United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

General Technical Report 

RMRS-GTR-307

July 2013

Production and Aerial Application of 

Wood Shreds as a Post-Fire Hillslope 

Erosion Mitigation Treatment

Peter R. Robichaud, Louise E. Ashmun, Randy B. Foltz, 

Charles G. Showers, J. Scott Groenier
Robichaud, Peter R.; Ashmun, Louise E.; Foltz, Randy B.; Showers, Charles 

G.; Groenier, J. Scott; Kesler, Jennifer; DeLeo, Claire; Moore, Mary. 2013. 

Production and aerial application of wood shreds as a post-fire hillslope 

erosion mitigation treatment. Gen. Tech. Rep. RMRS-GTR-307. Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research 

Station. 31 p.

Abstract

Guidelines for the production and aerial application of wood shred mulch as a postfire hillslope treatment were developed from laboratory and field studies, several field 

operations, and the evaluations of professionals involved in those operations. At two 

early trial sites, the wood shred mulch was produced off-site and transported to the 

area of use. At the 2010 Schultz Fire in Arizona, the wood mulches were produced 

on-site from burned hazard trees that were felled and skidded to a processing area 

where the logs were shredded by a horizontal grinder and piled. The subsequent 

aerial applications of the wood shreds were staged from the same landings where 

they were produced. At the 2010 Fourmile Canyon, 2012 High Park, and 2012 Waldo 

Canyon Fires in Colorado, wood shreds were produced from various combinations of 

on- and off-site burned and green trees that were generally shredded near the harvest 

or storage site. The wood shreds were transported by chip trucks to aerial application 

staging areas. The most challenging aspect of wood shred production was adjusting the 

grinder screens and through-put speed to maximize the proportion of shreds that were 

2 to 8 inches (50 to 200 mm) in length. The same equipment and techniques used 

for aerial mulching with agricultural straw worked, with some adjustments in flight 

altitude and speed, for wood shreds. The Heli-Claw, an experimental device designed 

to replace the cargo net in aerial mulching, was tested and used to apply 80 percent 

of the wood shred mulch at the Beal Mountain mine reclamation site. Because wood 

shreds are four to six times heavier than agricultural straw, wood shred mulch took 

longer to apply than agricultural straw for the same area (25 to 35 ac [10 to 14 ha] per 

day for wood shreds; approximately 200 ac [81 ha] per day for straw). The additional 

flight time makes mulching with wood shreds cost three to four times more than with 

agricultural straw ($1700 to $2200 per ac [$4200 to $5500 per ha] for wood shreds; 

$500 to $700 per acre [$1200 to 1700 per ha] for straw). However, the advantages 

of wood shreds—on- or near-site availability, greater stability in high winds and on 

steep slopes, and lack of unwanted plant seeds from off-site—make wood shred mulch 

useful in areas where agricultural straw mulch may not be desirable.

Keywords: heli-mulching, aerial mulching, wood mulch, post-fire, Burned Area 

Emergency Response (BAER), erosion mitigation

Authors

Peter R. Robichaud and Randy B. Foltz are Research Engineers and Louise E. Ashmun

is a Civil Engineer with the Air, Water and Aquatic Environments Science Program of 

the USDA Forest Service, Rocky Mountain Research Station located at the Forestry 

Science Laboratory, Moscow, Idaho.

Charles G. Showers is the Engineering Program Leader and J. Scott Groenier is a 

Project Leader for the National Technology and Development Program, National Forest 

Systems, Missoula, Montana.

Jennifer Kesler is a Plant Ecologist and Claire DeLeo is a Senior Plant Ecologist with 

the Colorado’s Boulder County Parks and Open Space Department.

Mary Moore is a Hydrologist in the Urban Forest Management Program of the Lake 

Tahoe Basin Management Unit, USDA Forest Service. She was the lead hydrologist 

on the 2012 Waldo Canyon Fire BAER team and the team leader of the BAER 

implementation team.
Contents

Introduction................................................................................................................1

Study Sites...................................................................................................................4

2007 Cascade Complex Fire ..............................................................................4

2010 Schultz Fire...............................................................................................4

2010 Fourmile Canyon Fire................................................................................4

2011 Beal Mountain Abandoned Mine Site........................................................5

2012 Waldo Canyon Fire ...................................................................................5

2012 High Park Fire ...........................................................................................5

Production of Wood Shreds ........................................................................................5

Controlling and monitoring the quality of the wood shreds being produced.......7

Off-site production and transportation ...............................................................8

Aerial Application of Wood Shreds.............................................................................9

Comparison of Wood Shred and Straw Mulches .......................................................11

Conclusions and Management Implications..............................................................12

Acknowledgments.....................................................................................................14

References ................................................................................................................14

Appendix A: 2010 Fourmile Canyon Fire Case Study.................................................17

Appendix B: 2012 Waldo Canyon Fire Case Study ....................................................22

USDA Forest Service RMRS-GTR-307. 2013. 1

Introduction

Aerial application of agricultural straw mulches, developed and refined in the 

past 12 years, has allowed mulch to be used as a post-fire hillslope treatment in 

remote burned areas that lacked road access. Because mulching provides effective 

ground cover immediately after application, it can effectively mitigate potential 

post-wildfire increases in runoff, flooding, and erosion (Robichaud and others 

2013a, b). Although aerial mulching is logistically demanding and expensive, the 

effectiveness of dry mulches as compared to other post-fire hillslope treatments 

has increased its use in areas where downstream values are at high risk for damage, such as the hillslopes above municipal water intakes, heavily used roads, and 

stream reaches that are critical habitat for protected species (Robichaud and others 

2010).

Problems associated with using agricultural straw mulch in burned forest environments emerged as the use of post-fire mulch treatments increased. These 

problems include 1) lack of available straw in the locations and quantities needed 

(Beyers 2004); 2) introduction of non-native seed species that can persist and compete with the re-establishment of native vegetation (Beyers 2004; Robichaud and 

others 2000, 2003); 3) susceptibility to displacement by wind (Copeland and others 2009) that may result in exposed hillslopes and deep piles of straw in gullies 

and channels; and 4) straw mulch physically blocking or shading emerging vegetation (Beyers 2004). As issues with straw mulch became apparent, alternatives 

were tried. Although many erosion-mitigating mulch products (e.g., geotextiles, 

compost, wood bark, hydromulches, etc.) were available, few of them were easily 

adapted to aerial application and had the potential to effectively reduce erosion on 

steep hillslopes with long flow paths.

Wood-based mulches, such as wood chips, wood shreds, and manufactured 

wood strands, have been tested and used along with various hydromulch products. 

Small rounded wood chips have not successfully reduced post-fire erosion and 

were easily displaced by overland flow when tested in Arizona and northern Spain 

(Fernández and others 2011; Riechers and others 2008). In contrast, limited testing has shown that wood mulches composed of coarse shredded pieces, flat slats, 

or strands (>2 inches [50 mm] and at least 4 times longer than they are wide) are 

less susceptible to wind displacement, degrade slowly, and reduce erosion as well 

or better than agricultural straw mulches (Copeland and others 2009; Foltz and 

Copeland 2007; Foltz and Dooley 2003; Robichaud and others 2013a, c). In addition, these wood mulches can be aerially applied using the same equipment and 

similar application protocols as agricultural straw mulch (Lynch 2008; Skeen and 

Becker 2007).

Wood-based mulch products often are produced from small diameter trees 

and slash removed during thinning operations, roadside clearing, and logging 

operations, and the production of wood mulch from local forest materials for 

post-wildfire application was a logical extension for these products (Groenier and 

Showers 2004)1. Burned Area Emergency Response (BAER) teams discussed the 

possibility of using local burned trees, such as hazard trees that were designated to 

be felled for safety reasons, to produce wood shreds for immediate application as a 

1 Logging companies and forest product manufactures that create wood mulching products may own and operate grinding 

equipment that can be adjusted to produce wood shreds for post-fire mulching. Groenier and Showers (2004) produced an 

Engineering Tech Tip that described tree shredding equipment, gave details, had photographs of three specific machines and 

the product they produced, and listed nine manufacturers of shredding/grinding equipment. This Tech Tip is available online 

at http://fsweb.mtdc.wo.fs.us/pubs/pdfpubs/pdf12282311/pdf12282311dpi100.pdf.
2 USDA Forest Service RMRS-GTR-307. 2013.

hillslope treatment. It seemed possible that burned trees could supply a significant 

quantity of wood mulch without the purchase and transportation costs associated 

with using agricultural straw or manufactured wood strands. In addition, local 

wood product manufacturers might also produce and transport wood shreds for 

post-fire mulching. Locally produced material is less likely to introduce unwanted 

plants or seeds from outside the burned area and may fit into a broader ecological restoration plan for the area (Bautista and others 2009; Groenier and Showers 

2004).

