BIODIVERSITY IN AGROECOSYSTEMS - CHAPTER 11 pps

Barrett, and John David Peles CONTENTS Introduction Cultural and Historical Perspectives of the Present Agrolandscape The Creation of an “Oxbow” Urban Area Linkages between Agricultural

CHAPTER 11

Managing Agroecosystems as Agrolandscapes: Reconnecting Agricultural and Urban Landscapes Gary W Barrett, Terry A Barrett, and John David Peles

CONTENTS

Introduction

Cultural and Historical Perspectives of the Present Agrolandscape

The Creation of an “Oxbow” Urban Area

Linkages between Agricultural and Urban Components of the Landscape

Linkages between Biodiversity and Sustainability

Toward Sustainability of Agrolandscapes

Concluding Remarks

Acknowledgment

References

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 agro-ecosystem (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 increas-ingly 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 agro-ecosystem 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 ecolog-ical 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 “main-tenance of natural capital.”

The sustainable landscape approach, which considers agroecosystems as com-ponents 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

inte-gration 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

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

CULTURAL AND HISTORICAL PERSPECTIVES OF THE

PRESENT AGROLANDSCAPE

The Roman writer Cicero termed what is currently considered the cultural

land-scape “a second nature” (alteram naturam) This cultural landland-scape, or second

nature, comprised all the elements introduced into the physical world by humankind

to make it more habitable Hunt (1992) interprets Cicero’s phrase, a second nature,

as implying a first, or primal nature before humans invaded, altered, or augmented the unmediated world

Various ideologies resulting from this second nature, especially how nature should be managed or controlled, have contributed to the present fragmented land-scape The evolutionary significance of the mature (model) system, including how natural selection has resulted in the evolution of efficient mechanisms for insect pest control, nutrient recycling, and mutualistic behavior, is often poorly understood A hallmark of these mature and sustainable ecological systems is also maximum biological diversity (Moffat, 1996; Tilman et al., 1996; Tilman, 1997) Environmental literacy must increase if societies are to develop sustainable agriculture and sustain-able agrolandscapes (Barrett, 1992; Orr, 1992) For example, natural processes and concepts such as pulsing, carrying capacity, natural pest control, nutrient cycling, positive and negative feedback (cybernetics), and net primary productivity must be understood by ecologically literate societies in order to provide a quality environment for future generations There exists an urgent need to understand these processes and concepts better, and to manage agroecosystems at the agrolandscape level (Barrett, 1992) It is now imperative to couple the heterotrophic urban environment with the autotrophic agricultural environment if societies are to establish or manage sustainable landscapes on a meaningful regional or global scale

Figure 1 Diagram depicting the new integrative field of study termed sustainable landscape

ecology

Environmental literacy also includes the aesthetic languages of diverse cultures and histories that determine what a people traditionally considers essential and nonessential resources within cultures Shifting economic, social, political, or artistic perspectives, for example, affect the definition of what is considered a resource and what is perceived as a nonresource The encoded messages endemic to these cultures influence human thought in the determination of what is of value in the life of a human being

The cultural landscape is an integral part of the holistic agro–urban landscape perspective Nassauer (1995), for example, recognized the need to investigate the relationship between cultural landscape patterns and ecological landscape processes The aesthetics that are intrinsic to various cultures have influenced the present agrolandscapes Acknowledging these relationships, including their present and future influences, will increase dialogue among biological, physical, and social scientists; among resource managers, landscape engineers, and urban planners; and among scholars investigating the role of sustainability at the landscape and global levels (Huntley et al., 1991; Lubchenco et al., 1991) The resulting interfaces among fields of study will lead to a deeper understanding of why and of how landscape elements (patches, corridors, and the agromatrices or urban matrices) are related to present regional/global patterns of belief systems, an understanding necessary to conserve biological diversity

