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The conservator’s dilemma

Christchurch recently formalised a scenic reserve west of the airport that’s almost as large as Hagley Park. Although it’s unlikely to be restored to pre-human purity, it could be improved.

Will Harvie reports.

Christchurch’s newest scenic reserve is a windswept, barren and flat paddock that’s grazed by sheep, rabbits and hares.

On a clear day, visitors might get a view of the Southern Alps, but otherwise the scenery is mostly yellow-brown pasture, high-voltage power lines, and a berm that marks the boundary with a gravel quarry – one of a half-dozen quarries in the area.

The Mcleans Grasslands Reserve is west of Christchurch International Airport and south of McLeans Island and Orana Wildlife Park.

At 154 hectares, it’s only slightly smaller than Hagley Park (165ha) but the differences could not be more stark.

This is one of the last remaining vestiges of the pre-human Canterbury Plains. Less than 1 per cent of the plains’ indigenous plant cover still exists, wrote Christchurch City Council ecologist Nicholas Head in a 2019 report on the reserve.

‘‘The remaining indigenous ecosystems on the Canterbury Plains are acutely threatened,’’ Head continued. Protecting and restoring the indigenous biodiversity remaining on the plains is a ‘‘national priority’’ and an ‘‘obligation for council as a matter of national importance’’.

Christchurch had been getting reports like this for years and on May 24, 2001, councillors resolved to create a reserve. But it took another 20 years for the final paperwork to be completed by current council chief executive Dawn Baxendale, on March 8 this year.

The council insists it has been ‘‘managing the land as a scenic reserve for many years’’ and indeed there are stiles that allow public access, some native vegetation is fenced, and the 360 Walking Trail marches straight through it.

Calling it a ‘‘scenic’’ reserve was only done because that’s the ‘‘most appropriate’’ designation available to a local council, says Kay Holder, council’s regional parks manager.

The newly formalised reserve complements about 3000 hectares of similar dry plain land further west that’s controlled by Environment Canterbury. It was initially set aside for stop banks and the leftover land was – and still is – mostly leased to farmers, says ECan senior land ecology scientist Jean Jack. The income is used as an endowment for other projects in the area.

A small portion is also owned by the airport company and the Defence Force has a holding in the area too.

Together, this is the ‘‘largest contiguous area of largely undeveloped alluvial soils remaining on the Canterbury Plains’’, wrote Head.

Lincoln ecologist Colin Meurk has been studying the plant life of this reserve and the plains for decades. For millennia, the mighty Waimakariri River flowed broadly over these plains, he says. Before the stopbanks were built, the river flooded regularly, broke its banks, created new braids, changed course and made new channels all across the plains.

At one point, the Waimak flowed into Lake Ellesmere-Te Waihora south of Banks Peninsula. In the

1930s, floodwaters got into the headwaters of the Avon RiverO¯ ta¯ karo and submerged much of north Christchurch.

These shifting channels laid down the shingle and sand that attracts quarry operators to the area. These also explain why this part of the plains are dry. The soil is mostly thin and the gravel underneath drains freely, leaving little moisture near the surface for plant life. There’s also relatively little rain.

This dynamic – dry unless flooded – was undone by the stopbanks that were built in the

1930s and in some cases earlier. They ended the flooding and there were signs that native tussocks and grasses were giving way to shrubs such as ko¯ whai.

But then came the sheep. And maybe cattle at some point. But definitely rabbits and hares and rats and mice.

Today, the dominant vegetation is native mosses, mixed with the exotic herbs and grasses necessary for pastoralism, wrote Head. Among the natives are onion orchid, which is notably abundant, as well as sun orchids and adder’s tongue fern.

Meurk remembers visiting the reserve one spring when the orchids were blooming, and it was lovely, he says.

‘‘Other perennial native vascular plants persist as scattered individuals in so few numbers that they barely constitute viable populations,’’ Head wrote.

At least one plant, plains olearia, is listed as ‘‘threatened – nationally critical’’. Other users of the reserve include banded dotterel birds and the canterbury spotted skink, both of which were listed as ‘‘nationally vulnerable’’.

Could the Mcleans Grasslands Reserve and maybe some of the ECan land ever be restored to their pre-human condition? Probably not.

‘‘The key objective of ecological

‘‘The remaining indigenous ecosystems on the Canterbury Plains are acutely threatened.’’ Protecting and restoring the indigenous biodiversity remaining on the plains is a ‘‘national priority’’ and an ‘‘obligation for council as a matter of national importance’’. Nicholas Head

Christchurch City Council ecologist in a 2019 report on the reserve

restoration is to undertake management that shifts the ecosystem from a degraded state to a less degraded or a more natural state,’’ wrote Head. ‘‘Successful restoration ultimately leads to natural ecological functioning, which in turn builds ecological resilience and long-term sustainability.’’

Achieving a more natural state would probably mean an end to grazing. Which leads to a problem known in some circles as the ‘‘conservator’s dilemma’’ and not just because the street address of the reserve is 151 Conservators Rd.

Many readers will know this problem in different contexts: Stock eat grasses and lower wildfire risk. Stock eat weeds. Stock create an equilibrium until some other land use can be implemented. Stock earn income.

At Mcleans, letting the grasses grow threatens the few remaining natives. It ‘‘carries the risk of losing indigenous biodiversity through increased competition resulting from the flush of exotic species that will inevitably occur’’, wrote Head.

This ‘‘conundrum of management’’ is already evident in the reserve. A few native plants and shrubs have been fenced – sometimes they’re given a square metre, sometimes 5sqm.

In some of these fenced plots, ‘‘exotic grasses completely dominate the vegetation, presumably at the expense of the native flora previously present’’, wrote Head.

In other plots, recovery of the native dryland ecosystem is impressive and native lizards have responded well, he observed.

Meurk notes that some native species like the protection afforded by exotic species, especially in the juvenile stages.

It should be noted that ECan says it is undertaking similar protection measure on its lands further west, including the exclusion of grazing in some places, as well as restoration planting with local seed, predator control and lizard habitat enhancements.

ECan has also established the Kowhai Savannah demonstration area, which is a ‘‘snapshot’’ of what the Canterbury Plains was like before European settlement, savannah being an alternative description of the landform.

For the time being, it seems as though the council and ECan are content with the status quo. Nick Head’s 2019 report on the Mcleans Grasslands Reserve is unfinished and not online. Both authorities have been renewing grazing leases. But the status quo contains its own promise.

Post-quakes, greater Christchurch extended north (Kaiapoi and Prestons, for example) and south (Halswell, Lincoln and Rolleston) and southwest (Templeton, West Melton).

But it hasn’t grown west of the airport. That’s partly because noise from the airport makes housing there undesirable, says the council’s head of planning and strategic transport, David Griffiths. Other barriers to development included the quarries, some versatile soils in some places, and a groundwater protection zone.

Our Space, the Greater Christchurch Settlement Pattern Update 2018-2048 doesn’t forecast much urban growth west of the airport in the next 30 years.

So, if barriers to subdivision such as airport noise are somehow overcome, there’s now a formal reserve west of the airport that’s almost the size of Hagley Park (plus the ECan lands) that could be restored to something like the grandeur of the Plains.

Mainlander

en-nz

2021-07-24T07:00:00.0000000Z

2021-07-24T07:00:00.0000000Z

https://fairfaxmedia.pressreader.com/article/282007560417830

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