Geographic Influences on Maize Seed Exchange in the Bajío, Mexico*

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Geographic Influences on MaizeSeed Exchange in the Bajío,MexicoKimberlee J. Chambers a & Steve B. Brush ba Willamette Universityb University of California , DavisPublished online: 01 Jun 2010.

To cite this article: Kimberlee J. Chambers & Steve B. Brush (2010) GeographicInfluences on Maize Seed Exchange in the Bajío, Mexico , The ProfessionalGeographer, 62:3, 305-322, DOI: 10.1080/00330124.2010.483624

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Geographic Influences on Maize Seed Exchange in the

Bajıo, Mexico∗

Kimberlee J. ChambersWillamette University

Steve B. BrushUniversity of California, Davis

To document the diversity of geographic (physical and human) influences on seed exchange, an importantcomponent of traditional agricultural systems, household surveys were conducted in four villages in theMexican Bajıo. This research reviews and contributes to an understanding of the purpose, structure, and scaleof seed exchange and threats to seed movement. Based on the household survey data, the main factors thatdistinguish seed exchange at the village level include whether or not the same seed was grown the previousyear, what farmers look for in a seed source, and where they have acquired their original seed. When thehousehold survey data are analyzed based on gender, rather than village, different results are obtained. Wediscuss the diversity of possible influences on the current seed systems in four Bajıo communities surveyedand address the possible consequences for agrobiodiversity conservation. Key Words: agrobiodiversityconservation, Bajıo, globalization, maize, seed exchange.

Los hogares de cuatro aldeas del Bajıo mejicano fueron estudiados con el fin de documentar la diversidadde influencias geograficas (fısicas y humanas) sobre el intercambio de semillas, importante componente delos sistemas agrıcolas tradicionales. En esta investigacion se hace un examen del proposito, estructura, escalade intercambio y obstaculos al movimiento de semillas, para contribuir a su mejor comprension. Con baseen los datos del estudio de hogares, se establecio que los principales factores que distinguen el intercambiode semillas dentro del ambito aldeano incluyen cosas como si la misma semilla fue o no cultivada el anoanterior, que es lo que buscan los agricultores en la fuente de la semilla, y en donde fue adquirida la semillaoriginal. Cuando los datos del estudio de hogares se analizaron por genero y no en terminos de aldeas, seobtuvieron resultados diferentes. Discutimos la diversidad de posibles influencias en los actuales sistemas desemillas de las cuatro comunidades del Bajıo estudiadas y consideramos las posibles consecuencias que esotiene para la conservacion de la agrobiodiversidad. Palabras clave: agrobiodiversidad, conservacion, Bajıo,globalizacion, maız, intercambio de semillas.

∗Partial funding for this research was provided by UCMEXUS, the University of California Davis Geography Graduate Group, HemisphericInstitute on the Americas, The Center for International Agricultural Development, and an Association of American Geographers DissertationResearch Grant. We are grateful to Alfonso Aguirre of INIFAP in Celaya for his assistance, three anonymous reviewers for their valuablecomments, Mark Grote for his critical input with the analysis, and the many people of the Bajıo who provided hospitality and information.

The Professional Geographer, 62(3) 2010, pages 305–322 C© Copyright 2010 by Association of American Geographers.Initial submission, November 2008; revised submission, August 2009; final acceptance, October 2009.

Published by Taylor & Francis Group, LLC.

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306 Volume 62, Number 3, August 2010

S eed distribution is a major component ofagriculture and seed replacement has been

mentioned since before Biblical times (Zeven1999). Seed exchange is a complex process ofnegotiation and reciprocity and is influencedby a variety of socioeconomic, agroecological,and cultural factors (Badstue et al. 2002). Theterm seed exchange, broadly defined, refers tothe movement of plant reproductive materials,including seeds and cuttings, from farmer tofarmer and between and across landscapes.1 Lo-cal exchange of seeds, seedlings, and plant ma-terials is commonly practiced in many agrariansocieties (Synnevag 1997). Although the signif-icance of seed exchange is widely recognized(e.g., see Brush, Carney, and Huaman 1981),until recently little research has been conductedon the movement of native, improved, and im-ported varieties between farmers, communities,and regions (Louette 1995). Understanding thelandscape of seed exchange—the factors thatinfluence it and its significance—is importantfor agrobiodiversity conservation.

Both human and physical geography in-fluence seed exchange. For example, seedexchange systems are typically local, in thatfarmers are more likely to acquire seed fromneighbors, family members, and those farmingsimilar land in terms of agroecological factorssuch as soils, elevation, rainfall, and terrain.This exchange pattern reflects Tobler’s (1970)First Law of Geography: “Everything is relatedto everything else, but near things are morerelated than distant things” (234). Althoughseed exchange patterns appear to conformto Tobler’s Law, it is important to keep inmind that the “small world” phenomena ofglobalization in social and other networks cancreate extensive interconnections in spatialsystems (Watts 1999). Thus, the dynamic na-ture of seed exchange in and across landscapesrequires an equally fluid level of understandingof the geographic distribution of “local.”

To acknowledge the influence of globaliza-tion on his First Law of Geography, Tobler(referenced in Miller 2004) noted in a 1999speech that while the world is shrinking, it is alsoshriveling; relative differences in transportationand communication costs are increasing at mostgeographic scales. When transportation tech-nology was limited to animal or wind power, allpersons could move only at the same speed. In-novations such as the automobile and airplanemake the world much smaller but only if these

technologies are accessible and affordable tothe individual. In effect, globalization might behaving accelerated impacts on seed exchange,exposing farmers to new varieties, landscapes,and social networks; however, even in a rela-tively small geographical area such as the Bajıo,globalization’s influences are not uniform. Therapid dispersal of transgenic maize in Mexicois perhaps the strongest evidence of the im-pact of globalization on maize populations in anational agroecosystem that was heretofore re-garded as relatively slow to change its biologi-cal base (Aquino et al. 2001; Dyer et al. 2009).Understanding the diversity of influences onseed exchange is important for the conserva-tion of agrobiodiversity not only within themaize fields of the Bajıo but in changing agrar-ian landscapes throughout the crop centers oforigins.

