Thursday, May 19, 2016

Don't be bullied - the science is on your side!

Landscape Architects and Parks and Gardens people in Perth are afraid.

They're afraid that if they don't recommend native trees they'll be considered "environmentally-insensitive".

Well my friends, be afraid no longer!

The jury is in: going all-native is a BAD idea.

In fact, we can now safely say that if you recommend native-only, YOU are not being environmentally-sensitive!

Diversity is king and that means using both natives and exotics in good measure. Until now this has made good sense purely from a pest and disease risk-mitigation perspective. But it's even more imperative now from a climate change perspective. A hotter, drier climate could significantly impact our local flora and if we're soley dependent on it for our urban forest we could end up in a bad way.

Don't be intimidated any more by those who refuse to see this. You are quite right to be using a tree palette which includes exotics"Native-only" is yesterday's news and those who advocate it are out of touch.


  1. Grayden I agree completely!
    However, the big issue that I'm facing in getting exotic trees into verges is the nutrient load from leaf litter.
    See this from DoW:
    "the Department of Water strongly recommends the use of non-deciduous native trees in streets and parks (Chapter 7, page 100 of the Stormwater management manual for Western Australia (Department of Water 2004–2007), because:
    • Deciduous trees drop large amounts of leaf litter that clogs up and interferes with the performance of stormwater infrastructure.
    • Seasonal leaf drop by exotic deciduous trees releases large amounts of nutrients into drainage systems. This adversely impacts water quality in waterways (refer to Water Note 25: The effects and management of deciduous trees on waterways (Water and Rivers Commission 2002). Even deciduous trees located a long distance from the nearest water body can deliver large amounts of nutrients and organic matter via artificial (traditional constructed) drainage systems.
    • Local native plants require less irrigation and maintenance (e.g. little or no nutrient or pesticide application) than exotic species which reduces risk to receiving water environments.
    • The seeds of invasive non-native tree species can be dispersed via drainage networks and invade wetlands and waterways degrading these habitats.
    Native trees provide habitat, food resources and nest sites for native fauna, and may act as corridors allowing mobile native species such as birds, insects and possums to move safely through residential areas to patches of native vegetation including waterways foreshores, thereby supporting biodiversity in urban areas"

    See the references are quite old so we need some new science to confirm/refute this position I think. Have you seen anything around?

    1. Hi Katherine

      The answer to autumn leaves getting into stormwater drains isn't to abandon deciduous trees - they have too much else going for them. The answer is to sweep the streets more often! Problem solved.

      You're right, these statements sound a bit old now. A quick Google search will find plenty of information about the need to use both natives AND exotics to build a resilient urban forest.

      The statement that really makes me smile though is that "local native plants require less maintenance". That clearly wasn't written by someone who has had to manage them! Australian street trees often require MORE maintenance than the old-fashioned exotics like Plane, Liquidambar, Poinciana etc.

      For your info I also talk about this in an earlier post called "Ideology vs Reality):

      Hope this helps. Thanks for your input!