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Extension > Garden > Yard and Garden > Trees and shrubs > A practioner's guide to stem girdling roots of trees > Glossary and appendix

Glossary and appendix

Gary R. Johnson
University of Minnesota

Richard J. Hauer
Minnesota Department of Agriculture

Copyright © 2002 Regents of the University of Minnesota. All rights reserved.


Adaptive growth. The elaborate shaping of individual tree designs well-adapted to external loading conditions in order to optimize against external loading factors.

Adventitious root. A root in an unusual position, such as on a stem.

Anatomy. The structure (traditionally internal) of a plant.

Deeply planted. Excessive soil over the root collar flare.

Encircling root. A root that encircles the stem of a tree, either contacting the stem or positioned to contact the stem tissues within a reasonable amount of time.

Etiology. The science of the causes or origins of disease, together with the relations of the causal factor(s) to the host; the study of the causal factor, its nature, and its relations with the host.

Girdling root (sign). Physical evidence that a root is directly impacting another root or stem. The physical evidence would be compression of woody tissues of another root or stem by encircling roots that have contacted the stem or root.

Girdling root syndrome. The etiology of the effects of (stem) girdling roots on the vitality and condition of trees.

Morphology. The (outward) physical structure of a plant (e.g., characteristics of the root system, branch attachment, foliage).

Multiple stress factors. Situations in which more than one soil, environmental, biological, or cultural factor is negatively impacting the vitality and/or condition of trees (e.g., droughty conditions compounded by deicing salt spray, compacted soil, and defoliation by an insect pest).

Physiology. The study of the activities and processes of living organisms (e.g., water movement, nutrient transport, respiration).

Pot bound. The impacted and encircling root system that often develops when a tree has been grown in a container that is too small for normal and uninterrupted root expansion; also referred to as root bound.

Premature fall color and leaf drop. A relative, symptomatic condition, associated with a decline in tree vitality, in which leaves change color and drop earlier than would be expected based on observations of other trees of the same species and other species at the same and other sites.

Root collar or root crown. The area of a tree where tissues differentiate into stem and root. Normally, this area appears swollen or tapered, and is located near or at soil level.

Root collar examination. The removal of soil, mulch, or other materials to sufficiently examine the entire root collar area, potential root aberrations, and/or root and stem conflicts (e.g., SGRs).

Root flare. The enlarged area where stem tissues begin to differentiate into main order, lateral root tissues.

Root graft. The phenomenon in which roots become grafted together, resulting in functional tissue connections.

Secondary and tertiary pests. Animals (usually insects) that attack and further damage stressed trees.

Sign. Physical evidence of a disease/disorder/damage causal agent (e.g., conks, spores, infesting insects).

Stem compression. A reduction in the normal diameter expansion of stems due to the presence of a physical barrier, such as SGRs.

Stem-girdling root syndrome. The accumulation of stress factors and symptoms associated with the compression of stem tissues from girdling roots.

Strain. An irreversible condition beyond stress in which plant mortality occurs.

Stress. A reversible disruption of the normal physiologic activities of a tree.

Stunt. An abnormal reduction in the growth rate and/or size of various morphological features of a tree (e.g., leaf size, stem caliper, root system, annual twig growth).

Symptom. A plant’s visible reaction to the presence of a biotic or abiotic causal agent.

Symptomology. The study of plant disorders and the symptoms associated with those disorders, as well as the characteristic progression from one symptom to another over time.

Vigor. An organism’s genetic capacity for survival or growth.

Vitality. A dynamic condition that distinguishes the living from the nonliving; used as a metric to conceptualize the relative health of a tree in response to its site condition.


Tree species observed by practitioners to have SGRs

Tree species

Acacia sp.

Aleppo Pine

Arizona Ash

Austrian Pine

Black Gum Tupelo

Bradford Pear

Bur Oak

Callery Pear

Canary Island Pine

Cherry sp.

Chilean Mesquite

Coral Tree

Crabapple sp.

Dogwood sp.

Elm sp.


Ficus sp.

Fruitless Mulberry


Goldenchain Tree

Green Ash



Holly sp.


Juniper sp.


Littleleaf Linden

Live Oak

Mesquite sp.

Monterey Pine

Norfolk Island Pine

Norway Maple

Norway Spruce

Pin Oak

Ponderosa Pine


Red Elm

Red Maple

Red Oak

Russian Olive

Sawtooth Oak


Scotch Pine

Shamel Ash

Shumard Oak

Siberian Elm

Silver Maple

Spruce sp.

Stone Pine

Sugar Maple



White Oak

White Pine


Scientific name

Acacia sp.

Pinus halepensis

Fraxinus velutina

Pinus nigra

Nyssa sylvatica

Pyrus calleryana Bradford

Quercus macrocarpa

Pyrus calleryana

Pinus canariensis

Prunus sp.

Prosopis chilensis

Erythrina sp.

Malus sp.

Cornus sp.

Ulmus sp.

Eucalyptus sp.

Ficus sp.

Morus alba

Ginkgo biloba

Laburnum x watereri

Fraxinus pennsylvanica

Celtis occidentalis

Tsuga canadensis

Ilex sp.

Gleditsia triacanthos

Juniperus sp.

Aleurites moluccane

Tilia cordata

Quercus virginiana

Prosopis sp.

Pinus radiata

Araucaria heterophylla

Acer platanoides

Picea abies

Quercus palustris

Pinus ponderosa

Populus sp.

Ulmus rubra

Acer rubrum

Quercus rubra

Elaeagnus angustifolia

Quercus acutissima

Schefflera sp.

Pinus sylvestris

Fraxinus uhdei

Quercus shumardii

Ulmus pumila

Acer saccharinum

Picea sp.

Pinus pinea

Acer saccharum

Celtis laevigata

Liquidambar styraciflua

Quercus alba

Pinus strobus

Zelkova sp.

Sources: d'Ambrosio (1990), Hauer and Johnson (1997), Johnson (1999), Johnson and Borst (1999), Johnson and Johnson (1997), Tate (1980), Van Wormer (1937), Van Wormer (1940), Watson et al. (1990)

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