Height development milestones for canopy recruitment after overstory removal in the Missouri Ozarks

Tree height development has been studied extensively. Nonetheless, there is limited quantitative guidance for height expectations during the regeneration period, particularly for common species with low commercial value. Site index models, for example, often omit the initial 15–20 years of development. We examined height development of juvenile trees during the first twenty years after overstory removal in naturally regenerated, mixed stands in the Missouri Ozarks to identify milestones indicative of eventual recruitment into the upper canopy by the end of the regeneration period. Such milestones quantify minimum height requirements for recruitment success from trees that occupied codominant and dominant crown classes at the end of the regeneration period. Results show these milestones differed statistically by site class and those differences increased over time. Species-specific milestones were similar and while some statistical differences were observed, the practical, if not ecological, consequences of those differences appeared limited. The similarity in milestones among species suggests that there is a minimum height threshold for eventual canopy recruitment success after overstory removal in the Missouri Ozarks. This was validated using independent data from a nearby long-term study with tagged individuals. Less than 1% of trees that failed the milestones by year 3 met them after 16 years, and less than 1% of trees failing the milestones at year 8 met them by year 16. Thus, the presented milestones are a tool that can be used to assess individual tree height development during the recruitment process. A tree that attains these milestones early in development is not guaranteed to remain successful throughout the regeneration period, but success without first reaching these milestones is highly improbable.