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Pressures on the land

Floods, drought, wind, earthquakes, lightning strikes and volcanoes are all natural pressures which affect soil and vegetation. At various times before and after the last ice age these pressures have briefly affected different parts of New Zealand, damaging forests, causing periods of accelerated erosion or laying down the foundations of new soil layers. Since the arrival of humans, however, these pressures have been augmented, and even overshadowed, by a sustained battery of additional pressures associated with human activities. The main human-induced pressures on New Zealand's land have been from:

  • vegetation change, principally deforestation, but also draining of wetlands, modification of tussock grasslands, and conversion of dunelands to pasture and exotic plantation forests;
  • land use pressures, principally the effects on soil and biodiversity of farming practices, but also forestry, and urban, industrial, and transport activities; and
  • pests and weeds, both the exotic species which threaten the biodiversity of natural ecosystems, and the exotic and indigenous species which threaten the productivity of pasture, crop, or forest land.

Vegetation change pressures

Polynesian and European settlers, and their descendants, put considerable pressure on the indigenous forests. In the space of 650-750 years (roughly 20-30 generations), humans reduced the indigenous forest cover from approximately 85 percent of the land area (23 million hectares) to about 23 percent (6.2 million hectares) (see Figures 8.3 & 8.5 and Box 8.1).

The period of early Māori deforestation had a dramatic impact on our biodiversity (see Chapter 9) and seems to have caused erosion and sand drift in some areas but not others (McGlone, 1989).

Soil and pollen studies have revealed that firing of the forest in the inland basins of the South Island was followed by erosion (Molloy, 1977). Research on estuary sediments shows that deforestation often led to a 3-4 fold increase in sedimentation (Hume and McGlone, 1986). In Canterbury, the increase may have been ten-fold (McSavaney and Whitehouse, 1989). Dunes also seem to have been affected (McGlone, 1983, 1989; Anderson and McGlone, 1992), though the extent of this is debated (McFadgen, 1985, 1989).

However, forest fires did not cause significant erosion everywhere. A study of sediment layers from Lake Tutira north of Napier found that, although the surrounding land (which is steep and erosion-prone) had been deforested in Māori times, erosion did not increase until European farmers arrived in the late 1800s (Trustrum and Page, 1991). The sediment record revealed that the natural erosion rate before human settlement was 2.1 millimetres per year. This remained unchanged throughout the period of Māori settlement, despite forest fires. Then, in the last 110 years, the erosion rate soared seven-fold to 14 mm per year. The reason for this appears to lie in the different types of vegetation change that occurred. In the Māori period, the forests were replaced with deep-rooted bracken fern and scrub, but in the European period they were replaced with shallow-rooted pasture grasses. It seems, therefore, that Polynesian forest fires only initiated large-scale erosion in areas of soft, weaker, rocks where the replacement vegetation was unable to sufficiently absorb rain or bind sand and soil (McGlone, 1989).

Although forests were the most extensive ecosystems to be dramatically affected by the pressure of humans and their farm animals, the native grasslands, wetlands and dunelands have also been heavily modified. All the major changes to these ecosystems have occurred in the past 150 years as a result of the expansion of farmland and the development of urban settlements near rivers and the coast. Drainage and flood protection schemes have been almost constant throughout this period.

Figure 8.3: The recent history of New Zealand's land cover
Textual description of figure 8.3

New Zealand’s land cover has changed in response to both the main period of Māori population expansion in 1300 to 1400 and the main period of European population expansion around the 1900s.

Prior to Māori population expansion, 80% of the land cover was native forest, 5% was scrub, wetlands or duneland, 5% was tussock and 10% was alpine. After this period, native forest cover declined, as well as tussock scrub, wetlands and duneland.

Prior to European population expansion 55% of land cover was native forest, 25% tussock and 10% scrub, wetlands or duneland. Today, native forest cover has further decreased to around 20%, tussock cover has increased to around 15%, scrub, wetland and dune cover has decreased to 15%. Exotic grassland now makes up around 35%, settlements and crops around 10%, and exotic forest around 5%. (percentages represent a proportion of the total land area).

Figure 8.4: Production of indigenous and exotic rough-sawn timber, 1876-1994
Textual description of figure 8.4

Production of indigenous rough sawn timber peaked in the early 1900s at around 1 million cubic metres with relatively constant production of around 750 thousand cubic metres until the 1960s. From 1960 onwards more exotic timber was produced than indigenous. Since then, indigenous timber production has declined, and by 1994 it was a very small proportion of the total produced.

Exotic timber production has steadily increased since it began in 1915-by 1994 around 2.5 million cubic metres were being produced.

Figure 8.5: Human impacts on New Zealand's natural forest and tall shrubland.
Textual description of figure 8.5

Before Polynesian settlement most of New Zealand, except for mountainous areas, was covered in natural forest and tall shrubland. Before European settlement, natural forest and tall shrubland cover was reduced, particularly in coastal areas. Today, Polynesian and European settlers and their descendants have reduced the indigenous forest cover from approximately 85 percent of the land area to about 23 Percent. Natural forest cover is vastly reduced and primarily limited to the west coast of the South Island and fragmented areas in the central North Island.

Source: McGlone (1989), New Zealand Map Service 262 (DOSLI)

Box 8.1: Deforestation - past and present

Since leaving the African savannas tens of thousands of years ago, humans have been turning the rest of the world's forests into grasslands or open woodlands. Explorers, such as Hanno in 500 b.c., Magellan in a.d. 1520, and Abel Tasman around a.d. 1640, remarked on the smoke clouds that emanated respectively from the coasts of Africa, South America, Australia, and New Zealand. People everywhere, it seems, from huntergatherers to modern farmers, set fire to forests to 'open them up', often leaving the fires to burn indiscriminately (Stewart, 1956; Flannery, 1994). There are many reasons why: to clear land for gardens and settlements, to encourage new growth for prey or domestic animals, to drive prey animals into traps, to improve visibility while hunting or travelling, to reduce the risk of ambush from predators and enemies, to remove the risk of forest fires near settlements, to dispel the near universal anxiety that comes with darkness, to fulfil religious or recreational needs, and simply to keep the flame burning lest it go out and have to be laboriously recreated.

The early Māori were no exception to this pattern, and the firestick formed an important part of their travelling kit (Walsh, 1896). Fire was particularly useful in encouraging the growth of bracken fern whose starchy rhizomes (underground stems) were a staple part of the diet (McGlone, 1978, 1983; Anderson and McGlone, 1992; Flannery, 1994; McGlone and Basher, 1995). Most of the destruction occurred between a.d. 1350 and 1550 as the population expanded. The impact was greatest in the dry eastern areas of both islands, and in the central South Island high country where tall red tussock and snow tussock replaced beech forests (at higher altitudes) and totara, matai and kahikatea dominated forests (at lower altitudes). From around 750 years ago, the inland Kaikoura Range was repeatedly burnt until it was dominated by bracken, tussock grass and scrub (McGlone and Basher, 1995). Beginning 600 years ago, repeated fires in Central Otago converted forests and tall scrub into bracken and then tussock (McGlone et al., 1995). In the drier parts of New Zealand, some forest types were nearly eliminated (e.g. dry inland conifer-broadleaved forests) or were reduced to unrepresentative fragments (e.g. lowland matai-totara forests).

Deforestation appears to have ceased after 1600, but large areas of regenerating forest and scrub continued to be burnt. Extensive burning was carried out along the east coast of the North Island when Captain Cook sailed by in 1769 (Salmond, 1992), and increased after European contact as Māori communities expanded their gardens to take advantage of new vegetables, crops, farm animals, and markets (Hargreaves, 1963; Cameron, 1964). Some Māori entrepreneurs began market gardening for export to New South Wales and California. Meanwhile, European entrepreneurs had begun logging the kauri forests. By 1840, just before large scale British and Irish immigration began, the total forested area had been reduced from 85 percent of the landcover to about 53 percent (14.3 million hectares) (Wendelken, 1976).

The European settlers and their descendants saw forests as both an obstacle to agriculture and an inexhaustible source of timber (Fleet, 1984; Halkett, 1991; Memon and Wilson, 1993; Park, 1995). As European numbers grew, particularly from the 1860s on, farming aided by timber production began to take a huge toll on the forests. Pasture increased rapidly from less than 70,000 hectares in 1861 to 1.4 million hectares by 1881 and 4.5 million hectares in 1901 (Department of Statistics, 1990). Banks Peninsula in Canterbury, for example, had 20 sawmills operating between 1860 and 1900 which reduced the luxuriant totaradominated podocarp forest from 75 percent of the land area to about 5 percent (Norton and Fuller, 1994).

In a single intensive decade, from 1890 to 1900, 27 percent of New Zealand's existing forest (or 13 percent of the total land area) was cleared, reducing the forest area from 13 million hectares to 9.5 million hectares. The deforestation rate during this period was four times the recent rate in tropical Asian rainforests (Glasby, 1991; World Resources Institute, 1992). The number of farms rose quickly from around 10,000 in 1871 to more than 80,000 in 1921 when the total occupied area reached its natural limitsome 17.6 million hectares. This occupied land included several million hectares of remnant indigenous forests, mostly in marginal (steep) areas, many of which were subsequently cleared to expand pasture. Burning was the prime means of forest clearance, accounting for probably 90 percent of New Zealand's deforestation (PureyCust, 1986). Pastoral landscapes that look idyllic today were clouded by wood smoke a century ago. When the smoke cleared, it left a vista of blackened hillsides and charred tree skeletons.

