The Root of the Problem

James Urban, FASLA: Landscape Architecture Magazine, April 2013

Excerpt: For now, only you can keep trees with ill-formed roots from leaving the nursery

In the mid-1990s, practitioners and researchers were noticing a disturbing trend. Trees were increasingly
declining as they reached maturity. The problem was not limited to one species but affected many nursery-grown trees. Gary Johnson, a scientist at the University of Minnesota Extension Service, looks at hundreds of dead or dying trees each year. He would inspect the trees’ leaves and bark for signs of disease or insect damage, but, at some point, he began to look at the bases of the trees as well. He saw many trees that were slowly strangling themselves with their own roots.

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The Bare-Root Cause

James Urban, FASLA: Landscape Architecture Magazine, June 2011

Excerpt: Bare-root planting is a better choice for tree health. 

Tree planting may be the essence of sustainable architecture, but the methods of harvesting and installation are not always specified in the most sustainable ways. Each of the most common options for tree planting - balled and burlapped, tree-spade planting, and container-grown trees - has environmental costs that reduce or even eliminate the trees' contributions to the sustainability equation. Before World War II, bare-root planting was the common method to move trees both large and small. Projects did not typically move at a fast pace, and people were more patient to wait until the right time to plant. After the war, increasingly larger trees were specified to meet both designer and client needs for instant gratification, and projects began to move more rapidly, with plantings often required at almost all times of year. 

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Alternatives to Structural Soil for Urban Trees and Rain Water

James Urban, FASLA: Paper presented at Designing with Nature: The Art of Balance - American Society of Landscape Architects Annual Meeting, October 2007

Abstract: Compacted soils to support pavements and infrastructure increase the run off rate of rainwater. Only a small percentage of each rain event, even if the pavement is porous, can infiltrate compacted soil for aquifer regeneration and vegetation hydration. Soil compaction also stunts the growth of trees by restricting root penetration. Absorbing soils that are not compacted, placed under pavement can be a significant tool for rainwater management and improvement of the urban forest.

By using the BMP methods discussed below, paved city plazas, streetscapes, and town centers can become areas for rainwater mitigation. They can transform the urban forest into a rainwater mitigation asset. The strategies discussed will support roadways, parking lots and sidewalks while providing un-compacted soil volumes to absorb large amounts of water and enable large tree growth. These methods can contribute to sustainable designs in varying effectiveness for increases in water management with no loss of the paving's structural integrity. 

Using trees and their required soil for rainwater management has additional advantages over other rainwater management strategies. The large healthy tree canopies created by large volumes of absorbing soil provide other benefits. The tree's canopy cools the air and paving which helps reduce urban heat island impacts and cools run off water temperature. A large canopy absorbs the initial 1/10th of an inch of the rain event and evapo-transpires large amounts of water increasing the effectiveness of the system. Healthy, long-lived trees also contribute to the social and economic health of urban communities.

Download the full paper here.

Tree Root Growth Requirements

Dr. Kim Coder: University of Georgia, July 2000

Roots utilize space in the soil. The more space controlled the more potential resources controlled. The volume of soil space controlled by tree roots is directly related to tree health. The resources required are water, oxygen, physical space for growth processes, and open soil surface area for replenishment of essential resources. Tree roots occupy the spaces and gaps around, under, and between infrastructures. In heavily compacted sites, roots will be concentrated around the edges of infrastructures and filling any moist air space. The soil matrix is only a significant concern for essential elements, surfaces holding biological cooperators, and frictional and inertial forces for structural integrity. 

Tree roots and the soil surrounding them are an ecological composite of living, once-living, and abiotic features facilitating life. Compaction initiates many negative impacts in the soil including: decreases the volume of ecologically active space available; tree rootable space is decreased and made more shallow; the detritus food web, the ecological engine responsible for powering a healthy soil, is disrupted and modified; the diversity of living things decline, beneficial associates are eliminated, and a few ecological niche generalists succeed; and, pests favored by the new conditions (i.e. Pythium & Phytophthora) consume organisms and roots not able to defend themselves. Tree roots become more prone to damage and attack at a time when sensor, defense, growth regulation, and carbon allocation processes are functioning at reduced levels.

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Street Tree Question

Report of the Special Committee Appointed by the Hartford Florist Club, February 1903

Excerpt: Beautiful cities without trees are impossible. While the trees in their native forests receive no care from human hands, yet in the environments of a city they must either have human care or become sickly and, long before their time, die. Under such unnatural conditions they must either have care to succeed, and care requires labor, and labor costs money. Nothing can be placed along the side of a street, not even a hitching post, but requires care, and ever so much more is that care demanded for a living tree. 

Hartford is to-day one of the foremost cities in its development of a useful and extensive park system, and its many tree-arched and shaded trees and avenues entitle it to the name which it is receiving throughout the country of "The beautiful city." We have in our city avenues and streets that are made more than attractive through the graceful arches of elms, like Washington street; yet in that very street, in the aristocratic part of the city, lined with beautiful residences, we find trees suffering under conditions which should not exist, and would be impossible under proper management. In some places there is good management, but next door there may be mismanagement and downright neglect and carelessness. Such undesirable conditions will always exist as long as street trees, although standing within the limit of the highway, are considered and treated as the property of the owners of the adjoining grounds. The property owner looks upon the street trees principally in their relation to his own house and grounds and loses sight of their importance as an ornament to the street. 

That municipal ownership alone can remedy such conditions is obvious, and the more the value of street trees, as being useful to the community at large, becomes recognized, the more will the public become convinced that city authorities should control the shade-giving street trees and that they are as essential to the welfare and attractiveness of the city as the roadways and sidewalks are important to its traffic and safety. 

Read the full report here.