15 Years of Root ResearchMinnesota Shade Tree Short Course 2010 Gary Johnson

University of Minnesota

Department of Forest Resourceswww.trees.umn.edu Gary’s Notes

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

Part 1: What is Normal, What is Abnormal What is Dysfunctional?

Heart-Root System

Lateral Root System

A Normal Root: The Beginning

The Seedling Root: First Out of the Seed

Tap Roots Tap Roots are “Seed Roots”…Radicles

A Normal Root

•Root is Suberized

•Vascular System Formed.

•Root Hairs Formed.•Constant Growth

A Normal Root Cell Growth is cell division and cell enlargement

Branch Roots: Normal Developments

Branch Roots Arise From the Pericycle

Sinker/Striker Roots: Normal Developments

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

A Plate-Root/ Lateral Root System

Heart-Root System

Tap-Root System with Laterals

Abnormal Roots and Root Systems Adventitious Roots Symbiotic Roots

Adventitious Roots: Abnormal Developments but Functional

Adventitious Roots and Clonal Propagation: Abnormal but Functional

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

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

Normal Root Depth and Width

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.

Trunk/Root Flare Transitions

Somewhere in this area, tissues are more like stems or roots.

Trunk/Root Flare Transitions

Trunk/Root Flare Transitions

So, What do Roots Really Need?

Dysfunctional Root Systems Stem Girdling Roots Permanently Pot-

Bound Roots Sidewalk Cut-Outs Containerized Root

Systems Bonsai Root Systems

Photo: Chicago Botanic Garden

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

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

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)

Compression of Vessels by SGRs

Photo: G. Hudler

Tree Decline and Dysfunctional Roots

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)

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)

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

Depth to Roots:SGRs:Tree ConditionSugar Maple Diagnostic Survey 1994-1996

•202 Sugar Maples in Decline

•7-18” d.b.h.

•No Verticillium wilt

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

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

A Survey of Practitioners : North American Members of ISA (1998, n = 282)

Minneapolis 1997 - Acer saccharum, 1999 - Fraxinus

pennsylvanica,1999 - Tilia cordata,

Rochester 2001 - Celtis occidentalis,

Saint Paul 2004 - Gleditsia triacanthos

Depth of Soil over Roots: Five Field Surveys

N = 100 (+/-)Per Species, Randomly Selected

•3-9” d.b.h. Trees

•Surveys included two teams.

•1st Team “blind” condition ratedcanopies and stems

•0-4 Rating System

Depth of Soil Over Roots: Survey Protocol

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

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.

•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.

Depth of Soil over Roots Surveys: Root Collar Exams

Frequency of Depth to First Main-Order Lateral Root

0

5

10

15

20

25

30

35

40

45

Depth(inches)

0 1 2 3 4 5 6 7 8 9 10 11

Fre

qu

en

cy

Green Ash (101)

Linden (101)

S. Maple (99)

Hackberry (96)

Honeylocust (106)

Frequency of Encircling Roots(Total of 504 Trees)

0

5

10

15

20

25

30

Depth(inches)

0 1 2 3 4 5 6 7 8 9 10 11

Fre

qu

en

cy

Green Ash (101)

Linden (101)

S. Maple (99)

Hackberry (96)

Honeylocust (106)

Frequency of Stem Girdling Roots(Total of 504 Trees)

0

2

4

6

8

10

12

14

16

Depth(inches)

0 1 2 3 4 5 6 7 8 9 10 11

Fre

qu

en

cy

Green Ash (101)

Linden (101)

S. Maple (99)

Hackberry (96)

Honeylocust (106)

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

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

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

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

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

Littleleaf Linden: 5” Too Deep, 6 Years in Ground, Stem Girdling Suckers

Correcting Container Problems: Buried Stems

Why Does it Happen? To Stabilize Trees in Containers.

