Explaining the spatial scale of campesino agriculture in Mexico: Implications for the supply and conservation of native maize

Mexico is the center of domestication and a center for diversity of maize. Area planted with maize is the country’s largest agricultural land use, mostly planted by smallholder family farmers known as campesinos. Due to the large area they plant with saved seed from native varieties in a wide variety of environments across the country, maize evolution under domestication continues today at a very large scale and under a multiplicity of selection pressures. Campesinos have been considered mainly subsistence farmers. Here we show that subsistence production is insufficient for explaining the scale of the area they plant with maize and on which its contemporary evolution under domestication depends. Our hypothesis is that beyond supplying their own consumption needs, campesinos across Mexico collectively produce maize to respond to the demand of non-maize producing local consumers. Here we quantify the extent of subsistence versus surplus production among campesinos, showing that subsistence production cannot explain the scale of their maize cultivation. Then, we test statistically the association between the scale of maize cultivation and socioeconomic variables that link campesino production to the demand by other consumers and examine the implications of the results for the supply and conservation of native maize in the country. Our results suggest that maize trading linking campesinos to other consumers may be important and widespread. We conclude that there are important opportunities for maintaining maize evolution under domestication at large scale by strengthening local maize markets.