This research reviews the current literatureon seed exchange and examines commonlyheld notions of seed transactions in comparisonto data collected in four villages in the Bajıoof Mexico. Here, geographical proximity isaltered with the effects of the global economy,which has resulted in an increasing number ofMexican farmers who migrate for months, ifnot years at a time, to Mexican cities as wellas throughout the United States and Canada.The objectives are to document human andphysical geographic factors that distinguishseed exchange in four Bajıo communities indifferent physiographic regions (mountains,mesa, plains, and valley) and to test whetherseed exchange patterns differ under the in-fluence of the effects of globalization such asoff-farm labor.

Research that contributes to our under-standing of seed exchange systems can beapplied to agrobiodiversity conservation policy(Zimmerer 2006), development strategies foragricultural sustainability, as well as an under-standing of how introduced varieties and poten-tial transgenes can move across the landscape.

Understanding Seed Exchange

PurposeJust as farmers continue to grow a diversityof landraces for a variety of motives, evidenceindicates that they also have varied reasonsfor exchanging seed. In the most basic cir-cumstances farmers exchange seed when they

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Geographical Influences on Maize Seed Exchange in the Bajıo, Mexico 307

are looking for something new or wish toexperiment with different seed (Smale et al.1999; Zeven 1999; Badstue et al. 2002; Bad-stue et al. 2007). Farmers also refresh olderseed stocks with new seed to introduce “freshblood” and boost up “tired seed” (Louette2000). In Guatemala, van Etten (2007) foundthat the main goal of regional seed exchangewas to obtain plant characteristics that arenot easily controlled by farmer seed selec-tion, including growing cycle and plant height.Farmers might also acquire seed because ofseed loss due to climate or storage problems(Brush, Carney, and Huaman 1981; AguirreG, Bellon, and Smale 1999; Badstue et al.2007).

Consequently seed exchange is a mechanismthat maintains and enhances the genetic di-versity and viability of landraces (Berthaud etal. 2002; vom Brocke et al. 2003). Zimmerer(1991) found that in a highland region of south-ern Peru the concentration of cultivars with en-demic distributions in areal clusters is shapedprimarily by seed exchange networks. Seed ex-change allows individuals to maintain only asmall fraction of the crop diversity present(even at the community level and certainly atthe regional level) and to recover lost vari-eties (Bellon 2000). A group of farmers canmaintain more diversity at a lower cost andwith less probability of loss than an individualfarmer. Seed exchange in agriculture thus cre-ates metapopulations that conserve diversity inthe same way that migration and colonizationmaintain diversity in wild populations (Brush2004). Seed exchange has ecological, economic,social, and cultural significance as well as bi-ological significance (Pionetti 2005). It allowsfarming systems to continue to evolve and adaptto changing local environments. Furthermore,seed transactions can play a role in buildingsocial capital and might ensure that no oneleaves land fallow for lack of seeds (Pionetti2005).

StructureThe structure of seed exchange is often com-plex and not easily generalized. It is usually in-formal and based on a variety of social networks,family relations, and transactions (Oldfield andAlcorn 1987; Smale et al. 1999; Zeven 1999;Tripp 2001; Badstue et al. 2006). Badstue et al.(2006) found that seed flow among farmers

in the Central Valleys of Oaxaca is influencedby a variety of social relations, agro-ecologicalconsiderations, and cultural factors. VanEtten (2007) found that communities at loweraltitudes in Guatemala exchange seed morefrequently, a factor that gives geographicaldirectionality to seed exchange patterns. Soleriet al. (2005) noted that seed exchange patternscan vary even within communities betweenthe extremes of never using off-farm seed tofrequent reliance on external seed sources.

Depending on the region, particular farm-ers might supply seed for the majority ofcommunity members, whereas elsewhere theremight be no specialized individuals or net-works. Berthaud et al. (2002) and Badstue et al.(2006) found a lack of structured networksamong maize farmers in the Oaxaca Valley ofMexico. In comparison, in Bolivia and Peru,Thiele (1999) found communities specializedin the production of quality seed form nodalpoints in seed flows that reach farmers throughlocal and personal contacts. On the DeccanPlateau of central and southern India, Pionetti(2005) noted that a few families are well knownfor their skill and success in seed keeping. Eliaset al. (2001) found that in French Guiana simi-lar trends characterize the exchange of cassavacuttings; certain families never interact, oth-ers are in the position to give cuttings, andothers are constantly in need, thus definingwhat the authors refer to as sources and wells.Brush, Carney, and Huaman (1981) noted a ge-ographic component to seed exchange centersas farmers in the wetter and relatively frost-free eastern Andes export seed to communitiesbordering the high, cold, and dry plateaus ofthe western ranges. Van Etten (2006b) foundthat maize exchange in Guatemala tends to oc-cur along the lines of preexisting social con-tacts both inside and outside local communitiesand that frequency of the contacts influencesthe rate of seed exchange. Kinship-based path-ways can also be significant for seed exchange(Nazarea 2005).

The cultural and social influences on seedexchange and importance of these networkshas not been widely documented. Soleri et al.(2005) have found differentiation in seedexchange practices in Guatemala. Pionetti(2005) noted that in semi-arid India, individualwomen’s seed work merges with practices ofseed exchange at the community level to forma localized seed economy and that the transfers

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of resources promote social networks basedon reciprocity and cooperation that extend farbeyond kin and caste relations. Regardless ofa lack of literature documenting the culturaland social significance of seed exchange, it islikely that it has played an important role inuniting communities and sustaining culturalpractices.

Research has stressed the importance of in-formal seed exchange systems (Cromwell 1990;Almekinders, Louwaars, and Debruijn 1994;Sperling, Heidegger, and Buruchara 1995;Thiele 1999; Seboka and Deressa 2000; Tripp2001; Nazarea 2005; Badstue et al. 2006), whicheffectively supply farmers with seed withoutgovernment or corporate involvement. For ex-ample, in Ethiopia over 80 percent of the na-tional seed demand is met through the informalsystem of local seed maintenance and exchange(Seboka and Deressa 2000). In comparison,Badstue et al. (2006) and Badstue et al. (2007)noted that seed exchange in the Central Valleysof Oaxaca often involves small quantities andtakes place primarily between people who haveprior knowledge of each other and often feel asocial obligation toward one another. Whetherin large or small quantities, seed exchange canbe significant for maintaining crop diversity.

ScaleTwo general patterns of seed exchange are de-scribed in the literature: local and long distance.The trend in the literature appears to reflect anoriginal focus on local exchange with an in-creasing recognition of the importance of re-gional or long-distance seed movements. Forexample, Johannessen, Wilson, and Davenport(1970) and Johannessen (1982) found that inhighland Guatemala maize seed exchange ismainly local in scope. Similarly, Smale et al.(1999) stated that maize seed exchange in theCentral Valleys of Oaxaca, Mexico is primar-ily local farmers exchanging with a neighbor orfamily member in the same community.