Does it Work? Depends…

2002 University of MN/Bailey Nursery Experiment

4 Tree Species, 460 Trees Total

4 Planting Depths: 0 – 2 – 4 – 6 Inches

If You’re a Nursery Retailer A Lean > 3.5 cm Off

Plumb Unacceptable Regardless of Planting

Depth, Leans Were Unacceptable Except for Birch

Planting Depth Showed No Advantage Except for Birch

If You’re a Landscape Contractor

All Leans Correctable at Planting Time

No Leans Unacceptable

Planting Depth Made No Difference in Acceptable Lean

Windthrow From Pots a Non-Issue

Premature Failure in Loading Events

When Roots and Stems Conflict

Soil Line

SGR compression point

Storm Damage in Minnesota: SGRs below ground with compression

Norway Maple (Acer platanoides)

Total Tree Failures In BoulevardsMost Commonly Damaged Size (d.b.h.) ranges

1998 1995-2005Size (d.b.h.) Range % of Total % of Total6-10 inches 28.6 29.0

>25 inches 25.7 26.0

20-25 inches 15.7 16.0

10-15 inches 14.3 14.0

15-20 inches 14.3 14.0

Storm Damage in Minnesota: 1998 n=564 1995-2005 n=1584

Commonly Damaged Species with Chronic Problems

1998 1995-2005

Little Leaf Lindens: 73% of all 76%that failed were 4”+ deep and had

stem girdling roots causing stem compression.These trees failed below the stem compression points.

Storm Damage in Minnesota:SGRs

•SGRs Were Associated With:

•32% of all tree failures , located on the edges of storms

•26% of all boulevard total tree failures (53% of 6-10” category)

•68% of Little-leaf Lindens that failed in boulevards (#3rd most common species)

•> 90% of trees that had SGRs had stems buried 4” or more.

Storm Damage in Minnesota: Failures due to Stem Girdling Roots

Root Pruning Pot-Bound Trees: Does it Work? Slicing?

Slicing

Does “Teasing” Work?

“Teasing”

Does “Butterflying” Work?

“Butterflying”

Did Root Pruning Work?

3 Treatments 1 Control 2 Species 14 Months 60 Trees

…No Differences Among Treatments and Controls

New Root Pruning Experiment Four Species Addition of New Treatment Longer Study (5 vs. 2 seasons) Condition of Trees Tracked

Four New Species, Including Thuja

Photo by Dave Hanson

Treatments Include Traditionals

Photo by Dave Hanson

The New Treatment: “Boxing”

Photo by Dave Hanson

Complete Randomized Block Design

Photo by Dave Hanson

Results to Date Planted November 2005 98 Trees Mortality Rate for All Trees: 0% Condition Ratings: No Difference

Among Trees and Treatments Growth Rates: No Difference Among

Trees and Treatments

Gravel Bed Research

Hydrated Pea Stone A Growing Season Holding Area 3 Treatments, 1 Control Survival Growth Condition Ratings Transplant Success Root Recovery Treatments

Developing Better Root Systems with Water and Oxygen: Gravel Bed Trees

Developing Better Root Systems with Water and Oxygen

6 Weeks in Gravel Bed Increases Fine Root Density

Survival, Growth Rate and Condition Followed for Two Seasons

Best and Worst Performers

Best Performers (partial list): Silver Maple Paper Birch Honeylocust Mt. Ash Gray and Silky Dogwood Ponderosa Pine Norway Spruce Northern White Cedar

Best and Worst Performers

Worst Performers (partial list): River Birch Red Maple Staghorn Sumac Hawthorns (Downy, Washington) Bur Oak Sugar Maple

Gravel Beds: Recovering Pot-Bound Trees

Container Production in Gravel

What Next? Alternative to plastic containers Eliminate encircling roots Better distribution of roots More expensive than smooth containers? More expensive labor involved?

Air-Pruning Pots

Conventional Smooth Pot

Mulberry

Air-Pruning Pots: No Encircling Roots & Better Distribution

‘Prairie Fire’ Crabapple

This Presentation is Available at: www.trees.umn.edu

Click on “Gary’s Notes”