nutrient cycling

The Westland petrel (Procellaria westlandica) is a 1200 g medium-sized seabird whose breeding colonies are dispersed across 700 ha of forest on the western coast of South Island, New Zealand. These birds represent the sole landscape-scale lowland remnant of formerly widespread petrel and shearwater colonies in mainland New Zealand and provide an opportunity to investigate maritime species’ impact on terrestrial ecosystems characteristic of pre-human New Zealand.

We estimated the annual production of honeydew per unit land area of beech (Nothofagus spp.) forest by measuring the amount of honeydew produced in 24 h by scale insects (Ultracoelostoma spp.) (Hemiptera: Margarodidae) every month for 2 years. We used exclosures to prevent animals (notably Vespula wasps) removing honeydew, and we compared the standing crop of honeydew inside permanently closed exclosures with that outside exclosures.

Before European settlement, most of the 750,000 ha of land comprising the Canterbury Plains was under native tussock grassland with pockets of podocarp forest. The dominant land use today is mixed cropping in which cereals and cash crops are grown for 2 to 4 years followed by grass-clover pasture for 2 to 4 years. These cropping rotations are generally too short for either a substantial build-up in soil organic matter under pasture or its breakdown under arable cropping to occur.

The improvement of New Zealands pastures over the last 150 years has increased the nutrient status of the soil as a result of the application of fertiliser, an increased soil organic matter content and increased biological activity. The grazing animal has also influenced the nutrient status of the soil by increasing the rate at which nutrients cycle between the soil, plants and animals.