Category: HortInsights

Assessing the Effectiveness of Urban Heat Reduction From Trees and Plants

Assessing the Effectiveness of Urban Heat Reduction From Trees and Plants

Many cities and regions across the world have now committed to expanded areas dedicated to greenspace to mitigate rising temperatures and the heat-trapping effects of the ‘urban heat island’.

The definitions of ‘increased urban green space’ include wider use of street trees, maintenance of remnant urban forests, green roofs and green walls, and other plantings that replace heat-absorbing surfaces such as concrete, glass and steel.

However, questions remain: how much area is needed to provide cooling? Which plants are most suited to reducing urban heat especially as both heating and moisture demands increase?


Some scientists have attempted to assess urban cooling by comparing the air temperature in parks with that of nearby streets, a simple measure that would assess an urban region side by side. One analysis from a range of other studies showed that there was comparatively little benefit, just 1.0 degree Celsius of cooling during the day and less at night (Bowler et al 2010) between parks and adjacent streets.

Two studies in Hong Kong and Manchester found that street trees offered greater cooling benefits than green roofs, and that mature street tree plantings with around five per cent density were sufficient to reduce the pavement temperature by one degree (and five per cent density from saplings was enough for half a degree reduction). As another point of comparison, replacing all vegetation with asphalt raised the surface temperature by 3.2 degrees Celsius, demonstrating the definite benefit from plantings (Skelhorn et al 2014).

Thermal image on the effects of trees on urban heat

Thermal image on the effects of trees on urban heat

Researchers at the University of Hull showed that the best measure of a tree’s ability to provide cooling could be determined by its water flow, which is measured using sap flow meters that assess evapotranspiration as water is moved from the roots to the leaves and outwards to the atmosphere.

A healthy, well-watered Callery Pear (Pyrus calleryana, a widely-used urban street tree in Australia and Europe) of around four metres in height could absorb around 60 per cent of the incoming solar radiation and offer a cooling benefit around six kilowatts (about the same as a mid-sized home air conditioning unit) (Ennos 2015).

Simple assessments of urban planting benefits provide mixed answers – the challenge for urban planners, landscape professionals and others in the quest for more greenspace is to account for the right area, type, selection and maintenance of urban greenspace that keeps its cooling benefits active and functioning.

This will require modelling and analysis across the engineering, urban planning, horticultural and other disciplines to provide a better assessment of the right planting mix for a given region.


  • Bowler D, Buyung-Ali L, Knight T M and Pullin A S (2012), ‘Urban greening to cool towns and cities: A systematic review of the empirical evidence’, Landscape and Urban Planning, Volume 97, Issue 3, 15 September 2010, Pages 147-155.
  • Skelhorn C, Lindley S and Levermore G (2014), ‘The impact of vegetation types on air and surface temperatures in a temperate city: A fine scale assessment in Manchester, UK’, Landscape and Urban Planning, Volume 121, January 2014, Pages 129-140.
  • Ennos, R (2015), ‘Can trees really cool our cities down?’, accessed on 19 April 2020, <>


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Power Plants: Can Electricity Boost Crop Yields?

Power Plants: Can Electricity Boost Crop Yields?

Could electricity help to reduce insect attack, boost yields and enhance the quality of fruit and vegetable crops? A series of research programs in China is underway using electric fields inside glasshouses, according to a profile article recently published in New Scientist.

Scientists are reporting that yields can be boosted significantly when the crops are exposed to a mild electric current, with yields of lettuce and cucumber increasing by up to 40 per cent. Research in Mexico using maize also reports that a mild electric current provided through soil electrodes increased the yield of the crop by over 85 per cent, a huge increase for a crop that feeds billions of people.

It is all a little bit mysterious. Research into the benefits of ‘electroculture’ is not new – experiments as far back as the 1880’s seemed to show that electricity stimulated crops. Finnish scientist Karl Selim Lemström was studying the northern lights in Lapland and noticed how well fir trees grew there, despite the harsh cold conditions. In his experiments on various crops, there were mixed results, but carrot and pea crops that he grew in France showed dramatic increases of 75 per cent and 125 per cent respectively.

Renowned English scientist J.H. Priestley replicated the experiments and also found that cucumbers increased their growth by 17 per cent, adding weight to Lemström’s claims. Oliver Lodge strung electric wires over a wheat crop which performed 24 per cent better than those without electricity. At the end of the First World War, the UK established an Electro Culture Committee that trialled cereals and potatoes, and despite apparent increases in yield of around 20 percent, they deed the cost of electricity to be too high to make these yields economical.

