The object of the investigation was to determine factors influencing the distribution of C. vitalba in New Zealand, and to distinguish areas which may be susceptible to infestation. Seed of C. vitalba required exposure to light for germination. Exposure 5 min/day to light resulted in significantly higher total germination than long exposure (16 hr photoperiod). Transplantation of C. vitalba seedlings into different forest types showed a strong correlation between survival and percentage of total photosynthetically active photon flux density (PPFD) received. Gas exchange measurements demonstrated a high PPFD saturation level for stomatal conductance and assimilation. Stomatal opening took 20 minutes to complete after transfer from shade to high PPFD. Shading of plants grown in a glasshouse experiment resulted in significantly less growth at light intensities of less than 14% of full sunlight. C. vitalba grew significantly faster on soil from a podocarp forest than on soil from a beech forest. Addition of phosphorus to the beech forest soil significantly increased growth but there was no response to added calcium. Seedlings of C. vitalba grew best in well drained soil. Waterlogged soil significantly reduced growth. The major factor influencing distribution of C. vitalba is soil drainage rather than a calcium requirement. Therefore C. vitalba is a light demanding plant which can establish only in relatively open sites. Podocarp forests south of Auckland on free-draining sites are extremely susceptible to invasion due to the high fertility of the soils under this forest type. Herbicide-soaked wooden plugs, inserted into mature sterns, proved to be a safe and effective control method.