GLOBAL WARNING

How will climate change affect our home gardens, plants and vegetable crops? Ruud Kleinpaste looks into the future.

Iwish I had a crystal ball that could tell me how my grandkids are coping on this planet 30, 40, 50 years from now. With a bit of luck, the projected graph of Homo sapiens populations will have become reality (a decline after 2050), either through effective education of birth control methodology or simply through the next waves of pandemics. Yes, our parasites and pathogens will still have human hosts, especially when we are so numerous and continue to increase our impact on this planet, while chasing economic growth at all cost.

Climate disruption is an extremely complex beast that will have an effect on everything we rely on. Everything is connected but that, of course, is no news to gardeners.

It’s not a simple matter of higher average temperatures. A lot of people tell me that it would be great to be able to grow lychees or custard apples with ease; others are thankful that the Port Hills are showing more pockets of frost-free zones, where avocados ripen on the tree.

The truth is, increasingly, we are facing unpredictable growing seasons largely caused by an increased variability of weather patterns.

Plants don’t just respond to temperature averages, they are far more affected by extreme events. Destructive storms will quickly teach you the best way to stake your brittle stems and branches or how to provide shelter through clever planting for the tricky nor’westers or southerly storms. Did you lose your stone fruit through a late snow? Or was it an early bloom period?

Of course, those record-breaking heatwaves will become more and more prevalent. That means that daytime soil temperatures may – at times – cause stress and damage to root systems especially in dry conditions. We are all fairly well aware of the preventative actions we can take: mulch, mulch mulch! A good layer of carbon-rich material can reduce soil temperatures by 10 degrees.

As far as these elements are concerned, we are simply in the business of managing risks.

This past growing season I literally lost the majority of my sanguine peaches through really poor risk management: I failed to properly thin the young fruit, resulting in overloaded, heavy branches on a relatively young tree, which was exposed to our famous Canterbury nor’wester – an example of having to think ahead when we grow gardens in such wild weather patterns.

But what about the long-term effects of this climate disruption? There’s no doubt that an overall increase in temperature and changing precipitation patterns will make our country far more susceptible to plant pests and diseases we’ve never seen before. The North Island will be looking at subtropical species that suddenly appear in our gardens.

Invertebrates are “ectotherm”, which means they rely on the environmental temperatures to heat their body. Fruitflies will be “at home” in warmer places and whiteflies really do not need any glasshouses to live in. Thrips, mites, leafminers, caterpillars, scales, mealybugs and certainly ants would welcome higher temperatures especially in the winter as it allows a much better survival rate during the “cool season”.

I always believe that clued-up gardeners are our important second line of defence when it comes to spotting new interlopers into our country. Gardeners all over the country can play an important role as the eyes and ears of biosecurity.

MPI are doing their job at the border, sniffing out exotic critters transported in aeroplanes, luggage and commercial shipments, but despite their best efforts some organisms get through. For that reason we might as well become familiar with that handy app iNaturalist and learn to identify the organisms in our garden, especially the ones we’ve never seen before.

With increasing storms and wind speed, we also run the risk of mites, moths, spiders and minute bugs as well as fungal spores travelling across the Tasman. It’s happened many times in the past and with stronger winds, it’ll happen again. That dreaded myrtle rust is currently distributed through the North Island and the top of the South Island. Some exotic and especially native Myrtaceae are dangerously affected by that fungus. Others (mainly in the South Island) are still doing OK, but this hideous pathogen

will certainly spread south when the climate changes and so far, we have no control or prevention technologies that would stop it. Yes, research is on its way, but it will likely take many years before we have a myrtle rust “vaccine”.

This means that, for the time being, gardeners are going to have to refrain from taking cuttings or transporting likely hosts through Aotearoa. It’s that old, common sense attitude of applying quarantine or biosecurity measures when it comes to propagating your garden plants.

And then there is the concept of “sleeper pests”: exotic species that are already established in Aotearoa but never seem to do much harm under current climatological conditions.

Tropical armyworm comes to mind – a caterpillar that can sometimes do some damage to an enormous range of garden plants (seedlings, perennials as well as annuals) but it usually gets knocked by frosts. This could well change in the future.

Another cool phenomenon I am looking forward to is the awakening of Locusta migratoria (migratory locust) which has been in our country for ages, especially north of Christchurch. So far it has never wanted to form those amazing swarms in late summer, but give it a few degrees and the genetic variants will kick in, I reckon.

And if that doesn’t change our economy, I don’t know what would.

Of course, we also have “sleeper weeds” that will escape further south: kahili ginger, that choking alligator weed in our waterways, strawberry guava and – dare I say it – kikuyu, all frost tender species that will spread and take over our gardens and the native ecosystems with all that unique biodiversity.

Gardeners and environmental warriors will become increasingly busy keeping an eye out for new, invasive plants, necessitating a lot of weeding, weeding and more weeding.

A change in climate will have direct effects on our biodiversity too: imagine what would happen with beech mast years. We are seeing more and more eruptions in the population of exotic predators and interlopers (rodents, stoats, ferrets, possums, but also pigs and deer, just to name a few) and increased mast years will no doubt make it worse, requiring a lot more control measures to keep our native biodiversity and unique habitats safe.

And then there is timing.

Pollinating species are often perfectly “timed” with the opening of their favourite flowers. The moment this synchronicity is disrupted, plant and pollinator will miss each other by days, weeks or even longer. This requires a very quick adjustment in the form of evolution or adaptation, which – as we all know – usually takes longer than a few years.

Another timing-related ecosystem service is predation and parasitism. The precise moment natural biological control organisms step forward to do their job is quite important. No point looking for a host or prey when this has already emerged a few weeks ago.

You simply miss the bus.

In the past, before humans decided to become the most “intelligent” species on this planet, changes in weather patterns and climate tended to progress really slowly; slow enough for the local biodiversity to adjust. Now the CO2 graph looks like a hockey stick, requiring us to act with great haste and supersonic speed. Former US Vice

President (and presidential candidate) Al Gore pointed that out in 2006, in his documentary film

An Inconvenient Truth.

When we think of solutions to quickly and efficiently reduce the amount of carbon in the air, we all have a reasonably good idea of what to do. Is there anybody out there that immediately thinks of commencing trading in carbon credits?

No, I didn’t think so. Yet that same Al Gore was the very first carbon billionaire on the planet!

Carbon mitigation would start by seriously reducing the CO2 output, followed by planting heaps and heaps of native trees to sequester the carbon that’s in the air, allowing it to go back into the soil profiles.

If we then build native forest corridors, we might even assist our native biodiversity to thrive in the landscape (which would obviate trading in biodiversity credits).

Imagine these corridors on dairy farms, providing wind shelter and soaking up excess nitrogen before it all gets into the waterways.

Perhaps this is a good opportunity to point to research published by Project Drawdown (you’ll find it online), where you can find a good series of proposed mitigation actions and strategies, presented science in order of values and outcomes.

Not surprisingly, reducing food waste (including composting!) and plant-rich diets are on top of the list, along with refrigerant management.

Health and education is squarely number two on the mitigation list, no doubt a reflection of the need to reduce the human population on Earth.

When I look at this impressive research, I am more and more hopeful that we might just pull it off, as long as we keep on gardening and growing in this disrupted climate. We may not need a crystal ball after all.

We know what to do. ✤

The moment this synchronicity is disrupted, plant and pollinator will miss each other by days, weeks or even longer.