This chapter outlines an empirical approach to understanding the determinants of farmers' access to, and use of, crop genetic resources (CGR) and the impacts of farmer behavior on crop populations. These are critical to modeling the current status of agricultural biodiversity on farm, as well as in designing and implementing effective programs for the in situ conservation of agricultural biodiversity. Recently, a series of applied studies of farmer seed systems has begun to generate data on local seed systems useful in seeking to understand farm level decisions on CGR

management (Brush, Taylor, and Bellon, 1993; Perales Rivera, 1996; Meng, 1997; Louette and Smale, 1998; Rice et al., 1998; Smale et al., 1999; Aguirre Gómez, Bellon, and Smale, 2000). However, there is still further need to model, document, and understand the human-mediated impacts upon crop populations, utilizing the involvement of applied social science to complement the work of crop breeders, geneticists, biologists, and ecologists. Socioeconomic assessments documenting behavior towards seed selection or exchange, based upon sample surveys and statistical analysis, are one area where further research is required. More work is also needed to document the role of a given crop within a household's set of activities, and the interaction of that crop in the village economy across varying socioeconomic and environmental conditions.

This chapter seeks to articulate some of the practical socioeconomic issues that have arisen in the attempt to understand farm level management of CGR and how these are necessary for the design and implementation of effective strategies for promoting in situ conservation. A case study from applied fieldwork in Mexico is also provided to illustrate the concepts presented. Empirical evidence is presented to demonstrate the type of data to be collected from farm level surveys that is necessary to measure population level processes from farmer behavior.

Deriving a deeper understanding of the factors that determine on-farm management of CGR is necessary for the design and implementation of policies to promote in situ conservation. For the purposes of the discussion here, in situ conservation will be defined as farmer-based maintenance of traditional crops in their fields (also referred to as on-farm conservation). This discussion will not cover wild species related to crops directly, but the maintenance of a traditional cropping system may contain wild relatives, favor geneflow between wild and cultivated species, and contain more complex ecological relationships such as with pests and symbiotic species. Traditional varieties are defined as crop varieties which are products of farmer selection processes and not the result of a scientific breeding program. The starting point for the empirical analysis of crop dynamics is to define the unit of analysis for conservation and for farmer management. This paper will use the definition of a seed lot (provided by Louette and Smale, 2000): the seed saved from a previous harvest for planting in the following year.

In identifying the empirical questions of farmer management of crop resources and the human-mediated impacts on crop genetics, it is important to keep in mind the following basic characteristics of in situ conservation:

(1) The maintenance of crop genetic diversity occurs in a dynamic, evolutionary context.

(2) Local farmer varieties or landraces can be maintained within larger crop populations with flows of genes into and out of such populations.

(3) In situ conservation is decentralized and disaggregated. The potential risks to long-term conservation of CGR are therefore diffuse, especially socioeconomic pressures such as economic development, market integration, and cultural change.

These characteristics provide a starting point for the design of in situ conservation programs, particularly in the ways in which they can complement existing ex situ conservation activities. Three related limitations of ex situ conservation are that (1) accessions are frozen in time, (2) accessions are kept in isolation from population characteristics and ecological contexts, and (3) ex situ collections are centralized in a single location and immune to economic conditions but are thus fragile to loss in fire, loss of power, natural disaster, etc. The dynamic component is a key difference, while an ex situ approach would seek to preserve materials and periodically regenerate them to maintain the original type, the in situ approach would seek to have farmers continuously selecting plants and populations in the face of, for example, pest pressure, climatic effects, or mutations.

The options for intervention and policy planning to conserve agricultural biodiversity can be described in three possible stages: monitoring, mitigation, and preservation. The most basic form of in situ conservation would be to monitor the viability of local crop populations. This starts from the documentation of the de facto conservation that takes place throughout the developing world, often in areas with marginal conditions where improved varieties may not offer superior performance (Brush and Meng, 1998). An intermediate step would be for the mitigation of the loss of local varieties, while seeking to enhance local crop production. These type of approaches have centered around improving local selection techniques or enhancing seed exchange and the seed distribution system, and also include attempts to encourage the integration of local crop populations into the breeding populations selected by formal breeders, often through collaboration with local farmers (MILPA Project, 1999). The most involved form of in situ conservation would entail the planned conservation of specific crop varieties, involving management planning and possibly some form of contract between farmers and conservation managers. A variety of issues remain unresolved for designing the institutions for this form of in situ conservation, including monitoring and compliance, moral hazard issues, and the opportunity costs of other activities.

For the above reasons, the focus of this chapter is not the costs of conservation, but practical issues that arise in the human management of crop populations. The policy relevance is not how to allocate scarce conservation funding between complementary forms of conservation, but specific characteristics of in situ conservation. However, an important contrast to ex situ conservation arises from dynamic nature of planning for future conservation. In ex situ conservation costs and activities can be reasonably forecast into the future given the current state of storage technology. In in situ conservation there is a need to predict from the current situation what risk or constraints will threaten the viability of a targeted crop population.

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