In comparison, an increasing body of litera-ture draws attention to the acquisition of seedoutside the community (e.g., Louette 1995;Louette, Charrier, and Berthaud 1997; Perales,Brush, and Qualset 2003; Perales, Benz, andBrush 2005). Indeed, research in different farm-ing systems reports that farmer seed flows crossinternational boundaries (Valdivia et al. 1998;Brush and Perales 2007; Pujol et al. 2007).

Buerkert et al. (2006) argued that the rela-tively rare presence of triticale in the Hin-dukush Mountains of Afghanistan is an indi-cation of active seed exchange with lowlandor long-distance seed sources. Using geneticanalysis, Berthaud et al. (2002) found evidencefor movement of maize varieties up to 100 kmfrom the Central Valley of Oaxaca. Brush, Car-ney, and Huaman (1981) noted that traditionalseed distribution for Andean potatoes involvingyearly treks on foot of up to 50 km to seed pro-ducing areas has been supplanted by trucks andcentralized markets, but seed still moves overthe same range.

Louette and Smale (2000) note evidencethat farmers exchange maize seed within theircommunities as well as throughout a widerregion, but other researchers observe local andregional exchange that diminishes with dis-tance (van Etten 2007; van Etten and De Bruin2007). Zimmerer (2003) demonstrated theinterdependence of multiscale procurementnetworks for seed resources and addresses scaleto specific environmental factors (agroecolog-ical range) and social factors (gender roles,level of social organization). Zimmerer addedthat scale-related differences exist in the seedprovisioning roles of male and female farmers.

The history of agricultural evolution anddevelopment is closely bound to the move-ment of seed. Thus, the movement of bothpeople and seed in pre-European times spreadmaize from southern Mexico northward asfar as southern Ontario, Canada, and theeastern United States and southward to Chile.Since the mid-twentieth century, agriculturaldevelopment programs, such as the GreenRevolution; rural development, such as roads,markets, and expansion of credit facilities; andcommercial development, such as the rise ofinternational seed companies, have expandedand accelerated the spread of seed from differ-ent places. Informal seed exchange networksplayed an important role in the movementof Green Revolution varieties and, as result,Tripp (2001) argued, it is thus misleadingto speak strictly of community seed systems.Similarly van Etten (2006a, 2007) found that inthe highlands of Guatemala, modern varietieswere mainly obtained outside the communityand generally are more common in areas ofhigher agricultural potential. Seed exchange,thus, historically and currently includes local,regional, and international movements shaped

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by a diversity of human and environmentalfactors.

ThreatsAlthough informal, seed exchange systemscan be dynamic and efficient; they mightsuffer significant weaknesses in incentives,information, and resources. A diversity offactors threaten to reduce seed exchange orchange its nature. Sperling and Loevinsohn(1993) documented a shift away from gifts tomore commercial transactions and possiblytoward involving smaller quantities of seed pertransaction. David and Sperling (1999) notedthat the importance of gift giving appears tobe declining in many localities. Pionetti (2005)suggested that growth of the commercial seedsector has had a profound impact on local seedexchange systems and where commercial cropshave displaced subsistence crops, the practiceof saving seeds itself is disappearing, seed ex-changes having stopped long before. Zimmerer(2003) and Soleri et al. (2005) have observedthat increased participation in nonfarm labormarkets might be the most obvious threatto seed exchange. Parzies, Spoor, and Ennos(2004) noted that the improved mobility offarmers and the presence of extension workerscan facilitate seed exchange of barley overlonger distances, consequently jeopardizing lo-cally adapted landraces. Current approaches toconservation could have similar consequences.Zimmerer (2003) noted that current methodsfor conserving agrobiodiversity in situ do notaccount for the multiscale geographies of seedflow.

Conversely, the use of informal seedexchange systems is being promoted fordevelopment in some instances. Seboka andDeressa (2000) argued for the transformationof indigenous social networks as a complementto national seed industries, a point made also byAlmekinders, Louwaars, and Debruijn (1994),who urged integrated approaches for improv-ing seed supply for small farmers. Hailye etal. (1998) have noted that nongovernmentalorganizations and relief agencies have playedan important role in emergency seed supplyfor survival during natural disasters but thatdistributing free seed creates dependencyand disrupts local farmer-to-farmer seedexchange.

Research in el Bajıo, Mexico

The literature review on seed exchange pro-vided a number of lines of geographic inquirythat guided research in the Bajıo. Research inareas where industrial and traditional agricul-ture coexist, such as the Bajıo, can help de-termine whether farmers practicing differenttypes of agriculture have different reasons forexchanging seed. Important questions emerg-ing from the literature on the structure ofseed exchange include whether seed transac-tions in the Bajıo are both formal or infor-mal, if nodes or seed sources exist within eachvillage, whether there are gender differencesin seed exchange practices, and how exchangein industrial agriculture might differ from thatin subsistence-oriented agriculture. Addition-ally, what is the scale of seed exchange in theBajıo and do different patterns exist in the fourvillages? Finally, we sought to understand ifthe expansion of industrial agriculture in theBajıo and labor migration from small farmsposed similar threats to the local and infor-mal seed exchange networks that have beenobserved elsewhere. The discipline of geogra-phy, with its highly interdisciplinary focus onhuman–environment interactions, has the op-portunity to contribute to our understandingof seed exchanges—purpose, structure, scale,and threats—by addressing questions such asthese.

Study AreaLocated in the heartland of Mexico and en-compassing parts of four states (Guanajuato,Jalisco, Michoacan, and Queretaro), the over-all landscape of the Bajıo is one of open plainsinterrupted by mountains. Although the wordBajıo means lowland, its elevation is on averagebetween 1,500 and 2,000 meters above sea level(Figure 1).

