A conceptual framework for the definition of the optimal width of riparian forests

Riparian ecosystems, often represented by riparian forests (RFs), are diverse systems which are being endangered primarily from the expansion of agricultural land and are protected by legislation in recognition of their role in preserving water resources. The methods usually employed to recommend maintenance or reclamation of RFs fail in not considering the full costs and benefits. In agroecosystems, the preservation of RFs will result in a permanent improvement in freshwater quality, but will also remove economically attractive space from crop production. This paper describes the principles of a procedure which uses data that is usually available (topographic maps, land use and soil data) to determine the optimal RF width, quantitatively and on a geo-referenced basis. An example, based on land-use scenarios representative of southeast Brazil is used to illustrate the suggested framework. Because of the simultaneous analysis of variables related to target effects on water quality, the effectiveness of the RF in retaining sediments and the forests capability for developing the multifunctional aspects of a riparian ecosystem could be considered. For the case study, the optimal RF width was calculated as 52 in, resulting in a sediment yield value of 12 Mg ha(-1) yr(-1) and a retention of 54% of the total amount of sediments. This RF width was wider and more efficient if compared with the official legal recommendation of 30 m. The decision process is logically based and the equations clearly described, and thus can be incorporated in Geographic Information Systems. (C) 2002 Elsevier Science B.V. All rights reserved.