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What would the public think - soil degrader or enhancer?

Grant Hunters blog
Sunday, February 11, 2024

On 17 December we public awoke to headlines: "New research uncovers how much damage pine forests are doing to our soil". (Adam Hollingworth, Newshub)

Ravensdown CSO Dr. Ants Roberts - known as Dr Dirt - had dug up statistics that it can take 30 years for the soil to return to full health and suitable for pastoral use once again, after the trees are chopped down, which he says may make farmers think twice about converting pastoral land to forest.

"That's because the soil in pine forests tends to be acidic, unlike the soil on a lifestyle block, and in the forest you don't get nearly as much organic matter, he explains. Additionally, forestry soil is looser and may be subject to erosion. Ravensdown and AgResearch scientists crunched these numbers from Ngāi Tahu land converted from forest to pastoral."

"Converting good pastoral land to pine forests - as an agricultural soil scientist, I cry when I see that," Dr Roberts said.

For a couple of days, that was the simple message reverberating between the ears of those who bothered to read yet more bad news about forestry, ...that a rotation of forest downgraded perfectly good agricultural soils for half our working lifetime.

Fortunately, within two days, the article was rebalanced using input from Scion’s Principal Scientist Dr. Peter Clinton, and NZ Institute of Forestry, but really who cares about two-day old revised news?

Clinton pointed out that it’s long been well- documented that most NZ soils developed under forest, and are acidic in their natural state.

"When forest is cleared to make pasture, soils need to be made less acidic through application of lime to reach a pH level that is best for pasture. It’s no surprise to see those changes reversing when forest is reestablished."

"When we have measured soil health under pasture, planted pine forest and indigenous forest, we have found that soils under pine are much more similar to those under indigenous forest than they are to soils under pasture. In fact, lime needs to be regularly added to pasture soils to maintain the pH suitable for pasture growth."

We have an extra perception liability here – the tendency for many of us (well, I do) to start with the proposition that acid is inherently bad, never mind the context.

Good irony here I reckon, given that most of the 'thinking public' is dead-keen to restore natural cover. Who would want to believe that a rotation of pines might assist that process?

Significantly, but likely unnoticed, Clinton went on "We see these similarities in a range of measures. Nutrient and water runoff under pine forest are much more like the nutrient and water runoff under natural forest than pasture too." i.e., the water quality from a pine runoff tends to a more natural chemistry, too, surely a good thing in our degraded world.

But who notices stuff re-run a few days later? And everyone knows carbon forests are laying landscapes and farming communities to waste, log debris has destroyed floodplains, infrastructure and coastlines and so on. Who would want to believe a good side of plantations.

Best pathway for forestry to recover from this public mindset, I reckon, lies firmly with our farm forestry model, where agriculture and forestry are complementary within the enterprise, enhancing each other not competing. But we just learn how to convey the message, at a range of levels.

Spray releasing young trees with glyphosate

Dean Satchell's blog
Friday, December 23, 2022

I'm often been questioned about spray releasing diverse species when helping landowners with the early stages of forest establishment. Spray releasing methods for radiata pine are well established and you can spray right over the top of them with the right herbicide. But what about "alternative" exotics and native species? The issue is that the efficacy of each herbicide tends to be species dependent, so it's risky to use herbicide around young trees unless there is good knowledge on its safety. The stakes are high and failure can be catastrophic.

Because there are so many tree species and so many herbicides, spray releasing can get complicated. It is also perhaps the most critically important part to get right with growing trees. Because I like to keep things simple but effective, I use glyphosate. Of course glyphosate kills just about any plant it comes into contact with, but there is a simple method for its safe application to release young trees from their weed competition. The advantage with a broad spectrum herbicide such as glyphosate is that its simple to get right and kill all the weeds surrounding your trees. Of course, if there is a herbicide that you know is safe to spray around your trees and kills all your problem weeds, then just go with that one and ignore my advice.

Firstly, the spray mix needs to be right. For every ten litres of spray mix I use 100ml glyphosate 360. The "360" bit is the concentration of glyphosate, meaning that there is 360g/litre of the active ingrediant (i.e. glyphosate). If the label says the concentration is different then adjust the mix accordingly.

Next, 20mls of penetrant should be added per ten litres of spray mix. This is important to kill legumes such as clover and gorse and other hard-to-kill weeds.

Lastly, spray dye is essential. I just use a splash for every ten litres, enough to see where you've applied the spray. This is not only because it's important to know where you've already sprayed, but also to alert you where you accidently get spray on your trees.

Then, the most important kit to prepare before you start is the "spray guard". This is to stop spray drifting onto your trees. This is essentail and I've demonstrated what I use in the video below.

Spraying a one metre circle around your trees seems to be standard practice. Best in late spring or early summer. Too late and your trees get lost or just don't grow because of root competition.

A simple but essential piece of equipment is a small spray bottle of water. Keep it on you at all times in case of accidental contact between glyphosate and tree. The glyphosate must be washed off immediately, because the penetrant quickly draws it into the plant.

Spray bottle, belt and "holster" made from a plastic milk bottle

Never spray if there is rain or too much wind. Keep the pressure low, don't pump the backpack up too much because you'll get more spray drift which is risky for both yourself and the plant. Apparently glyphosate isn't good for humans so I like to use leather gloves over disposable latex gloves and good trousers and gumboots to ensure spray doesn't get to the skin.

I take no responsibility for the advice I give here, it works for me but if you're careless then things won't go well. Because glyphosate is a systemic herbicide, it can translocate through the plant from one point of contact and kill it. You don't want to get it on your tree. That said, it only seems to soak into green leaves, so doesn't appear to cause issues from soil or stem contact at the base of the tree.

Disclaimer: Personal views expressed in this blog are those of the writers and do not necessarily represent those of the NZ Farm Forestry Association.

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