A Review of Concepts and Criteria for Assessing Agroecosystem Health Including a Preliminary Case Study of Southern Ontario Wei Xu∗, Julius A

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Agriculture, Ecosystems and Environment 83 (2001) 215–233

A review of concepts and criteria for assessing agroecosystem health including a preliminary case study of southern Ontario Wei Xu∗, Julius A. Mage Department of Geography, University of Guelph, Guelph, Ont., Canada N1G 2W1 Received 20 August 1998; received in revised form 21 April 1999; accepted 10 April 2000

Abstract The model of agroecosystem health has been advocated as an appealing guideline for agricultural research. Yet, some ambiguity remains in how the concept can be defined and how the general criteria for assessing the health of an agroecosystem at a particular scale can be selected. This paper reviews the literature from various disciplines pertinent to the concept of agroecosystem health. It focuses on assessing the applicability of assorted concepts, norms, and criteria to agroecosystem health assessment, and develops a general definition of agroecosystem health. A classification scheme is proposed which scattered while potentially useful concepts in the literature are discussed, using southern Ontario as a case study to further illustrate the usefulness of the conceptual framework in studying agroecosystem health. Agroecosystem health can be characterized from four different perspectives that are related to agroecosystem structure, function, organization, and dynamics. Given the complexity of agroecosystems, the health of the systems at different scales cannot be fully captured from one perspective only. Criteria, such as resource availability, diversity, and accessibility, are some of the existing concepts capable of depicting the structural state of agroecosystem health. Concepts including productivity, efficiency, and effectiveness appear very useful for assessing the functional performance of agroecosystems. As any agroecosystem interacts actively with its external environments and changes over time, such characteristics are not necessarily captured by structural or functional criteria. Organizational criteria, such as autonomy and self-dependence, are useful to characterize the organizational nature inherent to agroecosystem health. Stability and resilience on the other hand are two appealing concepts capable of revealing the temporal dimension of agroecosystem health. Numerous empirical studies that are used to illustrate how these concepts developed in different disciplines of agricultural research can be potentially employed to facilitate the assessment of agroecosystem health. It is argued that any holistic investigation of the health of an agroecosystem needs to examine biophysical, economic, and human conditions of the system and to evaluate these conditions from perspectives pertinent to system structure, function, organization, and dynamics. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: Agroecosystem; Agroecosystem health; Agroecosystem health assessment; Agroecosystem health criteria; Agricultural land use

1. Introduction a supportive biophysical resource base, the economic viability of production, and the continuation of a suf- Concerns over the long-term sustainable develop- ﬁcient supply of agricultural products, to the social ment of agriculture, range from the maintenance of vitality of agriculture-based rural communities (Dou- glas, 1984; Brklacich et al., 1991; Science Council of ∗ Corresponding author. Tel.: +1-519-824-4120/ext. 4860; Canada, 1992; Brown, 1995). These concerns have fax: +1-519-837-2940. stimulated considerable interest in the relationships E-mail address: [email protected] (W. Xu). that shape the development of agroecosystems, and

0167-8809/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S0167-8809(00)00159-6 216 W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 consequently generated various concepts, theories, interest of the individual researcher (Conway, 1985). and models for analysing the issues relating to agri- An agroecosystem might be defined as a functional culture. One of the models proposed recently is the unit, producing agricultural products and providing ‘health’ of agroecosystems. Analysts attempt to use rural services, which includes a set of agricultur- the health model to describe and evaluate the state ally related elements and interactions among those of agroecosystem conditions (Waltner-Toews et al., elements. For instance, agricultural land, labour, 1993). While there is considerable ambiguity as to capital, and management can be identified as the in- how the health of an agroecosystem could be defined put elements for an agroecosystem at the farm level and further analyzed, the model of agroecosystem (Ilbery, 1985). These elements inter-link with one health may provide new insight into how agroecosys- another and interact with external attributes. The tem conditions can be perceived. internal and external interactions determine various By reviewing the literature, this paper examines the functions of an agroecosystem. ways in which the health of agroecosystems may be To simplify the complex relationships in agroe- characterized. A discussion of various concepts rele- cosystems, one fundamental approach is to divide vant to agroecosystems research is presented followed the system into some broad dimensions or compo- by a definition of agroecosystem health with reference nents (Table 1 gives three examples of this approach). to the structural and functional performance of an For example, Smit and Smithers (1994a) propose a agroecosystem. A classification scheme is developed model for describing the relationship among agroe- as a framework to review and evaluate criteria and cosystem components. The model identifies three indicators appearing in the literature for their utility in essential dimensions constituting an agroecosystem: assessing different aspects of agroecosystem health. environmental, economic, and human dimensions. Based upon agricultural census information, a case of These dimensions exist in agroecosystems at different southern Ontario is given to illustrate the applicability scales. The fundamental idea of such an approach is of the developed framework to agroecosystem health to analyze the complexity of an agroecosystem by research. characterizing each component part separately and exploring the relationship among those parts. The understanding of an agroecosystem as a whole depends 2. Agroecosystems: dimensions and scales largely on how the inherent interactions among these dimensions are recognized and generalized. The notion of the agroecosystem represents One essential element of a systems approach to a way of perceiving agriculture, particularly its agriculture is the effect of spatial scale. According environment–production relationships, in systems to the hierarchical theory of systems analysis (Kast terms. This perspective has evolved from general and Rosenzweig, 1972; King, 1993), agroecosystems systems analysis in engineering (Tivy and O’Hare, can be defined at different spatial scales, ranging 1981). The concept of a system has been defined from field plots to the entire globe (Conway, 1985). in various ways depending on the objective and Fig. 1 is a schematic diagram that illustrates how

Table 1 Examples of agroecosystem classiﬁcation from different perspectives Agroecosystem constituentsa Agroecosystem and subsystemsb Agroecosystem dimensionsc Spatial organization Human subsystem Environmental dimension (e.g. soil) Crop-livestock production Environmental subsystem Economic dimension (e.g. market) Resource management system Generic subsystemd Human dimension (e.g. rural community) Labour management system a From Olmstead (1970). b From Turner and Brush (1987). c From Smit and Smithers (1994a,b). d This refers to genotypes and phenotypes of cultivars and animals, and population dynamics that affect crop and animal evolution. W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 217