Wood shreds have been produced and their erosion reducing capacity evaluated by the USDA Forest Service, Rocky Mountain Research Station (RMRS) 

and the Missoula Technology Development Center (MTDC) for nearly a decade 

(Foltz 2012; Foltz and Copeland 2007; Foltz and Wagenbrenner 2010; Groenier 

and Showers 2004; Robichaud and others 2013c). Horizontal shredding machines 

that can handle larger burned trees were identified and tested, which resulted in 

several commercially available machines being recommended (Groenier and 

Showers 2004). Laboratory rainfall and overland flow simulations were used to 

determine the optimum wood shreds specifications (dimensions and coverage) for 

reducing post-fire hillslope erosion. Blends containing 24, 18, or 2 percent or less 

of the shortest wood shreds (≤ 1 inch [25 mm]) at three coverage rates (0, 50 and 

70 percent) were tested (Foltz and Wagenbrenner 2010) (fig. 1). With rainfall only 

(no overland flow), all blends were equally effective in reducing sediment loss by 

90 to 98 percent compared to bare soil; but in the simulations of rainfall plus a 

high concentrated flow rate, the 2 percent blend was the most effective in reducing 

sediment loss (approximately 70 percent less than the bare soil control). Although 

the 70 percent coverage provided greater erosion reduction than the 50 percent 

coverage, Foltz and Wagenbrenner (2010) recommended 50 to 60 percent coverage of the 2 percent blend for the post-fire environment. The 

authors reasoned that the small increase in erosion reduction provided by the 70 percent coverage was not worth the 

added expense of obtaining that greater coverage (Foltz and 

Wagenbrenner 2010).

Following the 2009 Terrace Mountain Fire in Kelowna, 

British Columbia, Robichaud and others (2013c) conducted 

three experiments (rainfall simulation, rill simulations, and 

sediment yield from natural rainfall) to compare the runoff 

and erosion mitigation attained by agricultural straw and 

wood shreds. They found that wood shreds and agricultural straw were similar in their ability to reduce erosion in 

comparison to untreated controls and that the wood shreds 

remained on the soil longer than the straw during the 3 years 

of the study.

Foltz (2012) applied wood shred and agricultural straw 

mulch on bare soil after forest road obliteration. He found 

that agricultural straw and wood shreds were similar in reducing erosion as compared to the controls, but in contrast 

to Robichaud and others (2013c), he measured no difference 

in the longevity (based on the half-life of original cover proportion) of the agricultural straw and wood shred mulches.

Helicopters with cargo nets have been used for years to 

distribute agricultural straw over disturbed landscapes to 

help stabilize hillslopes and protect bare soil (Napper 2006) 

this was an obvious starting place for aerial application of 

Figure 1. A portion of the rainfall and overland flow 

simulation laboratory plot with a 70 percent cover 

of wood shred mulch.
USDA Forest Service RMRS-GTR-307. 2013. 3

wood shreds. In 2007, the first attempt to aerially apply wood shreds using a helicopter with a cargo net occurred at a research site established immediately after 

the Cascade Complex Fire in central Idaho and it continues to be the most common method for aerial application of dry mulches. Several trial productions and 

applications of wood shreds were completed as hillslope stabilization treatments 

on fires that occurred in 2010 to 2012 in the western United States. However, as 

wood shreds were being developed and tested for use, the MTDC developed and 

built a prototype Heli-Claw2 (fig. 2) as a potential alternative to cargo nets for 

the aerial application of mulches (Lynch 2008). The Heli-Claw was designed as a 

pilot-controlled device that could pick up and hold loose mulch material and, by 

controlling the flight speed and the width of the claw opening, allow the mulch to 

spill out more slowly and over a greater distance than can be done using a tethered 

cargo net (Groenier 2012; Lynch 2008). A trial use of the Heli-Claw for the aerial 

application of wood shred mulch is included in this report.

Based on the experience garnered from these trial productions and aerial applications of wood shreds, our goal was to develop a guide for the production and 

use of wood shreds as a post-fire hillslope treatment. Specifically, we described the 

1) equipment and procedures that were used, 2) labor and time requirements, and 

3) costs involved in producing, staging, and aerially applying wood shreds in the 

post-wildfire environment. In addition, if both wood shred mulch and straw mulch 

were aerially applied at the same location, the time, labor, and costs were compared. 

Since details of wood shreds production, transport, characteristics, and application 

2 MTDC hopes to continue the development of the Heli-Claw for aerial dry mulching. The current prototype is available 

for use in National Forests. If you are interested in using the Heli-Claw, please contact J. Scott Groenier at 406 329 4719, 

jgroenier@fs.fed.us. 

a) c)

b)

Figure 2. The prototype Heli-Claw being used for wood shred mulching at the Beal Mountain 

mine site: (a) picking up a load, (b) taking off with the claws closed on a load, (c) applying 

mulch by opening the claws while flying over the target area.
4 USDA Forest Service RMRS-GTR-307. 2013.

differed among the sites where it has been used, we have presented the information 

as individual case studies. Important issues, key decisions, contract specifications, 

and other aspects of using wood shred mulch as a post-fire hillslope treatment have 

been generalized in the conclusions and manager implications sections.

Study Sites

Reports from several sites were examined to determine the salient features 

of successful operations to produce and use wood shreds as a post-fire hillslope 

mulch treatment.

2007 Cascade Complex Fire

Following the 2007 Cascade Complex Fire on the Payette and Boise National 

Forests near McCall, Idaho, a set of three small catchments were installed to compare the treatment effectiveness of aerially applied wood shreds, agricultural straw, 

and no treatment. The wood shreds, produced off-site and transported to the staging 

area, were applied at a rate of 4.6 tons ac-1 (10.3 metric tons ha-1) by a helicopter 

equipped with cargo nets. This was the first aerial application of wood shreds as a 

post-fire treatment.

2010 Schultz Fire

The 2010 Schultz Fire occurred on the Coconino National Forest adjacent to 

the Kachina Peaks Wilderness near Flagstaff, Arizona. In the year after the fire occurred, a contractor produced and distributed nearly 2000 tons (1800 metric tons) 

of wood shred mulch on 330 ac (130 ha) of steep mountainous landscape burned at 

high severity. The contractor used burned hazard trees harvested from the sides of 

a forest road that were skidded on the road to a landing and subsequently ground 

to produce the required wood shreds. The wood shreds were then aerially applied 

to hillslopes by helicopters equipped with cargo nets.

2010 Fourmile Canyon Fire

In the fall of 2010, the Fourmile Canyon Fire burned 5 miles (8 km) west of 

Boulder, Colorado in a densely populated urban-wildland interface. In the spring 

of 2011, post-fire hillslope treatments included aerial application of agricultural 

straw mulch (1,620 ac [656 ha]; 1.3 tons ac-1 [2.9 metric tons ha-1]) and a commercially produced wood strand material (350 ac [140 ha]; 4.7 tons ac-1 [10.5 metric 

tons ha-1]). In the fall of 2011, 364 ac (147 ha) that had been treated previously 

were identified for retreatment based on the loss of treatment ground cover, limited 

recovery, high burn severity, and downstream values at continued risk. In April 

2012, a mix of agricultural straw and wood shreds was aerially applied (0.5 tons 

ac-1 [1.1 metric tons ha-1] of agricultural straw and 4 tons ac-1 [9.0 metric tons ha1] of wood shreds) on 20 to 60 percent slopes to attain 1 to 3 inches (25 to 76 mm) 

mulch depths and 60 percent mulch cover. (See Appendix A for a case study of the 

wood shred mulching project on the Fourmile Canyon Fire.)
USDA Forest Service RMRS-GTR-307. 2013. 5

2011 Beal Mountain Abandoned Mine Site

Beal Mountain on the Beaverhead-Deerlodge National Forest was an abandoned 

mine land reclamation site in the Pintler Mountains outside of Fairmont, Montana. 

The Heli-Claw and cargo nets were used with a helicopter to aerially apply wood 

shred mulch to the gentle hillslopes (0 to 20 percent) designated for rehabilitation.

2012 Waldo Canyon Fire

The Waldo Canyon Fire occurred on the Pike and San Isabel National Forest and 

Comanche and Cimarron National Grasslands near Colorado Springs, Colorado. 

A contractor produced and distributed nearly 11,750 tons (10,660 metric tons) of 

wood shred mulch on 1,960 ac (793 ha) of steep mountainous landscape (20 to 60 

percent slopes) burned at moderate and high burn severity. The contractor obtained 

wood shreds from four sources (burned roadside hazard trees and green trees from 

a fuel break construction, a stewardship area project, and a local timber products 

stock yard) and applied the mulch using up to five helicopters equipped with cargo 

nets. (See Appendix B for a case study of the wood shred mulching project on the 

Waldo Canyon Fire.)

2012 High Park Fire

The High Park Fire occurred 15 miles (24 km) west of Fort Collins, Colorado 

and burned 87,284 ac (35,323 ha) across multiple jurisdictions—49 percent on 

the Roosevelt National Forest, 44 percent on private holdings, and 6 percent on 

state lands. Wood shred mulch was aerially applied by helicopter with cargo nets 

on 881 ac (357 ha) burned at high severity. The wood shreds were produced from 

mostly green trees (there were some beetled-killed trees in the mix) from a timber 

sale. The same contractor that had worked the wood shred mulching project at the 

2012 Waldo Canyon Fire was hired for the High Park Fire and the same methods 

for wood shreds production, aerial application, and contract monitoring were used 

in both places.

