It is widely held that successive rotations and repeated disturbance by management activities will result in a decline in soil quality due to lack of forest ecosystem resistance and resilience and therefore loss of soil function, amongst other things. Changes in the state of the forest environment in the course of producing or extracting forest products will inevitably affect the value of future products in terms of both volume and quality. It is paramount that these environmental impacts do not reduce the opportunities for wealth and social benefits derived from New Zealand forests. Therefore, indicators of the state of soil quality and function of forest soils are vital for the early prediction or detection of loss of productive capacity.

Plantation forestry research concerned with soils is currently centred on three major national series of Long-Term Site Productivity (LTSP) experiments in order to address our goal of developing a suite of soil, plant and microbial-based indicators that accurately reflect the quality and productive capacity of sites within forest ecosystems. The outcomes of this research will provide best management practices for maintaining and improving soil quality for future generations as well as improved data for use in reporting to meet Montreal and other government commitments. This presentation reviews the relevant findings from these three trial series. The LTSP1 series, initiated in the 1980s at six sites representing a wide range of soil fertility spanning recent volcanic soils to highly weathered greywacke gravels, examines the long-term consequences of increasing levels of biomass removal at harvest, typical of a range of management practices. The LTSP2 series, initiated in 1999 at 35 sites covering the range of edaphic and environmental conditions found throughout New Zealand plantations, aims to define biophysical indicators of site quality and productive capacity using a unique experimental format of highly stocked mini plantations. The LTSP3 series, initiated in 2001 at 15 sites, again covers a wide range of edaphic and environmental conditions found throughout New Zealand. This series examines the utility of plants as indicators of site quality, specifically the use of genotypes of three species with different physiological characteristics to define sites in terms of water and nutrient supply.