I enjoy winter hiking—I enjoy the crisp air, the opportunity to hike without sweating too much, the snow on the peaks.
One of my favourite winter phenomena is frost heave. This is when moisture in the soil freezes. Since water expands when it freezes, the ice crystals push soil and rocks upward. We get frost heave at home, but in the mountains, where there is both more water and colder temperatures, the phenomenon can be spectacular.
On a cold Matariki morning a few weeks ago, I snapped a photo of five-centimetre-long ice needles near Foggy Peak. Each needle was topped by gravel—the whole top centimetre or more of the sloping surface lifted. As the sun rose and melted the ice, every rock fell a few centimetres downhill from where it started. I imagine this process happening daily all through winter—a slow-motion conveyor belt shifting the mountain downhill.
Meanwhile, higher up on the mountain, water seeping into the cracks in rocks and then freezing shatters them day by day into smaller fragments to be added to the icy conveyor belt.
It is such a small thing, frost heave. But its slow action has a big effect.
The Southern Alps are rising at a rate of 10 to 20 millimetres per year—some of the fastest rising mountains in the world. If no erosion had ever occurred, the mountains would currently stand over 20 kilometres tall. Our tallest mountain, Aoraki Mount Cook, is 3754 metres tall.
Of course, when we think of erosion, we think of the big events like landslides and rock avalanches. These events can be spectacular.
On 14 December 1991, a rock avalanche on Aoraki lowered the summit by 10 metres over the course of a few hours. Fourteen million cubic metres of rock and ice tumbled down the mountain at speeds of up to 300 kilometres per hour. The shock waves from the landslide were recorded on seismographs as far as 58 kilometres away.
But without frost heave, the 1991 Aoraki rock avalanche might never have happened. Frost heave slowly weakened the rocks, slowly snapped them into smaller and smaller pieces, slowly shifted their weight. Centimetre by centimetre, those little ice needles brought the mountainside down.
I like to think of frost heave as a metaphor. Each of those tiny ice crystals, by itself, can move a pebble, and together they bring down mountains.
As my regular readers all know, I spend a lot of time in the garden. I also spend a lot of time thinking about gardens, looking at gardens, planning gardens …
The bare paddock: former forest, future garden
I am fortunate to be part of a local group of keen vegetable gardeners. Of course, we don’t just grow vegetables—everyone has perennial food crops like fruit trees and berry bushes, and ornamental plants as well. All of us take pleasure in planting and maintaining our gardens, as well as relaxing in and enjoying them. Some of us are in the early stages of establishing our gardens, and others have spent decades cultivating one place. But we’re all focused on the future.
I’m reminded of the quote I copied years ago from the book 1491: New Revelations of the Americas before Columbus, by Charles C. Mann:
“Gardens are fashioned for many purposes with many different tools, but all are collaborations with natural forces. Rarely do their makers claim to be restoring or rebuilding anything from the past; and they are never in full control of the results. Instead, using the best tools they have and all the knowledge that they can gather, they work to create future environments.
If there is a lesson it is that to think like the original inhabitants of these lands we should not set our sights on rebuilding an environment from the past but concentrate on shaping a world to live in for the future.”
I look at the 3000 square metres of land my husband and I own. For thousands of years, this land was covered in forest and periodically scoured by the Waimakariri River, which deposited around 300 metres of rock and clay here on top of the bedrock. When Māori arrived in the region, they burnt the forest to flush out moa and other game birds. European settlers later brought in sheep and cows and planted European pasture grasses. From the mid 1800s to 2019, our little block of land was used to pasture sheep, and later, dairy cows. When it was subdivided to develop as residential housing, the topsoil was scraped off, leaving bare, highly compacted clay studded with rocks. Even weeds grew poorly (in places where we have done nothing to improve the soil, there are still bare patches, where nothing has been able to grow in the past 5 years).
Flaxes provide food for native birds, currents provide food for us.
