Sustainable indigenous forestry
Rob Allen of Landcare Research and the Chair of Tūhoe Tuawhenua Trust, Tahae Doherty
Much of the $1.5bn of hardwood imported into New Zealand each year for timber manufacturing and use with locally-grown softwood in paper production is logged unsustainably.
Landcare Research has been carrying out research and providing advice to support private owners of indigenous hardwood forests in this country to undertake sustainable forestry.
The key challenge for sustainable indigenous forestry is to extract timber while maintaining or even enhancing the non-extractive benefits of these forests, such as biodiversity, water quality, carbon storage and cultural identity.
We have studied seven beech forests where harvesting has occurred in accordance with strict 1993 regulations for low-impact extraction. Looking at tree recruitment, growth and mortality, as well as other natural values, we have found that with the correct management systems the mortality rate for remaining trees does not increase.
Harvesting since 1993 has typically led to prolific forest regeneration, especially following group or coupe harvesting. The >4 m height requirement (under the 1993 legislation) for adjacent harvesting has often been achieved in about 10 years.
With the research pointing to the value of forest thinning or pruning, we re-visited two forests where thinning trials were set up by the former NZ Forest Service in the 1970s. We found that the stem diameter of 58-year old beech trees in a thinned area of forest can be about double the stem diameter of trees in comparable unthinned stands.
Beech trees grow very slowly in natural forest and even-aged stands regenerating from felled forest tend to develop into dense thickets of saplings and pole-sized trees where competition between trees is strong and dominant trees are slow to emerge. The challenge is to manage the costs of the thinning operations for profitable timber production.
Our understanding of native forest regeneration is helping Tūhoe Tuawhenua Trust (TTT) restore its podocarp forests that were extensively logged last century. The podocarps are not regenerating in the shade of treeferns and broadleaved trees left behind after logging.
Applying the concept of ‘restoration silviculture’, tawa has been harvested in small 30m x 30m clearings to create the space and light to allow podocarp seedlings to prosper. Income from the harvested tawa is being used to help fund the restoration of podocarps, which are more valuable timber species.
Brenda Tahi of TTT says the Trust has developed a sustainable forest management plan (SFMP) with the dual goals of restoring the plant and birdlife in its forests while also creating an economic resource for future generations.
“The research programmes of Landcare Research are crucial to meeting these commitments, as they reach deeply into understanding the specific nature and structure of our forests and the impacts of pests and changes to our ecosystems.”