Transition forests that develop from exotics to indigenous over time are possible, but a leading forestry and ecology professor cautions there is a “yes, but” caveat to the forests’ long-term success.
David Norton, emeritus professor at the University of Canterbury, said the term “transition forests” has gained a lot of profile lately, promising landowners and investors a means to gain early-stage carbon credits while also dealing with the problematic spectre of long-term exotic forests.
But he cautions that the phrase is relatively new to the forest sector and research supporting it or otherwise remains thin on the ground.
The government is currently reviewing the permanent carbon forest category in the Emissions Trading Scheme, and this includes consideration for including transition forests alongside indigenous forests and long-lived exotics like redwoods.
A 2021 Ministry for Primary Industries report on the state of knowledge about transition forests noted that there was insufficient co-ordinated research to determine the timeframes required to successfully transition from exotic to native forests.
It also noted the lack of knowledge on regeneration levels and the role of species other than pine as suitable exotic species to start with.
Norton’s concern comes as interest in transition forests as investment options is on the rise nationally.
“My bottom line is yes, you can transition, but you need to put sufficient management in around how the canopy is opened up, how pests and weeds are controlled, and how mature forest indigenous species are established.”
Success also depends on transition forests being located in areas with reliable rainfall and a good native seed supply source.
He said it is still going to be necessary to physically plant mature forest species like rimu, miro and beech trees.
“So it is possible, but it requires a lot of management on the ground and this management will need to occur for many decades, perhaps even for a century or more.”
He said there are some entities offering to manage this transition for landowners.
“But it is this ‘trust us’ approach, when in fact we just don’t know how all forests will respond.”
He said there is no financial or legal mechanism in place to guarantee management will be maintained, and no consideration given to the many risks failed transitions will bring – including the financial liabilities.
Submissions are being received on the nature of permanent forestry, and at least one major forest management company is submitting strongly against inclusion of transition forests unless more definitive data can be provided on their success.
Norton’s concerns also extend to how the carbon credits earned from transition forests are paid out in terms of accounting for future risks and uncertainties. The permanent forest consultation report also highlights high level concerns about the financial risk transition forests present to investors.
It cites concerns that transition forests risk incurring significant surrender liabilities as fast-growing exotics are replaced by smaller, slower-growing natives after about year 40.
The resulting gap that opens up as the exotics switch to natives, with their lower carbon yield, has to be paid back.
“Landowners who have forests handed back later on are at particular risk here. Why not hold back some of the early carbon credits to guarantee that transition many years in the future does actually take place?” Norton said.
This money could be kept in a fund used to guarantee transition management will occur long after carbon income funds are finished.
The consultation document suggests a new carbon accounting method may be required to help address these concerns.
“And there is also the wilding pine issue there to be dealt with, who will manage those?”
Norton has been working closely with hill country farmers and believes indigenous forests’ future planting success also requires long-term management.
“This is why working with farmers is good. They recognise you can’t just plant a tree and leave it. But even here, having someone appointed to specifically look after these forests in the long-term is important.
“We are talking very long time frames here.”