

CONTEXTS. 



Page. 



Introduction 7 



Diverse systems of maize culture 8 



Occupation of cleared lands by grasses 11 



Extinction of grasses by forest 11 



Botanical indications that many forests are of recent growth 12 



Previous denudation shown by absence of undergrowth palms 13 



Previous denudation shown by absence of humus-inhabiting arthropods 13 



Desert vegetation in denuded areas 15 



Previous occupations shown by archaeological remains 16 



Prehistoric agriculture shown by terracing of land 17 



Effects of agriculture on forms of erosion 18 



Distribution of pines and oaks determined by clearing of land 19 



Buried roots show former extension of pines 20 



Denuded areas not naturally unsuited to forests 21 



Forests in rocky and precipitous places 21 



Summary 22 



Description of plates 26 



Index 27 



145 5 



