Story: Human effects on the environment
Page 1 – Early human impact
Like many groups of islands in the Pacific, New Zealand was very sensitive to human settlement. Its unique plants and animals had been isolated for millions of years, evolving in the absence of people and mammalian predators.
Almost as soon as the first humans (Polynesian peoples, later known as Māori) first arrived in New Zealand, around 1250–1300 AD, they began to have an impact on the environment. Their arrival, and that of the two mammals they brought with them – the kiore (Pacific rat) and kurī (dog) – marked the start of an extinction cascade.
Material from early archaeological sites, particularly the Wairau Bar in Marlborough, reveals that Māori first exploited the larger game animals (over 2–3 kilograms). Middens contain many bones from all the moa species, geese, swans, adzebills, takahē, shags, large penguins, New Zealand sea lions and fur seals.
Changes over time
In later archaeological sites (from the 14th century on), the larger vertebrates are absent or uncommon. These sites show a growing dependence on shellfish, fish, eels and plants. Some later middens, such as at the mouth of the Shag River (Waihemo) in Otago, show that smaller shellfish were taken as the larger ones became locally depleted.
Decline and extinction of large animals
The difference between early and late middens shows that intensive hunting caused most of the larger, slower-breeding birds to become extinct within a few hundred years. Māori also hunted fur seals and New Zealand sea lions, greatly reducing their natural range and causing them to become locally extinct. These animals once occurred up to the far north of New Zealand before becoming extinct there.
At the same time, many smaller animals were preyed on by kiore. Radiocarbon-dated fossil bones indicate that this caused the rapid extinction of Scarlett’s shearwater, the South Island snipe, the stout-legged wren, Hodgen’s rail, the New Zealand owlet-nightjar and the greater short-tailed bat.
Kiore had an impact on tuatara, lizards, frogs and invertebrates (animals without backbones). They also ate seeds. Rat-gnawed seeds of native trees such as miro, mataī, pōkākā and hīnau have been found, preserved in sediment. The oldest radiocarbon dates for rat-gnawed seeds are from the 13th century, around the time that Māori arrived in New Zealand, so it seems likely that kiore came to New Zealand with the earliest settlers. Whether they stowed away or were brought deliberately is not known.
Kurī (dogs) were domesticated, and were an important source of food and skins for capes. They were probably kept close to camp, and did not run wild in packs or contribute much to early extinctions.
Early introduced plants
Early Māori settlers brought tropical crop plants from their Polynesian homelands. While many species did not survive because of the cooler climate, others were grown successfully, providing carbohydrate or useful resources. They probably include kūmara (sweet potato, Ipomoea batatas), yams (Dioscorea species), taro (Colocasia antiquorum), gourd (Lagenaria siceraria), paper mulberry (Broussonetia papyrifera) and perhaps the Pacific Island cabbage tree (Cordyline fruticosa).
Archaeological evidence suggests that these plants were being cultivated soon after human arrival. There are stone garden walls, large terrace gardens, and pits for storing seasonally abundant tubers. There are also signs of soils that have been disturbed by deep cultivation, and ditches for taro cultivation in swampy areas. In some places the soil structure was deliberately improved by adding sand, gravel and pebbles, taken from quarry pits that are still visible.
As Māori grew crops, they changed the landscape by altering soils and wetlands, and by reducing forest areas.