Dr Terry Mabbett looks at a number of stakes and ties, designed to aid the growth and development of newly planted trees.
FACED with a phalanx of physical, chemical and biological threats to successful establishment, newly planted trees will require at least some of the accessories widely available to arborists. Tree guards and tree shelters to avoid herbivory, and the latter to provide an amenable micro-environment for tree growth and development, as well as additional accessories including tree stakes and ties, tree restraints, strimmer protectors and mulch mats.
STAKES AND TIES
Three factors, alone or in combination, will determine whether newly planted trees need staking and tying. They are:
- Size and nature of tree planting material
- Exposure of planting position, especially to wind
- Gradient (slope) on the planting site
Very small stock such as whips and trees under one metre in height and trees inserted into slots or notches using a spade or planting spear do not generally require staking and tying. Such stock will not significantly benefit from staking and tying because the minimal amount of above-ground growth presents a correspondingly low resistance to wind, while the rate and amount of root generation required to establish such small trees is correspondingly small.
WHY SECURE BIGGER TREES?
Unsecured tree stems may snap in the wind but the need to stake and tie bigger trees is mainly about minimising stem movements transmitted underground to cause root ball rocking. Tree establishment problems related to root ball rocking revolve around the regeneration of root hairs lost when trees are lifted in the nursery.
Planted trees, other than container-grown stock, will have been shorn of a high proportion of root hairs during lifting in the nursery. These minute, thin-walled and delicate structures are extensions of root hair cells formalised into a narrow band of tissue called the root hair zone, located just behind the apical meristem and zone of cell elongation at the root tip.
Root hairs are best known for efficient absorption of water and dissolved mineral nutrients. However, the root hair population, as millions per tree, has an additional critical, but less well-known, role in tree anchorage, and achieved by each root hair attaching to a microscopic mineral particle like sand.
Unsecured trees sway in the wind with tree movements transmitted down the stem and into the root ball, which rocks in the ground to create a gap or void between the root ball and the soil. The unbridgeable gap thus created prevents root hairs forming secure attachments to soil particles, inhibiting root growth and development. Trees cannot absorb sufficient water and nutrients and consequently fail to establish.
SITE CONDITIONS REQUIRING TREE SECUREMENT
Trees planted on exposed, windy sites, such as hillsides and embankments, but also urban sites where wind is funnelled between buildings, require staking and tying. As do trees planted on sites with a gradient and/or where topsoil is shallow or very sandy. Ground with a gradient is more likely to have shallow and sandy topsoil due to soil erosion and run-off.
Other candidate sites for tree staking and tying include those experiencing heavy vehicular and human traffic, such as ground maintenance crews and grass-cutting teams. Staking and tying helps to keep trees secure in the face of vibrations transmitted through the ground.
TREE STAKES – HOW MANY; HEIGHT AND DEPTH
How many stakes:
Generally speaking, a single stake is sufficient for feathered trees up to standard trees, especially if stock is field-grown. The stake should be inserted in the planting pit before positioning and settling the tree in place, and on the side facing the prevailing wind.
Double and triple staking is more appropriate for container-grown trees because the stakes can straddle the root ball. Stakes are best positioned and inserted after the root ball has been lowered into the planting hole to avoid root excision by sharp-ended stakes. Cross-boards can be used for extra support.
How high up the tree:
This will obviously depend on the height of the tree and whether the planter is following Forestry Commission (FC) guidelines recommending the stake should reach no more than one third of the way up the stem. FC judges this relative height as sufficient to hold the root ball steady in the ground and therefore to allow development of a well-established and sustainable root system. Tree tying at this position permits enough wind-induced movement in the upper part of the tree to generate the critically important natural stem thickening and strengthening, while encouraging the development of a strong root system.
Arguments levelled against staking and tying up into the crown focus on creation of a fulcrum, or point of leverage (at this high point in the tree) and predisposing the tree to snapping, due to wind or applied human pressure, at this high point. However, my observations in urban areas with a high incidence of vandalism suggest the presence of at least one sturdy stake reaching up into and secured to the tree crown is a useful deterrent against damage. Otherwise, the casual opportunist vandal is more tempted and likely to swing on the naked tree. A couple of extra quid for a much longer machine-rounded stake is a small price to pay to protect a £100 copper beech tree.
How deep into the ground:
How deeply tree stakes are driven into the ground is governed by soil type and level of soil preparation at the planting site, the site’s exposure level to wind and, not least, the size and form of the tree planting material. Generally speaking, stakes should be positioned so that at least one quarter of the stake is underground. Staking trees on gradients can be carried out pre- or post-planting using stakes driven in at a 45-degree angle leaning into the prevailing wind.