Timber production played a smaller role than fire, but a highly significant one. Profits from the 10 percent of logs that were milled helped offset the overall cost of land clearance and development. Kauri and the tall podocarps (e.g. rimu, totara, kahikatea) were particularly prized. Indigenous timber output peaked in 1907 with smaller peaks in the decades after the two world wars as many returned soldiers sought to create farms on marginal forest land provided by the government (see Figure 8.4). An attempt was made to slow the pace of forest destruction in the 1874 Forests Act, but this legislation was widely seen as an obstacle to development and was repealed.

Subsequent amendments to the Lands Act made provision for preserving steepland forests on erosionprone public land, and also for the establishment of scenic reserves, but did nothing to impede deforestation on potentially productive land. In fact, the Department of Lands actually considered it improper to leave trees standing on any land that might be farmable.

Although two national parks and a number of small reserves, were established towards the turn of the century, they were in the mountains or in other areas with little or no agricultural potential. Not until 1919, when virtually all the usable land had been occupied, was a State Forest Service established to husband what remained of the loggable public forests, and to protect four to five million hectares of steepland forest for erosion and flood control. These protection forests form the bulk of today's remaining indigenous forest.

With only 30-50 years of timber supply remaining in the loggable forests, the Forest Service aimed to manage them for sustained yield while planting fastgrowing exotic species to meet future timber needs. Sustained yield management came to be seen as impractical, however, due to the slow growth of the indigenous trees. Podocarps take hundreds of years to reach maturity. Beech trees take 60-120 years and are of poor timber quality. Exotic pine trees, by contrast, take only 2535 years. As a result, most of the loggable forests were not managed for sustained yield but for immediate economic and employment objectives, and exotic forests were planted over large areas to meet the next generation's timber needs.

A germinating environmental movement began to challenge the Forest Service in the 1930s over the fate of one forestWaipoua kauri forest. The campaign intensified in the 1940s and the government finally declared the forest a sanctuary in 1952. Six new national parks were established over the next decade, bringing the total number to ten by 1964. Like the first parks, these were limited to mountainous areas.

During the 1950s, forests on private land began to be felled with greater intensity following a wool boom triggered by the Korean war. This contributed to the last great surge of the indigenous timber industry. By 1960 it was on the wane, overtaken by exotic timber from the Forest Service's first pine forests. From then on, exotic timber output increased as indigenous timber production declined (see Figure 8.4). Export controls were placed on kauri and podocarp logs as supplies dwindled. From over 700,000 cubic metres (m3) in the mid 1950s, production of rough sawn native timber declined to less than 70,000 m 3 by 1993. In three decades, from 1960 to 1990, indigenous timber declined from 50 percent of total timber production to less than 5 percent.

The environmental movement contributed significantly to this decline. By the 1970s, it had become a force to be reckoned with, and clashed headon with the Forest Service over plans to clearfell some 340,000 hectares of beech and podocarp forest in the South Island (New Zealand Forest Service, 1971; Searle, 1975). The beech scheme was shelved in 1975 following wide public opposition, but subsequent battles raged over the fate of individual forestsOkarito, Pureora and Waihaha, Whirinaki, Paparoa and Waitutu. In 1987 the Government disbanded the Forest Service as part of a more general restructuring of the public sector. Existing national parks and reserves together with virtually all the Forest Service's indigenous forests were allocated to the newly created Department of Conservation-except for 152,000 hectares on the West Coast of the South Island and 12,000 hectares in Southland which were kept in timber production for employment purposes.

In the late 1980s, the attention of government and environmentalists turned from public forests to the 1.3 million hectares of privately owned native forest. Around 2,000 hectares were being cleared annually for farmland. In the North Island's Mamaku Plateau, this forest clearance was selffunded by the sale of tawa to the Kinleith pulp and paper mill. At both ends of the South Island it was funded by the export of beech woodchips to Japan. The Government responded by extending the earlier export controls on podocarps and kauri to include hardwood (e.g. beech) logs and woodchips, and by announcing that it would develop new legislation. It also set up two funds: the Forest Heritage Fund and Nga Whenua Rahui, to purchase key private forests or pay the owners to protect them. By mid-1995, about 60,000 hectares of private forest were formally protected, with a further 60-70,000 hectares committed for protection through these funds.

Finally, in 1993, the Government passed the Forests Amendment Act which requires that, from mid-1996, indigenous wood products may only be produced from forests with an approved sustainable management plan or permit. The Act also contains export controls on indigenous timber. While these measures were being developed, a separate initiative was undertaken by several environmental organisations and the major forest companies. They signed the New Zealand Forest Accord in 1992, with the industry representatives agreeing not to replace indigenous forest with exotic plantations and the environmentalists agreeing to support exotic forests as a renewable, environmentally friendly, alternative to the logging of native forests. The Accord does not bind all forest owners, but has significantly modified the behaviour of the larger companies.

Today, it is still legal to replace private indigenous forest with pasture or exotic forests, but to do so is generally uneconomic, particularly as the returns from sheep farming have been declining for some time. Furthermore, clearfelled indigenous forest can no longer be sold as timber. As a result, clearfelling for timber or woodchips has declined from several thousand hectares annually to just several hundred. The clearfelling which continues is confined to a few specially approved areas covered by the West Coast Accord and the South Island Landless Māoris Act 1906. Most of the remaining indigenous forest is now protected or is not on usable farmland. The main pressures now come from the degenerative effects of forest fragmentation and the impacts of alien plants and animals, particularly possums, goats and deer.

Land use pressures

Modern land uses impose a range of pressures on soil and vegetation. Agriculture has the greatest effect because it covers the largest land area (see Table 8.1), but virtually all land uses involve some removal or disturbance of vegetation and soil. The main land use pressures are from agriculture; forestry; urban, industrial and transport activities; and mining.

Agricultural land use pressures

The most obvious effect of agriculture on the land has been the reduction in natural vegetation cover which occurred as vast areas of forest and wetland were replaced by exotic species of grass and crops and domestic grazing animals were introduced. In modern agriculture, biodiversity is deliberately reduced, and forest regeneration is suppressed, so that energy and nutrient flows can be channelled into a narrow range of plant and animal products.

The impact on soils has been mixed. In many areas, soils have been improved by the development of dense grass cover using applications of lime and fertiliser and, where necessary, irrigation water. The organic carbon content of some soils has also been improved, as has the nutrient cycling capacity and the water-retention properties of others. However, in some areas, soil quality has come under a variety of pressures. These pressures can be broadly grouped as: too many animals; too much cultivation; too few deep-rooting plants (especially on hill pasture and newly ploughed fields); too little soil replenishment (in the form of fertilisers, lime, irrigation, organic matter); or (rarely) too many toxic substances (e.g. pesticide residues).

Farming in New Zealand spans a continuum from 'extensive' through to 'intensive' production systems. These terms refer to the amount of material and energy which pass through the system in a given period. At the extensive end of the continuum is a large land area with relatively few inputs of energy and material, while at the intensive end is a smaller land area with many more inputs.

Extensive pastoralism, for example, carries relatively few animals per hectare (mostly sheep with some beef cattle) but extends over large areas-about 12 million hectares (44 percent of the total land area). It is 'low cost', with relatively low applications of fertiliser and grass seed. In contrast, intensive forms of agriculture cover barely two million hectares (7 percent of the land). Three-quarters of this is pasture, mostly carrying dairy cows, some beef cattle and deer. The remainder is mostly crop and horticultural land. A very small area is devoted to factory farming which, in New Zealand, is restricted to pigs and poultry. Chickens are now our most numerous stock animals, but their accommodation uses very little land.

The two types of farming have significant but different impacts on the land. Intensive farming produces more biomass per hectare, higher concentrations of animal waste, fertilisers and pesticides, and makes more use of irrigation water. It therefore has a greater risk of contaminating soil, groundwater and streams and of reducing river flows. In addition, high stock densities, or the frequent use of heavy machinery, increase the risk of soil compaction, while the removal of high volumes of plant and animal products increases the risk of carbon and nutrient loss.

Extensive pastoralism puts less concentrated pressure on soil and water but, because of the vast area involved, it has had a greater impact on natural ecosystems and biodiversity. Also, because this sort of farming is often located on hilly terrain where the soils are naturally more susceptible to erosion and nutrient depletion, it has caused accelerated erosion in many areas and sedimentation of streams and rivers. Erosion and stock losses have often been exacerbated where hilly land has been managed for maximum production (through increased pasture area and stocking rates) rather than for minimum risk from climatic events, such as floods, droughts or unseasonal snowstorms.

Some farmers, through choice or the limitations imposed by terrain, have sustained natural forests or wetlands on their properties. In the past the overwhelming economic incentive was to convert as much land as possible to productive commercial use, even the natural riverbank vegetation, which normally protects waterways, soils and forest and aquatic biodiversity. Today, only a small area of land is being converted, such as in parts of Northland where the increase in dairy farming has led to some streambanks being cleared of native vegetation.

Agricultural pressures on the land are driven largely by economics and have fluctuated with export prices and past government subsidies. High market prices caused farmers to convert forest to pasture during the 1950s wool boom, and government subsidies for pastoral farming had the same effect in the 1970s and early 1980s. Since the incentives ended in the mid-1980s, sheep numbers have declined and several hundred thousand hectares of pasture has been converted to exotic pine forests. An even larger area of marginal pasture on steep erodible slopes has been left to regenerate in scrub and native forest.

