Survival and growth of planted seedlings of three native tree species in urban forest restoration in Wellington, New Zealand

Planting container-grown native seedlings is a restoration technique widely used to enhance biodiversity, including in urban areas in New Zealand. We measured survival and growth of seedlings of three native tree species (Aristotelia serrata, wineberry (n = 743); Cordyline australis, cabbage tree (n = 666); and Pittosporum eugenioides, lemonwood (n = 701)) planted in 11 forest restoration sites in Wellington, New Zealand, between 2008 and 2012. We used mixed-effect models to identify the relative importance of a range of variables affecting mortality in the early years after planting. Seedling mortality during the first year was 38%, 20% and 11% for A. serrata, C. australis and P. eugenioides, respectively. Although variables explaining mortality were species-specific, initial seedling height and the height of grass surrounding each seedling were present in the best ranked models explaining mortality in all three species. Contrary to expectations, trees were still at substantial risk of mortality ≥2 years after planting. Plants in forest restoration projects managed by community groups experienced similar mortality as those managed by local government. Our results suggest that reduction of cover of surrounding grasses is likely to enhance seedling survival and indicate that initial plant height, rather than time since planting, is the best predictor of the likelihood of mortality of planted seedlings.