Fig. 1. Agroecosystem scales and effects: a land use study example. agroecosystems at macro-, meso-, and micro-scales of little utility to agroecosystem research, especially are interrelated and nested in a systems hierarchy. when research focuses on economic or human aspects An agroecosystem at a lower level (e.g. a farm level of the system. This is due to the fact that our knowl- agroecosystem) is a subsystem of an agroecosystem edge of agroecosystem ‘diseases’ is limited, and also at a higher level (e.g. a regional agroecosystem). because a ‘negatively’ defined concept of agroecosys- Across various scales, agroecosystems may be com- tem health provides few directives for maintaining the posed of different components and exhibit different health of the system. The World Health Organization interactions among the components. A full grasp of describes health as one’s ability to satisfy needs and the functional and structural characteristics of an realize aspirations, as well as to cope with stresses agroecosystem may depend partly on how findings in (WHO, 1992). This description of health focuses on different studies are integrated across scales. the social and personal resources and supportive environments, as well as physical capacity (Waltner-Toews et al., 1993). It clarifies that defining the health of a 3. Agroecosystem health system also requires a consideration of the societal context with which people’s needs and wants are as- The concept of health is often loosely referred to sociated. The WHO (1992) description stresses that in medicine as a body free of disease (Rapport, 1989; health is directly related to one’s ability or capability Costanza, 1992). This type of definition of health is to function and adapt to changes in the environment. 218 W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233

Table 2 Characteristic response of ecosystems to stressa Nutrient pool Primary productivity Species diversity Size distribution System retrogression Harvesting of renewable resources Aquatic * * −−+ Terrestrial −− − − + Pollutant discharges Aquatic ++ − − + Terrestrial −− − − + Physical restructuring Aquatic * * −−+ Terrestrial −− − − + Introduction of exotics Aquatic * * * * + Terrestrial * * * * + Extreme natural events Aquatic * * −−+ Terrestrial −− − − + a The signs, + and −, indicate directions of change compared with normal functioning of relatively unstressed system. The asterisk denotes the characteristic response not sufﬁciently determined (Rapport et al., 1985).

One approach to define agroecosystem health stems (1995, p. 130) states ‘agroecosystems are particular from ecosystem health research. Many have attempted cases of socio-economic systems, or systems com- to capture the essence of what constitutes the health posed of at least a human subsystem and an ecolog- of ecosystems. Analysts in the field of stress ecology ical (or biological) subsystem’. The recognition of define the concept of ecosystem health from the ‘in- agroecosystem distinctiveness has meant that analysts dicative signs’ of stressed ecosystems (Odum, 1985; should be careful in defining agroecosystem health Rapport et al., 1985; Schaeffer et al., 1988). For ex- with ecological concepts, and indeed should interpret ample, Rapport (1995) identified a list of indicators the concept within a broad perspective relative to the for assessing and evaluating ecosystem under stress biophysical, economic, and human dimensions inher- (Table 2). Harvesting of renewable resources, for ent to the system. Despite efforts in establishing a instance, is considered as a stress to any terrestrial theoretical base for agroecosystem health assessment, ecosystem. Such activity may cause the ecosystem the actual meaning of agroecosystem health is yet to to respond as indicated by a decrease in the nutrient be clarified. pool, primary productivity, species diversity, and size of distribution, and an increase in system retrogression. Others interpret the concept from the standpoint 4. Defining agroecosystem health of ecosystem organization and changes in relation to stresses. For example, Costanza (1992) states that an At a regional level and higher, agroecosystems are ecological system is healthy and free from ‘distress designed and managed primarily for providing food, syndrome’ if it is stable and sustainable, i.e. if it is fibre, and other agricultural products for human uses active and maintains its organization and autonomy (Waltner-Toews, 1994; Gallopin, 1995). They also over time and is resilient to stress. provide a variety of services needed by society, such At times, ecological concepts have been directly as an agricultural landscape and biodiversity. To pro- employed to define the meaning of agroecosys- vide such end-products and services, agroecosystem tem health. However, there are differences between components are structured in such a way that various ecosystems, mostly unmanaged, and agroecosystems, functions and processes can be performed. Hence, which are directly managed by humans. Gallopin both functional and structural characteristics represent W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 219 the elements of agroecosystem health at a regional to biophysical transformation and cycling, economic level. production and social organization. With respect to the biophysical dimension, an agroecosystem 4.1. Agroecosystem structure functions largely in the same way as all ecosystems. It is suggested that there are two basic types of links The structure of an agroecosystem is referred to or flows between component parts of all ecosys- as the composition and distribution of the system’s tems: energy flow and biophysical cycling (Tivy and components. The focus on structural characterization O’Hare, 1981). The primary function of biophysical has been related to the biophysical resource type and components is realized through plant photosynthe- composition, the social and economic pattern and dis- sis and material transfer in food chains and webs. tribution, and the biophysical and human landscape The agroecosystem is a managed ecosystem and its form (Hoffman, 1976; Chidumayo, 1989; Burel and biophysical processes are controlled or affected by Baudry, 1995). The structural composition and dis- economic and social manipulation. Economically, the tribution of agroecosystem components vary among primary function of a regional agroecosystem is to different types of agroecosystems at different scales produce agricultural products needed by our soci- (Smit and Smithers, 1994a). Agroecosystem structure ety. The economic production is again a function of also changes over time due to the influence of vari- factors related to agricultural markets. ous factors both within and beyond an agroecosystem (Ilbery, 1991; Troughton, 1991). 4.3. Agroecosystem health defined The significance of agroecosystem structure is two-fold. First, the existence and distribution of struc- On the basis of the above, both functional and tural components provides a fundamental basis upon structural aspects represent the essential characteris- which an agroecosystem can function at all. In crop tics of agroecosystems. Thus, the health of a regional production systems, for instance, soil is one basic re- agroecosystem can be defined as the system’s ability source component that retains moisture and provides to realize its functions desired by society and to main- mineral substances so that the plant can perform vari- tain its structure needed both by its functions and by ous biological processes and grow. Structural states of society over a long time. soil, such as organic content in soil or thickness of top- This definition not only explicitly recognizes the soil, are crucial factors in determining the biophysical importance of functional and structural characteristics functioning of crop production. Second, agroecosys- in the context of societal needs, but also considers the tem structure is directly tied to societal needs. For significance of temporal changes of these characteris- instance, a biodiversified resource structure provides tics in the face of changing environments for assess- an opportunity to satisfy a variety of needs for differ- ing agroecosystem health. Such a consideration stems ent people (Burton et al., 1993). Also, the diversified from the recognition that agroecosystems are subject agricultural landscape structure provides different to various driving forces that have led to dramatic amenity values that are appreciated by different peo- changes in agroecosystem function and structure. ple. Therefore, the establishment of agroecosystem structural composition and morphology is significant not only in supporting various agroecosystem func- 5. Classification of agroecosystem health criteria tions, but also in providing services to people’s needs. In the literature on agroecosystem analyses, some 4.2. Agroecosystem function studies consider the biophysical processes of the system, and others focus on the social and economic The function of agroecosystems refers to how performance of the system. In order to facilitate the system operates, given a variety of components the review of the literature and the identification and structural forms, to generate agricultural prod- of general criteria of agroecosystem health, a sim- ucts and services. As a multi-dimensional entity, an ple framework is proposed. The framework catego- agroecosystem performs different functions related rizes the existing criteria into four groups relating 220 W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233