Production of Wood Shreds

The MTDC produced the wood shreds that were applied at the 2007 Cascade 

Complex Fire in Idaho. After grinding, the wood shreds were blown out onto the 

ground. To optimize the mix of wood shred sizes by reducing the largest and smallest pieces (Foltz and Wagenbrenner 2010), only the wood shreds from the middle 

two-thirds of the pile were used. The wood shreds used at the Beal Mountain mine 

site were produced off-site by a contractor and a post-grinding process was used 

to reduce the proportion of smaller shreds (<2 inches [50 mm]; “fines”) in the 

shreds mix. In both cases, the wood shreds were hauled unconsolidated in a bulk 

container (chip) truck to the project site.

The first time wood shreds were produced, staged, and aerially applied as a 

post-fire hillslope treatment was at the 2010 Schultz Fire. A week before the shredding was scheduled to begin, burned hazard trees along a forest road were felled 

and skidded (using a grapple skidder) on the forest road to a staging area. A forest 

material handler with a 12-ft (3.7-m) rotating grapple was used to stack the trees 

and then to load them into a radio-controlled horizontal grinder. The operator of 

the forest material handler also operated the grinder using the radio controls. The 
6 USDA Forest Service RMRS-GTR-307. 2013.

wood shreds were produced and piled at the staging areas (1,200 tons and 800 

tons [1090 and 730 metric tons], respectively). (See video at the Arizona State 

Geologist blog site—http://arizonageology.blogspot.com/2011/06/schultz-fireburn-area-mulching-to.html.)

Material for the wood shreds was harvested within or near the burned area of the 

Fourmile Canyon, Waldo Canyon, and High Park Fires. Burned hazard trees provided some of the wood shreds on the Waldo Canyon and High Park Fires but not 

on the Fourmile Canyon Fire. Stewardship projects (fuel management projects) 

provided green trees for wood shreds on all three fires, and in the case of the Waldo 

Canyon Fire, green trees also were obtained from a log deck that was a byproduct 

of fire break construction. Whatever the source of the trees, harvested trees were 

skidded to road-accessible landings where horizontal grinders and excavators or 

forest material handlers could be safely operated (fig. 3). Using front-end loaders, 

the wood shreds were loaded into chip trucks (fig. 4) and moved by road to a treatment staging area where they were piled and covered (fig. 5).

Figure 5. A helicopter with an 

empty cargo net is approaching 

a treatment staging area with a 

chip truck on the road at the 2012 

Waldo Canyon Fire.

Figure 3. Wood being fed into a horizontal 

grinder to produce wood shreds at the 

2012 Waldo Canyon Fire.

Figure 4. Wood shreds being loaded 

into a chip truck for transport to a 

treatment staging area at the 2012 

Waldo Canyon Fire.
USDA Forest Service RMRS-GTR-307. 2013. 7

Controlling and monitoring the quality of the wood shreds being produced

Based on research results (Foltz and Wagenbrenner 2010), it was assumed that 

the most effective wood shred mulch would have a minimal amount of small material (generally referred to as “fines”). However, research has not yet determined the 

specific wood shred length that should be designated a fine or what the maximum 

proportion (by weight or by volume) of fines should exist in the wood shred mulch 

applied to burned hillslopes. Among the post-fire treatment sites described here, 

the description of fines ranged from 0.5 to <2 inches (13 to <50 mm). No matter 

how fines were defined, the production of wood shreds at each site involved a 

trial period in which various grinder screen sizes and orientations were tried with 

a range of throughput speeds to minimize the amount of small shredded material 

in the product. At the Schultz Fire, a series of screens with openings ranging from 

2 to 4 inches (50 to 100 mm) were used to create wood shreds that were observed 

and reported to be “mostly” ≥2 inches (50 mm) and ≤6 inches (150 mm); however, no direct measurements of wood shreds samples were done. At the High 

Park and Fourmile Canyon Fires, the grinders were tested with 2-, 4-, and 6-inch 

Wood shreds can be highly variable. 

Based on our research and trial 

studies, wood shreds that are 2 to 

8 inches (50 to 200 mm) long 

and less than 1 inch (25 mm) 

in diameter are best suited to 

be aerially applied for hillslope 

stabilization (fig. 1).

Figure 2. Wood products that are not recommended for use as post-fire 

hillslope mulch: a) animal bedding, b) shavings, c) chips, d) shreds that are 

predominantly less than 2 inches (50 mm), and e) shreds that are mostly 

lightweight bark and less than 2 inches (50 mm).

A wide range of wood mulch 

products are manufactured for 

a variety of purposes. Many of 

these products are not well-suited 

for post-fire hillslope stabilization 

treatments as they are too light 

and/or do not interlock on the 

slope (fig. 2). In addition to the 

products pictured, pole peelings 

and extra-large excelsior (aspen 

shavings) have been suggested but 

are not desirable for use as postfire hillslope treatments (C. DeLeo, 

personal communication).

a) b)

a) b) c)

d) e)

Figure 1. (a) Wood shreds produced and piled for use at the 2012 High Park 

Fire. (b) Wood shred mulch applied by hand on a research plot at the 2012 

High Park Fire.
8 USDA Forest Service RMRS-GTR-307. 2013.

(50-, 100-, and 150-mm) screens, but the best wood shreds, based on visual inspection, were obtained with 4-inch (100 mm) screens only. At Waldo Canyon and 

High Park Fires, 2- to 4-inch (50- to 100-mm) grinder screens were delineated in 

the contract specifications along with a restriction of ≤30 percent fines in the wood 

shred product. The resulting wood shreds were sampled and the volume of fines 

(<0.5 in [13 mm]) within the samples were compared to the volume of the wood 

shreds in the desired size range (≥0.5 to 8 inches [50 to 200 mm]) to ensure contract 

compliance (for more details about this sampling procedure, see Appendix B).

Off-site production and transportation

Producing and transporting wood shreds to an area where trees for shredding 

are not readily available may be a viable option for some post-fire mulch treatment projects. For example, burned chaparral areas in southern California often 

are exposed to high winds, and wood shred mulch may be a desired hillslope treatment because of its resistance to wind displacement; however, there may not be 

adequate wood resources to support local production of wood shreds in the areas 

that are recommended for treatment. In this case, the added costs of transporting 

wood shreds produced off-site may be worth the potential erosion mitigation that 

the wood shreds can provide. Other situations may preclude the harvest of trees 

within or near a fire. For example, logging equipment may not be advised or safe 

on soils burned at high severity or on steep hillslopes. Fuel treatments in unburned 

areas near a wildfire may provide woody material needed for shredding, and shortdistance transportation costs to move the wood shreds to a staging area may be 

economically competitive with other hillslope mulches such as agricultural straw 

and on-site production of wood shreds.

A cost comparison of on-site production of wood shreds to off-site production and 

shipping of wood shreds was developed using production costs of wood shreds at the 

2010 Schultz Fire and wood shred transportation costs calculated by the contractor 

for the 2011 Beal Mountain mine reclamation project (table 1). The estimated cost 

for the on-site production of the 2,000 tons (1,800 metric tons) of wood shreds used 

at the Schultz Fire, based on the contractor’s costs for equipment and manpower, was 

approximately $37,800 or $18.90 per ton ($21 per metric ton) (table 1). Given that 

the first on-site production of wood shreds from burned trees occurred at the Schultz 

Fire, these costs may not be representative of the costs that would be incurred in 

different areas or from a more practiced and efficient process. The contracted cost 

to produce 31.7 tons (28.8 metric tons) of wood shreds off-site and deliver them to 

Table 1 Costs to obtain wood shreds at the 2010 Shultz Fire site and the Beal Mountain mine reclamation site are compared in 

the sub-tables a) and b) using $US and conventional units only. Both sites were mulched in 2011.

a) Evaluation of the cost of wood shreds produced on-site at the Schultz Fire. 

Process Cost per hour ($ h-1) Time (h) Total cost ($) Amount of shreds (t) Cost per ton ($ t-1)

Tree felling 280 80 22,400 2,000 $11.20

Shredding 385 40 15,400 2,000 $7.70

 Total cost per ton $18.90

b) Evaluation of cost of wood shreds produced off-site and shipped 100 miles to the Beal Mountain mine reclamation site.

------------------------------------------------Hauling--------------------------------------------------

Process Cost per ton ($ t-1) Cost per ton-mile ($ t-mi-1) Distance (mi) Cost per ton ($ t-1)

Wood shreds 19.84 0.50 100 69.84

 Total cost per ton $69.84
USDA Forest Service RMRS-GTR-307. 2013. 9

the Beal Mountain reclamation site (a distance of 100 miles [161 km]) was $2,214, 

or approximately $69.80 per ton ($76.90 per metric ton), with hauling expenses accounting for 72 percent of the cost (table 1). The cost for shredding the trees was not 

much different at the two locations—$18.90 per ton ($20.84 per metric ton) at the 

Schultz Fire and $19.84 per ton ($21.87 per metric ton) for the Beal Mountain site—

but the cost of transporting the wood shreds substantially impacted the total cost of 

the wood shreds. There is likely to be a significant economic advantage to producing 

wood shreds on or near the treatment site.

