KELATIONS BETWEEN PLANTS AND ENVIRONMENT 81 



Recapitulation. It should be noted that the pioneer-to-climax 

 succession is very similar to the evolutionary development of the 

 earth 's life forms to their present condition. While the over-all evolu- 

 tion must be reckoned in terms of millions of years, the recapitulation 

 of the process may occur on a bare area today in a matter of centuries 

 or even less time. The reason is that all the plant species involved 

 are already in existence and stand by, ready to invade when condi- 

 tions permit. 



Both the above developments are reflected in a general way by 

 the life cycle of the individual plant. Starting with a single fertile 

 cell, it proceeds to establish an increasing intimacy with the environ- 

 ment, and to become progressively more complex in organization as 

 it develops from an embryo to a mature structure. It reacts to the 

 habitat and the habitat reacts to it. In a stabilized environment, the 

 plant (or animal) or its successors can live indefinitely in its habitat, 

 because it will return to the soil, to the water, and to the air every- 

 thing it takes from those storehouses, to be used again by its off- 

 spring. 



Indicators of Environment. 5 Since plants are products of the 

 environment, they tell a story by their mere presence. The dominant 

 species are most reliable as indicators of living conditions, past and 

 present. Once scientists have, by detailed study of the ecological 

 factors associated with a dominant species, established the habitat 

 pattern, we can then know, whenever we see that species or associa- 

 tion, what the pattern is. Much such work has been done. Much 

 remains to be done. Ecology is a young science. 



A few examples: Reeds indicate a water table near the surface. 

 Mesquite roots go down for water as much as 50 feet. Beech-Maple 

 forest land is more productive as farms than Oak-Pine. Long-leaf 

 pine uplands will yield profitable corn crops for no more than three 

 years without fertilizer ; mixed Short-leaf and Long-leaf pine areas, 

 five to seven years of corn; Short-leaf Long-leaf Oak-Hickory 

 land, up to 12 years; Oak Short-leaf, 12 to 15 years of corn with- 

 out fertilizing. 6 Short-grass sod growing where it doesn't naturally 

 belong, on the western belt of the tall grass prairies, indicates over- 

 grazing the climate will support mixed prairie grasses which in- 

 clude much taller ones (wheat grass, for instance) than the short 

 grasses. Wild wheat grass itself indicates land fit for domestic 

 wheat crops. Sage-brush indicates deep, porous, non-salty, farmable 

 soil. Quaking aspen (a low-grade hardwood) dominating northern 

 softwood forest areas indicates past fires. Broomsedge and briars 

 indicate that a former hardwood forest site must be replanted to 

 pines if a forest is wanted, since the original fertility is greatly re- 

 duced. 



It can be seen that a knowledge of plant indicators, or even 

 knowing that such information exists and can be secured, is valuable 



5 Ibid., Chap. 17, passim. 



6 Hilgard, E. W., Soils, Macmillan, New York, 1911, p. 315. 