THE CREATION OF AN “OXBOW” URBAN AREA

Figure 2 depicts an urban environment, including the relationship of the inner urban landscape to the outer agricultural landscape Although much has been written regarding the pattern and shaping of the landscape from prehistory to present day (see review by Jellicoe and Jellicoe, 1987, for details), there exists the need to address and quantify the concept of landscape sustainability from an energetic (solar energy and energy subsidy) perspective One objective of this chapter is to increase trans-disciplinary dialogue concerning this need Although we recognize that markets have become increasingly global in structure and function (Brady, 1990), it appears that management practices, for example, integrated pest management and information processing, will be conducted on a regional basis (Elliott and Cole, 1989)

Traditionally, towns and cities were integrated in a sustainable manner (Figure

3) The town served as the marketplace for farmers to sell their goods and products (Mumford, 1961; Hough, 1995); goods and services radiated from the city to support the agricultural landscape, including providing cultural, educational, and social benefits (Le Corbusier, 1987) During the early part of this century in the agricultural Midwest, crop diversity was high (Barrett et al., 1990), as was species and habitat diversity (Barrett and Peles, 1994) The shift from a biologically diversified and, perhaps, a sustainable landscape to monoculture or diculture crops (especially corn and soybean) in the rural landscape was accompanied by the development of sub-urban areas that reduced not only the amount of arable land, but also the diversity

of wildlife habitats and cultural linkages between the inner city and the agricultural

landscape This created what we term an oxbow city, analogous to the creation of

an oxbow lake when it becomes separated (physically and functionally) from a flowing meandering stream once the stream changes its course This isolated city develops different functional processes (i.e., provides different services), resulting

in changes in niche and biodiversity (i.e., the inner city creates different occupations and provides habitats for different species of flora and fauna) The integrity of the city frequently becomes less closely related to the total watershed from which it evolved This developmental process is depicted in Figure 4

LINKAGES BETWEEN AGRICULTURAL AND

URBAN COMPONENTS OF THE LANDSCAPE

Odum (1997) classified ecosystems based on the proportions of solar and fossil fuel energy used to drive the system Most natural ecological systems are driven entirely by solar energy Subsidized systems depend, to varying degrees, on the input

of subsidies such as fossil fuel energy, fertilizers, and/or pesticides Agroecosystems, for example, are driven by both solar energy and subsidies; urban systems depend mainly on enormous inputs of fossil fuel subsidies (Odum, 1989)

These ecosystems may also be classified based on the ratio of energy produced

by primary productivity (P) to energy used for respiration or system maintenance (R) Natural and agricultural ecosystems, especially during ecosystem growth and development, represent autotrophic systems where P/R > 1 In contrast, urban areas have increasingly become heterotrophic (P/R < 1) We define sustainable systems

as those systems or landscapes where long-term P/R ratios equal 1 During the

growth and development of autotrophic systems (i.e., during ecological succession),

Figure 2 Diagram depicting urban, suburban, and exurban/agricultural systems

Solar-pow-ered (autotrophic) patches are shown within urban and suburban (heterotrophic) systems.

P/R decreases as biological (organic) materials accumulate (Figure 5) This results

in a balance between productivity and respiration (P/R = 1) in the climax stage of

succession (Odum, 1969) An increase in physical (inorganic) materials in urban

systems coincides with a decreasing P/R ratio (i.e., a significant increase in

main-tenance costs) Thus, the result of urban succession is a city where energy demands greatly exceed productivity During the past century, the large numbers of people living in urban and suburban areas have led to increased need for food produced in rural areas (Steinhart and Steinhart, 1974; Odum, 1989) This demographic and

cultural transition has led to increased reduction of P/R ratios in urban areas, as well

as increased subsidization of agriculture (including economic subsidies) to maximize crop yield (National Research Council, 1989; 1996)

More recently, suburban expansion has led to increased pressure on rural land used for agriculture (Lockeretz, 1988) A result of urban sprawl has been an increase

in the proportion of the agrolandscape occupied by heterotrophic systems This has serious implications regarding the conservation of biodiversity from a sustainable agrolandscape perspective (Rookwood, 1995) In addition, urban expansion into agricultural land has important consequences for aesthetic, social, and economic values (Lockeretz, 1988), including the need to understand more fully how human

