DRY-ROT OF INCENSE CEDAR. 29 



by 40-year age classes, grouping dominant and suppressed trees 

 separately, and the percentage of dry-rot was determined for each 

 age class. This was done by relating the total volume of dry-rot 

 in each age class to the total volume in cubic feet of the trees in that 

 age class. From these tables it was apparent that while there was 

 no tangible difference between the amount of decay in the dominant 

 and suppressed trees on the intermediate area, on the optimum area 

 there was a decided difference, most strongly shown in the younger 

 age classes, the dominant group having a lower percentage of decay 

 than the suppressed trees. 



That the trees in the intermediate area fail to bear out the relation- 

 ship between suppression and decay indicated by the results of other 

 workers on different species is after all logical. The reason for this 

 is not hard to find. These trees are in the intermediate range for 

 incense cedar, where the growth on the whole is relatively slow, and 

 while they may be placed in dominant and suppressed groups within 

 themselves, yet in relation to the trees in the optimum range they 

 are slow growing, practically all being included under suppressed, 

 with a few dominants. In other words, most of these trees are under 

 the influence of regional suppression. Another glance at figure 1, 

 which shows the great disparity between the volume-age curves for 

 the two regions, brings this out more clearly. The term "regional 

 suppression" is a new one. However, the concept which it embraces 

 has long been advanced in ecology and silviculture. That there is 

 a marked decrease in vigor and a decline in the rate of growth for 

 each tree species outside its optimum, becoming greater as the dis- 

 tance from the region of best development increases, until finally 

 the species becomes completely suppressed by other species either 

 in or closer to their own optimum, has been pointed out by Mayr 

 (13, pp. 73-79). This is exactly what has happened to incense cedar 

 in the intermediate range. At best a second-story tree, in this 

 region, away from its optimum, it has become, except for a few 

 scattered individuals, badly suppressed by Douglas fir, Jeffrey pine, 

 and yellow pine, which, while not in their own optimum, are yet 

 closer to such a condition than the incense cedar. Mitchell (17, p. 33) 

 recognizes how far this may go in suggesting that it may be advisable 

 to eliminate the species entirely on the sites less adapted to it. 



An analysis of the field notes reveals that this regional suppression 

 is not due to a pathological condition, which might be suspected from 

 the presence of the mistletoe (PTioradewdron juniperinum libocedri) or 

 of the needle and twig parasite (Gymnosporangium blasdaleanum) . 



A comparison of the trees on the intermediate area with the volume- 

 growth curve for the optimum area resulted in the classification of 

 only 38 out of the total of 495 trees as dominant. In other words, 

 457 of the trees on the intermediate area are actually suppressed 

 when compared to the average for the optimum area. 



