330 



ECOLOGICAL FACTORS: 



salinity, and alkalinity or acidity in the soil affects 

 the presence of many animals. 



Soil organisms, both plant and animal, have some 

 influence upon their environment. When death oc- 

 curs, the organic remains contribute to soil humus. 

 The burrowing of animals and growing of plant roots 

 contribute to breaking up of soil particles and its 

 parent material. In addition, such things as organic 

 decay and waste contribute to chemical decomposi- 

 tion of soil. Among the animals, the most influential 

 species include earthworms, ants, sowbugs, milli- 

 pedes, and rodents; but such creatures as amphibi- 

 ans and reptiles also play a part. The influence of 

 monerans and fungi was indicated in their taxonomic 

 accounts. 



ously present. When only some species are removed, 

 the surviving forms may assume an unnatural as- 

 semblage, or strange habitat. When all species are 

 removed, abnormal developmental stages, or habitats, 

 characterize recovery. 



FIRE ADAPTATIONS 



Certain plants possess structures and functions that 

 enable them to persist in repeatedly burned areas 

 (Figure 17.18). These many plant adaptations are 

 found in all stages of the life cycle of plants, but few 

 species have more than a few of the different speciali- 

 zations. Germination adaptations occur in the seeds 

 of some shrubs, which sprout only after being burned, 

 and the cones of some conifers, which shed their seeds 



FIRE 



In spite of man's efforts, fire is likely to be a major 

 ecological factor for some time. Even before the ad- 

 vent of man, wildfires were fairly common over much 

 of the globe. The only fire -exempted localities are the 

 very wet, very dry, and very cold regions. 



There are three main kinds of wildfires. Crown 

 fires extend from tree tops to ground surface and re- 

 move most of the vegetation. Surface fires remove 

 only the herbaceous and other low plants; trees may 

 not be affected too seriously. Ground fires cause the 

 burning of organic material in the soil, but usually 

 occur with other fire types. Because ground fires 

 normally burn with one or both of the other two 

 types, they are the most extensive and destructive of 

 the wildfires. Both ground and crown fires are limit- 

 ing factors for most creatures. Ground fires cause the 

 most damage to life in restricted areas, and lead to 

 entire habitats' taking the longest time to recover; but 

 even crown fires often remove the characteristic vege- 

 tation of a locale and so necessitate some habitat 

 recovery. Surface fires, too, cause removal of some 

 species. Although surface fires might not affect the 

 more fire -tolerant forms, they might cause a change 

 in the plant assemblage and necessitate recovery. 



Any fire is likely to alter an environment. An altera- 

 tion may be minor and produce no visible change in 

 the species composition of the area, but there is usu- 

 ally some visible fire injury to plants. These injuries 

 may be little more than fire scars or a greater amount 

 of parasitism on the species. More dramatic damage 

 causes the removal of some to all of the species previ- 



aeriai regeneration 



lignotuber 



Figure 17.18 Some fire adapted plants. 



