The Acadian Forest of New Brunswick in the 21st century: what shifting heat and water balance implies for future stand dynamics and management

Climate change is altering the dynamics of New Brunswick's forests. To mitigate the effects of climate change, it is crucial to account for future uncertainties in climate projections and natural disturbance trajectories when designing forestry practices. This paper presents the projected changes in key climatic drivers for New Brunswick's forests, examines the impacts of climate change on forest stand dynamics, and reviews adaptive silviculture tools for climate change adaptation. By 2071-2100, a projected 4-6°C increase in mean annual temperature will lead to a 39-77% rise in growing degree days and a reduction in summer atmospheric water balance by 48-79mm across New Brunswick. Foresters should anticipate a doubling of annual area burned, the northward migration of spruce budworm (Choristoneura fumiferana (Clemens)), and the introduction of novel insects and diseases. Forest simulation models project a severe decline in boreal tree species abundance, including a 50% decline in balsam fir (Abies balsamea (L.) Mill) and black spruce (Picea mariana (Mill) B.S.P.), offset by an increase in temperate species, notably red maple (Acer rubrum L.; +200%) and American beech (Fagus grandifolia Ehrh; +135%). Forests in the highlands and lowlands ecoregions, with 40-50% and 15-30% spruce and balsam fir composition respectively, are particularly vulnerable. To limit climate change effects on forest values, foresters must prioritize climate resiliency in their management plans. Strategies should ensure the steady provision of forest goods and services under changing climatic conditions. Forest thinning enhances stand productivity and resilience, while shelterwood and two-age harvest balances timber production with diversity. Clearcutting, despite drawbacks, establishes younger, more vigorous forests with higher carbon sequestration potential. Assisted migration offers promise in helping threatened tree species adapt. Climate change will have a significant impact on New Brunswick's forests, leading to changes in key climatic drivers, increased risks of disturbances, and a shift towards more temperate tree species. However, there are existing adaptation strategies available. It is crucial to consider future uncertainties when designing and evaluating forestry practices, as this is essential for mitigating the effects of climate change on forest values and ensuring the continued provision of forest goods and services over time.