Comparing LongComparing Long-Reach vs. Conventional Skyline Design 
Options:
      Impacts on Road Densities, Sediment Budgets, Economics and Silvicultural 
      Options

Executive Summary
By
Dr. Peter Schiess, Professor
Finn Krogstad, Research Associate II
Luke Rogers, Research Assistant
University of Washington
Forest Engineering
Box 352100
Seattle, WA 98195-2100
Completed under Contract
DNR Agreement # FY 99-001
June 1999
To
Christi Fisher
DNR Project Administrator
Engineering Division
Box 47014
Olympia, WA 98504-7014
Executive Summary 
Comparing Long-Reach vs. Conventional Skyline Design Options: Impacts on Road 
Densities, Sediment Budgets, Economics, and Silvicultural Options
Abstract
Several surprising results were identified in a study of the operational, 
economic, and environmental impacts of a long-span road-reducing alternative to 
conventional forest management in T12N R14E in the Ahtanum valley West of 
Yakima. The no-new-roads long-span approach didn’t reduce economic return below 
the conventional approach, but neither did it reduce sediment delivery to the 
stream network. The explanation for these counter-intuitive results can be found 
in the density and stream-proximity of the road network in the study area. The 
tenfold sediment increase over background might suggest a program of elimination 
and/or surfacing of existing roads, but our analysis suggests that the 
construction of a ridge-based road network will be both environmentally and 
economically superior. This sort of integrated approach to harvest and road 
system planning at the landscape or watershed level, which includes cumulative 
impacts from sediment budgets, appears to be most promising in identifying 
management options for reducing salmonid habitat degradation. 
Introduction
The Washington Department of Natural Resources (DNR) entered into an agreement 
with the federal government relating to the compliance with the federal 
endangered Species Act (16 US>C> 1531 et seq). As part of that agreement DNR 
developed a Habitat Conservation Plan (HCP) which would provide the framework 
for the management activities of its trust lands. Significant changes to timber 
sales requirements resulted. Rather than commit to a definite, upper limit on 
road densities, DNR agreed to provide for a comprehensive landscape-based road 
network management process. The major components of that process includes the 
minimization of the active road density and a site specific assessment of 
alternatives to new road construction such as extending yarding distances and 
their use where consistent with conservation objectives (DNR, 1997). 
Impacts on salmonid habitat or water resources in general are influenced by 
activities in any one of the six general phases of road system development: 
planning (yarding distance – road densities/locations), design, construction, 
use, maintenance, and decommissioning. The planning aspect includes the 
trade-off of yarding distance – road densities and within this general framework 
the location of roads based on the particular topographic and geologic 
conditions. A clear understanding of a total and true cost accounting of the 
road transportation system has to include aspects of sediment generation and 
sediment delivery to the stream network. 
The overall goal as stated in the HCP is to reduce road densities based on the 
assumptions that this is one of the significant factors that affect salmonid 
habitat. Road density reduction would be achieved through a combination of 
increased yarding distances and an aggressive road-decommissioning program. Both 
options (increased yarding distance, road decommissioning) have costs associated 
with them and both strategies will result in decreased road densities. However, 
as will be shown, neither strategy alone, or in combination may reduce the true 
agent of salmonid habitat degradation; sediment delivery. 
What is needed is an integrative approach to road system development including 
new road construction. What is not quite clear are the cumulative effects of 
either or what a combined strategy has on the natural resources and habitat of 
sensitive species. Any comparative analyze should attempt to quantify road use 
patterns (and with it the economic trade-off) and include sediment budgets as 
the true agents of salmonid habitat degradation
Objectives
The objective of this study was to develop a framework for comparing the 
economic and environmental costs of conventional harvest systems versus a road 
