LIVE STAKING
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1. CATEGORY
2.0 – Bank Armor and Protection
2. DESIGN STATUS
Level I
3. ALSO KNOWN AS
Live Cuttings, Sprigging, Joint Planting, Slope Pinning, Live Slope Nailing
4. DESCRIPTION
Live stakes are pieces of freshly cut woody plant stem planted in the ground or into erosion control or streambank stabilization structures. The branches vary from about 50 to100 cm (20 to 39 in) long, and typically 20 to 75 mm (3/4 to 3 in) in diameter. Pole Planting (see Willow Posts and Poles) is a related technique, however the poles are much longer (1 to 5 m (3.3 to16 ft) long) and can be installed and arrayed differently.
Live stakes are planted with the terminal buds or leaf nodes pointing up and the basal ends down into the soil. The buried portion of the cuttings develop roots, while the exposed portion produces branches and leaves. Depending on the species, the cuttings can grow into shrubs and/or trees. Because of its ability to root easily, the preferred plant species for Live Staking is Willow (Salix spp.), but Cottonwood (Poplar spp.), Dogwood (Cornus spp.), Elderberry (Sambucus spp.), Coyote brush (Baccharis spp.), and others have been used successfully. .5. PURPOSE
The concept behind live stake planting is that the live, vegetative cuttings are placed into the ground to allow the stakes to root and grow. Even if the branches do not grow the stakes can provide, at least temporarily, reinforcement much like a wooden stake or steel rebar stake. Live stakes generally accomplish several purposes concurrently:
The stakes grow vegetatively thereby providing cover and erosion control.
The vegetative cover can provide improved aesthetics.
The cover provides shade and canopy cover where thermal pollution may be a concern,
The leaves, branches and insects living on them can provide carbon and nutrient cycling and are an important food source for aquatic organisms.
The roots and branches provide for and improve geotechnical and soil stability. Using a system of live stakes creates a root mat that stabilizes the soil by reinforcing and binding soil particles together. Roots can also aid stabilization by extracting excess soil moisture, and by binding fill soils to existing native soils.
Live stakes used as slope nails can stabilize slumps and slides through the mechanisms of "buttressing and arching".
Leafy and brushy top growth benefits the streambank by increasing roughness thereby reducing boundary shear stress underneath the canopy.
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6. PLANNING
Useful for Erosion Processes:
Toe erosion with upper bank failure Scour of middle and upper banks by currents Local scour Erosion of local lenses or layers of noncohesive sediment Erosion by overbank runoff General bed degradation Headcutting Piping Erosion by navigation waves Erosion by wind waves Erosion by ice and debris gouging General bank instability or susceptibility to mass slope failure
Spatial Application:
Instream Toe Midbank Top of Bank
Hydrologic / Geomorphic Setting
Resistive Redirective Continuous Discontinuous Outer Bend Inner Bend Incision Lateral Migration Aggradation Conditions Where Practice Applies:
Live Staking has been successfully used in many different climactic, soil moisture regimes and elevations. The possible uses for and benefits of Live Staking is vast but the primary uses generally involve revegetation, anchoring, enhancing geotechnical strength (shear strength), or reducing erosion through increased cover (raindrop impact) and hydraulic roughness (reduced boundary shear). The practice is commonly used in combination with other practices to provide more stable site conditions and a more environmentally-sensitive design.One of the most important design considerations for vegetative success is determining whether the chosen species (willow, cottonwood, dogwood etc,) is naturally-occurring in the region and/or will the chosen species allow successional reclamation – natural succession from willow shrubs to tall riparian overstory.
Live Staking is commonly referred to as “Joint Planting” when used to plant the interstitial spaces between structural measures such as Riprap, Articulated Concrete Blocks, Geocellular Confinement Systems, etc.
This technique can also be used to repair small earth slips and slumps. The stakes are used as live slope pins and are arrayed in a manner to increase soil buttressing and soil arching. (Gray & Sotir, 1996).
Live Stakes are useful for the following situations:
Live Staking is useful as a revegetation technique and for establishing riparian plants in high flow or droughty situations.
