Keeping in mind the limitations of these simple 

 tests, it is notablethatthe most difficult treatments 

 coupled with more stems did, in fact, result in more 

 damage as we expected. Predicting actual killing 

 of leave trees was less dependable; the best 

 correlation (only 0.405) was with the volume cut. 



These relationships of stand conditions and 

 damage sustained are not surprising; the ranking 

 tests do, however, provide a quantified and statis- 

 tically significant measure of what is generally 

 assumed— namely, more stems in the stand and 

 more stems marked for leave increase the chance 

 of damage. 



Damage and Logging Conditions 



Damage to leave trees is also influenced by the 

 yarding operation itself. We examined the relation- 

 ship of yarding and tree damage by plotting on 

 maps missing leave trees and seriously damaged 

 trees, and relating these to logging conditions. 

 The conditions examined were: slope; the angle 

 between the "fall line" (direct downslope) and the 

 skyline; and the load capacity computed for each 

 skyline setting. These selected logging factors 

 were then drawn as zones on mylar overlays. 

 Within these overlays the number of seriously 

 damaged or missing trees was tallied. An example 

 is shown in figure 3. The relationship of these 

 factors to damaged or missing trees is summa- 

 rized in table 4. 



SLOPE 



We hypothesized that damage should increase 

 with steepness of slope, because logs would be 

 more likely to roll orslide downslope during lateral 

 yarding. This hypothesis is weakly supported in 

 block 21 , but contradicted by data from block 1 1 . 

 However, in block 1 1 most of the gentle slopes are 

 near the bottom of the block where numerous 

 corridors radiated out from a single common land- 

 ing (fig. 1). Most of the damage in this zone was 

 attributed to missing leave trees that were prob- 

 ably cut in creating the numerous corridors and 

 was not related to lateral yarding. 



If we omit the data from block 11 for to 25 

 percent slopes and combine the remaining data 

 from block 1 1 with that from block 21 , we do find a 



greater incidence of damage on steep slopes than 

 on moderate or gentle slopes. It is doubtful, how- 

 ever, that we can draw afirm conclusion, given the 

 relatively small area of steep slopes and the lim- 

 ited accuracy of plotting the damaged trees. 



ANGLES BETWEEN CORRIDORS AND 

 FALL LINE (CROSS-SLOPE ANGLE) 



We hypothesized that damage is greater when 

 the cross-slope angle increases. In particular, we 

 expect the damage to be more evident adjacent to, 

 and on the downslope side of, the corridors as 

 cross-slope increases under conditions of partial 

 suspension. This is because logs tend to slide 

 downhill during the yarding operation. 



The combined data from blocks 1 1 and 21 show 

 that damage frequency increases as cross-slope 

 angle increases, except for the angle class 60-90 

 percent, where damage was low. However, there 

 was less than 1 acre in this angle class (about 2 

 percent of the total area of blocks 1 1 and 21) and it 

 seems reasonable to conclude the data from the 

 area support our hypothesis. 



We noted also that plots of missing trees align 

 well with some downhill corridors in the lower 

 portion of block 11; in particular, with corridors 

 that are at moderate to high angles with the 

 contours. Personal observations during the yard- 

 ing operation also confirmed a relatively high 

 incidence of tree uprooting in such circum- 

 stances. Therefore, we expect a greater incidence 

 of damage adjoining corridors where cross-slope 

 angles are great— especially in downhill yarding 

 situations when logs are not fully suspended. 

 Perhaps a distinction between types of damage 

 would more strongly reinforce this expectation. 

 And perhapsthe basisfordeterminationshould be 

 number of damaged trees per unit length of 

 corridor— rather than per unit area of treatment— 

 to test this hypothesis. However, the accuracy of 

 plotting damaged trees was not reliable enough to 

 make this type of analysis. 



LOAD CAPACITY 



We hypothesize that damage incidence should 

 be reduced with increasing load capability. Our 

 rationale is that the greater the load capability the 



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