Multi layer urban forest, Benefits of urban forest and how urban forests cool cities

Multi layer urban forest

What is multi layer urban forest ? Briefly review

Don’t think that urban forest are just about planting some trees in a row. A multi layer urban forest mimics the structure of native woodlands by incorporating different layers of vegetation. Overall there are 4 layers- 

  1. Ground layer with grasses, mosses and decomposers 
  2. Shrubs layer with shade tolerant bushes and small woody plants
  3. Mid story layer made up of medium height that thrives under partial sunlight
  4. Canopy layer formed by tall native trees that define the uppermost forest cover.

Benefits of urban forest : multi layer urban forest

1. Improve air quality 

Trees trap fine particulate matters (PM2.5), filter ozone and nitrogen dioxide and they absorb CO2. Overall helping in reduction of urban pollution load.

2. Stormwater and flood control 

Tree roots and forest layers absorb rainfall which reduce surface water runoff and soil erosion. It Decreases pressure on urban drainage.

3. Urban biodiversity Boost 

Multi layer urban forest support birds, bees, butterflies fungi and insects. It creates micro habitat and that’s rarely found in city parks

4. Noise pollution and reduction 

Multi layer urban forest involves thick and layered vegetation which serves as a natural barrier to traffic, construction and crowd noise.

5. Soil health restoration 

Leave litter and root diversity improve quality of the soil. It increase fertility, moisture retention, microbial activity and reversing urban soil degradation. 

6. Mental health and stress reduction 

When you are regularly expose to nature your cortisol level will be down which overall promote healthy and well being life. 

7. Community gathering spaces 

Forested areas encourages social cohesion and interaction. People can come together specially in density zones lacking in parks and open areas. 

8. Environmental education

Multi layer urban forest provide opportunities for  children’s and adults can learn about ecosystems, conservation and climate actions directly through interaction.

9. Heat relief for vulnerables 

Multi layer urban forest provide refuge from heat to the elderly, children and outdoor workers during extreme wether events.

how do urban forests cool cities
10. Lower cooling cost 

Dense trees cover reduce the urban heating Island effect. It cut down air conditioning use and electricity bills in nearby buildings. 

11. Increase property value 

Areas around greenery often seen 5-20% raise in estate values. A simple logic Because greenery increase the aesthetic looks.

12. Low maintenance green investment 

Once a multi layer forest is established it just required minimal upkeep which reduces the municipal landscaping expenses.

13. Green jobs creation 

When a proper multi forest is being established it requires maintenance, biodiversity monitoring and eco tourism programs which gives employment to the local residents.

How do urban forest cool cities

Providing layered shade 

A Study from Lawrence berkeley national lab found tree shades can reduce surface temperature by 11-25°C during peak summer days. Urban surfaces like roads, pavements and parking lots absorb and radiate heat. In multi layer forest the canopy layer works as a broad sun shield while shrubs layers block lower angle sunlight that penetrates single layered trees. In Ahmedabad India, zones with multi layer trees shows a 4.5°C reduction in temperature compared to barren areas( CEPT University 2021) 

Cooling through transpiration and moisture 

Plants cools their surroundings naturally through transpiration. This natural process absorb heat from the surroundings it’s just like how sweat cools our body. According to USDA forest service, 1 mature tree transpires around 380-450 liters of water per day and that’s equivalent of 5 aur conditionner running 20 hours. A layered forest increases total leaf surface area which means that there could be more transpiration from shrubs and other plants.

Blocking solar radiation across building’s height 

In dense urban areas solar radiation heats vertical walls, grounds, glass facades, rooftops and upper balconies. Single layer of street trees can protect only ground level but multi layer protect overall area vertical walls, rooftop lower floors etc. Research in Melbourne(CSIRO, 2019) shows that multi story tree rows can reduce solar radiation on buildings upto 60%, directly  lowering internal room temperature by 2-4 °C. Real life example- Singapore’s housing development board uses layered planting around the buildings to reduce facade temperature and increase thermal insulation.

Lowering wind speed

Urban wind patterns tends to trap heat between high rise buildings. However multi layer urban forest disturbs and diffuses wind flow creating a stable and cooler microclimate. It improves thermal comfort for pedestrians and limits dust and hot air circulation. The UN FAO reports that multi layer green buffers can reduce wind is velocity by 10-30%. Which helps in stabilizing local climate and protecting City from hot air. In Tokyo layered forest near transportation corridors showed a 2°C drop in surroundings. 

