Pining for native cover

Fashions happen in farming as much as they do in other fields of life.

Once upon a time, farms were great swathes of grass, with barely a tree in sight. There might be a row of macrocarpas to act as a shelter belt for farm buildings, but the landscape would be a rolling view of grass, sliced into paddocks by wire fences.

Now, growing trees is a hobby and a profitable sideline for many farmers. There are native plantings in gullies and hillsides too steep and unstable to farm animals on. There are commercial forestry plantations, destined to fund retirements or grandchildren's education.

Farm forestry is a hot topic, and the New Zealand farm forestry conference earlier this month was one of the largest conferences in Marlborough this year. Hundreds of people interested in trees attended - nurserymen, scientists and farmers.

Organisers planned many field trips for members to see different aspects of forestry in Marlborough.

And while the pine tree - particularly pinus radiata - is a favourite species, because of its resilience and the commercial use of its wood, one field trip for about 100 people took them out to Tory Channel to see how the Marlborough Sounds Restoration Trust and Sounds landowners are getting rid of pine trees.

As Hitaua landowner Graeme Moore said when the group visited his property near Tory Channel, the pine trees were a feature of just about every Sounds farm. They sheltered the house and, as kids, everyone remembered collecting pine cones for the fire.

But when the farms failed, the trees took over.

Some farms were turned into forests, which were milled once, then left because the economics of harvesting just didn't stack up.

Unfortunately, where there is one pine tree, you end up with many more - known as wilding pines - as the tree sends out its cones and seeds to take over hillsides like a dark shroud over the Sounds. They keep the light from other plants on the ground, and the needles smother the soil, making sure nothing else grows through to compete with the pines.

Moore's property at Hitaua was used as an example of what could be done by landowners.

He had heard a programme on Radio New Zealand years ago about controlling pines and started work on his own land.

It had been a learning experience, trying different methods to get the space and light for native species to take hold.

Moore planted fast-growing Australian acacias and blackwoods to keep out the pines and he's now working to remove them and their persistent seedlings. Initially he ringbarked pine trees, but has learnt from the experience of others such as the Marlborough Sounds Restoration Trust, and now poisons the pines.

Restoration trust manager Andrew Macallister told the field trip group the felling of wilding pines had been tried in the Sounds in the past. But this could make the problem worse.

Large trees break down a lot of regenerating native vegetation as they hit the ground, opening up a "light well" on the forest floor. Pine seeds like high light conditions to germinate, and dozens of seedlings can appear around the felled tree.

Ringbarking the larger trees put them under stress and they threw out more seeds, leading to regrowth and even more trees to be eradicated later.

By contrast, the poisoning programme does not disturb the regenerating native vegetation and allows a seamless transition from wilding pines to native vegetation. Significantly less secondary pine regrowth is expected from poisoning.

"It is widely recognised as the preferred means of managing wilding pines in forested areas."

It also didn't cause a murmur from tourists - the trees went "ginger" and then grey as the poison took hold and killed the trees. Most tourists in the Sounds were from the Northern Hemisphere, he said, and were used to the sight of orange trees.

Seeing the dying ginger pines on the hillside didn't cause them any concerns.

The dead trees were also home to other species, such as wetas and geckos.

Moore said poisoning the pines coupled with lots of pest control had helped. His family had noticed a huge increase in bird life since the work started.

He planned to take the livestock off the land eventually, and hoped to open it to the public once they were rid of the dead trees. Some are close to walking tracks and could be dangerous if they fell.

Macallister said the trust set up a comprehensive programme seven years ago to tackle wilding pines. They towered above regenerating native forest canopy and in many areas became the dominant feature of the skyline, affecting scenic values.

A trust report concluded the landscape values of the Sounds would gradually diminish without wilding pine control, losing its distinctiveness.

For years, private landowners and the Department of Conservation had been doing small wilding pine-control projects, but without the size and scope to address the problem over the Sounds as a whole.

The trust aimed to establish a co-ordinated programme that tackled pine control in a strategic way, dividing its management areas into control blocks based on the extent of wilding pine infestation, access considerations, tenure, land use and landscape values, and working through these in order of priority.

Macallister said the trust employed professional contractors to do the control work, mainly from the top of the South Island.

Seedlings and young trees are either hand-pulled or felled using a pruning saw. Mature trees are generally poisoned by drilling holes into their trunks, and injecting a small amount of herbicide into each hole. The active ingredient is usually glyphosate or metsulfuron-methyl, common agricultural herbicides.

This method is environmentally friendly, with no discharge of herbicide to the land, into waterways or the air. Occasionally, trees in difficult-to-access areas, or where they are widely spaced, will be treated with herbicide applied onto the bark from a helicopter.

Technology lets them deal with the problem in a structured way. Aerial photos are used, and the area divided into blocks, assigned GPS waypoints, and the contractors work their way across the hillsides, treating the pines as they go.

Macallister says the GPS system enables him to check on progress, even from his base in Nelson. "I can ring the contractors at night and tell them they missed a couple of trees."

The trust started its work in the inner Queen Charlotte Sound, but has spread to D'Urville Island, Kenepuru Sound, Pelorus Sound and the outer Queen Charlotte Sound because of the community support.

Marlborough businesses were supportive, he said, including Cougar Lines supplying transport.

Commercial forestry is still a big industry in the Marlborough Sounds, and the pine tree is likely to stay the preferred tree for many farm foresters. However, the field trip gave a view of the "dark side" of the pine tree, with farm foresters learning from Sounds landowners moving to put their land in natives and dealing with the remnants of pine forests.