Table 3 General criteria for assessing agroecosystem health Structural criteria Functional criteria Organizational criteria Dynamics criteria Resource Productivity Integrity Stability Availability Efﬁciency Self-organization Resilience Accessibility Effectiveness Autonomy Capacity to respond Diversity Self-dependence/self-reliance Equitability Equity

to agroecosystem structure, function, organization, system functions. Availability describes the existence and dynamics (Table 3). These four sets of criteria and capacity of critical system components and indi- represent four different approaches to analyze the cates the resource potential of agroecosystems. Agroe- health of agroecosystems. Some distinctions can be cosystem functions are dependent upon a variety of made among these approaches although they are not resources. A certain amount of available resources of mutually exclusive. The first examines the structural various kinds is necessary for the agroecosystem to characteristics through which the appearance or the function at all (Gallopin, 1995). Further, The amount structural ‘health’ of agroecosystems can be described of resources available to an agroecosystem partly and/or evaluated. The second approach assesses the determines its capacity to meet the possible expansion performance of an agroecosystem by characteriz- of demands for agricultural products, as well as its ing its function. The third approach investigates the ability to cope with any environmental change (Wall agroecosystem conditions relative to its relationships et al., 1995). Hence, this criterion represents one char- with external environments. The focus here is to know acteristic of how well an agroecosystem is structured. if the agroecosystem organization is established by An agroecosystem with a higher level of resource self-regulation mechanisms or controlled by external availability could be argued to be healthier than the attributes. The fourth approach focuses on the dy- one with a lower level of resource availability, ceteris namics of agroecosystems. It attempts to assess the paribus. temporal aspect of agroecosystem health and evaluate In assessing the expected impact of prime agricul- the system’s ability to cope with any possible changes tural land conversion to non-farm uses in Ontario, in attributes within or beyond the system. At a re- Cocklin et al. (1983) indicate that the continuing gional scale, these approaches have all been adopted loss of prime farmland may adversely affect the food to assess the conditions of the agroecosystem across production capacity, especially the capability of ten- its three components. der fruit production in Ontario, Canada. In light of agroecosystem health, such conclusions can be 5.1. Structural criteria directly interpreted as a possible deterioration of the health of Ontario agroecosystem into the future. Many concepts have been employed in assessing and evaluating the structural well-being of agroecosys- 5.1.2. Resource accessibility tems. In this paper, five commonly employed con- Resource accessibility generally refers to the ease cepts are discussed and appraised as to their utility to with which the system’s resources can be accessed agroecosystem health assessment. They are resource and utilized. It depicts another character of agro- availability, resource accessibility, diversity, equitabil- ecosystem structure: the distributive relationship be- ity, and equity (Table 3). tween resource supply and demand. The importance of resource accessibility is two-fold. Firstly, acces- 5.1.1. Resource availability sibility to various resources and services largely Resource availability refers to the volume of re- determines how well the economic and social needs sources necessary to potentially achieve or maintain within an agroecosystem can be satisfied. Secondly, W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 221 an agroecosystem with accessibility to its resources Studies in different fields have suggested the po- can help maintain its functions over time. When an tential applicability of the concept for agroecosystem agroecosystem is under stress, its normal functioning health assessment. In ecological studies, for example, fluctuates, and needs to be supported by alternative many have provided evidence that the loss of ecosys- resources. Accessibility often becomes one of the tem biodiversity is indicative of potential system major determining factors in how well the system is dysfunction (Harris, 1984; Root, 1990). In farming able to adjust to the new situation and maintain its system research, it is indicated that farm diversifica- functions. An agroecosystem with high accessibility tion may increase the ability of the system to avoid to all its resources thus exhibits a high health level. the economic loss and uncertainty induced by price Many studies have demonstrated the utility of ac- fluctuation in a market, and to satisfy the societal need cessibility concept for assessing the conditions of for food in a changing pattern of food consumption an agroecosystem. In a case study on the long-term (Anosike and Coughenour, 1990; Ilbery, 1992; Nap- change of people’s accessibility to health service in ton, 1992). Furthermore, the value of agroecosystem the rural Ontario, Joseph and Bantock (1984) con- diversity by itself is a socially desired characteristic clude that the accessibility to general practitioner ser- for several reasons. Burton et al. (1993) state that the vices by the dispersed rural population have greatly biodiversified environment has an inherent aesthetic reduced. They argue that such changes threaten the value which is desired and appreciated by our soci- vitality of rural community well-being, which is ety. Therefore, a more diversified agroecosystem is a indicative of the decline of agroecosystem health. more healthy system than a less diversified one. In a comparative study of three agroecosystems in Many measures and indices of ecosystem diversity Bangladesh, Ali (1995) indicates that the success of exist in the literature (Goodman, 1975; Burton et al., rice crop production largely depends the accessibil- 1993). In ecology, two aspects are central in most di- ity of agricultural land to water during dry season, versity measures: number of species and size of pop- and the agroecosystem with a higher proportion of ulation. In agroecosystem analysis, the richness of a irrigated land out-performs (or is more healthy than) system’s components and the spatial evenness of the those with a lower level of irrigation. components are commonly used to measure agroecosystem diversity at a hierarchy of scales (Yeates, 5.1.3. Diversity 1968; Hoag, 1969). While examining the change of Diversity is defined in a variety of ways (Goodman, agroecosystem health, Xu (1999) employed a measure 1975; Rice, 1992; Burton et al., 1993). In ecology, of land use diversity based on the spatial composi- the concept of diversity stems from the analysis of tion of different land use types. Based on this measure the complexity in evolutionary ecology of ecosystem and remotely sensed data, substantial spatial variation succession (Goodman, 1975; Tivy, 1993). It is pro- were identified in the changing process of rural land posed that the concept captures the degree to which an use diversity, indicating that both improvement and ecosystem preserves its interactive pathways among deterioration in agroecosystem health had occurred components in a food-web. Such discourse on the in the County of Wellington, Ontario, over the study diversity concept forms the theoretical base of the period. ecosystem’s stability–diversity relation (Goodman, 1975). Despite the debate over the positive rela- 5.1.4. Equitability tionship between ecosystem stability and diversity Equitability has been defined as how evenly the (Shrader-Frechette and McCoy, 1993; Tivy, 1993), the products of an agroecosystem are distributed among concept of diversity is still extensively used in the lit- its human beneficiaries (Conway, 1985; Marten, erature, partly due to its capability in depicting system 1988). Conway (1985) claims that equitability can characteristics (Boster, 1983; Brush et al., 1988). In be readily described using distribution parameters the agroecosystem context, diversity could be broadly of the system’s structural components (e.g. land re- defined as the number of system components and source distribution among households in a village). the extent to which system components vary across From this definition, equitability becomes another space. measure of the structural distribution of agroecosys- 222 W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 tem components, which is equivalent to the spatial 5.2.1. Productivity evenness captured by the concept of diversity. In Productivity is generally referred to as the output of ecology, equitability is often considered as a mea- product per unit of resource input (Conway, 1987). It sure of ecosystem diversity (Putnam and Wratten, describes the ability of a system to produce outputs. 