Chapter 9: Tree Support and Lightning Protection Flashcards
Types of hardware in trees
tree cabling, bracing, guying, and propping
What is the point of hardware in trees?
to provide the tree with supplemental support by limiting the movement of limbs; may extend the life of the tree or reduce the risk of mechanical failure
codominant stems
forked stems nearly the same size in diameter, arising from a common junction and lacking a normal branch union
Purpose of cables installed in trees?
to limit movement of limbs with weak branch connections or to support heavy limbs by connecting two or more limbs
Types of hardware for cabling trees?
cables, eye bolts, and cabling hardware of different sizes and types
Types of steel cable commonly used in North American for cabling trees?
- ) 7-strand, common grade cable
2. ) extra-high-strength (EHS) cable
7-strand, common-grade cable
steel-cable construction in which seven strands are twisted together in a spiral pattern; used to add supplemental structural support to trees; terminated by wrapping onto itself; relatively malleable (bendable) and easy to work with
extra-high-strength cable
EHS; type of 7-strand steel cable, often used to cable trees; stronger but less flexible than common-grade cable; must be terminated with dead-end tree grips; much stronger and less flexible than common-grade cable
aircraft cable
steel wire ropes of various constructions designated by the number of strands in the rope and the number of wires in each strand; commonly used in cabling in Australia and New Zealand; 19 strands of galvanized wire; strong and flexible but has limited choices for attachment
anchor hardware
hardware to which the cable termination is affixed in a cabling or guying installation; passes through the limb and is fastened to the opposite side; dead-end hardware
eye bolts
cable anchor with a closed eye, usually machine threaded; only drop-forged eye bolts are accepted and approved for tree support systems in the United States; stronger than threaded rods with amon-eye nuts
threaded rods
metal rod used to support weak sections or crotches of a tree; also called bracing rods; easy to adjust the length for any job
amon-eye nuts
specialized nut used in cabling trees that has a large eye for attaching a cable to a threaded rod
Where do you set the washer?
directly against the bark or chisel away the bark or drill to countersink the washer against the sapwood (but not int) on trees with very thick bark
lag eye
lag-threaded cable anchor with a closed eye; drop-forged anchor with a closed eye
lag hook
lag-threaded cable anchor with an open eye (J-shape)
J-hook
lag-threaded, drop-forged device in the shape of a J; lag hook
What are standard sizes of J-hooks?
5/16-, 3/8-, 1/2-, and 5/8-inch diameter
Purpose of right- and left-handed threads on lag hooks?
so the cable will not come unlaid or unwound when the end is twisted into the branch to tension the cable
What do you anchor eye bolts and/or threaded rods with?
washers and nuts
Types of washers recommended?
heavy-duty, heat-treated round washers (larger in diameter and thicker than standard washers and have a greater metal strength when heat treated)
thimbles
in cabling, a device used to form and protect the termination loop in the cable; device used to increase the bend radius of and reduce wear on a rope when attached to hardware; protects the cable from abrasive wear and increases the cable’s bend radius; used when forming an eye in the end of the cable
bend radius
radius of an object around which a line passes
eye splice
in cabling, a closed termination loop, hand formed in common-grade cable by wrapping the successive strands back upon the standing part to attach the cable to anchor hardware; splice that forms a closed eye or loop
dead-end grip
cable-termination devices that must be used to terminate extra-high-strength (EHS) tree support system cable to anchor hardware; may be used with common-grade cable; manufactured spiral-wrap designed to form a termination at the end of a 7-strand EHS cable
What kind of thimble to use?
galvanized or stainless-steel, heavy-duty thimbles; used to attach EHS cables to anchor hardware using dead-end grips and pre-warps; reduces wear on the grip hardware
Why do wind conditions matter when installing hardware in trees?