The renewed push for research in China came about more from a push towards sustainable and eco-friendly agriculture than yield gains. Some of the research showed that electricity deterred insects and even bacteria, as a result of the production of charged particles that ‘zap’ these pathogens.

Scientists remain uncertain as to the exact mechanisms by which electricity might stimulate plant growth. Some believe that electricity simulates the electricity generated by lightning, suggesting that the electricity is a precursor to the arrival of nitrogen-rich rain. If, however, the electricity appears without rain perhaps that causes the results where sometimes yields did not increase.

“The mechanisms that underpin these observations remain elusive. But there is definitely a very interesting interaction between plants and their electrical environment – time will tell how this might actually benefit agriculture”, says Dr Ellard Hunting from the University of Bristol in the UK. “In a nutshell, plants do respond to electric fields”, says Jean Yong at the Swedish University of Agricultural Science at Uppsala University. “It is logical that an electric field could speed up the flow of crucial nutrient ions like nitrate or calcium. But the research is inconclusive.”

Perhaps with the rise of electricity-generating films for glasshouses and cheaper solar panels, more research into electric crops might be on the way. Maybe you’ll get your vegetables free of charge?

The original article was published in New Scientist on 24 August 2019 by Donna Lu and David Hambling.


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Member Spotlight: Meet Christian Jenkins MAIH RH0157

Member Spotlight: Meet Christian Jenkins MAIH RH0157

Christian Jenkins MAIH RH0157 recently became our newest Regional Convenor for the Victoria region. Christian is a highly-regarded landscape design specialist based in gorgeous Grovedale, right near Geelong in Victoria. With its proximity to Port Phillip Bay and the Great Ocean Road, Christian services clients throughout Victoria.

With an impressive array of awards, Christian is well-known in the landscape sector. His designs have been recognised with two awards in 2019: the People’s Choice Award for the ‘Dreaming’ garden and the SILVER Gilt Award at the Melbourne International Flower and Garden Show, as well as Gold at the New Zealand Flower and Garden Show 2018 winning Design Excellence, and Horticultural Excellence Awards and Gold in 2017.


Christian Jenkins MAIH RH0157 landscape design specialist. Image: Christian Jenkins Landscape Design.


Hello Christian! Tell us how you started out and built up a successful career in horticulture and landscape?

From a young age, my home duties were mowing the three-quarter acre lawn with the push mower, long summers at the beach, and being surrounded by nature created my love of the outdoors. I applied for an apprenticeship as a curator at a private school and missed out – he explained that a job as a gardener would shortly be available. For the next two years l was based at the Ivanhoe Grammar School gardens, and I attended Burnley College studying Horticulture with a love of garden design.

I spent many years with a wonderful landscaper who helped me find my craft in construction, design and horticulture. In 2003 I created my first Show Garden at MIFGS – something happened at that time, being in this creative forum surrounded by a wonderful selection of 100 year old trees, next to the city, in autumn the energy is addictive!

This led me to creating nine garden shows in a row, returning to do another seven from 2015 with two in New Zealand. This forum allows one to create garden designs that are more playful than I would generally create for clients. The awards and exposure that MIFGS has given me has helped my career.


‘Japanese Garden’ This Gold Medal Winning Garden was constructed for the New Zealand International Flower and Garden show in 2017. Surrounded by a lush green tapestry of tropical plant life, this boutique resort style garden includes an island style hut with contemporary furnishings. Image: Christian Jenkins Landscape Design.


What inspires and influences your award-winning design solutions?

Last year’s design at MIFGS “Dreaming” featured a sculptural metal pergola in the shape of a leaf. I also designed and built a 1.7m high sculptural egg that was painted by an Aboriginal artist from Uluru.

Getting back to the question, I am at the stage in my designing career where nature inspires me, without a doubt the greatest designer of all! As we are all horticultural enthusiasts I am inspired daily. The wonderful forms of dried seed pods amaze me with their artistry and I often think I would love a life-sized pod in the garden or how I could make one. Finding a point of difference as a designer is always the challenge, and most of all I like to challenge myself with the design concept. I love architecture and my designs generally include an outdoor room or sitting structure of some sort.

My love of water is always included in my designs with the reflective qualities the water brings, the calming influences and the wonderful soothing sound constantly brings me back to working with this medium. Functionality is also a major priority for my gardens, and I ensure that people can always enter my gardens and go on a journey to a calming sitting place.