Economic forces cut both ways, however. Recent studies of farmer attitudes and behaviour reveal that many farmers tend to respond to economic pressures by cutting back on maintenance expenditure, such as erosion control and pasture improvement, while continuing to maximise their stocking rates (Wilkinson, 1994; Wilson, 1994; Smith and Saunders, 1996). One study investigated the behaviour and attitudes of 25 hill country farmers in the Taranaki Region, where 20 percent of hill farmland is managed in a potentially unsustainable fashion (Taranaki Regional Council, 1996; Wilkinson, 1994). Most of the farmers managed their pasture to suit the stock rather than the land. Although they were generally aware of the long-term environmental risks of their management practices, they tended to feel constrained by more immediate economic factors.

Another example of economic forces intensifying environmental pressure was the classic boom and bust in goat farming during the late 1980s. During the boom, feral female goats were rounded up and captured for breeding stock. By 1988, the domestic goat population had quadrupled to a market-driven high of 1.3 million (Department of Statistics, 1990). The market crashed soon afterward and, by 1994, farm goats numbered less than 284,000 (Statistics New Zealand, 1996b). Because the market for goat meat is small and 90 percent of the goat population was bred for fibre production (e.g. mohair) and 'scrub control', most of the unwanted animals were simply released into the scrub and forest where their mothers had come from. The number of feral goats then soared, intensifying the pressures on native vegetation and regenerating forest (Parkes, 1993).

In the past decade, extensive pastoralism has declined while there has been an increase in intensive forms of agriculture. Between 1981 and 1995 sheep numbers fell by 30 percent, from a subsidy-driven peak of around 70 million to just under 49 million. However, cattle numbers rose to an all-time high of 9.3 million, largely reflecting the 40 percent increase in dairy cattle whose population went up from 2.9 million to 4.1 million (see Figure 8.6).

Figure 8.6: Changing cattle numbers, 1981-1995
Textual description of figure 8.6

Total cattle numbers declined during the early 1980s and then increased to an average of around 8 million over the late 1980s and early 1990s. Since 1991 numbers have increased, reaching a peak of 9.3 million in 1995. Throughout, there have been more beef cattle than dairy although the proportion has changed over time. The peak in total cattle numbers in 1995 largely reflected an increase in dairy cattle.

Source: Statistics New Zealand

The most notable areas of dairy increase have been at opposite ends of the country, in Northland and Southland. However, dairy herds have also expanded markedly in many other parts of the country, including the South Island regions of Canterbury, Otago and the West Coast. Expansion has been less dramatic in the North Island, since large areas were already devoted to dairying, but dramatic increases have occurred in some districts (e.g. around Taumaranui), and even traditional dairying areas, such as Taranaki, have shown a steady increase. Taranaki's dairy cattle population has grown by 16 percent since 1975 and its density has increased by 19 percent from 1.43 cows per hectare to 1.70 (Taranaki Regional Council, 1996). This nationwide increase in the dairy herd has raised concerns about the impacts on soil and water of animal urine, nitrogen fertilisers and stock trampling.

Beef cattle numbers have shown little overall change since 1981, despite falling prices, but their distribution has undergone some change in response to expanding dairy herds and shrinking sheep flocks. Although beef cattle declined during the 1980s they increased again in the 1990s, replacing the even less profitable sheep in many hill farms. This shift has aroused some concern because of the greater pressure which cattle place on soil and water in hill systems. Compared to sheep, cattle produce more waste, their grazing causes greater soil nutrient loss and more vegetation disturbance, and their trampling poses a greater threat to erodible pasture and stream banks (Lambert et al., 1985; Sheath, 1992).

Another pressure associated with the expansion of dairying comes from nitrogen fertiliser. Many dairy farmers are now applying large amounts of nitrogen fertiliser to their soils (Roberts et al., 1992a; Bolan and Podila, 1996). Until recently, nitrogen fertilisers were used mostly for crops, while pastures derived their nitrogen from clover, with a just a light application of fertiliser in winter. In the past six years, however, as dairy farming has led to more intensive pasture use, nitrogen fertiliser sales have more than trebled (see Figure 8.7). Most dairy farmers are now applying 25-100 kilograms of nitrogen fertiliser per hectare per year, and some are applying more than 200 kg/ha/yr. The use of nitrogen fertiliser on dairy pasture boosts grass growth, is cheaper than feed supplements, and returns $1.93 for every $1 spent (Bolan and Podila, 1996).

Increasing nitrogen use is part of a worldwide trend in which humans have dramatically altered the Earth's nitrogen cycle (Wedin and Tilman, 1996). The rate at which nitrogen is extracted from the air and fixed in the soil by legumes is now twice the natural rate. In the northern hemisphere, the rate at which atmospheric nitrogen is deposited on the land has increased more than tenfold in the past 40 years. Because some plants respond better to nitrogen than others, the increasing amount of nitrogen in the environment appears to be changing some grasslands and reducing their species diversity. A recent 12-year study in North America found that, under long-term continuous nitrogen use, weedy, cool-season, grasses tend to replace warm-season grasses (Wedin and Tilman, 1996). Because they have less root mass and slightly different chemistry, the weedy species contribute less organic matter to the soil, resulting in lower levels of soil carbon.

High levels of nitrogen can also make soils more acid, though this depends on the type of nitrogen. It is estimated that 1.7, 4.1 and 5.2 kg of lime are needed to overcome the acidity produced by 1 kg of nitrogen applied respectively as urea, diammonium phosphate and ammonium sulphate, (Bolan and Podila, 1996). Nitrogen also has impacts off the land by leaching through the soil into groundwater or washing off the land surface into streams (see Chapter 7).

In summary, the main agricultural pressures on the land include:

  • the conversion of native ecosystems to pasture (though this has largely ceased and native scrub is now regenerating in some unproductive steep areas);
  • the impacts of stock animals (namely sheep, cattle and goats) on natural forests, tussock grasslands and dunelands;
  • accelerated soil erosion (through insufficient deep-rooting vegetation on erodible soils, steep slopes, and ploughed fields exposed to wind, frost or heavy rain);
  • soil compaction (from loss of soil structure, continuous ploughing, or stock treading, when wet);
  • nutrient depletion (from insufficient fertiliser inputs to offset nutrient removals in plant and animal product and in unevenly deposited animal waste);
  • acidification of soil (through the increased leaching of nitrates from animal waste, legumes, and nitrogen fertilisers);
  • chemical contamination of soil (from farm landfills, trace elements in fertilisers, and pesticide residues-though these are minor compared to urban and industrial contamination sources).
Figure 8.7: Recent trends in nitrogen feriliser use
Textual description of figure 8.7

Nitrogen fertiliser has increased from around 45 tonnes in 1990/91 to around 135 tonnes in 1995/96.

Source: Bolan and Podila (1996)

Box 8.2: Farming with Care

The impacts of farming on animal welfare, human health and the environment are coming under closer scrutiny from the general public, law-makers and consumers. Issues of concern include water pollution, pesticide residues, soil erosion, wetland drainage, forest clearance, greenhouse gas emissions (i.e. methane), the treatment, shelter and transport of farm animals, and the perceived health effects of agricultural chemicals. An increasing number of farmers are responding to these concerns by modifying their farming practices. Examples include planting trees on erodible land, fencing off riparian vegetation on erodible stream banks, improving methods for disposing of dairyshed effluent, controlling pests through integrated pest management, and adhering to voluntary codes of practice on such issues as pesticide spraydrift and animal welfare.

Some of these responses are driven by law reforms which began in 1991 with the Resource Management Act and continue with the Biosecurity Act 1993, the Hazardous Substances and New Organisms Act 1996, the Agricultural Compounds Bill, the proposed Animal Welfare Bill, and the proposed Primary Produce Bill. The Agricultural Compounds Bill for example aims to "assist in managing risks to trade in primary produce, animal welfare, and agricultural security, and compliance with domestic food standards associated with the use of agricultural compounds" (Ministry of Agriculture and Fisheries, 1995). Economic factors contributing to the changes include lost production from soil erosion, the good prospects for farm forestry, and the fear that New Zealand's access to some export markets (e.g. the European Community) may be subjected to stringent animal welfare and pesticide residue standards. A further economic factor is the growth of niche markets for humane and chemical-free products, particularly in Europe and North America where organically grown produce, for example, accounts for just 1-2 percent of all food sold but is increasing its market share by up to 20 percent each year (Ministry of Agriculture and Fisheries, 1993a).

Humane products are those which cause no preventable animal suffering in their production. Humans, other mammals, birds, reptiles, amphibians, fish, and 'higher' invertebrates (e.g. squid and lobsters), share similar neuro-physiological mechanisms for pain perception (Ministry of Agriculture and Fisheries, 1991). Animal scientists have also recorded behavioural and physiological evidence of stress and similar emotional reactions in many species (Dawkins, 1993; Griffin, 1976, 1992; Masson and McCarthy, 1994; Mayes, 1979). These findings are reflected in growing concern for animal welfare, both in New Zealand and overseas. In Britain, for example, 77 percent of those polled oppose the export of live farm animals for slaughter (Worcester, 1995). In recognition of this trend, the Minister of Agriculture and Fisheries established the Animal Welfare Advisory Committee (AWAC) in 1989 to develop animal welfare policies and enable New Zealand to take a proactive role in animal welfare matters. AWAC undertook a review of the Animals Protection Act 1960 and, after wide consultation, recommended that it be replaced by new legislation (Ministry of Agriculture and Fisheries, 1990, 1991). A draft Animal Welfare Bill has been prepared and is awaiting introduction to Parliament.

