NATIVE WOODY PLANTS OF THE UNITED STATES ]_]_ 

 SELECTION OF SPECIES FOR PLANTING 



PRIMARY SUCCESSION 



The factors governing survival must be recognized when a plant 

 is placed among others to compete with them for a place in the sun. 

 These factors or survival values are measured in terms of species 

 requirements, although we often state them by speaking of the toler- 

 ance of a plant for shade, sun, acid or alkaline soil, drought, and 

 moisture. Because no experiments have been conducted, it has been 

 assumed by some technicians that there is no scientific basis on which 

 to judge the ability of one species to compete on the same ground and 

 under the same conditions with another species. This is by no 

 means true. 



For at least 20,000 years in the northern United States, and for a 

 much longer time in the southern part, the species comprising the 

 flora of the country have been competing for position, settling them- 

 selves little by little into their respective ecological niches and asso- 

 ciations. On any given area of ground there has grown a succession 

 of associations of plants which, as they have contributed to the 

 gradual modification of the soil (or rock) on which they grew, have 

 eventually been replaced by plants of a different association. Alter 

 sufficient time, an association of plants has appeared which, under 

 the existing environmental conditions appears to be the best adapted 

 to the area. This group is often known as a climax, and although it is 

 recognized that a completely stabilized environment never exists, the 

 climax regions for the country have been more or less accurately 

 mapped. Associations of grasses are considered to be the climax for 

 the Plains region; certain climax associations of deciduous trees 

 appear in the eastern part of the country ; evergreen trees constitute 

 a climax for the western coastal region; and there is a xerophiloua 

 association of succulents and leathery species that forms the climax 

 in the deserts of the Southwest. It should be kept clearly in mind 

 that every plant association, whether climax or preclimax, is the out- 

 come of long ages of natural selection. 



Enough work has been done to enable us to predict the climax for 

 most areas with some confidence, but it may be many years before 

 the date of the climax can be predicted, if that ever becomes possible. 

 In a general way we know what species tend to occur together, and on 

 what sites they are to be expected, in any given succession in any part 

 of the country. Careful observation of a species in its native, un- 

 disturbed (or disturbed) habitat will usually demonstrate where 

 and how it fits into its environment. According to Shantz (50h p. 

 357): 



A thorough understanding of the natural vegetation climax and of the second- 

 ary stages leading to its re-establishment when it is once destroyed is the best 

 basis for a revegetation and erosion-control program. 



For many years plant ecologists have been engaged in determining 

 the fundamental principles concerned with the initiation, develop- 

 ment, and maturity of plant associations on given sites. The slow 

 encroachment of lichens and mosses on bare rock, followed by gradual 

 appearance of higher plants, the development of soil, and the inva- 

 sion and succession of later associations tending toward a stable inter- 