Live Staking can be used in irrigated or non-irrigated conditions with the latter being more prevalent. Irrigation can greatly increase vegetative success. Most often live staking is installed during the dormant season or when climactic or soil moisture conditions are favorable for establishment in non-irrigated conditions.
Live Stakes provide an environmentally-sensitive anchoring technique for geotextiles and erosion control materials. The anchoring can be temporary or permanent depending on whether the stakes “take root”.
- Adding immediate failure resistance to the soil mass. While providing geotechnical benefits by "buttressing and arching", deep-seated failure planes underneath the bottom end of the cuttings will not usually be affected by live staking. These plants can remove excess soil moisture via evapotranspiration during the growing cycle, however these benefits will not be realized during dormancy.
Figure 3. This willow stake is only 9 mo old (note sunglasses in center of photo) but storm flow exposed roots-estimated over 30 m of roots help stabilize soil and provide exceptional pull out resistance. J. McCullah
Figure 4. This willow stake, used to revegetate a denuded slope, is 30 days old. The stake was 1.5 m long with 0.5 m inserted into the soil. The stake was soaked for 5 days prior to installation.
Figure 5. The same stake from Figure 4 was removed to measure root growth.
Complexity:
Low.
Design Guidelines / Typical Drawings:
The stakes shall be harvested from relatively straight, disease- and insect-free branches. Stakes shall be 20 to 75 mm (3/4 in to 3 in) diameter and a minimum of 0.5 m (18 in) long. The upper end of the stake shall be cut square and the basal end of the stake shall be cut on angle. Preparing the stakes in this manner will aide insertion into the soil and also ensure the stakes are oriented correctly when installed.
Generally the deeper the branch is inserted into the soil the better the chance of vegetative success and the greater the soil stabilization benefits, therefore the "80% Rule" must be strictly followed – at a minimum 80% of the branch shall be placed in the soil and with 20% protruding above. For instance, a 46 cm (18 in) stake will be installed 37 cm (14.5 in) minimum into the soil, and a 91 cm (30 in) stake shall be installed 61 cm (24 in). Deeper planting also reduces the chance that stakes can be pulled out by beavers, deer or other wildlife. Limited browsing of Willow by wildlife is generally not detrimental.
It is important not to damage the stakes during installation. Damaged and split stakes have increased incidence of dehydration, decay, and the introduction of disease. Most compacted soils or soils with rocks and gravel will require the use of a "pilot bar" to make a hole prior to driving the stake. The use of a polyurethane hammer or rubber mallet will reduce splitting damage to the stake. Using a high-powered water jet to pilot the holes is most favorable as the hole is also left well hydrated. The USDA-NRCS Plant Material Center has specifications for a water jet (Hoag et. al., 1993).
The successful implementation of this technique requires care and consideration of the stakes during harvest, storage, transport and installation. The stakes should never be allowed to dry out. Keep the stakes moist and covered at all times. Soaking the stakes will increase success (Briggs & Munda, 1992).
7. ENVIRONMENTAL CONSIDERATIONS / BENEFITS
The most direct environmental benefits are cover and shade, carbon and insects
for basic food web and nutrient cycling, and the ability to provide stable areas
for native plant re-establishment (successional reclamation) (Polster, 1998).
Live stakes establish a root mat that stabilizes the soil. Stake establishment
can improve aesthetics and provide wildlife habitat. The stems, branches, and
leaves slow high flows, provide shade, habitat, food, and shelter for stream
corridor biota. When Live Stakes are placed on upper banks, they provide habitat,
food and shelter for terrestrial fauna as well. As a temporary, immediate measure,
Live Staking performs an important function of stabilizing and modifying the
soil, serving as a pioneer species until other plants become established. Stakes
can play an important geotechnical function of buttressing and arching, which
provides increased friction in the soil mass, and helps stabilize small slumps
and failures.
8. HYDRAULIC LOADING
Allowable shear stress for this technique is approximately 120 N/m2 (2.5
lb/ft2) (Schiechtl & Stern,
1996), and allowable velocity is about 0.9 m/s (3 ft/s) (Gray & Sotir,
1996).
