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The history and trends of land use in the Middle Districts

Angus Gordon and Denis Hocking, New Zealand Tree Grower November 2008.

The Middle Districts branch, along with the associated Tararua branch, is as diverse as most you will find in New Zealand. Middle Districts is bounded by the four W's − Waitotara, Waiouru, Woodville and Waikanae, with Tararua east of Woodville. This includes the catchments of the Wanganui and other west coast rivers to the west, the Rangitikei and Manawatu rivers through the centre and east, with the smaller Horowhenua river catchments to the south.

It has diverse geology and geomorphology. These range from the volcanic landforms and soils in the north to the extensive areas of sedimentary mudstone, siltstone and unconsolidated sandstone that fill the Wanganui basin on the western side of the Ruahine ranges. In addition are the extensive areas of terraces, downland and flood plain built up by the major rivers with gravels and sediment from the major ranges and the slowly rising Wanganui basin. Tararua also has greywacke and limestone country in the Waewaepa and Puketoi ranges. There is also the wind formed sand dune country along the west coast. Altitude ranges from sea level to around 1,000 metres for farming and forestry.

Erosion prone

A lot of this land is moderately to extremely erosion prone, in particular the bands of unconsolidated sandstone that run from north of Wanganui east to the Ruahine ranges. Unconsolidated sandstone has very little resemblance to stone, it is basically just deep beds of old beach sand, very prone to all forms of erosion. The coastal sand country is another fragile land form, very prone to the wind erosion that originally formed it. On the other hand, the terraces and flood plains include some of New Zealand’s most productive farmland.

The climate is relatively mild, characterised by reliable westerly winds that power all the windmills, and a generally reasonably reliable rainfall. It is not an excessively wet area. Much of the region has average rainfall of no more than 1,000 mm to 1,200 mm with significant areas below 1,000mm, and most of this comes from the west. Snow can be an issue at higher altitudes but is rare below 300 metres. Summer droughts are a feature of the free draining, coastal sand country, but are seldom severe elsewhere, the summer and autumn of 2008 being the exception.

From north to south

As you travel from north to south through this region the land uses are in part dictated by the combination of soils, landforms and climate along with access and history. The northern, highest altitude parts of the region, adjacent to the volcanic plateau and Kaimanawa ranges have historically been used for extensive grazing, settled early because it was natural grassland. However much was abandoned during the 1930s and 1940s due to poor economics and wind erosion. Forestry took over some of this land, for example the Karioi forest, where plantation forestry rises to altitudes of over 1,000 metres. But there are also some very good, volcanic based soils of easy contour in this area, such as the carrot country of Ohakune and Raetihi and also some of the land to the northeast of Taihape.

As you move south you leave the free draining volcanic soils and move into sedimentary rocks and soils of increasingly younger age and increasing dissection. Between Taihape and Hunterville mudstone and siltstone rock dominate and the soil covers could be best described as thin and rather poorly drained but also relatively fertile. It is a difficult environment to grow and harvest trees. Sheep and beef farming have dominated this region, and the main tree cover is poplar planted under soil conservation schemes between the 1950s and the 1980s. Some whole farm to forest conversions took place during the 1990s but they are rare.

Sandstone country

Near Hunterville you meet the belts of unconsolidated sandstone that stretch from north of Wanganui to the Ruahine ranges. The spectacular vertical bluffs of Taihape and Mangaweka are replaced by steep slopes from ridge top to gully bottom − sand will not support a vertical cliff. The sands are one to two million years old, formed by river outwash as the Wanganui basin slowly sank.

There is generally a veneer of loess covering the surface which is often extremely fertile, but underneath there is little or no structural integrity and very limited fertility. This combination makes the moderate contour, especially terraced, parts of this landscape productive, but the steeper slopes very unproductive and extremely fragile. Once gully erosion starts it is almost impossible to stop as water and sand flow over, under and around any barrier. Goulter’s gully, a dramatic 60 metre deep gulch in what was a highly productive terrace above the Oroua river, is a graphic example.

Plantation forestry is a significant land use in this sandstone belt. This is especially the case to the west in the Turakina and Whangaehu valleys, Lismore forest and the Brunswick country north of Wanganui, but also on the western side of the Pohangina valley near the Ruahine ranges. Much more still needs tree cover and Horizons Regional Council’s Sustainable Land Use Initiative is targeting this land for assisted afforestation.

Dougal and Di McIntosh’s property north of Wanganui is a wonderful example of how to integrate livestock farming on the good terrace tops with forestry in the deep, erosion prone, intersecting gullies. The downturn in log prices and irrationally high land prices have restricted afforestation in recent years, but people have been looking at such country for possible carbon farming options.

South of Hunterville you move on to the terraces and rolling down country around Marton, Waituna West and Kiwitea. This is fertile land of good contour but is a complex of very poorly draining, heavy Marton soils and the free draining Kiwitea soils, the former developing on lower rainfall, summer dry country and the latter on slightly wetter, summer moist land. Kiwitea soils are very versatile and well suited for dairying, while the Marton soils are too winter wet and prone to pugging damage.

