Retention of large, old trees in alternatives to clearcutting with a comparison of ground- and helicopter-based assessments

•Large, old trees with hollows provide important habitat for hollow-using species.•Retention forestry can help retain habitat trees in harvested areas.•Aggregated retention retained more habitat trees than other silvicultural systems.•Aerial and ground-based surveys gave similar estimates of habitat tree abundance.•Helicopter surveys are a rapid, cost-effective approach for post-harvest assessment.