Hum Ecol DOI 10.1007/s10745-015-9771-z Population and Environmental Correlates of Maize Yields in Mesoamerica: a Test of Boserup’s Hypothesis in the Milpa Luis Pacheco-Cobos1 & Mark N. Grote2 & Douglas J. Kennett3 & Bruce Winterhalder2,4 # Springer Science+Business Media New York 2015 Abstract Using a sample of 40 sources reporting milpa and and yield. The multi-level modeling methods we adopt allow mucuna-intercropped maize yields in Mesoamerica, we test for data clustering, accurate estimates of group-level variation, Boserup’s(1965) prediction that fallow is reduced as a result and they generate conditional predictions, all features essential of growing population density. We further examine direct and to the comparative study of prehistoric and contemporary ag- indirect effects of population density on yield. We find only ricultural yields. mixed support for Boserupian intensification. Fallow periods decrease slightly with increasing population density in this Keywords Boserup . Agricultural intensification . Milpa . sample, but the relationship is weak. Controlling for other Maize . Agro-ecology . Multi-level analysis . Mesoamerican covariates, fallow-unadjusted maize yields first rise then fall and Maya subsistence with population density. Fallow-adjusted maize yields peak at 390 kg/ha/yr for low population densities (8 persons / km2) and decline to around 280 kg/ha/yr for the highest population Introduction densities observed in our dataset. Fallow practices do not ap- pear to mediate the relationship between population density In her 1965 book, The Conditions of Agricultural Growth, Esther Boserup proposes a synthetic, general account of agri- Electronic supplementary material The online version of this article cultural development. Taking population growth and conse- (doi:10.1007/s10745-015-9771-z) contains supplementary material, quently population Bpressure^ as an exogenous, driving vari- which is available to authorized users. able, Boserup argued that agricultural systems typically inten- * Luis Pacheco-Cobos sified from long-fallow, extensive systems to progressively [email protected] shorter fallows, and then to multi-cropped, intensive forms Mark N. Grote of agrarian production. Returns to labor diminish as human [email protected] effort, time and resource-intensive technologies like Douglas J. Kennett mulching, manuring and irrigation replace the regenerative [email protected] effects of long fallows. Yield per unit area of available land Bruce Winterhalder grows as land is more productive and more continuously cul- [email protected] tivated, elevating its capacity to support human population. 1 Facultad de Biologia, Universidad Veracruzana, Cto. Gonzalo Because humans generally avoid unnecessary exertion, Aguirre Beltran s/n, Zona Universitaria, C.P. Boserup noted that extensive forms of production prevail 91090 Xalapa, Veracruz, Mexico when land is abundant relative to population requirements; 2 Department Anthropology, University of California, One Shields intensive forms will prevail when it is scarce. Thus, while Avenue,Davis,CA95616,USA intensification predominates, agricultural development might 3 Department Anthropology, The Pennsylvania State University, 403B go in either direction depending on the availability of land and Carpenter Building, University Park, PA 16802, USA the distribution and density of populations (Netting 1993). 4 Graduate Group in Ecology, University of California, One Shields Boserup’s theory is taken to be a decisive alternative to the Avenue,Davis,CA95616,USA Malthusian claims that food shortages inevitably cap Hum Ecol population density at a level set by technology. The Descriptive Results theory has proven attractive not only to agricultural his- torians and development economists but also to prehis- Two Measures of Production torians, geographers and anthropologists eager to under- stand mechanisms involved in the development of early Two measures of production are important to the human societies dependent on agriculture (see “Discus- Boserup hypothesis. Unadjusted Yield is edible or useful sion: Boserup in the Milpa” for citations). offtake from one planting measured in weight, bulk, We perform a comparative, multilevel-analysis of pri- nutrient or other value per unit area. This is the variable mary data on fallow periods and yields of milpa found in the primary literature in most cases. Adjusted (shifting cultivation) maize agriculture, a form of pro- yield takes into account the frequency with which an duction widely practiced in Mesoamerica and adjacent area of soil will produce a particular amount of food regions. We present three related models involving pop- or materials. It corrects for agricultural intensification ulation density as a focal predictor