NATIVE or pines, forest soils are similar and not 'damaged' according to forest owners and scientists
THE fact soils under plantation forests are similar to soils under native trees does not make them damaged, New Zealand Forestry Owners Association president Grant Dodson says.
He has hit back at media reports in December 2023 about “damage” being done to the land by pine forests.
“Pasture soil is highly modified. It has been turned from its natural acidic state, by applying lime, to encourage grass and clover to grow,” Grant said.
“That’s what farmers need to do to get animal protein production from their farms.”
Pasture was not initially ideal for growing trees either, he said.
“Pasture is low in the essential mycorrhiza for optimum tree growth. That takes years to come back to help the trees grow.”
This applied to native species and pines.
“You can see from that, that the soils reflect the vegetation on top of them. There is nothing deficient about forest soil. It is just wrong to assume that if it’s not growing grass then it’s a production failure.”
“Forestry is very much a productive part of the economy and a major exporter, with no other primary sector anticipated to improve its export earnings by more in the period up to 2030.
“Trees absorb greenhouse gas – they don’t emit greenhouse gas. Forests don’t need fertiliser. They don’t discharge pollutants into rivers. They clean them.”
Grant is commenting on Ravensdown chief scientific officer Dr Ants Roberts statements on Newshub last year that it would take 20-30 years to restore soil health for pastoral farming after it had grown pines.
He said that was because the soil in pine forests tended to be acidic, unlike the soil on a lifestyle block, and in the forest there was not nearly as much organic matter.
Scion principal scientist Dr Peter Clinton said soils that had naturally developed under forest, like most soils in New Zealand, were acidic in their natural state.
“When forest is cleared to make pasture, soil needs 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 re-established.”
The changes have been well documented in long-term studies, he said.
“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 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.”
Soil pH was only one measure of soil health that is different under forests, Dr Clinton said.
“We see that soils under intensively managed pasture can be more compacted by animals and farm machinery than what we typically see under forested land.”
This could make it harder for roots to grow, and for soils to absorb water during heavy rain. In the worst cases, pugging of soil became a problem.
Most forests established under the Emissions Trading Scheme (ETS) have been on classes of land that have serious limitations for intensive agriculture but were well suited for forestry, he said.
Additionally, well-managed plantations of trees on farms, exotic as well as indigenous, provided a range of benefits for sustainable and economic farm management.
Extensive research also showed that forested landscapes improved water quality and soil structure, reduced erosion, enhanced biodiversity, and supported regional economic development.
Export earnings from forestry made a significant contribution to the national economy and locally grown timber was a key input to the New Zealand housing and construction industry.
Forests will also have an increasingly vital role to play in helping New Zealand meet its net-zero emissions targets by 2050 through carbon sequestration and providing feedstocks to meet growing demand for bioenergy, and for high-value products that offer an alternative to those made from fossil fuels.
