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    STEP Matters 202

    Which Urban Trees can Survive a Changing Climate?

    There is lots of research demonstrating the benefits of trees in urban areas. Not only do they camouflage the grey asphalt and concrete of roads and footpaths, they can reduce temperatures and the need for air conditioning in buildings. They also improve the microclimate by retaining moisture in the air and soil and they encourage residents to get out into the community and enjoy beautiful shaded areas.

    Tree planting is an effective and efficient way to adapt to climate change. However as climate change leads to higher temperatures and more variable and lower rainfall we need to consider how the popular trees used in urban areas will respond to the changes.

    Different species have different levels of tolerance of heat, lack of water and other threats posed by climate change.

    Research teams from Macquarie University (including former STEP president Prof Michelle Leishman) and Western Sydney University, have embarked on a project called Which Plant Where. The project is supported by Hort Innovation Australia, the Department of Planning, Industry and Environment and the Australian government. Their mission is to find the best plant species for urban landscapes that will be resilient to climate change.

    The project works with the nursery industry to gather evidence on species’ resilience to extreme heat and drought by testing plants to their limits in research glasshouses. This work will inform plant growers and nurseries on how to adapt their business, by identifying the new challenges posed by climate change, as well as selecting diverse ranges of climate-ready species. They advise landscape architects, designers and urban planners about not only the best planting choices, but also how to increase the biodiversity of our cities.

    We need to know how our current tree canopy will be affected as well as plan new plantings.

    The research team recently published a study (Burley et al) that investigated likely climate change impacts on 176 of the most common tree species planted across Australian cities. The analysis showed more than 70% of these species will experience harsher climatic conditions across Australian cities by 2070.

    Some of the most commonly planted trees are unlikely to survive. Conversely, in some cooler climate areas, such as Orange, the number of suitable species may increase. These impacts will progressively worsen as climate change intensifies. A proactive approach is needed to identify new climate-ready species and plantings. Tree species growing in warmer cities are more likely to be affected than those in cooler cities. Some species, such as the golden wattle (Acacia longifolia) or the prickly paperbark (Melaleuca styphelioides) might not make it in northern cities unless we invest precious resources – such as water – to maintain these civic assets. Other species, such as the native frangipani (Hymenosporum flavum) or the tuckeroo (Cupaniopsis anacardioides) will likely become more suitable for planting in southern cities.

    Australian cities are blessed with a higher diversity of tree species compared to other cities globally. However, the 30 most commonly planted species make up more than half of Australia’s urban forests. This poses a great risk for our cities. If we were to lose one or two of these common species, the impact on our urban tree cover would be immense. Trees are a long-term investment that will be affected by the very factors that they are meant to mitigate. Consequently, our best insurance is to increase the diversity of our trees.

    The study highlights the need for more research:

    • which species experience a reduction in growth or, even mortality, during extreme weather events and the duration of any growth reduction
    • variation of impacts in different climate zones, for example subtropical areas are likely to experience greater declines in growth than temperate areas
    • whether it is feasible with some species to mitigate impacts by providing more irrigation, selective pruning or planting in a more sheltered position
    • investigate new choices of species suitable for the urban environment from the huge range of Australian native species

    The NSW government announced a plan in February to plant five million trees in Greater Sydney by 2030. They are counting trees planted in streets, parks, backyards, neighbourhoods and schools with an objective of increasing the tree canopy from 16.8% to 40%. Councils can apply for grants for tree planting projects. Individuals can register the trees they plant.

    Reference

    Hugh Burley, Linda J. Beaumont, Alessandro Ossola, John B. Baumgartner, Rachael Gallagher, Shawn Laffan, Manuel Esperon-Rodriguez, Anthony Manea, Michelle R. Leishman (2019) Substantial declines in urban tree habitat predicted under climate change, Science of the Total Environment 685, 451–462

    Australia’s Possible Future in 40 Years Time

    CSIRO Futures released a report in June on Australia’s future in the next 40 years, called Australian National Outlook 2019 (ANO 2019).

