LB 10-126 - CANCELLED - A critical review of successional dynamics in boreal forests of North America

Background/Question/Methods:

Forest succession is a dynamic process of progressive compositional development of ecological communities of species following natural or anthropogenic disturbance. Despite a rich history of conceptual frameworks, models, and empirical advances, the complex interactions among climatic conditions, disturbances, edaphic factors, and silvicultural treatments still challenge our ability to accurately predict forest succession, hindering application to forest management. Our goal was to improve understanding of forest succession in the managed boreal forests of North America by clarifying advances in knowledge and limitations in our understanding. We reviewed 152 peer reviewed papers to (i) document conceptual developments in forest succession; (ii) summarize drivers of North American boreal forest succession, including changes to forest composition and successional trajectories given climate change; and (iii) discuss the implications of the synthesized information for boreal forest management. While the element of stochasticity is expected to increase under climate change, successional dynamics are anticipated to remain predominantly deterministic.

Results/Conclusions:

Southern boreal forests are at increased risk of mortality due to warming-driven drought and increased fires. Following disturbance, regeneration is likely to favour deciduous hardwoods. In boreal mixedwoods, increased fires would promote jack pine, and also black spruce on hydric and xeric sites. Dynamics of the northern boreal will depend on the balance between precipitation and evapotranspiration. Forest managers must carefully select prescriptions that considers the long-term effects of changing climate and disturbance regimes. Forest management interventions commonly used to direct succession trajectories include (i) combining retention cut with mechanical site preparation to maintain site productivity and reverse open black spruce stand development in northern boreal stands; (ii) thinning from below to minimize the evaporative demand on the forest floor and improve resistance and resilience against water deficits; (iii) dispersing retention cuts to maintain early seral composition and selective cutting to release tolerant understory to create species mixtures, improving resistance and resilience to budworm and windstorms; and (iv) prescribed burning after post-windthrow salvage logging to reduce the effects of harvesting on seedbed quality. Our work shows that multiple disturbances have compounding effects on forest development, but further work is needed to better define thresholds for synergistic and buffering interactions.