Thursday, October 1, 2020

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Home Issue 18 The elusive goal of deep shade in Alice

The elusive goal of deep shade in Alice

 
 

“Carbon sequestration is a co-benefit of the precipitation-recycling and cooling power of trees. As trees process and redistribute water, they simultaneously cool planetary surfaces.”

 

– Dr David Ellison *

 
COMMENT by PIP McMANUS
Last updated Thursday, 5 December 2019, 4.20pm. Links added.
 

Most days I walk along the shaded footpath which runs from the Wills Terrace  foot bridge to Schwarz Cres along the eastern edge of the river bed.  For many years now this lovely walkway (pictured above) has been becoming ever less shady. One morning this week I counted 42 dead or dying big trees along this short stretch.

 

Fortunately the native trees are doing well; the non-natives, particularly the Rain Trees and Pepper Trees all seem destined to die. It is not clear whether this creeping necrosis, which is signalled by a pale grey change in bark colour moving up the trunk, is due to disease or lack of water. 

 

Many locals have been dismayed too at the sudden loss, all around town, of magnificent mature Jacaranda trees (pictured below)  which have been unable to cope with prolonged drought.  Several beautiful specimens in the mall near the Flynn Church demonstrate this telling change in the bark along with shedding of dead branches.

 

So are we to abandon non-native trees and the dense shade canopies they afford in the face of long summers which appear destined to be hotter and drier? There is no argument that naturally adapted desert plants survive well in our arid environment but just as we choose to seek air conditioned interiors during the heat of the day, when we venture outside we seek dense shade and green lawn areas which are provided predominantly by exotic plantings.

 

The Stuart Highway features a significant and welcoming avenue of mature native trees. One has to wonder if the recent culling of a large number of these fabulous trees near the northern entrance to town was really a necessity. No warning, no discussion just suddenly they were decimated.  

 

We live in a town where many ancient trees and rocks have sacred site status. On a global scale some countries are granting legal rights to natural ecosystems (lakes, rivers), rights to exist and flourish. The destruction of these magnificent trees along the highway resonates with the attitude of  a consumer oriented society in which the natural world is automatically subordinate to the demands of urban efficiency. Could there not have been a compromise by widening the road from one side only, keeping a very narrow median strip and moving the eastern footpath further east, meandering perhaps through sections of bush?

 

From what I have observed there is ample space to do this, but it would mean a more considered and unconventional approach to standard road widening policy – God forbid! The Alice Springs Garden Cemetery in contrast is a refreshing oasis of flourishing greenery, a testament to considered plantings and observant care.

 

A request to meet directly with any relevant staff at the Town Council to discuss their tree policy was unsuccessful, though I was provided with a number of links to policy documents – most of which concentrate on statistical data.

 

While the Alice Springs Town Council’s Climate Action Plan 2018- 2021 has formally recommended 42 actions for the mitigation of and adaptation to climate change, these are largely in the area of renewable energy, lighting and power use efficiency. There is little if any mention of the role trees and gardens play in heat mitigation. 

 

It is great to see inclusion of  passive energy saving measures such as pool blankets, and an action ensuring new building are appropriately insulated and shaded. Local and NT governments must lead the way in respect to passive cooling measures but one only has to look at the ongoing construction of wildly inappropriate hotboxes (minimal or no eaves or verandahs , dark  metal cladding, basic insulation, poor orientation, glass cladding – The Supreme Court building!) to know that meaningful passive cooling has a long way to go.

 

It will only arrive when there is a mandated change in building codes which actually address our specific climatic conditions. Of relevance: one of the listed “actions” in council’s Climate Action Plan , no 6.5.37, states: Lobby the NT Government to provide strong leadership on climate action.

 

The NT government has committed $15 million dollars to Mparntwe/Alice Springs for CBD revitalisation which one would hope will include significant expenditure for greening our town.  The design and documentation works for this project were due to be completed last month and include shade structures and cooling initiatives, identified in the design tender awarded to GHD Ltd engineering for the first phase. 

 

Despite a number of direct inquiries to GHD and to the project supervisor and media manager  at DIPL (Department of Infrastructure, Planning and Logistics), I have not been able to find any more detail regarding this major proposal. The Katherine CBD revitalisation plan by Ashford Group Architects (Darwin) on the other hand, reveals a detailed vision (a six-minute video is easily found) following extensive consultation with community groups, and includes a transformative focus on re-greening the town.

 

This newspaper has reported on a number of occasions on the loss of nearly 1000 trees last summer. Are we to expect a similar lamentable loss by the end of this summer? The cost in dollar terms, not to mention the decades of growth time required to nurture a replacement young tree to maturity, could be readily avoided by a more vigilant attitude towards those trees which are well established but may manifest signs of sudden or gradual heat stress.