    The report is the outcome of a collaborative project that took two years involving more than 50 leaders from over 20 organisations across industry, non-profit and university sectors, including the National Australia Bank, Shell, Australian Red Cross, Monash University, the Grattan Institute and the Wentworth Group of Concerned Scientists. ANO 2019 uses CSIRO’s integrated modelling framework to project economic, environmental and social outcomes to 2060 under two scenarios in the context of responses to six identified future challenges. The challenges are:

    • risks and opportunities from the rise of Asia
    • technology development and implementation skills
    • climate change and environmental degradation – our response and that of the rest of the world
    • population aging
    • trust in government and business
    • social cohesion

    The report concludes that if we resist the changes needed to meet the challenges, essentially business as usual, the outcome is described as the Slow Decline. The alternative scenario of bold action is called Outlook Vision.

    In brief some of the environmental outcomes of the two scenarios are summarised in Table 1.

    Here is some context to the projections in the assumptions that have been made.

    Population Growth

    The report had to model a lot of information but the major factor has been taken as a given. They have assumed that population growth will continue on the current high path. Population will be 41 million by 2060 with Sydney and Melbourne growing to 8 or 9 million people and Brisbane and Perth growing to 4 or 5 million. That is an extra 16 million people in 40 years. Our population in 1980 was about 14.5 million. So by comparison the increase in the past 40 years was about 11 million. CSIRO expects this growth to be accommodated within our finite land and ecosystems.

    It is very sad that no mainstream organisation is willing to publicly countenance a reduction in population growth and demonstrate the implications this will have for our future.

    Water Supply

    Very little detail is provided about the costs of maintaining an adequate urban water supply for the burgeoning population. It seems the assumption is made that sufficient desalination can be installed. The cost of this is incorporated in the infrastructure costs of catering for the growth in population.

    Climate Change Scenarios

    This is what they say about the implications of climate change under the two scenarios (from https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018EF000922).

    The most reliable estimates aligned to the scenarios indicate that 4°C global warming without adaptation could lead to a global per annum GDP loss of 7.2% and an Australian per annum GDP loss of 1.6% by 2100. If mitigation can limit the global warming to 2°C by 2100, the global per annum GDP loss would be reduced to 0.5–1.6% by 2050–60 and to 1.8% by 2100, and the Australian per annum GDP loss would be reduced to 0.6% by 2100. The GDP loss would be further reduced by adaptation.

    There is a lot of detail in the modelling of the implications of climate change in the two scenarios. The quotation above gives a scale to the importance of reducing greenhouse gas emissions.

    Table 1

    table 1

    Land Use and Biodiversity

    Taking into account climate change and the need to maintain agricultural exports and feed our own population very radical change is envisaged under the Outlook Vision scenario. There is a strong message about the necessity to end the trend of rural land degradation and to restore ecosystems. Productivity improvements through plant genomics and digital agricultural mapping technology will not be enough. The statements about ecosystem health are significant in the context of the current federal and state governments’ attitudes towards exploiting the environment. Here are a few quotes from the report:

    … the high agricultural productivity rates necessary for the Outlook Vision outcomes will not be possible without sustaining broader ecosystem health, particularly in the face of effects associated with a changing climate.

    … agriculture not only affects the environment but is also highly dependent on the quality of natural assets and the ecosystem services they provide for its productivity and profitability.

    Soil Health

    The report highlights the negative trajectory of soil health that has resulted from intensive agriculture on fragile soils. Several aspects of current soil health will limit productivity, particularly long-term erosion, acidification, low carbon levels, soil compaction and soil nutrient decline. The risk of erosion increases with an increasing frequency of droughts and lower groundcover. Ecosystem and land management practices must turn around the deterioration of soil health.

    Agriculture is also dependant on access to a reliable supply of clean water, pollination services and shade and shelter provided through native vegetation. Land degradation needs to be halted and, where possible, remediated to ensure the long-term viability of agriculture.

