Prioritizing locations for the riparian establishment based on spatiotemporal change of riparian forest area at a watershed scale

Abstract

A majority of streams in Korea have been channelized and their adjacent flood plains have been converted for anthropogenic land use, especially in urbanized areas. Fortunately, recent elevated public recognition to the stream ecosystem has led to governmental efforts to conserve riparian areas. In this study, a simple method to prioritize locations for riparian establishment was developed at a watershed scale based on spatiotemporal change of riparian forest area. The developed method was applied for the Ansung and Sapkyo watersheds, which were under consideration for the stream riparian area establishment by the Korean Ministry of Environment. Two riparian forest indices, Riparian Forest Index (RFI) and Riparian Forest Change Index (RFCI) were developed to represent spatial and temporal change of watershed riparian forest, respectively. LANSAT satellite images with a 30 m × 30 m resolution were used to estimate the two riparian forest indices. A precautionary approach, which intends to preserve the existing riparian forests as much as possible, was applied by ranking sub-watersheds based on the two riparian forest indices to prioritize locations for the riparian establishment at a sub-watershed level. The results showed that overall urban land cover in riparian areas increased while forests and cropland decreased over the past 25 years. More importantly, riparian forest removal occurred more rapidly in the riparian area, which is one of the most important niches for riparian ecosystems, as compared to the entire watershed. Most riparian forests appeared to be located upstream of the watersheds, and thus it is important to develop management measures to preserve existing riparian forests from human activities. The developed approach could be a useful tool that can assist policy makers to prioritize locations for the riparian area establishment. However, this method has limitations of only considering riparian forest area and therefore, other aspects such as stream morphology as well as ecology needs to be incorporated into riparian area determination process as they become available in the future. In addition, considering that substantial portions of riparian areas have already been disturbed, the restoration aspect of the impaired riparian also needs to be investigated further.