Feature Article The environmental footprint of New Zealand,s plantation forests: nutrient fluxes and balances
T. Payn and P. Clinton
Concern over New Zealand's environmental quality and the long-term impacts of agricultural sector activities on water quality is increasing. Lake and river water quality is declining as a result of past and current land use practices and national and regional initiatives are being developed to halt and reverse the declines. Plantation forestry is a low impact land use by comparison to other agricultural sectors, requiring less nutrient input in terms of fertiliser and causing less environmental impact on ground and surface water from nutrient leaching. A nutrient balance model has been developed to predict nutrient fluxes within plantation systems, over one or more rotations. The model is a simple mass balance model; it predicts nutrient uptake by a crop and partitions nutrients into the various pools within the soil/plant system. The model predicts when there will be surpluses or deficits in the system and consequently when there is an increased risk of nutrient transfer or a need for fertiliser application. Running different scenarios demonstrates the effect of vegetation management, harvesting intensity, or change in productivity due to climate change on the pools of nitrogen during a rotation, and the effects of multiple rotations on soil phosphorus pools. Using the model to develop various scenarios will enable the development of multiple land use scenarios, with a focus on minimising the nutrient 'footprint' or impact for a specific catchment or region. Predictions of nutrient fluxes can contribute to the development of nutrient trading models, where the value of plantation forestry as a low nutrient footprint land use may be recognised as an additional economic benefit above the value of the tree crop.
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