The 1960 Act gives domestic animals some protection against deliberate cruelty but is limited or silent on such issues as: the lack of farm shelter belts to give shade in summer and shelter in winter, early lambing and shearing (which can result in stress and death in cold weather), stressful transport in lorries and on ships, the restrictive confinement of pigs and chickens in 'factory farms', and amputations performed without anaesthetic (e.g. docking cows' tails, removing the highly sensitive velvet from deer antlers, dehorning cattle, castrating pigs, mulesing merino lambs, and trimming the beaks and toes of chickens). Because of its scale, the treatment of battery hens is particularly controversial. With more than 60 million birds, poultry are our most abundant livestock. Most are bred for meat. About 2.4 million are egg layers. Although a niche market exists for eggs from uncaged hens, its influence has been limited. About 4 percent of all eggs sold are from free-range hens and a further 3 percent are barn-laid, but their higher prices deter most shoppers.

Some farmers have developed their own animal welfare measures. To reduce winter suffering and losses, for example, they plant shelter belts, use snow combs to shear ewes, and put jackets on calves. But many are less proactive, so nearly 20 welfare codes and minimum standards have been developed by AWAC to cover such practices as mulesing, tail docking, deer velvet removal, treatment of bobby calves, and live sheep exports (e.g. the live export of lambs under 10 months was banned in 1994 following high death rates en route to Saudi Arabia). The codes will underpin the new Animal Welfare Act and will be updated regularly to reflect changes in scientific knowledge, farm practices, and public attitudes (Ministry of Agriculture and Fisheries, 1996).

Chemical-free products are technically non-existent as everything contains chemicals. However, as generally used, the term means products that are free of synthetic pesticide residues. Pesticides are widely used in New Zealand because of the stringent food hygiene requirements of export markets. Statistics on agricultural chemicals are not published so it is not possible to say whether pesticide use has increased or declined from the 3,500 tonnes applied annually in the 1980s (McIntyre et al., 1989). However, food and groundwater monitoring show that pesticide residues in our food and water are generally very low and pose no detectable risk to health (Dick et al., 1978; Pickston et al., 1985; Close, 1994; Ministry of Health and Environmental Research Services Ltd, 1994; Reeve, 1994; van Oort et al., 1995a). Despite this, consumers are increasingly concerned about chemical residues (Jolly, 1994). As a result, the agricultural industry is modifying the way it does things. Newer chemicals have been developed which decay quickly and leave few residues, and pesticide users are being taught to apply chemicals more safely and selectively. Following the revelation several years ago that less than 1 percent of those applying pesticides had any training (MacIntyre et al., 1989) the industry developed an Agrichemical Users Code of Practice and set up the New Zealand Agrichemical Education Trust. The Trust's one-day training and accreditation programme, labelled 'Growsafe', is aimed at reaching all pesticide users in New Zealand (New Zealand Agrichemical Education Trust, 1994). In its first year, about 3,000 (5 percent) did the programme.

Some farmers and growers are choosing to reduce their reliance on chemicals. Integrated Pest Management (IPM) uses multiple methods of pest control, with the emphasis on biological and low-cost methods (Croft and Penman, 1989). Under IPM, pesticides are used sparingly and greater use is made of crop rotations and soil tillage (to stop pests building up), selective breeding (for pest-resistant crops and livestock), biocontrol species (to parasitise or prey on pests and weeds), and crop biodiversity (to reduce the risk to any one crop). IPM programmes using biocontrols have been developed for several pasture and horticultural pests, particularly in apple orchards. The Apple and Pear Marketing Board's Integrated Fruit Production programme and the Kiwifruit Marketing Board's 'Kiwigreen' programme both use the IPM approach.

Organic and biodynamic farms go further than IPM. They reject chemical pesticides and mineral fertilisers (e.g. superphosphate) and use only biological methods and approved organic pesticides and fertilisers (Fisher, 1989; Ministry of Agriculture and Fisheries, 1993a). Their methods include enhancing crop biodiversity, recycling nutrients (e.g. compost, animal waste, wastewater), and protecting soil by growing longer pasture cover, planting shelterbelts, avoiding overstocking and animal trampling, growing green crops between arable crops, digging in straw and other organic matter to improve soil structure, and using mulches, grass/herb cover and contour plantings in orchards. Most New Zealand organic farmers are registerd with BioGro NZ Ltd which requires them to follow strict production standards and to pay all inspection and certification costs. Despite these requirements, and the time and effort required to produce export quality organic produce, the number of registered BioGro producers in New Zealand rose from 90 in 1989 to over 230 in early 1997. Because of its small scale, the industry lacks an organised marketing, research, and information network so the New Zealand Trade Development Board (TRADENZ) has set up an Organic Products Export Group to assist exporters through market research and trade missions.

At present, many conventional farmers are still driven to environmentally unsustainable practices by short-term economic priorities (Wilkinson, 1994; Wilson, 1994; Smith and Saunders, 1996). However, in the past two years, environmental self-help groups, variously called landcare, farmcare, watercare and land management groups, have mushroomed in rural areas (Ministry of Agriculture and Fisheries, 1996). Many have partnership arrangements with regional councils and Crown Research Institutes (e.g. Landcare Research and AgResearch) and receive funding assistance from their regional council, the Ministry for the Environment's Sustainable Management Fund, or the Ministry of Agriculture's Sustainable Agriculture Facilitation Programme. Their main emphasis is on improving soil and water management.

Besides the sustainable agriculture programmes run by central and local government, industry groups, such as the Pork Industry Board, the Agricultural and Marketing Research and Development Trust, the New Zealand Dairy Board, Federated Farmers, and agrichemical users are also taking initiatives to promote sustainable agriculture. In recent years, too, a small number of farmers have become active conservationists by restoring wetlands on their farms or placing formal protection covenants on their surviving forest stands with funding from the Forest Heritage Fund, Nga Whenua Rahui, or the Queen Elizabeth II National Trust.

Forestry pressures

Compared to pastoral farming, forestry is a minor land use, but it still covers a substantial area and has impacts on the environment, some positive and some potentially negative. Each year about 20,000 hectares of forested land are harvested and replanted, and about 70,000 hectares of new forest are planted over disused pasture or regenerating scrub. Only a few hundred hectares of indigenous forest are now logged and these are left to regenerate naturally.

The total area of standing forest potentially available for timber production exceeds 2 million hectares. About 1.6 million hectares of this is exotic forest, 600,000 hectares is privately owned indigenous forest, and some 150,000 hectares is Crown-owned forest which has been allocated to Timberlands West Coast Ltd for timber production. However, most of these forests are not harvestable at present because roughly half the exotic trees are still maturing, and some three-quarters of the indigenous trees are regenerating from previous logging and land clearance.

The environmental effects of production forestry vary with the type of forest, the terrain, and the preceding land use. The effects can often be positive. Many exotic forests are now being established on erodible farmland where they can reduce soil erosion, stream sedimentation and flooding (see Chapter 7). The planting of forests on farmland also increases the amount of carbon dioxide which is absorbed from the atmosphere, thus helping to counteract the 'greenhouse effect' (see Chapter 5). Being primarily timber crops, New Zealand's exotic forests also remove the pressure to unsustainably log native forests, thus allowing these to be reserved for biodiversity habitat and recreational purposes.

Despite these advantages, production forestry can also have negative effects on soils, water, biodiversity and scenery. Soils on slopes face a risk of erosion in the first six years or so after planting when the young tree roots are becoming established. Because commercial forests are planted as single-age crops, they have no older trees to provide support and cover. However, this risk is no worse than if the site had remained in pasture. Soils can also be damaged by machinery and roading at harvesting time, with both erosion and soil compaction resulting.

Established forests, particularly after several planting and harvesting rotations, may cause changes in soil nutrients and acidity. Nutrient depletion, especially of nitrogen, is most likely in sandy soils. However, in more fertile soils, nutrients, particularly phosphorus, sometimes show an increase. Nutrient depletion associated with forestry is mainly caused by such poor practices as removing topsoil and humus. These practices are increasingly uncommon. In many instances, such as the exotic forests of the pumice-based central plateau, the organic matter has actually increased, improving soil fertility. Soils have occasionally been found to become more acidic under pine forests, but this is not common and the processes which create acidic humus under exotic forests are similar to those which occur under indigenous forests. A more indirect impact on soil chemistry may arise at the processing end of the forestry operation where toxic chemicals are often used to protect radiata pine from fungi and insects. Spills and leaks can contaminate soil at sawmills and timber treatment sites.

In most cases forestry pressures on water are probably offset by the benefits of flood and sediment reduction. Nevertheless, negative impacts can include sedimentation during harvesting, reduced flow levels in streams and rivers following the establishment of new forests (and increased flows following harvesting), and the contamination of groundwater and streams near contaminated timber treatment sites. Harvesting impacts are short term in relation to the effects over the whole of a forest rotation.

Forestry can also put pressure on biodiversity because logging removes the habitat of forest-dwelling species. The clearfelling of native forests is very rare today but caused considerable destruction to large areas of native habitat in the past. The clearfelling of exotic forests is less destructive to biodiversity because fewer native species live in them. Biodiversity concerns with exotic forestry have generally focused on the establishment phase of the plantation rather than the harvesting phase. In the past, many exotic forests were planted in cutover native forest, shrublands, tussocklands, or dunelands. This effectively reduced the area of native habitat. These days, however, the majority of new plantings are on pasture land and are probably beneficial to indigenous biodiversity by relieving the logging pressure on native forests and allowing indigenous habitats to regenerate on forest margins and beneath forest canopies.

