Monday, September 21, 2009

Pollarding
Examples of Pollarding
Photo: Example of Multi Knuckle Pollard
Multi Knuckle Pollard

(click on picture to enlarge)

For many centuries in Europe, trees were maintained at a certain height with regular pruning.
This practice called pollarding, maintains a tree at a specified height, sometimes for centuries, and provides a formal look to landscapes. Traditionally, trees have been maintained at 20-30ft tall. Pollarding can be used to keep a large, mature tree small if it was located in a place with restricted soil space, such as a planter, narrow soil strip, car park or footpath cut out. It is also useful to control size if a tree has been planted too close to structures such as buildings, street lighting or electric wires.

Once begun it is essential that pollarding continues. Preferably, the pollarding process should begin when a tree is very young. We would leave one to two inches of stub if necessary to ensure that there will be buds to initiate next years sprouts. A knuckle of tissue called the pollard head resembling a ball develops several years after the first cut was made. Most shoots grow from this tissue, which enlarges slightly each year. Most are orientated upright; they do not branch and grow at a rapid rate. We cut back to this knuckle at each pruning. Shoots originating below a pollard head should be removed each time the tree is pruned.

A clear distinction should be made between pollarding and topping. Topping can be harmful to trees and can initiate decay inside a tree. Pollarding is a high maintenance practice requiring repruning every 2 to 5 years, however it can create unique trees that live for a very long time.

It should be noted that different species of trees respond to pollarding in different ways and pollarding may not be suitable Willow Trees have approximately 95% survival rate whereas Beech Trees rarely survive the procedure.


Wednesday, September 9, 2009

Tree Roots Need Protection

This is an article from the TCIA, reposted by the Reader here:

Tree Roots Need Protection

Trees are hardy plants, and their roots fight back against man-made limits around them. In the urban and suburban landscape, tree roots often are forced to grow between buildings or under driveways and walkways. As roots grow, they will break walls, pipes and patios, causing damage to properties.

Plan before you plant
“Before you plant a new tree in your yard, you need to understand how a tree could damage your property and take appropriate measures to prevent that damage,” advises Tchukki Andersen, staff arborist with the Tree Care Industry Association.

Woody tree roots thicken as they grow, gradually pushing shallow roots toward the surface. Since soil near the surface is best suited for root growth, most tree roots are just below the surface – putting them in conflict with man-made obstacles. Where the soil is covered by a solid driveway or patio, upward growing roots don’t experience the normal signals (increased light and air) that they are reaching the surface. As a result, they often grow against the underside of pavement.

“Most damage is found six feet or less from the tree,” notes Andersen, “since roots become smaller and less damaging the further they are from the trunk. Keep this in mind before you plant. That small sapling could become a large shade tree with roots spreading 30 or 40 feet outward from the trunk.”

Fixing the problem
Some homeowners, masons and landscapers deal with intrusive roots by grinding down or removing them. This can be expensive and is very harmful to the tree. Wounding a tree’s roots creates points of entry for pathogens, leaving a tree vulnerable to disease. Cutting major roots also reduces a tree’s ability to take up nutrients and water, leaving it more susceptible to drought. Finally, reducing a tree’s structural support from the roots increases the danger the tree will topple onto your house in high winds.

Keep these cautions in mind when dealing with a problem tree:

  • The farther you cut from the trunk, the less threat to the tree’s health, and the less danger of creating a hazard.
  • Try not to cut roots greater than 2 inches in diameter.
  • Roots recover better from being severed when you: cut them cleanly with a saw instead of breaking them with a backhoe; mulch and water well after pruning; and fertilize in early fall or spring.
Deciding what to plant
TCIA advises selecting trees for your landscape that will cause less damage, that match species with site conditions and – most importantly – that you do not plant large shade trees within 12 feet of hardscapes (sidewalks, driveways). Since the health of trees in your yard is put at risk whenever root systems are cut back or damaged, anything that can be done to reduce the damage caused by tree roots will also benefit your trees.

In areas within 5 to 7 feet of a paved area or structure, plant trees that grow to a mature height of less than 30 feet. In areas within 7 to 10 feet of a paved area or structure, plant trees that grow to a mature height of less than 50 feet. Reserve trees that mature higher than 50 feet for areas with at least 12 feet of clearance. This allows adequate space for the roots. Also, before you plant check for overhead utility lines and leave adequate space for that tree to mature.

Find a professional
A professional arborist can assess your landscape and work with you to determine the best trees to plant. Contact the Tree Care Industry Association (TCIA), a 71-year-old public and professional resource on trees and arboriculture. It has more than 2,000 member companies who recognize stringent safety and performance standards and who are required to carry liability insurance. TCIA also has the nation’s only Accreditation program that helps consumers find tree care companies that have been inspected and accredited based on: adherence to industry standards for quality and safety; maintenance of trained, professional staff; and dedication to ethics and quality in business practices. An easy way to find a tree care service provider in your area is to use the “Locate Your Local TCIA Member Companies” program. You can use this service by calling 1-800-733-2622 or by doing a ZIP code search at TCIA

Thursday, September 3, 2009

Root Collar Excavations

This is a great article on Root Collar Excavations, from the University of Minnesota (original can be found here):

Normal vs. Abnormal Root Systems
Root collar examinations are used to determine if root system abnormalities are impacting a tree. To determine if a root system abnormality exists, one needs to compare against a normal root system. Field observation, along with a review of species-specific root system profiles, will help provide the practitioner with an understanding of a normal root system. An easy way to observe normal root systems is to take a walk in the woods. But in general terms, what is a normal or ideal root system?

