Science Supports Forest Regeneration
Media Release 8 August, 2007
Science Supports Forest Regeneration
Scientific research being carried out in the Ngāi Tūhoe forests in the central North Island is delivering valuable knowledge about indigenous forest ecosystems and giving Maori landowners tools to restore and preserve their native forest resource.
Over the past four years, Landcare Research scientists have been working with the Tuawhenua Trust, to investigate why some canopy tree species are not regenerating adequately in the mainly forest-covered 10,000 hectares of land which are dotted through the Urewera National Park and are managed by the Trust.
In around half the Trust’s forests most of the large trees, like rimu and matai were logged 40 years ago when demand for native timber was high. Landcare Research Project Leader Dr Rob Allen says with very few podocarp seedlings now evident in the forests, regeneration is not going to happen without intervention.
The forests are characterised by an abundance of tawa, with occasional other species.
Researchers have been gathering detailed information about what influences podocarp regeneration in logged forests. The research includes determining the fate of seeds in the forest, examining how seedling distribution relates to soil, the influence of light and competition from other plants and the effects of a dramatic decline in the number of kereru, which traditionally disperse seed. They are also examining the likely effects of climate change in the Trust’s forests, with warming temperatures expected to affect the growth and survival of some tree seedlings.
The results so far, says Dr Allen, indicate that once tall trees like rimu were logged, tawa grew into the space and it is now often too dark on the forest floor for podocarp seedlings to thrive.
Other factors compound the problem, such as a proliferation of predators like possums and rats, which eat the seeds and seedlings.
Dr Allen says a number of restoration measures are planned or under discussion, while the research continues. This includes planting podocarp seedlings in places with the right mix of conditions for them to survive and a possible trial removal of selected tawa trees to enhance regeneration of other species.
Chair of the Tuawhenua Trust, Jim Doherty, says while there may be an economic spin-off from selling logged tawa, which can be used for furniture making, that is a secondary benefit.
“We are not restoring these forests simply to cut them down again. We certainly need ways to generate income for our people in this region but if we do go ahead and mill tawa it will be to improve the overall health of the forest and help with regeneration of other species.”
Local Tūhoe are closely involved both in the research and in restoration measures. For example, funding is being sought for the podocarp seedling planting project, which will be carried out by the Trust and a business management group from a local school. Locals are also involved in pest control in the forests.
Understanding the decline in kereru numbers in the forests has resulted in 11 kaumatua being interviewed to build a picture of past population numbers, the foods kereru prefer and how changes in the forest and climatic factors have affected the bird population. Kereru, and some rats and possums, have also been fitted with transmitters and will be monitored over several years to examine the susceptibility of kereru nests to predators.
Much of the research being undertaken in the forests around Ruatahuna is being funded through investment by the Foundation for Research, Science and Technology.
Foundation Senior Business Manager Carmel Howley says in addition to local benefits, the project is delivering important new knowledge which will be applicable to other indigenous forests, something which could not have happened without the strong relationship Landcare Research has built with the Tuawhenua Trust.
‘The Foundation would not have had the opportunity to make this investment without the time Landcare Research has put into building the relationship with people in the area. It is because of the trust that now exists that we can all benefit from this research and development,” she says
A better understanding of the likely impact of global warming on indigenous forests is another spin-off from the work.
“There is concern that warmer temperatures will further increase the dominance of tawa and further restrict sites for podocarp regeneration. Planting seedlings at different altitudes and temperatures and monitoring their growth and survival will help us judge whether we need to take additional action to control tawa dominance,” says Dr Allen.
Findings from the work being done in the Tūhoe forests will also feed into the government’s recently established Indigenous Forestry Advisory Group, which is working towards sustainable harvesting of native timber from privately-owned forests. The group is examining the viability of establishing an industry based on species such as tawa and red and silver beech which can be harvested on a sustainable basis and regenerate quickly.