Aspects of nutrient cycling in indigenous and pine forests of the Grey Valley, Westland, were followed over a 2-year period. Four sites representing stages in exotic conversion from mature podocarp-hardwood to 10 year-old radiata pine were selected on similar sites. Nutrient flux in litterfall, rainfall, throughfall and soil drainage beneath the organic horizon and rooting zone were determined. A comparison of throughfall and litterfall was made between mature hard beech and closed-canopy 17 year-old radiata pine. Performance of tension and tray lysimeters was compared on a 1 year-old radiata pine site, at two soil depths. The standing crop of nutrients in components of podocarp-hardwood above-ground biomass was determined. Throughfall was the principal pathway for transfer of Na, Cl and K from canopy to forest floor. Ca, Mg and P were returned predominantly by litterfall. Nutrients may be recycled considerably faster by canopy leaching than by litterfall. Hard beech had substantially greater litterfall than podocarp-hardwood (PH 17) or 17 year-old radiata pine due, predominantly, to higher wood-fall. Litterfall in beech and pine was greatest in spring and autumn while in PH 17 a maximum occurred in summer. Litterfall in 10 year-old radiata pine doubled in the second year over the first year after thinning. Nutrient inputs to the forest floor were considerably greater in PH 17 than 10 year-old or younger pine. Of the three closed-canopy forests (hard beech, podocarp-hardwood and 17 year-old radiata pine) hard beech had largest inputs to the forest floor of Ca and P and lowest inputs of Na and Cl; inputs of K were intermediate. The forest floor of radiata pine had considerably lower inputs of Ca and Mg than for indigenous forest floors. In soil drainage, there was a net transfer of K, Ca, Mg and P from organic to mineral soil in 1 and 10 year-old radiata pine, but a net uptake from PH 17 organic soil drainage. Net uptake from mineral soil drainage occurred on all sites. It was greatest on the 10 year-old radiata pine site. Net loss of K from the ecosystem decreased rapidly with increasing biomass. Substantial losses occurred from a 1 year-old radiata pine site. Losses of Ca and Mg were greatest from 10 year-old pine which had recently been thinned. Net losses of P were nil or very low on all sites. Application of superphosphate fertiliser at the rate of 10 c.p.a. to a 10 year-old radiata pine stand caused negligible increases in leaching of Ca and P below the organic soil and rooting zone. For a 3-year study it was considered that 5 raingauges, 15-25 throughfall collectors, 20-30 lysimeters and 12-24 littertraps, depending on the site, were adequate to determine nutrient flux in the forested ecosystems studied. [Show full abstract]

NZMS 1 S45 map showing locations of the six forest sites used in this study not included in electronic file. See Archive copy held in Library.