1984). In this sense, the concept of equitability does In ecology, productivity is a term often used to refer not offer any utility beyond the concept of diversity. to chemical energy transformation. The total amount For agroecosystem health assessment, the utility of of chemical energy fixed by an ecosystem per unit equitability concept as a health component of agroe- area per unit of time is defined as the ‘gross primary cosystems is limited. Equitability is at most a subset productivity’ (Tivy and O’Hare, 1981). In economic or a measure of agroecosystem diversity. Diversity analyses of agriculture, productivity is often referred is a much broader notion capturing the structural to as economic returns or crop yields produced per characteristics of agroecosystems, and is measurable unit of resources including land and labour (Mage in a hierarchy of scales. Moreover, the definition of et al., 1989; Nguyen and Haynes, 1993). equitability is somewhat vague. Conway (1987) uses The utility of productivity concept is widely recog- the same description of equitability for the defini- nised in the literature. For example, in the ecological tion of equity, which is another broad notion in the literature, the concept of productivity is often em- literature. ployed as a descriptor to depict the functional characteristics of biotic components in ecosystems (e.g. 5.1.5. Equity grassland ecosystem by Risser (1988); forest ecosys- Equity is a normative notion that appears in the tem by Reiners (1988)). Some ecologists further sug- discussion of agricultural sustainability (Burkhardt, gest that declines in primary productivity are indicative 1989; Brklacich et al., 1991). In agricultural sustain- of stressed or unhealthy ecosystems (Odum, 1985). ability analysis, the equity theme focuses on the pro- In the context of agroecosystem research, the tection of rights and opportunity of future generations concept of productivity can provide a meaningful to derive benefits from resources which are in use measure as to whether or not an agroecosystem is today (intergenerational equity), and on the fairness of satisfying societal needs for agricultural products the distribution of benefits from agriculture between (Waltner-Toews, 1994; Gallopin, 1995; Okey, 1996). countries, regions or social groups (intragenerational While agroecosystem productivity is conditioned by equity) (Barbier, 1987; Burkhardt, 1989; Smit and various factors, it does represent one feature that Smithers, 1994b). In essence, the notion of agricultural indicates the functional performance or the health equity refers to the distributive fairness of agricultural of agroecosystems. An agroecosystem with a higher production among people across space and over time. productivity can be considered as healthier than one As a subjective norm, the concept of equity can be having a lower productivity, when other conditions assessed via such criteria as accessibility to resources associated with the two systems are the same. or resource diversity. In this sense, the concept of equity represents a very broad and general notion like 5.2.2. Efficiency the concept of health. Efficiency is often referred to as the ratio of some defined output or product to the input or cost during the system functioning (Wiegert, 1988). The efficiency 5.2. Functional criteria of an agroecosystem has been analyzed from both ecological and economic perspectives. In ecology, ef- Many concepts exist in the literature for charac- ficiency is a central concept for analysing ecological terizing the function of agroecosystems. Agroecosys- processes of photosynthesis and energy transforma- tem productivity, efficiency, and effectiveness are three tion. The photosynthetic efficiency, for example, is concepts representing the essential characteristics of defined as the ratio between the chemical energy fixed agroecosystem functions (Table 3), and their utilities by the plants in photosynthesis and the amount of so- for characterizing agroecosystem health are discussed lar energy involved in the process (Tivy and O’Hare, here. 1981; Wiegert, 1988). Thus, the ratio of energy output W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 223 per hectare to energy input per hectare is a common of village-based agroecosystems were identified at measure of the ecological efficiency of an ecosystem. various development stages around the world. The In economics, efficiency means absence of waste, comparative analysis of Bayliss-Smith (1982) further or using the resource as effectively as possible to sat- indicated that modern agroecosystems may be the isfy people’s needs and desires (Samuelson and Nord- most productive (i.e. healthiest) ones but they also haus, 1989). The agricultural economy is considered to promise to be the least efficient (i.e. least healthy) be producing efficiently when it cannot produce more (Table 4). of one product without producing less of another, or reaching the maximum desired production under given 5.2.3. Effectiveness resource conditions. Hence, the essence of economic Effectiveness is a concept recently proposed as a efficiency concerns minimising costs while maximis- criterion for assessing agroecosystem health (Wall ing the volume of economic returns or products. et al., 1995; Waltner-Toews and Nielson, 1995). The utility of efficiency concept for assessing the Waltner-Toews and Nielson (1995) define effective- functional health of an agroecosystem is obvious. A ness as the capability of an agroecosystem to meet highly efficient agroecosystem can be interpreted as a the reasonable goals of the stakeholder. This concept more healthy system than an inefficient one. is closely related to the concept of agroecosystem It is clear that the concept of efficiency is closely efficiency, in which the goals of the system are as- related to the concept of productivity. Both concepts sumed. Wall et al. (1995) argue that effectiveness can be used directly for assessing functional health modifies or qualifies the measurement of agroecosys- of an agroecosystem, but efficiency is not equivalent tem efficiency by taking into account the desirability to productivity. Efficiency is always in ratio value, of agricultural outputs. and can only be calculated using a system’s outputs The concept of effectiveness is a notion central to and inputs that share a common unit. Productivity is the evaluation of public policy and resource manage- however often calculated using outputs in one unit (e.g. ment (Mitchell, 1989). In a general sense, it can be mass, Mg) relative to inputs in another unit (e.g. area, referred to as the adequacy of a system to meet cer- ha). Furthermore, a productive agroecosystem may not tain requirements or needs through its processing and necessarily be an efficient one, because it may involve functioning. In economic analyses, the effectiveness in the inefficient use of resources and generate vast is often assumed as a premise upon which economic amounts of waste. efficiency is discussed. This is why the cost effec- In a comparative analysis of agricultural systems, tiveness in a defined economic production system is Bayliss-Smith (1982) provides an excellent example often a measure of the system’s economic efficiency of how these two concepts can be used as central (Samuelson and Nordhaus, 1989). criteria for assessing the health of an agroecosystem. In agroecosystem health analysis, Waltner-Toews Based on energy productivity and energy efficiency and Nielson (1995) argue that the effectiveness cri- as the criteria, the difference among different types terion explicitly includes the ethical and aesthetic