Figure 3 The development of an agro–urban sustainable ( P/R = 1) landscape The town

marketplace historically was closely linked to the agricultural landscape Sustain-ability in the modern agro–urban landscape increasingly must be based on the management of suburban areas (ecotones) as natural linkages between urban and agricultural systems.

values will likely define future landscape boundaries and resources, especially those values that relate to ecosystem/landscape sustainability

The present challenge for agrolandscape management is to minimize the infringe-ment of urbanization on agricultural land, to restore biological diversity (genetic niche, species, and landscape) at greater temporal and spatial scales, to establish linkages (ecological and economic) between urban and rural (heterotrophic and

autotrophic) patch elements, and to achieve sustainable productivity (P/R = 1) at

agro–urban (regional) scales Goals for achieving sustainable agrolandscape

man-agement should focus on (1) achieving stability regarding P/R ratios among

het-erotrophic and autotrophic systems at these scales; (2) creating both natural corridor and human transport linkages between rural and urban systems; (3) protecting the integrity of ecosystem/watershed processes, such as nutrient recycling and primary productivity; and (4) establishing management policies for optimal land use within transition suburban areas that ecologically and economically form an interface between urban and agricultural landscape systems As previously noted, sustainable agriculture is based on the coupling of agricultural ecosystems with natural ecosys-tems (Barrett et al., 1990) Here, we stress the need to integrate natural, agricultural,

Figure 4 Diagram depicting the development of urban areas into oxbow cities (1 to 3) and

then, we hope, into a modern, sustainable agro–urban landscape We argue that the modern landscape must be increasingly based on the ecological/economic management of suburban areas as natural linkages between urban and agricultural systems.

and urban components if societies are to design and implement the concept of sustainability at the agrolandscape scale (see Figure 1) This approach should simul-taneously conserve and enhance biotic diversity at greater temporal and spatial scales

LINKAGES BETWEEN BIODIVERSITY AND SUSTAINABILITY

Management of agrolandscapes for sustainability both influence and is influ-enced by biodiversity (Paoletti, 1995) Landscape planning is a process through

Figure 5 Changes in P/R ratios during ecological (autotrophic) and urban (heterotrophic)

succession Although P/R decreases as the amount of biological material increases during ecological succession, the result is a mature (climax), sustainable community.

In contrast, the accumulation of physical material during urban succession frequently results in a fragile, nonsustainable community.

which the conservation and management of biodiversity can be pursued (Rook-wood, 1995)

Turner et al (1995) stressed that there exists a three-way interaction of biodi-versity, ecosystem processes, and landscape dynamics at greater scales Sustainable agricultural practices leading to increased crop and genetic diversity have resulted

in increased agroecosystem stability (Cleveland, 1993) For example, increasing crop diversity benefits agriculture by reducing insect pests (Altieri et al., 1983) Other sustainable agricultural practices, such as conservation tillage, are known to increase habitat diversity, wildlife diversity, and numbers of beneficial insect species (Barrett, 1992; McLaughlin and Mineau, 1995)

Although the importance of a landscape approach for management of biodiversity

is well recognized (Franklin, 1993), little is known regarding how biodiversity affects landscape pattern and dynamics (Turner et al., 1995) Turner et al (1995) have suggested that there exists a three-way interaction among biodiversity, ecosystem processes, and landscape dynamics In addition, it is well documented that there exists a reciprocal relationship between sustainability and biodiversity (Paoletti, 1995) Thus, as biodiversity and sustainability are increased by management prac-tices at the landscape level (e.g., agrolandscape management), the resulting increase

in biodiversity will likely have important benefits concerning the conservation and efficiency of these processes and dynamics (Culotta, 1996; Tilman et al., 1996)