There are not sharp altitudinal variationswithin or among the four communities sur-veyed, however, the environments are diversein more than just access to irrigation. Table 1outlines the variations in climate, precipitation,freezing days, and average temperatures, whichresult in a diversity of agricultural potentialfrom none to high as suggested by the existingnatural plant communities. Butzer and Butzer(1997) divided the vegetation of the Bajıo into

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Figure 1 Elevation map of the approximate area of the Bajıo, located in the states of Guanajuato,Queretaro, Michoacan, and Jalisco. Elevation is not to scale but has been accentuated to emphasizecontrasts. Sources: Elevation data hole-filled seamless SRTM data V1, 2004, International Center forTropical Agriculture (CIAT), available from http://gisweb.ciat.cgiar.org/sig/90m data tropics.htm.

five vegetation communities: riparian wood-lands of mesquite, bald cypress, and willow withreed stands; vertisolic plains with a low-tree sa-vanna; steeper piedmont plains with stony sub-

strates; rough uplands with a mix of mesquite-acacia woodland, scrub oak, and thorn bush;and mountains dominated by live and decidu-ous oak woodlands. To aid in site identification

Table 1 Topographic, environmental, and demographic comparisons for the four villages studied

Area of Survey

Santa CruzFeature Bajıo de Bonillas Ojo de Agua San Juan Viejo de Gamboa

Physiographya Plains/hills Mountains Valley/plains Mesas/hillsElevation 1,790 m 2,050 m 1,850 m 2,010 mPopulationb 2,732 787 927 757Distance from nearest

urban center6 km 18 km 7 km 16 km

Road conditions Paved road Rough roads Paved road Rough and pavedApproximate travel

time to urban center15 minutes 45 minutes 20 minutes 45 minutes

Irrigation Minimal irrigation No irrigation Irrigation Minimum irrigationClimatea Semidry, rain in

summerSemidry, rain in

summerDry, chance winter

rainVery dry

Precipitationa 600–800 mm 600–800 mm 600–800 mm 600–800 mmFreezing daysa 10–20 days 10–20 days < 10 days > 30 daysAverage temperaturea >18◦C 16–18◦C > 18◦C 16–18◦CVegetationc Mesquite, thorn

bush, seasonalagriculture,induced pasture

Dense deciduousshrub, seasonalagriculture

Riparianwoodlands,irrigatedagriculture

Mesquitewoodlands,cactus scrub,irrigated andseasonal agric

aSource: Secretaria de Programacion y Resupuesto, Coordinacion General de los Servicios Nacionales de Estadistica,Geografia e Informatica (1980).bSource: Census data, 2000.cSource: Personal observations and classification based on Butzer and Butzer (1997) combined with information fromSecretaria de Programacion y Resupuesto, Coordinacion General de los Servicios Nacionales de Estadistica, Geografiae Informatica (1980).

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and description we combined the two plainscategories.

Agricultural production in the Bajıo includesboth traditional and industrial agriculture alongwith combinations of both. The Bajıo was notan agricultural landscape until after the middleof the sixteenth century when the plains weredeveloped to produce food for the nearby min-ing communities such as Guanajuato and Za-catecas. At this time the Bajıo became known as“the granary of Mexico” (el granero de Mexico).Today the Bajıo is a center of industrialization,with strong export-oriented agriculture dom-inated by modern varieties of cereal and cashcrops. Nevertheless, approximately 90 percentof farmers in the Bajıo are poor and occupyonly about 10 percent of the land. Located be-tween Mexico City and Guadalajara, the Bajıois experiencing increased population pressureand industrial expansion. Additionally, the stateof Guanajuato has Mexico’s second highestlabor migration to the United States (Smith2003).

The coexistence of traditional and modernagricultural systems in the Bajıo creates a com-plex and dynamic landscape of crop diversitythat is not easily explained by the simple re-placement of farmers’ (landrace) varieties (criol-los) with hybrid or modern varieties (hıbridos)(see Chambers et al. 2007). Despite market in-tegration, cash cropping, advanced infrastruc-ture, a predominance of modern crop varieties,and a high rate of outmigration, farmers inthe Bajıo continue to grow traditional vari-eties of maize (Aguirre G., Bellon, and Smale2000) principally for subsistence and domesticconsumption.

Method

Survey MethodsHousehold surveys were conducted in four vil-lages representing the four principal physio-graphic regions of the Bajıo (mountains, mesa,valley, and plains; see Table 1). Surveys werestructured to cover a representative sample offarms and villages providing a wide range ofgeographic, agroecological, agronomic, and so-cioeconomic diversity in areas where maizeis an important crop. In each village, thirty-five households were randomly selected fromlists of mestizo ejidatorios.2 The surveys were

completed between September and Decem-ber 2004 with a male and female from eachfarming household being interviewed simulta-neously and separately. The total number ofsurveys is 279.

Survey questions combined both open-ended and categorical questions. Questions re-lating to seed exchange and seed managementfocused on where seed has been obtained, whoexchanges seed, methods of exchange, why seedis exchanged, and attributes of seed sources.The questions covered both the seed exchangebehavior of the interviewee and the perceivedactions of other farmers in the community. Itis possible that informants are more willing todescribe their neighbors’ behaviors than theirown. Supplementary questions related to fac-tors that influence seed exchange such as off-farm employment, access to irrigation, numberand size of plots (indication of larger agricul-ture production areas), and whether crops otherthan maize were grown.

AnalysisClassification trees were used to analyze house-hold survey data. The goal of classification treesis to predict or explain responses on a categor-ical dependent variable to express knowledgeand aid in decision making (Venables and Rip-ley 2002). These trees help us understand therole of independent variables, such as village, onwhether or not farmers exchange seed. Classifi-cation trees accomplish this by repeatedly split-ting the data into more homogeneous groups,using combinations of independent variablesthat can be categorical, numeric, or both.De’ath and Fabricius (2000) noted that classi-fication trees are particularly effective becausethey combine flexible and analytical methodsthat can deal with nonlinear relationships, high-order interactions, and missing values, as wellas being simple to understand and providing in-terpretable results. We use classification treesto show key variables, and response categoriesof these variables, which best distinguish house-holds of different villages and gender. The treesrely on a statistical procedure that optimizesclassification using a small set of relatively in-formative variables, reduced from a larger setof seed exchange and management variables (inthis case forty-seven). The statistical softwareR (R Development Core Team 2005) “rpart”

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function was used for classification. Twenty-one variables relating to seed exchange and seedmanagement were used in the analysis.

Cost-complexity pruning, first introduced byBreiman et al. (1984), was used to perform vari-able selection. The purpose of pruning was toreduce the number of variables used in theclassification trees to those that are most op-timal. Cost-complexity pruning evaluates thetrade-off between accuracy of classification andtree complexity, as measured by the numberof variables used in the tree, aiming to limitthe tree to a few good classifiers. Beyond acertain number of variables a point of dimin-ishing returns is reached with the remainingvariables having relatively little discriminationpower.

