Although plantation forests may exhaust soil nutrients, research in the South Island shows that the opposite can also be true. Exotic conifers have ectomycorrhizae (fungal associates) on their roots, which mobilise nutrients from organic matter deep in the soil, speeding up the rate at which these can be used by other plants. Some native species, such as beech and mānuka, have the same effect.
Research shows that forests help stabilise soil in erosion-prone country. As a result forests have been planted on steep hills on the East Coast. Plantations have also been established on unstable coastal dunes that were threatening other land uses, such as farming, particularly on the west coast of the North Island from Northland to Manawatū.
Rain on the plain?
Do trees attract rain? This popular belief is not borne out by rainfall records from the central North Island. No increase in rainfall has been observed as a result of widespread forest planting there.
To research sustainable forestry management, plots were established throughout New Zealand in 2000 to test the impact of forestry practices on soil nutrition. Data will be used to manage plantation forests so they do not deplete the productive capacity of the land.
Forests help stabilise land and protect waterways. Studies have shown that forested catchments have less erosion, produce less sediment and provide better aquatic habitats than pastoral catchments.
Forestry and the Kyoto Protocol
Under the Kyoto Protocol, New Zealand must reduce its greenhouse gas emissions to 1990 levels. Forestry can help achieve this goal because trees convert carbon dioxide in the atmosphere to carbon, which is stored in the form of wood and soil organic matter.
Forests can absorb large amounts of carbon dioxide, so they can assist in balancing the greenhouse effect. Since New Zealand ratified the Kyoto Protocol in 2002, national monitoring systems have measured carbon flows across indigenous and plantation forests. This data is necessary for New Zealand to meet its reporting obligations.