Transitional forestry in New Zealand: re-evaluating the design and management of forest systems through the lens of forest purpose.

Forestry management worldwide has become increasingly effective at obtaining high timber yields from productive forests. In New Zealand, a focus on improving an increasingly successful and largely Pinus radiata plantation forestry model over the last 150 years has resulted in some of the most productive timber forests in the temperate zone. In contrast to this success, the full range of forested landscapes across New Zealand, including native forests, are impacted by an array of pressures from introduced pests, diseases, and a changing climate, presenting a collective risk of losses in biological, social and economic value. As the national government policies incentivise reforestation and afforestation, the social acceptability of some forms of newly planted forests is also being challenged. Here, we review relevant literature in the area of integrated forest landscape management to optimise forests as nature-based solutions, presenting 'transitional forestry' as a model design and management paradigm appropriate to a range of forest types, where forest purpose is placed at the heart of decision making. We use New Zealand as a case study region, describing how this purpose-led transitional forestry model can benefit a cross section of forest types, from industrialised forest plantations to dedicated conservation forests and a range of multiple-purpose forests in between. Transitional forestry is an ongoing multi-decade process of change from current 'business-as-usual' forest management to future systems of forest management, embedded across a continuum of forest types. This holistic framework incorporates elements to enhance efficiencies of timber production, improve overall forest landscape resilience, and reduce some potential negative environmental impacts of commercial plantation forestry, while allowing the ecosystem functioning of commercial and non-commercial forests to be maximised, with increased public and biodiversity conservation value. Implementation of transitional forestry addresses tensions that arise between meeting climate mitigation targets and improving biodiversity criteria through afforestation, alongside increasing demand for forest biomass feedstocks to meet the demands of near-term bioenergy and bioeconomy goals. As ambitious government international targets are set for reforestation and afforestation using both native and exotic species, there is an increasing opportunity to make such transitions via integrated thinking that optimises forest values across a continuum of forest types, while embracing the diversity of ways in which such targets can be reached.

Diversification of forestry portfolios for climate change and market risk mitigation.

Investments in forestry are long-term and thus subject to numerous sources of risk. In addition to the volatility from markets, forestry investments are directly exposed to future impacts from climate change. We examined how diversification of forest management regimes can mitigate the expected risks associated with forestry activities in New Zealand based on an application of Modern Portfolio Theory. Uncertainties in the responses of Pinus radiata (D. Don) productivity to climate change, from 2050 to 2090, were simulated with 3-PG, a process-based forest growth model, based on future climate scenarios and Representative Concentration Pathways (RCPs). Future timber market scenarios were based on RCP-specific projections from the Global Timber Model and historical log grade prices. Outputs from 3-PG and the market scenarios were combined to compute annualized forestry returns for four P. radiata regimes for 2050-2090. This information was then used to construct optimal forestry portfolios that minimize investment risk for a given target return under different RCPs, forest productivity and market scenarios. While current P. radiata regimes in New Zealand are largely homogenous, our results suggest that regime diversification can mitigate future risks imposed by climate change and market uncertainty. Nevertheless, optimal portfolio compositions varied substantially across our range of scenarios and portfolio objectives. The application of this framework can help forest managers to better account for future risks in their management decisions.