PART IX — TERRESTRIAL ECOSYSTEMS 



2. FOREST ECOSYSTEMS 



The Forest As An Ecosystem 



A forest is a natural or artificial 

 vegetation unit encompassing many 

 different tree associations and harbor- 

 ing a multitude of other life forms 

 which use it for food or shelter or 

 both. Man has used the forest since 

 his ascent to a dominant position, 

 either for direct products or indirectly 

 by destroying large areas and con- 

 verting the land to other uses — 

 mainly food production or urban de- 

 velopment. Currently men consider 

 forests and forest areas useful for 

 the following purposes: wood and 

 fiber production; forage production; 

 water production; aesthetic values — 

 with the many ramifications of this 

 subject. In many instances, attempts 

 to convert forests to other land uses 

 have proved unwise, and large areas 

 have gradually reverted to forest use 

 or have been converted by planting 

 of tree species; the species used were 

 often different from the endemic 

 populations and, therefore, the forest 

 ecology has changed. 



Generalized Description of Forest 



A forest is best regarded as a 

 system. As such, it is composed of 

 subsystems, which can be defined in 

 various ways, depending on the sub- 

 ject under discussion. Here we prefer 

 to consider two principal subsystems: 

 (a) the abiotic, consisting of the non- 

 living components of the soil on 

 which trees and other green plants 

 grow, the atmosphere surrounding 

 and interacting with the living mem- 

 bers of the system, and water and 

 nutrient elements, which are in con- 

 tinual movement through both biotic 

 and other abiotic parts of the forest 

 system; and (b) the biotic subsystem, 

 consisting of living plants and an- 

 imals. 



Trees are the dominant biotic fea- 

 ture of forest ecosystems, constitute 



the framework of any structure it 

 may possess, and affect importantly 

 nearly all other components, biotic 

 and abiotic. Shrubs, herbs, and non- 

 vascular plants such as fungi, algae, 

 mosses, and liverworts make up a 

 smaller proportion of the total bio- 

 mass of the forest system but play 

 vitally significant roles in its dy- 

 namics. Fungi and bacteria, for ex- 

 ample, are the principal agents of 

 decomposition, and all known tree 

 roots function in symbiosis with my- 

 corrhizal fungi in the uptake of water 

 and nutrient elements. Insects, mam- 

 mals, birds, and other animals are 

 primary consumers of vegetational 

 biomass manufactured by trees and 

 other primary producers and, hence, 

 affect the functioning of the system 

 importantly; their numbers are af- 

 fected by numerous predators and 

 parasites. 



Where Science Stands Today 



To a large degree we are still in 

 the descriptive stage of forest-eco- 

 system understanding and, in some 

 instances, not very far along in this 

 stage. Most of the higher plants have 

 been described and catalogued for 

 most forests of the world. However, 

 a multitude of other life forms exist 

 and large numbers have not been 

 identified; certainly their function is 

 not understood, except for such com- 

 mon forms as earthworms. 



The multiplicity of life forms exist- 

 ing in forest soils is an example 

 of the deficiency in our knowledge. 

 As a more definitive case, if one 

 looks at a tropical forest in detail 

 one soon discovers that major spe- 

 cies have been identified by indus- 

 trious plant explorers but that our 

 knowledge largely ceases at that 

 point. Information on detailed inter- 



relationships, even those necessary 

 to manage and predict the effects 

 of common manipulations, is largely 

 nonexistent in the case of tropical 

 forests. 



For forests of temperate regions, 

 which for the most part have been 

 studied more by man and on the 

 whole used more intensively, we 

 presumably have better information. 

 The complexity of our problems in 

 these forests is reduced because spe- 

 cies composition is simpler, especially 

 as it relates to the dominant species. 

 Thus, a northern coniferous forest 

 may be almost a single-species forest 

 whereas several hundred tree species 

 may be found in a few square kilo- 

 meters in many tropical forests. It 

 is doubtful, however, that the same 

 simplicity applies to all other life 

 forms. 



In many instances, man has man- 

 aged temperate and boreal forests 

 rather intensively for relatively long 

 periods of time to various ends — 

 principally the production of wood. 

 It is not surprising, therefore, that 

 a considerable body of information 

 has been built up relating to growth 

 rates of certain important species in 

 a given environment. In such cases, 

 much is also known about the man- 

 agement of water resources or the 

 provision of forage for wild or do- 

 mestic animals, and we have fre- 

 quently acquired considerable prac- 

 tical information on forest insect 

 populations and diseases. 



Despite the relatively large amount 

 of work on forests, the conclusions 

 seem justified that much of it has 

 been descriptive, on relatively small 

 areas of a large forest resource, and 

 so far has not materially enhanced 

 our ability to make accurate predic- 

 tions of important processes occur- 



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