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ESC 200 - Spring 2003
Trees in Our Environment

Prof: Linda Brubaker

 

TREES FOR THE URBAN ENVIRONMENT (web, ppt)

LECTURE OVERVIEW

Basic statement:

Throughout most of the United States, trees are an integral part of cities. While the urban environment does not favor tree growth, the reverse is even more likely: trees can significantly improve life in the city.

Key ideas:

During the past century, Americans have moved from rural environments to cities. In the process, we brought certain aspects of the rural environment, namely trees, to the urban setting--even where the local climate does not support the growth of trees. What is the reason for our dependence on trees? What benefits do we derive from them? What are the consequences of the urban environment to trees? What are selection criteria for successful urban trees? What is the formula for the successful greening of our cities?

LECTURE OUTLINE

Introduction

  • Trees are part of most urban landscapes (high human densities)
  • In North America, as street trees and in parks, since mid 1800s. People started visiting cemeteries in 1800s when green space had been eliminated from most eastern US cities). Represented new attitude about wooded areas, previously forests were considered dangerous, and an impediment to human survival/agriculture:
  • In European urban areas, parks and noble estates have existed for 100s of years.
  • Many "domesticated" urban trees come from Asia and southeast Asia, indicating long association. Parks and gardens have existed in Asia for more than 1000 years.
  • Today we ask: Why do we like trees in cities? and What are special problems they face?

 

Why Trees in Cities?

Important question, since there are so many problems with trees in cities.

  • Accidents: limb breakage, trunk failure, electrocution (powerline in tree) root trip and fall, tree blocks traffic signs
  • Litter cleanup: in fall, after storms
  • Block views (issue in scenic areas like Seattle)

    Practical Values: for some "use"

  • mark boundaries (edge of yard, property line)
  • "clean air"—catch particulates along dusty road
  • Shade-- houses, reduce air conditioning costs
  • Food and habitat for animals— urban wildlife, many locations for birds squirrels

Amenity value: Aesthetic/emotional value of trees

  • Beauty—derived from varieties of shapes (triangular, columnar, round), colors (leaves, flowers, fruits), textures (leave sizes and shapes) and their juxtaposition. (SEE BELOW)
  • Shade—streets and yards
  • Habitat—for urban wildlife, particularly birds
  • Calming effects—psychological tests show effects on blood pressure etc. Visual blocks, sound blocks, a place to rest
  • Recreation (trees require large areas which result in other activities e.g., in parks) picnic, walk, jog, frizbee, walk dog,
  • Historic and symbolic value: "Washington elm" symbol of US history; Old oaks in represent longevity and permanence.
  • Familiarity with "home"—New world issue (tree species and plantings remind people of environment from which they moved—e.g., So. California (Australia) planted with trees that recreate eastern North American wooded environments)
  • Seasonal change-- variation during year (spring, fall color; presence, absence of leaves adds some variation to appearance of cities

Urban vs. "Natural" Environments

Clearly, people want trees in cities, but it is a difficult task to grow them in cities

Cities are stressful environments for trees:

  • Hot—reradiated heat, and internal heat production
  • Dry—water never reach soil, diverted from soil via sewers, storm drains
  • Windy—wind is funneled through city streets by sky scrapers
  • Soil compaction—by heavy traffic on sidewalks and streets
  • Pollution—air (ozone, carbon monoxide, particulates), and soil (salts to melt snow, lead from gasoline, heavy metals)
  • Physical damage—vandalism by people, damage by cars
  

What are efforts to ensure successful use of trees in cities?

  • Appropriate money—(Seattle street tree bond in 1960s, failed Seattle Commons) for initial planting and upkeep
  • Volunteer groups—Planting street trees very successful volunteer activity in Portland, e.g., ARBOR DAYS
  • Select the "right" species—requires physiological, ecological understanding
    -pollution resistant—
    -drought resistant—early successional species
    -disease resistant—Acer platanoides, planted in place of Ulmus americana
    -"right kind of shade"—depends on geographic region—deciduous trees are shady in summer and open in winter (lombardy poplars are good around farm houses), evergreens are prohibited as street tree in Seattle.
    -minimum litter—branches, leaves, fruit—Aesculus heavy leaf, flower, fruit fall; Salix, Populus weak branches
    -non-aggressive root system—all willows are problems, Platanu

Aesthetic qualities of trees

What makes trees beautiful (or not??)
Same qualities we use to describe technical features of paintings

Note: Names of examples below are from our species list (not necessarily the names of plants in pictures).

