The Bioeconomy Science Institute’s research aims to enhance soil health to help ensure long-term sustainability for New Zealand.
This means growers across horticulture, viticulture, arable and pastoral farming industries can better address the challenges they each face, such as climate change mitigation.
Generally, New Zealand’s soils are naturally acidic, with low levels of nitrogen, phosphorus and sulphur. Radiata pine forests are usually established on less fertile, steeper land with poor-quality soil that makes it unsuitable for agricultural and horticultural use. The impacts of this planting on New Zealand soil have been studied, with positive results.
Evidence suggests well-managed planted forests can maintain or improve soil health while supporting a diverse range of soil microorganisms and other flora and fauna, as well as filtering groundwater and regulating flooding.
Bioeconomy Science Institute researchers have studied the nutrient uptake and demand on these sites for over 30 years.
“We’ve found that, depending on how those trees are harvested, we can control the quantity of nutrients removed,” said Christchurch-based Bioeconomy Science Institute principal researcher Peter Clinton.
“We’ve also done experiments on how harvesting intensity can impact long-term productivity and have seen many of these plantation sites go through a second rotation without any loss of productivity.”
Throughout their full lifecycle, plantation forests and natural forests can withstand a similar level of soil disturbance.
“Natural forests undergo quite catastrophic disturbances at times, through weather events that might see trees topple and root plates come out of the ground,” he added.
“But they recover. The same is true of the soil disruption caused by harvesting in planted forests. Soil is quite robust – if you don’t burn it, you won’t typically see a big shift in nutrients.”
Over the past 40 years, the practice of establishing planted forests on pasture has increased. In doing so, farmers have seen significant improvements in nearby water quality indicators, including better sediment and nutrient concentrations and reduced microbial contamination.
On balance, planted forests are ecologically closer to native forests than any other productive systems we have in New Zealand, including food production and dairy farming.
Foresters determine the quantity of nutrients removed during harvest, controlling the impact on the long-term productivity of the site. Disrupting soil in the harvesting process can be beneficial, bringing unweathered material and subsoil to the surface.
That process happens naturally as part of forest management. The other thing that happens is nutrient cycling, where you will see nutrients entering a forest with rain or dust. There are lots of natural processes going on that help maintain the fertility of a forest site.
Planted pine forests can provide many long-term ecosystem services, such as soil stabilisation. They can also help recharge nearby aquifers and maintain groundwater flow in dry seasons, contributing to the security of water resources downstream. The deep roots of planted forests can also bind soil and slow slip movement, reducing erosion and decreasing run-off.
The Bioeconomy Science Institute’s research into forest soil carbon and sequestration is also contributing to New Zealand’s climate change goals and long-term sustainability.
More about soil health in the latest issue here