9. COMBINATION OPPORTUNITIES
Live stakes are often used to anchor and enhance the effectiveness of Willow (Salix spp) wattles, straw rolls, coir rolls, Turf Reinforcement Mats, coir mats, continuous berms and other erosion control materials. They can be inserted or driven through interstices or openings in Gabions, Riprap, Articulated Block, or Geocellular Confinement Systems. For revegetation they can be used in combination with rooted container plants, seed, and mulches.
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Figure 9. As the stake
grows it stabilizes the soil while providing cover and habitat.
Photo by Don Harley. |
10. ADVANTAGES
• Stake sources are plentiful and inexpensive.
• Installation is rapid and inexpensive.
• Stakes can be planted with minimal surface preparation or disturbance, and can be placed into irregular (but stable) slope surfaces.
• Stakes can be planted into already-existing structures.
• Stakes root rapidly and help to reduce slope soil moisture soon after installation.
• Provides both environmental and aesthetic benefits.
11. LIMITATIONS
Without temporary irrigation, stakes have the highest survival rate when installed
during dormant season, which may not coincide with the best time for construction
of the rest of the project. Stakes do not become fully effective until one growing
season after installation, and thus provide limited immediate and aerial stabilization
unless combined with other practices.
12. MATERIALS AND EQUIPMENT
Live stakes are typically made of woody riparian plant stems, although fleshy
plant stems can have some success as well. Willow, cottonwood, and dogwood
are the most used woody plants; however, willow cuttings make the best material
for live stakes. Willow species choice is highly dependent on locale; the best
species for a given site are those found growing near the site. Stakes are
typically harvested and planted when the willows, or other chosen species,
are dormant, although the cuttings can do well other times of year when soil
moisture is available.
When harvesting cuttings, select healthy, live wood that is reasonably straight, and at least 2 years old. Make clean cuts without splitting ends. Trim branches from cutting as closely as possible. Cuttings should generally be 19 mm (¾ in) in diameter and 46 cm (18 in) long, or larger depending on the species. The butt end of the cutting should be pointed or angled and the top end should be cut square to help identify the top and bottom when planting. The top, square end can be painted and sealed by dipping the top 2.5 to 5 cm (1 to 2 in.) into a 50 to 50 mix of light colored latex paint and water. Sealing the top of stake will reduce desiccation, ensure the stakes are planted with the top up, and make the stakes more visible for subsequent planting evaluations. Stakes must not be allowed to dry out. All cuttings should be soaked in water for 5 to 7 days (a minimum of 24 hours) and planted the same day they are removed from water.
A metal pilot bar and 2 to 3 lb sledge hammer may be necessary. A dead blow hammer or hard rubber mallet should be used to drive the Live Stake. Using a high-powered water jet to pilot the holes is most favorable as the hole is also left well hydrated. The USDA-NRCS Plant Material Center has specifications for a water jet (Hoag et. al., 1993).
Please see Special Topic: Harvesting and Handling of Woody Cuttings for further detail.
13. CONSTRUCTION / INSTALLATION
Use an iron stake or bar to make a pilot hole in firm soil. Plant the basal ends into the ground, with the leaf bud scars or emerging buds always pointing up. Be careful not to damage the buds, strip the bark or split the stake during installation. Ideally, the stakes should not be planted in rows or at regular intervals, but at random in the most suitable places at a rate of 2 to 5 cuttings/m2 (2 to 5 cuttings/10 ft2). However, if trying to control a group of people planting several thousand of these, it may be easier to specify an average set interval.
Set the stake as deep as possible into the soil, with 80% of its length into the soil. Deep planting will increase the chances of survival. The stake should never protrude more than one-quarter of its length above the ground level to prevent it from drying. The excess stake or any damage or split ends can be cut off after installation. At least 2 buds and/or bud scars should remain above the ground after planting. Add soil to the planting hole if necessary to ensure soil contact with the stem. It is important to tamp the soil around the cutting to ensure good soil-stem contact. The best installations, especially on droughty sites, will include "watering in" and slightly compacting the backfill or hole. "Watering in", much like transplanting a container plant, can successfully be accomplished by pouring one to two gallons of water into the soil around the stake and planting hole, then slightly tamping or otherwise jarring the soil. This procedure will ensure intimate soil to stem contact.