Aerial Application of Wood Shreds

Generally, wood shred mulch was aerially applied using the 

same equipment and processes as the aerial application of agricultural straw. A 4-point cargo net (50 ft2 [4.6 m2] or larger) was 

spread out on the ground in the staging area and a small front end 

loader piled the wood shreds onto the center of the net. As the 

helicopter hovered above a loaded net, ground personnel attached 

the corners of the cargo net to a long line cable (50 to 150 ft [15 

to 46 m]) equipped with a remote hook and tether. The pilot then 

flew to the treatment area with the loaded net hanging below the 

helicopter. When over the target treatment area, the pilot remotely 

unhooked three corners of the cargo net and let the mulch drop 

and spread over the area (fig. 6). The pilot returned to the staging 

area, the single tethered corner of the empty cargo net was released 

to drop the empty cargo net, and the process was repeated (fig. 

6). To keep the aerial application running smoothly and minimize 

helicopter hover-time, three to four cargo nets may be used, which 

allows the ground crew to have at least one loaded net ready to go 

during most of the operation. At the Beal Mountain mine reclamation site, the aerial application of wood shreds with a Heli-Claw 

was used in addition to the standard process described above.

The first aerial application of wood shred mulch was on a 4.7 ac 

(1.9 ha) research catchment at the Cascade Complex site. The helicopter pilot found that the wood shreds dropped more quickly 

and with less spread than agricultural straw and made adjustments 

to flight height and speed to compensate for the greater density of 

the wood shreds. Pilots generally fly at 100 to 200 ft. (30 to 60 m) above mean 

tree height at 30 to 50 mph (26 to 44 knots) for aerial straw mulching. This was 

increased to 200 to 300 ft. (60 to 90 m) elevation and 70 to 90 mph (60 to 80 knots) 

for wood shreds. The wood shreds were applied at a rate of 4.6 tons ac-1 (10.3 

metric tons ha-1). Immediately after application, ground cover was assessed using 

25 ground cover plots (five 160-ft [50-m] transects with five evenly spaced ground 

cover plots along each transect) within the research catchment. The adapted flight 

speed and altitude resulted in a relatively even spread of mulch in the research watershed (fig. 7). Immediately after application, the total average ground cover was 

57 percent with wood shreds providing 37 percent of the cover and rock, charred 

woody debris, litter, etc. making up the remaining 20 percent.

At the Schultz Fire, the contract specified 6 tons ac-1 (13 metric tons 

ha-1) of wood shred mulch to provide 50 percent cover on steep slopes 

(30 to 65 percent). The burned area had 15 to 50 percent rock fragment cover; 

thus, the combination of rock fragments and wood shred mulch was to provide 

Figure 6. Wood shred mulch falling from a cargo 

net that had been released by the pilot at the 

2012 Waldo Canyon Fire.
10 USDA Forest Service RMRS-GTR-307. 2013.

at least 60 percent coverage of the bare 

soil. The average cargo net load was about 

1.25 tons (1.13 metric tons) and at 6 tons 

ac-1 (13 metric tons ha-1) it took nearly five 

loads to treat each acre (0.4 ha). The single 

helicopter treated 25 to 35 ac (10 to 14 ha) 

per day. Cover plots and photos from the 

wood shred mulched areas measured 49 to 

68 percent cover (fig. 8).

At the Beal Mountain mining site, a 

contract for site rehabilitation included the 

off-site production and delivery of 30 tons 

(27 metric tons) of wood shreds that were 

aerially applied by helicopter using both 

cargo nets and the Heli-Claw. After some 

trial and error, the pilot discerned that the 

Heli-Claw could pick up the largest loads 

when the wood shred pile was flat-topped 

rather than peaked, “fluffed up” (un-compacted), and the claw was set down partially 

closed on the pile, opened up to its maximum width, then closed as the 

helicopter slowly lifted. When the wood shred piles were too small for 

the claw to efficiently pick up the material, the helicopter was reconfigured for cargo nets and the remaining wood shreds (about 20 percent of 

the total) were applied. (A video of a flight test can be viewed at: http://

fsweb.mtdc.wo.fs.fed.us/pubs/htmlpubs/htm12282311/.) The application 

rate was 4.2 tons ac-1 (9.4 metric tons ha-1) for 50 percent coverage. The 

average wood shred load with the Heli-Claw was 0.34 tons (0.31 metric 

tons) and the pilot was able to distribute approximately 6 tons (5.4 metric 

tons) of wood shreds per hour. Although the Heli-Claw operation was 

efficiently supported by a smaller ground crew than generally needed for 

aerial mulch applications with cargo nets, the smaller loads resulted in 

more helicopter trips from the staging area to the treatment area. Given 

the high cost of helicopter time ($1000 to $1800 per hour), the greater helicopter expense of the Heli-Claw operation would potentially offset any 

cost advantage of a smaller ground crew.

Helicopters with cargo nets were used to aerially apply both agricultural straw 

and wood shred mulches at the 2010 Fourmile Canyon, 2012 Waldo Canyon, and 

2012 High Park Fires. At Fourmile Canyon, wood shreds and agricultural straw 

were mixed at the treatment staging area and the mixed mulch (4 t ac-1 [6 metric 

tons ha-1] of wood shreds plus 0.5 t ac-1 [1.1 metric tons ha-1] of agricultural straw) 

was applied in the spring of 2012 as a retreatment on areas previously mulched. 

Details of wood shred production and the mixed mulch application are provided 

in Appendix A. At Waldo Canyon, the wood shreds were applied at 6 tons ac-1

(13 metric tons ha-1) and the agricultural straw at 1.5 t ac-1 (3.4 metric tons ha-1); 

the contracted production and application of wood shreds are covered in detail in 

Appendix B. The same contractor and processes that were used at the 2012 Waldo 

Canyon Fire were subsequently used at the 2012 High Park Fire.

All of the aerial applications of wood shreds used “weight per acre” as a criterion for the operation or a contract specification. However, researchers (Foltz 

and Copeland 2007) and managers of the treatment installations have commented 

Figure 8. Ground cover of wood shred 

mulch being measured on a steep 

slope at the 2010 Schultz Fire.

Figure 7. Wood shred mulch cover on a research catchment at the 2007 

Cascade Complex Fire.
USDA Forest Service RMRS-GTR-307. 2013. 11

about the inadequacy of that approach. Since the weight of wood shreds is dependent on moisture content (and may also vary by type of tree, location, etc.), 

a designation of 6 tons ac-1 (13 metric tons ha-1) may provide various amount of 

ground cover. There was general agreement that the contract specifications should 

delineate the amount of ground cover provided by the wood shreds as applied, but 

such contract specifications would require field personnel doing cover measurements to ensure contract compliance. It is more costly and time consuming to 

monitor ground cover than the weight of mulch applied per unit area—a specification that can be estimated from truck load weights or helicopter flight logs.

Comparison of Wood Shred and Straw Mulches

Both agricultural straw and wood shred mulch were aerially applied using helicopters and cargo nets at the Schultz, Waldo Canyon, and High Park Fires. This 

allowed for some comparisons of application processes, performance characteristics, and costs between the two mulch types. Given that the wood shreds were about 

four times denser than agricultural straw, it required three to five times as many 

round trips to treat a unit area with wood shreds as with straw. This factor made 

wood shred application take longer and cost more than straw application—$1700 

to $2200 ac-1 ($4200 to $5500 ha-1) for wood shreds compared to $500 to $700 

ac-1 ($1200 to 1700 ha-1) for agricultural straw (table 2).

On the Schultz Fire, the decrease in ground cover provided by the straw mulch 

compared to wood shred mulch during the first year after treatment differed by 

slope steepness. On steep slopes (>35 percent), the straw mulch ground cover 

decreased from 60 to 20 percent (a 67 percent decrease). The greatest loss of agricultural straw was on south-facing slopes where wind was most intense due to the 

orographic position and the weather patterns associated with the mountain range. 

During the same period, the wood shred ground cover, which had been applied to 

very steep slopes (about 65 percent) only decreased 25 percent—it went from 68 

to 52 percent. However, on moderately steep slopes (about 25 percent) the straw 

mulch decreased less than the wood shred mulch. One year after treatment, the 

average straw mulch ground cover on moderate slopes had decreased 19 percent 

(going from 70 to 57 percent) while the average wood shred mulch ground cover 

Table 2. Cost comparisons for wood shred and agricultural straw mulching treatment. The application rates—6 tons ac-1 for 

wood shreds and 1 ton ac-1 for agricultural straw—were the same for the three fires, with the exception noted in the Shultz 

Fire comment section using US$ and conventional units only.

Straw mulch Wood shreds mulch

Fire ($ ac-1) ($ ac-1) Comments

2010 Schultz 395-750 1700 The differences in cost for agricultural straw 

mulching were mostly dependent on the distance 

the straw had to be shipped; however, the highest 

cost ($750 ac-1) was for the mulching done with 

straw shipped the longest distance and applied at a 

higher rate (1.5 tons ac-1).

2012 Waldo Canyon 548 2141 Direct contract costs

679 2272 These amounts include the direct costs as well as 

the costs of contract preparation and administration.