There was no restoring or remaking what was once here, but when we bought the land, we envisioned a place rich in native plants that might attract native lizards, birds and insects. We envisioned a place full of plants that would provide food—an orchard, berry crops, nuts, herbs and vegetables. We envisioned a place that was beautiful, and bright with flowers.
A volunteer lancewood.
We cannot erase the fact that the soil here has been sorely abused for nearly two hundred years. We can’t erase the fact that we sit over an old river bed full of rock and clay. Not everything we plant flourishes, and other plants have done so well, they’ve become weeds. Some insects and birds have returned, but glaring absences remain, and non-native pests still dominate.
But like all gardeners, we look to the future, our imaginations filling the gaps in what we see today. We do our best to collaborate with the natural forces at work here in order to shape a little pocket of plenty for ourselves and others.
Yesterday I wrote about strategies for preventing pest problems. If you’ve taken all the measures you can to prevent pests, but the pests arrive anyway, there are different questions to ask:
Centipedes are predators of many garden pests.
Do I need to worry? Low levels of pests aren’t a big deal. A few aphids, a caterpillar here or there, the odd bite out of a leaf—these things aren’t going to have a big impact on the quality or quantity of your harvest. Just keep an eye on them to be sure the problem doesn’t get worse.
Can I physically remove them? I’m a huge fan of squishing and hosing pests off plants. For example, I have problems every spring with aphids on my roses. If I do nothing, the plants become completely covered, and the blooms are destroyed. So in spring, I keep an eye on the plants, and once the aphids start reproducing, I hose the plants down once a week, knocking off most of the aphids. Usually I only have to do this about three times before the aphids’ natural enemies build up enough to keep them under control without my help.
Can you disrupt a critical part of your pest’s life cycle? Is there a life stage that can be easily killed, or has specific requirements you can disrupt? For example, I keep a close eye on my brassica seedlings, looking out for cabbage white butterfly eggs on the undersides of the leaves. All it takes is a quick swipe of the thumb across the bottom of each leaf to squash the eggs and eliminate future problems with caterpillars. Another example is my recent problems with slaters in my greenhouses. Discovering that the slaters are congregating between cement blocks stacked beside the greenhouse, I’ve started regularly checking and squashing all the slaters in those blocks. (I could also have moved the blocks, to eliminate the slaters’ shelter, but since the population was quite high, I thought squishing a whole lot of them would be more effective for now. Later I will probably move the blocks to make the area around the greenhouse less attractive to slaters).
Can I make use of them? Pest-covered plants, grass grubs and slugs all get thrown over the fence to my chickens, who turn them into beautiful eggs for me and save me from the disgusting task of squishing the bugs.
Can I pull out badly infested plants? If there’s a couple of plants badly infested, but the pests haven’t spread much, rip out those infested plants and destroy the pests on them. You’ll lose a few plants, but you’ll protect the rest of your crop.
Pest-gobbling chickens.
In an IPM system, you don’t consider any sort of chemical control until you’d exhausted all the possibilities above. In practice in my garden, I almost never need anything else. Occasionally, if I’ve missed an aphid infestation on a crop that can’t handle a strong spray of water, I’ll use a soap solution to kill aphids. That’s the extent of my chemical control. But if you do need to resort to chemicals, it’s important to choose the right one. The more specific it is to your pest, the better. Many modern pesticides are narrowly focused, and target specific pests, and that’s great. With a narrow target, the pesticide is less likely to kill beneficial insects or harm people and pets. Stay away from broad spectrum pesticides. Also, if you do use pesticides, be sure to follow the label directions carefully, wear protective gear, and dispose of leftover product and empty containers properly.
It’s nearly spring, so naturally my thoughts turn to the subject of pests. Our big pest-related project in the garden this year is bird netting a third of the vegetable garden, so we don’t lose most of our tomatoes and peas to the feathered rats.
Aphids–the one on the right is healthy, the one on the left has been parasitised by a wasp, one of the many natural enemies that keep aphids under control in the garden.