In the four villages surveyed we found thatfarmers differentiate maize primarily on thebasis of color: white, yellow, red, black, andpurple. White maize is preferred and domi-nant. Farmers referred to a diversity of vari-eties as the generic name local white (criolloblanco), but in some villages, they specificallyrecognize a few other white varieties, such asPancho Villa, Prieto, and Pipitillo. White po-zolero is also a criollo (local) type but is rec-ognized separately for its large, fat grains andgrown specifically for a special soup (pozole).Table 2 summarizes the number of white maizevarieties grown in each village. Because ofthe dominant position of white maize (differ-entiated as local [criollo] or hybrid/improved[hıbrido]), only white maize was used for thepurpose of analysis. Four surveys were omit-ted because the farmers did not grow whitemaize.

Results and Discussion

Figure 2 and Figure 3 present classificationtrees for seed exchange and seed managementvariables for four villages in the Bajıo of Mex-ico. The uppermost variable in each representsthe root node or classifier, which best differen-tiates between the villages (Figure 2) or gender(Figure 3). A classifier is a particular value of avariable or a range of values of a variable thatis characteristic of one or more of the villages.The branch length between variables is pro-portional to the error in the fit. Short branchlengths indicate relatively little additional dis-

crimination contribution by the variable rela-tive to the error in just using the root. Countsat the terminal points (e.g., 8/44/3/30) repre-sent number of observations having the par-ticular pattern of variables given by followingthe classification tree from the root node tothe terminal point in question. Counts corre-spond to the villages in the order Bajıo de Bonil-las/Ojo de Agua/San Juan Viejo/Santa Cruz deGamboa.

The classification tree presented in Figure2 represents the most distinguishing classifiersfor seed exchange at the village level. Theroot classifier for the villages is in responseto the question “Did you sow the same seed thisyear as last year?” (Same Seed Sown PreviousYear in Figure 2). The answer to this questiondistinguishes farmers from San Juan Viejofrom farmers of the other villages, with a largemajority of San Juan Viejo households sur-veyed sowing different white maize seed fromthe previous year (fifty-five of seventy farmerssurveyed did not sow the same maize last year).In the villages of Bajıo de Bonillas, Ojo de Aguaand Santa Cruz de Gamboa, farmers who didnot sow the same seed the previous year are six-teen, four, and four respondents, respectively.

If a farmer saved and resowed maize seedfrom the previous year, the next most distin-guishing variable is from the question “Whatfactor is the most important when choosing awhite maize variety to sow?” (Important Fac-tors for Seed Sources in Figure 2). Farmerswere asked to select from responses that werebased on a literature review of what farmerslooked for when they change seed. Berthaudet al. (2002) noted that in Oaxaca farmers listedthe following considerations before enteringa seed transaction: origin in the same region,the seller’s trustworthiness, the owner’s will-ingness to sell seed, and production objectives.In our study, the response categories were fromthe same area, higher yield, drought tolerance,comes from a good farmer, and other. The tworesponses that discriminate best are that seedcame from a good farmer or other trustworthysources. Farmers were asked to specify what“other” referred to and seventeen farmers inthe village of San Juan Viejo responded withthe broad term of Ingeniero agronomo. This termwas used to refer to an agricultural scientistor agronomist, usually representative of a seedcompany or a government extension agent, but

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Table 2 White maize varieties grown by households in each village (based on farmers’ classifications)

Bajıo de Bonillas Ojo de Agua San Juan Viejo Santa Cruz de Gamboa

Farmer variety name Male Female Male Female Male Female Male Female

Hybrid maizea 13 11 0 0 32 30 4 1White criollo 31 29 35 35 3 5 25 31Pancho Villa 0 0 1 0 0 0 0 0Prieto 0 0 0 0 1 1 0 1Pipitillo 0 0 0 0 0 0 11 4White pozolero 7 2 0 0 0 0 1 0

aRefers to a number of varieties from different seed companies.

also was used to refer to sales representativesfrom major seed companies typically identifiedby the farmers as Monsanto brands Asgrow,Lince (an Asgrow brand of seed), and DEKALBas well as Cargill and Pioneer. In the villages ofOjo de Agua and Santa Cruz de Gamboa theterm “other” was defined by farmers to meanthat they would go to whomever had the bestseed sources. For Bajıo de Bonillas, the eighteenrespondents selecting “other” were divided be-tween the person with the best seed and whatan Ingeniero agronomo (or the equivalent of) sug-gested. Factors that are important for choosinga new variety varied from community to com-munity with the most important being higheryield (see Table 3). Thus, the purpose for seed

exchange is influenced by yield expectations asmuch as the source of seed; however, the source(from a good farmer, same area) might providean indication to farmers of yield potential. Forthe frequency of each response see Table 3.

If the preference is for white maize seedfrom a good farmer or other, then the villagemost clearly distinguished is Bajıo de Bonil-las. For Ojo de Agua and Santa Cruz de Gam-boa factors such as drought tolerance, higheryield, and seed from a similar area are moreimportant. Both the root node (Did you sowthe same white maize seed this year as lastyear?) and the second most distinguishing clas-sifier (What factor is the most important whenchoosing a maize variety to sow?) reflect the

Figure 2 Classification tree for household survey data based on villages.

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Figure 3 Classification tree for household survey data based on gender.

purpose of seed exchange. Not sowing the sameseed as the year before indicates frequent seedflows. Frequent seed flows were more charac-teristic of the village of San Juan Viejo, which islikely a reflection of the dominance of moderncommercial agriculture.

In San Juan Viejo almost all households sur-veyed planted hybrid varieties of white maize.This is in contrast to the relative absence of hy-brids in the remaining villages. In Ojo de Agua,no households planted white hybrid maize seed,and four males and one female in Santa Cruzde Gamboa indicated that they planted hybrids.In Bajıo de Bonillas, thirteen males and elevenfemales reported this practice. (For a compar-ison of the number of farmers in each villagewho planted hybrids, farmer varieties of whitemaize, or both, see Table 2.)

