Biophysical indicators of sustainability of North Island hill pasture systems

Abstract

"Sustainability" is a social construct, and is difficult to define in precise value-free terms. It has ecological (biophysical) and socio-economic dimensions. Biophysical indicators are tools that can be used to define resource status. They cannot directly measure sustainability, but are useful for comparing present resource status with defined limits set within a socio-economic framework. We measured vegetation and soil variables in 4 areas of grazed North Island hill country with different management (fertiliser application/stocking rate) histories (1973 to 1994) and sub-divided into 36 paddocks. Nineteen vegetation (including herbage production); soil chemical, physical and biological; and soil water variables were selected as potentially useful biophysical indicators. Analysis of the results for these variables suggested that pasture botanical composition (especially content of high-fertility responsive grasses and of herbaceous weed species) and earthworm mass/unit area explained most of the variance of the data matrix. These variables were also highly correlated with herbage production, an indicator of likely economic performance. Development of the most suitable indicators requires good understanding of agro-ecosystem function, and is hampered by our lack of understanding of critical processes. Keywords: biophysical indicators, hill country, pasture, soil, sustainability