Predicting oak regeneration success at the stem exclusion stage of stand development in upland hardwood forests

Abstract

Oaks (Quercus spp.) are becoming less abundant in most of the Central Hardwood Region of the eastern United States, and this is creating shifts in forest composition that will likely have important economic and ecological consequences. In large measure, these changes originate with deficiencies in the oak regeneration cohort preceding stand-replacement disturbances such as timber harvest. To sustain the oak resource, managers need better information on the connection between pre-harvest and early stand conditions and regeneration outcomes. In this study, we used direct observations of oak seedling dominance in the stem exclusion stage of stand development (mean age = 17.4 years) to model the probability of successful regeneration during stand initiation as a function of stand conditions before and after harvest (ages −1, 1, 4, and 7 years). For pre-harvest conditions, the most predictive model was based solely on the aggregate height of advance regeneration oak seedlings >15 cm in sample plots. As expected, post-harvest models were more predictive, and increasingly more predictive with the passage of time, and they were optimized by contrasting the height of the plot-dominant oak seedling with the heights of competing tree species. The predictive power of post-harvest models increased most between ages 1 and 4 years and only slightly between ages 4 and 7, indicating that age 4 is an optimal time to evaluate opportunities to favor oak regeneration with early silvicultural interventions. Of the two most common competitors, black birch (Betula lenta) had the more inhibitory effect on the success of oak regeneration when it was present. However, red maple (Acer rubrum) was the more important competitor because of its very high frequency of occurrence in plots occupied by oak seedlings.