The decision to plant white hybrid varietiesof maize appears to be closely associated with

the nature of agriculture. In Bajıo de Bonil-las, four households surveyed stated that theyhad access to irrigation compared to San JuanViejo with 100 percent having irrigation, andin Ojo de Agua and Santa Cruz de Gamboa100 percent did not. San Juan Viejo’s locationin the Lerma River Valley, the only perennialriver in the Bajıo, gives the community a uniquegeographical location for the development ofmodern agriculture. Thus, seed flows in SanJuan Viejo likely differ from transactions in thethree other villages with more traditional agri-culture (absence of irrigation, smaller plot sizes,and less productive agricultural land) that donot feature commercial varieties. The house-holds surveyed in San Juan Viejo tended to havefewer plots than the other three communitiesbut, with the exception of Ojo de Agua, whichhad on average the least number of hectares perhousehold, was similar to the other villages in

Table 3 Frequency of farmers’ responses to the question “What factor is most important whenchoosing a maize variety to sow?”

Village Drought tolerance Good farmer Higher yield Same area Other

Bajıo de Bonillas 5 24 11 10 18Ojo de Agua 5 2 30 25 8San Juan Viejo 10 7 32 2 17Santa Cruz de Gamboa 10 4 30 17 8Total responses 30 37 103 54 51

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Table 4 A comparison of number of plots and area cultivated by household for each of the villagessurveyed

Bajıo de Ojo de San Juan Santa CruzPlot characteristics Bonillas Agua Viejo de Gamboa

Average number of plots per household 2.5 2.5 1.5 4.5Range in number of plots per household 1–6 1–4 1–5 1–9Average area cultivated per household (hectares) 6.5 4 7 8Range in total area cultivated per household (hectares) 0.5–26.5 1–12 1–19 2.5–8

Note: The data presented in this table are first averaged between the male and female respondents for each household.We found in our surveys of men and women from the same household that the number of plots in cultivation was notalways the same for each respondent per household. For a further discussion of the differences in data for men andwomen from the same household, see Chambers and Momsen (2007).

the area of land cultivated in maize (see Table4 for a comparison of the average number ofplots and area cultivated in each village).

The situation in San Juan Viejo might in-creasingly reflect what Pionetti (2005) notedwhere the growth of the commercial seed sec-tor results in the disappearance of informal seedexchanges. Of the farmers in the village of SanJuan Viejo, 54 percent of men and 74 per-cent of women indicated that their householdswere growing maize, and sometimes sorghum,for commercial production. Other informantsin the community, such as an owner of agrain storage facility and a political represen-tative, told us that everyone in the communitygrew maize for commercial sale. In Bajıo deBonillas only 50 percent of men stated thatthey sold maize, compared with 60 percentof women. The numbers growing maize forsale were below 50 percent in the remainingtwo communities: Santa Cruz de Gamboa, 40percent of men, 46 percent of women; Ojode Agua, 29 percent of men, 60 percent ofwomen. We also asked interviewees if theyreceived income through retail activities, sell-ing of crafts, or other sources of income fromthings such as cheese and tortilla sales, but veryfew people indicated that they had any incomesources other than off-farm labor or the sale ofcrops.

The villages of Bajıo de Bonillas, Ojo deAgua, and Santa Cruz de Gamboa are located inregions dependent primarily on rain-fed agri-culture, and hybrid maize is correspondinglyabsent, whether because it cannot grow with-out irrigation or because it is not competi-tive with local seed. In several places in theBajıo reservoirs were previously excavated (e.g.,

Santa Cruz de Gamboa), however, many of thereservoirs are silting up, and there is increas-ing pressure from industrial development, re-sulting in additional loss of water quality andquantity. In Santa Cruz de Gamboa we weretold that the government took the pump awaywhen the community members could not affordthe fees for it and now only the wealthy fam-ilies with their own pumps have access to thereservoir for irrigation. Thus, both the physicaland human geography of these landscapes is in-fluencing the varieties of maize grown and thusthe seed acquisition practices. For a further dis-cussion of the role of irrigation in shaping themaize landscape of the Bajıo see Chambers et al.(2007).

The third most distinguishing classifier atthe village level for seed exchange is “Wherefarmers originally got the seed that they arecurrently sowing?” (Seed Source in Figure 2).Again categories for responses were providedbased on a literature review (father, neighbor,other village, and agricultural store). If respon-dents primarily indicated that it was importantfor seed to come from a good farmer or othertrustworthy source, then along with a posi-tive response for the root classifier, this dis-tinguishes famers from the village of Bajıo deBonillas from other farmers. If they originallygot their seed from their father or parents3 oranother village then they are likely to be in Ojode Agua, whereas if they got seed from a neigh-bor or an agricultural supply store then they arelikely in Santa Cruz de Gamboa (see Table 5for frequencies). Similar studies by others suchas Badstue et al. (2007) note that when house-holds start farming on their own they usuallyget seed from parents or other close relatives.

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Table 5 Frequency of farmers’ responses tothe question “Where did you originally get theseed that you are currently sowing?”

Other AgricultureVillage Father Neighbor village store

Bajıo de Bonillas 18 31 7 12Ojo de Agua 48 16 6 0San Juan Viejo 7 6 9 44Santa Cruz de

Gamboa37 30 2 0

Total responses 110 83 24 56

This classifier reflects both the structure andscale of seed exchange.

To investigate the process of seed acquisitionand the influence on structure of seed systems,we asked farmers how they would acquire newseed—through exchange (nonmonetary froma neighbor or family member), purchase, orother.4 In Bajıo de Bonillas, more farmers in-dicated that they exchanged seed (see Table 6)than the other three villages. In the other vil-lages the majority of the farmers indicated thatthey purchased seed or acquired it from anothersource such as an Ingeniero agronomo (explana-tion given earlier). Similar practices are notedby Tripp (2001), who observed that farmersoften have to pay cash if receiving seed from aneighbor. These results are an indication of thedifficulty with simply referring to maize seedflows as exchange. When asked about the lasttime they received seed from a neighbor with-out paying for it, the average was three to fouryears for all villages. Furthermore, farmers in-dicated that they regularly gave or lent seed toother farmers as frequently as each year (seeTable 7). Thus, similar to the findings of Rice,Smale, and Blanco (1998) and others, frequentseed movement is ubiquitous but can be diffi-cult to document because of farmers’ perspec-

Table 6 Responses to the question “If youneeded new white maize seed how would youacquire it: exchange, purchase, or other?”

