Labour of Hercules

Conservation volunteers battle a mythical beast in the forest (11 minute read)

A couple of months ago, I was at the local dog park when I heard the sound of a chainsaw. The sound was coming from somewhere beyond the small area of wetland at one end of the park, an area thick with blackberry and sedge. I’ve never ventured in there, because I don’t fancy the blackberry thorns and the sharp edges of the sedge leaves. I wondered who it was, and what they were attacking with a chainsaw. But the last thing I wanted was Donna bounding up to them – which she would definitely do given the chance, as she loves people. So I headed to the other end of the park and kept her entertained there.

Cashmere Park is strange – that’s the only way I can describe it. There have obviously been earthworks at the site, but I haven’t been able to work out what they were in aid of. Just around the corner from Cashmere Park there’s another grassy area where a gully has been filled in – very  obviously an old rubbish tip. Further on from there, the road twists and turns until it reaches the park across the road from me, Homebush Park, also built on top of a rubbish tip. Cashmere Park is different. There is an area which has been filled in, but it doesn’t look like a tip. For a start, old tips are usually below roads, while the filled-in part of Cashmere Park is uphill from the road. The grassy area runs from the bottom of the park and up a steep slope, and the higher up you go the wetter the ground gets. At the top of the grassy slope the land flattens out – that’s where the wetland is. It’s counter to what I expect, but it looks as if filling in part of the gully has held back some water, creating the wetland. There’s a small stream running through the wetland which then disappears down a drain which runs under the grassy slope.

The dog park is relatively small – I can walk all the way around the perimeter of the grass in five minutes – but the whole of Cashmere Park is much larger. Most of it is forest. However, the forested land is all steeply sloping and has always seemed completely inaccessible. I’ve been looking at it from the grass and wishing there was a way in, but although I’d looked around under the trees at the edge of the wetland, I’d never found a route.

However, the day I heard the chainsaw, I got a clue. As Donna and I played at the other end of the park, a couple of men clad in protective clothing came out from the trees. One carried not a chainsaw but a scrubcutter. Donna and I wandered over to say hi.

They told me that they’d been clearing a dense patch of blackberry, where there had once been some restoration planting done. Unfortunately, there wasn’t much left of the plants – they had been swamped by the mass of blackberry. But once the blackberry was gone, there were volunteers looking after the park who would replant the area and keep the weeds under control.

I filed the information away in my head. Clearly, the spot they had emerged from was the way in. I wasn’t going to go exploring while they were working, but I could go there later.

The men spent about a week clearing the blackberry. Once they were gone, Donna and I found the spot where they’d emerged from the trees and followed their tracks. First, we walked past an enormous pukio. It’s a grass-like plant which lives in wetlands and grows a trunk when mature. This one was spectacular – as tall as me. Then, we hit an area of dense shrubs and small trees. By the look of them, these had been planted, perhaps 15-20 years ago. The track actually went through the middle of one of the trees – it had fallen over and there was a fork in the trunk. I stepped through the fork, feeling as though I was at the back of a wardrobe finding Narnia. But, actually, the real Narnia moment was still to come.

Once we had passed through the tree, I could see where the men had been working with their scrubcutter. There was an open area where the ground was thick with chopped up blackberry branches. I was wearing gumboots, so the blackberry didn’t bother me, but I worried about Donna’s feet. She, however, had no concerns, and was trotting around having a good sniff.

I could see the bed of the stream – there was an obvious trail of gravel running through the ex-blackberry patch – but there was no water. This struck me as strange, because we weren’t far above the area where the stream flows steadily year-round. How could one part of the stream be dry, and yet around 50 metres down another part have a good flow?

I was keen to keep Donna away from the blackberry, so I followed the streambed uphill. At the edge of the forest, there was a large clump of flax hanging over the streambed, so I fought my way through the leaves and then suddenly I was under the forest canopy. This was my Narnia moment.

A waterfall further up the stream. The light levels in this photo are misleading, it’s much gloomier in reality. One day I’ll take my proper camera and take a more accurate photo (image credit: Melanie Newfield)

A forest is more than a group of trees. In New Zealand, a crucial part of what makes forest is a closed canopy. Unless a tree falls, or there’s a slip, this canopy is largely unbroken. Under the canopy, the environment is completely different from outside. It’s gloomy, humid, cool and sheltered. Very few introduced plants tolerate the conditions, but many native species thrive. As I looked around, I could already see several species of native fern.

There was one introduced plant under the canopy, though, an old foe from my time in the Department of Conservation. It goes by a number of common names, but many people just call it by its scientific name, Tradescantia, often shortened to trad¹. It’s the bane of anyone in New Zealand who is involved with lowland forest restoration. A dense patch of blackberry can be defeated by a couple of men with scrubcutters and a bit of herbicide to stop the stumps resprouting. Tradescantia is a different beast, a botanical version of the mythical hydra – the monster slain by Hercules as one of his twelve labours.

Tradescantia originally came from Brazil, and for many years it was a popular house plant, for good reason. As house plants go, it’s almost bomb-proof. It tolerates sun, shade, dryness, overwatering, being left in the same pot for years… it’s basically impossible to kill. It sits there, biding its time, until someone takes mercy on it and puts the pot outside and forgets about it.

Quietly, the tradescantia grows, its stems sprawling out of the pot and along the ground. Stems which touch the ground grow roots, and soon the plant is spreading through the garden. When a frustrated gardener pulls it out, any tiny piece of stem left behind grows a new plant. If they leave the stems they pulled out lying on the ground, they continue growing. If they dump them in the compost bin, they keep growing. If they drop a few pieces of stem on the way to the compost bin, the dropped pieces keep growing.

