This chapter provides information on why the condition of our land is important, and presents information on the pressures and state of our land, and how this state is changing over time.
Our land – a summary
New Zealand has been occupied by humans for only 700–800 years, but in that time our land has gone through transformative change. When humans arrived, we think that forests covered all but the tops of mountains and the wettest parts of the lowlands. Wetlands covered extensive areas of both islands, particularly in lowland and coastal areas. Today, about one-third of this forest remains, concentrated mainly in upland and mountainous areas. Wetlands are reduced to about 10 percent of their original extent.
Farmland has taken the place of most of our forests and wetlands. Agricultural and horticultural land occupies about 42 percent of New Zealand, while plantation forestry covers a further 7.5 percent. The extent of agricultural land has not changed significantly since 1996, but its use has become more intensive in some regions. Agriculture is central to our economy, and along with other production from the land, it makes a major contribution to New Zealand’s export earnings. The ongoing productivity of our land is therefore important, as it underpins our economic and social well-being.
The most critical issue affecting the productivity of land is erosion, which first became a major problem in the early 20th century. Large areas of steep terrain, unstable underlying rock, and high rainfall make our land prone to erosion. Natural erosion occurs particularly in alpine areas like the Southern Alps, where little vegetation exists and high rainfall occurs. When humans settled, they cleared forests and turned large areas into pasture, which expanded the area of the country vulnerable to erosion. From the 1940s, tree planting and other methods of soil conservation were successful in curbing soil erosion to some extent, especially in its most extreme forms. However, erosion remains a problem in New Zealand, particularly in the north and east of the North Island. Erosion affects productivity because topsoil, which has built up over millennia, contains most of the nutrients in the soil. When topsoil is washed into waterways, the underlying soil’s fertility is degraded. Erosion also affects water quality because it adds sediment and nutrients to waterways.
Compacted soils also affect land productivity. Soil compaction is evident on land used for farming animals for dairy, meat, wool, and velvet, and is made worse by higher stocking rates and heavier stock. Over half of the land used for dry stock and nearly 80 percent of soils under dairy farming are affected by compaction. This can adversely affect productivity because compacted soils can impede pasture growth and the capacity of the soil to hold water, resulting in greater run-off.
The leaching of nutrients from farmland is an issue affecting our rivers, lakes, and estuaries. This happens when we apply more nutrients to the land than grass and other plants can use. When an excess of nutrients flow into waterways, they cause unwanted plants to grow, affecting water quality. Nitrate leaching has been an issue for some decades, but has grown in significance as farming intensified in many parts of the country.
We are also interested in the ability of the land to support indigenous animals and plants. The decrease in the extent of indigenous forests, wetlands, and other habitats since human settlement has reduced the area where indigenous plants and animals can live. In addition, humans brought with them numerous animals and plants from other parts of the world. Some of these animals prey on indigenous species or compete with them for food or habitat, while many introduced plants invade indigenous habitats. These pressures have led to a significant number of species becoming extinct, and many species continue to face this risk.
While the loss of indigenous habitats has slowed, pests continue to pose a serious threat to our indigenous animals, plants, and habitats. Today, possums, rats, and stoats are the most widespread of our pests – they are found across at least 94 percent of the country.