Figure 4. — The net effect of roads 

 on total stand volime produc- 

 tion by pooling data from above 

 and below the road. (Zones 

 connected by the bracket are 

 not significantly different ^ 

 P <0.05.) 



VOLUME/A. (M.caft.) 







:v:-::v>.x> 



0' 22' 44' 66' 



DISTANCE FROM ROAD 



DISCUSSION 



The obvious additional grovtfth of below-road trees indicates improved site produc- 

 tivity due to additional water availability. Precipitation falling on an outsloped 

 road is redistributed below the road and the unvegetated fill should provide a reser- 

 voir of available water for adjacent trees during part of the summer drought period. 



A normal growth increase in border trees in response to additional growing space 

 is apparently masked by water distribution effects. Below-road trees would have 

 this effect included as part of the total response. Conversely, n m" g^i fi l-■an^ growth 

 response in above-the-road trees may indicate that the expected additional growth 

 due to space is reduced by the loss of moisture from the cut bank. These roadside 

 effects indicate that disruption of water movement through the soil mantle because 

 of roads (see footnote 2) is not a serious consideration for soils similar to those in 

 this study. 



The common method of multiplying clearing width times road length to obtain 

 estimates of area in roads does not take into account the capacity of trees to utilize 

 at least part of the opening. Silen and Gratkowski (1953) presented an enlightened 

 view on use of road measurements in their analysis of a staggered-setting system 

 of clear-cutting on the H. J. 7\ndrews Experimental Forest' in Oregon. The total area 

 disturbed by roads and landings amounted to 9.8 percent, but the estimated loss in 

 productive area was only 4.1 percent when reasonable assumptions on crouTi expansion 

 and productivity were included in the calculations. 



6 



