Selwyn District Council work - Oak tree de-compaction, Oaks Drive, Lincoln, Selwyn.

11 English Oak trees and 1 Sycamore tree aged 25-50 years are de-compacted after the development of a sub-division where the soil levels had been increased up to 300mm up against the tree bases and around the root plate and the area heavily compacted by machinery movement.

The area was reduced back to the original height post development by excavating the area down removing 108 cube (approx.160t) of soil off around the root collars and the root plate in the process.

The area was then de-compacted by air spading columns to 500mm under high pressure and in the process of creating the columns also created fissures in the soil crust beneath. NPK fertiliser, washed granular sand and coconut fibre was then inserted into the columns to keep the columns open in the long-term. The columns will allow free water drainage allowing water to penetrate into the fissures breaking the lower soil crust up over time as well as allowing air movement into the columns and the fissures created allowing the roots to breath.

The area was then mulched with 36 cube of aged mulch.

The trees will be monitored and managed in the short and long-term to see how the trees respond to the work done.

Several roots were tested for the relative density of wood using an IML Resi F500-S Resistograph instrument. These roots were identified for a closer inspection by acoustic testing and their appearance in what appeared to be damage sustained in the sub-division of the land. The trees are located within a densely populated area and are located next to the busy accessway into the the sub-division.


The work was carried out on behalf of the Parks and Reserves Unit, Selwyn District Council, who were committed to ensuring the survival of the trees and have an admirable vision of tree retention as opposed to the easier (and sometimes cheaper) option of tree removal to ensure that the trees can be enjoyed by future generations.

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