INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 279 



the quinquennium and are included for the first time in the 

 1915 board-measure computations, the annual increment per 

 acre as shown in board feet is perhaps somewhat greater than 

 the mean annual increment would be for a longer period. The 

 annual increment per acre in cubic feet is therefore considered 

 as a better criterion of the relative productivity of each site. 

 It is noteworthy that Site I produced 25.1 cubic leet per acre 

 per year as against 15.3 cubic feet for Site II or, in other words 

 Site I produced a cubic volume of 64% more than Site II during 

 the same five-year period. 



It is also interesting to compare the average breast high 

 diameter growth of both forms of western yellow pine on the 

 two sites. ''Black jack" averaged 0.85 inch on Site I while 

 the diameter growth of this form on Site II was only 0.71 inch. 

 The breast high diameter growth of ''yellow pine" on Site I 

 averaged 0.75 inch, while on Site II it averaged only 0.54 inch. 

 The mean diameter growth for the species as a w^hole amounted 

 to 0.83 inch on Site I and 0.68 inch on Site II. 



During the course of the compilation of the pertinent data 

 presented above an opportunity was offered to compare the 

 average increment per tree of the different crown classes. All 

 of the trees on the permanent sample plots were classified ac- 

 cording to their dominance or relative position in the crown 

 cover, into the following crown classes: 



X = Isolated: Trees growing in the open which do not form a 

 con'tiguous part of the regular forest canopy. 



D = Dominant: Trees with crowns extending above the general 

 level of the forest canopy and receiving full light from above 

 and partly from the side; larger than the average trees in 

 the stand, and with crowns well-developed but possibly 

 somewhat crowded. 



C = . Codominant: Trees with crowns forming the general level 

 of the forest canopy and recei\nng full light from above 

 but comparatively little from the sides; usually with me- 

 dium-sized crowns more or less crowded on the sides. 

 I = Intermediate: Trees with crowns below, but still extending 

 into the general level of the forest canopy, receiving a little 