WHAT’S AT STAKE?
Every year, the UK arb sector plants many millions of trees of widely varying size, shape and type and within a wide spectrum of planting sites and environmental conditions. As such, Britain’s mainstream suppliers of tree planting accessories offer a correspondingly wide range of stakes (machine-rounded or square-sawn) of various, though generally standard, lengths and diameters. The following are widely available:
Machine-rounded, pointed and tanalised softwood tree stakes
Diameter(D) Length(L)
D: 50 mm L: 1.2 m; 1.5 m; 1.65 m; 1.8 m; 2.4 m
D: 60 mm L: 1.2 m; 1.65 m; 1.8 m; 2.1 m; 2.4 m
D: 75 mm L: 1.65 m; 1.8 m; 2.1 m; 2.4 m
Machine-rounded stakes are cut and crafted mainly from softwood. Tanalised tree stakes are pressure-treated with an appropriate chemical preservative to prolong the structure, integrity and working life of the wood. The use of a pressure treatment ensures that chemical preservatives penetrate deeply into the cells of the wood for long-lasting protection against fungal decay and attack from wood-boring coleopteran insects such as beetles and weevils, and physical deterioration caused by alternating saturation and drying out of the underground portion of the tree stake.
SQUARE-SAWN, POINTED AND TANALISED SOFTWOOD TREE STAKES
Diameter(D) Length(L)
D: 25 mm x 25 mm L: 0.75 m; 0.9 m; 1.2 m
D: 32 mm x 32 mm L: 1.2 m; 1.5 m
TREE TIES
Apart from cost in relation to the job in hand, purchase and use of tree ties in conjunction with tree stakes will depend on:
- Size and form of the tree
- How long stake-tie support is expected to last
- Planned post-planting inspection and maintenance schedule
For instance, if support is only wanted for a relatively short duration of say one to two years, then there is no point investing in a relatively expensive buckle tie with a 10-year lifespan and requiring periodic loosening of the buckle. Use of a cheaper system, such as natural hessian webbing, requiring virtually no maintenance, is much more appropriate. Similarly, use of strong, durable and snap-resistant polycarbonate ties is pointless if it will be impossible to regularly inspect planted trees as they grow and increase in girth.
CUSTOM-DESIGNED,
FORMALISED TREE TIES
Buckle ties are used in exactly the same way as trouser belts for a secure but adjustable fit to accommodate increase in stem girth. Buckle ties are manufactured in polycarbonate, an essentially unbreakable thermoplastic polymer, required to withstand the strong forces exerted by wind on the centre of the buckle.
Buckle ties invariably come with an integral hoop collar-spacer to prevent bark damage caused by tree-stake contact and bark abrasion. It also permits a degree of stretch and therefore some movement, which helps the tree develop an intrinsic resistance to wind. A degree of stretch allows otherwise annual inspections and adjustments to become biennial.
That said, inspection intervals should never be longer than 24 months to avoid the risk of bulging damage to trees. Polycarbonate material offers a long working life of at least 10 years and, therefore, reuse. Buckle ties can be purchased in several size types including ‘mini-tree tie buckles’ for shrubs, standard buckle ties of 38 cm, 45 cm and 60 cm length and even larger buckle ties for use with semi-mature trees.
Chain-lock ties are custom-designed and formalised but, strictly speaking, are not available in an immediately ready-to-use form, as they are sold as rolls from which the individual chain-lock tie is cut off at the length required. Designed and developed in the 1960s, this versatile system of tree tying is sophisticated in its simplicity and available in a range of sizes and of different material types. The chain-lock tie is simply fed through itself and twisted to form a figure of eight between the stake and the tree. These ties are easily adjusted, can be reused if required and come in various widths of 11.4 mm and 25.4 mm and on 25-metre rolls.
Other custom-designed and formalised tree ties include fixed or releasable cable ties and anchor fix ties.
TREE BELTING AND STRAPPING
Rubber tree belting – Extremely simple, but exceptionally effective and economic, the length of rubber belting or strapping used per tree will last at least 10 years, with some stretch capability that benefits the tree, while enhancing tie strength. Rubber belting or strapping is therefore most appropriate for securing larger trees. The product is most safely and effectively used in conjunction with spacers including various length hoop collars, simple rubber cushions or heavier duty rubber blocks. These spacers are positioned between the stake and the tree to prevent mutual contact and bark abrasion. The rubber webbing/strapping is fixed securely to the tree stake using a pair of flat-headed galvanised nails. Rubber webbing/strapping typically comes in widths of 25 mm, 40 mm or 50 mm and on roll lengths of 15 m or 25 m.
