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What would the public think - soil degrader or enhancer?

Sunday, February 11, 2024, Grant Hunters blog

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.

One post

Post from Vaughan Kearns on March 25, 2024 at 7:26PM

It's over a month late, but thank you Grant for your blog.

Yes, it's a disgrace the nonsense that comes from the Fertilizer companies.

Accoring to them, if a bovine animal comes within a 100 metres of a Macrocarpa tree, it will immediately abort any offspring that it may be carrying. Just plain nonsense.

Vaughan Kearns

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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