Farm Forestry New Zealand

The Gordon Trust property 60 years on

Angus Gordon, New Zealand Tree Grower November 2008.

The altitude ranges from 500 to 700 metres above sea level with snow falls being common in winter. It has an average yearly rainfall of 1,200 mm. Geologically the parent rock type on the property is a massive concretionary mudstone which forms a moisture-retentive and poorly drained silty clay soil. There is very little influence on the soils of this farm from volcanic ash fallout from the volcanic plateau to the north, with volcanic soils latter making up less than five per cent of the soil.

Large steep sided hills with slopes over 35 degrees make up 40 per cent of the property. Moderate hills and poorly drained foot slopes greater than 20 degrees make up a further 40 per cent of the property. The remaining 20 per cent is divided between some elevated, slightly better drained rolling hilltops and alluvial flats adjoining the streams on the property.

This combination of soils and climate has resulted in a property that was traditionally dominated by sheep with a moderate cattle component in the livestock mix. As a result of the limitations of soils and climate there was little room to move in terms of conventional diversification. It has required a considerable amount of tree cover for soil stabilisation, but has not lent itself to conventional re-afforestation.

Farm development

The Gordon property was cleared out of forest in the early 1900s with much of the larger timber going to a local mill via steam haulers and a bush tramway. It was developed into a sheep and cattle farm, with a component of dairying in the farming mix on the moderately contoured parts of the property. This property was offered to the soldier resettlement scheme in 1947 and Ron took up ownership of the farm at that stage.

In the late 1940s severe erosion took place after warm rain-melted heavy snow, with the resulting soil slipping closing roads for months. This spurred Ron to extend his tree planting beyond that of amenity plantings around the original house.

Many of the original amenity conifers were imported from Hilliars in England or grown from imported seed, which was normal practice in those days for exotic species on farms. At the beginning of what became a process of land stabilisation the dominant trees used were Lombardy poplar and crack willow. As a greater range of trees became available, mainly other poplar species and hybrids, these were used as well.

Slump zone

Ron was a founder member of the Middle Districts farm forestry branch, and the first chairman of the fledgling Rangitikei catchment board’s soil conservation committee. In the early 1950s a new house was built in a warm north-east facing undulating basin at the foot of a steep escarpment, out of the prevailing westerly winds and close to a couple of springs and an orchard on the site of an old surveyors’ camp.

An idyllic site to put one’s new architecturally designed home you would think, that is, until the day in the middle of winter that the whole site moved and subsided. The house had been built in the middle of a previously unrecognised slump zone. This had been dormant for many years but had suddenly become active, delaying final completion of the house by two years.

What followed was a substantial drainage programme over the entire site, followed by a massive planting programme using poplar poles to dry the ground out and hold it together. Much of the site became a giant pole nursery for some years and following the successful stabilisation evergreen conifers were planted in amongst the coppicing poplar stumps.

Soil conservation plan

Much of the old exotic conifer planting that took place on this property in the 1950s and early 1960s took place within this 10 hectare slump basin. This consisted of Douglas fir, radiata pine, western red cedar, redwood, two larch species and one interspecies larch hybrid, Japanese cedar, and a variety of eucalyptus species, including Eucalyptus regnans, E. delegatensis, E. saligna, E. muelleriana and E. ovata. The latter coped extremely well with the wet heavy conditions in the foot of the slump, and being a prodigious flowerer in winter, has its nectar harvest raided by all the local tui.

In the early 1960s a soil conservation plan was produced by the Rangitikei catchment board which identified key areas for soil stabilisation. This included the other eight slump zones that exist on the property, and the hillsides and gully systems that had previously gone unprotected, especially those that eroded directly to water.

Extensive hillside plantings using poplar were undertaken, as well paired willow plantings in gully bottoms. Many surface drains cut diagonally across some of the more moderate slopes to direct overland water flow away from vulnerable areas and into natural drainage systems.

Poplar nurseries were established on the farm at key geographical points where the poles could be carried downhill to the planting site, because vehicle access in winter was impossible at the time. Pole planting took place in late winter with many of the poles simply being pushed into saturated clay soils after heavy rain.

