Relationsliips between total crown weight (live plus dead) and d.b.h. are shown in 

 figure 4. Crown weight estimates for individual species of each group are within 10 

 percent of the average for the combined species curve. Figure 4 indicates that species 

 tolerance is unrelated to crown weight per tree. The heaviest crowns are developed by 

 ponderosa pine, a relatively intolerant species, probably because its branches grow to 

 large diameters. The lightest crov\fns are also developed by an intolerant species-- 

 we stern larch. 



For most species, the fraction of total crown weight that is dead increases with 

 increasing d.b.h. and thus generally with increasing age (as shown in figure 5). This 

 is expected because as trees age, branches die and can accumulate. Branch retention 

 varies significantly among species. However, the pattern of differences in figure 5 

 does not appear readily explainable. The curve for grand fir and subalpine fir should 

 level off for trees larger than about 15 inches d.b.h. Larch and lodgepole pine are 

 omitted from figure 5 because of negligible branchwood for larch and insufficient data 

 for lodgepole pine. 



Dominants 1 Inch and Less in D.B.H. 



Separation of data into two groups, one for trees greater than 1 inch d.b.h. and 

 one for smaller trees, permitted derivation of more accurate relationships than handling 

 all data together. To obtain adequate data for the small tree group, trees less than 

 2 inches d.b.h. were treated as a data set with tree height as an independent variable. 

 As expected, live crown weight was strongly related to tree height (table 3). Generally, 

 crowns of shade-tolerant species weighed more than crowns of less tolerant species. An 

 exception is the shade-tolerant western hemlock, which was only heavier than western 

 larch. The tolerant trees were also older than the intolerant trees; thus, age may help 

 explain the major differences in weight. Dead crown weight was essentially negligible. 

 For all species, it averaged 1 percent of total crown weight. The largest dead percent- 

 age was 2.4 for western larch, which is interesting because larch greater than 2 inches 

 d.b.h. supported the least quantity of dead branches among all species. 



Intermediates > 



Trees greater than 1 inch d.i. /z, --Best-fitting equations for estimating live and 

 dead crown weights are shown in table 4. 



As species increased in shade tolerance, the difference between total crown weights 

 of dominants and intermediates decreased (fig. 6). This was also true for live crown 

 weights. For western redcedar, the most tolerant of the four species studied, crown 

 class essentially had no effect on total weight and live crown weight per tree. For 

 ponderosa pine, the most intolerant species, total crown weight of intermediates was 

 about one-half of that for dominants. 



For ponderosa pine and Douglas-fir, differences in crown weights between crown 

 classes can be explained by crown ratio and crown length. For these species (trees 

 1 to 12 inches d.b.h.), crown ratio averaged 7.2 for dominants and 5.3 for intermediates. 

 A test of differences between pooled residuals of dominants and intermediates and resid- 

 uals from a composite regression showed that weight predictions based on d.b.h. were 

 significantly different (95 percent confidence level). However, weight predictions 

 based on d.b.h. and crown ratio were from a common population. Although crown ratio and 

 crown length accounted for differences in weight between crown classes, the proportions 

 of foliage and certain branchwood size classes varied considerably by crown class. 



The importance of crown ratio in predicting weights of grand fir and western red- 

 cedar was unclear. The test of differences in live and total crown weight between 

 crown classes was nonsignificant for grand fir and significant for western redcedar. 



13 