2012 High Park na 2136 The agricultural straw mulching has not been 

completed (work scheduled for Spring 2013) and 

final costs are not available.
12 USDA Forest Service RMRS-GTR-307. 2013.

decreased 31 percent (going from 49 to 34 percent) (USDA 2011). Field observers reported that in areas where the wood shred ground cover was <50 percent, 

overland flow displaced the thinly scattered wood shreds more easily than in areas 

with greater wood shred coverage (R. Steinke, personal communication, email to 

P. Robichaud 18 Sep 2012). Observations during research studies have described 

the tendency of mulches made up of wood strands or pine needles to interlock and 

pile up into “mini-dams” that slow overland flow rates and increase the lengths 

of flow paths (Foltz and Copeland 2008; Foltz and Dooley 2003; Pannkuk and 

Robichaud 2003). This may happen with wood shreds as well, and if so, there may 

be a threshold cover amount below which the wood shreds formed fewer interlocking “mini-dams” and were more easily displaced.

Conclusions and Management Implications

Laboratory and field studies have shown that wood shred mulch can be an effective post-fire hillslope treatment. Experience and information from six wood 

shred mulching operations were combined to develop this guide for the production, transport, and application of wood shred mulch as a hillslope stabilization 

treatment. Wood shreds have been successfully produced from burned and green 

trees and the same equipment and techniques that are used for aerial mulching of 

agricultural straw have worked, with some adjustments in flight altitude and speed, 

for wood shreds. At the Beal Mountain mine reclamation site, the Heli-Claw (an 

experimental replacement for the cargo net in aerial mulching) was successfully 

used to apply 80 percent of the aerial application of wood shred mulch.

The general function of any post-fire mulch treatment is to provide immediate ground cover on hillslopes where erosion mitigation is needed. A mulching 

rate of about 6 tons ac-1 (13 metric tons ha-1) of wood shreds can provide the 

60 percent ground cover needed to protect the soil; yet that application rate does 

not always ensure adequate cover for bare soil if the wood shreds are heavier 

than average (due to wood type, higher moisture content, etc.) or unevenly spread. 

Starting points for wood shred production based on field trials

• Maximize the proportion of wood shreds in the 2- to 8-inch 

(50- to 200-mm) range.

• Green trees generally produce less fines than dry or burned trees.

• Including branches and needles will increase fines.

• Take time to “calibrate” tree/grinder system to minimize fines (particles 

<1 inch [25 mm]) prior to moving into operational mode.

• Use 4-inch (100-mm) screens in a horizontal grinder as a starting point 

for production of wood shreds.

• Increase the through-put rate of the grinder to decrease fines.

• Align the 4 to 5 ft (1.2 to1.5 m) tree trunk sections perpendicular to the 

direction of the feed; i.e., set the logs on the conveyor belt so that the 

logs approach the screens sideways (bark side), not endwise.

• Monitor wood shred production for compliance to standards/contract 

specifications.
USDA Forest Service RMRS-GTR-307. 2013. 13

Figure 9. Ground cover assessment of 

aerially applied wood shred mulch at 

the 2012 Waldo Canyon Fire.

Starting points for wood shred application based on field trials

• Contract for an average ground cover amount (60 to 70 percent), rather 

than a weight per unit area.

• In steep areas, compute the treatment area using calculation applications 

that factor in slope angle to more accurately determine the amount of 

wood shreds needed for the desired coverage.

• Buy or produce 6 to 8 tons ac-1 (13 to 18 metric tons ha-1) of wood 

shreds to get 60 to 70 percent ground cover.

• Wood shreds produced from green trees weigh more than wood shreds 

from dry and/or burned trees.

• Cover wood shreds piled at staging areas to keep dry.

• Make ground cover assessments early in the application operation 

process so that pilots can adjust speed and altitude to get the desired 

coverage. Recognize that this may need to be repeated when there are 

changes in the qualities of the wood shreds, wind, terrain, pilots, or 

equipment.

• Monitor ground cover throughout the application operation to identify 

low coverage areas that need to be reworked prior to the contractor 

leaving.

Post-fire mulch applications, including wood shred mulch, should be monitored 

by uniformity of ground cover spread and the percent ground cover achieved as 

opposed to a weight-based application rate. Getting a relatively even spread of 

the mulch is mostly dependent on pilot skill and experience and somewhat on the 

characteristics of the mulch. Ground cover assessments need to be made at the 

start of the application process so that adjustments in flight altitude and speed can 

be made to attain the needed ground cover (fig. 9). In addition, if the contractor is 

going to be required to re-work areas where the ground cover does not meet the 

contract specifications, ground cover monitoring needs to occur throughout the 

application operation so deficient areas can be reworked before the contractor is 

finished and equipment has been moved off-site. In the future, monitoring ground 

cover amounts and uniformity may be done using remote sensing techniques that 

could provide more comprehensive examinations of mulched areas (Lewis and 

Robichaud 2011).
14 USDA Forest Service RMRS-GTR-307. 2013.

The development of post-fire wood shred mulching was motivated largely by 

its potential on-site availability, stability in windy conditions, and lack of unwanted seeds from off-site. Since wood shreds weigh about four times more than 

agricultural straw, application requires more round trips between the staging and 

treatment areas and takes longer when compared to straw. This generally makes 

the economics more favorable to agricultural straw mulch when choosing between 

the two types of mulch. At the Schultz Fire, wood shreds were significantly more 

stable than straw on the steeper slopes (above 35 percent) but the difference in 

mulch stability was not so obvious on moderate and low slopes. Consequently, 

there may be advantages to applying both mulches to optimize the time and expense of treating the burned area. Wood shreds may be prescribed for treatment 

areas where straw is unlikely to work well, such as steep slopes and open areas 

with high wind exposure. Straw may be preferred for other areas because it provides adequate protection at less cost.

Like all forest operations, we expect that these guidelines for producing and 

applying wood shreds will be refined and improved by experience. Safety practices that are in place for machine operation, hazard tree felling, heli-mulching, 

general aviation, etc., may need to be adjusted to accommodate new situations 

that arise from processing and handling burned tees. The information in this report 

reflects what we have learned from research and the initial treatment projects—it 

is a starting place for BAER treatment implementation teams, forest managers, and 

contractors. Input from practitioners will improve these guidelines to make the operations of producing and applying wood shreds more efficient and cost effective.

Acknowledgments

The portions of this project related to the production and application of wood 

shreds as a post-fire hillslope treatment were funded by the U.S. Department of 

the Interior and USDA Forest Service, Joint Fire Science Program, Project 07-1-1-

01. Development of the Heli-Claw was jointly funded by the U.S. Department of 

Agriculture, Forest Service, Fire & Aviation Program and Engineering Program of 

the National Technology and Development Center. We are grateful for the generous sharing of information, observations, photographs, and lessons learned as well 

as manuscript review by:

Schultz Fire: Rory Steinke, Soil Scientist; Sean Untalan, Civil Engineer

Fourmile Canyon Fire: Claire DeLeo, Plant Ecologist

Waldo Canyon Fire: Mary Moore, Hydrologist

High Park Fire: Eric Schroder, Soil Scientist; Deborah Entwistle, Hydrologist

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Beyers, J. 2004. Postfire seeding for erosion control: effectiveness and impacts on 

native plant communities. Conservation Biology. 18(4): 947-956.

Copeland, N.S.; Sharratt, B.S.; Wu, J.Q.; Foltz, R.B.; Dooley, J.H. 2009. A woodstrand material for wind erosion control: Effects on total sediment loss, PM10

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effectiveness for hillslope stabilization. Gen. Tech. Rep. RMRS-GTR-240. Fort 

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2013a. Post-fire mulching for runoff and erosion mitigation: Part I: Effectiveness 

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R.E. 2013c. Evaluating the effectiveness of wood shred and agricultural straw 

mulches as a treatment to reduce post-wildfire hillslope erosion in southern 

British Columbia, Canada. Geomorphology http://dx.doi.org/10.1016/j.

geomorph.2013.04.024.

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0757–1305–SDTDC. San Dimas, CA: U.S. Department of Agriculture, Forest 

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effectiveness and lessons learned (abstract). Presented at: Southwest Wildfire 

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Flagstaff, AZ. 12 p.
USDA Forest Service RMRS-GTR-307. 2013. 17

Appendix A: 2010 Fourmile Canyon Fire Case Study

Post-fire Hillslope Retreatment with Wood Shred Mulch on the 

Fourmile Canyon Fire

Jennifer Kesler, Plant Ecologist and Claire DeLeo, Senior Plant Ecologist

Boulder County Parks and Open Space

Only English standard units are used in the following case study. 

The following conversions apply:

• 1 inch = 25.4 millimeters

• 1 acre = 0.405 hectare

• 1 ton ac-1 = 2.24 metric tons ha-1

Introduction

The Fourmile Canyon Fire started on 6 September 2010 and burned approximately 6,200 acres just west of Boulder, Colorado, in one of the most densely 

populated urban interfaces in Boulder County. The burned area was aerial mulched 

in 2011 with certified weed-free straw on 1,620 acres at a rate of 1.3 tons ac-1

and WoodStraw® (manufactured wood mulch produced by Forest Concepts, LLC, 

Auburn, WA) on 350 acres at a rate of approximately 4.7 tons ac-1.