Table 4 The state of agroecosystem health: some empirical evidence Criteria Pre-industrial Semi-industrial Industrial Levels of agroecosystem health agroecosystems agroecosystems agroecosystems Productivitya Low Moderate High Less to more healthy Efficiencyb High Moderate Low More to less healthy Self-dependencec High Moderate Low More to less healthy Stabilityd High Low – More to less healthy a Measured by energy output per hectare. b Measured by energy ratio. c Measured by fossil fuel input per hectare. d Qualitatively measured by considering impacts of the socio-economic and biophysical environments (Bayliss-Smith, 1982). 224 W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 dimensions of human goals and suggest the use of and Schneider, 1991; Waltner-Toews and Nielson, an ‘overlapping consensus’ approach to measure 1995). While this concept is widely used, particu- the goals of decision makers in different levels for larly in ecosystem research, there is no commonly agroecosystem effectiveness assessment. While this accepted definition of integrity. Some define integrity approach seems appealing, they acknowledge that the as the ability of a system to maintain its organiza- analysis can become a complex socio-political task. tion (Kay and Schneider, 1991). Others consider that In their comparative analysis of farmland preser- a system exhibits integrity if it sustains an organis- vation programmes in North America, Furuseth and ing, self-correcting capability to recover toward an Pierce (1982) demonstrate potential utility of the con- end-state that is normal and ‘good’ for that system cept of effectiveness as a criterion for assessing the (Regier, 1993). More generally, Waltner-Toews and health of agroecosystems. With respect to the goal Nielson (1995) claim that a system has integrity when of retarding the conversion of prime agricultural land it maintains its natural, human and economic capital. in the majority of farmland protection programmes, In essence, system integrity means the wholeness they conclude that the comprehensive mandatory pro- in system functioning. Some analysts have thereby gramme, adopted in Oregon, proved to be more effec- argued that ecosystem health is synonymous with, tive than other programmes adopted elsewhere, since even a dimension of, ecosystem integrity (Kay, 1990; evidence showed the reduced rate of farmland loss af- Karr, 1993; Allen et al., 1994). Many researchers are ter implementing the programme. aware that assessing ecosystem integrity requires one to dissect an ecosystem by characterizing its func- 5.3. Organizational criteria tion and structure (Allen et al., 1994). This is the task that agroecosystem health analysts attempt to Biophysical and human attributes beyond an undertake (Waltner-Toews et al., 1993). In this sense, agroecosystem’s boundary have been recognized as agroecosystem integrity should be considered as an driving forces of the system (Smit et al., 1998). These equivalent concept to agroecosystem health rather external factors and interactions among them provide than an analytical criterion of it. a broader environment within which an agroecosystem operates its functions and maintains its structure. 5.3.2. Self-organization They also cause changes in agroecosystem function Self-organization is loosely referred to as the degree and structure. One approach to the health of agroe- to which a system maintains its organization (Kay cosystems is to assess how decisively those exter- and Schneider, 1991; Waltner-Toews and Nielson, nal factors/inputs have influenced the function and 1995). The concept of self-organization originated structure of an agroecosystem. Or alternatively, the from analyses of physical and chemical systems. The approach is to determine if the self-regulation mech- attempt is to understand certain spontaneous behavior anisms of an agroecosystem dominate the realization when the system is unstable or far-from-equilibrium. of agroecosystem functions and the maintenance of The self-organization theory, developed by Prigogine system structure. In essence, the approach is to iden- (1976), provides a framework to describe and explain tify the organizational criteria to assess or evaluate the organizational behaviors of complex systems the health of an agroecosystem. Many concepts re- with a dissipative structure (i.e. the maintenance of lated to this approach exist in the literature (Table 3). system structure is achieved through its continuous However, for some concepts such as integrity and dissipation of energy). The self-organising behavior self-organization, although they are commonly em- occurs in open, far-from-equilibrium systems involv- ployed, their meanings still need to be clarified and ing non-linear, auto-catalytic processes, and large their applicability to agroecosystem health research flows of energy or matter from outside the system remains unjustified. that are dissipated in maintaining its structure (Grzy- bowski and Slocombec, 1988). While the applica- 5.3.1. Integrity tions of self-organization theories to the large scale Integrity is often considered as a concept that cap- ecological and socio-economic systems are growing tures the characteristics of system organization (Kay in the literature, some fundamental questions as to W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 225 the applicability of such concepts to non-physical tegration, and is considered as an essential property systems remain unanswered. For example, is the sys- for assessing the performance of an agroecosystem tem energy analysis an appropriate way of studying (Marten, 1988). ecological and socio-economic organizations where While cross-disciplinary usage of the autonomy human behavior is involved? concept remains vague, the essential meaning of Ecologically, the significance of the self-organiza- autonomy is that a system can absorb the exter- tion concept is tied to recognition of the chaotic nature nal disturbance by self-reorganising its structural of dynamic ecosystems and the role of self-regulation and functional units and continue to function by mechanisms in balancing the relationship between the self-regulating the flows of energy, information, and system and environmental attributes. In agroecosys- materials. Leckie (1989) in a case study on farm com- tem health analyses, the concept of self-organization munity change in Brooke Township, Ontario, demon- is often considered as a measure or subset attribute of strated the potential utility of autonomy for analysing a system’s integrity (Kay and Schneider, 1991; Wall agroecosystem health. Using formal participation and et al., 1995; Waltner-Toews and Nielson, 1995). Kay informal interaction as measures, it was shown that and Schneider (1991, p. 13) state explicitly that ‘(a this particular rural community has remained socially system’s) integrity has to do with its ability to main- quite vibrant (coherent) despite tremendous changes, tain its organization and to continue its process of triggered by the rapid industrialization of agriculture, self-organization. ... If a system is unable to maintain to individual farms and to the earlier social fabric of its organization then it has lost its integrity’. The util- the countryside (Leckie, 1989). Although the concept ity of the self-organization concept may lie in some of autonomy is not directly employed in the above qualitative description of ‘wellness’ of agroecosystem case, the theoretical and methodological approach in organization. However, there is no practical measure the Leckie (1989) study shares much the same line of of the concept. Furthermore, few, if any, have pro- thought as with agroecosystem autonomy assessment. vided empirical examples that demonstrate the applicability of the concept in the context of agroecosystem 5.3.4. Self-dependence/self-reliance research. The discussion of self-organization concept Self-dependence and self-reliance are the inter- largely remains at the conceptual level. changeable concepts that describe a system’s organizational relationship with external environments 5.3.3. Autonomy (Gallopin, 1995). The concept of self-dependence Autonomy is another concept that describes a refers to the degree to which system-generated inputs system’s organizational identity. Autonomy means, lit- contribute to the accomplishment of system function erally, self-law, or self-government, or self-regulation and the maintenance of system structure. It stresses (Varela, 1979). In ecosystem and agroecosystem that to be self-dependent a system should rely on its analysis, autonomy and self-organization are essen- own resources and efforts. Generally speaking, a sys- tially interchangeable terms. While the concept of tem with a high degree of self-dependence means that self-organization is formalized in physics and chem- the functioning and structuring of the system is not istry, the concept of autonomy is popularly used in in- determined by external attributes (Gallopin, 1995). formation and life science as well as in socio-political For assessing agroecosystem health, the utility of studies. In cognitive information research, autonomy self-dependence is multi-faceted. Many have argued is referred to as the generation, internal regulation, that the development of agriculture should not ex- and assertion of a system’s own identity (Varela, cessively depend on human-generated subsidies or 1979). In the field of social impact analysis, auton- damage adjacent ecosystems (Altieri, 1989, 1992; omy of the community is often referred to as the Giampietro et al., 1992). Various observations indicate extent to which it (the community subsystem) is de- that current agricultural practices depend on massive pendent on, or independent of, extra-community units uses of fossil fuel energy and