As an entomologist whose research focused on Integrated Pest Management, I always have a lot to say about pests. And it’s an important topic—globally, 30-40% of crop yield is lost to pests (interestingly, this figure didn’t change with the advent of chemical pesticides—insect pests are incredibly quick to evolve pesticide resistance). That’s a lot of wasted food!
For home gardeners, fighting pests is a daily task. Every place I’ve gardened has its own unique pest problems. Growing up in Lancaster Country, Pennsylvania, I remember the rabbits munching through the garden. In State College, Pennsylvania it was flea beetles that shot so many holes through my eggplants’ leaves they never had a chance to grow, and the squash bugs that clustered in masses under the leaves of my zucchinis. In Panama, leaf cutter ants could strip a plant bare in no time.
In my first garden in New Zealand, aphids and rabbits were my main problems. When we first arrived on the property, there were so many rabbits I wondered if I’d be able to grow anything. A rabbit-proof fence was the first garden project there.
In my current garden, birds are my worst enemy—mostly English sparrows and European blackbirds. They strip seedlings bare, eat tomatoes, pull out onions, and scratch away mulch and soil, leaving plant roots to dry out (never mind the amount of chicken feed they snarf down every day!).
Fortunately for me (and unfortunately for the pests), my masters degree focused on Integrated Pest Management (IPM), so I’m well-armed when it comes to tackling pest problems.
IPM is often called common sense pest control. In IPM, the goal isn’t to eliminate pests, but to minimise the damage pests cause, while choosing the most environmentally-friendly control methods that do the job.
To successfully use IPM, you must first know your enemy. What conditions does it like? What’s its life cycle? What are its natural enemies? How does it find your plants, and how does it travel? Books and the internet can tell you a lot, but careful observation of the pests in your garden is key. The particular conditions in your garden will affect how pests behave, and where their weaknesses are. If you know exactly where pests are and what they’re doing in your garden, you can begin to tackle them more effectively. For example, I know that in my current garden, there are particular varieties of squash the aphids like. By keeping an eye on those particular plants, I can catch aphid infestations early and deal with them before they spread to more plants.
Bird netting protecting pea seedlings
Once you know your pest’s habits, you can begin to consider control methods. Questions to ask:
Can you time your plantings to avoid the damaging stage of the pest’s life cycle? For example, I don’t grow brassicas during the summer here—I have an early spring crop and a winter crop. By avoiding brassicas in summer, I eliminate bad problems with cabbage white butterflies, which tend to reach damaging levels around Christmas. I still have to be on the lookout for butterfly eggs on my seedlings, but once the plants are growing, they easily stay ahead of the caterpillars.
Can you exclude the pests from your crops during critical time periods? For example, psyllids can transmit disease to potatoes and tomatoes, leading to poor growth and damaged tubers. By covering the plants with a fine mesh cloth, I can keep the psyllids out for most of the summer (until the plants are too big for the covers, by which point the psyllids don’t seem to be much of a problem). I do the same for my peas and lettuces—netting out birds until the plants are large enough to handle losing a few leaves. I also net my berry crops and olives before the fruits start ripening, so the birds don’t pick them before I do.
Can you plant varieties the pests don’t like as much? For example, I plant mostly red varieties of lettuce, because the aphids take longer to discover them than they do the green ones. Usually, by the time the aphids find my red lettuces, they’re bolting and ready to pull out anyway.
Can you plant a ‘trap’ crop that the pests like more than your favourite vegetables? I haven’t done this explicitly, but as I mentioned earlier, there are certain varieties of plants I know are particularly tasty to pests, and I closely monitor them and kill the pests on them before they can spread to other crops. A true trap crop is something you’re willing to pull out entirely when it is infested by your pest, in order to destroy the pest.
Can you prevent pests from finding your crop? Interplanting different crops can help disrupt the spread of pests, because they struggle to find new plants to feed on. It can also help you make the most of the space in your garden. For example, I sometimes plant summer lettuces in the shade of my sweetcorn—not only does the shade help prevent the lettuce from bolting, it also seems to hide the lettuce from aphids.