In the fall of 2011, 364 acres were identified for retreatment based on limited 

recovery, high burn severity, and downstream values at-risk primarily to the Town 

of Salina. Problems with the mulch from the 2011 treatments included agricultural 

straw blowing off of treated areas and WoodStraw® moving in high intensity thunderstorm events. Of the 364 acres that were retreated in 2012, 145 acres had been 

treated with agricultural straw and 219 acres had been treated with WoodStraw®

the previous year.

Wood shreds were chosen for this 2012 retreatment because, while the 

WoodStraw® treatment performed well overall, the cost was prohibitive. With 

many fuels reduction and forest restoration projects in Boulder County and along 

the Front Range, shredded wood is an abundant locally available resource. After 

speaking with R. Steinke about the first large contracted wood shred aerial mulching project done as a post-fire rehabilitation treatment (the wood shred mulching on 

the 2010 Schultz Fire) and with other contractors, we determined that wood shreds 

would be a viable wood mulch treatment at about half the cost of a comparable 

re-treatment with WoodStraw®. In addition, we decided to mix agricultural straw 

with the wood shreds because it reduced the amount of “heavy” wood material in 

the mulch (making it less costly to apply) and retained some of the advantages of 

agricultural straw. These advantages included the residual crop seed in the straw 

which, if it sprouted and grew, provides additional vegetative cover and the better soil moisture conservation with the straw mulch as compared to wood-based 

mulches. Thus, we decided to aerially mulch with a combination of agricultural 

straw and wood shreds for retreating burned areas in 2012.
18 USDA Forest Service RMRS-GTR-307. 2013.

Production of Wood Shreds

The wood shred specifications required the material be from pine, spruce, or 

fir trees. Urban tree removal was restricted because of possible contamination of 

seed from undesirable non-native tree species, particularly Russian olive trees 

(Elaeagnus angustifolia). The wood shred size specifications were for two dominant sizes with an even mix of small strands (2 to 3 inches in length) and large 

strands (up to 8 inches in length). The diameter of the strands could range from 

1⁄8 to 1⁄4 inch for shorter shreds and up to 1 inch for longer shreds. Finer materials 

(less than about 1 inch) were allowed, but at a much lower percentage compared to 

the two dominant sizes. Our wood shred contract specifications, unfortunately, did 

not give a specific percentage of fines allowed. The specifications required wood 

shreds that were free from dirt and rocks.

The wood shreds were produced from unmarketable trees from a U.S. Forest 

Service Stewardship Project in Allenspark, Colorado, (fig. A1) using a new 

Peterson horizontal grinder (fig. A2). Boulder County Parks and Open Space staff 

only inspected the wood shreds during the initial calibration of the horizontal 

grinder. Several combinations of screens from 2-inch combined with 4- and 6-inch 

screens were tested (fig. A3). We determined through trial and error that using 

4-inch screens only produces the best wood shreds (fig. A4). The raw tree material 

did include some limbs with pine needles still attached.

Figure A2. Peterson horizontal 

grinder.

Figure A1. Raw material for wood 

shred production from USFS Forest 

Stewardship Project.
USDA Forest Service RMRS-GTR-307. 2013. 19

Mixed agricultural straw and wood shred mulch

Our specifications for the aerial mulching required 60 percent cover on 20 to 60 

percent slopes with a minimum of 0.5 tons of agricultural straw and 4 tons of wood 

shreds per acre, equating to 1 to 3 inch mulch depth on the ground. These proportions for the straw-wood shred mix were determined by using one-third the typical 

application rate of agricultural straw (0.5 ton ac-1 given the typical application of 

1.5 ton ac-1) and two-thirds the typical application rate of wood shreds (4 ton ac-1

given the typical application of 6 ton ac-1). The resulting mix was calculated to be 

4.5 ton ac-1. The wood shreds and agricultural straw were mixed at the staging area 

before the mulch was loaded into the cargo nets (fig. A5).

Aerial Application of the Mixed Mulch

Two County inspectors were on the ground inside the treatment polygons during the mulching aerial operations. They examined the proportion of ground cover 

provided the mulch components (straw versus wood shreds), the depth of mulch, 

the evenness of the mulch spread, and any clumping of the mulch. There was 

Figure A3. Wood shred product 

test.

Figure A4. Final approved wood 

shreds (C. DeLeo in photo).
20 USDA Forest Service RMRS-GTR-307. 2013.

minimal clumping of either mulch product. Despite consistent mixing of the agricultural straw and the wood shreds on the ground prior to loading the nets, we 

found that in most areas, the two mulch types separated while falling to the ground, 

with the straw always landing on the top (fig. A6).

The mulch application inspections included measuring the mulch component of 

the ground cover. The measurements were taken at 10 sampling points along 10 

transects that were randomly located within the treatment polygons. The observer 

took samples 10 paces (approximating 30 feet) apart along the transect line. At 

each sampling point, the grid was placed on the surface of the ground and the grid 

intersections that overlaid mulch were counted (fig. A7). The counted intersection 

number was converted to a percentage and recorded. The percentages for the 10 

samples were averaged for each transect and the 10 transects were then averaged 

for the treatment polygon. The Ingram Gulch treatment polygon had 69 percent 

mulch cover rate and the Melvina Gulch treatment polygon had 70 percent mulch 

cover. These mulch measurements did not include mulch that was applied in 2011. 

The proportion of cover that was agricultural straw versus wood shreds was not 

determined.

Figure A7. Ground cover monitoring grid (Forest 

Concepts, LLC, Auburn, WA).

Figure A5. Wood shreds and agricultural straw mixed in 

staging area prior to loading into cargo net. Figure A6. Applied mixed mulch.
USDA Forest Service RMRS-GTR-307. 2013. 21

Table A1. The 2010 Fourmile Canyon Fire treatment costs for mulching with a 

combination of wood shreds (4 tons ac-1) and agricultural straw (0.5 tons ac-1).

Item Cost per unit area ($ ac-1) Total cost ($)

Certified weed-free straw, delivered 170 61,880

Wood shreds only, delivered 408 148,519

Mixed mulch application 996 362,459

Total for mixed wood shreds and 

agricultural straw mulch treatment 1,574 572,858

Project Costs

The cost per acre of the mixed mulch we applied will likely be less than the 

costs of mulching with wood shreds only because the agricultural straw portion of 

the mulch is less costly than wood shreds (table A1).

Lessons Learned

• The weight of wood shreds varied because of moisture content. Green trees had a 

higher wood shred weight than burned and/or dead trees. Also, the wood shreds 

dried out between the time they were shredded and when they were flown. 

Therefore, an application rate based on tons per acre needs to take into account 

moisture content if this is used as a contract specification.

• If you must base the wood shreds on tons per acre, each truck-load should be 

weighed and percent moisture content estimated. Moisture content must be 

part of the contract specifications if an application rate of tons per acre is used. 

However, it may not be practical or cost-effective to weigh each truck delivering 

wood shreds.

• The treatment should not be based on the weight of the mulch; rather it should 

be based on the percent cover desired. While our contract had specifications for 

both percent cover and weight per acre, we concentrated too much on weight 

or tons per acre. As a result, some areas did not get treated near the bottoms of 

the watersheds.

• Use 3-D slope calculations in GIS to estimate hillslope acreage to get an accurate 

estimation of surface area, especially in areas with steep slopes.

• Do not mix straw and wood shreds as a mulch treatment. No matter how well 

they are mixed, the lighter weight straw will drop more slowly than the wood 

shreds and will always end up on the top. If using the two mulches together, lay 

down agricultural straw first, then overlay with wood shreds to hold the straw 

down and prevent it from blowing away. However, the flying costs for two separate mulch applications would likely be cost prohibitive, in which case, only 

wood shreds should be used.

• The quality of the wood shreds was not consistent because of the inclusion of 

a high percentage of smaller-than-desired shreds and pine needles. We did not 

specify a percent of fines as part of our contract specifications, nor did we have 

a way to measure the percent fines. However, the Waldo Canyon Fire BAER 

Implementation Team devised a good way to measure fines in the field for contract enforcement (see Appendix B).

• If using a percent cover as a contract specification for wood shred application 

(recommended), an adequate number of inspectors are needed on the ground to 

make ground cover assessments during the aerial application.

• The even spread of wood shreds varied by helicopter operator.
22 USDA Forest Service RMRS-GTR-307. 2013.

Appendix B: 2012 Waldo Canyon Fire Case Study

Post-fire Wood Shred Mulching After the 2012 Waldo Canyon 

Fire in Colorado

Mary Moore, Hydrologist, Lake Tahoe Basin Management Unit, South Lake Tahoe, California; 

BAER Implementation Team Leader on the 2012 Waldo Canyon Fire

Only English standard units are used in the following case study. 

The following conversions apply:

• 1 inch = 25.4 millimeters

• 1 square foot (ft2) = 0.0929 square meter (m2)

• 1 acre = 0.405 hectare

• 1 ton ac-1 = 2.24 metric tons (Mg) ha-1

Introduction

The 2012 Waldo Canyon Fire occurred on the Pike and San Isabel National 

Forest and Comanche and Cimarron National Grasslands near Colorado Springs 

and Manitou Springs, Colorado. A contractor produced and distributed nearly 

11,750 tons of wood shred mulch on 1,958 acres in 49 units of steep mountainous 

landscape (20 to 60 percent slopes) burned at moderate and high burn severity.

