Forests and climate change

Urban forests and climate change g Challenges and opportunities

• Forests are part of the solution • 4th Assessment Report of the United Nations Framework Convention on Climate Change (UNFCCC, 2007): – “sustainable sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks, while producing an annual sustained yield of timber, fibre or energy from the forest, will generate the largest sustained mitigation”.

• How about urban forests?? Cecil C. Konijnendijk [email protected]

Contents • • • •

Climate change and urban forestry Impacts of climate change on urban forests Mitigation of climate change by urban forests Buffering effects on the results of climate change • Educational and symbolic roles of urban forests in the climate change debate • Conclusions

Climate change and urban areas • Urban areas are main polluters and have a large carbon footprint • Urban areas are heavily affected by the results of climate change – Urban heat island effect is worsened – City centres are often ‘deserts’ in terms of microclimate due to the many hard surfaces

• Most people live in cities and towns today

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“Playing Field” of Urban Forestry

Urban Heath Island

The Urban Forest Individual trees

Tree groups and small woods (e.g. in parks)

Urban & periurban woodlands

Policies, planning, form and design

Technical activities, including selection and establishment

Management

Source: Oke (1994), in Sieghardt et al. (2005) Modified from Konijnendijk & Randrup (2002) Urb. For. & Urb. Green. 1:1-4.

Source: Thomas Randrup

Urban forest are affected by climate change • • • • • •

Changes in temperatures, humidity, wind, etc. Higher levels of smog and air pollution Impacts on growing conditions, species choice Extreme weather conditions, hurricanes, flooding Expected increases in (invasive) pests and diseases Urban-wildland interface: more frequent fires

Wikimedia Commons

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Compensation Forests

Urban forests mitigate climate change (1) • Do urban forests sequester carbon? • YES, see various studies: – United States: 93 kg C/yr for large, healthy trees – 1 kg C/yr for small trees (Nowak 1994, 2006) – Beijing urban forest: 0.2 million tons of C stored by 2.4 million trees (Yang et al. 2004) – Roots store 17-23% of carbon (Nowak 1994; Johnson & Gerhold 2003)

• BUT, direct contributions are still relatively small: – Considering present emission trading etc.: only few, specially designed urban tree projects are cost effective (McHale et al. 2007)

• FACE Foundation in The Netherlands www.stichtingface.nl

• “Help abate enhanced greenhouse effect by planting and protecting forest” • Funded by Dutch electricity generation board • Total of 50,000 ha of plantations, mostly abroad • Very first project: urban forest near Leeuwarden • 312 ha on local authority land

Urban forests mitigate climate change (2) • Some of the problems with urban trees and carbon sequestration: – Low survival rates of urban trees – many stresses – Not many large trees (short life span) – Dead/removed trees: within 1 year, up to 80% of carbon is released (McPherson &

Buffering climate change effects (1) • • • • •

Reduce flooding Reduce air pollution Cool temperatures Shading Buffering of extreme winds

Simpson 2000)

– High costs of urban tree planting and management (while carbon credits still have a low value)

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– Trees close to buildings: shading, reducing wind – Cooling effects and air conditioning

• Moderation of urban micro-climates

– Shading, evapo-transpiration, etc. – Microclimatic conditions important for comfort and recreational use (air temperature, wind speed, cloud cover)

(e.g. Eliasson et al. 2007)

– Urban trees and ‘climate sensitive planning’ (Eliasson et al. 2007)

Max surfa ace temp (deg C)

Nowak 1993, McPherson 1998)

ce di en nt re er h strib ma gy ig u nu re p r h d tio fac tai n od en & tu l uc sit s rin t io y r t o g n e s r ag & id e re dist e nti fu r ib a l se u d t io m isp n aj os or a ro l ad s m ed r of a il m ium fic in h e o er de sp s al n it a w sit lo ork y re airp ls w in s o de gs ide rts ns & nt ity qu ial d re ar r wa isu sid ie te se d en s rs & to d sc tial r e h un ag e rel o o im & ict ls pr tr la ce ov ea nd m ed tm et fa en er ie a rm t s llo la fo & tm nd rm cr e al e m nt fo op a to s e r im ma n s ria l in pro rec pac fo ve re e re rma d f a tio m l o arm n na p nt e n lan co sp d un a c riv tr ys e er id e , wo can od al la nd

Time of max temp

max surface temp

30

25

10

5

0 13:06

13:06

13:06

13:12

13:12

13:12

13:18

13:18

13:18

13:06

13:18

13:18

13:48

13:54

13:12

14:30

14:18

14:36

14:36

13:18

15:00

13:12

14:48

15:12

15:00

15:00

15:30

15:42

Buffering climate change effects (2)

0.9

20 0.8

0.7

15 0.6 0.5

0.4

0.3

0.2

0.1

Evapotrans spiring proportion

• Reducing energy needs for cooling and heating (e.g.

to wn

Adaptation to climate change in the urban environment

ASCCUE

1961-1990 Surface Temperatures

(Greater Manchester)

1.0

0.0

UMT

evaporating fraction

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Some ASCCUE findings

Copenhagen Metropolpark (1)

(with thanks to S. Pauleit & colleagues)

• Green space can moderate temperatures in residential areas & town centres • Mature trees critical for shading • Water W surfaces f stay cooll during d i drought d h • Green space on its own less effective in regulating surface runoff expected with climate change… • …but most effective on high infiltration soils

Education and symbolic role of urban forests in climate change debate

Source: SLA Architects http://www.metropolparken.dk/

Copenhagen Metropolpark (2)

• Urban forests have important educational functions – Raising public awareness – Learning how to deal with climate change (e.g. species choice for different conditions)

• One of the arguments mentioned by SLA Architects: “If we plant 3,000 to 4,000 trees, this will result in a significant reduction of CO2”

• Urban forests have important symbolic functions – – – –

Climate change mitigation at people’s doorstep Climate change mitigation where most emissions occur Facilitating local action, acting as a ‘flagship’ Action in the centre of power and the political debate

Source: Politiken, cartoon by P.M. Otzen

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‘Klimaatbosjes’ - Netherlands • Campaign hier.nu (here.now) – “The Netherlands climateneutral” • Establishment of climate woods with at least three walnut (Juglans regia) trees • High profile locations • Involvements of schools, companies • Sequestering CO2, but mostly symbolic

Conclusions (2) • Urban forests play a very important role in reducing the effects of climate change – Keeping cities liveable through cooling, shading etc.

• Urban forests can have important educational and symbolic functions in the climate change debate – Mitigation at people’s doorstep; making climate change visible

• Importance of selection of the right trees • Climate change is only one aspect of multifunctional urban forestry!

Source: www.hier.nu

Conclusions (1) • Urban forestry and climate change have close links • Urban forests are affected by climate change in different ways – E.g., storms, higher temperatures, drought, pests

Thank you!

• Urban forests help reduce the effects of climate change in urban areas – although direct mitigation effects of urban forests are relatively limited

[email protected]

• Urban forestry projects are not yet attractive for investors – but carefully designed projects and evolving credit markets will help

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