Container size and site quality affect survival and early growth performance of New Zealand native tree species

Abstract As part of the global effort to mitigate climate change effects, New Zealand’s Climate Change Commission has recommended the establishment of 300,000 ha of native trees across the country by 2035. To achieve this goal, significant improvement in seedling production and field establishment is needed. Across New Zealand, there is a trade-off between seedling size and early seedling establishment success; plants grown in large pots are more resistant to weeds, pests and frost; however, they are more expensive and take longer to grow. We tested this trade-off between cost and establishment success by raising seedlings of twelve key native species in three container grade sizes: small, large, and revegetation grade, and tracking their success across five sites around Rotorua, in the Central North Island of New Zealand. After two-year post-planting, we found that high-quality sites and larger container systems tended to promote higher survival and faster early growth (plant height and root collar diameter). Some species, such as Kunzea ericoides and Leptospermum scoparium, survived and grew well (> 75%) even when raised in small container sizes. Other species such as Sophora microphylla had very low survival (< 25%) even when raised in revegetation container grade sizes. If the quality of the planting site is high, the container size seems to be less important for most species. Other species such as Aristotelia serrata , Cordyline australis , Plagianthus regius and Podocarpus totara appear to depend more on site quality. In conclusion, nursery container systems for raising New Zealand native plants should be chosen based on the biology of the species, nursery management practices, quality of the planting site, and a balance between cost and benefit for each situation.