Does single-tree selection work? Observations from 56 years of measurements at Parkside Gully, Algonquin Park, Ontario

Parkside Gully was established in 1967, with an unharvested side added in 1974 in response to growing interest in single-tree selection silviculture in Ontario. The site was last operationally harvested in the early 1930s. Since 1967, it has been experimentally harvested four times. Measurement methodologies have evolved and it is not replicated. However, it remains one of Canada’s longest single-tree selection experiments and can offer valuable insights. In this study, we use data from 15 one acre plots (10 harvested, 5 unharvested) to show that over 56 years, the harvested side consistently met sustainable stocking, structure, and quality improvement objectives. At the same time, stocking in the unharvested side declined while quality increased, albeit at a slower pace. We also found that high quality stems have much lower mortality risk and grow faster than lower quality stems. Despite meeting all stand-level objectives, we demonstrated that ingress of beech remains a pernicious issue: beech outgrows maple, and has dominated the regeneration layer since at least 2005 despite the absence of beech bark disease. Understanding what drives the ingress of beech into Ontario’s single-tree selection systems will be essential to maintaining the sustainability of the system into the future.