 

SHAPE:

Straight, vertical lines
excurrent form—early successional
Examples: Pinus and most Gymnosperms, Populus, Liquidambar, Liriodendron, Prunus,Sequoiadendron (triangular)

Rounded, horizontal lines
deliquescent form—late successional
Examples: Aesculus, Acer, Cornus, Quercus

 


Arrangement emphasizing variation in tree forms (several are mutations)


Irregular lines
forms found naturally in stressful environments
Example: Pinus ponderosa on Greyrock CO

TEXTURE:
Size of units, makes objects distinctive from surroundings


Fine textures (small leaves)
Examples: most Gymnosperms, Betula, Sorbus, Prunus

 
Coarse textures (large leaves)
Examples: Acer macrophyllum, Aesuculus hippocastanum

COLOR
Fruit: Bird dispersed fruit is usually colorful (see lecture on seed dispersal)

Example: Sorbus

 

Bark: Variations in color, lines, textures


Examples: Betula pendula, Betula papyrifera, Thuja plicata, Robinia pseudoacacia

Flowers (Inflorescences): Color in spring


Examples: Prunus, Cornus, Aesculus, Sorbus

Leaves: wide range of "greens"

"Natural" color of foliage

  • Gynmonsperms—generally dark green, glaucous covering results in bluish
  • Angiosperms—generally bright green

Above: Mixture of Pseudotsuga menziesii, Alnus rubra and Populus trichocarpa near Bellingham WA, middle May.

Mutations:

Some mutations affect leaf color or result in variegated leaves

Spring color

  • light, bright green of emerging foliage
  • sometimes reddish color (protects from UV)

Above: Mixture of Pseudotsuga menziesii, Alnus rubra and Populus trichocarpa, Betula pendula north of Vancouver BC, middle May
 

Fall color

  • Results from extraction of chlorophyll (reuse, see lecture on tree biology), revealing other pigments
  • Examples: Acer, Liquidambar

Arrangements of trees and other features of interest :

In natural setting, parks, yards
  • foreground
  • background
  • frame
  • points of interest
  • borrowed scenery (view of landscape surrounding park)
Example of arrangement in "natural" landscape, Greyrock CO

Gardens and Parks:

Types and Arrangement of trees make them attractive

Design of parks varies greatly :

  • Formal gardens of Europe, Japan etc
  • Expansive parks of US (Arboretum)

    Throughout the course at the Washington Park Arboretum, we’ve experienced the massive, relatively "natural" (ie unmanicured style) in the Olmstead tradition of North American Parks — a tradition of a little more than 100 years.

Let’s discuss formal, highly kept style of Japanese Garden—tradition can be traced back 1000’s of years

  • Japanese Garden of Washington Park:
  • Established in early 1960’s, 3.5 acres (small space)
  • Designed by Juki Iida, -- designed >1000 parks worldwide
  • Used traditional themes and techniques of Japanese gardens

Background to Japanese Gardens:

History:

  • 1000s yrs ago, people felt gods/spirits resided in elements of nature (i.e. animism)—typical
  • attracted spirits to earth by clearing patch in forest, with gravel in opening and rice rope for spirits to descend to spot
  • started to plant plants around opening—1st gardens
  • 1st gardens were for gods
  • eventually gardens were for nobility/emporers (emporers were considered gods)
  • 1st documented garden in ~600s AD—had hill, lake, island
  • set 3 major traditions of gardesn: water (with island), stones, plants
  • often took advantage of surrounding areas= borrowed scenery

Plants:

  • trees important (Buddha reached enlightenment under a tree
  • certain trees especially revered
    • pines—durability and longevity
    • cherry for blossoms
    • plum for hardness
  • gardens became idealized landscapes
  • pines easily manipulated to look old and windswept, needles handpicked to reveal view between branches, branches cut and bent to give gnarled appearance, covered in winter to prevent snow from breaking branches.

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Contact Linda Brubaker at: lbru@u.washington.edu

 

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