Multidisciplinary research has been undertaken at the Purukohukohu experimental basin, particularly in the Puruki catchment over the past 15 years. This period covers the conversion of Puruki from pasture to Pinus radiata
D. Don, the development of the trees to canopy closure, and the effects of differential intensities of thinning on growth to the middle of the rotation. Results of investigations into tree growth, nutrient cycling, and catchment hydrology are presented in papers collected in this issue of the Journal. This paper backgrounds the site, climate, history, and management of the catchment, and the development of the trees.
Puruki is a 35-ha catchment located at the southern end of the Paeroa Range in the central North Island of New Zealand, at an elevation of 600 m. The rhyolitic pumice soil, previously under rye grass/clover pasture and regularly treated with fertiliser, provides ample moisture and nutrients for P. radiata growth under the climatic conditions: 1500 mm of evenly distributed rainfall annually, 5 GJ/m2 of solar irradiance annually, and average monthly temperatures of between 5° and 15°C. Puruki was uniformly planted with P. radiata at 2200 stems/ha in 1973 and trees in the individual subcatchments (Tahi, Rua, and Toru) were progressively pruned to 2.2 m height and thinned to 160, 550, and 290 stems/ha respectively by 1985, with further thinning intended. A part of Rua was left unthinned as a control. In closed canopy stands periodic volume increment attains 52 m3/ha/year. The removal of between half and three-quarters of the tree basal area every 3 to 4 years reduced volume increment to between 25 and 30 m3/ha/year, but this is likely to increase when management thinning is completed and the stand leaf area can increase uninterrupted to unthinned levels.
The interrelationships between aspects of the research work covered in the accompanying papers are illustrated using a conceptual modelling framework. The data collected at Puruki have proved valuable for testing theoretically based models and calibrating empirical models of P. radiata growth under conditions of ample moisture and nutrient supply.