Sapling Stocking Targets for Multiple Management Goals in Northern Hardwood Forests: How Do Stands Measure Up?

AbstractWell-stocked natural tree regeneration is critical to sustainable management of northern hardwood forests (NHF) by selection silviculture, but explicit goals and stocking criteria for sapling recruit size classes are lacking. For stems 0–2 in. (0–5.1 cm), we define 171 and 691 stems ac−1 (422.5 and 1,707.5 ha−1) as lower and upper full stocking thresholds for basic NHF management goals (wood and biomass productivity) and overabundant/pest–pathogen-challenged species. We define component stocking targets as 15% of full stocking targets for six additional wildlife (e.g., nut producers) and resilience (e.g., pest–pathogen) goals and individual species representation. Applying our system to 141 managed stands in Michigan, USA, we found several areas of concern. At low threshold, 33% of stands were understocked for biomass and wood goals, whereas 67% were fully stocked with overabundant/pest–pathogen-challenged species. Among goals, component stocking (low threshold) was as low as 5% (nut producers), with more than half the stands component stocked for ≤ 2 goals and ≤ 2 individual species. Stocking varied geographically and decreased with increasing site quality, overstory basal area, and deer use.Study ImplicationsThe stocking goals and density criteria we developed can help managers objectively identify areas where current silvicultural practices are ineffective and need modification. Our system is based on an interactive platform that can be readily modified to accommodate new information and management goals. Several management suggestions emerged from applying our system to selection-managed NHF stands in Michigan. First, highest quality sites have the greatest stocking challenges. Stocking outcomes could likely be improved via more intense overstory harvests and mitigation of deer impacts. Second, most stands meeting stocking goals are vulnerable to future changes in climate and pest–pathogen outbreaks, given stocking is often dominated by a small subset of candidate species. Planting, including the incorporation of assisted migration species candidates could help ameliorate this problem, as species could be evaluated based on their contribution to multiple component stocking goals.