Culture and Ecology of Chaco Canyon and the San Juan Basin

The Classic Adaptation 179were above-normal PDSI values for fewer years thanthose below normal. Thus, farmers contended withincipient drought and mild drought more often thanthey had with either wet spells or moderate to severedroughts. Six severe droughts (A.D. 907 to 908,924,980 to 982, 992 to 994, 1035, and 1047) were followedby rebounds in precipitation. He concludedthat a three-year storage capacity would have carriedpeople through any crop failures.That the storage would have been sufficient toover-come most environmental perturbations is supportedby two other studies. Bums (1983) examinedthe effects of several variables on com and dry beanproduction. His simulation indicated that dry beancrop yields are more susceptible to variation in precipitationthan com. He used three years of storage and24 years of shortfalls to indicate fawine. Althoughseveral periods of famine were identified, noneoccurred during the Chaco florescence. However,Bums (1983:232-235) suggested that two periods(A.D. 995 to 1041, and 1146 to 1193) were timeswhen agriculturalists would have faced severe agriculturaland nutritional problems. Years of surpluscrops also occurred at A.D. 730 to 737, 785 to 787,797 to 808, 820 to 822, 832 to 839, 899 and 900, 987to 989, 1050 to 1065 (the second largest surplus in theseries), 1112 to 1118, and 1201 to 1213. In a laterstudy, Sebastian (1992: 106-114) based her simulationon com units. Allowing for a five-year surplus, yearsof low production or little or no social surplus occurredfrom A.D. 937 to 942, from 1142 to 1154,from 1167 to 1178, and from 1190 to 1195. Cropsurpluses would have occurred around A.D. 990, andfrom A.D. 1050 to 1130.In summary, although precIpItation was alimiting factor, the Chacoans would have been able tofarm and store crops successfully during incipient ormild drought. During three major periods of stress(identified by Bums [1983] as around A.D. 705 to726, during the mid-A.D. 11 OOs , and again aroundA.D. 1276 to 1299) one expects major cultural disruptions.Other fluctuations in precipitation wereprobably overcome by changes in storage practices andother adjustments.To better understand the constraints of precipitationon agricultural production, Chaco Project archaeologistsplanted crops in nine locations during1977, 1978, and 1979 (H. Toll et al. 1985). Due toa lack of success with beans and gourds during thefirst year, only com was planted during the followingtwo. Com plots were located in several topographiclocations. Some were not watered; some were wateredonce a week; and some were watered twice a week.Differences in results between plots were marked.Com did grow in the sodium-rich black alkali soilsfound on the main canyon floor. Dunes along thesouth side of the canyon produced com but seemedmore prone to destruction by pests than plots on valleyfloor. There were greater high and low temperatureextremeS on the north side of the canyon. Preci=pitation events varied at three different stations. Eventhough watering helped, natural precipitation wasrequired. Based on their experiences, H. Toll et al.(1985) concluded that Chaco is a marginal environmentin which to grow com. Even with irrigationsystems, there is no guarantee of success because thetiming of precipitation events is crucial. Farmerswould have to have been very attentive to precipitationevents in order to provide extra water when needed.The horticultural methods employed on the south sideof the canyon may have been more reliable on a longtermbasis.Precipitation is not the only factor that wouldaffect crop production. Gillespie (1985:18-19) consideredtemperature and a frost-free season crucial toagricultural success. He indicated that the frost-freeperiod in Chaco Canyon is between 110 and 130 days,which is quite close to M. Bradfield's (1971) estimateof 115 to 130 days needed for historic Hopi com.Faster maturing strains of com may have beenavailable to the Chacoans.Although the species of com grown in ChacoCanyon have not been determined, general patterns ofchange have been described. For the Southwest, M.Toll (1985:260-263) indicated that a new type introducedby A.D. 500 probably increased yields. AfterA.D. 700, the number of cob rows also shifted. The"broad pattern of continuity in com morphology fromlate Basketmaker through Pueblo II, followed by achange to a lower-rowed Pueblo III type" in the SanJuan Basin did not accurately model what she observedin Chaco Canyon samples (M. Toll 1985:260). Sitesin Chaco Canyon generally average 1O-rowed cobsfrom Basketmaker III through Pueblo III. At PuebloAlto, however, the Red Mesa ceramic assemblage had