Healthy Urban Tree Root Crown Balances: Soil Properties, Soil Volumes

Summary: Angela Hewitt of The Morton Arboretum associates healthy urban tree root crown balances with forest-like soil properties, soil resources and soil volumes.

An unhealthy urban tree, with severely restricted roots, exhibits crown imbalances; parking lot compresses tree roots, causing dieback, Columbia, Richland County, central South Carolina: Robert L. Anderson/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images

Healthy urban tree root crown balances are dependent upon soil resources, according to Root Management Challenges in Urban Sites: Achieving a Healthy Root-Crown Balance in the December 2012 issue of Arborist News.

Angela Hewitt, research specialist with The Morton Arboretum in Lisle, Illinois, balances the crown's consuming nutrients and water from, and producing carbohydrates and energy for, roots. The biologic, nutrient and physical soil properties in proper soil volumes create an environment "integral to maintaining the natural balance between the crown and root system." The series of closed canopies and spreading roots formed by consecutively planted tree "species that can tolerate the site conditions" describes the environment and fosters balance.

Forests, high in fungi and other organic matter but low in pH levels and surface clay, epitomize sites with the healthiest above- and below-ground tree growth.

Arthropods, bacteria, earthworms, fungi, nematodes and protozoa fill slightly acidic forest soil resources with organic matter by excreting wastes and by leaving behind dead, decaying bodies. Organic matter gives roots soluble nitrogen, one of six macro-nutrients along with calcium, magnesium, phosphorus, potassium and sulfur needed for healthy urban tree root crown balances.

"[T]ightly disturbed and more alkaline" urban soils help leach calcium, magnesium, potassium and sodium and hinder iron and manganese availability and surface-level and underground animal diversity.

Products that are marketed as biostimulants and that include compost teas, humates, mycorrhizal fungi and plant extracts intend to "increase soil biological activity and root growth."

Aluminum's and sulfur's pH-lowering compounds join biostimulants as prescriptions "based on sound scientific concepts, but not specifically formulated to mimic" forest-like soil properties and soil volumes.

Forest soils keep air circulating, animals excreting, moisture infiltrating and percolating, nutrients solubilizing and pH stabilizing because of five physical properties that "affect fine root development."

Soils look structured because of their capacity for holding particles together into larger aggregates and textured because of their proportions of clay, sand and silt particles. The patterns and the proportions of particles make it possible for clayey, loamy, sandy and silty soils to manage different densities, penetration resistances and pore spaces. Healthy urban tree root crown balances need forest-like loamy soil properties, soil resources and soil volumes, not air-poor, penetration-resistant, soil-compacted clay or macropore-poor, nutrient-leached, water-drained sand.

Drainage and surface soil quality offer evidence as "the two factors most altered from the natural state, and most limiting of root growth" in non-forest-like soils.

Parking lot islands, pavement cutouts, residential lots and streets push roots down into cramped undergrounds and crowns up through heat- and light-reflected, sun- and wind-exposed surfaces.

Soil volumes for supporting tree-friendly soil properties quantify at 2 cubic feet (56.6 liters) per square foot (meter) of "expected mature tree crown protection" within drip-lines. Three-foot- (0.9-meter-) deep planting pits in permeable pavements suspended over load-bearing, skeletal, structural stone-soil mixes and root paths to forest-quality soil reinforce downward- and outward-growing roots. Tilling and using pneumatic excavation tools to de-compact soils before composting, cultivating forest understory-like plants, minimizing turf, and mulching support healthy urban tree root crown balances.

It takes "[t]he same careful preservation of soil resources that has become standard practice in farming" to make urban trees look as pretty as a forest.

Effective protection of tree root system during construction encourages healthy urban tree root crown balances: Peter Bedker/Bugwood.org, CC BY 3.0 United States, via Forestry Images

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

An unhealthy urban tree, with severely restricted roots, exhibits crown imbalances; parking lot compresses tree roots, causing dieback, Columbia, Richland County, central South Carolina: Robert L. Anderson/USDA Forest Service/Bugwood.org, CC BY 3.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=3036037

Effective protection of tree root system during construction encourages healthy urban tree root crown balances: Peter Bedker/Bugwood.org, CC BY 3.0 United States, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=5028086

For further information:

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

Hewitt, Angela. December 2012. "Root Management Challenges in Urban Sites: Achieving a Healthy Root-Crown Balance." Arborist News 21(6): 16-20.
Available @ http://viewer.epaperflip.com/Viewer.aspx?docid=c2e5b52e-8268-468c-b40a-a2a700c6a919#?page=16

Marriner, Derdriu. 13 October 2012. “Tree Adaptive Growth: Tree Risk Assessment of Tree Failure, Tree Strength.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/10/tree-adaptive-growth-tree-risk.html

Marriner, Derdriu. 11 August 2012. “Tree Risk Assessment Mitigation Reports: Tree Removal, Tree Retention?” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/08/tree-risk-assessment-mitigation-reports.html

Marriner, Derdriu. 16 June 2012. “Internally Stressed, Response Growing, Wind Loaded Tree Strength.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/06/internally-stressed-response-growing.html

Marriner, Derdriu. 14 April 2012. “Three Tree Risk Assessment Levels: Limited Visual, Basic and Advanced.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/04/three-tree-risk-assessment-levels.html

Marriner, Derdriu. 19 February 2012. “Qualitative Tree Risk Assessment: Risk Ratings for Targets and Trees.” Earth and Space News. Sunday.
Available @ https://earth-and-space-news.blogspot.com/2012/02/qualitative-tree-risk-assessment-risk.html

Marriner, Derdriu. 18 February 2012. “Qualitative Tree Risk Assessment: Falling Trees Impacting Targets.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/02/qualitative-tree-risk-assessment.html

Marriner, Derdriu. 10 December 2011. “Tree Risk Assessment: Tree Failures From Defects and From Wind Loads.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/12/tree-risk-assessment-tree-failures-from.html

Marriner, Derdriu. 15 October 2011. “Five Tree Felling Plan Steps for Successful Removals and Worker Safety.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/10/five-tree-felling-plan-steps-for.html

Marriner, Derdriu. 13 August 2011. “Natives and Non-Natives as Successfully Urbanized Plant Species.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/08/natives-and-non-natives-as-successfully.html

Marriner, Derdriu. 11 June 2011. “Tree Ring Patterns for Ecosystem Ages, Dates, Health and Stress.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/06/tree-ring-patterns-for-ecosystem-ages.html

Marriner, Derdriu. 9 April 2011. “Benignly Ugly Tree Disorders: Oak Galls, Powdery Mildew, Sooty Mold, Tar Spot.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/04/benignly-ugly-tree-disorders-oak-galls.html

Marriner, Derdriu. 12 February 2011. “Tree Load Can Turn Tree Health Into Tree Failure or Tree Fatigue.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/02/tree-load-can-turn-tree-health-into.html

Marriner, Derdriu. 11 December 2010. “Tree Electrical Safety Knowledge, Precautions, Risks and Standards.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2010/12/tree-electrical-safety-knowledge.html