The BAER Implementation Team designed a program to provide quality control and ensure that contract specifications were met in all aspects of the project. 

We developed methods to measure the quality of the wood shreds being produced 

and to measure the cover provided by the aerial application. We had up to 12 

Inspectors and two Level III Contracting Officer Representatives on site for most 

of the project. We had foresters and forestry technicians as inspectors for the production of wood shreds (at the felling operations, site sources, and landings) and 

we had inspectors for the aerial mulch application. Additionally, we had an agricultural inspector examine and certify the agricultural straw that arrived onsite 

each day. We also had several other support staff, such as an archeologist and 

botanist, clearing the hazard tree removal units, landings, staging areas, etc., to 

ensure that natural and cultural resources were recognized and protected before 

project implementation.

Production of Wood Shreds

Prior to contract preparation, we determined the amount of material available for 

shredding and if site conditions were conducive to roadside hazard tree removal. 

The Timber Management Officer (TMO) was brought into the project to determine 

the available wood material (estimated in tons per acre) as hazard trees within the 

burned area and in close proximity to the burned area. Additionally, the BAER 

Implementation Team contacted several local timber contractors to determine the 
USDA Forest Service RMRS-GTR-307. 2013. 23

amount of available material in their “stock yards.” As a result, before advertising 

the contract, we knew there was enough material in local area to mulch the designated treatment area, but hazard trees from the burned area only would provide 

about a third of the needed trees for the project. We clearly indicated in the solicitation that the contractor would have to find off-site material (that met FS approval 

before it was brought into the project area) to complete the project. Additionally, 

we indicated in the contract language that a Stewardship Contract Area may be

available to the contractor awarded the mulching contract, but the contract would 

be separately negotiated with the local forest. The Roadside Hazard Tree removal 

units and the Stewardship Contract Area were depicted on the contract maps submitted with the request for solicitation.

The contractor obtained the needed trees to produce the wood shreds from four 

sites:

1. Burnt roadside hazard trees on <30 percent slopes

Hazard trees were identified as burnt trees that were within one-and-half tree 

lengths of the road or any other target (such as dispersed camp sites, roads, etc.) 

or dead or dying (>30 percent of the canopy was burnt) such that they would 

create long term hazards for the forest. A Forester determined the designation of 

questionable trees. Individual trees were not marked; we cut in areas based on a 

designated prescription. Hazard trees were cut using hand fellers and mechanized 

equipment (table B1). A grapple skidder forwarded the trees to landings or large 

piles. A horizontal grinder was later moved to each landing to shred the trees. 

Some of the material was flown directly from designated landings. The remainder 

of the wood shreds were loaded into chip “trucks/vans” and hauled to treatment 

staging areas or other landings (table B2).

2. Green trees from a Stewardship Contract Area partially in the burn

The Stewardship Contract Area was laid out and marked, but not awarded, prior 

to the fire. Using the same harvesting procedure described above, the material was 

Table B1. Harvest of trees for wood shreds production on the 2012 Waldo Canyon Fire. The 

mechanized harvest was done with two feller-bunchers.

 Area per Wood mass Wood

Workers Time Area unit time per unit area shreds

Production type (#) (days) (ac) (ac day-1) (t ac-1) (t)

Hand felling 4 8 36 4.5 45 1620

Mechanized harvest 2 10 39 3.9 45 1755

Table B2. The contractor’s equipment from 

the 2012 Waldo Canyon Fire included the 

following items for producing wood shreds.

Equipment type Quantity

horizontal grinder 2

bobcat 2

8’ bucket for bobcat 2

excavator 5

dozer 3

fuel truck 1

skid steer 2

grapple skidder 3

road grader 1
24 USDA Forest Service RMRS-GTR-307. 2013.

processed at the cutting area and hauled in chip trucks to treatment staging areas 

and landings in the burn.

3. Green trees from a fuel break construction (Mount Herman deck)

Trees had been removed and piled during the construction of a fuel break during 

the fire. After the fire, the log deck was sold to the contractor. This was a win-win 

for the forest since the stacked timber was a fuel problem (liability) and the sale to 

the post-fire treatment contractor resulted in remuneration and removal of the fuel 

problem. A horizontal grinder was brought to the deck and processed the material 

into wood shreds, which were then loaded into chip trucks/vans and hauled to the 

various landings.

4. Off-forest green wood from a local vendor’s stock yard

Due to haul-weight requirements (ratio of dead wood to green wood being 

hauled), the vendor (subcontractor) processed the green trees purchased from their 

stock yard. This material was processed using a horizontal grinder at the yard, 

dumped into chip trucks, and hauled to the treatment staging area. We inspected 

several pick-up bed loads of these off-forest wood shreds before we gave the contractor approval to use this source.

Contract specifications for wood shreds

Based on limited wood shred research data and trial studies, we knew that the 

wood shreds produced by the contractor should meet size specifications and that 

the amount of “fines” (small wood shreds—not specifically defined in the contract) 

should be restricted. The contract specifications for the wood shreds are listed below. Changes we would make in the next wood shred mulching project are listed 

in italic text.

a) Wood shreds shall meet the following specifications. Product may be rejected 

if these specifications are not upheld. At least 70 percent of the shreds shall 

meet these specifications with 30 percent or less being fines. If I had to do it 

again I would quantify the 30 percent of fines to accept 15 percent as a sizeequivalent to the local needle cast and 15 percent of “dusty” fines (≤0.5 inch).

b) The wood shreds should be processed in a manner that promotes even 

distribution when aerially released from cargo nets or similar equipment to 

at least a 70 percent cover within the treatment unit and to a depth of at least 

0.5 inches. Would ask for 85 percent coverage next time rather than just 70 

percent and depth up to 0.5 inch; in other words, emphasize the coverage and 

depth over the weight of wood shreds per acre.

c) Wood shreds shall have a stubble length of 4 to 8 inches, less than 1 inch 

diameter, and minimal fines. After seeing the product produced and applied to 

the hill slopes, we decided to accept material that measured 2 to 4 inches in 

length as this size was equivalent to the local needle cast.

d) It is recommended that a horizontal grinder be used on trees and a tub grinder 

be used for the resulting slash. Grinder screens of 2 to 4 inches will be used to 

meet the desired specifications.

e) Wood shreds shall be covered during transportation and when staged to 

prevent material from blowing around on site.
USDA Forest Service RMRS-GTR-307. 2013. 25

To enforce these contract specifications, each source site, landing, and large 

collection area of wood shreds material was inspected using a random sampling 

method. To evaluate the quality of the wood shreds, we constructed a 2-ft2 frame 

with a 1-inch edge and a solid bottom panel (white) divided into four 1-ft2 quadrants. A 0.5-inch mesh screen fit over the frame and the wood shred sample was 

poured onto the screen. Through trial and error we determined the volume of wood 

shred material the sample frame and screen could support and marked 5-gal sample 

buckets with a fill line that indicated the sample volume needed—approximately 

1

/2 to 2/3 of a bucket. The screen allowed fine wood shreds to pass through while 

the remainder of the wood shred sample stayed on the screen. The fines and large 

pieces (>8 inches) were pushed into the upper right quadrant of the frame. All the 

remaining sample wood shreds were placed in the remaining frame space. Using a 

visual examination of the area occupied by the wood shreds in each size category, 

the percentage of fines in the sample was estimated. (A video that shows the sample frame, screen, and sampling process is available at: http://www.youtube.com/

watch?v=n2pqAxBaCTc&list=UU7oCsexW1Y_ibLkzkc6QRDQ.)

A photo of each sample laid out in the frame was used to document the inspector’s evaluation of the wood shred compliance with contract specifications 

(fig. B1). Depending on the distance between inspection sites, 40 to 50 samples per 

day were processed and documented by each inspector.

Figure B1. Two wood shred samples that 

passed inspection for BAER treatment 

implementation at the 2012 Waldo Canyon 

Fire. Both samples had been screened and 

are shown distributed in the quadrants 

of the sample frame. Note that sample b) 

contains green needles and is generally 

more finely shredded as compared to a).

a)

b)
26 USDA Forest Service RMRS-GTR-307. 2013.

Aerial Application of Wood Shreds

The contract specified:

a) Wood shreds were to be applied at 6 tons ac-1 to provide 70 percent coverage 

and a depth of 0.5 inch (table B3). Next time we would ask for 85 percent 

coverage and up to 0.5 inches in depth. We easily got 100 percent coverage in 

the interior of the units and areas of lighter coverage only were observed at 

the edges of the units. This was likely due to edge effect or missed areas.

b) Agricultural straw was to be applied to provide 85 percent coverage at 1 inch 

depth.

c) All designated treatment units will meet the coverage specifications delineated 

above.

Note that the contractor is paid in full for meeting 90 percent of the contract 

specification. Given that 90 percent of 70 percent coverage is 63 percent, under 

this contract full payment could be received for wood shred treatment units that 

averaged 63 percent coverage. This is why we would increase the contract specifications for percent coverage of wood shreds in the next contract—we are confident 

that we can ask and get greater than 63 percent wood shreds treatment coverage. 