Rubber cushions – Cushions are made of thermoplastic rubber and designed with a ribbed surface for a secure grip. Those that come with a hollow centre can accommodate any change in tree stem shape with growth.
Rubber blocks – Equipped with two concave surfaces that allows for a tight fit between the tree and the stake to ensure minimal movement. Look out for the ones which allow easy feed of the rubber belting/strapping and which are manufactured from 100 per cent recycled rubber material.
Hoop collars – These are the most lightweight and simple spacers commonly used in conjunction with rubber belting to secure trees to their stakes, while preventing any direct physical contact between stake and tree.
Other materials of equivalent strength which are used as webbing/strapping include PVC and nylon-reinforced rubber. Where less strength and durability are acceptable then synthetic webbed belting or natural hessian belting can be used.
Super-soft tree ties made of very soft plastic ,which acts as a cushion between tree and stake, eliminates the need for spacers.
TREE RESTRAINTS
Tree restraints offer an engineered solution to securing trees and a generally maintenance-free option throughout their required working life. They are double-wire devices with one end secured by stapling to the top cut surface of the stake. The other end opens out into a plastic-cushioned and flexible double wire placed around but not in contact with the tree stem about halfway up its height.
Manufacturers claim clearance between restraint ring and tree promotes natural growth responses to wind movement. They are essentially maintenance-free and dispense with revisits to release, readjust and sometimes refit straps. Restraints are designed to last throughout tree establishment and will continue to restrain and support trees with stem girth (circumference) up to 20 cm to 24 cm.
SHIN GUARDS AND FOOTWEAR – STRIMMER GUARDS AND MULCH MATS
Strimmer guards – Plastic guards fitted around the root/stem collar region of a tree, primarily to prevent physical damage to the bark when using a strimmer or mower, but also doubling up as vole guards. The most basic are wrap-around guards of thin, pliable plastic which expands with tree growth, although unavoidably leaving an increasingly wide unprotected gap as the two cut edges of the guard are forced further apart. Heavy duty and interlocking strimmer guards which do not ride up the tree stem are also available. Any strimmer guard will clearly help to prevent chemical damage to the collar region of the tree from herbicide sprays used to control grass and soft (vegetative) or woody broadleaf weed growth.
Mulch (tree) mats – Weed growth, which is often fast and furious in the fertile and friable soil around newly planted trees, must be suppressed, and where spraying is not practical nor possible, tree mats are the answer. Individual tree mats, typically made of woven black polypropylene, are pre-cut to order (e.g. 50 cm x 50 cm or 100 cm x 100 cm) and ideally equipped with a pre-cut slit from the centre to one side for easy fitting around the base of the tree. Mats are secured with six pegs, one at each corner and two for the overlapping cut edges.
Working life is about five years, which should be plenty to see the tree through to establishment. Bare minimum requirement of a two-year lifespan is provided by black polythene tree mats. In addition to suppressing weed growth, and therefore competition with the tree for water and nutrients, they help conserve soil moisture levels around the base of the tree by reducing evaporation.
For green-minded arborists, 100 per cent biodegradable tree mats manufactured from various combinations of mostly recycled materials, including wool, hemp fibres, coir (coconut shell fibre), jute, hessian, and cashmere hair, is the integrated answer to weed suppression and environmental ethics.
During degradation, these natural materials release a spectrum of plant nutrients, including nitrogen, phosphorous and potassium into the soil. However, while degradation is the ultimate order of the day, you don’t want this to happen too quickly and before the weed suppression function has been achieved. Therefore, biodegradable mats should be secured to the ground using biodegradable plastic pegs, rather than the edges of the mat being buried in the soil. Like other tree mats, they are usually sold with a pre-cut slit from the centre to one edge for easy fitting around the tree.
100 per cent biodegradable tree matting sold in long rolls is the answer to effective and efficient weed suppression along linear tree plantings. The roll can be laid by manual or mechanical means and is sufficiently strong to walk on, thus making planting and maintenance work that much easier. Materials made from 100 per cent biodegradable materials but equipped with a stitched-on, non-biodegradable backing such as polythene are called hybrid mats and matting.
Where trees are subject and susceptible to infection by soil-borne pathogens and diseases at the collar region, the use of mulch mats will prevent splash of potentially contaminated and infectious soil onto the bark of the tree.
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