Shade Trees for Cows & Profit

Back in the 1930s Audrey Mill leaned out of the open cockpit and took images of the Canterbury Plains while her husband Doug flew their air survey plane. One landscaped property beneath them clearly stood out – an oasis of trees on the flat landscape – worthy of its own photo. 

The Canterbury Plains were a prosperous agricultural area even then, a patchwork of pasture and cropping land, and had been for 80 years.

Nearly a century later, trees figure even less in the landscape. While windbreak trees run along some boundaries, the remaining small pine forestry blocks were felled 25 years ago when dairying picked up in the area. But meeting the challenges of a warming climate may yet see trees making a comeback.

Milder winters and an extended growing period over the warmer months will be of particular benefit to pastoral farming. But this will go hand-in-hand with longer, hotter summers with Canterbury’s legendary nor’wester winds also becoming hotter and stronger, and pulling more moisture out of soil and vegetation.

Water availability and irrigation are likely to be the biggest issue for the region in coming years, with efficient water use and holding onto soil moisture becoming more important.

Farms around Twizel already see temperatures over 25 degrees Celsius for 40-50 days a year, says NIWA climate scientist Nava Fedaeff. By the end of the century there could be an additional 60 to 85 days.

Slowing Canterbury’s Foehn wind which sweeps down off the Southern Alps after dropping its moisture as rain on the west coast, will help. Without its moisture, the same air flow with a temperature of 15 degrees Celsius at Westport can rise to 25 degrees Celsius or higher at Darfield. “The nor’west wind is very dry – it has low humidity as all the moisture is lost over the alps and it sucks up moisture east of the divide,” Nava says.

Much of that air flow off the Tasman Sea, getting squeezed up and over the alps, also comes off the Australian continent which is also heating up. “When Australia has temperature extremes we connect and import some of their air.”

For the most part dairy animals are grazing out in the open and start to feel heat stress at around 20 degrees Celsius. This sees them eating less, reducing milk production. Lower levels of moisture in the pasture they’re eating also increases their body temperatures.

Kyle Wills, a farming systems consultant with WSP, is among agronomists who see the slow uptake on providing shade and shelter for livestock, despite Ministry of Primary Industry prompting, likely to see stricter regulations on the horizon, where providing shade may become mandatory. “Adding trees to the mix on farms is going to increase complexity for farmers to manage pasture, but if giving shelter and shade to dairy cows becomes a legal requirement it’ll almost be a necessity – whether its trees or a physical shelter.”

But trees for shade and irrigators don’t mix.

With funding from Our Land and Waters’ Rural Professional Fund Kyle has been looking into the economics of planting up the poorer pasture areas outside the reach of irrigators with widely spaced deciduous fodder trees to provide shade and feed for stock (agroforestry), slowing down the Foehn wind while also bringing in a new income stream from carbon credits. There are an estimated 35,000ha of these dryland corners across the plains.

Dairy farmers are initially quite dismissive of the idea when he discusses it with them, he says. They see agroforestry as strictly pine trees with high density planting and not a lot of grass growing underneath. But they usually come around and start seeing the possibilities, he says.

“If we can plant [fodder] trees in a way that they reduce the wind speed, and reduce the temperature through shade we should significantly reduce trans evaporation, which will provide a better environment for growing grass,” he says.“Weather protection from trees is 10-15 times their height down wind. And they don’t have to be tall but a significant amount of land would get shelter from wind.”

This should also provide some shelter to pivots which can struggle in very strong winds.

Depending on the trees used, these wooded areas, with cooler micro climates underneath, could also provide increased biodiversity across the plains – not just for birds and other native wildlife but also for insect pollinators for agriculture and predator control of pest insects.

In a desktop study Kyle modelled two dairy farms at Waimakariri which had around 95% irrigation coverage. Wind and drought tolerant forage poplars and mulberry, with honey locust to fix nitrogen, would go in the paddock corners of both farms. The 647ha Claxby farm property had 61ha of dry paddock corners, while Ngāi Tahu’s – 335ha Hamua farm had 25ha dry corners.

The Claxby farm would include a handful of high value black walnut timber trees, while the Ngāi Tahu farm would include nitrogen fixing kowhai and fast-growing ribbonwood to attract native birds and over time natives would replace the exotics to become solely native agroforestry.

The modelling had trees running north to south where possible for the most sunlight on pasture and to screen the wind to reduce trans evaporation under the trees and in pasture downwind. The rows of trees were 20m apart, with trees 10m apart within the rows. Native trees were planted 2.5m apart.

There was more expensive double fencing on the Ngāi Tahu farm to allow for more vegetation for wildlife, and individual tree protectors and stakes for the Claxby trees.

This layout with 40% canopy cover would see the planted areas qualifying for carbon credits under the permanent forest category with the Emissions Trading Scheme.

During spring growth, the deciduous trees would allow good levels of daylight to fall on pasture, with the roots drawing moisture and minerals closer to the surface and nitrogen fixing species adding additional nutrients.

The project showed the numbers stacked up for the trees. Carbon credits would climb to around $170,000 annually for Claxby, and $70,000 for Ngai Tahu, at the seven-year mark. From here they would fall slowly to the 35-year mark where revenue from increased milk solid production would see a modest income off the trees after that.

Other shade/sharing options include trees inoculated with mushrooms; highly palatable hazelnut trees inoculated for truffle fungi – not intended to be felled. While oaks are another popular truffle tree, they are a health hazard to cattle.

Material off orchard trees containing condensed tannin like pears, reduces both bloat and methane when eaten in small amounts.

Slash and fallen trees can also be chipped to replace flooring material in loafing areas and composting shelters – which also offer good shade in summer and shelter in winter.

The full report on agroforestry on irrigated dairy farms can be found in this year’s Rural Professional Fund project summaries ourlandandwater.nz/project/rural-professionals-fund-2023-24/

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