The Continuing Evolution of Tree Installation Specifications

Most landscape tree installation specifications include as one of their components a requirement of some form of tree stabilization or support. In addition, if the trees were field grown and when dug, their root balls placed in wire baskets, there may also be a recommendation or requirement relative to alteration or removal of the wire basket. These two practices are a source of continuing debate and controversy within the green industry, with nurserymen, landscape designers and architects, landscape contractors and managers, and arborists often in heated disagreement about what should be done and what is best for our trees.

Unfortunately, our trees are often the inadvertent victims of these practices. When a tree dies, if either a stabilization method or wire basket alteration may have been involved in the tree’s demise, there is often finger pointing relative to responsibility. A landscape manager may blame the original landscape architect if a tree dies because it consumed the trunk guying attached to support stakes that were specified by the landscape architect. An arborist removing a dead tree may blame the production nurseryman for the tree’s death if a wire basket is found embedded in the root collar and the nurseryman refused to guarantee the tree if the wire basket was altered in any way. We feel it’s time to review these areas of contention and undertake field research that will help resolve these problems to the benefit of all involved, especially our trees.

Wire Baskets

For the protection of roots of field grown and dug trees, root balls are generally drum laced in burlap or placed into burlap lined wire baskets. Many anecdotal reports exist that attribute tree stress, decline or death to wire baskets left intact (unaltered) when B&B trees are installed. This implied damage is never immediate, but generally occurs years after installation, when burlap may have deteriorated but wire baskets are still intact. The possible involvement of wire baskets in this reported problem is often not detected until tree removal becomes necessary.

Controversy exists within the green industry relative to the need to remove or alter wire baskets during installation. Many nurseries say removal/alteration is unnecessary, and consequently won’t guarantee plants if such occurs. However, many planting specifications mandate either total basket removal, or require baskets be split and laid into the planting hole, or have the top loops removed or bent back (4). Specifications requiring alteration or removal do so supposedly to prevent detrimental cutting or girdling of tree roots or stems by the wire. This required removal or alteration places landscape contractors in a no win situation between nursery non-removal policies and specification removal/alteration requirements. In addition, landscape maintenance personnel often report encountering basket wires sticking above ground, especially if trees were planted shallow. Wire extending above ground poses a danger to people and equipment.

On the “other end” of a tree’s life, many arborists who remove dying, dead and hazardous trees frequently point to unaltered baskets as “tree killers” when they encounter wires cutting into roots. Many question why removal or alteration is not required of landscape contractors. A negative view of nursery production and landscape installation practices exists within much of the arboricultural community.

To date, limited research has been conducted to specifically address if or how wire baskets should be removed or altered during installation. Wire baskets can last up to 30 years according to Dr. Gary Watson, tree root physiologist at the Morton Arboretum (Watson, G.W. and E.B. Himelick. 1997. Principles and Practices of Planting Trees and Shrubs. International Society of Arboriculture, Champaign, IL). Tops of flare roots generally grow into the upper horizontal basket wires, causing partial girdling of roots and restricting vascular flow (xylem water and nutrient transport up and phloem carbohydrate transport down). Though root tissue may eventually grow around the wires and graft together on the other side, this reestablishment of unrestricted vascular transport may take several years (articles and research by Fuecht, Goodwin, Holmes, Lumis, Struger – citations available upon request).

In addition to the question concerning unrestricted vascular flow there is also the question of anchoring stability. Trees that appeared to have blown over due to flare root girdling have been observed (Appleton). It has been reported that in Europe, baskets made of supposedly breakable plastic, rather than of wire, are used (Gardner-Young, J.W. 1981. A new method of planting trees and shrubs. Arboric. J. 5:45-48.). However, a literature search did not provide any published reports of what effects the plastic has had on root growth, or of research addressing the practice of wire basket removal, non-removal, or alteration.

The practice of using wire baskets to protect root balls of field grown trees is not being challenged or questioned. Protection of the root balls during harvest, transport and installation into the planting hole is necessary, and is adequately provided through the use of wire baskets. What is in question is what to do with wire baskets prior to back filling soil around the root ball during transplant.

