The irregular shelterwood silviculture system and managing for stand complexity from a North American perspective

Structurally and compositionally, diverse forests are associated with increased resilience and provision of desirable ecosystem services. Such forests can be created and maintained by silvicultural systems that foster natural regeneration, emulate natural disturbances, and promote the development of old growth features. Irregular shelterwood is increasingly applied to fill this niche. However, the implied meanings of both “stand irregularity” and the “irregular shelterwood system” are varied across sources, resulting in inconsistent application in forestry research. We revisited definitions of the term “irregular shelterwood,” reviewed studies of its applications, and examined it in the broader context of natural disturbance ecology and forest complexity, with a focus on the North American silvicultural perspective. We found two irregular shelterwood approaches – group-based and two-aged – that share conventional shelterwood traits. Both approaches produce multiage stands. We also found approaches to irregular shelterwood that resemble types of selection or that are non-systematic. Inconsistent terminology and naming conventions were evident across all approaches. These variable and contrasting portrayals inhibit the synthesis of study results by researchers and forestry practitioners. To clarify these ambiguities, we identified the features that best characterize the different types of partial cuttings reflected in the irregular shelterwood literature. • Group-based and two-aged irregular shelterwoods show typical shelterwood traits. • Other irregular shelterwood representations are more selection-like. • These various approaches can achieve disturbance emulation and structural objectives. • Inconsistent terminology complicates understanding of silvicultural methods. • Consistent reporting of silviculture treatment features is needed for future analyses.