Urban Design to Accommodate Trees: Introduction by Dr. Edward F. Gilman, professor Department of...

Urban Design to Urban Design to Accommodate Accommodate

Trees: IntroductionTrees: Introductionby Dr. Edward F. Gilman, professor

Department of Environmental Horticulture

University of Florida, Gainesville

http://hort.ufl.edu/woody/planting

Outline of topicsOutline of topics

Introduction Site evaluation Species selection Formula for success Roots/hardscape conflicts Trees/sidewalk solutions Parking lot/buffer strip solutions Structural soils

Urban design to encourage Urban design to encourage tree canopy tree canopy

Trees often grow poorly in urban areas unless the infrastructure has been specially designed to accommodate tree root growth

This presentation is designed to help guide you through the design and species selection process

Introduction

Few citizens want cities Few citizens want cities without treeswithout trees

A city without trees is hotter in summer, receives less rainfall, has greater runoff following storms, has fewer shoppers, and is not inviting

Introduction

Good design leads to Good design leads to successsuccess

Trees thrive when good designs are executed properly

Healthy trees increase property value, intercept air pollutants, buffer temperatures, reduce wind speed, cool the city, reduce runoff from storms, encourage people to visit and spend money at shops, and create a more inviting community

Introduction

Site evaluationSite evaluation

A thorough site evaluation insures that you will select the right tree for your planting site

Examples of some of the Examples of some of the components of site evaluationcomponents of site evaluation

Above ground USDA hardiness zone Light, heat, and wind exposure

Below ground Soil volume – is there enough root space? Soil pH and drainage Soil texture, compaction

Maintenance issues Availability of regular irrigation Pruning program in place or not

evaluation

The dilemmaThe dilemma

Certain trees grow well in tough urban sites so we use them often..monoculture results

They grow well in small spaces but disrupt and destroy sidewalks/curbs, grow into wires

We “fix” the problem by cutting roots and resurfacing hardscape, or cutting tops

Trees decline or look ugly as a result and…… …..our vision of the urban forest never develops

because trees never make it more than 20 to 40 years We can do better with appropriate design

Selection

…the design…

The dilemma continuedThe dilemma continued

We could try different species or cultivars but they may perform poorly and besides “no one else has tried these”

And alternative trees may be difficult to find at nurseries, especially in the size and quantity you want

So……we plant what we know will work; i.e. what everyone else plants, because it is safe

We are more or less stuck in this pattern now

…the trees…

Solution – be creativeSolution – be creative

Restrict one genera or species to < 20% for few years

Develop a list of alternatives for each commonly planted tree

For example alternatives to live oak: Swamp chestnut, redbay, trident maple,

sugarberry, ash, sweetgum, american elm, cedar elm, overcup oak,

Match species to site Match species to site characteristicscharacteristics

Choose the right tree that will grow in the conditions present at the site: use books, software, web sites, your experience

…or… Design the right place to

fit the trees you want: this is covered in detail next

Don’t try to shoehorn a tree you want into a site not designed to support that tree, unless you are a short term planner, in which case go for it

Selection

Trees can form a canopy Trees can form a canopy over the street over the street

With appropriate spacing Access to open soil space Open soil space is soil that is not covered by a

hard surface such as a sidewalk, pavement or a building

Success

Complete canopy closureComplete canopy closure Trees were planted 40 to

50 feet apart in a planting strip 10 feet wide; this spacing allowed for the crowns of individual trees to touch, encouraging development of a more natural upright form

The 10' wide planting strip allowed the trunk flare to develop appropriately

State College, Pennsylvania

Success

Complete canopy closureComplete canopy closure Trees were planted about

30 feet apart; this spacing allowed for the crowns of individual trees to touch when they were fairly young and encouraged a more natural upright form

Trees gained tremendous size due to the almost unlimited access roots had to soil space

Saint Augustine, Florida

Success

Complete canopy closureComplete canopy closure

Trees were planted 15 to 40 feet apart; this spacing allowed for the crowns of individual trees to touch when they were fairly young encouraging a more natural upright form


Seattle, Washington

Success

Barely complete canopy Barely complete canopy closureclosure

Trees were planted about 50 feet apart. Because trees were spaced this far apart, they began to grow aggressive lower limbs. Lower limbs are drooping, creating a more spreading habit than would have occurred with closer spacingMiami, Florida

Success


No canopy closure—No canopy closure—spacing too farspacing too far

Trees were planted about 50 feet apart. Because trees were spaced this far apart, they began to grow aggressive lower limbs. Lower limbs are drooping, creating a more spreading habit than would have occurred with closer spacing


Charleston, South Carolina

Success

No canopy closureNo canopy closure

Trees were planted about 60-70 feet apart. Because trees were spaced this far apart, they began to grow aggressive lower limbs.

The planting strip is twenty feet wide and roots can grow into the lawns of the homes along the streetCoral Gables, Florida

Success

The formulaThe formula

Plenty of root space Closer spacing for canopy closure and reduced

maintenance

Roots can destroy Roots can destroy hardscape with improper hardscape with improper

design design

Tree roots grow under sidewalks and asphalt in many instances because that is where the soil oxygen and moisture are located

The hardscape is often inadvertently designed to encourage roots to grow there; better urban design can reduce the likelihood of roots proliferating under hardscape

Conflicts

Root spread on shade Root spread on shade treestrees

Shade trees extend their roots way beyond the tree canopy

Note the root that is growing in the lawn (two arrows); it is located well beyond the branch tips

Conflicts

Roots grow well beyond Roots grow well beyond canopy edgecanopy edge

Trees that normally grow a very expansive root system can become stressed and grow poorly in urban landscapes where soil space is limited

The result can be poor tree health, damaged sidewalks and curbs, and other problems

Conflicts

Root flare needs room to Root flare needs room to expand expand

The swelling at the base of the tree (where the large roots meet the trunk) is commonly referred to as the root flare or buttress

Roots normally raise out of the ground as shown here

Adequate open soil space must be designed into the system to accommodate expansion of the root flare

Conflicts

Flare commonly 2.5 to Flare commonly 2.5 to 3.5 times trunk diameter3.5 times trunk diameter

Misfits and poor designMisfits and poor design

The oaks planted in this narrow soil strip have two choices: grow poorly due to

the limited amount of soil space available for root expansion, or

grow well by sending roots under the pavement which will quickly crumble the curb and asphalt

Conflicts

Sidewalks liftedSidewalks lifted

Roots often grow just under the slab because that is where moisture and oxygen are abundant

Roots lift the walk as they grow in diameter

Conflicts


Introduction Site evaluation Species selection Formula for success Roots/hardscape conflicts Trees/sidewalk solutions (go to sidewalk solutions PP file)

Parking lot/buffer strip solutions Structural soils

Urban Design to Accommodate Trees: Introduction by Dr. Edward F. Gilman, professor Department of...

Documents

Transcript of Urban Design to Accommodate Trees: Introduction by Dr. Edward F. Gilman, professor Department of...