider critical lands. Erosion process itself is triggered by poor land management which ignores land conservation and land shape selection which does not fit with land capability.
UGM lecturer of Faculty of Forestry, Ir. Ambar Kusumandari, M.E.S, assessed that land degradation is very influential on human life as it can reduce guarantee of continuity, existence and function of natural resources in the region to support humans for present and future needs. Various people's activities in managing the land give little attention to elements of environment sustainability that results in the tendency of decrease in the quality of sub-watershed.
Research in Ngrancah Sub-watershed concluded that it is in an alarming condition, characterized by poor quality of land, 85.17% of the Sub watershed belongs to the poor to very bad quality. The current condition is due to a very high attrition rate, as much as 77% of the sub-watershed is in danger of heavy to very heavy erosion. "The design of Soil and Water Conservation (KTA) technique that had been developed previously, in its application in the field still does not give results as expected. This is exacerbated by the selection of land uses that are inconsistent with the carrying capacity and land," Ambar Kusumandari said in the Auditorium of the Faculty, Monday (6/2).
She made the statement during an open examination for her Forestry Doctoral Program. Accompanied by Supervisor Team, Prof. Dr. Djoko Marsono, Prof (ret), Dr. M. Sambas Sabarnurdin and Prof. Dr. Totok Gunawan, Kusmandari defended her dissertation entitled The handling of Soil and Water Conservation Based on Ecological Unit in Ngrancah Sub- Watershed, Kulonprogo.
Critical land map made by BRLKT Serayu Opak Progo shows that Ngrancah sub-watershed is critical land in the category that 84 ha is critical area and 506.4 ha is very critical. Kusumandari’s research results in 2008 concluded that 48% of Ngrancah sub-watershed area is classified as having high vulnerability of landslides. Especially when considering the Ngrancah sub-watershed as catchment area of Sermo Reservoir, there is a close link between the processes occurring in the catchment and sedimentation in the reservoir. "Related to that, the problem is necessary and urgent to be addressed to inhibit sedimentation to make reservoir work longer and to achieve sustainable land management," the Academic Quality Internal Auditor said.
Ambar Kusumandari stressed when the process is ignored, in a long time it certainly will take considerable expense, especially in terms of adverse effects of ecological and economic aspects. Therefore, the problem of erosion, sedimentation and degraded land is urgent to be studied, researched and addressed in order to inhibit degradation rate.
The research showed, based on the characteristics of land, Ngrancah sub-watershed can form 77 ecological units. Meanwhile, vegetation characteristic indicates there are 45 tree species. From density, relative density (KR), Frequency, Relative Frequency (FR), dominance, relative dominance (DR), and Importance Value Index (IVI), the Coconut Tree has the highest IVI (102.92), which is followed by Mahogany (IVI = 43.91), Durian (IVI = 32.01), Sengon (IVI = 23.85), Teak (IVI = 18.54) and Melinjo (IVI = 10.02). The other types which have INP about 7 are Sungkai, Jackfruit, Sonokeling and Waru. "In addition to these species, there are 35 other tree species in the study which have relatively small INP," the woman born in Yogyakarta, August 21, 1962 explained, adding that if the land clustering based on vegetation parameters, soil, erosion and all land parameters, the main determinants that are obtained in a row are canopy percentage, soil chemical fertility, soil erodibility, and soil fertility, subsequently giving relative contribution of 93.55: 76.83: 94.49 and 81.46 in discriminant analysis.