History of Forest Ecology 385 



with the subdivision of these floristic districts into minor units, 

 and with the geographical distribution of taxonomic groups, such 

 as species, genera, and families. Ecological plant geography 

 investigates the distribution of plant associations and formations 

 and inquires into the relation of the factors of the habitat to the 

 distribution of plants, plant forms, and plant communities. In 

 other words, this is plant ecology. Generally speaking, floristic 

 plant geography is concerned with species, ecological plant 

 geography with vegetation. As has been intimated above, the 

 study of the distribution of species dates back to the time of the 

 early systematists, the study of vegetation to the time of the early 

 botanical travelers. So far as this paper is concerned, it will 

 treat largely of ecological plant geography. 



The Philosophical Trend of the Science (1). 



The earliest and simplest development of plant ecology, there- 

 fore, concerned itself with the distribution of plants;, and this 

 phase of botanical knowledge may be said to have originated as an 

 off-shoot of systematic botany. Plant geography, which at that 

 time was merely a study of the effect of the distribution of plants, 

 may therefore be looked upon as the embryonic stage of plant 

 ecology. Curiously, though perhaps naturally, botanists studied 

 the effect before inquiring into the cause of the geographical dis- 

 tribution of plants. 



The first important step in the development of plant ecology 

 was the recognition by Grisebach, in 1838, that the plant forma- 

 tion zvas the funda^iental unit of vegetation. (This date also 

 marks an important step in the organization and development of 

 forest ecology, since the term forest type, used by foresters, is 

 synonymous with the term plant formation. While foresters well 

 knew before 1838 what a forest type was in forestry practice, 

 they did not appreciate its significance to forest ecology. Forest 

 ecologists are therefore indebted to Grisebach for pointng out the 

 true significance of this unit.) Grisebach may be said to have laid 

 the foundation of plant ecology (and forest ecology as well) by 

 inquiring into the structure of vegetation and reducing his in- 

 quiry to a definite principle. He defined a phytogeographic for- 

 mation as a group of plants, such as a meadow or a forest, which 

 bears a definite physiognomic character. Besides Grisebach, the 

 phytogeographers of the 19th century who contributed most 



