14 CONCEPT AND HISTORY. 



FOREST INDICATORS. 



A general idea of indicator plants has existed in forestry for nearly a century, 

 and it is strange that the forester was not the first to formulate a system of 

 indicators. His nearest approach to this is found in the tables of tolerance 

 (Graves and Zon, 1911 : 20). The fact that the forester's attention was 

 fixed primarily upon reproduction and little or not at all upon the shrubs 

 and herbs of the forest floor probably explains the long absence of any definite 

 recognition of indicators. In forestry as elsewhere, but even to a greater 

 degree, a system of indicator plants and communities was impossible before 

 the use of instruments and quadrats and the application of successional prin- 

 ciples. As is shown later, however, forestry already possesses a large amount 

 of indicator material which only needs to be organized upon a systematic basis. 

 Practically all site studies have much and some of them great indicator value. 

 However, the researches directed primarily toward this have been few, and it 

 is necessary here to consider only the following: 



Cajander, 1909. — Cajander (1909; Zon, 1914 : 119) has made an interest- 

 ing endeavor to recognize forest types on the basis of the living ground-cover 

 as indicators of the soil conditions. He classified the forests of Germany, 

 composed largely of spruce, fir, beech, and oak, into three types: 



1. Oxalis type (forests with a layer society of Oxalis acetosella). 



2. Myrtillus type (forests with a layer society of MyrtiUus nigra). 



3. Calluna heath type (forests with a layer society of Calluna vulgaris). 



The Oxalis type characterizes the best soiLs and comprises nearly all the 

 dominant trees. It is further divided into four subtypes, marked by Impa- 

 tiens-Asperula, Asperula, Oxalis, and Oxalis-Myrtillus respectively. As Zon 

 points out, the dominant species of trees are assumed to play no part in deter- 

 mining the type. The author also dismisses the effect of light as of no impor- 

 tance. This appears to be quite unwarranted, as no measurements seem to 

 have been made of light, as is apparently true of the other factors as well, and 

 consequently the correlation between communities and conditions is super- 

 latively general. Little or no attention is paid to the successional sequence 

 of dominants or subdominants, and here again the real indicator values are 

 overlooked or lost. Zon further points out that the author's own statements 

 are contradictory, in that he states in one place that the layer societies indicate 

 the physical conditions independent of the tree species, while in another the 

 trees are said to determine the character of the herbaceous vegetation beneath 

 them. While Cajander has erred in assigning greater importance to the sub- 

 dominant herbs and low shrubs than to the dominant trees, his use of the 

 forest societies as indicators is sound, and will serve to correct the usual prac- 

 tice of foresters who have neglected the undergrowth. 



Clements, 1910. — The investigation of the lodgepole-burn forests of 

 northern Colorado in 1907-1908 was essentially a study of fire indicators, 

 herbaceous as well as woody. Its real importance in this connection lay in the 

 fact that it was the first study of forests made on the complete basis of instru- 

 ments, quadrats, and succession. It was pointed out that lodgepole pine and 

 aspen are practically universal indicators of fire and not of mineral soil or other 

 conditions, at least for the Rocky Mountains. Agrostis hiemalis, Chamaene- 

 rium angustifolium and Vaccinium oreophilum were recognized as the chief 



