Tree Biology, Benefits, and the Urban Environment

Massachusetts Tree Steward Training October 19, 2012, Harvard ForestEric Seaborn & Mollie Freilicher

MA-DCR Urban & Community Forestry Program

Tree Biology

• What makes a tree a tree?– Wood– Grow radially as well

as vertically– Can you climb it?

2009 San Diego Urban Tree Exhibit

Tree AnatomyXylem

• Dead and living cells• Conduct water and

minerals• Structural support• Store carbohydrates• Defend against disease

spread & decay• Made of tracheids,

fibers, parenchyma, and vessel elements (hardwoods)

Tree AnatomyPhloem

• Moves sugars produced by photosynthesis in leaves to other parts of the tree

• Innermost layer of bark; old phloem becomes part of bark

• Made of sieve tube elements and companion cells in hardwoods and sieve cells in conifers

Tree AnatomyRays

• Transport sugars and other compounds through trunk

• Store starch• Restrict decay

bio.tamu.edu

Tree AnatomyBark

• Protects– Moderate temperature– Provide defense– Reduce water loss– Made of old (non-

functioning) phloem and cork tissue

– Lenticels are small openings in the bark that allow gas exchange

Image: TX A&M Extension

Leaves• Photosynthesis • Transpiration

Image: Maricopa.edu

Image: Arbor Day Foundation

Parts of a Stem

Image: Clemson.edu

Branch Structure

Image: U.S. Forest Service

Image: Univ. of Kentucky

Branch Structure

Roots

• Functions– Anchorage– Absorption– Storage– Conduction

• Grow outward– Most roots are in top 6-12 inches of soil

Importance of Urban Trees

Pittsfield, MA

Percent Urban – Suburban 2010

Percent Urban – Suburban 2020

Percent Urban – Suburban 2030

Percent Urban – Suburban 2040

Percent Urban – Suburban 2050

FOREST COVER BY STATE

STATE %TREECOVER

LANDAREA km

% AGR.

%FOR.

%URB.

% POP.CHANGE

DENSITYPer km

CT 45.1 12550 11.2 54.2 25.0 -0.4 260.9

MA 50.4 20300 8.2 48.5 24.6 1.3 300.1

ME 70.0 79939 3.1 82.1 2.1 1.3 15.6

NH 73.7 23231 5.0 75.6 8.6 4.8 50.0

NY 54.6 122310

29.4 52.3 9.0 1.1 148.7

RI 35.2 2707 7.7 49.1 21.7 -1.3 365.9

VT 73.3 23956 17.4 71.5 3.7 4.6 24.6

TREE COVER IN MA COMMUNITIES

PLACE TREECOVER

LANDAREA

WATERAREA

1990POP.

POP.DENSITY

NEEDHAM

29.5 32.7 .02 27557 843

AMHERST

23.2 12.7 0.0 17824 1404

DOVER 50.4 11.3 0.0 2003 177

WIN-CHESTER

16.8 15.6 .07 20267 1295

BROOK-LINE

14.1 17.6 .1 54718 3111

Nature is a continuum with wilderness at one pole and the city at the other. But the same natural processes operate

in the wilderness and in the city. - Anne Whiston Spirn

Tree Benefits

• Stormwater– Reduction & retention

• Air pollution– Reduction & retention– Temperature

Reduction• Energy savings

– Reduce cooling costs

• Social– Reduced crime– “Sense of Place”– Property values– Screening & privacy– Noise reduction

New Bedford, MA

A 20-inch swamp white oak in our area can intercept 2,564 gallons of water per year

Air Pollution

Roots stabilize soil and prevent soil erosion

Evapo-transpiration from leaves cools surrounding air reducing the formation of ground-level ozone

Leaves filter pollutants from airBranches and form

provide shade, reducing the need for air conditioning

Blocks wind to help reduce heating needs

Larger Trees, Greater Benefits

Image: Arbor Day Foundation

Large Tree Argument• Large trees provide nearly 8 times the benefits as smaller trees

over the life of a large tree• Ornamental trees are often shorter-lived than large shade trees

– A crabapple may only live 40 years– An elm may live for 100s of years

Urban EnvironmentUrban Heat Island

Urban EnvironmentPeople

Urban EnvironmentLimited Planting Space

The Real World – Tree Decisions

We Make it Tough on Trees

Urban EnvironmentPeople

Important for us to be stewards of our trees to help them in the difficult urban environment

Urban EnvironmentPoor Urban Soils

Urban EnvironmentCompaction

After removals

Proximity to Wachusett Reservoir

“ The wind up here is terrible now! My windows were rattling and I think I lost shingles from my

roof”

“I never used to be able to see I-190 and all that stuff down there”

“The sun baked us this summer”

“My Dad planted that tree. It was hard to see it go”

“Welcome to the wasteland”