Saturday, 12 May 2012

A New Threat To Our Precious Oaks

    After all that we have been through this past 18 months, the last thing we want to think about is the plight of our oaks. But think about it we must.
    Some of you have expressed concern about possible root damage causing premature end of Summer leaf loss, and there is some evidence of negative long term effects of the earthquakes of these wonderful trees. Margaret met recently with the CCC to discuss the problem and to look at possible solutions

The issue

    There are two parts to this problem. The first is the ongoing problem of root damage due to cars rutting the berm and directly impacting on the roots and compacting the soil around the roots. Even where seal is present, soil compaction will be still occurring. Parking close to the trunk not only compacts the soil around the roots, but it also increases the likelihood of bark damage and the risk of infection.
    The second problem relates to the earthquakes themselves. We have all seen the effects of liquefaction at the southern end of the avenue. Recent ground radar on Margaret and Dave’s property at the northern end shows the water table has risen substantially and is now only 1.2m below ground level. Silt accumulation in the upper soil layers adds to soil compaction, which starves the roots of water, nutrients and oxygen.
    The area necessary for the trees survival is 1.5m either side of where their main root mass is. The most important requirement right now is to stop cars being parked close to the trees.

What are the options?

How about parking wardens? Yeah right!
    Yellow lines? Better, but a lot of the areas are still in grass or mud now, and there is no desire to pave this as it will be worse for the trees. For yellow lines we will have to apply to the Community Board (according to CCC rules) who will want reports from Roading, Traffic and Street Trees then further meetings – a long process for 6 months or more with no guarantee they will approve this.
    Roadside planting? Roading division would have preferred this to push the cars out from the trees but as the money for any of these options is emergency funding the solution must be cheap and quick. Still, this is a long term option worth keeping in the backs of our minds.
    Are you saying we need to fence our trees in? Well almost. Bollards are a simple and relatively easy solution. Bollards can be put in urgently without a drawn out Community Board approval process, and we have support from the CCC to use emergency rules/funding. They provide a physical barrier, and they don’t go far into the ground and so won’t cause root damage if they are placed carefully.

Won’t the roots be damaged when the bollards are put in place?

    The holes for the bollards will be only 300mm deep and hand dug. If large roots are encountered the bollard will be shifted. They will not be placed necessarily in an ordered symmetrical way, just where they can safely fit between roots. Every endeavour will be made not to cause damage and the work will be done under arborist supervision. We can also be there if we wish.

The downside?

    This will cut down the available parking greatly. Also, for those of you that park in on the street in your driveway, if this is close to a tree, this potentially also damages the roots. Obviously a bollard cannot be placed to protect it, so we will end up relying on community awareness. However, hopefully residents will realise the importance of keeping their tree safe and not park near the tree.

The upside?

    Happy healthy trees, of course! So many mature trees have died due to liquefaction that whole areas of the city will be deforested as a result, making our mature trees and those in the park a real asset worthy of CCC investment.

What do I do next?

    Talk it over amongst your neighbours and fellow residents. Think about the advantages and disadvantages and what the options will mean for you. Have a look at the websites listed below.
    Feel free to email to Margaret (margaret.dave@xtra.co.nz) or myself (mhurrell@xtra.co.nz).

Useful websites

1. Colorado State University fact sheet Healthy Roots and Healthy Trees (http://www.ext.colostate.edu/pubs/garden/02926.html) - a succinct easy to read summary.
2. Auckland Transport (Auckland City Council) Code of Practice for Working in the Road - Part 8 (http://www.aucklandtransport.govt.nz/improving-transport/maintenance/Road/Documents/Original/AT_ACC_Policy_CoPWiRPart8.pdf). Good to see the Auckland City Council taking this seriously with decent guidelines. This PDF has an excellent Appendix 1 - Guideline for Working in the Vicinity of Trees.
3. Mississippi State University Preserving Trees in Construction Sites (http://msucares.com/pubs/publications/p2339.pdf) - a more detailed look at the issues for the more inquisitive. This site has some formulas for working out what root area is required, and our oaks do not measure up well at all.

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