NoVillage Exchange Purchase Other maize

Bajıo de Bonillas 36 32 0 2Ojo de Agua 10 51 9 0San Juan Viejo 3 63 2 2Santa Cruz de

Gamboa18 46 5 0

Total responses 67 192 16 4

Table 7 Number of farmers that participated inseed exchange

Gave seed last Lent seed last NoVillage year (2004) year (2004) maize

Bajıo de Bonillas 56 25 2Ojo de Agua 56 28 0San Juan Viejo 55 9 2Santa Cruz de

Gamboa42 34 0

Total responses 209 96 4

tives on the source of the crops that they aregrowing and results of seed transactions.

To determine the geographic locations(scale) of seed exchange we asked where farm-ers acquired seed. Most responded from thevillage where they live. When we asked farm-ers how far they would be prepared to travel toobtain maize seed (see Table 8), however, wereceived a greater diversity of locations and dis-tances. For Bajıo de Bonillas, farmers are will-ing to travel on average 10 km. In San JuanViejo, farmers are primarily growing modernvarieties and acquire seed from an Ingenieroagronomo who come to the village from thenearest city, Acambaro (7 km away), to marketdifferent brands of seed. Farmers in this vil-lage, however, indicated that they would seekseed, on average, up to 32 km away, exclud-ing the two farmers who stated that they wouldbe willing to get seed from anywhere in theworld. For Santa Cruz de Gamboa and Ojo deAgua, farmers would travel 22 km and 13 km,respectively.

These results support findings by Louetteand Smale (1996) and Zimmerer (2003) thatseed flow is not circumscribed by the householdand community. Nor does it appear that farm-ers strictly seek similar microenvironmentswhen searching for replacement seed or seed totry. Even villages at the greatest distance frommajor urban centers, Ojo de Agua (18 km onrough roads, approximately forty-five minutestravel time by car) and Santa Cruz de Gam-boa (16 km on rough and paved roads, approx-imately forty-five minutes travel time by car),with low agricultural potential, absence of ir-rigation, hilly terrain, and rocky soils, farmersare willing to travel beyond the local commu-nity and neighboring villages to seek out othersources of seed. (See Table 1 for comparison ofdistances, road conditions, and travel times for

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Table 8 Villages and frequency of responses for the greatest distance farmers are willing to travel formaize seed

Bajıo de Ojo de San Juan Santa CruzBonillas Agua Viejo de Gamboa

Number of destinations 10 11 7 11Median distance (km), excluding “world” 8 20 10 5Average distance (km), excluding “world” 10 13 32 22Greatest distance (km), excluding “world” 100 30 400 750

all villages.) These results indicate that farm-ers are willing to try seed from areas furtheraway than their local village, possibly in situ-ations where they know little about the skillsof the farmer providing the seed or growingconditions of the source crop. Badstue et al.(2007) noted similar results from the OaxacaValley, stating that farmers are willing to tryseed from a different environment recognizingthat other maize varieties might not work forthem but believing that the seeds might even-tually acclimatize.

Generalizing about the scale of seed ac-quisition is hampered by diverse concerns inmeeting family subsistence and commercialproduction needs as well as unequal exposureto opportunities for seed acquisition, but theseinfluences on seed exchange need to be recog-nized when considering possible forms of agro-biodiversity conservation. An additional factorthat might influence farmers’ willingness to ex-periment with seed from distant geographic lo-cations is off-farm labor. Increased migrationof Mexican farmers for off-farm work increasesopportunities to acquire seed at greater dis-tances from their communities. For the fourvillages surveyed, the majority of men partici-pated in off-farm labor. The data indicate thatin all four villages over four fifths of the meninterviewed have worked outside their commu-nity at some time (Ojo de Agua, 88.57 percent;San Juan Viejo, 85.71 percent; Santa Cruz deGamboa, 82.86 percent; and Bajıo de Bonil-las, 85.71 percent). For those who said thatthey had ever migrated to work, many gavetime frames of over forty years in which theyleft every year for a variety of locations in theUnited States, Mexico, and as far as northernAlberta in Canada.5 In Santa Cruz de Gamboa(20 percent), Bajıo de Bonillas (17.14 percent),and Ojo de Agua (2.85 percent), women hadworked away from home, although, in compar-

ison to men, they travel shorter distances and ona daily basis, mostly to work as receptionists andhouse cleaners. In the village of San Juan Viejo,no women interviewed indicated that they hadworked away from home. Visually we found thisvillage to be the wealthiest (e.g., having mod-ern home appliances, larger homes, and pavedstreets), so perhaps the household income fromcommercial agriculture and male off-farm workwas sufficient.

Illustrating the modification of Tobler’sFirst Law, which predicts the importance ofproximity, is the fact that influences on seedexchange are not uniform in agricultural land-scapes or among households within villages.Thus the scale of seed exchange in the four vil-lages surveyed in the Bajıo is diverse and reflectspatterns dating back to the origins of agricul-ture where seed is exchanged both locally andover long distances.

Further analysis based on gender rather thanvillage (Figure 3) reveals that whether the re-spondent is a woman or man is the most distin-guishing variable in affecting seed exchange andwhether or not maize seed acquired for con-sumption was sown (Sown Seed Purchased forConsumption in Figure 3). Many more womenthan men stated that they had sown seed boughtfor consumption, reflecting the fact that womenselect seed for sowing during food preparation(Rice, Smale, and Blanco 1998). The result ofwomen sowing seed that was purchased for con-sumption increases the likelihood of seed beingacquired from greater distances as commercialfood seed might be from a local, regional, na-tional, or even international (e.g., U.S.) source.Drawing attention to the fact that farmersare sowing grain purchased for consumptioncan help in understanding the dynamic scaleof seed flow and how transgenic varieties ofmaize might become established (Dyer et al.2009).

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Table 9 Frequencies of responses to the categories for the question “Why have you planted differentseed?”

Bajıo de Bonillas Ojo de Agua San Juan Viejo Santa Cruz de GamboaReason forchanging seed Male Female Male Female Male Female Male Female

Low yield 3 4 3 4 4 3 3 3Changed land 1 2 0 0 1 0 0 0Lost seed 8 2 7 2 2 4 6 3To try 6 6 3 4 12 3 6 4Other 5 0 2 0 14 0 1 0No change 11 20 20 25 1 24 18 25

If respondents said that they had not sowngrain bought for consumption, the next dis-tinguishing variable is the number of timesa year that seed was given to neighbors orother farmers (Number of Times Seed Givento Neighbors or Other Farmers/Year in Figure3). Men were more likely to respond that theyhad given seed away more than once a year.Tripp (2001) noted that many farmers differ-entiate between giving seed and lending seed.Seed that is lent requires some form of pay-ment, whether cash or in-kind. For the majorityof the farmers surveyed in the Bajıo, seed wasmuch more frequently given than lent. Theseresults contribute to our understanding of seedstructure in that men in the four villages sur-veyed are more likely than women to exchangeseed and the form of transaction appears to beprimarily gifts. These data also help us to un-derstand the complexity of seed movement,which, as discussed earlier, is not always rec-ognized by farmers as seed exchange. Fur-thermore, as Badstue et al. (2007) noted, seedexchange in the form of gifts and lending of-ten occurs among community members whoalready have a trusting relationship; thus, thisaction is likely to continue to foster socialbonds.

