INTRODUCTION 



The system of "jammer" logging commonly used for harvesting timber on steep slopes 

 in northern Idaho requires a network of roads spaced 300 to 500 feet apart. A well- 

 designed and maintained road layout gives the land manager ready access for fire pro- 

 tection and application of cultural treatments. On the other hand, such a permanent 

 road system requires preemption of timber-producing land for roadbeds, cuts, and fills. 

 Estimates of land area used for roads have ranged from 5 to 21 percent of the total 

 land area according to varying criteria and different sources (Moessner 1960; Olson 

 1952; Roffler-^). Thus, some land managers assume a 10- to 15-percent loss of timber- 

 production area when establishing and maintaining this type of road system. Further- 

 more, watershed managers have been concerned about a possible disruption of water 

 movement through the soil mantle caused by roadcuts, with a consequent effect on 

 adjacent and downslope stand development.^ 



A pertinent question facing the land manager is whether the open area actually 

 occupied by the road is a legitimate estimate of the percentage loss in total area 

 productivity. Is 10 to 15 percent an accurate estimate of timber-production area 

 loss, or do roads affect production in the adjacent stands? In Germany, Kramer (1958) 

 studied 108 temporary sample strips along roads that were 4 meters to greater than 

 20 meters in width in pure beech ( Fagus sylvatica L.) and pure Norway spruce ( Picea 

 abies (L.) l^arst.) stands from 30 to 150 years old. Roadside trees had greater growth 

 in both height and diameter than those located farther within the stand. Volume 

 effects were calculated by expanding the width of the 10-meter roadside strip to 

 include half of the road width. For Norway spruce, the volume per hectare of these 

 "expanded" roadside strips did not decrease until the unstocked area exceeded 5 meters 

 (16.4 feet). For beech, the critical width of the unstocked area was 12 meters (39.4 

 feet). The capacity of beech to utilize larger openings than spruce was attributed 

 to the large difference in crown expansion potential between the two species. 



Landbeck (1965), conducting his studies in East Germany, followed the methods 

 of Kramer (1958) and established 95 temporary plots along roads 3 to 6.5 meters (9.8 

 to 21.3 feet) wide in pure Scotch pine ( Pinus sylvestris L.) stands aged 60 to 120 

 years. Here, too, the diameter of roadside trees was greater than that of interior 

 trees, but height was slightly less and quality was lower. The volume per hectare 

 of the "expanded" roadside strips (strip plus half of road width) was less than 2 

 percent lower than the volume per hectare within the stand. No critical width for 

 the unstocked area could be established because the range of road widths was so narrow. 



If roads seriously affect timber production in northern Idaho, land managers 

 need a quantitative estimate of production losses to aid in management planning and 

 evaluation of logging systems. The objective of this study was to estimate the poten- 

 tial timber production loss caused by a permanent road system. A projection of such 

 loss was established by determining the magnitude of "edge effect" in managed stands 

 in northern Idaho and comparing it with the width of road opening. 



Roffler, H. C. Lost Block Road Study. USDA Forest Serv., Northern Region, 

 Coeur d'Alene Forest, Unpub . Rep., 4 pp. i950. 



2Coile, T. S. Forest and range soil problem analysis for the Northern Rocky 

 Mountain Region. USDA Forest Serv., Intermountain Forest and Range Exp. Sta., Unpub. 

 Rep . , 33 pp. 1950. 