Tradescantia I’ve weeded from my garden - it just keeps going (image credit: Melanie Newfield)

If the gardener is responsible, perhaps they will fill up a trailer and take it to a council green waste facility. There, the commercial composting methods they use will kill it. But any fragment which dropped off the trailer on the way to dump? It will grow.

If the gardener is not responsible, they will simply tip their garden waste over a bank somewhere. It’s something I’ve seen hundreds of times around New Zealand – sometimes right on the edge of precious forest reserves – a pile of lawn clippings and various trimmings from the garden. Usually, some of the trimmings are sprouting. Often, the plants that sprout from the pile are invasive species. The worst of them is probably tradescantia.

Although it does produce flowers, the tradescantia which grows in New Zealand doesn’t produce seeds. It can’t blow on the wind like a dandelion or thistle. There are no berries to attract birds, which then poo out the seeds far from the parent plant. If the plant is removed, there are no seeds left behind to sprout years later, as with gorse.

But every tiny piece of tradescantia stem can grow a new plant. That’s why I compare it to the hydra, a multi-headed monster which grew two new heads for every one which was cut off. This trait has makes tradescantia a successful weed and resulted in it finding its way into forest fragments around New Zealand.

When conditions are right for it, the tradescantia grows lush and thick. The stems are not woody, but soft and fleshy, so it can’t grow tall on its own. But it grows densely in light shade, and the plants support each other, carpeting the ground and smothering anything less than a foot high. If there’s anything to climb on, it can scramble up a metre or so.

In Cashmere Park, tradescantia forms a band at the forest edge, just as it does in many of Wellington’s forest reserves. In full sun, it can’t compete with grass, especially when the grass is getting mown regularly. But in the shade of the trees, nothing grows as thick and dense as tradescantia. Parts of Cashmere Park were planted in native trees 15-20 years ago, and underneath them there’s a mass of it. Nothing else will regenerate while it’s there.

No chance of any seedlings growing through this (image credit: Melanie Newfield)

Once I get into the deep shade under the closed canopy, however, the tradescantia isn’t so dense. It can grow in these conditions, but it doesn’t form the smothering masses that it does in light shade. The problem is that if a gap opens up and the tradescantia is there, it will take off and prevent the regrowth of native trees.

I keep walking up the dry streambed, watching where the tradescantia is growing, and where it is not. Then I see something odd – there is water in the streambed again, trickling over the rocks as steadily as it did further down. As I said earlier, Cashmere Park is strange.

I pick up a stick and toss it into the water. Donna leaps on it, pulling the stick out of the water then ripping it apart. She loves chasing sticks, but I’ve got to be careful, because she tries to catch them in mid-air and risks one going down her throat. If I toss them away from her, though, it’s safe.

As we move up the stream, deeper into the forest, it begins to look better and better. There is less tradescantia, and there are more native plants, including many kohekohe seedlings. I even spot some flowers of kohekohe on the ground. This is a hopeful sign – kohekohe should be one of the main canopy trees in this area, but it won’t thrive without possum control. When I was at university in the early 1990s, possums were so out of control around the country that the fate of kohekohe was deeply troubling forest scientists. These days, around Wellington, it's thriving because of Greater Wellington’s possum control.

Kohekohe seedlings in the foreground. Again, my phone has made this image much lighter than it really is in here (image credit: Melanie Newfield)

Every now and again, though, there’s another patch of tradescantia. Wherever there’s a break in the canopy, it’s there. There even are a few patches growing in deep shade. These aren’t dense, but they are ready to grow if a tree falls. Still, the amount isn’t overwhelming, and most of it is close to the stream, as it’s carried by the water.

A plan is forming in my mind. This park is almost around the corner from me – it’s the place I bring Donna at lunchtime on work days when I don’t have the time to go further afield. Donna loves it, but I’m sick of walking around the same patch of grass several times a week. I could bring a bag and some gardening gloves, and tackle the small patches of tradescantia, while tossing Donna a few sticks to keep her entertained.

I know what I can do with the tradescantia I collect too. On the edge of the bush in the main part of the park, there are already some giant black weed bags. These are supplied by the council and can be found on the edge of forest reserves around Wellington, wherever there are volunteers which have taken on their own labour of Hercules in controlling tradescantia. It might be hard to kill, but if left in those bags for a year or so, it will eventually die and turn into compost. So I’ve got somewhere to put the tradescantia I collect.

Putting my plan together, listening to the water in the stream, I feel a sense of peace come over me. Sure, this isn’t the primeval forest of Pureora, with trees which are centuries old. Nor is it the vibrant forest of Zealandia, where every step is accompanied by a chorus of birdsong. It’s just a scrappy patch of forest in a gully, a few decades old, where the land is too steep to build on, so it is left to its own devices. Still, in time, this can be lush rainforest again. It just needs a little help.

Today’s haul (in the plastic bag). It may not look much when you consider how much is in the bush, but I’ve nearly cleared two isolated patches (image credit: Melanie Newfield)

1. It used to be known as wandering Jew, but for the same reason that we now refer to spongy moth rather than gypsy moth, that name is no longer used. It’s also sometimes known as wandering willie, or wandering dew, and Google says it’s sometimes called small-leaved spiderwort, but I’ve never heard anyone call it that.