 
Right: The vines were removed from this walkway many years ago and have never been replaced. The tree died last summer and is still standing.
 

Local gardening expert Geoff Miers urges us to consider the key value afforded by trees with big canopies because of their multiple benefits –  shade, colour, coolness. Whether Australian natives like the Burdekin plum or exotic favourites like the Jacaranda, the Ilawarra Flame Tree or the Poinciana, their spectacular displays in bloom can transform the feel of a town.

 

Dense groupings of native shade trees such as Whitewood and Bottlebrush can provide windbreaks and refreshing colour and shade.  Native tree canopies are less dense than exotics but an intelligent mixture of both makes sense. Corridors of dense tree shade would encourage people to walk, lower air temperature, reduce people’s exposure to UV radiation and give direct shade to buildings.

 

The NT government commissioned a heat mapping and heat mitigation study carried out in 2018 by a team from the Faculty of Built Environment at the University of NSW. As result of this study’s recommendations the City of Darwin is  undertaking measures to mitigate urban heat sink in Darwin with a trial project in Cavenagh St.  A 55 meter shade structure across the entire street is projected to be covered with green vines. Other cooling recommendations include lightening surface treatments, and installing instant planter boxes of medium sized trees and vertical green walls.

 

The same UNSW team also carried out a heat mapping study in Mparntwe/Alice Springs.  This study revealed that the average difference in surface temperature between street pavements and green areas (or reflective roofs) is of the order of 22-24 ºC. Trees produce lower reflected solar radiation than areas like pavements, dark asphalt or metal shade structures, combining the beneficial effect of vegetation with shading.

 

The specific plantings and approach will certainly require relevant changes for our desert climate but the fundamental proposition is the same –  smart environmentally sustainable heat mitigation initiatives which do not rely on closing people away in energy guzzling concrete boxes, but rather create naturally appealing spaces where passive cooling is paramount.

 

In the late afternoon I often take the river walks to the Telegraph Station. On these blazing days when the hills are still reflecting unwelcome heat I am constantly surprised by how noticeably cooler it is to suddenly dip down into a narrow dry creek crossing. Even half a meter beneath baking ground level there is a refreshing difference.

 

It’s ludicrously simple. Hot air rises. We all know that. But why do we not create parks and public spaces with sunken gardens. Within traditional urban desert cultures, in places such as Iran, Dubai, the  Middle East and North Africa, vernacular and public landscaping has employed central courtyards, water elements and sunken gardens in order to create cool, green living spaces protected from winds and sandstorms.

 

Paddington Reservoir Gardens (pictured) in Sydney is an award-winning re-imagining of a public industrial site which features a delightful sunken garden, a calm, cool space in the middle of a huge city.

 

For many of us who call Mparntwe/Alice Springs home the prospect of innovative and sustainable urban greenery measures could be a key factor in our decision to stay.

 

So imagine if you will parks, gardens and pedestrian linkages in Mparntwe/Alice which feature dedicated channels or gardens, gently sloped grassy banks, oriented to catch winter sun but also to funnel a cooling breeze in summer, to capture runoff and to water sheltering clusters of healthy trees –  places to stroll comfortably or to sit a while in deep shade. 

 
 

* “Trees, forests and water: cool insights for a hot world” by Dr David Ellison,  Swedish University of Agricultural Sciences, in Global Environmental Change, vol. 43, pp. 51-61.

 
 
 

16 COMMENTS

  1. Good luck getting anything changed at council in relation to tree planting. They are still stuck on planting trees 2 feet from the gutter on every street. At a rate of 700 a year.

  2. Hear, hear, Pip. It seems little or nothing has been learned or adapted from so many cultures that have not only maintained but flourished in locations not dissimilar to ours for centuries prior to industrialisation. I join your cry for tree health and the grand hope of public sunken gardens. We visit family in Deniliquin each year. Sure it’s blessed being on the banks of the Edwards River but more than a century ago, magnificent adjacent water gardens were created, surrounded now, by equally impressive trees that exemplify all that your thoughts might hope for.

  3. The council is replacing trees but not adequately watering the new ones.
    If I had not stepped in and watered the 7 new trees in my street they would all be dead by now.
    Also, they should be removing all the dead and now dangerous trees in our town.

  4. Good to hear I am not the only Alice local worrying for the health of existing trees this summer.
    After finally managing to meet with relevant DIPL staff today I can report that the CBD revitalisation plan does include shade structures and new tree plantings for major exposed streets in the CBD.
    Beyond that there is little detail available at this stage and no indication of developing new shady parklands.

