Farm Forestry New Zealand

Lessons for owners of forests on erosion-prone land

Hamish Levack, New Zealand Tree Grower February 2021.

The report concluded that complete afforestation in what was defined then as the critical headwaters would provide the greatest economic benefit to the district in the control of erosion, and recommended commercial forestry on a large scale to combat erosion and stimulate the economic development of the whole district.

These were not novel concepts. The problem had been recognised almost as soon as the native forest had been cleared. Apparently, on their return from World War I, some of local soldier farmers were upset to find that many of their family-owned fertile paddocks had been washed downhill by the big 1916 flood.

More trees needed

The New Zealand Forest Service had already begun extensive afforestation at Mangatu Forest in the headwaters of the Waipoa River by the early 1960s. If it had not begun as soon as this, Gisborne city’s stop banks would have been breached in 1988 during Cyclone Bola, probably causing billions of dollars of damage instead of just millions.

Continued afforestation of erosion-prone pasture was clearly needed. Just before Cyclone Bola the Forest Service had been dis-established. The solution was to set up a contestable private forest subsidy called the East Coast Forestry Project, which apart from subsequent reviews, name changes and other modifications, has resulted in more than 40,000 hectares of forest.

Fast forward to 2018. Heavy rain flooded the Tolaga Bay catchment, damaging roads and bridges, piled forestry debris and sediment on farms and required a $10 million clean-up. This was mainly caused by the fact that substantial areas of such privately owned radiata pine had recently been harvested in one catchment. The restocked radiata pine plantations were in the vulnerable window when the extensive roots of the felled trees had rotted, but the new crop had not yet developed an adequate enough root system to bind the soil well, nor had they yet reached canopy closure which would have helped buffer the force of the rain.

Responsibility

There was a scramble to evade responsibility. Central government had encouraged the establishment of the relevant forests via its grant systems, and the Gisborne District Council had provided the consents to harvest them. However, it was the forest owners who were made into scapegoats on the dubious basis that they had not strictly adhered to the conditions of their consents to harvest.

It is very unlikely all the companies, whose consents the Gisborne District Council were supposed to be monitoring, were guilty of malpractice resulting in the forest waste being washed off-site. Two of these companies, Juken New Zealand and Aratu, decided not to contest the prosecutions and instead decided to plead guilty, even if they were not. Their justification was that this saved them substantial legal costs, and helped repair their bruised relationships with the community. Their respective fines were $152,000 and $379,000, not particularly painful to companies with scale economies and adequate insurance.

Relationship breakdown

However, the focus of this article is not so much about the effect of the Tolaga Bay flood on large forest companies but the shock to a smaller forest owner, in this case a company called DNS Forest Products 2209 Ltd. They had a resource consent to harvest 398 hectares of pine trees from Makiri Forest in the headwaters of the Waihora Valley. It had contracted A & R Logging Ltd, to harvest the wood and to build skid sites and associated internal forest roads, and had hired Logic Forest Solutions to oversee and audit the work. Unfortunately, relationships between DNS and the other two companies deteriorated, and in January 2018 A & R Logging and Logic Forest Solutions left the site. Five months later, on 4 June 2018, the Tolaga Bay storms struck, bringing massive amounts of forest waste down on to neighbouring properties, blocking waterways, damaging roads and covering the coast in debris.

Matthew Atkinson, the legal counsel for DNS, argued in defence that although large-scale forest owners should have been well able to ensure best forest practice, it is not reasonable to expect small-scale forest owners to be fully conversant with all aspects of forestry, particularly all the complicated operations associated with roading and harvesting. This is why DNS had contracted Logic Forest Solutions to manage, and A&R Logging to harvest the forest. Among other things the contract with Logic Forest Solutions and A&R Logging mentioned that they were obliged to ‘comply with all necessary resource consents ... and the RMA’.

Unfortunately, Makiri Forest was in a vulnerable condition after the relationship broke down. Completed, and semi-completed landings contained unstable accumulations of slash, log ends, tree heads and waste logging material mixed in spoil. Such material needs to be pulled back before the wood starts to deteriorate, and the piles become impermanent and exposed to downward movement into watercourses. DNS realised this, but also wanted to contract a replacement harvesting gang to minimise tree windthrow risk, and get an earlier return on the capital already expended.

DNS tried hard. However, during the first half of 2018 log prices were unusually high and seemed to be trending upwards. Consequently, increasing numbers of forest owners were wanting to cash in on the rising prices, and harvest their forests as well. All available harvesting gangs had already been secured.

This is why DNS was unable to obtain a gang to undertake remedial work before June 2018. Because of these mitigating circumstances, and the fact that the Gisborne District Council had withdrawn charges against A&R Logging and Logic Forest Solutions, DNS decided to plead guilty. To DNS’s dismay Judge Dwyer was not particularly lenient. He fined the company $124,700 and ordered it to pay $6,500 reparation to the owners of Makutu station, which had sustained a large amount of damage. Dwyer said that while DNS had been badly let down by its manager and contractor, it held the resource consent and therefore ‘the buck stopped with it’.

Implications

Debris flows do not only occur in the Gisborne District. Scion has estimated that more than half a million hectares of plantation forest is on erodible steep land in New Zealand. Much of this area, which was originally planted as erosion control forests, is now being harvested.

Debris flows are a natural mass movement which take place where there is a combination of steep slopes, intense rainstorms and high sediment supply. There is a risk of this happening whenever forests are harvested from such land. Much of the North Island and the top of the South Island are susceptible.

There are three components to identifying risk − erosion susceptibility, storm frequency and magnitude, and down-stream consequences of an erosion or debris flow. If you think that this applies to your forest consider contacting Scion or Landcare for a professional assessment. Work can be done to reduce your risk. These include minimising soil disturbance and compaction when harvesting, rapid replanting using high stocking rates to shorten the time it takes to get canopy closure, replanting with coppicing species such as redwoods, and plenty of public liability insurance.

In high hazard situations it may be wise to consider providing engineered structures to trap or store debris which can later be extracted in a controlled manner.

Woody residues can also be trapped by wide buffers or riparian zones of trees which are not harvested.

If an area is recognised as having a very high risk of erosion then a planned conversion to permanent forest cover may be the best option. This becomes even more attractive if the area in question can be registered in the Emissions Trading Scheme.

It is worth noting that standard practice, radiata pine clearfell regimes are now no longer a permitted activity on steeper red zoned slopes greater than two hectares in area. The National Environmental Standard for Plantation Forests specifies that red zone land can now only be planted or replanted with a territorial authority resource consent and the application will be subject to detailed risk assessment. The assessment aims to mitigate adverse environmental effects, such as storm-initiated slope failures with the potential to form debris flows that could result in damage to downstream infrastructure and property, but this requirement will undoubtably increase compliance costs for steeper terrain.

Hamish Levack helped with management plans for Gisborne District in the early 1970s, led the team which helped set up the government’s response to Cyclone Bola including the subsequent contestable forest grant scheme, and in 2020 acted as an expert witness for DNS Forest Products.