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15 Years of Root Research

15 Years of Root Research. Minnesota Shade Tree Short Course 2010 Gary Johnson University of Minnesota Department of Forest Resources

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15 Years of Root Research

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  1. 15 Years of Root Research Minnesota Shade Tree Short Course 2010 Gary Johnson University of Minnesota Department of Forest Resources www.trees.umn.edu Gary’s Notes

  2. What Will Be Covered? • What is Normal, Abnormal and Dysfunctional • A Bit of History • What Six Studies Revealed • What Next?

  3. Part 1: What is Normal, What is Abnormal What is Dysfunctional? Heart-Root System Lateral Root System

  4. A Normal Root: The Beginning The Seedling Root: First Out of the Seed

  5. Tap Roots • Tap Roots are “Seed Roots”…Radicles

  6. A Normal Root • Root is Suberized • Vascular System Formed. • Root Hairs Formed. • Constant Growth

  7. A Normal Root Cell • Growth is cell division and cell enlargement

  8. Branch Roots: Normal Developments • Branch Roots Arise From the Pericycle

  9. Sinker/Striker Roots: Normal Developments

  10. Categories of Normal Root Systems* • Plate-root or lateral root systems – 82.5% • Heart-root systems – 15% • True tap-root systems w/laterals – 2.5% *n = 4000 trees. Cutter, Gasson, Farmer, 1990. Arboricultural Journal

  11. A Plate-Root/ Lateral Root System

  12. Heart-Root System

  13. Tap-Root System with Laterals

  14. Adventitious Roots Symbiotic Roots Abnormal Roots and Root Systems

  15. Adventitious Roots: Abnormal Developments but Functional

  16. Adventitious Roots and Clonal Propagation: Abnormal but Functional

  17. Mycorrhizal Roots: A Fungus-Root Relationship in 90% of Trees

  18. Symbiotic Roots: Abnormal but Common • Improves water and nutrient uptake efficiency • Maintain soils structure • Imparts some deicing salt tolerance to host • Protects trees from heavy metal toxicity • Protects trees from root pathogens by using excess carbohydrates • Act as physical barriers to pathogens

  19. 99% of root biomass in top 3 feet. Fine roots in top foot. Fine roots grow where there’s oxygen and moisture. Greater than 50% of roots beyond drip line. Normal Root Depth and Width

  20. Trunk/Root Flare Transitions Somewhere in this area, tissues are more like stems or roots.

  21. Trunk/Root Flare Transitions

  22. Trunk/Root Flare Transitions

  23. So, What do Roots Really Need?

  24. Stem Girdling Roots Permanently Pot-Bound Roots Sidewalk Cut-Outs Containerized Root Systems Bonsai Root Systems Dysfunctional Root Systems Photo: Chicago Botanic Garden

  25. Root Research: A Brief History • Young Trees vs. Mature Trees: Fine Roots • Stem Girdling Roots • Pot-Bound Root Pruning • Depth to First Roots

  26. Root Research: Fine Roots and Age • Fine root density greater on mature trees • Fine roots concentrate in upper 8 inches • Surface mulch encourages shallow fine roots • Fine roots arise from lateral roots • Lateral roots radiate away from stems

  27. Root Research: Stem Girdling Roots • Compression of stem reduces water and nutrient flow (1981) • Stem Girdling Roots directly related to sugar maple health decline (1937, 1940) • Roots compress far less than stems (1981) • Red and sugar maples more vulnerable to girdling than Norway maples (1984) • SGRs not related to boulevard width (1990) • 10-20% of Norway maples die @ 8-10” d.b.h. (1983)

  28. Compression of Vessels by SGRs Photo: G. Hudler

  29. Tree Decline and Dysfunctional Roots

  30. Root Research: Pot-Bound Trees and Root Pruning Practices • Short-term effects of slicing is retarded shoot growth (1987, 1996-1) • Resulting benefits are inconsistent (1996-2) • Root ball slicing and removing bottom eliminates encircling roots (1984)