along with environ- based on fallow length and intra-annual multi-cropping: mental and geographical covariates. In the first model Adjusted yield we examine the frequency of planting relative to fallow; . and in subsequent models we examine two different ¼ total yield*years cropped ðÞyears cropped þ years fallow formsofmaizeyields.Weassesswhetherornot small-scale farmers intensify agricultural production by where total yield corresponds to the sum of the first and shortening the fallow period. Our study recognizes that second harvest season of maize produced during the intensified production might also be a result of en- agricultural year. A total yield of 1000 kg/ha for 1 year hanced yield per unit of land (Netting 1993:262),in- of production in an agro-ecological system requiring dependently of fallow. 9 years of fallow implies an adjusted yield over the full Coincident with our test of the Boserup hypothesis, we agricultural cycle of 100 kg/ha/yr. The system that pro- evaluate the importance of population density relative to other duces 1500 kg/ha for 2 years followed by a fallow of potential predictors of yield (e.g., elevation, rainfall and soils) 3 years is capable of an adjusted yield of 600 kg/ha/yr. and suggest how the resulting analysis may be used to address This six-fold difference is of significance to the farmer issues ranging from the ability of milpa production to support and also to the political economy of the region. It also the populations presumed to be associated with Classic Period is important to Boserup’s theory, because intensification Maya societies (Ford and Clarke n.d.) to the contemporary can occur through squeezing more yield/unit area from outlook for this form of agro-ecological production. each planting, or by planting each area more frequently relative to fallow, or by a combination of the two. The Sample Unadjusted Yields Milpa Maize Data Sources Figure 2 shows the range of reported unadjusted yields (kg/ha) by source, arrayed from low to high by medians Through library searches and personal correspondence for the full dataset. The median for all milpa cases is with scholars working on questions of agricultural pro- 1133 kg/ha, while the median for all mucuna cases is duction in Mesoamerica and adjacent regions we identi- 3121 kg/ha. The wide range of unadjusted yields ob- fied 40 primary sources reporting original data on maize served from some sources reflects in part differences yields between 1931 and 2011. We focused on traditional between first and second season maize harvests. Cases slash-and-burn milpa practices as well as mucuna,amod- for which milpa unadjusted yields rest close to mucuna ification in which maize is intercropped with a cover crop, unadjusted yields (those nearer the top of Fig. 2)were the velvet bean (Triomphe and Sain 2004). Our sample observed among the Lacandones in Chiapas, Mexico produced a total of 297 records from 92 communities. (Diemont, et al. 2006; Nations and Nigh 1980), the Figure 1 shows the geographical distribution of the sam- Kekchi in Uaxactun (Urrutia 1967), the Mestizos in Ve- ple locations. Table S1 (Supplemental Materials)provides racruz (Coe and Diehl 1980) and other groups in Gua- a full description of the dataset; Table S2 describes the list temala (Stadelman 1940). Of these, the Lacandones are of variables we have derived from these primary refer- known for intensively managing their environment ences or from supplementary sources where that proved (Nigh and Diemont 2013). Table S3 provides median necessary. The Supplemental Materials section titled and 1st and 3rd quartile values for the unadjusted yields BSample Preparation^ describes our methods. presented in Fig. 2. Hum Ecol Fig. 1 Geographical distribution of data sources by country and biome. Brainerd 1956). (22) (Nations and Nigh 1980). (23) (Nigh 1976). (24) The 40 sample locations are: (1)(Alcorn1989). (2) (Altieri and Trujillo (Pascual and Barbier 2006). (25)(Perales,et al. 2005). (26) (Philipp and 1987). (3) (Arias Reyes 1980). (4) (Askinasy 1935 & Shuman 1974, as Gamboa 2003). (27) (Pool Novelo, et al. 1998). (28) (Popenoe 1967). cited in Ringle 1985). (5) (Baraona and Montalvo 1981). (6) (Barlett (29) (Preciado Llamas 1976). (30) (Redfield and Villa Rojas 1962). (31) 1977). (7) (Carr 2008). (8) (Carter 1969). (9) (Coe and Diehl 1980). (Reina 1967). (32) (Sanders & Rice 1993, as cited in Griffin 2012). (33) (10) (Cowgill 1961). (11) (Culleton 2012). (12) (Diemont, et al. 2006). (Schwartz 1990). (34) (Stadelman 1940). (35) (Steggerda 1941). (36) (13) (Drucker and Heizer 1960). (14) (Eilittä, et al. 2004). (15)(Graefe (Triomphe and Sain 2004). (37) (Urrutia 1967). (38)(VillaRojas1945). 2003). (16) (Higbee 1947). (17) (Lambert and Arnason 1986). (18) (Lara (39)(Wilk1997);