Another impact of forestry is the unsightly landscape which can result where logging and road construction are visible from roads and tourist walking tracks (Kilvert, 1995). This aesthetic impact can also have an economic impact because much of New Zealand's tourism is based on the attractiveness of our pastoral and forest scenery. Three quarters (74 percent) of the respondents in a 1994 public opinion survey by the New Zealand Forest Owners Association, thought that most exotic forests are a pleasure to look at, but 45 percent felt that clearfelling ruins landscapes and soil (New Zealand Forest Owners Association, 1995).

In recent years, Government and industry have adopted measures to limit the pressure which forestry can have on the environment. Under the indigenous forests provisions of the Forests Act 1949 (which were introduced through the Forests Amendment Act 1993), most indigenous timber production must to be subject to a sustainable management plan or permit. The only significant exceptions are several defined areas on the West Coast and in Southland, totalling less than 200,000 hectares. Under the New Zealand Forest Accord 1992, the main forestry companies have agreed not to replace native forest, regenerating scrub or other significant natural habitats with exotic forests. The forestry industry also has safeguards for soil, water, scenery and native habitats in its Forestry Code of Practice. The effectiveness of these measures has yet to be assessed. The 1993 amendment to the Forests Act only came into full effect in mid-1996 and the Forest Accord is a voluntary agreement which applies to the large companies but not to farmers and small landholders who are doing most of the new planting.

In summary, forestry exerts a range of pressures on vegetation and soil (Hunter and Douglas, 1984; Vaughan, 1984; Hunter et al., 1988; Ledgard, 1988; Davis and Lang, 1991; Balneaves and Dyck, 1992; Dyck and Bow, 1992; Hawke and O'Connor, 1993; Smith, 1994; McLaren, 1995; O'Loughlin, 1995; Rosoman, 1995b). These pressures include:

  • restricted biodiversity (but only where plantations replace native ecosystems; biodiversity is enhanced where they replace pasture land);
  • temporarily increased erosion potential after harvesting (particularly on erodible hill country soils), associated with the exposure of bare soil, the construction of roads and tracks, and the time between the decay of the roots of the harvested trees and the establishment of a complete root mesh by the replanted trees (i.e. the period from 3 to up to 10 years after harvest);
  • soil compaction (near roads, tracks, and, to a lesser extent, logging sites);
  • nutrient depletion, especially of nitrogen (less dramatic than on agricultural land and more likely in sandy soils than fertile soils and where forestry operations are practiced poorly);
  • acidification of soil (to which most of the South Island and large parts of the North Island are susceptible);
  • chemical contamination of soil from the treatment of radiata pine at sawmills and timber treatment plants;
  • unsightly landscapes where logging operations and road construction are within sight of walking tracks, tourist routes and main roads; and
  • invasion of wilding exotic trees into tussock, dune, and forest ecosystems (mostly lodgepole pine, Pinus contorta, in the central North Island, but also radiata pine in coastal areas and Pinus contorta and Pinus nigra in South Island high country ecosystems).

Urban, industrial, and transport pressures

Urban, industrial and transport land covers almost 900,000 hectares-nearly double the current area of crops and orchards, and about 3 percent of the total land area. Urban areas, as classified by Statistics New Zealand, include any town, suburb or city with more than 1,000 people. They are currently estimated to cover 730,000 hectares while the nation's network of non-urban railways and roads is estimated at 160,000 hectares.

Although the urban population has increased by only 30 percent since 1969, the area of land classed as urban has almost trebled. Some of this will reflect the redrawing of administrative boundaries and, in particular, the growth of small towns over the 1,000 person threshold. Other contributing factors include social changes such as the increasing number of one-person households, and the expansion of industrial and commercial land. In contrast, the area taken up by rural roads and railways is approximately the same as in 1965.

When averaged, the rate of urban expansion over the past 25 years has been around 4 percent per year, increasing from nearly 270,000 hectares in the late 1960s to 730,000 hectares (see Figure 8.8). This represents an average expansion of around 15,000 hectares per year through the 1970s, rising to 30,000 hectares by the early 1990s. The fact that many urban areas are located on floodplains and estuaries suggests this expansion has been at the expense of some of the nation's wetlands and more fertile, or "elite", soils. Of the nearly half million hectares of rural land urbanised since the mid-1960s, it is not known how much contained Class 1 and 2 soils, nor how much contained natural forest, wetland or duneland.

Figure 8.8: The expansion of New Zealand's urban area
Textual description of figure 8.8

New Zealand's urban area steadily increased from around 250 thousand hectares in 1969 to around 750 thousand hectares in 1993.

Source: Department of Statistics (1970; 1978; 1985; 1994)

Also unknown is the extent of soil contamination in urban, industrial and transport land, though an estimated 7,800 industrial sites, transport sites and landfills may be contaminated (Ministry for the Environment, 1993). Investigations are under way to assess the full extent of the problem and the number of sites that will need cleaning up.

Apart from their direct effects on land, urban areas also have a pervasive influence on other land uses. Their highly concentrated populations provide the market, and hence the economic justification, for much agricultural land use. Urban gardens are also the major source of introduced plant species that can become noxious weeds in indigenous forests, wetlands and agricultural systems. Auckland is both the largest and fastest growing urban area as well as the main entry point for most alien plants and insects into New Zealand.

In summary, the main pressures on land from urban, industrial and transport activities include:

  • loss of biodiversity where urban development and roads have encroached on natural ecosystems;
  • soil erosion from excavation and construction sites;
  • soil coverage and compaction from roads, buildings and other hard surfacing;
  • soil contamination from landfills, industrial sites, and domestic sources; and
  • indirect pressures from the activities and consumption patterns of large urban populations.

Mining pressures

Stone tools and ornaments were vital to Māori culture and economy. Argillite, obsidian and West Coast jade or greenstone (pounamu) were quarried to make tools and artefacts which were sharpened on coarse sandstone grinding stones. Clays were used to obtain blue, yellow and white pigments. A complex distribution system of gifts and exchange ensured that this stoneware was used all over New Zealand.

Traditional Māori use of minerals seems to have caused little disturbance to the environment (Barker, 1994). In contrast, the much larger scale of modern mining creates considerable disturbance to soil and vegetation which can be very significant at the local level (Ministry of Commerce, 1991). At the national level, however, the affected area is very small, totalling about 25,000 hectares since European settlement, or less than 0.1 percent of the land surface (Barker and Hurley, 1993). In addition, most modern mines are now subject to strict environmental standards which require waste water and sediment to be safely treated or stored and mined landscapes to be rehabilitated.

The total amount of sediment ever disturbed by mining in New Zealand is estimated to be around seven billion cubic metres, or around 15-20 billion tonnes. Averaged over the last 150 years this amounts to about 15 percent of the natural erosion rate (Fricker, 1986; Glasby, 1991). These estimates cover all types of mining, as well as quarrying and sand and gravel extraction. They also include an allowance for offsite effects, such as access roads and processing plants.

Most of the land disturbance was caused by alluvial gold mining in Central Otago and the West Coast which began in the 1850s. The total area affected by gold sluicing and dredging was around 15,000 hectares, and the total volume of sediment removed about five billion cubic metres (Glasby, 1991). This represents 60 percent of the total area disturbed by mining, and 70 percent of the total sediment disturbed by mining since European settlement. Today's hard rock gold mines, by contrast, affect barely 1,000 hectares (Barker and Hurley, 1993).

While these figures put the scale of mining impacts into national perspective, they do not change the fact that local impacts may be considerable. Access roads can cause erosion and stream sedimentation and the piles of waste rock and slurry can contain elevated levels of heavy metals which may enter surrounding soils and streams (Carter, 1982). This is often a problem with disused sites where waste piles were not subject to modern waste handling procedures. The Tui mine near Te Aroha in the Coromandel is a prime example. Abandoned in the early 1970s, its tailings pile continues to contaminate land and water (Morrell et al., 1995). Contamination is also a potential problem at another Coromandel mine, Golden Cross near Waihi, whose vast waste pile is situated on land subject to sub-surface movement of several millimetres per year. The regional council would like the tailings pile relocated. In the meantime, the mining company has spent some $20 million on stabilising the slope.

Mining activities can also disrupt ecosystems and landscapes, such as forests, dunelands, karst landscapes and glow-worm caves. For example, commercially valuable ironsand reserves occur on about 30 beaches along the western North Island, ranging from Kaipara in the north to the Wanganui and Whangaehu Rivers in the south (Stokes et al., 1989). Half of these beaches also contain rare and ecologically important dunelands (Partridge, 1992).

On one of these beaches, Taharoa, New Zealand Steel is mining the ironsands. Several Māori historical sites among the dunes have been protected and the foredunes have been left undisturbed. However, the inland dunes have been extensively modified. Marram grass, lupin, and pine trees have been planted and some tailing mounds converted to pasture. The ecological status of the mined area at Taharoa has been scored at 1 out of a possible 20, compared to a score of 12 for the undisturbed, though still ecologically modified, foredunes (Partridge, 1992).