Multi layer urban forest

Reducing energy demand 

We know that multi layer urban forest naturally insulate building and public spaces which help in reducing dependencies on artificial cooling. Home and offices surrounded by trees requires less air conditioning. According to EPA USA properly placed trees can reduce household cooling cost by 15-30%, in commercial buildings it can reach $0.20 – $0.40 per sq. Foot. Los Angele’s cool city program planted layered vegetation and reported 20% reduction in energy demand.

Preventing heat absorption 

Traditional urban surfaces materials like Asphalt cement and stones have high thermal masses which means they absorb and store the heat and then slowly release them even after sunset. Bhai replacing them with vegetated ground layers we interrupt heat storage cycle. Bare concrete can reach 60-65°C in peak summer days on the other hand shaded or green mulched surfaces remains around 30-35°C, literally cutting down thermal masses into half.

Creating temperature buffer zone

 In compact zones high rise buildings reflects and amplify each other’s heat. Placing a multilayer forest Between these structure work as a barrier which reduce thermal stress on building’s and heat reflection. Research in Germany ( TU Munich) found that building surrounded by greenery stayed 2.5°C cooler internally. It also helps in increasing the lifespan of materials ulto 8-10 years. In Shaded urban zones urban thermal comfort index ( UTCI) improved by 12 points.

Where can be multi layer forest be planted ?

Now you know how do urban forest cool cities but how they are planted. Multi layer forest does not need a wide area their ideal for small under-used area. Hence In dense cities they can be grown along – Highway buffers and flyover slopes, metro rail corridor, schools and hospitals compound, lakeside and river fronts and near slum zones. Even small spaces 100-300sq.m can also grow a micro forest by using miyawaki method.

What challenges do cities face in growing multi layer Forest.

You might be thinking that if multi layer forest have this much of benefits then why every cities do not implement this. And here comes the real hurdle.

  1. Land scarcity, in most of Indian metro cities even civic bodies struggle to find land due to expensive rate.
  2. Soil degradation, construction waste and soil in cities make it hard for native trees to thrive. 
  3. Water , first one or two year require regular watering.
  4. Limited nurseries, there is a shortage of reliable native saplings species. 

Which cities has used multilayer forest

There are many cities which has used multi layer forest – 

  1. Melbourne, Australia as implemented layered forest to reduce urban heat by over 4°C in certain zones.
  2. Munich, germany is experimenting  with native forest in old industrial areas to boost biodiversity. 
  3. Singapore has integrated vertical and multi layer planting in its city in a garden approach.
  4.  Toronto, canada has adopted dense urban forestry in public housing zones to combat heat and social isolation.
  5. Barcelona, Spain has turned abandoned lots into shaded forest parks using diverse plant layers. 

How long does it take for multi layer urban. Forest

Multi layer forest grow surprisingly fast especially when native plants and dense miyawaki technique is used. Unlike traditional forest which take decades to be mature multi layer urban forest start cooling micro climate within 18 to 36 month. Shrubs and ground covers mature in 6 to 12 months. Sub-canopy trees grow rapidly and start blocking solar radiation by year 2. If you want to know about miyawaki technique visit this blog

Research in countries like Japan Germany and Malaysia has shown temperature reduction by 2-5°C in just few years around multi layered urban forest sites. The layered design also accelerate moisture cycling and Evaporisation. It boost its climate impact faster than sparse tree planting.

Final thought : why multi layer is smart investment ?

As in the current situation cities are fighting against rising temperatures, unusual climate change and declining biodiversity, it becomes important to have a nature based solutions. Multi layer forest offer not only patch of green but also a layered living system. Unlike the traditional tree planting method, multi layer forest is a high efficient microclimate generator that shades and transform the city.

Multi layer forest are proving that urban greening doesn’t require massive land area. With the right mix of ecological understanding, political will, and community engagement these forest can be implemented anywhere. Multi layer forest remind us that it is don’t have to be sterile, concrete wasteland. They can be vibrant, breathable and biodivers ecosystem where nature and humans coexist.Some important things to know 

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