Can I encourage the pests’ natural enemies? Many pest insects are preyed upon or parasitised by the larvae of beetles , flies and wasps. The adults often eat pollen and nectar, so planting herbs and flowers is a great way to encourage many pests’ natural enemies.
All six of the questions above will help you avoid a pest problem in the first place. They are changes in the way you plant or grow your crops that make it less likely you’ll have pest problems. Tomorrow, I’ll look at what you can do once you’ve discovered pests in your garden.
As an entomologist, I love early autumn. Insect numbers are at their peak, and most insects are adults—their most active and visible life stage.
As a kid growing up in rural Pennsylvania, early autumn nights were nearly deafening with the cacophony of cricket and katydid chirps. Days buzzed with the sounds of cicadas and grasshoppers.
New Zealand is quieter, but autumn still has its distinct voices. Our katydids’ sharp ‘zit zit’ seems to echo from their favourite ake ake trees. Crickets twitter in the grass on sunny days. Cicadas and grasshoppers buzz from trees and bushes.
Bees and butterflies are particularly active on autumnal blooms. Many of our showy butterflies overwinter as adults, so they can be seen flitting about on warm days into late autumn.
Of course the clouds of invasive cabbage white butterflies on the brassicas and the German wasps swarming the compost pile aren’t terribly welcome. But still, I enjoy the leggy hum and flutter of the season.
Monarch butterfly–not native, but lovely anywayHoney bees are busy getting ready for winterYellow admiral butterflies by the dozen on the garlic chivesBumble bees seem to love the zinniasAn adult male katydidA katydid nymph doing what they do best–hiding
Not long ago, I spent a glorious sunny day wandering around Cass Field Station while my husband met with some students there. It was nice to take a solo walk and go at my own pace, stopping at whatever plants, bugs or rocks caught my fancy.
Once nice find was this beautiful lichen, Rhizocarpon geographicum.
Lichens are strange organisms comprised of an alga living within a fungus. The alga provides food through photosynthesis and the fungus provides protection and nutrients for the alga.
R. geographicum is an alpine/subalpine lichen and, like many lichens, is sensitive to air pollution, thriving only where the air is clean. It is not, however, a fragile organism.
In 2005, R. geographicum was one of two lichens launched into space. The lichens were exposed to 14.6 days of open space—vacuum, wide temperature fluctuations, intense UV light and cosmic radiation. Upon return, R. geographicum showed little harm from the experience.
Not only is R. geographicum tough, some individuals in the Arctic are estimated to be 8,600 years old, making them the oldest living organisms on Earth. Their longevity and predictable growth rate make them useful tools for determining when glaciers retreated from an area.
But I didn’t know all this about R. geographicum when I found it on the rocks at Cass. I simply admired its beautiful mottled colours and soft texture.
It’s not often you witness outright thuggery in nature. Predators hunt prey—they have to, because otherwise they starve. Predation is never pretty, but it is what it is.
Sitting at my desk, procrastinating … er … writing this morning, I saw brutality, pure and simple.
A pair of magpies was chasing a starling. They caught it and brought it to the ground. Standing over it, they pecked at its eyes. At first, I thought they were trying to kill and eat it. But after a few minutes, they got bored. The starling managed to fly off. The magpies followed, caught it and brought it back, only to repeat the eye pecking routine. Three times while I watched, they allowed the starling to escape, then brought it back to peck at it. Always at the eyes.
Eventually, they bored of the sport. They wandered away from the hapless starling to forage in the lawn nearby. After a few minutes, starling and magpies flew off in opposite directions.
I suppose it shouldn’t come as a surprise. Australian magpies have a reputation as aggressive, intelligent birds that like to play. They brazenly steal food from the chickens, fighting right back when a chicken lunges at them. And I’ve watched as gangs of juvenile magpies have tormented my cat, swooping low over him as a team, trying to get a peck in while he swats at them. And I’ve been on the receiving end of magpie parents defending their nests with noisy dives at my head.
In general, magpies eat invertebrates—they were originally introduced to New Zealand to help control crop pests. Research on their effects on native birds indicates they only rarely kill other birds, and their aggressive pursuit of larger predators like harriers may even provide some protection to smaller birds.
