June 15, 2020
By Hilary Lennox
Restoration of native forests in New Zealand has previously been undertaken by planting young trees raised in nurseries and tending to those trees for several years to protect them from environmental risk factors. More recently, there have been studies into restoration methodologies using seed rather than seedlings. One such project was the 3-year Wakatipu Beech Seeding Project (WBSP), which trialed different methods of collecting, processing, treating and broadcasting seeds into areas of controlled (sprayed) wilding conifer forest around the Wakatipu with the aim of facilitating the restoration of exotic conifer stands back into native forest.
This was a joint venture between the Wakatipu Wilding Conifer Control Group and the Wakatipu Reforestation Trust, with funding from the Ministry for the Environment’s Community Environmental Fund. Further support was provided by Scion, the University of Otago, Ahika Consulting Ltd, and a dedicated team of keen volunteers.
Several challenges were encountered along the way, including an extremely dry spring, lack of locally available viable seed, weed inundation and dangers associated with working beneath dead trees. Despite these challenges, by Year 3 a range of locally sourced native tree species had been broadcast into several areas of controlled wilding conifers and seedlings had begun to emerge.
Coprosma propinqua and Mānuka seeds proved to be the easiest to collect, process, store and propagate. The germination strike rate of Pittosporum tenuifolium and Griselinia littoralis was also very good, but it was a bit more difficult to collect, process and store this seed. Mountain beech seed was relatively easy to collect (during the mast season) but germination strike rate was relatively low compared to the other species and then there is also the added complication of how to inoculate the seedlings with beneficial mycorrhizae at a large scale.
The germination strike rate of all species was improved greatly by removing the thick layer of decaying pine needles on the forest floor and exposing a more suitable growth medium. Seedling survival rate was improved by excluding herbivores from the trial sites.
Through this trial, it became apparent that when it comes to restoring controlled wilding stands back into native forest, there is a “sweet spot” between the control work being undertaken and the point where dead trees have decayed sufficiently to allow light-loving weeds to proliferate. It is during this sweet spot that seeding operations should be focused. Ensuring that the sweet spot is not missed would require planning of the restoration strategy prior to the wildings being sprayed, rather than this being an afterthought.
It also became apparent which factors must be considered for any seed-based restoration project to be successful. These include:
Another key success factor is how to manage people’s expectations. Natural native forest restoration may take decades. However, there are growing expectations that restoration objectives should be achieved much more quickly than this. This may be due to a combination of funding timeframes (usually 3 years), election cycles and the ever-growing human cultural traits of impatience and the need for instant gratification. The human pace of life may have sped up, but native species have not evolved at the same pace.
Restoration projects which involve planting nursery-raised seedlings can provide instant gratification when the seedlings are planted in the ground, but seed-based restoration projects require a lot more patience. It is vitally important that the expectations of funders, landowners, volunteers, peer groups, employees and stakeholders are managed effectively with ongoing education.
By focusing restoration efforts on “seed islands” rather than diluting efforts across the whole site, localised success is far more likely, which helps to keep everyone involved engaged. It’s more rewarding to take people to an island where a blanket of emerging seedlings can be seen, rather than scouring the whole site for the occasional seedling emerging here and there. By keeping people engaged, more seed islands can be added in subsequent years when seed becomes locally available, therefore accelerating and maintaining momentum of the restoration project.
Full results of the Wakatipu Beech Seeding Project and a several helpful resources to assist other groups seeking to embark on seed-based restoration projects are available on both the Wakatipu Wilding Conifer Control Group website (www.wakatipuwilding.co.nz) and the Wakatipu Reforestation Trust website (www.wrtqt.org.nz).