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The Re-Greening of Symonds Hill

Keith Barber Symonds Hill Quarry

ALAN TITCHALL visits Symonds Hill Quarry in Auckland to catch up on its consent mitigation programme, as the new quarry gears up to start production.

Keith Barber, with a Master of Science, from Lincoln University, joined GBC Winstone nine and half years ago as the company was preparing its Symonds Hill consents.
Keith Barber, with a Master of Science, from Lincoln University, joined GBC Winstone nine and half years ago as the company was preparing its Symonds Hill consents.

Keith Barber tries to nail down his actual title. “My business card still says ‘National Biodiversity Co-ordinator’.”

Keith, with a Master of Science, from Lincoln University, joined GBC Winstone nine and half years ago as the company was preparing its Symonds Hill consents, which were to involve a great deal of environmental mitigation.

Symonds Hill in South Auckland sits on a 40-year resource of greywacke that has sat untouched for over half a century. It is part of the same resource as Winstone’s Hunua Quarry. The adjacent quarries sit on two different sides of the same 240 hectare hill divided by the Hunua fault. As the Hunua pit winds down, Symonds Hill will wind up. Full stripping of the site began in May this year, with the overburden (around 6000 bank cubic metres [BCM] a day) back-filling one end of the Hunua pit, while excavation (around 3500BCM) continues at the other end. Blasting at Symonds Hill is about to start about now.

“My role has changed a bit since I started when the focus was on consent mitigation. Now the focus has moved into developing the Symonds Hill quarry site, ensuring we make full use of the existing Hunua pit resource, and making sure we get the mitigation right to make good environmental effects of the new development.”

This has also involved helping out with environmental aspects at Winstone’s other quarry sites around the country, from time to time.

I last visited Symonds Hill in 2009 when the site was mostly grass farmland and the proposed mitigation programme was about to begin. This time, during the spring of 2015, Keith Barber explains how, seven years later, that exercise was carried out. Suffice to add, that it turned out to be one of the biggest mitigations of its kind in this country and added a unique native nursery to the Hunua Quarry that has become a fascinating part of Winstone’s overall quarry operations.

Any mitigation process involving a new quarry site, explains Keith, is complicated, and there aren’t many new quarry sites that don’t involve knocking down trees and removing vegetation, so Symonds Hill is a valuable lesson for the industry.

Every site has to be valued differently, based on a number of aspects such as the ‘quality’ of the forestation. In some cases it is a simple matter of replacing one hectare with another in another location, or planting as much as 20 hectares for every hectare removed. Pest control is another mitigating feature and, in the case of Symonds Hill, played a major part in the consenting process.

“The bush on Symonds Hill was protected under the Auckland Regional Plan for its ‘wildlife value’, and as a habitat for the birds and animals that lived in it, as opposed to the vegetative value.

“So a big part of our mitigation programme is pest control, not just planting. We have a lot of bush we are not cutting down and pest control provides more protection for native wildlife and more fruit from the trees.”

As the site features a large forested area pest control is extensive and involves targeting deer, goats, possums, stoats, ferrets, cats, hedgehogs, rats, mice and wasps and a lot of traps. There are at least 29 kilometres of walking tracks to coordinate this pest programme.

In addition to this, mitigation involves a lot of planting. Over half of the new quarry site will eventually be ‘green’.

Developing a quarry nursery

View of the nursery in spring 2015 after most planting had been done to avoid the risk of summer drought. The freshly planted trees need at least a few weeks with good ground water. However, plant too early and there’s a late frost risk.
View of the nursery in spring 2015 after most planting had been done to avoid the risk of summer drought. The freshly planted trees need at least a few weeks with good ground water. However, plant too early and there’s a late frost risk.

In terms of vegetative value, the Symonds Hill mitigation involved an ‘mitigation and offset’ package that required planting an equivalent area of any native bush removed from the quarry site.

“We went to the market and bought a lot of trees, but there were key species we needed that were not commonly available, or were expensive, and it made sense to grow these on site.”

The background to this is the concept of ‘eco-sourcing’. Plants and trees develop under local environmental conditions and different species dominate in different locations.

“The forest at Hunua has certain species that are more prolific than others and form a dominate part of the canopy,” says Keith. At Hunua these trees are broad-leaf tawa and taraire, two related species that often form the subcanopy in forests throughout the country beneath podocarps such as kahikatea, matai, miro and rimu. Both trees produce a dark red plum-like fruit that is solely dispersed by our native wood pigeon.

“The canopy on Symonds Hill was a result of logging for kauri and rimu in the 19th century,” explains Keith. “Tawa and taraire didn’t, at the time, represent high value timber and were left. Tawa now forms 60 percent of the canopy in the area, which is not common.”

These trees are not commonly propagated in nurseries either so, in 2009, a rudimentary germination shade house was constructed adjacent to the Hunua Quarry office car park.

“Then we started collecting seeds from around the quarry; climbing up trees, and collecting off the forest floor. All our workers still carry seed bags in case of an opportunistic find.”

Seven years later the nursery is about half a hectare in size; divided between a germination shed and different shaded and open areas. A rabbit-proof fence guards the compound, a green oasis in the middle of a grey quarry buzzing with machines and crushers. A dark green canopy of forest stretches uphill above nursery and quarry.

Some seeds need to be soaked for a while, or rotted for six months, explains Keith, while others are simply bagged and put in a fridge, or planted straight away. They take different lengths of time to germinate, with kauri being the quickest.

Nursery enemies

Planting taraire seeds on the surface of potting mix to replicate nature’s conditions. Taraire (related to the tawa and tawaroa canopy trees) seeds are eaten and digested by New Zealand wood pigeons, which gets their germination started.
Planting taraire seeds on the surface of potting mix to replicate nature’s conditions. Taraire (related to the tawa and tawaroa canopy trees) seeds are eaten and digested by New Zealand wood pigeons, which gets their germination started.

“We had a rabbit get in one night and you would be surprised how many seedlings one of them can eat at one time, so we put up a rabbit-proof fence.

“Slugs are also a big issue, snails aren’t so bad, and there’s a little earthworm that will reside under the trays and comes out at night to eat the seedlings. Mice love taraire seeds.

“We use a lot of bait, and someone needs to keep an eye on the nursery every day, especially over watering during the summer when irrigation becomes an issue. Fortunately, the nursery is next to the office car park.

“Other than that, there is not much too it,” he adds with surprising modesty.

“These plants have already evolved to look after themselves for millions of years.”

The Hunua nursery was never set up to grow all of the trees the quarry needs, Keith says, “only enough to spread the risk of obtaining key species and guard against market shortfalls.”

However, the busy little hectare now propagates between 10,000 to 14,000 trees a year and produces plants for other Winstone quarries. The seeds are collected specifically from each quarry site, grown into trees, and sent back home.

Spare trees, and there are quite a few, are given away to ‘neighbours’ in the area as community goodwill, Keith adds. This is one of the country’s largest quarries and is surrounded by lifestyle blocks and new residences, but that’s another story. Meantime, their view remains green.

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