minimizing option using a combination of long-reach skylines, helicopters, and 
conventional skyline systems. Each management plan would be assessed based on 
the economics and the resulting sediment budgets 
  Develop appropriate production and costing models for long-span cable yarding 
  and review the appropriate information for long-reach ground systems. 
  Analyze the impacts and trade-offs of long-span yarding systems and reduced 
  roading on total costs and revenues. 
  Assess the impacts of roads on sediment generation and delivery to salmonid 
  habitat. 
Approach
The project was organized along three major activities in order to address the 
issues mentioned earlier. First, a thorough literature search and assessment of 
current knowledge with regard to long-span cable yarding production and costs 
was carried out. This is an area where little information currently exists. The 
second activity developed the operational and economic parameters for a harvest 
and transportation plan comparison of a portion of the Ahtanum watershed. It s 
purpose was to develop a long-span yarding alternative with the resulting road 
system and compare the results (revenues and road densities) with the current 
harvest and transportation plan that had been developed by DNR harvest planners 
using conventional yarding systems and yarding distances. The third activity was 
to use the road systems (road use pattern and traffic loads) from each plan and 
develop the corresponding sediment budgets (sediment generation and delivery)
Results
Long-span cable yarding cost and production estimates
Most current harvest and road systems are based on a yarding technology with an 
upper limit of approximately 2000 ft external yarding distance (EYD). Available 
information shows a wealth of information for the conventional spans but very 
little information exists for the extended spans beyond 2000 ft
Long-span skyline systems (also referred to as Wyssen systems) developed 
primarily in Central Europe. The Swiss Federal Forest Research Institute 
developed a series of production and cost tables for the forest districts to be 
used in their production and cost appraisals based on a database that covered 
four years. They provided detailed information for corridor layout, system setup 
(rigging and move times) and production as a function of yarding distance.
The observed North American experiences with Wyssen-type cable systems appeared 
well correlated with Central European experiences as far as cycle times were 
concerned. Production was primarily a function of distance and did not vary with 
silviculture such as clearcut or selective cut. By increasing log lengths 
production could be increased without impacting cycle times. In most, if not all 
cases turns were usually fully suspended making the yarding cycle independent of 
ground or stand conditions. Currently there are no Wyssen systems working on the 
U.S. West coast. A Wyssen system was used on a Plum Creek Co. timber sale near 
Cle Elum WA in 1998. One Wyssen system is currently operating near Boston Bar, 
BC, Canada.
Production data for slackline operations with yarding distances beyond 2000 ft 
EYD are rare. Only one reported study was found documenting performance over 
4000 ft. Average turn times of 9.02 minutes were reported for an AYD of 1300 ft. 
The production rates reported were not significantly different for uphill and 
downhill (gravity) yarding. However, in general practice the downhill yarding 
was discouraged because of the high level of engineering and fieldwork required 
to insure full suspension of turns.
European long-span skylines systems differ from their North American counterpart 
in horsepower rating and therefore line speeds. The effect of line speeds on 
cycle times is shown in Figure 1. Over comparable distances (< 1000 ft) cycle 
times for the conventional tower yarders are half the time for the Wyssen 
systems indicating the effect of line speeds. Cycle times for the Swiss and the 
Hensel model (North American experiences) are very close for the uphill yarding 
operation and differ by about 15% for the downhill operation. Downhill yarding 
results in faster cycle times than for uphill yarding for the Wyssen systems 
because of higher speeds that are attainable with gravity inhaul due to the 
load. Full suspension, however, is critical. The cycle times for the tower 
yarder are about 60% of the cycle times reported for the Wyssen system operating 
in the downhill direction.
 