To win awards at garden shows you must be fortunate to have wonderful plant sponsors, so displaying a wonderful selection of plants and trees of the highest quality brings the design together, and generally securing my plant sponsor for a show will quite often determine the style of my garden. Last year at MIFGS I worked with Carl from Botanix Nursery, Joel from Tall Trees and Michelle from Established Tree Planters and with their enthusiasm and love for MIFGS that helped me make “Dreaming” a celebration of Australian native plants.


Award winning garden for the 2019 Melbourne International Flower and Garden Show. This Garden is called Dreaming and is a tribute to the native parts we are so lucky to have in Australia. This Garden won People’s Choice Award 2019 and the Gilt Award 2019. Image: Christian Jenkins Landscape Design.


What is your advice for fellow horticultural professionals in navigating a rapidly-changing world?

I really find this a difficult question to answer – the world is changing very quickly and both agriculture and horticulture will be relied upon and have even greater importance in the years to come. Making organisations stronger, more approachable and exchanging our knowledge with each other will be very valuable. To remain successful in our chosen field we must be constantly evolving as a business owner, improving our existing skill set, looking to strengthen areas for improvement.

The great thing about our industry is artificial intelligence won’t be able to prune the roses, our best practise comes from our home garden so keep experimenting at home, and putting ourselves outside our comfort zone always creates great results. The changing world needs to get back to basics, and the simple things in life bring the most enjoyment – our industry brings so much enjoyment to so many age groups.

What big trends do you think horticulturists should look towards in 2020 and beyond?

Rainwater harvesting is something we can all do, and my home in the Otway Ranges relies solely on rainwater. Both local councils and governments support rainwater capture for sustainability and resilience.

The connection between mental health and nature will only become more important every year, with wellness gardens to become more popular. Fruit trees need to be planted more often using dwarf varieties and our gardens need to be planted with thoughtfulness for our local wildlife. Overall the design style will be less and less formal – I would like to think naturalistic gardens will be more common than a structured garden, with plant selection becoming increasingly important with the harsh environmental conditions.

I think we need to experiment more with soil media in the garden with the standard garden blended soil sold by the landscape supply yards needing some clever input. The houses are bigger and the gardens are smaller so we must continue to be creative with the small spaces.


Check out Christian’s beautiful designs on his website and social media – visit and stay tuned for news and updates from our Victoria region.


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Andrew Prowse Landscape Architect Awarded For the Stunning Cairns Performing Arts Precinct

Andrew Prowse Landscape Architect Awarded For the Stunning Cairns Performing Arts Precinct

Images: Andrew Prowse MAIH RH0053

The Cairns Performing Arts Precinct by CA Architects, Cox Architecture and Andrew Prowse Landscape Architect with Cairns Regional Council has won Queensland’s top prize for urban design, the Minister’s Award for Urban Design.

The Precinct was once a place viewed as dangerous and unattractive, sited next to a major highway at the edge of the Central Business District of Cairns. Residents and visitors alike tended to avoid it and the few plantings mainly consisted of mature figs and little else. Now transformed into an incredible, vibrant precinct, it is rich in indigenous planting specimens, with showy foliage and flowers, lush tropical greens and carefully-planned architectural features. The result is absolutely stunning, an amazing transformation making the precinct a top Cairns destination.


Mucuna novo-guineensis – the New Guinea Creeper

“Our goal was primarily to maximise the difference between Cairns Performing Arts Precinct and the popular Cairns Botanic Gardens”, explains Andrew Prowse MAIH RH0053.

“We set out to create a unique and distinctive area that made the best use of tropical plant selections. With their fast growth rate and size, we built a structural pergola to direct their growth into pleasing arches that bring shade and overhead form. This pergola creates a vast outdoor gallery room with cameos of significant people associated with the park over the years and a selection of flamboyant foliage plantings giving the park a distinct local and tropical experience”, said Andrew.


Shower of Orchids Vine – Congea velutina


Jade Vine – Strongylodon macrobotrys, the milky green vine from the Philippines. These vines are only found in the tropics and rapidly form gigantic vines that grow up forest trees and along the rainforest canopy. Often seen at the edges of clearings.


The jury said the precinct offers a valuable, high-quality contribution to the urban fabric of the city, ticking all the boxes – it challenged the status quo, demonstrated leadership and design excellence, and will leave a lasting, sustainable legacy for the broader community.

The jury said “the seamless integration between theatre infrastructure within the parkland allows visitors to experience the open space all year round, even when performances are not scheduled, contributing to the civic life of the city. The beautifully-executed gabion rock walls of the parkland stage deliver a clear sense of performance and authority to the overall placemaking qualities of the space.”

The Registered Horticulturist membership is increasingly sought after as a marker of professional quality, and Andrew is proud to have led a project with such stellar outcomes.


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