Rice crop diversity hasdecreased dramatically in the recent past.Understanding the causes that underlie theevident genetic erosion is critical for thefood security of subsistence rice farmers andbiodiversity. Our study shows that farmers inthe northeastern Philippines had a markedreduction in rice diversity from 1996 to 1998.The ultimate causes were a drought resultingfrom the El Niño phenomenon in 1997 andflooding due to two successive typhoons in1998. The proximate causes, however, includedlocal water control factors, limitations in thehousehold and village-level seedinfrastructure, farm location in relation (...) tothe goods and services necessary to obtainseeds, policies and programs of the Departmentof Agriculture, and the characteristics of therice varieties themselves. The implications ofour study are that genetic erosion is notalways the result of purposeful acts by farmersnor is it necessarily gradual. Improvingon-farm seed technology will stabilize the seedproduction, distribution, and use system andthereby enhance household food security.Ultimately, rice diversity will be improvedonly if diversity is a safe and viable optionfor farmers. Therefore, public policy thatsupports farmers who maintain a diverse set ofcultivars is critical for any on-farmconservation strategy. (shrink)