where yarding is conducted with cable systems, 

 increases with steeper slope and greater cross- 

 slope angle. Regarding the influence of system 

 load capability, our data are inconclusive. 



Overall, about 23 percent of the marked leave 

 trees were killed in logging, and consequently 

 some "cut" trees were left as replacement. This 

 indicates the importance in marking timber sales 

 under these conditions that an adequate allow- 

 ance be made for leave trees that must be cut for 

 skyline corridors or are killed in the yarding 

 operation. 



Unit and subtreatment 



1 1- 4 (shelterwood) 



21- 4 (shelterwood) 



12- 4 (group selection) 



22- 4 (group selection) 



13- 4 (clearcut) 



23- 4 (clearcut) 



The understory trees were measured on 20 

 sample plots in each unit, so it was not possible to 

 map individual trees relative to skyline roads as 

 was done with the shelterwood trees. The damage 

 reported is an average that varies, depending on 

 whether the plot was in or near a skyline road or 

 lateral skid trail. 



Damage to Understory 



Because understory trees are usually small, we 

 considered virtually any substantial damage likely 

 to kill or to render the tree unsuitable for manage- 

 ment. Therefore, we classed damage in only a few 

 categories as follows: 



No damage - A few scrapes, or broken 

 branches. 



UNDERSTORY TREE DAMAGE 

 Description of Cutting Units 



In the two shelterwood units discussed above, 

 subtreatment 4 called for logging to protect the 

 understory trees below the cutting diameter limit 

 (7 inches [18 cm] d.b.h.). This same subtreatment 

 was also prescribed in two group selection cutting 

 units (units 1 2 and 22, each composed of 8 cutting 

 groups of about 1 acre) and in two clearcut units 

 (units 13 and 23). 



The area and volume of logs removed from 

 subtreatment 4 in the six units were as follows: 



Volume of 

 logs removed 



Ft 3 /acre 



m 3 /ha 



2,950 



206 



2,570 



180 



7,655 



536 



6,241 



437 



4,962 



347 



3,533 



247 



Serious damage - Bent, debarked bole, top 

 broken. 



Cut or missing - Tree no longer present. 



Buried or broken - Whole tree broken off, 

 uprooted, or buried under slash. 



Serious damage and tree killing averaged more 

 than 40 percent in selection and clearcut units, 

 and under 30 percent in shelterwood units (table 

 5). Units were too few to draw statistically valid 

 conclusions on this difference, but it is consistent 

 with logging activities. The process of carefully 

 yarding to avoid damaging large shelterwood 

 trees probably protected some understory trees. 

 Furthermore, the larger leave trees in the shelter- 

 wood units probably prevented logs from sliding or 

 rolling downhill during lateral yarding. 



Area of 

 subtreatment 4 



Acres ha 



6.2 2.5 



4.6 1.9 



1.7 .7 

 1.5 .7 

 3.2 1.3 

 3.4 1.4 



10 



