As long as farmers continue to select landraces for cultivation, the in situ conservation that we currently observe will continue, and it is possible that the establishment of a formal in situ programme might not be necessary. In this scenario, an estimate of the value of the resources to the farm households could instead provide a basis for responding to demands for farmers' rights and for the acknowledgement of the roles of farmers in the conservation process rather than them being used as a mechanism to ensure cultivation. However, if the continued cultivation of landraces appears uncertain and if on-site maintenance of a specific target level of diversity is indeed a stated objective, then information on valuation or some other method ranking the landraces from the viewpoint of the farm household could provide crucial information towards estimating the cost of policies to guarantee their existence in the future.
The cost of in situ conservation is the cost of assisting the necessary number of farms in key farming systems to maintain local resources and knowledge in order to maintain the crop evolutionary system of the centre of agricultural biodiversity. It is difficult to estimate the cost because of uncertainties regarding the social and biological status of farming systems and prerequisites for maintaining crop evolutionary systems in some semblance of their natural or historic order. The goal of in situ conservation is not to preserve a given number of alleles or genotypes (i.e. diversity perse) but to maintain an agricultural system which generates crop genetic resistance in a manner similar to the historic system. An object of in situ conservation should be to locate sites to represent a sample of the general eco-geographics zones of the crop in its centre of origin. The lower bounds of such a programme are not known and are probably both crop- and region-specific.
Both biological and socioeconomic data are important for estimating costs of in situ conservation. The dimensions, composition and distribution of land-race populations needed to maintain a crop's evolutionary system comprise the biological data. Obtaining and analysing this type of data for farming systems is likely to be as problematic for agricultural scientists as it has been for bio-geographers and ecologists of 'natural' populations (MacArthur and Wilson, 1967; Tilman and Pacala,1993). A starting point is to identify major eco-geographic patterns of crop populations, but the conservation biology of crops needs to address finer spatial levels. In Turkey, for instance, geographers conventionally divide the country into nine major agricultural zones. It is, therefore, possible to imagine in situ conservation of wheat in Turkey as requiring nine or more locales, depending on the heterogeneity of wheat within each of the nine zones. The number of farms involved in on-farm conservation depends on the degree of diversity that is found within crop populations at various levels (e.g. farms, villages, micro-region, etc.) as opposed to between populations. The exchange of seed between farms and communities is also an important factor to consider. The number of farms necessary to support in situ conservation may be relatively small if most of the diversity at a single location is found within the individual farm store.
On the socioeconomic side, information on any future comparative disadvantages, if any, for a farm household that selects landraces over MVs, other crops, or economic pursuits, is necessary to estimate the costs of in situ conservation. The pressures against landraces may include lower unit costs of production, broad resistance of MVs, and commercial and official factors which favour MVs. How disadvantageous are landraces? Currently, for those farmers selecting them, they are not disadvantageous; on the contrary, landraces are the optimal choice given the multiple criteria used in the varietal selection process. Yield is certainly a primary consideration, but it is only one of several. Bellon (1996) describes how farmers' concerns are met by infraspecific diversity within a crop. He cites five general concerns, environmental heterogeneity, pests and pathogens, risk management, culture and ritual, and diet, which are met by infraspecific diversity Bellon (1996) details specific concerns which explain the persistence of maize landraces in Chiapas, Mexico: drought, lodging, uneven (poor) soils, labour availability, fertilizer availability, yield, storage, use and taste. These concerns can be satisfied in other ways, for instance by purchased inputs (e.g. irrigation, fertilizer, pesticides), but markets in peasant agricultural systems are often unreliable or too costly to change household production strategies (de Janvry et al., 1991). The conclusion from Bellon's and other research (Brush, 1995) is that landraces occupy specific niches in peasant economies and that these niches are difficult to close altogether. Environmental heterogeneity and high household transaction costs for substituting market goods and services for those provided by landraces are important factors in the observed inertia of peasant cultivators who keep selecting land-races.
Currently, there are no costs to bear for in situ conservation in centres of diversity such as Turkey and Mexico because numerous farmers continue to plant landraces, a form of de facto on-farm conservation. Wheat landraces are reported in eight out of nine major agricultural zones in Turkey, with Thrace being the single exception. This de facto conservation could be eliminated if all farmers chose to stop planting landraces or if sufficient numbers stopped, making seed supplies of traditional varieties all but impossible to obtain. However, this scenario depends on investment to create viable substitutions for landraces for the households that now rely on them. These investments include crop breeding for the marginal areas where landraces persist, improving the physical infrastructure such as irrigation, and improving the market infrastructure so as to lower the transaction costs of households. There is also a threat to landraces from farmers shifting out of staple crops or exiting from crop production altogether.
These scenarios for the replacement of landraces appear unrealistic. At present, many of the farmers who cultivate landraces are minimally affected by crop improvement programmes, largely because they till small parcels of land for home consumption in marginal agroeconomic zones. This farm sector can be reached by agricultural development, but most national agricultural research programmes in countries with important genetic resources, including Turkey, lack the means to accomplish this. Public investment historically favours prime production zones rather than marginal ones, and the costs to upgrade the physical and market infrastructure in these marginal and heterogeneous agro-ecosystems are relatively high. At a local level, peasants may have multiple and different reasons for keeping landraces.
Both aggregate and local factors serve to maintain landraces, as much as the pressures of population, technology and market favour their replacement. The future of landraces may depend on relatively small advantages, rather than the strong yield advantages seemingly offered by MVs. Consequently, a relatively small investment in landraces may suffice to maintain their advantage in a particular farming system. The cost of in situ conservation can thus alternatively be expressed as the cost necessary to raise the comparative advantage of land-races above that of competing varieties, crops or off-farm activities. This cost may require a subsidy to one agricultural sector (e.g. producers of landraces in selected regions) but it need not be a direct payment to farmers. Indirect methods are arguably more sustainable for meeting long-term conservation and agricultural development goals.
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