64 Arnold et al.: Below-Grade Planting Affects Survival and Growth Arboriculture & Urban Forestry 2007. 33(1):64–69. Below-Grade Planting Adversely Affects Survival and Growth of Tree Species from Five Different Families Michael A. Arnold, Garry V. McDonald, Donita L. Bryan, Geoffrey C. Denny, W. Todd Watson, and Leonardo Lombardini Abstract. Adverse impacts of planting the root collar or main structural roots below grade on survival and growth were demonstrated for five species of container-grown trees from genetically diverse families. Adverse effects were demon- strated when root collars were located as little as 7.6 cm (3 in) below grade on all taxa tested, but severity of the responses varied among taxa. These responses were confirmed for both seed-propagated species, Fraxinus pennsylvanica Marsh. (green ash, family Oleaceae Hoffmansegg & Link) and Platanus occidentalis L. (sycamore, family Platanaceae Dumort.) as well as cutting-propagated taxa, Lagerstroemia indica L. × Lagerstroemia fauriei Koehne. ‘Basham’s Party Pink’ (crapemyrtle, family Lythraceae St.-Hilaire), Nerium oleander L. ‘Cranberry Cooler’ (oleander, family Apocynaceae Juss.), and Vitex agnus-castus L. ‘LeCompte’ (vitex, family Verbenaceae St.-Hilaire). In some cases, planting above grade by 7.6 cm (3 in) improved growth of plants over that of those planted either at or below grade. This effect was pronounced with sycamore and oleander. Key Words. Apocynaceae; landscape installation; Lythraceae; Oleaceae; pine bark mulch; planting depth; Platanaceae; transplant establishment; tree planting; Verbenaceae. Each year, millions of container-grown trees and shrubs are planted in landscapes worldwide. Many factors impact the initial establishment as well as the long-term development of these trees. Some factors such as circling roots in containers are related to the production system used to grow the tree (Watson and Himelick 1997; Ball 1999; Watson and Hewitt 2006). Others are the result of techniques used during the physical planting of the tree in the landscape (South 2005), whereas still others factors center around maintenance prac- tices implemented after planting. However, in many cases, the successful establishment and long-term growth of a tree in the landscape is a result of interactions among multiple factors. One of the practices receiving increased scrutiny during recent years is that of how deeply the root flare (also known as the root-to-shoot transition, root collar, or origin of the first of the primary structural roots) is placed in the planting hole (Watson and Hewitt 2006). In nature, trees often develop a spreading trunk flare, sometimes manifesting itself as a broad basal plate (Figure 1). However, trees planted in the land- scape may be placed substantially below the surface resulting in a telephone pole-like base to the trunk. The fate of a deeply planted root system is often unknown, but in recent years, deeply planted root systems have become suspects in tree failures (Watson and Hewitt 2006). In general, trees are ©2007 International Society of Arboriculture planted with the trunk flare deeper than would have occurred if the seedling naturally germinated in place, either by acci- dent, as a result of practices used during production or trans- planting, or by intent. Intentional below-grade planting of trees is attributed to one of four reasons. Trees, particularly some species of palms [family Arecaceae Schultz (Palmae)] are sometimes intentionally planted at different depths to achieve a uniform height (Broschat 1995). More commonly, trees are sometimes planted below grade in an attempt to reduce windthrow during establishment or to reduce the need for staking. In operational forestry plantings, small liners are sometimes intentionally planted deeper for improved access to moisture (South 2005); however, even then, there is con- troversy about whether it is a beneficial or detrimental prac- tice. Finally, trees are sometimes planted with the root flare deeper than grade in an attempt to avoid root growth conflicts with components of the manmade infrastructures in the land- scape (McPherson et al. 2001). Most reports of tree responses to planting depth are based on anecdotal information. Little information on planting depth of trees is presently available in the scientific literature based on replicated, peer-reviewed studies (Browne and Tilt 1992; Broschat 1995; Gilman and Grabosky 2004; Arnold et al. 2005). Even less information is available on the interac- tions of cultural practices with planting depth (Gilman and
January 2007
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