  Figure 1. Total cycle times for uphill and downhill yarding for three 
  long-span and one conventional span systems; a Wyssen system(Swiss 
  conditions-Abegg and PNW conditions-Hensel) a large tower yarder and a 
  conventional-span yarder 
The results revealed higher production costs for EYD >2000 ft. This is in 
agreement with surveys of logging contractors who clearly showed a preference 
for yarding distances less than 1000 ft. Reasons were increased rigging times 
and the increased risk for operational delays. In general, optimal AYD increased 
with increasing rigging times and/or decreasing harvest volumes (MBF/acre) and 
log/turn size.
To explore the effect of silviculture on yarding costs two cases were 
considered. The first case was typical of a regeneration cut of second-growth 
forests, 50-60 years old with an average volume of 35 MBF/acre and log size of 
approximately 120 BF/log resulting in a turn size of 6200 lbs. Stump-to-truck 
cost for a conventional system with an AYD of 600 ft was $103.-/MBF. A 
comparable large tower system in the same silvicultural situation had 
stump-to-truck costs of $124.- and $136.-/MBF for AYD’s of 1000 and 2000 ft 
respectively compared with $116.- and $119.-/MBF for a Wyssen system.
The second case was a selection cut in older stands with log sizes of 20 -22 
inch (167 BF/log and payload of 9000 lbs. (indicative of east-side condition) 
and volume removals of 15 MBF/acre. Production costs for a large tower yarder 
were $116.- and 117.-/MBF for AYD’s of 1000 and 2000 ft. Decreasing volumes with 
increased turn size (such as in selection cuts) had the effect of increasing the 
optimal AYD. Noticeable was the impact it had on making yarding costs almost 
independent of distance. Long-span production costs of $116 to 117.-/MBF (AYD’s 
of 1000 – 2000 ft) compared favorably with conventional systems despite higher 
volume and shorter yarding distances ($103.-/MBF, AYD = 600 ft). Piece or turn 
size played an important role. With the longer cycle times opportunities exist 
to maximize payloads in a similar fashion as with helicopter yarding and 
therefore minimize the impact of distance on yarding costs.
Long-span systems appeared promising as an appropriate alternative where 
silvicultural goals included significant dispersed or aggregated retention. In 
both cases rigging requirements would increase while at the same time reduce the 
available, total extraction volume but not necessarily the log and turn sizes. 
Long-span systems had comparable costs to conventional systems, if applied under 
appropriate silvicultural conditions. Such silvicultural goals might help 
long-span yarding systems because of the interaction of total volume available, 
piece size and rigging time requirements.
Scheduling and Network Analysis
The Ahtanum is characterized by its checkerboard ownership pattern where various 
other landowners are involved, each with different land management goals. To 
reduce those impacts a township was selected for further analysis where DNR had 
substantial (although no exclusive) ownership. The original harvest and 
transportation plan developed by DNR harvest planners was adjusted to reflect 
the new planning boundaries. However, the stated goals and harvest volume 
targets were used in the adjusted areas (Figure 2).