human capital (King, in the performance of its functions (Warrent, 1978; 1990; Altieri, 1992; Dick, 1992). It is suggested Bowles, 1981). In agroecosystem research, autonomy that such biological dependence on non-ecologically is often referred to as the degree of the system’s in- based technology may reduce the capability of the 226 W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 system to sustain its productivity over time, cause the respond are among those considered as the system’s contamination of adjacent environments, and increase dynamic properties (Table 3). the scarcity of non-renewable resources (Brady, 1990; Altieri, 1992). The significance of self-generated bio- 5.4.1. Stability physical inputs for agroecosystem development is Stability is one commonly used concept for assess- well recognized by policy makers at different levels ing the dynamics of agroecosystems, and ecosystems (Brady, 1990), and has led to the development and in general. The concept of stability originated from adoption of low-input and conservative farming prac- ecosystem analysis, where an ecological system is tra- tices in many regions (NRC, 1989). Self-dependence ditionally described in terms of an equilibrium state also represents the desirable economic state of an (Okey, 1996). The definition of ecological stability agroecosystem. For example, excessive economic has been vague (Hills, 1987). Analysts in ecosystem dependence of agroecosystems upon external finan- dynamics research even challenge the existence of a cial subsidies potentially threatens the economic via- single steady-state of an ecosystem and argue that bility of the systems when rapid changes occur in the ecosystems encompass both multiple states of equi- external financial conditions. libria and chaos (Holling, 1986; Schneider and Kay, In studying the relationship between agricultural 1993). However, Holling (1986) definition, i.e. ‘the development and government policies, Pierce (1992, propensity of a system to attain or retain an equi- 1993) found that the economic functions of Canadian librium condition of steady state’, still represents the agroecosystems had been maintained through a va- common ground for defining ecological stability. Dis- riety of financial programs funded by governments cussions on ecosystem stability are also related to the over the last 30 years. For example, the costs of in- disturbances from the environment. As Holling (1986, come transfers to farmers in 1986 were CAN$3.4 p. 296) claims, ‘systems of high stability resist any de- billion (Pierce, 1992), and grain and oilseed produc- parture from that (equilibrium) condition and, if per- tion alone in Canada consumed up to 50% of federal turbed, return rapidly to it with the least fluctuation.’ expenditures on agriculture in the early 1980s (Pierce, Hence, analysing the stress–response relationships in 1993). It was concluded that the level of economic ecosystems can enhance an understanding of the char- self-dependence and therefore the health of agroe- acteristics of ecosystem stability. cosystems had steadily decreased since the 1960s. Agroecosystems are different from natural ecosys- Bayliss-Smith (1982) indicated that the transforma- tems, and are composed of socio-economic dimen- tion from traditional to industrialized agroecosystems sions. The stable development of agroecosystems was associated with a decline in the self-dependence represents a societal goal in agriculture. Agricultural of the systems (Table 4). From the organizational per- stabilization has been the goal of agroecosystem man- spective, such decline means that the modern agroe- agement and public policy initiatives (NRC, 1989; cosystems are less healthy than the pre-industrial ones Troughton, 1992; Pierce, 1993). Hence, from a tem- for they are incapable of generating and providing poral dimension, agroecosystem stability represents sufficient inputs to support the desired productivity. an essential component of agroecosystem health. Defined as production constancy relative to various 5.4. Dynamics criteria stresses, the concept of agroecosystem stability describes the dynamic nature of agroecosystem health. When attempts are made to characterize agroe- In this context, a stable agroecosystem is healthier cosystem health from a temporal point of view, the than an instable one. system dynamics themselves may provide some in- Studies on agroecosystem stability are abundant dication of the state of agroecosystem health. Such in the literature. In studying California agriculture, a temporal dimension of agroecosystem health is Altieri (1992) provided some empirical evidence not necessarily captured by the criteria mentioned showing the instability of the agroecosystem by using earlier. One approach is to directly employ concepts a measure of changing yields of cotton crops from representing the system dynamics as health criteria. 1910 to 1980. Bayliss-Smith (1982) discussed the Agroecosystem stability, resilience, and capacity to stability of different agroecosystems by examining W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 227 qualitative changes in the relationships between the to a more social, recreational, educational, residential systems and their external environments (Table 4). It emphasis, rural communities in Ontario continue to was suggested that the modern agricultural systems function well, and more prominently, the social core have lower stability than the pre-industrial systems of rural communities remains strong (Leckie, 1989). (Bayliss-Smith, 1982). This is largely due to the fact that the industrialized agroecosystems depend 5.4.3. Capacity to respond more upon external inputs and conditions. These ex- Capacity to respond refers to a system’s capacity ternal inputs and conditions are difficult to manage to respond to various stresses. In the field of impact and control, and therefore may threaten the stable assessment, capacity to respond is loosely defined as development of the systems (Bayliss-Smith, 1982; a system’s coping capacity or coping range (Burton Altieri, 1992). et al., 1993). In discussing the properties of agroecosystem health, Gallopin (1995) refers to ‘capacity 5.4.2. Resilience to respond’ as the ability of the system to react to Resilience refers to the ability of a system to main- new situations. According to Gallopin (1995), the con- tain its structure and pattern of behavior in the face cept brings into play both the capacity to change and of disturbance (Holling, 1973, 1986). It is argued the tendencies towards permanence. This interpreta- that resilience emphasizes the boundary of a stability tion for capacity to respond is essentially synonymous domain and events far from equilibrium, high vari- to resilience. Statements that equate capacity to re- ability, and adaptation to change (Holling, 1986). In spond to resilience can also be seen in many ecological the agroecosystem context, resilience refers to the writings (Rapport, 1989, 1995; Costanza, 1992), and ability of an agroecosystem to cope with natural and in agroecosystem health literature (Wall et al., 1995). socio-economic stresses (Waltner-Toews, 1994). It is Most discussions on the concept of agroecosystem also interpreted as the ability to maintain productivity capacity to respond remain at the conceptual level. in the face of stress (Gallopin, 1995). To date, few, if any, have adopted the concept in any Resilience, although recognized as an agroecosys- empirical studies of agroecosystems. Such situation tem property, is similar to stability. While stability may continue to exist since the two concepts discussed focuses on the constancy of the structural and func- above not only capture the essence of agroecosystem tional states of an agroecosystem, resilience describes dynamics, but are also closely related to societal goals the system’s maintenance ability, or more precisely, attached to agroecosystems. the coping mechanisms and strategies of the system. Hence, resilience is related to how the system uses its resources to absorb the external disturbance for 6. Changing agroecosystem health: a case study maintaining its functionality. According to this understanding, some have suggested the use of resilience as Using many case study examples published in the a key component of agroecosystem health (Rapport, literature, the proceeding sections have assessed the 1989, 1995; Waltner-Toews, 1994). Notwithstanding applicability of numerous concepts to agroecosystem the theoretical appeal of the concept, there are dif- health assessment. The framework outlined above il- ficulties in implementing the notion of resilience in lustrates, at a conceptual level, how the health of an the practical analysis of agroecosystem health. Few agroecosystem and its changes can be characterized researchers, if any, have proposed a practical or nu- from a variety of perspectives. While presenting a merical measure of resilience. However, qualitative detailed case study based on the above framework is analyses on agroecosystem resilience still exist in beyond the purpose and scope of this paper, the case the literature. For example, Leckie (1989) concludes study presented here helps demonstrate the real sig- that rural communities in Ontario have been quite nificance of the concept of agroecosystem health, and resilient. Despite rapid agricultural industrialization the utility of the developed conceptual framework to during the past 50 years, rural community systems in empirical analyses to agroecosystem health. the region have been able to adapt to change. Through From a perspective of change in agricultural land a shift from a more traditional economic/retail focus use, the objective of this case study was to investigate 228 W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233