The straw mulch coverage was similar. Ninety percent of 85 percent straw mulch 

coverage is 77 percent and, based on these contract specifications, distribution of 

straw mulch that averaged 77 percent coverage would receive full payment.

The wood shreds (and the agricultural straw) were distributed by up to five helicopters equipped with cargo nets over several mapped treatment areas (fig. B2). 

On-the-ground inspectors worked in two-person teams and assessed contract compliance for the aerial mulching. Treated units that were smaller than 40 acres were 

sampled at 10 points along a directional (as determined by a compass bearing) 

transect line and units that were larger than 40 acres were sampled at a minimum 

Table B3. Final coverage (in percent) of the 49 units treated with wood shreds on the 2012 Waldo 

Canyon Fire. Some of these units may have been re-worked to achieve contract completion.

Unit (#) Coverage (%) Unit (#) Coverage (%) Unit (#) Coverage (%)

W10 71 W38 80 W59 88

W11 92 W39 81 W60 73

W12 90 W40 87 W61 79

W14 63 W41 63 W62 68

W15 92 W43 73 W63 75

W22 71 W44 65 W64 78

W23 63 W46 77 W65 38

W24 67 W47 66 W66 75

W25 75 W50 84 W67 80

W26 69 W51 63 W68 90

W27 73 W52 77 W69 81

W28 72 W53 81 W72 83

W29 74 W54 79 W74 74

W30 67 W55 63 W75 63

W32 70 W57 82 W8 65

W36 81 W58 75 W9 73

W37 88

Average coverage = 75%
USDA Forest Service RMRS-GTR-307. 2013. 27

Figure B2. The 2012 Waldo Canyon Fire BAER aerial treatment map. Wood shreds and agricultural straw treatment 

units are designated by color-coded perimeters.
28 USDA Forest Service RMRS-GTR-307. 2013.

of 10 random points. Some of the bigger units were sampled at 20 or 30 points 

depending on access and entry points available.

A WoodStraw® grid (Forest Concepts, LLC, Auburn, WA) (fig. B3) was used 

to measure the ground coverage at each sampling point. Each intersection of the 

grid was counted if a ground cover component (mulch treatment, live vegetation, 

or needle cast) was visible beneath the plastic sheet at that point. The total count of 

covered intersections was converted to a percentage using the table printed on the 

grid. All sample points were photo-documented and labeled by GPS-determined 

coordinates (fig. B4). Units that did not pass were re-worked by the contractor 

(table B4). Experienced inspectors occasionally used a visual inspection from 

vantage point when circumstances precluded direct measurement. Inspectors designated ten “random points” across the unit and predicted the percent coverage 

from the vantage point. Photo documentation of the selected random points occurred to the best of the inspectors’ abilities. Some re-worked areas were visually 

inspected.

Figure B4. Photo documentation of 

wood shred cover at a sampling 

point in the field at the 2012 

Waldo Canyon Fire.

Figure B3. The WoodStraw® grid (Forest Concepts, LLC) 

being used to sample ground cover for contract 

compliance during treatment implementation at 2012 

Waldo Canyon Fire.
USDA Forest Service RMRS-GTR-307. 2013. 29

Table B4. A sample Application Summary Report from the contractor for the 2012 Waldo Canyon BAER implementation 

project. The contractor provided this information daily as part of the required contract documentation.

SUMMARY REPORT OF WOOD SHRED APPLICATIONa

Unit Unit area Treated area Exempt area Touch-up USDA Flight time Wood shreds applied 

no. (ac) (ac) (ac) (ac) (h) (@ 6 t ac-1)

8 13.4 13.4 3.0 80.4

9 10.2 10.2 3.2 61.2

10 16.4 16.4 2.8 98.4

11 246.8 246.8 33.0 1481.1

12 3.4 3.4 0.9 20.4

14 200.3 186.3 14.0 60.5 1201.9

15 96.6 84.8 11.8 20.3 579.7

22 18.0 14.5 3.5 3.8 108.0

23 69.5 69.5 19.6 417.0

24 19.5 17.0 2.5 5.5 117.2

25 26.6 26.6 8.1 159.7

26 15.0 14.6 0.4 4.0 89.7

27 10.0 10.0 3.5 60.0

28 17.1 17.1 6.1 102.6

29 16.5 16.5 5.8 99.0

30 17.8 17.8 5.0 106.6

32 45.5 45.5 10.9 273.0

36 65.5 58.5 7.0 20.7 393.3

37 60.6 60.6 15.3 363.5

38 64.9 62.9 2.0 14.1 389.4

39 492.9 492.9 105.8 2957.1

40 40.8 40.8 10.3 244.8

41 13.2 13.2 3.3 79.2

43 6.2 6.2 1.8 37.2

44 48.7 48.7 13.7 291.9

46 13.1 13.1 3.0 78.5

47 16.7 16.7 3.7 100.2

50 4.5 4.5 1.0 27.0

51 4.3 4.3 0.9 25.9

52 4.4 3.6 0.8 1.0 26.2

53 44.4 44.4 8.8 266.3

54 20.5 15.5 5.0 1.9 122.9

55 46.4 44.5 1.9 5.2 278.2

57 25.5 24.5 1.0 2.7 153.0

58 9.9 9.5 0.4 1.9 59.2

59 45.2 45.2 6.6 271.2

60 3.1 3.1 0.7 18.7

61 2.5 1.9 0.6 0.2 14.8

62 2.1 2.1 0.3 12.4

63 1.1 1.1 0.3 6.8

64 4.4 3.3 1.1 0.7 26.3

65 5.4 5.4 2.3 32.5

66 14.5 14.5 2.6 87.0

67 12.8 12.8 4.2 76.6

68 12.9 8.7 4.0 0.2 2.4 77.3

69 13.3 5.2 7.4 0.8 1.9 79.9

72 17.9 14.9 3.0 3.1 107.3

74 8.4 4.2 4.2 1.0 50.6

75 37.7 37.7 5.9 226.4

Total 2006.2 1934.7 65.7 5.8 442.9 12037.4

a This table has been adapted from the original submitted by the contractor. Some repetitive columns have been removed and column headings 

were revised to be more self-explanatory.
30 USDA Forest Service RMRS-GTR-307. 2013.

Documentation and document tracking

Each evening, inspectors filed reports that delineated the units that passed inspection and the units that needed to be reworked because of a failed inspection 

(table B3). All GPS units were downloaded to a master shapefile (map component 

files in GIS) and electronic copies of all photo-documentation were filed by unit 

number. Hard copies of photographs, maps, and the attribute tables for the shapefiles were filed by date in the Unit Inspection Log folder. All original data sheets 

were organized by date and kept in a separate log folder.

Reporting required from the contractor

The contractor was required to file written reports of the work done each day. 

These reports included general information about the day and the progress on the 

contract from their perspective (table B4). Project maps indicating the locations 

and extent of work done were also required at the end of each day. A full written 

report was required upon completion of the contract.

Monitoring

Ten percent of the mulched acres may be monitored for treatment effectiveness 

for the next 3 years. To facilitate future monitoring, the BAER Implementation 

Team identified several contract inspection plots that are easily accessed from existing roads or unit access points as potential monitoring points.

Costs

Post-fire mulching with wood shreds is not inexpensive. Based on the data in 

the Waldo Canyon 2500-8 Interim #1, we estimate the following cost factors for 

the aerial mulching project: 3,038 acres were treated—1,958 acres of wood shred 

treatment and 1,080 acres of agricultural straw treatment. The contract cost was 

$4,783,918 ($2,141 per acre for wood shred mulching and $548 per acre for agricultural straw mulching). A field team (post-assessment team) that inspected the 

treatment areas and confirmed the area estimates and determined the size and scope 

of the treatment implementation was used as part of the contract preparation and 

cost approximately $50,000. The contract administration team cost was $348,000 

for a total of $398,000. Thus the total cost (contract plus overhead) for wood shred 

treatment was $2272 per acre and for agricultural straw treatment was $679, which 

brought the total project cost to $5,181,896.
USDA Forest Service RMRS-GTR-307. 2013. 31

Acknowledgments

This case study used the comments, charts, images, etc. from the combined 

effort of the entire Waldo Canyon BAER Implementation Team. The success of 

the entire operation, and of the wood shred mulching in particular, reflects their 

knowledge, skill, and hard work.

Waldo Canyon BAER Implementation Team

R2/ Pikes Peak Ranger District: Adam LaSalle, Alex Doud, Dan Kleist, Leah 

Lessard, Lisa Gowe, Rachael Blair, Rob Hoey, Ryan Kolling

R5/Lake Tahoe Management Unit: Mary Moore, George Gusses, Jen 

Bridgewater, Travis Buckalew, Nadia Aslami, Brian Hansen, Matt Panks

R5/Modoc National Forest: Cathy Carlock

R5/San Bernardino National Forest: Angelica Mendoza

Inquiries related to this Waldo Canyon Case Study should be directed to Mary 

Moore (marymoore@fs.fed.us)
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