The terrace country extends to the coastal sand country north of Bulls and also the Horowhenua. However, south of Palmerston North and Feilding is an extensive flood plain built up from alluvial material eroded from the main rivers with alternating bands of silts, sands, gravels and peat. It is all relatively recent and despite the best efforts of river engineers, the flood plain building process is going to continue as seen by the 2004 floods. Historically kahikatea forest and flax swamps dominated much of this region of wet, heavy and generally poorly drained soils, not a land for extensive afforestation.

Coastal sand country

The coastal sand country covers 100,000 hectares from Paekakariki to Patea and extends 20 km inland south of Palmerston North. It is another land form favoured for farm forestry with more extensive afforestation serving a protection and production role adjacent to the coast. There are quite diverse land forms in the sand country, including spectacular parabolic dune fields and some very productive soil types, especially the old swamp country used for dairying. However the higher dunes are generally poor pastoral land and erosion prone, but well suited for forestry. Radiata pine has been planted on and harvested from these dunes for well over 100 years.

One of the authors has written more extensively on the sand country in the November 2002 Tree Grower. Perhaps the biggest change since 2002 has been the growth of dairying on the back of centre pivot irrigators, deforestation and the flattening of low dunes.

Range foothills

Along the foothills of the Ruahine and Tararua ranges is a different land form again − uplifted, folded and shattered greywacke. Altitude and alignment to the prevailing westerlies mean higher rainfall, wind and snow, while the soils are generally free draining, relatively stable at steep slope angles but of only moderate fertility. There is significant plantation forestry, especially in the northern Tararua range. Wind farms continue to proliferate.

East of the Manawatu gorge lies the Tararua district, including the upper Manawatu river and tributaries and their extensive terraces and flood plains, along with a number of smaller rivers flowing to the east coast. The area is characterised by a series of north south aligned mountain ranges, including the Waewaepa, and Puketoi ranges along with the coastal argyllite belt, pushed up by the tectonic movement underneath them. The same issues of accelerated erosion are present but wind is perhaps Tararua’s defining characteristic. In short, the Middle Districts area is diverse, but then, so are most parts of New Zealand.

Early settlement

The first settlement of this area was by Polynesians, probably around the 14th century. At that time most of this landscape would have been forested with mixed podocarp forest, except for the younger volcanic country and high altitude uplands where tussock grasslands and herb fields dominated. Significant areas of coastal sand country were also probably under grass and bracken. Early Maori were familiar with fire and there is widespread evidence of burning, not least in the sand country where burning may have led to significant reactivation of dune fields.

European colonisation and settlement

The first Europeans to arrive in the Middle Districts region were probably traders or sealers along the coastal strip prior to 1840, and the first government land purchase, the Rangitikei block, was completed in 1849. Early exports from this region included wool, grain and most importantly flax which principally came from the Manawatu river flood plain and swamps. This was shipped out from the small ports of Foxton, Rangitikei and Wanganui, initially in single-masted wooden cutters and finally in large streamers. Port Rangitikei was lost in a huge flood in 1897. All purchases of Maori owned land by the crown had been concluded by 1896, and by the early 1900s the majority of it had been converted from a mixed podocarp rain forest into the exotic grasslands that we see today.

The building of infrastructure

During the early years of settlement by European immigrants, settlement largely took place on the coastal lands and the adjacent river floodplains. As time went on, people moved inland on to increasingly higher rolling land and then into the dissected hill country of inland Manawatu, Rangitikei and Wanganui. The infrastructure, such as roading, was expensive or grossly inadequate.

The soft sedimentary rock types and lack of naturally occurring gravels, meant roads were initially little more than muddy bullock tracks. The main trunk rail line had terminated at Marton in 1883, and it took 21 years to push it north to Taihape with a lot of tunnelling and bridging required.

Soil erosion became a major issue approximately 15 to 20 years after the bush had been cleared in the steep hill country. It took time to clear all this forest so erosion was a staggered process. All areas were not affected to the same degree due to the differences in rock type, slope and rainfall patterns. However vast amounts of soil were lost from hill slopes steeper than 25 degrees, and on slopes greater than 35 degrees there is very little left.

The only saving grace for the occupiers of these farms is that the mudstones of the middle and upper Rangitikei valley are inherently fertile and weather quite quickly. Slip scars will grass over relatively quickly, but lack the moisture holding capacity and productivity of un-eroded soils. In the north of this region, and along the foothills of the Ruahine and Tararua ranges, the farmland has greywacke and limestone geology underneath with a volcanic ash top soil. This is relatively free of slip erosion due to its inherently better drainage capability and low clay content.

