FOREST ECOSYSTEMS 



ing undisturbed and man-manipulated 

 ecosystems would be a modest start. 



Other Needed Activity 



Several other deficiencies are ev- 

 ident when one considers comprehen- 

 sive ecosystem studies. One of the 

 major goals of ecosystem study is to 

 improve our capacity to predict the 

 behavior of ecosystems under various 

 kinds of stress. Modeling, ecosystem 

 analysis, and simulation of ecosys- 



tems are aimed at improving predic- 

 tive capacity. Our capacity to meet 

 these needs is growing haltingly, 

 although there is a strong need for 

 a centralized laboratory dealing with 

 the mathematical aspects of ecosys- 

 tem analysis. This lab could do 

 research on its own and cooperate in 

 modeling, analysis, or simulation of 

 various ecosystem studies under way 

 or planned. 



One of the great problems facing 



teams of scientists ana i forest 



(or other ecosystems) is physical 

 and chemical analysis of thousands 

 of samples of plant and animal tissue, 

 air, water, soil, and the like. Service 

 laboratories charged with these types 

 of analyses and with the develop- 

 ment of new sampling techniques 

 would be of great utility in accelerat- 

 ing and expanding studies of the 

 many terrestrial and aquatic ecosys- 

 tems that make up the continental 

 United States. 



Tropical Forests 



Tropical forests now cover about 

 5 billion of the approximately 10.6 

 billion acres of the world that are 

 still forested. These forests are 

 among the most poorly known areas 

 of the world, especially with respect 

 to their ecology. This condition is 

 particularly unfortunate because there 

 is no other system with comparable 

 productivity that covers more than 

 a small fraction of the area occupied 

 by the tropical forests. Because of 

 our ignorance, these forests remain 

 one of the most poorly used of the 

 earth's resources. 



General Description of Tropical 

 Forests and Soils 



Evergreen "tropical rain forest," 

 the most productive of the tropical 

 forests, is found in the lowlands 

 where rainfall is high and where dry 

 periods, if they occur, are very short. 

 Evidence suggests that the forest 

 itself appreciably increases its own 

 rainfall through the water that evapo- 

 rates from its canopy. Semi-decidu- 

 ous and deciduous forests are found 

 in areas with high humidity but dry 

 seasons of several weeks to months. 

 Dry seasons of several months permit 

 development of a continuous, but 

 relatively dry and less well-developed, 

 forest; if dry seasons are longer, 

 forests can exist only as patches, 



small groups, or single trees separated 

 by grassland. 



The adaptive characteristics of 

 tropical forests (and the problems 

 from man's point of view) are largely 

 the result of interactions between 

 the rather uniformly high tempera- 

 tures and the amount of rainfall. 

 The physical character of most tropi- 

 cal soils is such that both water and 

 air can move through at least the 

 surface layers relatively easily; thus, 

 as long as the forest canopy is intact, 

 rainfall does not cause much erosion. 

 In over half the tropical land area, 

 however, heavy precipitation has re- 

 sulted in the solution and leaching 

 away of almost all but the most 

 resistant oxides of iron and alu- 

 minum. Where leaching has been 

 extensive, availability of plant nutri- 

 ents and soil fertility is generally 

 very low. 



Tropical trees are successful under 

 these conditions largely because they 

 have developed efficient mechanisms 

 for nutrient cycling. This is accom- 

 plished by the shallow root systems, 

 which acquire minerals as fast as 

 they are released from fallen leaves 

 and branches during their rapid de- 

 cay. Thus, the few minerals obtained 

 from the soil and the rain per unit 

 of time are not allowed to escape. 

 Because of the efficiency with which 



minerals are captured following their 

 release through decomposition of 

 dead organic matter, the amount of 

 minerals tied up in the vegetation 

 frequently rivals — and for a few 

 elements exceeds — the amount in 

 the soil. (Even so, productivity of 

 many tropical forests is limited by 

 lack of some mineral nutrients; dis- 

 covery of effective methods of pro- 

 viding more of these minerals could 

 greatly improve forest production.) 



Nutrient availability is higher in 

 some of the younger volcanic soils 

 scattered throughout the tropics be- 

 cause there has not yet been time 

 for complete leaching to take place. 

 Some of the relatively shallow soils 

 on steeper slopes are also richer than 

 the deeper soils on level areas be- 

 cause erosion keeps sending the most 

 leached soil down the slope, permit- 

 ting tree-root systems to penetrate 

 to newer soil formed from the parent 

 rock below. By temperate-zone stand- 

 ards, however, even these relatively 

 rich tropical soils are often of low 

 fertility. 



Land Management in the Tropics 



Traditional native practice in tropi- 

 cal forests is to cut some or all of 

 the trees in a small area and then 

 to burn them. Nitrogen supplies are 



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