426 Forestry Quarterly 



individual tree have been studied. Problems in nursery practice 

 and in field planting have been treated extensively. The chaparral 

 type on 'the Pacific Coast has attracted no little attention, prin- 

 cipally on account of its planting problems and its value as a 

 watershed protection. There have been good articles upon the 

 tolerance of trees and there have been symposia upon the principles 

 involved in determining and classifying forest types. Some work 

 has been done to determine the effect of exposure upon coniferous 

 seedlings during transplanting. By far the greatest emphasis, 

 however, has been placed upon reforestation. Men who have had 

 direct charge of such work have described their experiences in 

 various forest regions of the country: in Arizona and New Mexico; 

 in the sandhills of Nebraska; on the sand plains of Michigan; 

 in the brushfields of California; in the prairie states; and in the 

 Black Hills. 



In all this work, whether experimental or observational in 

 character, modern ecological ideas have been brought into play. 

 It is apparent that the attempt is being made to correlate the results 

 obtained in various branches of silvicultural work with habitat factors . 

 We have in our possession a vast and rapidly growing body of 

 ecological facts concerning the individual tree, the forest formation, 

 and almost every silvicultiu'al practice, from which a few general 

 principles are gradually being crystallized out; each established 

 principle is one step nearer to our iiltimate goal in the develop- 

 ment of the science of forest ecology, and therefore in the gradual 

 building up of a rational American silvicultural system. 



IV. HISTORICAL SUMMARY 



Plant ecology, as we have seen, is the latest stage on the develop- 

 ment of plant geography; the earliest stages of plant geography 

 dealt merely with the description of vegetation and the distribu- 

 tion of plants. The science of plant ecology was founded in 1838 

 when the plant formation was recognized as the fundamental unit 

 of vegetation and the unit with which plant ecology is chiefly 

 concerned. The next step was the study of the plant formation 

 and its various phenomena. This led to the development of 

 ecological plant geography, which was first treated in a systematic 

 manner by Warming in 1895. Then followed the development 

 of experimental plant ecology and a more critical study of the 

 plant formation. Beginning with 1895, the emphasis has shifted 



