The severe impacts of Cyclone Gabrielle on the North Island, and the five severe weather events experienced by the Thames–Coromandel region in just the first two months of 2023, are merely the latest examples of more frequent erosion-triggering rainfall events over the past decade.

Inevitably with the heavy rain, soil, rocks and woody material (also known as “slash”) from landslides have flowed down onto valleys and flood plains, damaging the environment and risking human safety.

Clear-fell harvesting of pine forests on steep erosion-prone land has been identified as a key source of this phenomenon.

So we need to ask why we harvest pine forests on such fragile land, and what needs to change to prevent erosion debris and slash being washed from harvested land.

Pine was a solution
Ironically, most of these pine forests were planted as a solution to soil erosion that had resulted from the clearing of native forests to create hill country pastoral farms.

The clearing of native forests happened in the 19th and early 20th centuries, but the consequences — erosion, flooding and floodplains covered in silt and rocks — only became apparent decades later.

Research has shown that pastoral farming on our most erosion-susceptible soils is not sustainable. The productivity of the land is being degraded by loss of soil and large areas have been buried with sediment eroded from hill country farms upstream.

So the need to reforest large areas of erosion-prone farmland is scientifically well accepted.

Why pine?
But why did we choose radiata pine for our reforestation efforts instead of other tree species?

Even today, it is hard to find affordable and feasible alternatives to radiata pine. Affordable is the key word here.

We are not a rich country and our liking for “Number 8 wire” solutions makes a virtue out of necessity — we don’t have the money to pay for anything fancier.

Radiata pine is a cheap and easy tree to establish and it grows fast and reliably. Planting native or other exotic trees, such as redwoods, is possible, but it costs more and needs more skill and care to grow a good crop.

‘Has to be done’: Forestry industry under fire as McAnulty calls for slash to be investigated https://t.co/7lx5G2t07W

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The problem with radiata pine is that if grown as a commercial crop, it is clear-fell harvested after about 28 years.

The clear-felled land is just as erosion-prone as it was before trees were planted — with the added threat of large amounts of logging slash now mixed in with the erosion debris.

It can take six years or more after harvesting before the replanted pine trees cover the ground and once again provide protection to the soil.

Benefits of pine come with a cost
If we take a long-term perspective, research shows that even a radiata pine forest that is clear-felled once every 28 years will still significantly reduce erosion, compared with a pastoral farm on erosion-prone hill country.

This is because the erosion from the clear-felled forest is outweighed by the reduced erosion once the replanted trees cover the land.

However, this is not much comfort to communities in the path of the flood-borne soil and logs from that clear-felled forest. It’s difficult to take a long-term perspective when your backyards and beaches are covered with tonnes of wood and soil.

Slash a byproduct of efficiency
Whatever benefits radiata pine forests bring, we need to transition forest management away from “business as usual” clear-felling on erosion-prone hill country.

This transition is possible, but one important problem is not often discussed. The pine forests are privately owned by a range of people including iwi, partnerships made up of mum-and-dad investors and large international forestry companies.

All these people have created or acquired these forests as an investment.

A typical pine forest investment makes a good financial return, but this assumes normal efficient forestry, including clear-felling large areas with highly-productive mechanised logging gangs.

It has become clear that we need to manage forests differently from this large-scale “efficient” model to reduce the risk of erosion and slash from erosion-prone forests.

Changing how we manage these forests will inevitably reduce the economic return, and forest investors will absorb this reduction.

When a cyclone bears down on the East Coast, it’s not just wind and rain residents brace for. https://t.co/h9TJr3Q2dv

— Stuff Business (@NZStuffBusiness) February 15, 2023

Time for a permanent fix
If we go back to when the pine forests being harvested today were planted, the forests had a social value — not just in reducing erosion but in providing employment in rural areas where few jobs were available.

This social value was recognised by government funding, initially through tree planting by a government department, the NZ Forest Service. With the rise of free market economics in the 1980s, such direct government investment was considered inefficient and wasteful.

The Forest Service was disbanded in 1987 and its forests were sold to forestry companies. However, the government continued to promote tree planting on erosion-prone land with subsidies to private investors.

As these forests grew, they came to be considered purely as business investments and were bought and sold on that basis. When the time came to harvest the trees, the expectation was that these could be clear-fell harvested in the same conventional way as commercial forests growing on land with no erosion risk.

As erosion started occurring on the harvested sites, it became clear why these trees were originally planted as a social investment to protect the land and communities from soil erosion.

Aotearoa New Zealand has achieved control of erosion with a Number 8 wire solution- encouraging private investors to grow commercial pine forests on erosion-prone land. The problem with Number 8 wire solutions is that after a while the wire fails, and you have to find a permanent fix.

Conventional commercial pine forestry was a good temporary solution, but now we need to find a more sustainable way to grow forests on our most erosion-prone lands – and it won’t be as cheap.

Mark Bloomberg, adjunct senior fellow Te Kura Ngahere — New Zealand School of Forestry, University of Canterbury.  This article is republished from The Conversation under a Creative Commons licence. Read the original article.

Article by AsiaPacificReport.nz

Widespread damage has hit farms across Aotearoa New Zealand’s North Island with those in parts of Gisborne and Hawke’s Bay particularly hard hit and forestry slash is once again a huge problem.

Tolaga Bay farmer Bridget Parker told how forestry slash has caused a huge amount of damage to her farm yet again as the death toll from Cyclone Gabrielle rose to six.

“It’s enormous — there is silt all over the road. It’s so thick you can’t walk through it; there are logs as far as the eye can see,” she said.

“There are so many logs all the fences are down; wherever you look it’s total carnage.”

Parker, whose farm has been destroyed by forestry slash during storms multiple times, said they can look at forecasts for rain, wind, drought and even tides but they could not predict what was going to happen when it came to the logs.

“We don’t farm logs. Their logs [the forestry companies] and their friggin’ silt needs to stay inside their friggin’ estate gates.

“It does not have the right to be spewed over the 3000ha of beautiful land that is farmed on the flats below it.”

Parker said Minister for Forestry Stuart Nash needed to visit the region within the next week to answer to farmers.

“There’s floodwaters everywhere, in our house, in our sheds. It’s far higher than last time and we are really really struggling to cope; we’re really angry.”

Hawke’s Bay area ‘smashed’
Forestry slash has also caused issues on farms in Hawke’s Bay where there was widespread flooding and slips.

Suz Bremner, who runs sheep, beef and friesian bulls along the Taihape Napier Road, said she had never seen damage like it.

“I tipped out the rain gauge this morning. It was overflowing at 170mm so we don’t know how much we’ve had.

“The power is out but from what we are hearing from people nearby is that the wider Hawke’s Bay area has just been smashed.”

Bremner said she went for a drive around her farm yesterday morning to assess the damage but roads were blocked by trees while tracks had been washed away.

“Looking at some of our neighbours who have big cliff faces on their properties the slip damage is horrendous.

“We have a road through the top end of our farm and we turned down there this morning and my husband and I could not believe our eyes. The slash that had washed down through the creeks is unreal; I’ve never seen that before.

“I think the forestry has come down and created a dam and then during the night it’s just exploded and now there’s slash everywhere,” she said.

Other farmers RNZ spoke to in Hawke’s Bay said they were hunkering down waiting for the worst of the weather to pass before getting out to assess the level of damage.

This article is republished under a community partnership agreement with RNZ.

Article by AsiaPacificReport.nz