    New forms of investment that provide financial support for carbon farming are recommended as a means of providing a return to landowners for the benefits of improving ecosystem services.

    Emissions Reduction through Carbon Sequestration

    Under Outlook Vision carbon sequestration will play an essential part. By 2060, up to 30 million hectares – or roughly half of Australia’s marginal land within more intensively farmed areas – could be profitably transitioned to carbon plantings, which would increase returns to landholders and offset emissions from other sectors. The success of this scenario depends on increases in productivity so that less land is needed to produce the required food. Table 2 shows the potential sources of change from the current annual emissions of greenhouse gases of 532 million tonnes under the Outlook Vision scenario.

    Table 2

    table 2

    In theory there could be an excess of carbon sequestration that could be sold on the international carbon market. However it would be more prudent to keep this stored carbon as a buffer against bushfire and other risks.

    Out of the 30 million hectares 11–20 Mha is defined as environmental plantings rather than direct carbon forestry (i.e. native–endemic mixed environmental plantings that provide the most suitable habitat for biodiversity). This will build resilience against future climate change. This translates to between 12 and 24% of intensive agricultural land (or between 32 and 42% of the total land area used for carbon forestry). The overall transition of land use is shown in Figure 1.

    The wide range of returns to landowners of $42 to 84 billion in Table 1 is indicative of the complex interplay between the impacts of climate on modelled agricultural production and tree growth, among other factors. The modelling results show that additional income from other land use change can more than offset any reductions in agricultural production due, in part, to the fact that agricultural production will be concentrated on more productive land, with less productive land transitioned to other uses. However the returns to landowners are affected by carbon prices that will be dependent of the level of global cooperation in reducing emissions.

    oz in 40 years

    Carbon and environmental plantings on this scale are a significant land use shift, and so require careful planning, consultation and engagement with the community, particularly regional communities. Such considerations will include protecting prime agricultural land for food and fibre production and avoiding adverse effects on water supplies.

    Conclusion

    CSIRO has produced several of these big picture reports before:

    • Future Dilemmas: Options to 2050 for Australia's Population, Technology, Resources and Environment in 2002
    • Balancing Act: A Triple Bottom Line Analysis of the Australian Economy in 2005

    Where are they now?

    The Morrison government has been re-elected despite having a very limited set of policies for change. We need a government with a long-term vision and a willingness to explain convincingly the reasons for change. We should be able to reach a consensus despite there being some losers as well as winners.

    Buy a Bundle of Books and Save

    This is a great opportunity to do some Christmas shopping. We have decided to reduce the price of our books if they are purchased in a bundle.

    Postage costs about $11 but it is free to pick up from South Turramurra.

    Contact This email address is being protected from spambots. You need JavaScript enabled to view it. for more information.

    Book bundle 1 = $25 ($17.50 for members)

    • Field Guide to the Bushland of the Lane Cove Valley +
    • Sydney's Natural World +
    • Understanding the Weather

    This is a saving of $45 (or $31.50 for members)!

    Click here to order 

    Book bundle 2 = $80 ($56 for members)

    • Book bundle 1 +
    • Rocks and Trees

    This is a saving of $50 (or $35 for members)!

    Click here to order

    2040 – Join the Regeneration

    STEP is supporting the screening of the film 2040 at Roseville Cinema. Booking is essential. We need a minimum of 68 bookings before the screening can go ahead. Your payment will be refunded if this number is not reached.

    The previous screening organised by Ku-ring-gai Council in July was booked out.

    2040 is a hybrid feature documentary that looks to the future, but is vitally important NOW! Award-winning director Damon Gameau (That Sugar Film) embarks on journey to explore what the future could look like by the year 2040 if we simply embraced the best solutions already available to us to improve our planet and shifted them rapidly into the mainstream.

    Structured as a visual letter to his 4-year-old daughter, Damon blends traditional documentary with dramatised sequences and high-end visual effects to create a vision board of how these solutions could regenerate the world for future generations.