Abstract
Ecological restoration has been proposed as a tool to combat mounting environmental damage. Despite recent emphasis on tree planting programmes to reduce the impacts of climate change and improve environmental and socioeconomic outcomes in Aotearoa New Zealand, there is a lack of empirical evidence on how to achieve this. ‘Local is best’ is a cornerstone in restoration ecology, in which local plant provenances are favoured over non-local provenances. This practice has guided seed sourcing policy for many decades. However, there is a lack of research in this area and there is an international move to include more diverse non-local germplasm. To determine if local is experimentally best, I established a reciprocal transplant provenancing trial with the early successional shrub, mānuka, Leptospermum scoparium, at three sites in Te Waipounamu, South Island of Aotearoa New Zealand. Seedling recruitment and mortality were monitored for eight months post-establishment and seedling biomass was quantified. 18,247 mānuka seedlings were counted across all three sites. At all sites, there was evidence of the home provenance not performing the best in at least one measure of plant performance. Despite the confounding influence of maternal effects, I suspect that at least some the variation observed is from some genetic effects. This adds to the body of evidence for diversifying seed sourcing in Aotearoa New Zealand. Seed priming, the controlled hydration of seeds that activates pre-germinative metabolism but not germination, is one of many seed enhancement techniques that have been widely applied to agricultural species, with a range of benefits. However, this method has seldom been used for restoration. I halo- (sodium chloride) and osmo-primed (hydrogen peroxide) Sophora microphylla, L. scoparium, and Veronica salicifolia and conducted a water deficit trial to test for potential benefits. While seed priming increased the germination rate and total mean germination in many instances, I found no evidence that it increased tolerance to water deficit at the early seedling stage. Methodological improvements are discussed. Poor understanding of seed dormancy is a barrier to upscaling restoration efforts in Aotearoa New Zealand. Accordingly, there is room for the development of chemical treatments to overcome dormancy. I applied a series of seed pre-treatments including combinations of wet stratification, gibberellic acid, and potassium nitrate on Aristotelia serrata, Carpodetus serratus, Corokia cotoneaster, Fuscospora cliffortioides, Phormium tenax, and Melicytus ramiflorus, six forest species that exhibit seed dormancy. I found the effect of seed pre-treatment was highly species-specific; three of the six species germinated. Benefits of pre-treatment on P. tenax were uniformly high, with a total mean germination between 66±6.2% and 80±3.5%. C. serratus benefitted the most from wet stratification and gibberellic acid at 100 mg L-1, with a total mean germination of 18±4.9%. The greatest benefits for the germinability of F. cliffortioides were in the 10-week wet stratification treatment, with a total mean germination of 28±5.8%. This research provides empirical evidence that may improve restoration practices in Aotearoa New Zealand.