A gap-based approach for development of silvicultural systems to address ecosystem management objectives

Foresters have traditionally managed forests with silvicultural systems that prescribe stand homogeneity for optimized tree growth. The primacy of timber as the dominant objective is giving way to broader objectives such as sustaining the function and dynamics of ecosystems, maintaining ecosystem diversity and resilience or protecting sensitive species, while providing for a variety of ecosystem services of value to humanity. Protection and production of more diverse forest values demands consideration of the fine-scale variability found within forest stands and an understanding of the spatial and temporal response of forest ecosystems to manipulation. Studies of gap dynamics have contributed significantly to our understanding of the role of small-scale disturbance in forest ecosystems, but have been used little by foresters for predicting ecosystem response to partial cutting. We review the gap dynamics literature paying special attention to papers that use gap size or position as predictive variables for responses indicative of silvicultural success or maintenance of ecosystem function. Like canopy gaps created by natural tree death or windthrow, gaps are also generated by silvicultural systems which remove dominant trees. Results from the Date Creek silvicultural systems study in northwestern British Columbia presented here demonstrate the utility of a gap-based approach for understanding ecosystem responses to tree cutting. We propose a gap-based approach for study response to silvicultural manipulation that: (1) aids development of cutting prescriptions that maintain functional mature or old-growth conditions; (2) refines and extends our understanding of how biological structures, organisms and ecosystem processes are affected by fine-scale variation within stands; and (3) leads to development of novel silvicultural systems that meet timber production objectives, without compromising ecosystem management principles.