5.3 Settlement, deforestation and endangered species
Box 4: Some indicators of New Zealand's environment*
The proportion of New Zealand converted to farmland is large by world standards (52 percent compared to the world's 37 percent in 1993). Although our human population density is comparatively low (13 people for each square kilometre (km2) compared to the world's 43) our livestock density is high (180 sheep per km2 compared to the world's 14 and 35 cattle per km2 compared to the world's 10). This amounts to 13 sheep and 3 cattle for every person, and makes pastoral agriculture the country's main land use.
* The figures presented here are based on careful definitions, which can always be challenged. Without access to that background information the safest approach is to accept the figures as a reliable guide, but not necessarily to the accuracy given.
Since human settlement approximately 700–800 years ago, the indigenous forests, which once covered about 85 percent of the land area, have been reduced from some 23 million hectares to approximately 6.2 million (23 percent of the land area) – mostly confined to mountainous areas and to some low-lying parts of the West Coast, Southland and Northland. In most areas lowland forests have been reduced to fragments and will need considerable expansion if biodiversity within them is to be sustained.
Grasslands covered 1–2 million hectares (roughly 5 percent of the land area) before humans arrived but expanded to almost 8 million hectares as a result of deforestation by early Maori fires. Further deforestation in the past 100 years by farmers and timber millers has extended the grassland area to 14 million hectares – over 50 percent of the total land area.
The main source of pressure on water is pastoral agriculture which has polluted many surface waters and some groundwater with sediment, animal waste and nutrients, and has also increased flooding and erosion in many areas by removing deep-rooted vegetation from hillsides and riverbanks. (The use of irrigation water, mainly for pasture, is also a source of pressure on water levels in some South Island rivers, as is land drainage for agriculture which has caused an 85 percent reduction in New Zealand wetlands.)
Floods can occur in any season, and in all regions of New Zealand. The rate of flooding increased 50–150 years ago following widespread replacement of forests, scrub and tussock with shallow-rooted pasture grasses. Despite extensive river and catchment control schemes, damage from flooding is estimated to cost at least NZ$125 million a year.
From a land that was originally 85 per cent forested and occupied by mostly unique species of plants and animals, New Zealand has changed into a largely managed landscape, two-thirds of which is given over to farming and forestry with introduced species. The majority of this land is now under pasture, much of it on hilly and mountainous terrain. Many of the key effects on New Zealand's environment arise from this intensive period of human settlement and the introduction of livestock in the late nineteenth century. The combination of habitat loss and the introduction of new species has had a dramatic effect on the native flora and fauna. In particular:
The displacement of native forest and grasses by agriculture led to loss of habitat and severe pressure for many native species. Over 30 species of land birds are known to have disappeared after the arrival of the Maori, and since European settlement a further 16 land birds have become extinct, together with a native bat, one fish, at least a dozen invertebrates and possibly as many plants.
Just as significant, the new pressures from the settlers and their agricultural practice has greatly increased the number of species threatened with extinction. The main threat comes from the loss of suitable habitat or its fragmentation – the agricultural landscape is hostile to many native species. In addition, introduced pests and weeds prey on or compete with native species or destroy their habitat. The Kea is one of the endangered species:
'Many [native species] are still coping with the fallout from habitat destruction and predation. One such is a native parrot, the Kea (Nestor notabilis). Once widespread in the South Island, its original range was first reduced by Maori deforestation, then by the conversion of the high country into sheep pasture.
Last century, when it became known that some Keas attack sheep, a bounty was paid for their destruction and continued to be paid well into this century. At 10 shillings a beak in the 1920s (equivalent to NZ$65 or £20 today) Keas provided a lucrative living for bounty hunters … it is estimated that about 150,000 Keas were killed between 1870 and 1970, bringing the population down from about 50,000 to 5,000–15,000 today.
The Kea only received formal protection in 1986 after an agreement was reached between the Department of Conservation and high country farmers, in which the Department undertook to control 'rogue' birds. Keas were also shot [as a pest – they have powerful beaks with which they like to test to destruction modern materials such as rubber] in the early days of ski-field development but today most ski-fields are Kea-proofed.'
(Taylor & Smith, 1998, p. 9.30)
The Kea is a unique bird. It is highly intelligent and curious about human artefacts – both a strength and a weakness for an endangered species. It is the only example in the world of a most unexpected adaptation: an alpine parrot. To what extent do you think that the development of refrigeration can be blamed for the current state of the environment in New Zealand, including the near demise of the Kea?
Have a look now at Figure 14. How well does it represent the processes which have led to the decline of the Kea? Spend five minutes to review and list other possible influences on this linear chain of cause, then draw a modified version of Figure 11 which incorporates the additional factors.
The short answer is that it is both an over-simplification and misleading to suggest, as Figure 14 does, that the problems faced by the Kea are solely the result of the development of refrigeration. While a case can be made for each causal link in the diagram, it is extremely unlikely that these are the only factors at work. At each point in the diagram there are likely to be several other contributory factors. The true picture is much more complicated and the diagram should represent multiple causes for each stage (if they are known). My own attempt, a multiple-cause diagram, based mostly on information given so far, is shown in Figure 15.