GROWTH METHODS. 441 



Bmn-scars. — The method of using ring-counts and the scars left by fire upon 

 trees and shrubs for determining successional changes, as well as the dates of 

 their occurrence, is described in the following extract (Clements, 1910 : 9) 

 (plate 61 a) : 



"The basic method of reconstructing a burn has been to determine the ages ' 

 of the oldest plants which have come in since the fire, appUed both to the trees 

 and to the shrubs and perennial herbs of each type. It takes account of dead 

 trees and shrubs, standing and fallen, in addition to the hving ones. The 

 method of fire-scars is of equal importance, though often less available. 

 Where the same area has been burned over two or more times this method is 

 of unique value, for it is not unusual to find double and even triple scars. 

 The natiu:e, position, and extent of fire scars are of equal importance. Any 

 evidence left by a fire upon a woody plant i§ regarded as a scar. Hence it is 

 possible to distinguish top scars, trunk scars, and base scars with respect to 

 position, and bark scars and wood scars with respect to depth. Heal scars 

 and hidden scars occur on living trees, while white scars and cinder scars are 

 foimd on dead or dying trees. In addition to ages and scars, the observation 

 of sou layers is often of great help. The presence or absence of a cinder layer 

 or of cinder pockets or of an organic layer or cover often goes far to check or 

 confirm the evidence drawn from ages or scars. 



"The evidence of age drawn from annual rings is usually so clear and deci- 

 sive as to be beyond question. Occasionally with seedlings, and often in the 

 case of suppressed trees, it is impossible to make an absolute count of rings, 

 even by means of microscopical sections. In practically all such cases an 

 examination of other individuals is conclusive. 



"A distinction between fire-scars and scars due to other causes is sometimes 

 made with the greatest difficulty, and in rare cases is altogether impossible. 

 In most cases, however, it is possible to recognize a fire scar with certainty. 

 In actual practice the method was to require evidence of charring wherever 

 the age of the scar did not check with that of neighboring scars. Chance 

 scarring by lightning or by a camp fire, often m imexpected places, is of suffi- 

 cient frequence to explain the departure of any charred scar from the normal. 

 The position of a scar often serves to determine whether it belongs to a particu- 

 lar fire or is a mere chance scar. Heal scars aboimd at the edges of a bum, and 

 consequently those caused by the same fire occur on the same side, namely, 

 that from which the fire came. Occasional exceptions arise where a ground 

 fire has unexpectedly worked to the surface, but these are nearly always 

 determined by a careful scrutiny. The nature of fires and their severity is 

 indicated, as a rule, by the depth of scars, and the predominance of bark scars 

 or wood scars is used to determme the relative order of two or more successive 

 fires. Scars from successive fires are often imited in double or triple scars on 

 either dead or Hving trees, and these give the best of all evidence upon the 

 succession of fires and the b\im forests which foUow them. In using the 

 depth or nature of scars as a guide the fact was considered that forests regu- 

 larly contain dead standing trees, some of which may have lost their bark. 

 It is evident that the same fire would cause at least three different kinds of 

 scars in such stands; that is, heal scars, usually basal, on the surviving trees; 

 bark scars on the living trees killed by the fire; and wood scars on the dead 

 trees. The wood scars would, moreover, be cinder scars wherever the bark 

 had fallen off before the fire had occurred. 



"Finally, the data obtained from fire scars were checked by a count of the 

 annual rings formed since the scar was made. The most careful use of the 