Normal root systems are often described as having main (first order) laterals that radiate from all sides of the stem/root interface (Figure 23). The number of main laterals ranges from a few to more than a dozen. Trees in forests with a greater number of main laterals than other trees tend to become dominant survivors in a competitive forest community (Kormanik 1986). The root diameter of main order laterals decreases rapidly through the zone of rapid taper into ropelike roots with approximate diameters of 0.5 to 3 inches. Root spread is usually well beyond the drip line, commonly to about three times the branch spread (Gilman 1997).

Stem Girdling
Fig. 23 - A normal littleleaf linden's root system, showing the larger, main order roots radiating out from the stem/root interface (root collar).

Most main-order laterals originate from the root collar and parallel the soil surface at depths of a few inches to a foot or more. Many tree species also produce oblique roots, which grow at a sharp angle into the soil and stabilize trees. Sinker roots grow downward from lateral roots on approximately 75% of tree species, function in support and absorption, and usually are located within 6 to 10 feet of the stem.

From main-order laterals arise secondary and tertiary woody and nonwoody roots, which magnify the absorption of water and nutrients. These roots proliferate in zones of favorable moisture and nutrition. Most exist within the top foot of the soil surface.

Stem diameter normally increases from the top downward. Root flares and/or stem tapers are common (except in some conifers) due to a growth pattern in which growth is greater on the top of the root than the bottom. When trees are planted deep or soil fill is placed over the root system, this characteristic pattern might not be visible.

In landscape trees, abnormal root systems often develop through cultural practices (Figure 25). Nursery production methods such as the use of containers that induce encircling roots, propagation that encourages stem-origin adventitious roots, or tillage practices such as "hilling-up" plowing to control weeds can create abnormal root systems, as can planting practices such as deep planting, narrow planting holes, and confined planting locations such as small planters. Tree vitality and longevity is not always harmed by production and planting methods. In some forest plantations developed from seedlings with abnormal root systems, seedlings successfully developed into mature trees because of adventitious root development and fusion of the abnormal root system into a central mass (Van Eerden and Kinghorn 1978). In landscape trees a clear picture is also lacking, but the development of a new root system can overcome an existing abnormal root system (Gilman 1997). Regardless of the rules and exceptions, an examination of the root system and its relationship to stem condition is a vital aspect of tree health evaluation, problem diagnosis, and assessment of root system condition.

Stem Girdling Stem Girdling
Fig. 25 - Abnormal root systems such as these often develop through propagation and or cultural practices. Stem Girdling

Performing the Examination
A root collar examination typically takes from fewer than 20 minutes for smaller trees and less invasive examinations, to more than two hours for larger trees or more extensive operations. Equipment can range from simple and basic-trowels, knives, pruners, stiff brushes, saws, and shovels-to elaborate and specialized-tile probes, portable generators, air excavation (Smiley 1999b), wet/dry vacuums, wood gouges, chisels, and water.

Most diagnostic examinations need not be extensive. Begin by probing into the soil near the trunk flare with a 3/8-inch-diameter tile probe or stiff wire (coat hanger gauge) to detect the depth of branch and encircling roots and to determine the soil area around the tree stem you need to remove (Figure 28). For the average size landscape tree (9 to15 inches d.b.h.) with roots 6 to 10 inches from the surface, a 12- to18-inch-wide examination area is usually sufficient. If primary branch roots are deeper than that, you will need to widen the examination area as the examination progresses (Figure 29).

Stem Girdling
Fig. 28 - Probing the soil area near the root flare can help determine the extent (depth and width) of the examination and if it's warranted.

If sod surrounds the trunk, strip it away to a depth of approximately 2 inches. If the tree is mulched, carefully remove the mulch and any plastic or fabric ground cover beneath the mulch. Loosen the soil gently in the examination area with a trowel, hand cultivator, or knife and remove with a trowel or wet/dry vacuum. Do not use spades or shovels unless absolutely certain that no roots exist in the excavated soil. Gradually loosen and remove deeper layers of soil until the stem/root conflict or the root collar flare is exposed (Figure 30).

You can also use compressed air or water to expose tree roots. Air is blown at the soil through a tool called an Air Spade� to expose the roots. Water under low to high pressure has been used for more than 50 years to expose roots.

Choose a method based on availability of equipment, available time, and your objectives. Shallow examinations of smaller trees do not warrant elaborate equipment, such as vacuums and generators. However, with larger trees and examination areas, vacuums and portable generators are much more efficient and safe. Vacuuming loosened or water-saturated soil is less destructive to roots, reduces the chances of cutting through utility cables, and offers a clearer view of the root/stem conflict area.

Stem Girdling Stem Girdling
Fig. 29 - The examination area for this 7.5-inch d.b.h. sugar maple was 11 inches deep and 30 inches wide. Total time involved with a vacuum was approximately 30 minutes. Fig. 30 - A small towel and vacuum may be used to loosen and remove soil during a nondestructive examination

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