Figure 1. --Average annual 

 board- foot growth per acre 

 following cormeroial 

 thinning, (Increments 

 oonnected by brackets 

 are not significantly 

 different, P < 0.05.) 



400 



D- 300 



200 



100 



161 



308 



338 



HEAVY 



MODERATE 



CONTROL 



While mortality following cutting varied considerably among plots, treatment effects 

 were obscured by other causes. In terms of sawtimber volume, overall differences were 

 slight, averaging between 37 and 45 board feet per acre per year for the three treatments 



Cutting treatments affected cubic volume increment in the same way they affected 

 board-foot growth (figures 1 and 2). Heavy cutting significantly reduced the growth of 

 the residual stand while moderate cutting resulted in cubic volume growth nearly equal 

 to that of the uncut stand. On the average, the heavily cut stands produced only 25 

 cubic feet per acre per year compared to 53 cubic feet and 49 cubic feet on the control 

 and lightly cut stands. 



Both of the cutting treatments accelerated diameter growth of the residual trees, 

 but this effect was not evident until during the second 5-year period following cutting 

 (table 2). Average diameter growth for 5 years was slightly more on the treated plots, 

 but the increase was not statistically significant. However, during the second 5-year 

 period differences between all three treatments were significant. Apparently it took 

 several years for the released trees to fully utilize the increased growing space. 

 During the second 5 years, trees on the moderately cut plots grew 50 percent faster than 

 trees on the control plots, and trees on the heavily cut plots grew 100 percent faster 

 than the controls. 



Irrigation and fertilization also have been shown to increase diameter growth in 

 stands similar to those in the commercial thinning experiment.^ Some combinations of 

 these intensive practices with thinning may be feasible methods of growing high quality 

 sawlogs on Inland Empire woodlots, especially if management is started early in the 

 life of the stand. 



'^Mosher, Milton M. Irrigation and fertilization of ponderosa pine. Wash. Agr. Exp. 

 Sta. Circ. 365. 1960. 



3 