Fig. 2. Study areas: southern Ontario. temporal trends and spatial patterns in the change temporal consistency of spatial units in the analysis, of agroecosystem health in southern Ontario from any subdivision unit, which lacked information on any 1971–1991. Southern Ontario is a major agricultural one of the required variables, was eliminated from the region in Canada (Fig. 2). It contains metropolitan analysis. A total of 319 census subdivisions were in- areas, rural-urban fringe areas, areas of ex-urban res- cluded in this case study. idential development in rural districts, agricultural Three land use indicators, i.e. changes in agricul- heartland, and some physically marginal areas. The tural land availability, land use productivity, and land diversity of the region provided an opportunity for use self-dependence, are used to capture the structural, the identiﬁcation of different patterns and processes functional, and organizational aspects of changes in of change in agricultural land use. Furthermore, many agroecosystem health (see Table 5). The precise mea- concerns have been expressed over the long-term sures of the indicators are listed in column three of sustainability of the southern Ontario agroecosystem Table 5. The results of empirical data analysis are sum- (Brklacich et al., 1991; MacDonald and Bretz, 1995). marized in Table 6 to generalize the spatial patterns of Healthy agroecosystem development could contribute change in agroecosystem health in southern Ontario to the provincial economy and rural community between 1971 and 1991. stability. According to the results of analyses on changes in To facilitate the empirical analysis, data on agricul- land resource availability during the period of 1971 tural land use were derived from agricultural census and 1991, the study area experienced a noticeable de- of Canada, and the information on land use change cline in its improved farmland base (−9%). From this was retained at the spatial unit of agricultural census particular perspective, it is reasonable to argue that subdivision (equivalent to a township). To maintain the overall level of the structural health of the agro- W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 229