After the initial clearance of the mixed podocarp forests, the resulting landscape was sown in introduced grass species and there was a brief rush of growth that soaked up the fertility from 10,000 years of rainforest cover. However, without fertiliser to replenish depleted nutrients, native woody species such as manuka re-colonised farmland and dominated the introduced grasses. Between 1900 and 1945 the economics of farming see-sawed, first with dairy products being valuable, and then wool. Timber was just a resource to be mined.

Meanwhile in the sand country extensive grazing with cattle and enthusiastic burning rapidly mobilised the sand, and wind erosion was a serious problem by the end of the 19th century. Significant plantings of radiata pine and maritime pine were under way by the turn of the century with more extensive plantings by central government throughout most of the 20th century.

Soil conservation

While soil conservation was not suddenly invented in the 1940s, the passage of the Soil Conservation and Rivers Control Act of 1941 was a significant step forward. In March 1945 the local catchment boards were established and in the 1950s and 1960s their work really started to create the landscape that we see today. Tree planting became the norm, mainly poplar poles in the hill country and pines on the sand dunes, with many of these trees still present today.

As with all new practices some plantings were more successful than others, and trees were seen as playing a supporting role to grass. Production forest was reserved for areas that were no good for grass, which was almost nowhere in mainstream farmer thinking. Still, significant areas were planted in the sand country and in the high country west of Waiouru.

The wool boom

At about the same time, the farm forestry movement came into being, providing a useful bridge between the catchment boards and forest service on one side and the broader farming community on the other. The 1951 wool boom, when wool reached the equivalent of over $50 a kilogram, provided a huge boost to hill country sheep farmers and many ballot farmers on soldier resettlement blocks paid off their entire debt in that one season.

Another post-war phenomenon was aerial top dressing. The application of superphosphate and lime had started before World War II, but was largely done by hand. This was transformed by the return, after the war, of many young men with flying skills along with cheap war surplus aircraft. This was probably the most important technological advance lifting the productivity of pastoral farming and ensuring the dominance of the grass and clover pasture ecosystems. Combined with drugs that effectively controlled internal parasites in sheep and cattle and electric fencing, it pushed New Zealand agriculture into sustained production increases, even if some the land use practices left something to be desired.

Limited planting

Forestry therefore has not been a dominant land use across most of this region. For the early settlers there was a surfeit of wood and the bush was the enemy. The pastoral culture became well established. Even today, when it is obvious that significant areas of the more erosion-prone hill country needs closed canopy forest cover, there is widespread resistance.

In the early days planting was pretty much limited to homestead plantings of pine or macrocarpa for shelter and ornamental species. After World War II, and with the advent of the soil conservation movement, the planting of willows alongside rivers and streams, and poplars in the gully bottoms and on hill slopes to limit erosion began to take hold. But this was only on farms where the land owner was sympathetic to trees and was probably a member of the NZFFA. The farm foresters started planting woodlots of radiata pine, Douglas fir, macrocarpa, larch, eucalypts and other species, but with the exception of some sand country plantings these were generally fairly small.

Floods and storms

For most farmers of that period trees simply got in the way of being a good farmer,and interfered with the mustering of livestock especially when the trees fell over. This attitude was even more strident with respect to native manuka which arrived on the wind, covered up grass, and enabled sheep to easily hide from man and dog when being moved. No thought was given to the soil reinforcement that its roots provided. Gorse was even worse as it smothered grass, hid sheep and it was prickly.

However, after the widespread erosion in the winter of 1992 and the 2004 flood at least some people started to take notice of the level of destruction and the financial cost of repairing it. Almost five years on from the 2004 storm the hardships of blocked roads, wrecked fences and lost assets are largely forgotten as someone else paid to fix much of the damage, and the slip scars have a veneer of green on them.

Attitudes have not really changed that much. Helicopters are cruising the back country spraying out manuka re-growth. In some cases old conservation plantings are being removed, but not replanted by the new purchasers of properties in an effort to ‘clean them up’. The ability to buy, window dress, and then sell on a property in what has been a very buoyant rural property market, free of any capital gains tax has not helped. There has been a change in mindset by some, but it is slow, as most of the present crop of farmers, both young and old, are thoroughly imbued with the pastoral culture. Do not under-estimate the changes needed to move to a more sustainable pattern of land use.

Radiata limitations

Another issue that needs addressing is getting a suite of higher value species that can handle the micro-sites found in this heavily dissected hill country, with its various climatic extremes and skeletal soils, while providing a higher value product that can handle access and extraction costs.

Radiata pine has its limitations, especially at higher altitudes with snow risk and the wider forest industry is shy of investing in anything else. There are very limited areas of Douglas fir and cypresses but in recent years the NZ Redwood Company has been planting coastal redwood near Hunterville. Progress will be watched with interest. There is a significant low quality poplar resource on the hills but to date there has been little progress on building industry based on poplar.

The challenge is finding a woody species that is not culturally threatening, cheap to establish, has low intensity management, does not grow too big, generates a positive cash-flow, and does not damage the pasture. Any suggestions?

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