excessive wind sway can cause bending and twisting, leading to metal fatigue, which could cause failure; must take wind conditions and potential for twisting into account
come-along
portable winching device, using cable or rope to draw two objects closer together; simple arrangement of rope knots and loops to create mechanical advantage; brings two branches closer together
cable grip
mechanical device that grasps and holds the cable during installation; grips the cable and helps the arborist pull the cable for tensioning or attaching to anchor hardware
cable aid
device used to tighten lags and aid in cable installation; can spread open thimbles, tighten lags, and help wrap dead-end grips onto the cable
What type of equipment to use when drilling holes into a tree?
brace and bit or drill
ship auger
type of drill bit with an open spiral form; used to drill holes in trees for cable or bracing installation; pulls out shavings from the hole (good for green wood)
Tools in cabling operations
come-along, cable grip, cable aid, drills (electric, gasoline-powered, or rechargeable) ship auger, hacksaws, hammers, chisels, mallets, slings, wires, and wire cutters
Where to install cables?
at least 2/3 the distance from the defective (weak) branch union to the ends of the limbs; more than 2/3 might have branches that are too small (in diameter) for cables to be placed; perpendicular to an imaginary line through the center of the crotch
cable stops
metal knob that can be affixed to the ends of steel cable strands to terminate a cable installation; protrudes through the drilled hole in a host limb or stem; larger than the hole therefore don’t allow the cable to retreat
How tight should cables be?
just taut - not slack and not too tight; too tight puts excessive stress on the wood fibers, resulting in more damage at the defect or causing the hardware to pull out; just tight enough
simple cable
direct cable; one cable between two limbs; most common cable installation
triangular combination
multiple cable configuration; a diamond with a cable across the middle (two triangles formed)
hub-and-spoke system
cable configuration that connects multiple leaders while allowing some independent movement; most complex configuration to install (all cables meet at one central point on a stem)
box configuration
forms a diamond
How close can you install cables on the same limb?
no closer than the distance equal to the diameter of the limb (or 12 inches whichever is less); never attach in longitudinal alignment with other hardware; only attach one cable to any one anchor
What kind of wood can you install anchors into?
never install lags in limbs with decay; do not install anchors into decayed areas where the amount of sound wood is less than 30% of the trunk or branch diameter
dynamic cable systems
any of several cabling systems that utilize nonrigid materials (usually ropes of various constructions) for tree support systems; nonrigid (synthetic fiber) support systems
What is an alternative to rigid support systems?
dynamic cable systems; allow for more tree sway - more tree movement allows a tree to produce supporting wood where needed, so with time, the tree becomes stronger
Cobra
German-made dynamic system that connects limbs using a simple splice in polypropylene rope; the ends of the rope feed back into the core, like a Chinese finger-trap device
TreeSave
U.S.-made dynamic support system; uses hardware similar to that of traditional rigid systems for anchoring the cable in the tree, along with a shock-dampening rope product for the actual “cable)
bracing
use of steel rod(s) in limbs, leaders, or trunks to provide support for a junction; reinforces weak crotches or strengthen decayed areas; usually used in combination with cabling, not as a substitute
lag-threaded rods
bracing rod with a coarse thread pattern that is typically screwed into a pre-drilled hole that is smaller in diameter than the anchor or rod; fewer and deeper threads per inch than machine threaded rods
machine-threaded rods
bracing rod with a fine-thread pattern that is used with a nut and water and installed through a pre-drilled hole that is larger in diameter than the rod
Types of steel rods used in tree bracing?
lag-threaded rods and machine threaded rods
peen
act of bending, rounding, or flattening the end of through-hardware for the purpose of preventing the nut from backing off
Where to install a single rod used to support a crotch that is not split?
the distance of about one to two times the branch diameter above the crotch
Benefits of multiple rods?
added strength and reinforcement to a split or weak crotch; can be staged to avoid longitudinal alignment which may add to the formation of decay columns in the tree
Where to install multiple rods?
space rods apart a distance greater than the diameter of the woods being braced (or 12 inches, whichever is less)
guying
installing a guy and associated anchor; installation of a cable (or rope) between a tree and an external anchor to provide supplemental support and reduce tree movement
What to consider when installing tree-to-ground guys?