Table 5 Characterizing change in agroecosystem health: land use indicators and empirical measures used in a case study of southern Ontario Themes Indicators Deﬁnition of measures Scale of Data source and spatial unit measurements Structural health Change of land Percent change in the area of Ratio Agricultural census of resource availability improved farmland between Canada at the census 1971 and 1991 subdivision level Functional health Change in land Absolute change in the gross Ratio Agricultural census of use productivity value of agricultural products Canada at the census sold per acre of improved farm- subdivision level land between 1971 and 1991a Organizational health Change in land use Change in the proportion of Ratio Agricultural census of self-dependence cropland area sprayed with her- Canada at the census bicides and insecticides be- subdivision level tween 1971 and 1991b a This is calculated based on 1990 comparable price. b An increase in the proportion of cropland area sprayed with herbicides and insecticides over time indicates a decrease of land use self-dependence.

ecosystem has declined noticeably in the study area. change in land use productivity over improved The spatial patterns of change in the structural health farmland as an indicator, the functional health of of the southern Ontario agroecosystem are far from the southern Ontario agroecosystem had improved uniform. Among six conventionally deﬁned regions greatly (CAN$ 347.2 per acre). Spatially, the im- (see Fig. 2), townships in eastern Ontario and the provement of functional health was more apparent ‘golden horseshoe’ experienced the most severe de- in central-western Ontario, the ‘golden horseshoe’ cline in the structural health (<−15% in most town- around the western shore of Lake Ontario, eastern ships), while the improved farmland base in the most Ontario than in the rest of the study region (Table 6). productive southwestern Ontario remained constant. The agriculturally marginal areas in the Canadian Central-western Ontario as a part of agricultural heart- Shield experienced the least improvement in the func- land had a slight decline in its improved farmland tional health of the agroecosystem. It is noteworthy (Table 6). In the rest of southern Ontario, the decline that southwestern Ontario, which possesses the best of improved farmland was moderate (−5to−15%). biophysical conditions for agricultural production, The spatial pattern of change in functional health did not have a marked improvement in its functional was different from the structural changes. Using health in terms of land use productivity.

Table 6 Change of regional agroecosystem health in southern Ontario, 1971–1991a Theme Agroecosystem health change Region A Region B Region C Region D Region E Region F

Structural healthb Constant Slight decrease Severe decrease Moderate decrease Moderate decrease Severe decrease Functional healthc Slight increase Great increase Great increase Moderate increase Slight increase Great increase Organizational healthd Severe decrease Moderate decrease Moderate decrease Slight decrease Slight decrease Moderate decrease a For location of the regions, see Fig. 2. b Slight, moderate, and severe decreases denote a change in improved farmland availability of −0to−5%, −5to−15%, and −15% and less, respectively. c Slight, moderate, and great increases denote a change in land use productivity of CAN$ 0–280, CAN$ 280–400, and CAN$ 400 per acre and above, respectively. d Slight, moderate, and severe decreases denote a change of land use self-dependence according to an increase of 0–10, 10–20, and 20 and above, respectively, in the percentage of crop land area sprayed with herbicides and insecticides. 230 W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233

Changes in land use self-dependence are indicative reality of different human and biophysical phenomena of changes in an agroecosystem’s ability to maintain and processes at a variety scales (Smit et al., 1998). its structure and function. Increasing use of pesticides, Given the nature of agroecosystem health, it is particularly insecticides and fungicides (in this case, not surprising that many concepts and approaches decreasing land use self-dependence) not only brings developed in different disciplines contribute to the about more detrimental environmental effects and understanding of agroecosystem health. However, the presents greater risks to human health, but it also wipes complexity of agroecosystem health cannot be fully out more certain beneﬁcial species, which often lead captured from one perspective only. For any holistic to the emergence of their prey as even more serious investigation of agroecosystem health, which is the pest problem of crop production (NRC, 1989). Inves- emerging position of the health paradigm, analysts tigation into the changes of land use self-dependence may need to examine the conditions of agroecosys- showed that the maintenance of agroecosystem func- tem health from many aspects of the system including tion and structure in the study region had become structural, functional, organizational, and dynamic more and more dependent upon external inputs, i.e. characteristics. pesticides. Overall, the level of the organizational Empirical investigation of agroecosystem health health of the agroecosystem had declined during the can be conducted at different spatial scales. As an period from 1971 to 1991, as indicated by a 16.7% in- initial attempt, the case study presented above demon- crease in the proportion of crop land area sprayed with strates how the conceptual framework described can toxic chemicals. Spatially, the most severe decline of be implemented in agroecosystem health research at organizational health was observed in southwestern a broad regional scale. The case study reveals the Ontario (Table 6), as most townships in this region ex- complexity involved in the change of agroecosystem perienced a greater increase in the use of pesticides to health. The improvement of one aspect of the agroe- maintain agricultural production. In other parts of pro- cosystem, such as increasing productivity and hence ductive areas, including townships in central-western improving functional health, does not promise any Ontario, the ‘golden horseshoe’ area, and eastern enhancement in the other aspects. Such complexity Ontario, a moderate decline of organizational health is also evident in agroecosystems at a village level occurred during the period 1971–1991. The level of (e.g. Bayliss-Smith, 1982) or a regional level (e.g. organizational health declined only slightly in less Smit et al., 1998). There is a need to simultaneously productive regions of central Ontario and at the edge investigate different aspects of agroecosystem health of the Canadian Shield (Table 6). at different scales so that the nature of agroecosystem health can be better understood. 7. Conclusions

Any new ideas and thoughts in agricultural research Acknowledgements are deeply embedded in the experience and lessons generated in the established scholarship and this is We gratefully acknowledge the support of the no exception for the emerging theoretical framework Eco-Research Program of the Tri-Council of Canada, of agroecosystem health. The concept of agroecosys- through the Agroecosystem Health Program at Uni- tem health is ﬁrst based on the approach developed versity of Guelph. We also like to thank Drs. P.D. in agroecosystem analysis, in which the system is Keddie, B. Smit, and R. McBride and anonymous deﬁned at different scales and composed of biophys- referees for constructive comments on the earlier ical, economic, and human dimensions. The concept versions of the article. of health lies in the centre of agroecosystem health assessment. As an evaluative notion, assessing the References health of any system demands a set of criteria relating to the structure, function, organization, and dynamics Ali, A.M.S., 1995. Population pressure, environmental constraints, aspects of the system. Agroecosystem health is thus and agricultural change in Bangladesh: examples from three an evaluative concept intended to integrate a complex agroecosystems. Agric. Ecosyst. Environ. 55, 95–109. W. Xu, J.A. Mage / Agriculture, Ecosystems and Environment 83 (2001) 215–233 231

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