Perspectives in Sustainable Management of Urban Forests in Central Arizona

Perspectives in Sustainable Management of Urban Forests in Central Arizona

Chris A. Martin, PhDDepartment of Applied Sciences and MathematicsArizona State University

Topics

Urban forestry management: Tree selection, health and mortality in the greater Phoenix area

Factors affecting present day urban forest diversity and cover characteristics

Sustainable Site Initiative (SII) – Prerequisites and credits specific to the urban forest

Urban forestry management: Tree selection and mortality in the greater Phoenix area

1. Urban tree cover is in a long-term decline and is presently about 12%.

2. Approximate rates of tree mortality are between 5% and 10% per annum.

3. 55% of urban trees have severe structural and/or disease issues mostly caused by improper design and management.

4. The ‘quality’ of urban tree selection has declined with the increased focus water conservation and xeric and desert landscaping design motifs.

Native desert adapted trees have a sprawling, shrub like form unsuitable for spatially congested urban spaces

Native desert adapted trees have a sprawling, shrub like form unsuitable for spatially congested urban spaces

An unsustainable trajectoryAn unsustainable trajectory

An unsustainable trajectoryAn unsustainable trajectory

12

3

June 2005Crown thinnedJune 2005Crown thinned

1

2

3

January 2007January 2007

October 2008Crown raisedOctober 2008Crown raised

September 2010September 2010

Relative Tree Age

100%

75%

50%

25%

0%

Mature

Productive

EstablishmentFra

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f tr

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The capacity to recover from crown thinning deceases with tree age.

Factors affecting present day forest diversity and health in the greater Phoenix area

1. Overall, tree diversity and health in residential areas is higher than in public areas.

2. Bottom-up driving forces are the principal means of increasing urban forest tree diversity.

3. Urban tree diversity is strongly correlated to medium family income.

4. Tree cover in lower income areas of the greater Phoenix metropolitan is in very decline.

Social History – Origins of Social History – Origins of Residential SegregationResidential SegregationSocial History – Origins of Social History – Origins of Residential SegregationResidential Segregation

1920 Phoenix Chamber of Commerce Report “Phoenix is a modern town of forty thousand people, and the best kind of people too. A very small percentage of Mexicans, Negroes, or foreigners.” (courtesy of Bob Bolin)

Early 20th century

Flood irrigation and shade

1950s and 60s Advent of A/C and sprinkler irrigation

1970s Advent of drip irrigation

1980s Advent of XeriscapeTM principles

1990s to present

Popularization and decline of desert landscaping

Social and Technological LegaciesA change from function to form

South Phoenix neighborhoodSouth Phoenix neighborhood

The inequities in tree coverwithin lower income neighborhoods

Tree height (m)Park 4.0+1.7Neighborhood 3.9+1.9

Tree canopy width (m)Park 4.9+2.3Neighborhood 3.8+2.2

Percent total tree coverPark 3.7%Neighborhood front yards 23.3%

Top 5 neighborhood tree species

Leucaena glauca 39%Prosopis hybrid 12%Melia azederach 6%Washingtonia filifera 4%

61%

South Phoenix neighborhoodSouth Phoenix neighborhood

Naturalizing trees – an urban forest resource?Naturalizing trees – an urban forest resource?

Leucaena glauca (lead tree)Leucaena glauca (lead tree)

What is the Sustainable Sites Initiative (SSI)?

An interdisciplinary effort to create voluntary national guidelines and performance benchmarks for sustainable landscape design, construction and maintenance practices.

1. Site Selection2. Pre-Design Assessment and Planning3. Site Design—Water4. Site Design—Soil and Vegetation5. Site Design—Materials Selection6. Site Design—Human Health and Well-

Being7. Construction8. Operations and Maintenance9. Monitoring and Innovation

Sustainable FactsIn the continental U.S., carbon sequestration provided by urban trees is estimated to be about 25 million tons per year, which is equivalent to the carbon emitted by almost 18 million cars in one year.   ~ Nowak and Crane, 2002; U.S. Climate Technology Cooperation, 2007

Why is it important that my company know about the SSI guidelines now?

Early transformation of company operations to adopt relevant sustainable landscaping practices will place the company in a competitively favorable position.

Sustainable FactWeather-based irrigation systems can reduce irrigation water use by 20 percent in the United States, which is 24 billion gallons per year.   ~ U.S. EPA, 2007

What are Ecosystem Services?

The SSI guidelines are based on the concept of ecosystem services.

