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Clarky's Comment - Mud and Logs – A big problem

The Tolaga Bay floods of 4th June brought with them logging slash from recently harvested forests in the hills above. This follows similar events over the past two years in Hunua, Motueka and the Port Hills. There are three main reasons that these outcomes are becoming more frequent:

  1. Logging activity on steep, erosion-prone topography is increasing in line with the age-class profile of the exotic plantation estate.
  2. The frequency and intensity of localized heavy downpours is increasing, presumably reflecting climate change.
  3. There have been instances where harvesting managers have been found wanting in the placement and management of logging slash on the slopes.

There is not a lot that can be done about the first two causes. Strong monitoring and prosecutions from time to time by the Regional Councils should send the signals to harvest managers to apply best practice.

But my thesis is that even with best practice in harvesting and slash management this problem will not go away. New Zealand’s geology is fragile, being largely crushed or weak sedimentary rock formed by successive tectonic plate uplift and erosion periods. Should we be surprised that our flood plains occasionally flood? That is what made them in the first place and why they are attractive fertile places to live and farm crops.

English and European settlers cleared the native forest for pastoral farming, but there is evidence that prior to that native logs and slash would inundate floodplains and beaches from time to time. Much of the East Coast pine forest has been planted on this farmland that became uneconomic to farm in the 1980s and 1990s. Cyclone Bola in 1988 was a catalyst for many East Coast farmers to sell up and move on. Local authorities and the central government have been offering subsidies to encourage the establishment of commercial plantation forests on erodible farmland on the East Coast.

So what can be done?

Under the new National Environmental Standard – Plantation Forestry (NES-PF) our most erosion prone land is classified Red Zone and needs a resource consent, involving a Land Management Plan to establish a plantation forest. Conditions may be imposed by Regional Councils, even for a replant, that seek to avoid excess erosion or debris flows at harvest time. The conditions may cover species, timing of harvest, harvest coup size and unplantable reserve or retirement areas. Riparian or other land deemed too risky to harvest would be excluded from planting, other than in permanent species. In practical terms the productive area of much of the East Coast hill country will shrink as more land gets retired from harvesting. Honey and trees for long-term carbon capture are options for that retired land. Land values for such land will likely fall and some investors will simply avoid the region, rather than risk extremely costly mitigation measures or community backlash against forestry.

The NES-PF has been promoted and supported by the forest industry as a critical first step to adaption to increased frequency and severity of storm events. An unintended consequence may be that Red Zone steep grassland that is eroding badly during intense storms will not be of interest to forest investors. This will reduce the land available nationally for planting of fast-growing exotics. The availability of such land is the single biggest constraint to achieving the national greenhouse gas reduction targets required to meet international commitments.

These intense rainstorms can be quite isolated, and unpredictable as to when and where they will happen. Rather than overreact by exiting productive forestry on susceptible land perhaps the government and industry could work together to form a “Storm Remediation Fund” to respond quickly to clean up debris arising from harvesting that has been legally conducted.

Those living on and cropping the flood plains will also need to adapt as many recent reports on Climate Change have noted that these fertile flats and coastal zones will be impacted by increased flooding. There can be no assumptions of “business as usual” in the future in such areas.

Regardless of how the steep land is managed to minimize erosion risk from harvesting the next crop of trees, we have the current large areas of maturing pine on steep land to deal with. Other than best practice during the harvest phase my single piece of advice to both forest landowners and to those living and cropping on the flood plains below our steep hill country is to check your insurance policies. You may need to call on them.