THE ENVIRONMENT 



331 



only after fire. Many "fire plants" grow and become 

 sexually mature very rapidly, enabling the life cycle 

 to have a good chance of completion prior to another 

 fire. Other growth adaptations are displayed by im- 

 mature stages that have great fire tolerance. Adult 

 modifications are of many kinds. Many species have 

 fire-resistant leaves or bark. Others have means of 

 rejuvenation after much of their aerial parts have 

 been destroyed. For example, some plants have buds 

 that regenerate from the remains of aerial parts; other 

 plants have enlarged structures (near the ground sur- 

 face but mostly or entirely below the surface), ligno- 

 tubers, that sprout after all aerial parts are consumed. 



CHAPARRAL 



The western North American (especially Cali- 

 fornian) shrub habitat called chaparral grows in semi- 

 arid areas having long, dry summers — conditions that 

 are associated with frequent fires. The various species 

 that compose this habitat display the gamut of fire 

 adaptations. After a fire there is usually profuse 

 germinating and sprouting of plants and the habitat 

 returns to normal in about ten years. Because chap- 

 arral is subject to recurring fires, the average habitat 

 is about twenty-five years old and few are more than 

 fifty years old. However, even the specialized plants 

 of this scrub cannot withstand too frequent fires. 

 Recurring fires will cause the habitat to revert to 

 bunch grass. 



CONTROLLED BURNING 



The value of man's use of fire to "improve" land is 

 debatable. It is definitely known that burning can 

 cause moderate to severe damage to a habitat, but so 

 many ecological factors are involved that one cannot 

 predict with any real accuracy the full consequences 

 of burning a given landscape. In some instances 

 burning would appear to benefit the land use of an 

 area; however, the efTects of this treatment are diffi- 

 cult to appraise because they are likely to be delayed. 

 Any seeming benefit, even if pronounced, may be a 

 temporary thing. Often after variable periods of time, 

 the nutrients released by fire are removed; then, al- 

 though some time may be required, soil depletion and 

 consequent vegetation destruction allow the area to 

 erode, perhaps even to a badland situation. 



The possible eflfects of burning can be related to the 

 cycle of development of habitats (succession). All 



that need be said here is that succession is a process 

 characterized by soil improvement and that burning 

 of a forest, woodland, or shrub habitat causes regres- 

 sion and sets soil and other environmental factors 

 back to the point where herbs, usually certain grasses 

 and forbs, can grow. This fire setback does not create 

 the natural environment that supports a native her- 

 baceous habitat because the soil is such that weedy 

 herbs, ac-tually less nutritious than the native ones, 

 often prevail. Unfortunately, there is an all too com- 

 mon belief that some of these weeds, especially fila- 

 rees {Erodium spp.) are ideal forage plants. However, 

 in spite of any temporary good that comes from such 

 plants, these weeds indicate a disturbed habitat that 

 is more subject to erosion from natural causes or 

 grazing activities than is native vegetation. Fre- 

 quently such areas, whether they are the consequence 

 of burning or overgrazing, are short-lived forage lands 

 that soon become wastelands in a destroyed water- 

 shed. 



The differences between a mature watershed and a 

 cleared or overgrazed one can be extreme. When 

 such drainage areas that contribute to the supply of a 

 river or lake contain mature and stable (climax) vege- 

 tation, there are the best possible soil and vegetation 

 conditions for water retention and for reduction of 

 both runoff and erosion. Therefore, when land is 

 either cleared or caused to have a different plant 

 growth, the consequences usually are less water re- 

 tention, greater runoff and erosion, and poorer soil. 

 Although the mature vegetation uses much of the 

 water that it and its soil trap, mature watersheds 

 normally yield water over a much longer period and 

 a more nearly constant rate than do disturbed water- 

 sheds. Even if streams in cleared or modified drain 

 age areas are dammed, the water gain most likely is 

 offset by the degradation of the watershed and the 

 accumulation of erosion products in the dams. 



TOPOGRAPHY 



Physiography is related to some dramatic aspects 

 of the distribution of plants and animals. Some of the 

 physiographic effects can be very puzzling. For ex- 

 ample, an area of higher elevation may have more 

 luxuriant vegetation than a lower one, partly because 

 of lower temperatures and greater precipitation. The 

 lower temperatures cause near maximum conserva- 

 tion of the moisture that is available. On the other 



