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Do not let harvesting mishaps paint a false picture of forestry

Nick Ledgard, New Zealand Tree Grower August 2018.

I recently wrote an article for our branch newsletter about forests on the move. This focused on the so-called window of vulnerability, a period of about six years after a plantation is clear felled, during which the land lies unprotected and at the mercy of rainstorms and cyclones.

We have all read about the flows of forest debris which inundated coastal farms in the Tolaga Bay area. Needless to say, some of the reaction has gone to the extremes of saying that all forestry should be banned on hill slopes. This is ill-informed thinking.

On the shelf alongside me there is a box of videos, which I used to show to Stage 1 forestry students when talking about soil erosion and forestry. One is titled The trees come back. It is a documentary showing the history of why the East Coast plantation forests were planted in the first place.

It describes how, starting in the latter years of the 1800s, the native forest covering those hill slopes were removed, mostly by burning, to make way for farms and pastoralism, and how this resulted in widespread and severe erosion over the following decades. The video shows dramatic footage of huge areas of collapsing pasture slopes resulting in soil-flled streams and rivers, blocked roads and fence lines stacked with the carcasses of drowned sheep. Many farms were abandoned due to this soil loss, and essential infrastructure such as roads and power lines were severely damaged.

East Coast project

As a result of this widespread erosion, the local Poverty Bay Catchment Board started the East Coast project, which initiated a multi-year tree and plantation forest planting operation to halt the loss of soil. The core area involved over 200 farms, but lesser damage was far more widespread. The video, made in the 1970s, ends with scenes of afforested slopes and tree-lined streams carrying clean water into stable riverbeds. In other words, the severe accelerated erosion problem was solved by the strategic use of trees and plantations.

During my days of working for the Forest Research Institute in Rangiora and Christchurch, I often used to fly north to our headquarters in Rotorua. I always made sure I got a window seat to get a good view of the land passing below. We flew over the hill country of the upper Rangitaiki and Manawatu catchments. The scenes were, and generally still are, typical of what I saw – treeless farms dominated by slip-covered eroding hills.

Much of the soil lost from these slopes ended up on the productive farmland of the downriver plains, where the aggraded rivers frequently flood the surrounding intensively managed farms. Those headwater slopes should never have had their forest cover removed in the first place. It is inevitable that we will soon be talking about widespread planting of such land – as much as anything for the protection of those remnant soils.

Without a doubt, we foresters have to be more careful with our harvesting practices to minimise the opportunities for accelerated erosion and debris flows during that window of vulnerability which opens for a few years after a clear fell harvest. But everyone must also acknowledge that trees and plantations have a large role to play in holding soils on site and ensuring clean streams and rivers. Only the uniformed make claims that forestry should be banned from our erosion-prone hill country.


Another result of the latest damage resulting from plantation harvesting, is increasing comment about abandoning clear-felling and moving more towards continuous cover forestry, where only a percentage of mature trees are felled at any one time, in order to maintain an intact forest canopy.

I fully support the concept, but unfortunately the big forest companies are just not set up for this to be commercially viable at present.

Recent articles have expounded the virtues of continuous cover forestry (see page 25), and cited many examples of its successful use offshore. Many of us would have seen this in the forests of Europe. But what the commentators have almost completely ignored is an excellent working example right on our doorstep. I am of course talking about Woodside, the farm forestry property of John and Rosalie Wardle near Oxford.

Since the 1980s they have managed 70 hectares of beech forest and 28 hectares of radiata plantation on a single-tree-harvest, continuous cover regime. This is described in detail in John’s recent book Woodside – a small forest managed on multiple use principles published in 2016 by the Indigenous Forest Section of the NZFFA. It is a well-written story of not only how they make this regime pay its way, but also how well it lends itself to a long-term sustainable and stable landscape with improved indigenous biodiversity such as bird-life.

Therefore, clear-fell harvesting does not have to be an essential part of viable plantation forestry. But it will need a huge change in New Zealand’s current plantation forest management thinking before meaningful moves are made in that direction.


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