Measures and yields of products and residues 3321 



TOPS AND BRANCHES 



One reason hardwood utilization lags behind softwood is that many hard- 

 woods have large, spreading crowns. In hardwoods with excurrent branching, 

 such as yellow-poplar, sweetgum, and black tupelo, the main stem outgrows the 

 lateral branches, resulting in cone-shaped crowns with clearly defined central 

 boles. In trees with deliquescent branching, the lateral branches grow almost as 

 fast as the terminal stem, and the central stem becomes lost in the upper crown. 

 Over 70 percent of the commercial hardwood volume in the southeastern United 

 States — and most of the hardwood volume on southern pine sites — is in trees 

 with deliquescent branching, such as oaks, elms, hickories, and maples. The 

 marked difference in crown volume for excurrent and deliquescent species can 

 be illustrated by a comparison of yellow-poplar and red oak (table 27-127). In 

 12-inch-dbh yellow-poplars, 1 1 percent of the wood and 16 percent of the bark is 

 in the crown; in red oaks of this size, crowns contain 30 percent of the wood and 

 32 percent of the bark. 



Section 16-1, DISTRIBUTION OF TREE BIOMASS, page 1428, provides 

 detailed information on crown volumes and weights and on the proportion of total 

 tree weight in the crown for various species. Perhaps the most pertinent data is that 

 compiled for 6-inch-diameter hardwoods in the 23 species commonly found on 

 southern pine sites. For these trees, branches 0.5 inch and larger in diameter 

 contributed from 4.5 percent (yellow-poplar) to 27.4 percent (red maple) of the 

 complete-tree ovendry weight (including stumps and roots); the average for all 

 species was 11.9 percent (table 16-2). Branchwood and branch bark as a per- 

 centage of the foliage-free, whole-tree weight (above-ground portions only) is 

 given in table 16-10. On the average, 9.7 percent of the whole-tree ovendry 

 weight is in branchwood and 2.4 percent is in branch bark. 



Other studies have also shown that crowns make up a significant portion of the 

 biomass of small hardwoods. In the North Carolina mountains and Georgia 

 Piedmont, six species with all sample trees between 1 and 5 inches in dbh had 12 

 to 33 percent of their above-ground volume in branches (table 16-7). Hickories 

 under 20 inches in dbh were found to have more wood (by weight) in the crown 

 than in the merchantable bole (Schnell 1978). For results of other studies on 

 crown size and weight, see section 16-1 and tables 16-1, 16-4, 16-9, and 16-13 

 through 16-33. 



Consequently, the amount of topwood available for use is large indeed. In 

 hardwood saw log operations in Alabama and Louisiana, nearly two-thirds of all 

 logging residue was in tops (Beltz 1976). Clearcuts in Alabama left behind about 

 3 cords per acre of pine and hardwood tops (Chappell and Beltz 1973). 



The volume of topwood remaining after saw logs are removed varies substan- 

 tially with tree size, and the greatest amount comes from large diameter trees that 

 yield few saw logs (tables 27-8 and 16-31). For example, a 31-inch oak contain- 

 ing one 16-foot and one 8-foot saw log yielded 100 cubic feet of bark-free 

 topwood (defined as the volume of upper stem and branches at least 5 inches in 

 diameter inside bark and 5 feet long). A 20-inch tree with one saw log had about 

 30 cu ft of bark-free topwood, but a four-log tree of the same diameter had only 

 5.8 cu ft of topwood. 



