4 BULLETIN 1294, U. S. DEPARTMENT OF AGRICULTURE 
Repeated fires in a scar, resuiting as they generally do in enlarging 
the wound, often obliterate the successive callouses and render impos- 
sible a precise determination of the number of fires that have caused 
it. Nevertheless, if a sufficient number of scarred trees can be stud- 
ied in detail, it is eee: ossible to reconstruct with essential com- 
pleteness the fire history of a given area. 
The most complete records bearing on fire scars for California were 
obtained by Boyce (3) in his study of dry rot in incense cedar. For 
each tree studied the dates of all juries were determined with un- 
usual care, since it was essential to know how long the decay had 
been working in a particular tree in order to determine the age of in- 
fection, the rate of growth, and the rate of spread of the fungus. 
This study was conducted on six areas extending from the Klamath 
National Forest near the Oregon line through the Sierras to the Sierra 
National Forest near the southern end of the great belt of the Cali- 
fornia pine region. It was to be anticipated that these investigations 
would disclose with reasonable completeness the fire history of the 
fe ee within the period represented by the age of the trees 
studied. 
RECURRENCE OF FIRE YEARS 
In analyzing the data from fire scars each area was treated as a unit 
and the dates of all fire injuries were plotted on cross-section paper. 
From these charts it was at once evident that certain years in the 
record were characterized by a large number of scars and might 
safely be considered fire years. Even with the slight errors that 
are iikeely to occur in counting the rings—errors that no doubt 
account in part for a sprinkling of fire scars in the years between 
the principal peaks—there was no reason to doubt that in the past 
the forests have been subjected to periodically recurring fires. 
The earliest date of past fires found on any of the trees studied 
was 1530, and for more than a century after that date comparatively 
few scars were observed, for the reason, no doubt, that of the trees 
growing in the sixteenth and seventeenth centuries only a few have 
survived to the present.’ There is the further fact, already explained, © 
that repeated fires in a particular wound tend to obliterate the evi- 
dence teuiber fires, even if they do not destroy thetree. From about 
the year 1700 on the frequency of the scars is such that the fire his- 
tory of most of the areas studied can be stated with a fair degree of 
precision. 
During the past three centuries the years 1685, 1690, 1699, 1702, 
1708, 1719, 1726, 1735, 1743, 1747, 1750, 1757, 1766, 1786, 1796, 1804 
1809, 1815, 1822, 1829, 1887, 1843, 1851, 1856, 1865, 1870, 1879, 
1889 are indicated cleary as years of extensive fires. Naturally 
enough the latter part of the record is marked by a greater num- 
ber of scars than the earlier part, owing to the oradual elimination 
of the older and more heavily scarred trees. 
During the two centuries for which the data can be regarded as 
fairly complete 25 clearly marked fire years are found and it isa fact 
of high significance that this general average periodicity of eight years 
holds true for all areas studied. The shortest period between fire 
years is 3 years and the longest 11 years. 
