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Determining the Best Method of Road Decommissioning based on Vegetative Succession

Jacinda ThomasClair Thomas, M.S.

March 2007

Lake County Resources Initiative

Chewaucan Biophysical Monitoring Team25 North E StreetLakeview, OR 97630

lcri.org

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IntroductionVegetation on decommissioned roads differs in specie type and density to that

of vegetation off decommissioned roads. It is assumed this is due to compaction.Observations showed that vegetation on scarified, sub-soiled, and blocked roadsdiffered from each other, even when the percent cover was similar. Plant

diversity on blocked roads appeared to be less. Could vegetation diversity and density be used to determine a best method fordecommissioning roads?

BackgroundCompaction in roads is caused by machinery such as skidders, feller bunchers,

de-limbers, as well as hard-hoofed animals. Clay soils tend to compact easily while pumice souls and soils high in organic material tend to resist compaction.Concerns surrounding soil structure arise from compactions effect oncompressing and reducing the number of air and water spaces in soil.Compaction results in greater surface flow and less absorbance of water, causingincreased erosion and higher peak flows as well as lower base flows in associatedstreams.

Brittney Price found that subsurface water channels changed according tolevels of compaction on roads. (The Effect of Soil Compaction on SubsurfaceHydrology with respect to Maintained and Non Maintained Roads, ISEF, March,2005.

A soil profile is composed of several layers: litter; organic material, and humusmake up the O horizon; sand, silt, and clay from the topsoil or A horizon; theB horizon contains silts and clay; and the lowest layer, the C horizon iscomposed of boulders, bedrock, and more bedrock. Compaction affects the soilsprofile, ped structure, temperature, moisture, erosion, and plant cover.

The Bestcha report states Roads are associated with a variety of negative effects on aquatic resources including disruption of basinhydrology and increased chronic and acute sedimentation. (Bestcha,et al. Wildfire and Salvage logging, Bestcha Report. March, 1995).

The existing road system on the Fremont Winema National Forest wasdesigned and constructed primarily to accommodate logging systems thatrequired a significantly denser road network than is required by the systemscommonly used today. Furthermore, funding for road maintenance is insufficientto sustain the existing road network. Consequently, the Forest Service rarely builds new roads and instead has begun to close and decommission many roadsin order to restore hydrological function and reduce maintenance costs.

The Fremont Winema National Forest has road densities ranging from 2.9miles per square mile in the Paisley Ranger District to 2.4 miles per square milein the Lakeview Ranger District. (Upper Chewaucan Watershed Assessment, p R-2, 1999) The Lakeview Ranger District completed transportation plansfor the North and South Warner Mountains and Thomas Creek

Watershed (location this research project) and identified 120 miles of road slated for decommissioning. (Lakeview Federal Stewardship Unit2001-2002 Annual Report).

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The roads chosen for this study are secondary logging roads built for the solepurpose of accessing timber for harvest. The roads chosen for analysis are notmaintained, dead end spurs created when timber harvest was at its peak, 20-25 years ago. These roads often cause more erosion and sediment delivery tostreams than primary, managed roads. Secondary logging roads, as true of all

roads, interrupt the hydrology of a watershed by collecting water in barrow ditches on the upper side of the road. The collected water is funneled throughculverts or over water bars creating ephemeral creeks greatly modifying wateravailability for plant use below roads. We need to reduce the number of roads in our forests and find the

best way to decommission them.There are three solutions to help promote vegetation recovery on

decommissioned roads: block the road entirely and leave it to its own recovery;scarify the soil by using 4-6 inch teeth to break the surface crust; and subsoil theroad with teeth 18-24 inches, ripping up layers of soil.

It is commonly assumed that ripping forest soils is the best way to prepare for vegetation recovery. This is demonstrated by the overwhelming use of sub-soilingto decommission roads and skid trails. During this study, we observed andphotographed many sub-soiled sites where vegetation and soil structure has notrecovered for 20 to 25 years.

Richard Hart found that sub-soiled areas, while initially releasingcompaction, ultimately become more compacted than their immediatesurroundings. The furls formed by the rippers become beds for invasive plants.Loss of effective ground cover is also dramatic. (Richard Hart. Assessing TheUse of Sub-Soiling Within the Upper Chewaucan Watershed. LFSU report June4, 2004). The Chewaucan Biophysical Monitoring Team commonly found largerocks on the surface, mixed soil horizons, and exposed roots where diseases could be established. The Fremont Winema National Forest Resource Advisory Counsel recommended that the general use of sub-soiling beeliminated. (WFNF RAC minutes. June, 2004).

Because of the Fremont Winema National Forest Resource Advisory Committees recommendation to discontinue the use of sub-soiling, for thisstudy, sub-soiling has been ignored.

This research project focuses on two methods of road decommissioning: blocking and scarification. The two methods are compared with respect to soilcharacteristics, including compaction, and vegetative recovery of these roads.The question of which method, blocking or scarifying, is best for roadrecovery is addressed with recommendations to the Fremont WinemaNational Forest for decommissioning roads.

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Results:

Soil Compaction at 3 inch Depths in

Decommissioned Road Areas310.4

92.8

216.1

39

0

50

100

150

200

250

300

350

P S I

On Blocked

On Scar ified

Off Blocke d

Off Scarified

Compaction varies greatly, as expected, on and off roads; from 1.5 to 2 timesmore compact on roads than surrounding landscape. However, compaction also varies greatly between blocked and scarified off road samples where compactionshould have been similar. Decommissioned off road samples were 3 times morecompacted that scarified off road samples. This was not expected since we hadchosen sites based on soil type, slope and aspect. An analysis of varianceindicated that the difference was indeed significant and could not be ignored. A possible explanation for this may be the criterion used to make a decision on

blocking or scarifying a road. Roads are often blocked rather that scarified if theforest service feels that the road may be needed in the future. This could indicatethat the blocked roads were more important having a greater volume of trafficresulting in higher compaction. The blocked roads often had landings associated with them. It is possible that the blocked road-side areas (off road samples) weremore highly compacted due to the increase of road use. Reflecting back on theproject, taking off road samples farther from the road, 6-9 meters, rather than 0-3 meters would have provided a statistically comparable control between blockedand scarified roads.

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Soil Characteristics in DecommissionedRoad Areas

0

5

10

1520

2530

35

40

Soil Rhizome

D e p

t h ( c m

)On Blocked

On Scarified

Off BlockedOff Scarified

Soil depth on blocked roads was that compared to all other samples on andoff decommissioned roads which were relatively the same. Rhizome depthshowed the same pattern as soil depth, being the depth on blocked roadscompared to all other on and off decommissioned roads. Soil temperature wassimilar in all conditions. Variance was insignificant and could have been due tothe time and day. Moisture readings were also similar in all soil samples.

Despite anomalies with compaction, decommissioned roads are indeedrecovering as indicated by the establishing vegetation. There were severaldecommissioned roads where it was difficult to identify the said road.

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Vegetation Cover On and Off Decommissioned Roads

0

50

100150

200

Blocked Road Scarified Road

p e r c e n t c o v e

r

Off

On

It was discovered that scarified roads recover 1.8 to 2 times quicker than that of blocked roads based on plant cover. Analysis of variance showed the difference

was statistically significant; F = 0.00132. This was interesting because plantdensities on both types of decommissioned roads were similar, however withcloser analysis became apparent that the median width of the plant species onscarified roads was twice as great resulting in the greater percent cover.

Number of Plant Species On and Off Decommissioned Roads

0

10

2030

40

50

On>Off On=Off On

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