Analysing integration and diversity in agro-ecosystems by using indicators of network analysis

M. C. Rufino 0 1 H. Hengsdijk 0 1 A. Verhagen 0 1 0 M. C. Rufino Plant Production Systems Group, Wageningen University , P.O. Box 430, 6700 AK Wageningen, The Netherlands 1 M. C. Rufino (&) H. Hengsdijk A. Verhagen Plant Research International, Wageningen University and Research Centre , P.O. Box 16, 6700 AA Wageningen, The Netherlands Diversity of farming activities may increase income stability and reduce risks to resourcepoor households, while integrationusing the outputs of one activity as input in another activitymay reduce dependency on external resources. In practice, diversity and integration are poorly defined, and there is no method to characterise them, hampering the exploration of their benefits. We introduce a method based on network analysis (NA) to assess the diversity and integration in farm household systems by using the Finn cycling index to characterise integration of farming activities, and the average mutual information, and the statistical uncertainty (HR) to characterise diversity of flows. We used nitrogen (N) flows in an application of NA to crop-livestock systems of the highlands of Northern Ethiopia. N recycling was low (FCI 3%) in these systems independently of the farm type. Even with improved N management FCI was lower than 10%. Since large amounts of N are withdrawn from the system with the harvests, there are relatively few opportunities for recycling. The diversity in N flows increased from the poor to the wealthier farm households, but differences were small. The wealthier farm households did not recycle more N than the relatively less diverse and poorer farm household. The definition of the system and compartments boundaries must be made explicit in any application of the method as these strongly affect the results. NA appears useful to assess the effects of farm management practices on system performance and to support discussions on diversity and integration of agro-ecosystems. - Farm household systems are agro-ecosystems in which rural households are a central component. Diverse and integrated farm household systems are often associated with sustainable agro-ecosystems (Dalsgaard and Oficial 1997), because diversity and integration enable the realisation of complementarities between different activities and may improve resource use efficiencies. Diversity in farming activities may increase income stability and reduce income risks of resource-poor households (Ellis 2000; Niehof 2004). Integrated farm household systems use the outputs of one activity as inputs in another activity, which may reduce adverse effects to the environment and decrease the dependency on external resources through recycling (Edwards et al. 1993; Vereijken 2002). Cycling of energy and nutrients are considered two of the most important features that confers stability to ecosystem functioning (Allesina and Ulanowicz 2004). In practice, diversity and integration are still poorly defined and, although there have been several studies that focus on integrated agro-ecosystems (Prein 2002; Pant et al. 2005), there is no practical method to characterise, quantify, and assess integration of diverse agro-ecosystems. We define integration in agro-ecosystems as the degree to which the compartments (or activities in such systems) are interconnected by flows of material. In agro-ecosystems that are diverse, the number of options for flows of material is larger than in relatively simple, often specialised non-diverse agro-ecosystems. We introduce and apply network analysis (NA) to quantify the degree of integration and diversity of farm household systems using a set of indicators. NA is basically an inputoutput analysis originally developed in economics (Leontief 1951) that was introduced into ecology by Hannon (1973) to quantify relationships within ecosystems (Fath and Patten 1999). Leontief developed inputoutput analysis to estimate the amount of materials needed to produce a certain quantity of goods. It is applied in systems analysis, which conceptualizes systems as networks of interacting compartments exchanging resources. In farm household systems, it may be used to analyse input output relationships among different compartments or household activities. The flow analysis of Finn (1980), belongs to the early developments of NA where it was used to study throughflow of nutrients or energy, and cycling in ecosystems. The Shannon index, derived from communication theory (Shannon 1948), was introduced in ecology by MacArthur (1955) to evaluate flow patterns in ecosystems. Later, Rutledge et al. (1976) introduced another measure of communication theory, i.e. the average mutual information (AMI) to study the organisation of nutrients and energy flows in ecosystems. AMI has been proposed by Ulanowicz (1980, 1997, 2001) to measure systems organisation, and how the structure of the flows in an ecosystem is refined to increase autocatalysis (Odum 1969). Since the earlier developments of NA, there have been several applications to study ecosystem properties (e.g. Baird and Ulanowicz 1993; Christian et al. 1996; Heymans et al. 2002), but seldom to study agro-ecosystems (e.g. Fores and Christian 1993; Dalsgaard and Oficial 1997; Groot et al. 2003). The objective of this study was to assess the potentials and limitations of NA to evaluate integration of diverse agro-ecosystems, specifically indicators of flow analysis (throughflow, throughput and cycling) and indicators from communication theory (i.e. measures of organisation and diversity) are addressed. We introduce the method, the system conceptualisation and the indicators using theoretical examples to illustrate their meaning. Then we present a case study from the highlands of Northern Ethiopia where the method was applied, and the consequences of different management options for the degree of integration and diversity were explored. We end the article with conclusions on the appropriateness of the indicators to characterise diversity and integration of agro-ecosystems. Materials and methods Network analysis of nutrient flows The NA uses matrices built with the resource flows of the systems under study, and a number of indicators. The resource flows characterise the organisation of the system. In this study, we use flows of nitrogen (N) to perform the NA because this resource is often the most limiting production factor in low-input agriculture, and it canto a large extentbe managed by farm households. The selection of the system boundary depends on the purpose of the study. In the application presented later the system definitions were defined by the resource base of the farm household, which consists of a number of compartments that interact. We used one year as the temporal unit of analysis, because this is a common time horizon for agricultural production. Conceptualising the system After having defined the boundaries of the system/ network, the next steps in NA are to define the n compartments, and to quantify the (...truncated)