CLIMATIC AND EDAPHIC INDICATORS. 353 



Burn indicators. — It is a general rule that subclimax dominants serve as 

 the typical indicators of forest burns. This is in conformity with the principle 

 that almost any consocies and many socies of the subsere may indicate fire 

 as well as other similar disturbances, the particular initial stage depending 

 upon the degree of disturbance or the frequency of its repetition. The uni- 

 versal occurrence of tree and shrub consocies as burn indicators is explained 

 by the fact that fire not only produces areas temporarily free from the com- 

 petition of the climax species, but also characterized by conditions favorable 

 to less exacting species. Their characteristic dominance is chiefly due to the 

 rapidity and completeness with which they occupy the ground, as a conse- 

 quence of excessive seed production, the opening of cones by fire, or the ability 

 to produce root-sprouts. The conifers rely almost wholly upon the first 

 two methods and chiefly the second, while the deciduous trees depend mainly 

 upon root-sprouts. Among trees, the three types are represented respectively 

 by Pseudotsuga and Larix, such pines as Pinus contorta and attenuata, and by 

 aspen, birch, and alder. The scrub indicators owe their character almost 

 wholly to root-sprouting, reinforced more or less by seed production and 

 mobility. 



The burn subsere consists of the usual stages of annual and perennial herbs, 

 grasses, shrubs, and trees. However, the number and distinctness of the stages 

 and the duration of the subsere depend chiefly upon the severity of the burn. 

 In the most severe burns the initial community often consists largely or wholly 

 of mosses and liverworts, Bryum, Funaria, and Marchantia, and is followed 

 by one of annuals, and this by one of perennials. The species, and to a less 

 extent the genera, of these vary with the climax association, but such species 

 as Agrostis hiemalis, Epilobium spicatum, Achillea millefolium, and Pteris 

 aquilina are more or less universal. The development of a grass stage is less 

 regular, since its place is often taken by scrub when the root-sprouting shrubs 

 are abundant. The scrub is normally replaced by aspen, birch or alder, and 

 these may yield to a subclimax forest, such as that of lodgepole pine, or be 

 replaced directly by the climax. It is obvious that fire may sweep through 

 the scrub, aspen, or lodgepole communities, and initiate new subseres, pro- 

 ducing an intricate pattern of seres and communities. In the great majority 

 of cases, the succession is more or less telescoped, and often completely so. 

 The root-sprouting ability of the shrubs and aspen and the release of the seeds 

 inclosed in cones or buried in the duff enable the shrubs and trees to begin 

 development the first year, at the same time that the herbs appear. In such 

 cases practically all the dominants appear at once, but the development still 

 exhibits many of the features of succession. The stages, though brief, give 

 character to the area in the normal sequence and each disappears in turn as 

 the competition of the next one becomes too great for it. 



For the reasons just given, the herbs are relatively unimportant indicators 

 in complete burns, though they are characteristic in the case of light ground 

 fires. The burn subsere is characterized almost wholly by scrub, deciduous 

 woodland, or subclimax forest, not only because of the duration of the latter, 

 but also because repeated fires tend to make them relatively permanent. On 

 account of differences of distribution as well as the general similarity in require- 

 ments, the three types rarely occur in the same subsere. Two, however, are 

 frequent, aspen and lodgepole being the most common. The rule is that the 



