Snip. Snip. Snap. Yank. “Ninety-eight, ninety-nine, a hundred!” Putting down my giant secateurs, I surveyed the skinny corpses of lodge-pole pine saplings around my feet.

When I booked into an eco-lodge to help assuage my guilt over clocking up 5.55 tonnes of carbon emissions flying round-trip to New Zealand, a morning planting trees would have seemed more like it. But here I was laying waste to an infant forest.

Helping to rid Craigieburn Forest Park of invading pines, introduced in the 1950s and now running rampant, choking delicate native plants, is one of the activities led by Dr Gerry McSweeney, an ecologist and co-owner of two conservationally minded Wilderness Lodges.

My tree felling was a short finale to an uplifting day through the spectacular scenery of the national parks and nature reserves surrounding Arthur’s Pass in the high and rugged middle of the South Island, with him as my guide.

The low-rise lodge, which scores top marks for its eco-credentials in Alastair Sawday’s Guide to Green Places to Stay, is built from local stone and wood to blend into the landscape. The 24 rooms are spacious with big beds, tiptop bathrooms and views of the Southern Alps, but no televisions or internet. The emphasis is on comfort rather than luxury.

Before dinner I walked over to Cora Lynn, the 2,400ha (6,000 acre) home farm with 4,000 sheep, where the farm manager, Neil Wood, demonstrated mustering with his two dogs, Tess and Ty. Afterwards in the woolshed I had a go at shearing with old-fashioned hand-clippers.

Neil held down a particularly uncooperative ewe while I did my best not to cut his finger off. He deftly finished the job to produce a huge and remarkably light fleece. The high-quality merino wool goes into Icebreaker garments sold in the small hotel shop and outdoor stores around the world.

After a fine dinner (lamb from the farm is on the menu) we walked to an observation point where Wally, one of the lodge managers, pointed out the constellations in the clear Southern sky, unmarred by light pollution.

Stripping out saplings had been unexpected, what came next was even more of an eye-opener. After canoeing on beautiful and tranquil Lake Pearson (thanks to a campaign led by the lodge, rid of power boats that harmed the rare crested grebes) we played hunt the trap.

Seeking out traps hidden on the banks we checked their contents to find a stoat pinned in one of them, orange and sharp-toothed, the first I’d ever seen, and no longer a threat to the grebe nests. Fired by Gerry’s passion for the protection of native wildlife (stoats were introduced in the 1870s in a misguided attempt to control rabbits), I surprised myself by feeling pleased to find a furry animal cut off in its prime.

Although there are some great organised activities such as picnicking among the Henry Moore-esque limestone boulders of Castle Hill reserve and a seven waterfalls walk, many visitors use the lodge as a comfortable base for independent tramps. There are 30km (18 miles) of trails on the lodge’s land leading to hundreds more in the National Park.

On my last morning I did the Rainbow Walk, starting and ending at the breakfast-room door. Armed with a set of notes from reception I had a fascinating, solitary 90 minutes of easy walking through beech forest, stopping to hear tomtits, examine mosses or look out for whistling tree frogs.

And the shine on the eco-halo is that Arthur’s Pass can be reached by train, two and a half hours from Christchurch on the coast-to-coast TranzAlpine railway to Greymouth.

Although run on similar top-end, low-impact lines, Wilderness Lodge Lake Moeraki offers a complementary experience. An eight-hour drive from high country Arthur’s Pass, taking in the dramatic west coast and Franz Josef and Fox glaciers, brought me down to the sea-level lodge surrounded by rainforest.

The four child stars of Prince Caspian, the second film in the Chronicles of Narnia series, stayed at the lodge while filming scenes on a beach on the Tasman Sea.

We walked down the valley through rainforest so thick with plants that light barely pierced the canopy. Then paddling downriver in canoes into the Moeraki lagoon, we slid silently through waterways thick with flax and home to tui and bellbirds. After dinner at a table made from reclaimed wood, lit by electricity from the lodge’s own hydroelectric generator, I joined a guided walk to see glowworms, freshwater crayfish and stars in a bright, clear sky.

I would have been happy to stay in this carbon-neutral environment for ever, but instead returned home more in tune with nature and aware that there is more to saving the planet than planting trees.

Need to know

Caroline Hendrie travelled with Tourism New Zealand (www.newzealand.com), Cathay Pacific (020-8834 8800, www.cathaypacific.com) and Discover The World (01737 218800, www.discover-the-world.co.uk/newzealand). Discover the World has an 11-night South Island self-drive holiday from £2,289pp, including two nights at each of the Wilderness Lodges, and other accommodation, car rental, flights from Heathrow to Auckland and on to Christchurch.

Wilderness Lodges (www.wildernesslodge.co.nz) offers dinner, bed and breakfast at Arthur’s Pass and Lake Moeraki from about £107pp (NZ$290). The cost includes two short guided activities a day. Longer ones are offered at extra charge.

The TranzAlpine railway (00 64 4 495 0775, www.tranzscenic.co.nz).

Reading: Alastair Sawday’s Green Places to Stay, edited by Richard Hammond (£13.99).

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