14 VEGETATION IN CENTRAL AMERICA. 



will persist, but when denudation is complete or when the soil be- 

 comes sticky and impervious the humus-inhabiting types entirely 

 disappear, as in many of the tenacious " gumbo " soils of the Texas 

 prairies. 



Many forested places in Central America which now afford con- 

 ditions favorable for these humus-loving animals are occupied by 

 small and incomplete faunas. This shows that the period of re- 

 forestation has not been long enough to permit these sedentary, slow- 

 moving creatures to spread again over the reforested areas. Thus, 

 in the valley of Ocosingo in southern Mexico are many such tracts 

 of new forest in which the humus fauna is still very poorly repre- 

 sented. Nevertheless, the woody growth which now crowns the ex- 

 tensive ruins of Tanina, a few miles from Ocosingo, shelters a rich 

 fauna of humus-inhabiting types. It seems impossible to account for 

 the presence of such a fauna except by supposing that there Avas a 

 complete and long-continued reforestation of the district after the 

 ruins were built, but before the present population came in and 

 cleared the land anew. 



Of the periods of time required for such changes to be accom- 

 plished only rude estimates are possible in the present state of our 

 knowledge. A thousand years appears a small allowance for the 

 complete reforestation of a thoroughly denuded region and for the 

 spread of the humus-inhabiting organisms over the reforested coun- 

 try. The survival of the humus-inhabiting animals on the ruin- 

 covered hill is hardly to be considered possible, for the pyramids and 

 chambered buildings which covered the summit, as well as large 

 areas of the elaborately terraced approaches, appear to have been 

 faced all over with cement. 



Populous Indian communities, such as the builders of these ruins 

 must have formed, not only cut down all the accessible forests to 

 plant corn, but keep the surrounding country stripped of woody 

 growth to supply the never-ceasing demand for fuel. Long after all 

 the lands for many miles around are exhausted the community may 

 persist, so great is the disinclination of the Indian to leave the place 

 where his forefathers have lived. Thus the abandonment and re- 

 forestation of a district has always to be thought of as a slow and 

 gradual process, requiring much more time than would be needed 

 if the vegetation could be left entirely alone. In like manner it must 

 be considered that a long period is required for the reoccupation and 

 development of a new native culture in a district in which the forest 

 growth has been allowed to become fully restored. 



Of the sudden movements of large bodies of population as results 

 of wars and conquests there are no indications in the habits and tradi- 

 tions of the peaceable, sedentary agricultural natives of this region. 

 Each successive occupation is to be thought of as slowly growing 



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