  31. Root Research: Effects of Depth to First Roots on Tree Health • More depth, more death: Yoshino cherries (2006) • More depth, no difference: red maples (2006)

  32. Six Research Studies • Depth to Roots:SGRs:Tree Condition • Diagnostic Survey of Sugar Maple • 5 Field Surveys • 9-Year Field Experiment • Depth to Roots and Tree Stability • Tree Failure and Loading Events • Root Pruning Pot-Bound Trees • Gravel Bed Trees

  33. Depth to Roots:SGRs:Tree ConditionSugar Maple Diagnostic Survey 1994-1996 • 202 Sugar Maples in Decline • 7-18” d.b.h. • No Verticillium wilt

  34. Depth to Roots:SGRs:Tree ConditionSugar Maple Diagnostic Survey 1994-1996 • 202/202 had 4-18” soil over 1st main order root • 162/202 had only SGRs associated with the decline • Trees with >50% of stem circumference compressed had most severe symptoms • Trees w/SGRs planted 12-20 years previous • Common Symptoms: scorch, stunt, frost cracks

  35. A Survey of Practitioners :North American Members of ISA (1998, n = 282) • Stem Girdling Roots and Tree Loss…Practitioners Stated: • Relationship to tree decline and death - 82% of the time. • Relationship to the sudden failure of trees – 18% of the time

  36. Depth of Soil over Roots: Five Field Surveys Minneapolis 1997 - Acer saccharum, 1999 - Fraxinus pennsylvanica, 1999 - Tilia cordata, Rochester 2001 - Celtis occidentalis, Saint Paul 2004 - Gleditsia triacanthos N = 100 (+/-)Per Species, Randomly Selected

  37. Depth of Soil Over Roots: Survey Protocol • 3-9” d.b.h. Trees • Surveys included two teams. • 1st Team “blind” condition rated • canopies and stems • 0-4 Rating System

  38. Condition Rating: Canopies • 0-4 Rating System: • 0 = Dead • 4 = No obvious defects. • Canopy condition rating factors: • Characteristic density for the Species • Live crown ratio (60% standard) • Crown symmetry • Dieback

  39. Condition Rating: Stems • Factors: • Lost Bark/Living Cambium • Cracks/Ribs • Decay • Stem Girdling Roots (above ground) • 0-4 Rating System: • 0 = No living cambium in stem, • 4 = No obvious defects.

  40. Depth of Soil over Roots Surveys: Root Collar Exams • 2nd Team performed root collar examination: • Data Recorded: • Depth to first order roots, • Frequency and location of • Stem Encircling Roots (SERs) and Stem Girdling Roots (SGRs), • % of stem affected.

  41. Summaries • Majority Had > 1” Soil Over Roots* • Tilia, Acer and Fraxinus Worst: > 90% w/4”+ • 1”+ Soil = More SER’s • Most Vulnerable Species: Tilia, Celtis, Fraxinus • Worst Condition Rating:Soil Depth – Tilia, Acer, Fraxinus • Most Common SGR’s:Soil Depth – Tilia, Fraxinus, Celtis, Acer

  42. Nursery Stock Survey 2001-2002* • 881 Trees Sampled out of 5500 Total • B&B and Containerized • 87%: Stem Buried 2+ Inches • 50%: Stem Buried 4+ Inches *Minneapolis Park and Recreation Board; St. Paul Division of Forestry

  43. Planting Depth Study: 2000-2009 • Two Species: Littleleaf Linden, Sugar Maple • 360 Trees @180 • 3 Depths: 0, 5, 10 inches • Harvest 1/3 @ 3, 6, 9 years

  44. Planting Depth Study: Results • Significantly higher mortality rate for Sugar Maples at 5 and 10 inch depths • More suckering on Lindens at 5-10 inch depths • High mortality rate on Lindens due to Stem Girdling Suckers • Higher frequency of SERs and SGRs as depth increased

  45. Littleleaf Linden: Planted 5” Too Deep, 5 Years in Ground

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