Ecosystem services are one way that people can use to derive landscape value.

Ecosystem services are the capacity of natural process to provide goods and deliver values that satisfy human needs either directly of indirectly.

Sustainable FactWeather-based irrigation systems can reduce irrigation water use by 20 percent in the United States, which is 24 billion gallons per year.   ~ U.S. EPA, 2007

What are Ecosystem Services?

Deliverables are broadly placed into four major groups:

1. Regulation functions – Greenhouse gases (CO2) and microclimate regulation, soil disturbance and retention, and water conservation, soil retention, nutrient cycling, waste treatment, pollination.

2. Habitat functions - Refugium and nursery functions for the dwelling and reproduction of other organisms such as birds, hummingbirds, butterflies, etc.

What are Ecosystem Services?

Deliverables broadly placed into four major groups:

3. Production functions - Food, raw material, and genetic, medicinal, and ornamental resources.

4. Information functions - Beauty, recreation and tourism, cultural and altruistic inspiration, spiritual and historic inference, and science and education.

Sustainable FactSediment runoff rates from construction sites can be up to 20 times greater than agricultural sediment loss rates and 1,000 to 2,000 greater than those of forested lands.   ~ U.S. EPA, 2005

Sustainable FactAn estimated 32 million tons of construction and demolition wood waste are generated each year in the United States, 14 million tons of which are potentially available for recovery.   ~ McKeever, 1996

How are the SSI guidelines organized?

The SSI guidelines will be organized into suites of landscape pre-requisites and credit options.

Landscape pre-requisites will first need to be adopted as a precursor for the implementation of any desired suite of credit options.

2009 Rating System: 250 Points Total

100 points (40% of total points)125 points (50% of total points)150 points (60% of total points)200 points (80% of total points)

How are the SSI guidelines organized?

Credit options will be assigned point values associated with low, moderate or high levels of compliance for each and any credit option.

Sustainable FactMaintenance over a 20-year span for a non-native turf grass landscape can cost almost seven times more than the cumulative costs of maintenance for a native prairie or wetland.   ~ U.S. EPA, 2007

How are the SSI guidelines organized?

Sustainability accreditation and levels of sustainability certification will be derived through demonstrations of a project’s adoption of a suite of pre-requisite and credit options that collectively sum to some standardize cumulative point total.

Sustainable FactThirty-six states anticipate local, regional or state-wide water shortages in the next five years.  

~ U.S. EPA, 2007

Credit 3.5 - Minimize or eliminate potable water consumption for irrigation

IntentLimit or eliminate the use of potable water, or other natural surface or subsurface water resources available on or near the project site, for landscape irrigation. Non potable water is defined as captured rainwater, recycled wastewater, recycled gray water, air-conditioner condensate, or water treated and conveyed by a public agency specifically for non-potable uses.

• Note: Water volume used to irrigate community vegetable gardens is exempt from total site irrigation calculations.

Credit 3.9 - Use native plants

IntentPlant appropriate vegetation that is native to the ecoregion of the site.

Note: Native plants are defined as: plants native to the EPA Level III ecoregion of the site OR known to naturally occur within 200 miles of the site.

5.2 Credit - Support sustainable practices in plant production

IntentPurchase seeds and plants from providers that reduce resourceconsumption, waste, and risks of invasive species.

7.3 Credit - Recycle organic matter generated during site operations and maintenance

Intent Use vegetation trimmings generated during operations and maintenance as compost and mulch to improve soil health and reduce the need for chemical fertilizers, irrigation, and pesticides.

4.11 Credit - Use vegetation to minimize building cooling requirements

IntentPlace vegetation and/or vegetated structures in strategic locations aroundbuildings to reduce energy consumption and costs associated with indoorclimate control.

Sustainable urban tree selectionSustainable urban tree selection

Conclusion

Five keys to developing a sustainable urban forest

Key #1: Irrigation technologies

Key #2: Oasis Landscape Design Motifs

Key #3: Cluster planting of trees

Key #4: Green waste recycling

Key #5: Pruning practices

Where did all the trees go?Where did all the trees go?

Acknowledgements

Research CollaboratorsDr. Bob Bolin, Arizona State University Dr. Anthony Brazel, Arizona State UniversityDr. Sharon Harlan, Arizona State UniversityDr. Jean Stutz, Arizona State UniversityDr. Darrel Jennerette, University California RiversideDr. William Stefanov, NASA

Grant FundingInternational Society ArboricultureNational Science Foundation

UVCC ProjectCAP LTER Project