Figure 2. SNAP analysis for the conventional plan (as developed by DNR). Shown 
are the harvest areas (by period and silvicultural harvest method) and resulting 
road use pattern. Non-DNR ownership is usually characterized by an absence of 
setting boundaries. A total of 12.2 miles of new roads were constructed with 
11.5 miles on DNR land. A total of 2551 acres are harvested of which 2031 acres 
as partial cut and 520 acres as regenration cut over a 25-year time span (5 
planning periods). 
The long-span management plan had as its stated goal the reduction of overall 
road densities. This could be achieved by extending the yarding distances beyond 
the conventional reach (>2000 feet) and/or by not allowing any new road 
construction. We chose to use both goals. In order to approach the extremes of 
extending conventional yarding distances beyond 2000 feet we specified that any 
setting not currently served by an existing road would be harvested by 
helicopter (Figure 3).
The HCP dispersal and NRF habitat requirements as well as the late seral stage 
requirements agreed upon with local tribes were adhered to for the area-adjusted 
base plan (DNR’s conventional plan) and the long-span plan. Target volumes for 
both plans were set at 10 MMBF for the first three periods and then 1 MMBF for 
periods 4 and 5 as stated in DNR’s original base plan. The software used for 
scheduling and network analysis was SNAP 3.19.

Figure 3. SNAP analysis for the long-span. Shown are the harvest areas (by 
period and silvicultural harvest method) and resulting road use pattern. Non-DNR 
ownership is usually characterized by the absence of setting boundaries. Note 
the absence of any new raod construction. A total of 2557 acres are harvested of 
which 2158 acres as partial cut and 399 acres as regeneration cut over a 25-year 
time span (5 planning periods). 
The results for the two management plans are shown in Table 1. Neither plan is 
able to meet the stated harvest volumes without violating any of the adopted HCP 
or adjacency requirements. Harvest volumes achieved were about 10 MMBF over the 
five periods for both plans. The long-span plan results in lower total costs 
(yarding, construction, haul) than the conventional plan despite the higher use 
of helicopters which are more expensive on a per unit basis than cable yarding 
(637 acres yarded by helicopters). However, those higher helicopter costs are 
recovered through the absence of 12.2 miles of new road construction costs in 
the conventional plan ($ 397,000). The conventional management plan, despite 
shorter yarding distances results in lower, total revenues than the long-span 
management plan (2.88 million versus 2.31 million dollars).
The helicopter use and related harvest patterns reveal some interesting aspects. 
The conventional plan never used a helicopter despite its potential 
availability. Targeted volumes could be achieved within the other constraints 
without resorting to the more expensive yarding method. However, in the 
long-span plan, helicopters had to be used in order to meet stated harvest goals 
from areas that were not constrained by other requirements such as adjacency, 
seral stage and HCP requirements. As a result the long-span plan met stated 
harvest goals by harvesting more areas in closer proximity to existing roads 
despite the smaller tree sizes and lower standing volumes. More mature stands 
further removed from the existing road network proved economically not as viable 
because of the high yarding costs brought about by long cycle times.
Table 1. Results from the scheduling and networking analysis for the two 
management plans. Shown are the harvest systems utilized, road uses and road 
construction requirements together with costs and revenues. Note that the 
long-span plan requires no new road construction.
      Period12345Total
      Conventional Plan
      Ground Systems (Acres)118349944646752,249
      Cable Yarding (Acres)891773700303
      Heli (Acres)000000
      Roads used (miles) Existing29.417.914.05.27.374
      Roads used (miles) New roads 5.23.03.20.1011.5
      Yarding costs ($ 1,000)4702562091301351,200
      Haul costs ($ 1,000)210112933359507
      Construction costs ($ 1,000)1591221114.40396
      Total Costs ($ 1,000)8394904131681942,104
      Volume harvested (Mbf)4,7602,2761,71799993610,688
      Revenues (million $)2.88
      Long-span alternative (no new roads)
      Ground Systems (Acres)81437140610401,695
      Cable Yarding (Acres)48177000225
      Heli (Acres)4331287600637
      Roads used (miles) Existing25.314.79.12.6051.7
      Yarding costs ($ 1,000)9585083464901,861
      Haul costs ($ 1,000)21010492250431
      Construction costs000000
      Total Cost ($ 1,000)1,1696134387402,294
      Volume harvested (Mbf)48512276171737409218
      Revenues (million $)2.31

 
 
Delivered Sediment 
The harvest and haul activities identified by SNAP, provided a unique 
opportunity to estimate sediment production for the two options and delivery to 
the stream network. The topography was divided into a grid, and information 
relevant to sediment production and delivery (e.g. local slope, distance to 
stream, road surfacing) were recorded for each cell. The Washington Forest 
Practices watershed analysis manual was used as the basis of a GIS program to 
estimate sediment production and delivery from each grid cell. Road usage was 
estimated from SNAP’s timber haul estimates (MBF/period). Vegetation on cut and 
fill slopes was assumed to increase by 1% per year, while all existing were 
assumed to be 30% vegetated at the start of the simulation. Harvest related soil 
disturbance was assumed to produce 810 tons/acre during the period of harvest. 
Overland filtering/delivery to streams was estimated by assuming that half the 
sediment was filtered every 90’. 
Table 2. Sediment Delivered to the Stream Network (tons/year) is estimated for 
each management plan, study period, and source area. Concentrating haul onto 
native surface roads in close proximity to the stream network results in a tread 
volume that dwarfs all other sources. 
      Period12345mean
      Conventional Plan
      Background747747747747747747
      Harvest 262152311
      Cut Slopes380371350318314347
      Fill slopes184177167151150166
      Tread 747164234375346642915205
      Long Span (no new roads)
      Background747747747747747747
      Harvest 302344012
      Cut Slopes354330303276276308
      Fill slopes175164151137137153
      Tread 965874444498306930695548
       