Still, I can’t help thinking magpies are the bullies of the playground. They’re fine as long as you’re not their target. Fascinating for me as an armchair naturalist, but I’m thankful I’m not a small songbird.
On a whim, my husband and I spent last weekend on the west coast. We stayed in our favourite west coast town—Hokitika—and hiked in the mountains nearby.
The view from the top of Mt Greenland
Having lived in a rainforest for two and a half years, I know I wouldn’t want to live on the west coast (where rainfall ranges from 2 to 11 metres per year), but I love visiting.
On this visit, we hiked up Mount Greenland. The path up is an abandoned road that used to connect the small gold mining settlement of Veronica to the township of Ross. An article in the West Coast Times in 1888 records Veronica as a promising settlement, complete with a hotel and two stores. Even then, the road from Ross was apparently atrocious—other newspaper accounts from the 1880s colourfully describe knee- and waist-deep mud on the way to Veronica.
The mine near Veronica was abandoned in 1940, and the rainforest has been reclaiming the road ever since. The day we hiked it was sunny and cool, but even without active precipitation, the road streamed with water in places. There were a few short stretches without washouts, deep puddles or slips, but only a few. Ferns leaned over the edges of the narrow track, so that in spots, even hikers were forced into single file. It is clear some informal maintenance of the track still goes on, but the forest is doing its best to erase it.
And this is probably what I appreciate most about the west coast—nature is in charge, and humans maintain only tenuous grip. The settlement of Veronica has all but vanished under vines and tree ferns. The gold rush of the 1800s left no ghost towns—the forest has swallowed them all up. Other west coast townships, like Franz Josef Glacier, Fox Glacier, and Kumara Junction, feel equally under siege by Mother Nature, as though it would only take a few moments of inattention before the trees would creep down the streets, and the vines snake over the houses.
As apocalyptic as that vision is, it gives me hope. Hope that one day, the planet will erase the scars of our fleeting presence here and carry on in a riot of life.
Over the long Waitangi Day weekend, we hiked up the Waimakariri River to Carrington Hut. Using Carrington Hut as a base, we took day walks to Kilmarnock Falls and Waimakariri Falls Hut.
The weather was glorious, and hiking on the riverbed, it was easy to cool off with a quick dip in icy water. The hike to Waimakariri Falls Hut was particularly rewarding: there are two ‘official’ falls on the river, and dozens of smaller streams dropping off the surrounding peaks in spectacular fashion, so you feel as though you’re walking through a watery wonderland.
Wading in to see Waimakariri Falls.
The upper falls, just below the hut, are hidden in a deep, narrow fissure in the rock. Waist deep in icy water is the only way to see the water roaring down—great fun, but not something you’d want to do on a cold day.
Above the falls, the river is narrow enough to jump across with dry feet, and flows through a fabulous alpine landscape. We didn’t hike all the way to the snowfield where the river actually begins, but we were close.
The fuzzy flower of a South Island edelweiss
My favourite two things on the hike were the South Island edelweiss (Leucogenes grandiceps), which looks like it was made out of felt by someone named Aunty Flo, and the river water itself. The water was crystal clear, yet colourful (the gorgeous turquoise of glacier-fed rivers) and full of substance. I could have watched it flow over the rocks for hours (come to think, I did watch it flow over the rocks for hours).
Waimakariri Falls Hut. The snowfield visible to the right of the hut is the source of the Waimakariri River.
Least favourite part of the hike was Carrington Hut. It’s a great hut in a stunning location, but last weekend, it felt as though everyone from Christchurch was there. Carrington Hut has 36 bunks, but only 1 toilet and 1 sink. With about 40 people in the hut and another 20 or so tenting nearby, it was way over its capacity. As usual, everyone was considerate and did their best to make it work, but it was still unpleasant.
All in all, a lovely weekend getaway, and an easy hike, as long as you’re comfortable with river crossings.
Robinne Weiss 