Mining in New Zealand requires permission from the local authorities which sets the environmental standards that must be adhered to. Mining also requires permission from the land owner. If a mining or exploration site, or access to it, happens to be on Conservation Department land, the Minister's permission is required. Although exact figures are not available, several hundred licences or permits for mining-related activities are currently in effect on conservation land. However, this gives a misleadingly high impression of the amount of mining-related activity on conservation land, as the majority of permits and licences are for exploration and prospecting, rather than mining and, at any one time, only a relatively small proportion of licences and permits are actually being used.

In the late 1980s, the Minister received more than 160 applications per year to mine or prospect on conservation land for periods ranging from one to ten years. Approval was granted in about 90 percent of cases. By 1994, the number of applications had fallen to fewer than 30, partly because of the new environmental management regime ushered in by the Crown Minerals Act 1991 and the Resource Management Act 1991, with their provision for Planning Tribunal appeals against licences, and partly because of changing commodity prices.

Mining activity increased between 1975 and 1989 as coal and gold exploration intensified and improvements in mining technology made lower grade ores and deposits morerecoverable. The trend for mining activity in New Zealand is similar to world trends which have shown an increase as more minerals have become recoverable.

The world's currently known mineral resources are considered adequate to supply a growing global population and meet rising consumption for the next 100 years and are expected to expand further with more intensive exploration and advances in mining technology (Hodges, 1995). Between 1950 and 1990, world consumption of six major base metals (aluminium, copper, lead, nickel, tin and zinc) increased more than eightfold. Yet, even as consumption increased, the estimated recoverable reserves of three of these (copper, lead and zinc) became three to five times larger, while known aluminium reserves increased eightfold. Known gold reserves have also increased, despite rising consumption, from about 31,000 tonnes in 1971 to some 42,000 tonnes by 1990 (Hodges, 1995).

In New Zealand, low-grade hard rock ores and alluvial deposits became recoverable with the development of new methods of extraction. Between 1978 and 1988, local and overseas companies spent about $100 million on gold exploration. As a result, gold resources increased from apparently negligible amounts in the 1970s to around 1,210 tonnes in 1993 (820 "proven" tonnes and 390 "potential" tonnes). This is enough to maintain the current rate of production for more than 100 years (Barker and Hurley, 1993).

Table 8.4: Economically significant minerals in New Zealand, 1995.
Mineral Quantity mined (tonnes) Value ($ million) Estimated size of remaining resource (tonnes)
Gold 12.1 249 approx. 1,190
Silver 27.8 8

approx. 90

Ironsand 2.4 million 24 1.4 billion
Coal 3.4 million 161 8.6 billion
Aggregates 22.6 million 415 -
Limestone 3.2 million 36 -
Other - 298 -
Total - 911 -

Source: Ministry of Commerce (1996); Barker and Hurley (1993)

 

Gold production was one of New Zealand's first industries. Discoveries in the 1850s and 1860s led to gold rushes in Coromandel, Central Otago, the West Coast and Nelson. Alluvial gold (which occurs as grains or nuggets in gravel and sediment) was panned by swarms of miners and then dredged from river beds from the 1880s to the 1940s. Miners also sought veins of hard rock gold in underground mines. Up until 1915 annual production regularly exceeded 10 tonnes. By 1955 it had slipped below one tonne, and in 1975 fell to only 80 kilograms.

Today output again exceeds 10 tonnes. Renewed exploration led to three new hard rock mines being established in the late 1980s, one at Macraes Flat in Central Otago and two at the base of the Coromandel Peninsula-Martha Hill and Golden Cross. A fourth, the Globe Progress mine near Reefton on the West Coast, may be developed later. Reserves in the Nelson area are also being assessed for mining potential.

The Macraes and Martha Hill mines are open pit mines where ore is mined by excavating a large crater in the earth's surface. Golden Cross also has an open-pit but its main production is from an underground mine. Alluvial mining, in riverbeds, has increased on the West Coast and in Otago.

In 1993, for the first time in nearly 80 years, gold production exceeded ten tonnes and is expected to continue doing so for at least the next decade. Although gold is the most valuable mineral mined in New Zealand, coal, ironsand and aggregates of rock, sand and gravel have a greater combined value (see Table 8.4). Limestone and dolomite are also valuable.

New Zealand coal ranges from highgrade bituminous, through subbituminous, to lowgrade lignite. Total annual coal production in 1995 was 3.4 million tonnes. Nearly 30 percent of this was exported, and a quarter consumed by the Glenbrook Steel mill. The remainder of our annual coal production is consumed by factories, households, cement manufacturers, power stations and other users (Barker, 1994).

The main coal production areas are Waikato and Taranaki, Buller and Greymouth on the South Island's West Coast, Southland and Central Otago. With increasing exploration, coal reserves have 'increased' from 1,400 million tonnes in 1975 to 8,600 million tonnes in 1994. This is sufficient to maintain the current level of output for several hundred years (Barker and Hurley, 1993).

Ironsand containing titanomagnetite occurs along the west coast of the North Island. This black sand has eroded over thousands of years from the Taranaki volcanoes. All the current production is dredgemined by New Zealand Steel at Taharoa Beach or at Waikato North Head. A similar sand mining operation near Wanganui ran from 1971 to 1987. The resource is estimated to be at least 1.4 billion tonnes, sufficient to maintain the current rate of extraction for several hundred years.

Aggregates of rocks, sand, and gravel are used for building, road construction, ship ballast and harbour fill. They are produced at several hundred mostly small quarries located throughout the country. Very large quantities of suitable material occur in many parts of the country but shortages occur near some urban areas, such as Auckland, where most of the suitable local rocks have been exhausted. Aggregates are transported from other regions, and in recent years sand and gravel have been dredged from the sea bed to maintain supplies (Barker and Hurley, 1993).

Limestone also is widely available. It is used in a variety of applications from cement production to carpet making, as well as lime fertiliser. The other minerals are mostly sand and clays used in manufacturing. Their distribution is often limited to one or two localities, and extraction is generally not on a large scale.

In summary, the main potential pressures on land from mining and mineral exploration are:

  • removal of topsoil and vegetation, including destruction of plant and animal habitat;
  • changes to the landscape and scenery;
  • contamination of soil and water;
  • destruction of fossils and archaeological sites; and
  • changes to water channels, resulting in disturbance of aquatic ecosystems.

Pressures from pests and weeds

Pests and weeds are unwanted organisms, though use of the term often depends on the situation. On farmland, regenerating native vegetation may be unwanted, while weeds in native forest, tussock or dunelands may include exotic pasture grasses. The important point is that both natural and planted vegetation are vulnerable to invasion by unwanted species. Table 8.5 lists the main animal and plant pests monitored by one regional council.

In our indigenous ecosystems, the invaders are nearly always exotic plants and animals-though, in some cases, native species can proliferate into pests where the natural environment has been disturbed or modified. Examples are: the subalpine herb scabweed, which is widespread in tussock pasture lands; algae and the native reed raupo, which have proliferated in eutrophic lakes and wetlands; and pinhole borer beetles (Platypus spp.) which normally parasitise beech trees without killing them but can proliferate after catastrophic events to cause die-off in beech stands.

The indigenous trees have co-evolved with their parasites and have reached a mutual tolerance. Fungi, such as the leaf parasite Corynelia tropica on totara, the rust Caeomoa peltatum on tanekaha, and the gall-forming fungi, Cyttaria spp., on silver beech are common, but cause little damage (Gadgil et al., 1995). Native insects, such as the moth Proteodes carnifex, and the beech leafroller moth ('Epichorista' emphanes) can cause periodic defoliation of mountain beech stands but this does not cause lasting damage. No introduced insects have yet caused serious problems to indigenous forests. The main pests and weeds in indigenous ecosystems are a dozen or so alien mammals and numerous exotic plants (see Chapter 9).

Exotic forests are vulnerable to several dozen insect pests, such as the introduced wood wasp (Sirex spp.) which used to be a serious problem in some untended stands, and also some moth and beetle larvae. However, the most serious pests are various fungi which can infect pine needles, leaves or roots, and sometimes cause dieback of the tree canopy (Alma, 1986; Gadgil et al., 1995). The worst of these is an introduced fungus, Dothistroma pini, which causes needle blight in young pine trees in warm, wet, areas. Another is a genus of related species, Cyclaneusma spp., which were introduced last century. They cause needle cast which destroys about 2 percent of each year's total pine needle production.

Table 8.5: Pests and weeds monitored in Canterbury region.
Pest or weed Environmental or agricultural impact
Rabbit Competes with grazing animals and destroys vegetation in dry areas.
Rook Destroys emerging grain crops.
Wallaby Destroys native bush and snow tussock and competes with grazing animals.
African Feather Grass Unpalatable to stock. Replaces palatable grasses, especially in moist areas.
African Love Grass Unpalatable to stock. Of limited distribution, but invades pasture.
Baccharis Competes with native plants on arid rocky sites, mainly Banks Peninsula.
Barberry Invades lightly or ungrazed areas forming impenetrable thickets.
Bogbean Aquatic weed with potential to choke waterways.
Bur Daisy Burs contaminate wool and injure stock. Of very limited distribution.
Coltsfoot Can dominate in waterways and lightly irrigated land. Of very limited distribution.
Egeria densa Aquatic weed with potential to choke waterways.
Entire marshwort Whiteedged Nightshade
Lagarosiphon major Aquatic weed with potential to choke waterways.
Grecian Thistle Competes with more palatable species. Of limited distribution.
Hawthorn Spreads into lightly or ungrazed areas impeding stock access.
Nassella Tussock Invades dry low producing areas, excluding more productive plants.
Nodding Thistle Excludes more productive plants.
Old Man's Beard Vine climbs over trees, excluding light, and eventually kills them.
Ragwort Toxic to most stock.
Saffron Thistle Excludes more productive species. Limited distribution.
Spanish Heath Potential to spread into and exclude tussock.
Taurian Thistle Potential to exclude more productive plants, but so far limited to one site in New Zealand.
Variegated Thistle Excludes more productive plants.
White-edged Nightshade Suspected poisonous plant and may exclude other vegetation.

