Sunday, January 24, 2016

Why "local indigenous" isn't sound logic

A lot of people call for the street trees in an area to be the locally indigenous species - ie the trees that were there before the city was built. The logic is that they are perfectly adapted to the local conditions.

This sounds logical but it's not.


Because "the local conditions" have changed so drastically.

As soon as you build a city you change everything; the topography, the vegetation, the soil, the drainage, the temperatures, the winds….everything. Nothing even remotely resembles the conditions that were there before so it's totally unreasonable to expect the local indigenous trees to perform as they did before.

The City of Sydney Street Tree Masterplan puts it this way:
Whilst locally indigenous species may be the most appropriate for local environmental conditions, the growing conditions within the urban environment are often now very different, particularly in a street situation. Disturbed soil profiles, compaction, higher nutrient status, altered drainage patterns and paved surfaces are just a few of the problems with which urban trees must contend.

Cities are a completely artificial construct. The avenues of trees that shade them (usually) need to be the same.


  1. A great article. So much has changed in cities around Australia that makes local indigenous species potentially problematic. But I think you need to nuance your position a little more to take into account that many urban situations are not that profoundly altered. Perth is almost certainly a special case, between the massive reduction in rainfall in the last thirty years, the intrinsically harsh conditions and the various aesthetic and other challenges presented to city dwellers by the indigenous tree species. But this really doesn't hold on a national basis. I'd like to see you qualify your argument to take into account the wide range of conditions and contexts, many of which will still provide excellent conditions for local native species.

  2. Agreed, I should clarify that I'm talking specifically about street trees. And I think the argument DOES hold nationally - the City of Sydney excerpt shows that. Urban streets bear virtually no resemblance to natural local conditions yet it is these very streets - or artificial landscapes like them - that councils' "Landscaping Guidelines" are aimed at.

  3. I agree the landscape has altered! Native trees dont like compaction under them, added fertilizer! Solutions are underplantings with local plants, it's called a nature strip! Reduced fertiiser use is good for our waterways as well! Let alone some support for our dwindling bird population! Even the insects provide control for pesky insects in our gardens!
    Our black cockatoos are in crisis! Maybe we should plant a few deciduous pecan trees for them? This would keep some people happy!
    Why not use a variety of trees in the one street? Alternate locals with decidusous!
    I have been photographing when the London Plane tree leaves turn brown in Mosman Park if they are not watered! It is getting earlier and earlier in February each year! That's not many months of cool green! Not that I would ever advocate London Plane trees unless I wanted to be sued as the World Health Organisation says "dont plant them because of the almost all year round allergies!" Professor Giles Hardy from Murdoch University is a native tree health expert. He accepts that some native trees dont like verge conditions but he says we shouldn't stop planting them! I enjoy waking with birdsong in the morning! I also enjoy the privacy evergreen gives to houses! I have also noted that if people dont have a street tree they tend to plant way too big a tree in their yard. Let's have a large native street tree! We have such great trees in Australia to choose from! Variety is the key!

    1. I think there's something wrong with your computer - the exclamation mark key seems to be jammed on.