Wednesday, January 6, 2016

Street tree spacing should equal canopy diameter, no wider

If you plant street trees too far apart the end result is not so much an avenue as a collection of individual trees.

Something like this:





The spacing required to achieve an avenue is surprisingly close.

Here's the rule of thumb:

Spacing = canopy width*

At this spacing the canopies will theoretically touch at maturity but in reality they will still feel slightly separate because two circles only touch at a single point. This means you still get the alternating light and shade patterns that make a street such a pleasure to be in.

The streetscape will now look more like this:





Using this as a guide, street tree spacings on the Perth sandplain should be something like this:

WA Peppermint (Agonis flexuosa)              10m
Jacaranda (Jacaranda mimosaefolia)           10m
Poinciana (Delonix regia)                            12m
Liquidambar (Liquidambar styraciflua)         15m
Flame (Erythrina x sykesii)                         15m
London Plane (Platanus x acerifolia)          18m

And these are maximum spacings. Planting even closer will still result in a good streetscape but any wider and the avenue effect starts to break down.

BOTTOM LINE: we are still planting too wide in Perth!

We must get away from the one-tree-per-frontage mentality and start using the canopy width* of the tree as our spacing guide.

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* By this I mean the canopy width the species will achieve in the location you are planting into. This is important. Don't go by what the tree does in the wild or in a well-watered garden. Trees rarely achieve those dimensions in the tough environment of a city street.

2 comments:

  1. Thanks, Grayden.

    In our suburb (Nedlands) I have noticed that the trees are planted very far apart; no chance for a decent streetscape sadly!

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    Replies
    1. You're right Sean - and that's one of the reasons much of Nedlands doesn't have the "leafy" feel of neighbouring Claremont which, generally, has much closer spacings. (The other reason is that Claremont just has more BIG trees I would suggest.)

      The good news however is it's easily fixed by interplanting!

      I suggest you petition your Council with as many signatures as you can get from your street. (Having sat in the Manager Parks and Gardens chair, I can tell you they will be more supportive if they can see they're not going to run into a maelstrom of protests ;) ). Ask them to interplant your street to start with and hopefully there will be a flow on effect to others.

      Good luck with it and I would love to hear how you get on.

      Regards,

      Grayden

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