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Leucaena, Maize Mosaic Virus, and the Rise and Fallof the Classic Maya Civilization: 

Leucaena, Maize Mosaic Virus, and the Rise and Fall of the Classic Maya Civilization James L. Brewbaker Dept. Tropical Plant and Soil Science University of Hawaii W. Forest Genetics Association Merida, Yucatan, Mexico July 2000

The Maya Civilization: 

The Maya Civilization Formative, Olmec 500 B.C. to 325 A.D. Classic 325 to 925 A.D. Early Classic 325 to 625 A.D. Florescence 635 to 800 A.D. Abandonment 800 to 925 A.D. Post-Classic, Toltec 975 to 1200 A.D.

The MAYA-- A Remarkable Civilization --: 

The MAYA -- A Remarkable Civilization -- Maya built a culture that survived 6 times as long as the Roman Empire Their cities outnumbered those of ancient Egypt They flourished while Europe suffered Dark Ages Their calendar was the equal of ours, dating back 0000 years Their math employed the concept of zero They predicted eclipses of sun and moon

MAYA LANDS: 

MAYA LANDS 15° - 21° N, 88° - 92° W; 20 million ha Atop a Giant Calcareous Plateau pH 6.5 - 8.0, High base status (Ca, K) Fine soils -- Mollisols, Inceptisols Tropical, Mean Annual Temp. 25° - 30°C Rainfall; 1000 mm (north), 3000 mm (south) South = 2 crops, Central = 1-2 crops; North = 1 crop

The Classic Maya lacked:: 

The Classic Maya lacked: Metal tools Beasts of burden (ruminants) The wheel Good sources of protein

Intensive Maize Cropping Systems of the Classic Maya Civilization: 

Intensive Maize Cropping Systems of the Classic Maya Civilization Farms created out of high forests without metal tools Maize was the primary dietary energy source Yucatan Peninsula is calcareous, superb for year-round production of maize Much evidence for increasing intensity of cultivation Nal-Tel is excellent variety; 1.5 t/ha on 20 kg N, to 5t/ha on 150 kg Maya ate 2 kg maize/day/family (1t/yr ~ 1 ha)

N-fixing Trees and Maize Cropping Systems : 

N-fixing Trees and Maize Cropping Systems Mimosoids abundant in Meso-America Leucaena species are found around most of the 1300 Maya ceremonial centers Leafdrop nitrogen avg. 300 kg/ha with rainfall >1500 mm/yr N recovered by maize avg. 25% from leafdrop Rapid regrowth upon coppicing (e.g., canopy closure from randomly spaced trees in a year) Alley-farm systems more effective, “green manure” applied before/during maize growth

Tikal, Guatemala: 

Tikal, Guatemala Earliest Date = 292 A.D.; Latest = 771 Population; estimated 200,000 Major center of Maya (2 million people) 60,000 hectares Tropical rain forest to 50 m Five main pyramids, to 70 m Two (+) maize crops per year

Civilizations; Some Premises: 

Civilizations; Some Premises Civilizations Rise and Fall on Their Stomachs Classic Maya Civilization Rose due to High Maize Productivity They Abandoned due to Failure to Sustain High Maize Productivity But it only affected the 2-crop Region

Collapsed Maize-based Civilizations: 

Collapsed Maize-based Civilizations Olmec, Vera Cruz (100 A.D.) Teotihuacan, Mexico (650 A.D.) Zapotec, Oaxaca (750 A.D.) Maya, Yucatan & Guatemala (880 A.D.) Anasazi, Southwest USA (1050 A.D.)

Why Abandon Good Maize Land?: 

Why Abandon Good Maize Land? Soil is lost, e.g. erosion on sloping land Phosphorus is lost, e.g., harvested off Nitrogen is lost Soil irreparably damaged, e.g. salinization Protracted flooding or drought Protracted maize diseases or pest damage

Maize Mosaic Virus (MMV): 

Maize Mosaic Virus (MMV) Worldwide; Tropical; Lowlands only Severe in continuous plantings (e.g. Hawaii) Only hosts; Maize, Teosinte Only vector; Peregrinus maidis planthopper • Thrives only in lowland tropics • Thrives only on maize and teosinte • Virus is persistent, transmissible 30 days

Resistance to MMV: 

Resistance to MMV First described (1910) in Cuban Flint in Hawaii Shown to be monogenic, Mv locus (1967) • General resistance, non-racially specific • Heterozygotes intermediate; Mv BC’d into >100 inbreds • Mapped with RFLP to 3:80 (1995) ¤ Mv confined to Caribbean races • Haitian Chandelle (25%), Coastal Tropical Flint (35%), Cuban Flint (20%), Early Caribbean (10%), Haitian Yellow (15%), St. Croix (40%), Tuson (35%) ¤ Mv essentially absent from 78 other tested races • Including all Races conceivably available to Classic Maya

Hypothesis No. 1High-yield, sustainable maize productionof the Classic Maya civilization wasenabled by the use of Leucaena species: 

Hypothesis No. 1 High-yield, sustainable maize production of the Classic Maya civilization was enabled by the use of Leucaena species Leucaena spp. are abundant around Maya ruins L. leucocephala, L. shannonii, L. collinsii Maize + Leucaena = excellent agroforestry They have similar environmental requirements: e.g., Non-acid soils, High P, High Ca, Good drainage, Temperature/Moisture Leucaena regrowth in a 3-year fallow is ideal for restoration of maize soil fertility Added benefits: food (pods), fuelwood, lumber

Hypothesis No. 2Collapse of Classic Maya (9th century)was precipitated by introductionof Maize Mosaic Virus: 

Hypothesis No. 2 Collapse of Classic Maya (9th century) was precipitated by introduction of Maize Mosaic Virus Classic Maya were limited to one major genetic source of maize, the variety Nal-Tel No Mexican or Meso-American varieties of maize were resistant to MMV All Caribbean varieties were tolerant to MMV; the Arawak grew maize in Haiti/Dom.Rep Virus-borne leafhoppers easily introduced from Caribbean islands (e.g., by hurricanes)

CONCLUSIONS: 

CONCLUSIONS Classic Maya civilization “rose” to great heights due to excellent yields of year-round maize in mimosoid-rich lowland tropics Classic Maya civilization “collapsed” due to persistent failure of maize crops in 9th century Maize mosaic virus is most likely cause of failure; Nal-Tel highly susceptible Virus restricted to year-round production areas in lowlands Maya retreated to north (Yucatan) and to south (Guatemala highlands), escaping virus