Source: Canterbury Regional Council (1995)

Up to a dozen other fungi can damage pine trees, including some native species. Two of these belong to the genus Armillaria. They cause a serious root disease, particularly in tree crops planted over cutover indigenous forest. Some pine plantations have lost half their trees to the disease within the first five years.

Other exotic trees are also victimised by pests (Alma, 1986; Gadgil et al., 1995). Douglas fir trees are vulnerable to native pinhole borer and several species of leafroller moths as well as to an introduced fungus called Phaeocryptopus gaeumannii which causes Swiss needle-cast. This fungus was first recorded near Taupo in 1959 and is now widespread throughout the country. Eucalypts (gum trees) and acacias (blackwoods), which are grown in some areas for timber, are vulnerable to a wide range of insects and fungi, mostly of Australian origin. Poplars, which are generally grown as windbreaks, are little troubled by insect pests, but a rust fungus, Melamspora larici-populina, has almost eliminated semi-evergreen poplars and necessitated their replacement by rust-resistant varieties.

Table 8.6: The area of Department of Conservation land at risk from browsing mammals.
Likely impact if no control operations were in place 1 North Island (hectares) South Island (hectares) Total DoC estate (hectares)
Total forest collapse2 245,000 305,000 550,000
Major composition change3 364,000 681,000 1,045,000
Major loss of biodiversity4 20,000 149,000 169,000
Area at risk of major change 629,000 1,135,000 1,764,000
Minor loss of biodiversity5 213,000 1,100.000 1,313,000
Area at risk of major or minor change 842,000 2,235,000 3,077,000

Source: Department of Conservation

1 In fact, control operations covered 1.3 million hectares in the 1995/96 year, 70 percent of the major risk areas.

2 Total canopy loss, significant species loss, replacement of forest by shrubland/grassland.

3 Significant canopy and species loss, change in forest structure from complex to simple.

4 Significant species loss and change.

5 Some species loss and change.

Elm trees, which are popular in urban areas, are vulnerable to the lethal Dutch elm disease which was discovered here in 1989. It is caused by the fungus Ophiotoma novo-ulma which is transmitted by the small elm beetle (Scolytus multistriatus ). Fruit trees in orchards are particularly vulnerable to a wide range of insect and fungal pests which attack fruit and leaves. Fruit and vegetable growers account for a considerable portion of the fungicide and pesticide use in New Zealand.

Agricultural land is also under siege from pests and weeds, ranging from the native vegetation patiently striving to regenerate in its home soil, through to exotic weeds, and a variety of animals and fungi of both native and exotic origin. Among the more serious exotic weeds in pasture and crop land are nodding thistle (Carduus nutans), Californian thistle (Cirsium arvense), ragwort (Senecio jacobaea), gorse (Ulex europaeus), broom (Cystisus scoparius), giant buttercup (Ranunculus acris), fat-hen (Chenopodium album), willow weed (Polygonum persicaria), and hawkweed (Hieracium spp). Fungal diseases, such as stripe rust, also affect crops.

The most significant pasture pests are native insects which cause millions of dollars worth of lost production each year. Grass grub, which attacks ryegrass, is the larval or immature form of a native chafer beetle (Costelytra zealandica). The porina caterpillar, which attacks ryegrass and other grasses, is the immature form of several closely related native moths (Wiseana spp.). Several species of Sitona weevil attack the grass grub resistant pasture legume, lucerne.

Another, much larger, pasture pest is the European rabbit (Oryctolagus cuniculus) which also affects young forest plantations. It was introduced last century and is now found over some 15 million hectares of farmland and light scrub. Throughout most of their range, rabbit numbers are controlled by climate, harrier hawks and introduced predators such as cats, ferrets and stoats (Robson, 1993). However, they are a serious pest over on about 1.2 million hectares of pastoral tussock land and are an 'intractable' problem on some 300,000 hectares of this (Kettle, 1996).

The Australian brush-tailed possum (Trichosurus vulpecula) is an even more widespread pest. Possums are well known for their impact on indigenous vegetation, orchards and cropland (see Tables 8.6 and 8.7). However, they also affect pastoral agriculture by transmitting the highly contagious bovine tuberculosis bacterium (Mycobacterium bovis) to cattle and deer. Possums are not the only carriers of bovine Tb, but they are the most numerous, outnumbering all the other vectors combined-pigs, cats, stoats, ferrets, deer, hares, and feral goats.

Table 8.7: Typical possum densities and impacts in various habitat types natural and modified.
Habitat Density (possums/ha) Conservation Risk Tuberculosis Risk Other Risk
Mixed forest-scrub-pasture margins 5>15 medium very high -
Tree-lined waterways on farmland 5-15 low high -
Small isolated forest patches 5-15 medium-high medium Tourism losses from lost scenery and biodiversity
Rata/kamahi and mixed hardwood forests 5-15 high low

Tourism losses from lost scenery and biodiversity

Lowland indigenous podocarp forests 2-5 low low -
Alpine shrublands 2-5 low - -
Exotic forests 1-3 - low

Browsing of young trees, replanting costs

Beech forests <2 low low -
Alpine grasslands <2 low - -
Open pasture and cropland <2 - high Lost production through eating pasture and crops.
Erosion control tree plantings ? - medium Browsing of plantings; increased soil erosion
Horticultural and ornamental crops ? - - Lost production (generally localised)

Sources: Department of Conservation (1994); Parliamentary Commission for the Environment (1994)

Other important livestock pests include about five species of blowfly (Lucilia spp.) which kill an estimated 200,000-250,000 sheep annually by laying eggs in the fleece which then hatch into maggots that feed on the animals' flesh. All the pest blowflies are from overseas, as are the common houseflies which arrived on fly-blown meat in the European migrant ships. New Zealand's only native blowfly, a large blue species which lives in tussock country, is a vegetarian.

Parasitic nematodes or roundworms are also serious pests. Nematodes are a very successful group of animals. Most are free-living inhabitants of ocean mud, soils and water, in environments which range from tropical forests to deserts and polar regions. However, a significant number are intestinal parasites, living inside other species. Most of New Zealand's nematodes are harmless soil-dwellers, and some are even beneficial, but about 50 parasitise humans, and even more parasitise our livestock, impairing their growth and health and costing large sums of money in lost production.

Pest control pressures

Controlling pests and weeds is a large and costly component of agriculture and nature conservation in New Zealand and requires a formidable arsenal of animal poisons, insecticides, herbicides, fungicides and parasitekilling drenches. These diverse toxins are collectively referred to as 'pesticides'.

New Zealand has more than 900 registered pesticide products, using at least 270 different active ingredients (MacIntyre et al., 1989). In 1993, around $150 million was spent on pesticides-including $90 million to control weeds (estimated to cause about $340 million in lost production each year), and $20 million to control roundworm parasites (which cause losses of around $260 million in reduced animal production). Most of the remaining $40 million was spent on fungicides to control fungal pests in gardens and orchards. These figures do not include the roughly $50 million spent by the government on controlling possums, nor the sums spent on controlling other mammalian pests such as rabbits, goats, deer, rats, cats and mustelids (ferrets, stoats and weasels).

Three-quarters of the pesticides sold in New Zealand are used in the North Island. About two-thirds are used by orchardists and market gardeners. About a third are used by pastoral farmers. This reliance on chemical weapons began with two innovations in the 1940s. Laboratorymade organochlorines, such as DDT, replaced the earlier generation of heavy metal pesticides, such as the highly toxic arsenates. At the same time, the Second World War produced a crop of experienced pilots able to drop bulk quantities of fertiliser and apply pesticides from light aircraft. The idea was first pioneered in New Zealand in the 1920s but not taken up on a large scale until the 1940s. Following the passing of the Soil Conservation and Rivers Control Act 1941 bulk quantities of fertiliser began to be dropped on steeper country to improve the pasture cover. Later, pesticides and poison baits also began to be air-dropped.

Synthetic pesticides, and air-dropped fertilisers, triggered an agricultural revolution through the 1950s and 1960s, and ended the insect attacks which had destroyed large areas of crops in the 1920s and 1930s. But when DDT was withdrawn because of its health and environ-mental impacts in the 1970s the resurgence of grass grub and porina led to annual agricultural losses of up to $100 million (MacIntyre et al., 1989). Research then swung dramatically back toward biological means of controlling pests. In fact, of all the alien species introduced to control pests between 1870 and 1990, 31 percent were released in a single decade, as organochlorines were being withdrawn (Cameron et al., 1993).

Today research into biological control methods is increasing. One approach is to breed pestresistant strains of livestock and crops (e.g. the recent development of a Romney sheep which is 70 percent resistant to roundworms). The other is to introduce biocontrol organisms that can kill pests and weeds-either predators, which eat them from the outside, or parasitoids, which eat them from within. Parasitoids are tiny insects (often wasps) which are only parasitic during their larval stage. The adults lay eggs inside a target organism and, when the eggs hatch, the larvae eat their way out, finally emerging as adult insects from the remains of their host.