It is important to recognize that, by definition, the agrolandscape approach requires the consideration of biological diversity in the management of agroecosys-tems (Paoletti et al., 1992) Paoletti et al (1992) and Paoletti (1995) note that sustainable strategies in food production in agriculture improve the existing biodi-versity These strategies include proper management of natural vegetation, better use and recycling of organic residues, introduction of integrated farming systems, reduced tillage, intercropping, crop rotation, biological pest control, and increased number of biota involved in human food webs McLaughlin and Mineau (1995) point out, however, that agricultural activities such as tillage, drainage, rotation, grazing, and extensive usage of pesticides and fertilizers have significant implications for wild species of flora and fauna Therefore, reduced or (no-till) farming, in contrast

to conventional tillage, benefits biological diversity in terms of maintaining wild or native species populations

Increased biodiversity at the landscape level (in the form of increased habitat or agroecosystem diversity) will play a key role in protecting diversity and in providing

a linkage between urban and rural areas in our sustainable landscape approach For example, that an optimum balance between solar-powered and subsidized systems

in suburban areas is critical to this linkage The success of obtaining this optimum balance will almost certainly be enhanced by increasing the diversity of habitat types across the total landscape Greenways or natural corridors will also enhance the linkage and conserve biological diversity between urban and rural areas (Little, 1990) Management of agroecosystems and agrolandscapes for sustainability will lead to increased habitat and genetic diversity, which, in turn, will lead to increased agroecosystem stability (Altieri et al., 1983; Cleveland, 1993) Likewise, increased biodiversity within individual systems should also increase the diversity and stability

of these systems within the total landscape or watershed

Agrolandscapes should also be managed to increase species diversity within landscape patches and to increase and/or to conserve genetic material among land-scape patches (Barrett and Bohlen, 1991) In recent years, there has been increased emphasis on the connectivity and integration of the agricultural landscape with the

urban landscape (see Lockeretz, 1988, including a special issue of Landscape and

Urban Planning, Volume 16, for details) However, most studies at the watershed

or agrolandscape levels have failed to encompass or integrate the urban environment into the agrolandscape concept Since the approach to sustainable agriculture is based on natural ecosystems serving as the model system for efficient agricultural management (Jackson and Piper, 1989; Barrett, 1990), urban systems should also

be designed and based on natural ecological systems serving as model systems to ensure maximum ecological and economic efficiency Thus, sustainability and biodi-versity share an important interrelationship that is more fully understood when questions are addressed at the agro–urban landscape scale, and when research designs and management strategies are based on ecological theory

Importantly, there is growing recognition that cities need to be managed based

on the concept of sustainability (Stren et al., 1992) This approach is based on an ecological understanding of how natural ecological systems are organized, and most important, how they function As with sustainable agriculture, an urban perspective based on sustainability means working with, rather than against, nature Recently, there has been increased effort in urban areas to maximize the efficiency of energy use, to increase the rate of recycling of goods and materials, and to reduce pollutants entering the system In addition, “green city” movements have placed emphasis on preservation of natural areas, and on the establishment of vegetable gardens (i.e., solar-powered patches, Figure 2) in urban areas (Stren et al., 1992) Continued efforts

to increase solar-driven productivity, while simultaneously decreasing maintenance costs, in urban areas will greatly enhance the sustainability of the total agro–urban landscape Equally important is the need to plan for (or to zone) future suburban areas, encompassing a productivity/maintenance ratio equal to 1, if we are to achieve regional landscape sustainability (Figure 4) This strategy must also make every effort to increase biodiversity at the genetic, species, and landscape levels

Lockeretz (1988) stressed the importance of protecting and creating natural linkages between urban and rural areas Urban greenways (Little, 1990) provide noteworthy examples of these natural linkages Although greenways take many different forms, they are primarily natural areas set aside for their ecological, rec-reational, or aesthetic value within urban areas Greenways also provide natural corridors for movement of wildlife species and transfer of genetic materials between urban and rural areas

Suburban areas also represent a vital linkage (transition or ecotone) between urban and rural systems Therefore, it is important to manage these areas as a

“transitional zone” between urban population centers and rural farmland (Figure 4) with an optimum balance existing between land area devoted to natural (solar-powered) systems and those managed as subsidized systems Management plans aimed at establishing a new approach to suburban development should strive to attain

an integration of autotrophic and heterotrophic systems The success of these