Introduction

During the past decade, several interface fields of study, including agroecosystem ecology and landscape ecology, have emerged that integrate ecological theory and management practices within the realm of applied ecology (Barrett, 1984; 1992). Agroecosystem ecology is based on the premise that natural ecosystems are models for the long-term management of agriculture and on the philosophy of working with nature rather than against it (Jackson and Piper, 1989; Barrett, 1990). Landscape ecology considers the development and dynamics of (1) spatial heterogeneity, (2) spatial and temporal interactions and exchanges across the landscape, (3) influences of spatial heterogeneity on biotic and abiotic processes, and (4) the management of spatial heterogeneity for societal benefit (Risser et al., 1984).

The management of agricultural systems has traditionally focused on the agroecosystem (i.e., crop field or landscape patch), rather than on the total agrolandscape (i.e., watershed or region in which the crop fields are elements in the landscape matrix) level of resolution (Barrett, 1992). Increasing the crop yield has been the main management goal (National Research Council, 1989). Policies and practices to maximize crop yield have involved the use of increased subsidies such as for fossil fuels, fertilizers, and pesticides (National Research Council, 1989). These management strategies have resulted in (1) decreased crop and biotic diversity, (2) net energy loss, (3) profit loss for farmers, and (4) extensive nonpoint pollution of the environment (Altieri et al., 1983; National Research Council, 1989; Barrett and Peles, 1994).

In recent years, agricultural management strategies have begun to focus on increasing biotic (genetic, species, landscape) diversity (Barrett, 1992), on reducing energy inputs (Odum, 1989), and on increasing food safety (see National Research Council, 1996, for a review) rather than only on crop yield. It has become increasingly clear that we cannot sustain agricultural productivity by viewing agricultural systems independent from other landscape elements or ecological/urban systems (i.e., we must develop a holistic agrolandscape perspective in addition to an agroecosystem perspective). We argue that a landscape approach must be established in which landscape units, such as watersheds, are managed as functional systems based on the concept of holistic, long-term sustainability (Lowrance et al., 1986; Barrett, 1992). This holistic approach differs from a picture of the world according to Callicott (1989) which breaks a highly integrated functional system into separate, discrete, and functionally unrelated sets of particulars. A piecemeal or fragmented approach permits the radical rearrangement of parts of the landscape without concern for upsetting the functional integrity and organic unity of the whole. By definition, and by necessity, the agrolandscape approach must integrate aesthetic, biological, physical, and ecological factors; must couple urban (heterotrophic) with rural (autotrophic) systems; and must establish land-use policies based on sound ecological theory (Barrett, 1989; Elliott and Cole, 1989). Sustainability, a common theme of many recent paradigms, is defined here as the ability to keep a system in existence or to prevent it from falling below a given threshold of health (Barrett, 1989). Goodland (1995) defined sustainability, as it pertains to the environment, as "maintenance of natural capital."

The sustainable landscape approach, which considers agroecosystems as components of the total landscape (Jackson and Piper, 1989), encourages the integration of concepts such as sustainable agriculture, biotic diversity, and levels of organization (Barrett, 1992; Barrett et al., 1997). The focus of this approach is to manage for sustainability of the total landscape based on an understanding of how agroecosystem units function as an integrated whole (Figure 1).

In this chapter, we provide a perspective regarding the development and integration of modern agrolandscapes based on the ratio of primary productivity (P) to maintenance costs (R) at the agro-urban landscape scale. This perspective is intended to provide long-term sustainability and increased biodiversity. We discuss

Figure 1 Diagram depicting the new integrative field of study termed sustannable landscape ecology.

the importance of providing linkages between agricultural systems and urban systems and note the importance of developing land-use policies necessary to manage for sustainability and biodiversity based on a total landscape approach.

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