Biocontrol organisms have always been economically attractive because, once established, they require little maintenance or re-application. Two new factors have added to their appeal: increasing public concern about the potential effects of pesticides, and the evolution of chemical resistance in some pests and weeds. So far, four New Zealand weed species are known to have developed resistance to herbicides. Two of these, fat-hen and willow weed, affect cropland. The other two, nodding thistle and giant buttercup, are pasture weeds. Now drench-resistant roundworms and insecticide-resistant blowflies are appearing in livestock.

The move to biological methods is not new. At least 321 alien species have been introduced to New Zealand since 1874 to control pests and weeds and in some cases to disperse animal dung. Of the 75 biocontrol species that became established, 36 have had significant impacts on 26 of the 70 or so pests they were targeting (Moller et al., 1993; Cameron, 1994). Six of these pests are now fully controlled and 11 partially controlled. They include major pests of barley and small grain cereals, pasture grasses and maize or sweet corn, lucerne, white clover, forage brassicas, greenhouse crops, apples, citrus fruit, eucalypts and radiata pine trees (Cameron et al., 1993; Hill et al., 1994).

One example is a moth (Mythimna separata) whose caterpillar, known as army worm, attacks grain crops. Since 1972, it has been controlled by an introduced parasitoid wasp (Apanteles ruficrus) for an annual saving of $410 million. Another pest, the Sirex wasp in pine forests, is controlled by a multi-species team of four parasatoid insects and a sterilising nematode (Beggingia siricidicola). One of the eucalypt tree pests which has succumbed to biocontrols is the gum-tree scale (Eriococcus coriaceus) which is controlled by a combined effort from the ladybird (Rhizobius ventralis) and a predatory caterpillar (Stathmopoda melanochra).

Biocontrols for pasture pests include a bacterial control agent for grass grub (Jackson et al., 1993) and the ragwort flea beetle which was introduced from Oregon in 1983 to control the weed, ragwort. Ragwort reduces the area of pasture suitable for dairy production, as it is toxic to cattle and taints milk. Other weeds for which biocontrols are being researched are gorse, broom, nodding thistle, Californian thistle, hawkweed, old man's beard, heather and buddleia (Zhang et al., 1993; Hill et al., 1994).

New biocontrol organisms are being tested and proposed all the time. Most are insects, but fungi, bacteria and even viruses are also under investigation. The best known viruses are probably the controversial Myxoma virus and its even more controversial replacement, a calicivirus which causes Rabbit Haemorrhagic Disease (RHD). The Myxoma virus was released successfully in several countries, including Australia, forty years ago and caused outrage among animal welfare groups because of the prolonged suffering it caused the rabbits.

Myxomatosis had a high short-term impact on the rabbit populations but became less potent as rabbits and viruses evolved tolerances to each other. It failed to establish in New Zealand and several applications to re-release it have been declined on both humanitarian and ecological grounds. Work is currently underway in Australia on the development of a genetically modified Myxoma strain which causes sterility rather than a painful disease. As of late 1996, however, this work was overshadowed by the premature release of RHD in Australia and applications for its release in New Zealand (see Box 8.3).

A careful evaluation process for RHD has been necessary before deciding whether or not to allow it into New Zealand because, in the past, pesticides and biocontrols have sometimes had unintended environmental impacts. DDT residues, for example, turned out to be highly persistent, accumulating in animal fat rather than breaking down. Today's pesticides are designed to decompose more rapidly, though the effects of their breakdown products on soil organisms and stream life are still poorly understood.

Biocontrols have sometimes hit nontarget species harder than the pest they were meant to control. The hedgehog was introduced to control the introduced garden snail but also preys on native snails and insects (Moller et al., 1993). Stoats, ferrets and weasels were introduced to control rabbits, but they also attack native birds and reptiles. However, biocontrol scientists are quick to distinguish between these introduced mammals and the biocontrol invertebrates. Although little research has been done on their ecological impacts, few recently introduced biocontrol species seem to have penetrated into native bush (Cameron, 1994; Barratt, 1996).

To date the only introduced insect biocontrol known to have become established in non-target native species is the bristly tachinid fly, Trigonospila brevifacies. Tachinid flies belong to a family which can parasitise a wide range of insects. This particular tachinid was introduced into orchards to control leafroller caterpillars. At the time, the impact on native insects was of little concern. The parasitoid has since infected six different families of harmless native moths. It is not known whether any of the affected species have declined as a result (Atkinson and Cameron, 1993; Cameron et al., 1993; Cameron, 1994).

Today, efforts are made to ensure that new organisms will not harm nontarget species. Unpredictable impacts still occur, but, to date, they have involved other introduced species rather than native ones. Recently, for example, it was found that an exotic parasitoid, Microtonus aethiopoides, introduced to control Sitona weevils, is parasitising another biocontrol insect, Rhinocyllus conicus, which was introduced to control nodding thistle (New Zealand Science Monthly, 1995).

In order to maximise the effectiveness of pest control programmes, the concept of Integrated Pest Management has become more widely accepted in recent years. It involves a mix of measures, including not only biocontrols, selective breeding and selective use of pesticides, but also environmental measures, such as changing crops or grazing regimes to reduce exposure to pests and weeds.

In summary, the pressures which pests and weeds put on our land include:

  • reducing indigenous biodiversity, through predation and competition;
  • reducing production from livestock, pasture and crops; and
  • necessitating the use of pesticides and biocontrols which carry a risk of unintended environmental impacts.
Box 8.3: Viral control of rabbits

The virus that causes Rabbit Haemorhagic Disease (RHD) reached Australia very recently (Munro and Williams, 1994). In fact it arrived in the world very recently, first appearing in China only a dozen years ago (in rabbits imported from Europe). It belongs to a family of viruses called caliciviruses. The five known calicivirus groups contain some strains which infect only one species and others which can infect several different species (e.g. pigs and sea lions). Some caliciviruses can cause infections in humans (Matson and Smith, 1996).

Since its appearance in China, the RHD strain has spread to more than 40 countries on four continents, killing millions of rabbits in the process but apparently causing no problems to humans or any other species. It was accidentally released from a joint New Zealand/Australian research facility in Australia in September 1995 and quickly spread to many parts of the country (Anderson 1995a, 1995b; Drollette, 1996). For media purposes, the disease began to be referred to as Rabbit Calicivirus Disease (RCD), rather than by its formal name. As of early 1997, the New Zealand Government was considering an application under the Biosecurity Act from five regional councils, Federated Farmers and the Commissioner of Crown Lands, to have the RHD virus released here.

In deciding whether or not to approve the release of the virus, the Government has had to consider such issues as: its humaneness; any possible effects (harmful or beneficial) that it may have on New Zealand's natural resources, including its possible impact on other species (including rare indigenous species); and its likely effectiveness in actually reducing rabbit populations. The Government has also had to consider the possible advantages of a controlled release over an accidental or unauthorised release.

Scientists and animal welfare organisations are in broad agreement that the virus is relatively humane. Blood clots form in vital organs and the adult rabbits die quietly of respiratory failure within 30-70 hours. Young rabbits are unharmed. In fact, once exposed, those under 58 weeks acquire life-long immunity. In parts of Europe a significant number of immune adult rabbits have mysteriously developed antibodies before being exposed to the disease. This has led researchers to speculate that the virus may be a mutant strain of some pre-existing rabbit calicivirus which is harmless and so has remained undiscovered. Others have speculated that it may have mutated from a calicivirus which normally infects other species. One possible candidate is the virus which causes European Brown Hare Syndrome (EBHS). At present, nobody knows for sure and this raises the most controversial question about the virus: how might it affect other, non-rabbit, species?

Although 'species jumping' has not been observed in the 12 years since the virus was discovered, estimates of the risk vary among the scientific community, with some scientists judging it to be small and others, significant. In Australia, 30 species have been tested, including the North Island brown kiwi and the New Zealand short-tailed bat. Antibodies developed in the blood of five species (dog, fox, human, kiwi and mouse) but, due to perceived irregularities in the tests, scientific opinion is undecided as to whether this constituted infection. The Australian Government finally approved the controlled release of the virus in October 1996.

Apart from the risk of infection, however, there is also a risk that the virus may harm other species through ecological disruption. Rabbits are a major food item for predators such as stoats, ferrets, cats and harrier hawks. If rabbit numbers were to fall dramatically, the predators may switch to hunting other species. Scientists are unable to predict whether these changed predation patterns would drive starving ferrets and cats to eat more native birds and reptiles, thereby increasing the pressure on them, or eat more rats, thereby reducing the pressure on native species. Early results in Australia show an increase in indigenous animals and a sharp fall in predators (Drollette, 1997). Cat numbers in some areas have fallen by 90%. Most had bellies full of insects, indicating that they were unable to quickly learn how to target new prey.

As for the virus's impact on the rabbits themselves, the results from overseas have been variable, depending on such factors as the season (and hence the number of young that become immune), the percentage of adults with pre-existing immunity, and the presence or absence of suitable carriers (e.g. mosquitoes, bush flies). In parts of Australia rabbit numbers have fallen by 95%, but there are concerns that the reduction may only be temporary if other methods are not used to eliminate the survivors (Drollette, 1997). New Zealand's Ministry of Agriculture has pointed out that, while there are many uncertainties about RHD, one certainty is that it will not be a 'magic bullet'. It's use in New Zealand would need to be accompanied by other methods, such as poisoning, shooting, and 'other control technologies' in an integrated pest management strategy (Kettle, 1996).