14. COST
Costs range from $1.50 to $3.00 per stake, including harvesting, transportation, storage, and installation. Typically, costs are closer to $1.50 per stake, but may be higher if labor costs are especially high or the harvesting location is a long way from the project site. Estimated labor allocations are 2 to 5 m2 (20 to 50 ft2) of live staking per work hour or approximately 10 to 25 stakes per hour. These estimates include all preparations.
15. MAINTENANCE / MONITORING
Stakes should be inspected every few weeks until well established, and irrigation,
browse control (from livestock, deer, beavers, etc), pruning, weed control and
fertilization should be implemented as needed.
16. COMMON REASONS / CIRCUMSTANCES FOR FAILURE
Live staking can fail if vegetation is not handled properly prior to installation,
is installed incorrectly (less than 80% of the cutting in the ground, bud scars
facing down, poor soil contact, etc.) or not irrigated
or "watered in" when installed in arid
areas.
17. CASE STUDIES AND EXAMPLES
Scour was occurring on an outer bend of Cedar Creek in Northern California, which was causing serious erosion that had the potential to impact Highway 299. Riprap was used to armor the bank, and 9 bendway weirs were used to redirect flow away from the sensitive bank. Live stakes were installed at the toe, and willow posts were planted into and around all structures.
Please visit the Photo Gallery for more pictures.
Hwy 299W, Shasta PM 1.0.
A Caltrans cutslope research site in Northern California experienced some slope failure due to excess moisture. The site is 2000 ft elevation, the average summer temperature is 100° F, average annual precipitation is 127 to 152 cm (50-60 inches) and the underlying geology is highly erosive decomposed granite. Willow (Salix spp) has been successfully used in the past in this area to repair small mass wasting and road related erosion. In December, 2002 a large rain on snow event triggered a slump in the center of a recently constructed slope and research project. The toe of the slide “caught” on an access bench but the non-cohesive material threatened to move downslope onto the highway.
Live willow stakes, 25.4 mm (1 in) diameter x 76.2 cm (30 in) long were driven into the slumping material at .91 m (3 ft) on center. Immediately, the soil mass stopped moving. By the following spring, almost all the stakes had sprouted and over 80% remained alive through the following summer and winter. The slope has since naturally settled and has stabilized with the exception of a concentrated-flow, drainage gully.
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 September 2003 |
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Please visit the Photo Gallery for more pictures.
18. RESEARCH OPPORTUNITIES
Studies would be valuable regarding the effect live staking has on increasing
the ability of other measures to withstand higher velocities and shear stresses.
19. REFERENCES
Briggs, J.A., & Munda, B. (1992). Collection, Evaluation and Production
of Cottonwood Poles for Riparian Area Improvement. Final Report to
the U.S.F.W. Service, U.S.D.A.-S.C.S., Tucson Plant Materials Center,
Tucson, AZ.
Gray, D. H. & Leiser, A. (1982). Biotechnical Slope Protection and Erosion Control. Van Nostrand Reinhold, New York, N. Y.
Gray, D. H. & Sotir, R. (1996). Biotechnical and Soil Bioengineering Slope Stabilization. John Wiley and Sons, New York, N. Y.
Hoag, J. C., (1993). How to plant willows and cottonwoods for riparian rehabilitation. USDA Natural Resources Conservation Service, (Idaho Plant Materials Technical Note #23), Boise, ID.(pdf)
IECA Short Course, Bioengineering Techniques for Streambank and Lake Shore
Erosion Control; John McCullah-CPESC.
McCullah, J., 2004. Erosion Draw 5.0 - Erosion and Sediment Control
Manual with Typical Drawing Files for Computer-Aided Drafting, Redding,
California
Polster, D. F. (1999). Soil Bioengineering for Forest Land Reclamation and Slope Stabilization (Course material for training professional and technical staff). Polster Environmental Services. pp. 53-56.
Schiechtl, H. M.& Stern, R. (1996). Ground Bioengineering Techniques for Slope Protection and Erosion Control. Blackwell Science. London, England.
USDA, Soil Conservation Service. (1992). Engineering Field Handbook
- Chapter 18 – Soil Bioengineering for Upland Slope Protection and
Erosion Reduction. Part 650, 210-EFH, Engineering
Field Handbook, 53 pp. (pdf)