 

Tree Stabilization

Current tree stabilization systems frequently contribute to deformation, stress or death of trees to which these materials are attached (6). Shading of one side of the tree by a single stake can lead to uneven trunk development and lean in the opposite direction.

Due to reduced compression wood formation, rigid staking can lead to reduced trunk caliper and taper formation. In addition, guying that is not removed in a timely fashion can lead to bark abrasion and trunk constriction, the latter blocking movement of materials in tree vascular systems (8).

Tree trunk stabilization systems can be justified for several reasons. Physical support may be needed in landscape sites that are windy, and where trees may lean due to unsettled or amended back fill soil. Physical support may also be needed where tree crowns are large or dense and their weight may cause trees to lean, or where tree crowns are large in proportion to the size of their root balls.

An indirect reason for stabilization systems is to create a physical barrier that reduces physical damage from landscape maintenance equipment, and to reduce uprooting vandalism. All of these reasons relate to the need to allow tree roots to grow from the root ball into the surrounding soil, anchoring the tree and reestablishing the absorptive function of the roots. Unfortunately, many trees that do not need stabilization due to size or location are needlessly staked (10), often due to outdated or “one size fits all” planting specifications.

Published research on tree stabilization is limited. Neel (Neel, P.L. 1971. Factors influencing tree trunk growth. Special Report, I.S.T.C. Research Project, 115-138.) showed that motion, light and growth regulators influenced trunk development (in particular, reaction wood formation) of most species studied. Harris (Harris, R.W. 1984. Effects of pruning and staking on landscape trees. J. of Environ. Hort. 2(4):140-142.) showed that trunk staking is often not only unnecessary, but can be detrimental to tree growth. The most recently published research comparing actual trunk support systems was conducted by Svihra, et. al (Svihra, P., D. Burger, and D. Ellis. 1999. Effects of 3 trunk support systems on growth of young Pyrus calleryana trees. J. of Arboric. 25(6):319-324.). However, only one tree species and three systems were used. No research literature has been found comparing the relatively unknown system of tree stabilization via root ball anchoring with trunk staking (one article from England mentioned using root ball anchoring but gave no post transplant results).

New guying products.

The most commonly used tree stabilization systems use one or more wooden stakes with hose covered wire guying attaching the stakes to the trunk (11). Unfortunately many of these staking and guying systems restrict trunk movement or cause trunk damage. Even where tree stabilization is justified, above ground supports are frequently left in place for an excessive period of time, often leading to inferior trunk development and damage. In urban areas, above ground supports can be a physical safety concern for grounds management personnel, pedestrians, cyclists, and pets due to the potential of entanglement in the stakes or guying.

Numerous alternative products (16) and systems to above ground wooden stakes and hose-covered wire exist. Research is needed to compare these productions and systems. Also needed is evaluation of and comparison with below ground stabilization systems. These systems can potentially provide needed support, via root ball anchoring, without restricting trunk movement or causing any bark damage or trunk constriction.

Industry Help Needed!

 Here’s where we need your help. We are planning field research projects to address both wire basket alteration and tree stabilization. The wire basket stabilization research will compare basket removal, non-removal, and various types of alteration over a long period of time, with yearly root excavations to document tree root responses to the treatments. The tree stabilization research will be designed to compare newer staking and guying products and systems with both the common wooden stake/hose-covered wire system, and with new root ball anchoring systems.

Before designing these studies, however, we want to know what really happens “in the real world”. What do you do to wire baskets and why? How do you stabilize and with what?

To help us compile an accurate assessment of current industry practices would you please take just a few minutes to complete our questionnaires. They can be returned to Dr. Appleton via fax – 757-363-3950, or by mail – Hampton Roads AREC, 1444 Diamond Springs Road, Virginia Beach, VA 23455. The start of field research is planned for Spring 2003 so please return the questionnaires as soon as possible. Individual responses will be kept confidential but the data will be compiled and used to help design the research projects. It will also be shared in future articles on this topic. In our opinion it’s time the various segments of our green industry worked more closely together, and with university researchers, to address some of these problematic areas. Thank you for supporting our new research projects!