ground anchor must have sufficient strength to support the tree (even under wet conditions)
Where to place ground anchors for guys?
no closer to the trunk than two-thirds the distance from the ground to the lowest attachment in the tree
Where to install guys on an anchor tree?
on the lower half of the trunk; preferably greater than 7 ft from the ground if there is pedestrian traffic under the guy or greater than 14 ft if there is vehicular traffic
Where to install guys on the tree to be supported?
above the midpoint, preferably at about 2/3 the height of the tree
How to protect tree-to-ground guys?
clearly marked and protected from inadvertent contact; advisable to place a mulch ring around the ground attachment point to avoid lawn mower damage
propping
rigid brace, acting in compression to support a tree, tree branch, or utility pole; prop pole; installation of rigid structures between the ground and a branch or trunk to provide support to keep the branch or leaning trunk off of the ground or a structure
What kind of branches require props?
under branches that are nearly horizontal or downward growing
What are props made of?
wood, steel, concrete, or other materials; must have sufficient strength to support the expected load
side flash
phenomenon of a lightning strike leaving its current path and “jumping” to reach a better-ground conductor
step voltage
significant difference in electrical potential, which can lead to electrocution if contacted simultaneously
Where does lightning exit an unprotected tree?
through the roots and dissipates into the soil
Purpose of lightning protection systems installed in trees?
reduces the risk of damage to trees by lightning strikes; protects trees by providing an alternate path (of lower resistance) to the ground instead of lightning passing down a tree, a conductor is used to take the lightning from the top of the tree down to to the ground
How many trees struck by lightning carry no visible injuries?
20%; trees presenting no immediate sign of lightning damage might enclose a damaged vascular system and are still prone to increased stress, inefficient defense systems, and pest attacks
What do lightning strikes do to trees?
can destroy the whole tree at once or may cause significant structural damage that creates a hazard requiring removal of the tree; disrupts the tree’s nutrient and water flow long term; might serve as an “open door” for borers, decay, and future structural degradation
What affects the extent of damage lightning causes?
bark thickness, wood porosity, and moisture content
What trees to consider for lightning protection?
trees close to houses or other buildings but much taller than buildings and trees, or trees of historic interest and high economic value; trees in recreational areas, parks, and golf courses are more prone to lightning strikes; tallest trees in geographic regions where lightning is common
What is in a lightning protection system?
copper conductor that extends from the top of the tree, down the main branches and trunk, and out, into the soil where it is grounded; air terminal, conductors, and ground terminal
air terminal
uppermost point of a tree lightning protection system; top end intended to intercept the lightning strike; should be installed as high on the tree as possible
conductors
blunt tip; metal wires, cables, and bus bar used for carrying electric current; conductors may be solid or stranded (i.e., built up by an assembly of smaller, solid conductors); copper cable connected to the air terminal that run down a major branch or the trunk
ground terminal
either a ground rod or ground plate; used in grounding a tree lightning protection system; provides electrical contact with the ground; consist of ground conductors, ground rots or plates, and all other associated connectors
How should the main conductor/primary conductor be connected to the tree in lightning protection systems?
path should follow the natural shape of the tree, avoiding sharp bends, kinks, and crotches; attached at regular intervals (usually 3-6 feet) using approved conductor attachments; primary conductor should run straight down the trunk on the side of the tree toward the ground site
How many conductors is required in tree in lightning protection systems?
one - if crown radius is smaller than 35 ft
one plus secondary conductors - recommended if has greater spread radius that 35 ft
branch conductors
secondary conductors that connect to the main conductor on the trunk
ground rod
metal rod used in grounding a tree lightning protection system
How many ground rods should be installed in lightning protection systems?
2 - if dry, sandy, or gravel/rocky soil
Where should ground terminals be installed
not within 2 ft of a structures foundation and not within 2 feet of other underground installations; trench as close to the trunk as practical and at least 8 in deep unless restricted by roots, rocks, or impenetrable soil (avoid damaging roots greater than 2 in in diameter)
