1 Sep 2016

Restoring the trees above and the fungi below

From Our Changing World, 9:15 pm on 1 September 2016

Community restoration groups around the country are out and about, taking advantage of winter’s damp soils to get native plants well established in the ground before summer.

The Nature Space web site says there are nearly 400 such groups in New Zealand. And between them they’ve planted more than 1.7 million native plants in the last few years. That’s a lot of plants. But many of them won’t make it.

That’s where Stephen Hartley from Victoria University of Wellington comes in. Stephen and his students are restoration ecologists, and they want to help all those community groups by coming up with the best ways of re-establishing native forests and wetlands.

This is long-term research – it takes many years to find out which plants are thriving and which have died.

Stephen began working at the Wairio Wetlands, on the eastern shore of Lake Wairarapa, five years ago. The work that he and his students are carrying out is part of a larger wetland restoration programme run by conservation group Ducks Unlimited.

Local farmer and wildfowl enthusiast Jim Law say he is pleased with the research collaboration.

“Initially people perceived us as a bunch of greenies, out here planting a few trees and having a happy time; but it’s much more than that,” says Jim. “To dispel that view … we formed an alliance with Victoria University, and allocated them one of the stages that we have created here and it’s essentially their scientific classroom.”

“The over-arching objective that they have – and which we are very interested in – is to determine cost effective ways for wetland restoration.”

Stephen Hartley

Stephen Hartley checks the growth of 5-year old seedlings at the Wairio wetlands. Photo: RNZ / Alison Ballance

The first results

Stephen says that the first experiments involved 2000 plants, and “used a variety of different pre-treatments [before planting].”

“The idea was to see what is the best way to get good plant growth and survival in a restoration situation in a wetland.”

In one experiment, for example, some areas had all the rank grass and top soil scraped away by a bulldozer and plants were put into bare dirt. In other areas herbicide was used to spot spray small patches for planting. The idea was that plants might grow better if they didn’t have to compete with long grass. But while plant survival is about the same, those that were planted amongst the grass have grown much taller.

Stephen suspects that the long grass may have helped shelter small plants from the strong prevailing wind. He also wonders if the bulldozer compacted the soil, and thinks that removing the top soil may have meant the loss of the most nutrient-rich soil.

Plant roots

The nodules on the roots of this plant are mycorrhizal fungi. Photo: RNZ / Alison Ballance

Stage two – looking underground

The Wairio wetland project is now turning its attention underground, to see if what happens with the roots and soil has an impact on the health and survival of the trees above.

Julie Deslippe, from Victoria University of Wellington, is an expert in soil mycorrhizal fungi.

”Mycorrhizal fungi are a symbiosis, so two organisms living together. They’re a plant root – that’s the ‘rrhiza part’ - and the myco is the fungus part, and they are a soil fungus that lives in symbiosis with a plant root.”

Julie says that it’s a partnership: “the plant makes sugars by photosynthesis. It feeds that sugar to the fungi in exchange for soil nutrients and water.”

As well, she says that the fungi connect different trees, which communicate and exchange resources via the fungal network.

Mycorrhizal fungi are a vital part of a healthy forest ecosystem, but Julie says they don’t know what fungi still exist in the soil at Wairio, which has been grazed as rough pasture since the original forest was cleared more than a century ago.

She hopes that the few remaining large native trees may have maintained a network of fungi that will help the next generations of trees.

Over the next five years, Julie and students such as Garth Fabbro will be carrying out experiments to find out how the roots of the seedlings establish relationships with the local soil fungi.

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