Basal Area by Diameter Class The basal area by diameter class for the 

 average acre of commercial softwood forest land in 1978 is displayed by pro- 

 ductivity class in Figures 10 and 11. The average basal area per acre was 

 lower on the 20-49 site class timberlands than on the more productive tim- 

 berlands. 



Figure 9 shows the expected basal area per acre by diameter class 

 curve for an average acre of forest land if the forest land base were brought 

 under full management and were fully regulated. The shape of the desired 

 curve is based on a theoretical situation where the forest is fully regulated 

 and a variety of round-wood materials (pulp, poles, and saw logs) are prod- 

 uct objectives (Green 1976). When regulated, the forest would consist of 

 many individual stands of trees with different ages and sizes. All of these 

 different stands, viewed as one, would give the appearance of a forest man- 

 aged by the selection method. The basal area in trees less than 10 inches 

 d.b.h. should be about 40 percent of the basal area in trees 10 inches 

 d.b.h. and larger, or about 30 percent of the total basal area (Green 1976). 

 The desired amount of basal area stocking under the curve is the average 

 level of stocking which should be carried over the life of the stand. Under 

 intensive management, the stand would be allowed to grow to a higher basal 

 area per acre stocking level than desired. It then would be thinned back to 

 a level below the desired stocking level. This process might be repeated 

 several times until the stand is finally harvested. Under an uneven-aged 

 management scheme, certain trees in a stand would be harvested on a periodic 

 basis but the desired average basal area per acre would still be maintained. 



The percent of total basal area per acre below the 10-inch diameter class 

 at the time of sampling was 50 percent for the 20-49 site class timberlands 

 and 44 percent for the 50 plus site class timberlands. At first glance, the 

 percentage of basal area below the 10-inch diameter class would indicate 

 thinning is needed to balance out the diameter distribution on the privately 

 owned lower site land. This would probably be true if the average acre were 

 stocked at or above the desired amount. However, this does not appear to 

 be the case when the average stand age, site class, and forest type composi- 

 tion of the forest represented by each curve are taken into account. All the 

 sites appear to be understocked, especially when compared to basal area stan- 



-52- 



