Optimal enrichment planting conditions for white oak (Quercus alba L.) regeneration in expanding group shelterwood systems

For several decades, the ecological dominance of white oak ( Quercus alba ) has been declining throughout the species’ native range with failure to recruit new individuals into the overstory. White oak’s decline is concerning as the species is of great cultural, ecological and economic value. Shelterwood harvests and artificial regeneration have frequently been suggested as means of bolstering flagging natural white oak regeneration. In a study installed in southern Indiana (USA), we examined the impacts of competition control duration (0, 2 and 4 years), geographic seed source (Arkansas, Illinois, Indiana, and Wisconsin), and canopy closure on growth and survival of white oak artificial regeneration within an expanding group shelterwood system. After four growing seasons, a combination of increased canopy openness and control of competing vegetation was found to benefit diameter growth and biomass production of seedlings. Survival and growth were greatest in areas of up to approximately 50 % canopy closure; these conditions were present in the harvested groups adjacent to the edge of the forest matrix. Seedlings of Indiana, Arkansas, and Illinois stock displayed the greatest increases in height and diameter after planting. Indiana (134 % height, 94 % diameter), Arkansas (127 % height, 126 % diameter), and Illinois (81 % height, 86 % diameter) stocks displayed nearly double the average growth of the Wisconsin stock (26 % height, 52 % diameter). Illinois and Arkansas stocks also survived at the highest rates (61 % and 57 % respectively). These results suggest that artificial regeneration combined with shelterwood harvests and control of competing vegetation can be utilized as an effective means of supplementing natural white oak regeneration. • Groundline diameter growth was greatest in areas experiencing competition control. • Growth and survival were greatest in areas of up to 50 % canopy closure. • Combined competition control and open canopy resulted in the greatest growth. • Geographic seed sources varied in growth rates along a gradient of canopy closure.