  5. I also plant a lot of trees and water them at my own expense.
    They provide a town with peace and beauty.
    It’s not necessary to have the hot house surrounded by dirt here.
    Start by planting a number of shade trees and water between 8 and 11 during the heat.
    Cools everything down, de-stresses the house ambience, cleans the air, helps control the dust and keeps us all sane.

  6. As I said in a previous post: For our part, we have five trees at the front of our rented Northside home.
    At least once a year we put pea straw at their base and at least a bucket of grey water to each tree a fortnight.
    It takes very little time and effort and, hopefully, keeps these trees in good shape through our increasingly hot summers.
    There is no reason to be constantly depending on the Council to do everything when we, as citizens, can also pitch in and help.

  7. Thanks, Pip, for your timely raising of this issue as we enter another long and hot summer.
    Quite apart from Council’s inept attempts at addressing the tree deaths of last year, it may be helpful to consider whether falling groundwater levels in the Town Basin are contributing to the tree losses.
    Water Resources Division’s Technical Report No 6/2019A, “Alice Springs Town Basin: Groundwater level assessment” , by M.A.Short, dated April 2019, states that:
    “Groundwater levels recorded at many key monitoring bores within the Alice Springs Town Basin aquifer are (as of April 2019) at their lowest levels in recent history, and have declined below their previous low levels recorded during 2008-09 at many locations.”
    The report attributes the falls to an imbalance between extraction, by parties such as the “golf club, parks, schools and other green spaces”, and insufficient re-charge resulting from the current period of reduced rainfall.
    All of this points to the fact that greening up our town requires a multi-pronged approach that will only stand a chance of succeeding if and when all contributing factors are considered.

  8. @ Domenico Pecorari (Posted December 10, 2019 at 11:02 am): Isn’t this a telling observation: “Groundwater levels recorded at many key monitoring bores within the Alice Springs Town Basin aquifer are (as of April 2019) at their lowest levels in recent history, and have declined below their previous low levels recorded during 2008-09 at many locations.”
    The year 2009 is currently the driest on record for Alice Springs – the total for the year was 76.8mm, and about 5mm less than the previous record set in 1965, the last full year of the 1960s drought (and it’s not generally remembered there was widespread tree mortality across the region during the early 1960s).
    The town basin provided the water supply for Alice Springs at the time, and restrictions were a normal part of life.
    So far this year only 53.4mm of rainfall has been recorded at the Alice Springs Airport, and there’s only three weeks left to go.
    That’s only a smidgeon above two inches of rain for the year, and almost an inch lower than the 2009 total.
    There is a high probability that the record for driest year in the Alice won’t just be broken, it will be smashed out of the ball park.
    We also need to take into account the hotter weather we’ve experienced for longer periods of time which means that evaporation rates are substantially higher.
    Small wonder that trees are struggling.

  9. We should be trying to capture and store as much of the rain as we can from our own rooftops when it does rain to ease the burden on the groundwater levels, with rain water tanks.
    If you drive around town and look many houses don’t even have gutters on them.
    Some governments and councils interstate make it mandatory for a rainwater tank on new buildings or offer a rebate to have a rainwater tank connected to the house.

  10. Still manage to pump litres onto the ovals around town. Surely the council will have to stop watering at some point.

  11. Chiara, I could not agree more re we residents taking on a more proactive role around individual trees located near where we live, which may be heat stressed.
    It’s not entirely up to the council, but a formal policy which encourages locals to adopt trees in their street and report to council trees which are suffering could make a big difference.
    No argument either with Alex’s report on critically low water table. A more calculated use of sprinklers (capture run off in sunken gardens and sloping banks) can create concentrated areas of cooling greenery – mini oasis in strategically located sites.

  12. The ponds do have a recycled water component, about a million litres a day is treated and pumped into an aquifer for potential later reuse.
    Power Water Corporation has stopped pumping from the town basin due to basin water levels being critically low, but has the golf course stopped?
    I hope the street trees get a big top up to get through this summer!

  13. I live rural and a little while ago we have put all our trees back on drippers (water bill is not too bad). Most of my trees are over 20 years old and I don’t want to see them die.

  14. Where the hell are the water trucks?
    I water the trees in our short street, running out 50 metres of hose and then use a bucket to water the last of them.
    Around the corner is a line of dead or dying trees.
    Everywhere residents are not watering them our street trees are in a terrible state.

  15. Sad to see a lot of old established Kurrajong trees along roads dying off plus other significant non native shade trees.
    Replanting of drought tolerant shade trees around town should be considered, I remember there use to be lots of magnificent Athel pines and Tamaris trees around town but have been removed for some reason.
    Athel pines are a good choice as they grow easily and provide nice shade and Peppercorn trees as well.

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