Root Research Progress – Kānuka and Tōtara
Blog post.
Raphael Spiekermann and Tom Mackay-Smith
8/12/20253 min read
This winter we’ve been deep in the mud (literally!) working on an exciting project in the Auckland Region with support from Auckland Council.
We’re comparing the root systems of kānuka, tōtara, and poplar in low-density silvopastoral systems to determine how effective these tree systems are at stablising slopes and reducing landslide erosion.
We’ve been digging 1 m trenches to measure root distribution and using a pull-out rig to test root strength.
Realities of fieldwork
Before we get into some results, we want to give you a taste of life in the field.
Over the past four months, a total of 9 people have been involved in the fieldwork, taking turns battling clay soils, losing callipers, and nearly disappearing into the mud! It’s been tough work — but also exciting.
This has been a MASSIVE team effort, led by Nicola Wilson — our farmer-cum-scientist from Northland — who knew exactly what the team was getting into tackling clay soils in winter! We are very lucky to have her.
Root distribution of kānuka and tōtara
We measured the root distribution of kānuka and tōtara at four distances from the trunk (1.5, 2.5, 3.5, and 4.5 m) and down to 1 m deep.
Below are the compiled graphs of root area ratio for each species, shown by soil type.
Soil type 1 – Mottled yellow ultic soil, Auckland
Kānuka
Tōtara
Soil type 2 – Typic Yellow Ultic, Auckland
Kānuka
Tōtara
Preliminary thoughts
At 4.5 m from the trunk, tōtara appear to have a slightly greater root distribution. We’ve yet to statistically analyse. We are also yet to compare the root mechanical properties (strength) using the pull-out data.
As farmers will know, tōtara have large, shallow roots (see photos below), which is evident at the 1.5 and 2.5 m distances.
Photo of the month
This photo shows a kānuka root with a 25 cm diameter that took 1,103 kg of force to break while pulling out — yes that’s 1.1 tonnes!