The same variable, Why Planted DifferentSeed?, appears twice on the gender-based clas-sification tree. Different aggregated categoriesfor this variable are used on the left and rightsides of the tree. On the right side the variableWhy Planted Different Seed? is subsidiary tothe variable Number of Times Seed Given toNeighbor or Other Farm/Year and helps dis-tinguish the response patterns of the few menwho rarely gave seed away (like the women onthis branch) but who otherwise differ from fe-male response patterns. For those who statedthat they gave seed less than once a year, the re-

sponses to the question “Why have you planteddifferent seed?” include low yield, changedland, lost seed, to try, and other. Table 9presents frequencies of responses for men andwomen at the village level. Women were morelikely to respond that low yield was the reasonfor changing seed or that no change had takenplace. In general, women in the four villagessurveyed were more critical of the qualities ofthe varieties that were grown (see Chambersand Momsen 2007).

If they did sow grain purchased for con-sumption, then why farmers acquired new seedwas the next distinguishing variable (left sideof classification tree). Women more typicallyresponded that low yield, change of land, andseed to try were significant or that they didnot exchange at all. Men were more likely tosay that they changed seed because of low yieldor lost seed. In the Bajıo, where maize is botha commercial and a subsistence crop, men aremore involved in commercial maize growingand it is possible that this reflects differences ingendered responsibilities for particular plots offarmland and for crops grown for commercialuse versus domestic consumption. For a fur-ther discussion of possible influences resultingin gendered differences for maize seed selec-tion and crop management, see Chambers andMomsen (2007).

Adding a gender perspective can contributeto understanding seed exchange systems as notonly might women have different practices(e.g., the timing of seed selection) or be respon-sible for different crops, but the off-farm labor,particularly by men, might result in a shift inseed exchange behavior. These results are simi-lar to the observations by Zimmerer (2003) andSoleri et al. (2005) that increased participationin nonfarm labor markets might be the mostobvious threat to seed exchange. Ultimately

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the introduction of seed bought for food intofields, as well as experimenting with seed ac-quired from different environments might, asParzies, Spoor, and Ennos (2004) noted, jeop-ardize locally adapted landraces.

Conclusion

Using household survey data for four villagesin the Bajıo of Mexico, this article has ana-lyzed the purpose, structure, scale, and threatsto seed exchange. Both the literature reviewand the survey results indicate that seed ex-change is a complex process, not easily definedand difficult to model for purposes of conserva-tion and other policy initiatives. Seed exchangeseems to be primarily opportunistic and basedon individual farmers’ needs, preferences, andpossibilities. The purpose, scale, and structureof seed exchange in the Bajıo appears to beinfluenced by agroecological conditions withregions of high agricultural potential havinggreater capacity for modern varieties (e.g., SanJuan Viejo) acquiring seed annually from com-mercial sources. The scale of seed exchange isbecoming increasingly influenced by globaliz-ing factors such as migration for off-farm la-bor. The influence of the global economy isnot even, however, and seed exchange mightnot be necessarily shrinking but, as Tobler hassuggested, shriveling.

Seed exchange is important for maintain-ing maize diversity in farmers’ fields as wellas sustaining cultural and social practices.Furthermore, understanding seed exchange isnecessary in helping to predict the possiblemovement of transgenic maize from farmer tofarmer. To conserve crop diversity and culturaldiversity, it is important to document existingseed exchange systems as well as attempt to un-derstand past systems and the factors that haveinfluenced change. Conservation of crop diver-sity depends not only on preservation of thegenetic material of landraces but also on thefarmers’ systems that have maintained these forthousands of years. �

Notes

1 The biological impact of seed exchange on croppopulations is strongly affected by a crop’s repro-ductive system (i.e., whether it is selfing or out-

crossing) and the method of crop propagation (i.e.,by seed or by vegetative propagation). For thepurpose of this article, and to further the discus-sion of seed exchange in general, we have chosento present a combined literature review on seedexchange purpose, scale, structure, and threats.Our goal is to focus on the human and physicallandscape influences on seed exchange rather thanthe biological consequences or the specific croprequirements.

2 All four communities referred to their villages asan ejido; however, the status of land ownership dif-fers between communities. In Bajıo de Bonillas andSan Juan Viejo, farmers have opted to allow the pri-vatization and sale of land according to the 1992change made in the Mexican Constitution. In Ojode Agua and Santa Cruz de Gamboa, farmers con-tinue to hold the land communally.

3 Rice, Smale, and Blanco (1998) noted that althoughfarmers might report that the seed they are plant-ing was given to them by their parents, this mightmean that they are growing the same type of seedeven though the actual seed has been replaced morethan once from another source.

4 According to a few farmers they received seeds as“gifts” or were “given seed” from seed companies.On questioning the farmers, this appears to be away for these companies to build interest and thusfuture clients.

5 For a discussion of the potential impacts of off-farm labor on the conservation of crop diversitysee Chambers and Momsen (2007).

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KIMBERLEE J. CHAMBERS is an Assistant Profes-sor in the Department of Environmental and EarthSciences at Willamette University, Salem, OR 97301.E-mail: [email protected]. Her research in-terests span a diversity of food and agricultural top-ics linked to conservation and human–environmentinteractions.

STEVE B. BRUSH is Professor of Human and Com-munity Development at the University of California,Davis, One Shields Avenue, Davis, CA 95616. E-mail: [email protected]. His research focuses onthe human ecology of traditional agricultural systems.His current research concerns the landscape factorsrelating to maize diversity in Mexico and he has pub-lished extensively on the ecology and conservation ofcrop genetic resources in cradle areas of domestica-tion as well as on farmers’ rights.

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Documents

Geographic Influences on Maize Seed Exchange in the Bajío, Mexico*