The results of this analysis are summarized in Table 2. Contrary to 
expectations, the long-span (no new roads) option actually produced more total 
sediments than the conventional harvest/transportation plan. The no-new-roads 
option produced less sediment from cut and fill slopes, but this reduction was 
dwarfed by haul related erosion from the tread surface. In the long-span case 
SNAP routed more of the long-span haul along roads in proximity to the stream 
network. The resulting increase in total sediment delivery does not represent a 
failure of the long-span system, but rather that usage of specific roads is far 
more significant than road density. 
These estimates of delivered road sediment are much higher (~7Xbackground) than 
those predicted by Ahtanum Watershed Analysis report (~3Xbackground), even 
though similar methodology and numbers are used. The main difference between 
this study and the watershed analysis report is that this study used SNAP 
outputs to identify traffic loads and patterns (Figure 4). 
 
Figure 4. Twenty-five years of haul in the long-span option. While the road 
network covers the entire planning area (Figure 2), haul is concentrated along a 
relatively few roads. Thicker lines indicate more haul volume. 
The reason that minimizing road density did not reduce road sediment is that the 
existing road network (Figure 5) routes most of the haul traffic (Figure 4) onto 
roads that closely parallel the stream network (Figure 5). The problem with 
using road density to describe road impacts is that the vast majority of the 
road network gets little or no haul, and the vast majority of the haul traffic 
goes over relatively few road segments. This concentration of haul volume over 
roads located very close to streams produces the large tread derived sediment 
load, which in turn dwarfs the sediment produced on all other roads and all 
other sediment sources in Table 2. 
A traditional program of road density reduction would eliminate many unused spur 
roads, which being unused would thus not be the ones producing the sediment. 
According to the watershed analysis manual, applying a thick gravel to this 
native surface road network would eliminate 80% of the tread sediment production 
but the remaining 20% of the tread related sediment will still approximately 
double the background sediment. In fact, even if every road in the study area 
were paved, the cut and fill slopes alone would still provide more than 50% of 
background levels.

Figure 5. Sediment delivery and the existing road network. While areas near 
streams have near 100% delivery (darker areas), a large fraction of the 
landscape has <0.1% delivery (white areas), in which road networks can be 
constructed that will deliver almost no sediment to the stream network. Examples 
of such ridge road networks exist in the Northwest and Southeast portions of the 
planning area. 
An alternative approach to reducing delivered sediment is suggested by Figure 5 
in which long linear segments of the study area can be identified that deliver 
little or no sediment to the road network. A network of primary and secondary 
roads following this ridge network (and crossing the stream network only rarely) 
would deliver almost no sediment to the stream network, even if native surfaced. 
Assuming that rock accounts for half the cost of a new rocked road, then for the 
same cost as rocking a mile of existing road, it is possible to build a mile of 
ridgeline road, with much less sediment delivery. 
These results show that sediment budgets and their spatial origins are most 
critical to effectively address salmonid habitat impacts. As shown here and in 
the Hoodsport analysis, road density management in isolation is not an effective 
tool to management impacts. To the contrary, uninformed road de-commissioning 
might result in no improvement at all. 
Conclusion
Effective management to improve salmonid habitat depends on a clear 
understanding of the agents of sediment generation and delivery. Both processes 
are directly linked to transportation issues (both yarding and truck haul) which 
include the earlier stated six general phases of road system development. 
Paradoxically as it may sound, new road construction may actually improve 
salmonid habitat by routing traffic over less sensitive roads. However, such a 
solution is only possible in the context of comprehensive harvest and 
transportation planning at the landscape or watershed level, which includes 
cumulative assessment tools, among them a sediment budget. As part of a 
different project, we are pursuing such an approach.