More planting

This property remained largely unchanged in terms of tree cover until the early 1990s. The long abnormally wet winter of 1992 and the subsequent erosion issues provided the impetus for more tree planting. The timber price spike of 1993/94 enabled some older macrocarpa and pines on another property to be harvested to provide the capital. A re-afforestation programme began on some of the harder eroding hill country adjacent to the local road. The species chosen was radiata pine, and in keeping with the regimes of the early 1990s, high GF rated planting stock was used and planted at only moderate stocking rates of 700 stems per hectare.

Initial survival was good, but the combination of heavy soils, fertile soil conditions, and no competition from either grass or other trees soon began to take its toll. In the third year with tree heights of up to two metres a wet sticky snow fall occurred in combination with strong wind. This resulted in many of the trees toppling on the gentler exposed sites on the gulley rims in particular. In addition the continual wet conditions on one slope caused the trees planted there to die due to the anoxic soil conditions.

Snow damage

Five years later another site was retired from grazing, this time a steep scarp slope behind one of the slump zones. A higher initial planting density of 1,000 stems per hectre was used, and E. nitens was planted as a shelterbelt around the edge of the most exposed parts of the stand. The site was steep and dry with a 40 degree slope over most of it and facing north east. Similar challenges occurred with snowfall on young trees and toppling occurred, but only on stands on moderately sloped micro-sites of less than 20 degrees.

In 2001 a very heavy snow occurred that blanketed this entire region. On this farm the depth ranged from 200 to 400 mm and caused considerable damage, especially to power lines and trees with less than upright form, including many indigenous trees. The exotic tree species planted on this farm largely came through unscathed apart from the radiata pine.

This snow just reinforced the fact that the combination of pine trees, heavy clay soils that loose their structural integrity when wet, and snow or wind are a fairly lethal cocktail. Pine damage was not just confined to radiata, with many of the ornamental species in the arboretum succumbing to general destruction. However it is worth noting that no damage occurred in the Douglas fir or redwood, and only limited damage in the eucalypt and cypress plantings.

Storm and slips

In February 2004 a subtropical low tracked down the east coast of the north island and then moved westwards to savage the Manawatu-Wanganui region. This is a well reported storm so I will not repeat all the details here. It would be fair to say that while the Gordon Trust property did not go totally unscathed, had it not been for the large amount money spent on tree planting for land stabilisation in the previous 60 years, then it would have been far worse.

Due to the rain intensity of this storm the slip erosion initiated from totally different sites from that which had previously been the case. It was the easy colluvial slopes at the bottom of hills that moved, along with the shoulders of the elevated hill top plateaus where there was the greatest soil depth and a gentle contour that allowed water to soak in before it ran off. The latter caused the most damage as the debris avalanches gained speed and size as they moved downhill.

Ironically when the government storm recovery package was put into place this property received no assistance as it did not reach the financial threshold required. However neighbouring properties that did get assistance did so because they had not spent any money on soil stabilisation works and so were devastated. This is one of the downsides of political intervention after a disaster, as sometimes those that are the least worthy of help get the most, with little change in attitude or behaviour.

The challenge

These experiences exemplify the challenges that grassland sites on the sedimentary soils of the middle and upper regions of the Middle Districts region pose. On the one hand, there is the need to fit in with the current forest industry in terms of species selection if planting trees for eventual sale is your long term goal. On the other hand are the problems that are incurred by going with the status quo in terms of species and regimes that are associated with radiata pine in this particular environment.

One thing that sets this property apart from many similar properties is that it has a long history of tree planting − for amenity, soil conservation and to a lesser extent for timber production. There has been longer period of time available to sort out which trees are the real winners and losers for this and similar sites and which are valuable. This assumes that people are prepared to open their eyes to what is in front of them.

This property became involved in the Horizons Regional Council sustainable land use initiative two years ago. It will be interesting to see how it evolves in combination with that initiative. One thing is certain, it has quite a head start on those properties that are starting from scratch.