White oak (Quercus alba) has a wide geographic distribution and frequency throughout eastern US forests. It and other oak species is being replaced by shade tolerant species such as red maple after 70+ years of active fire suppression. Light levels in undisturbed forest stands are typically around 2 to 5% of full sun. Understanding how white oak seedlings respond to varying light levels and site conditions such as soil nutrients are vital to better develop tools to promote oak sustainability in these forests. White oak acorns from two Ohio sites were collected in the fall and immediately potted in one of two native soils mixes (OH or WV) then grown outdoors in shade tents with varying light levels (100, 25, 18, and 6% of full sun). Seedling germination, survival, growth, biomass, and physiology were studied for two growing seasons.
Results/Conclusions
After one growing season, seedling survival did not differ among light levels and averaged 99%. At the end of the second growing season, survival averaged 50% in seedlings grown at either 6% or 18% full sun compared with those grown in 25, and 100% full sun, which averaged 63% and 99%, respectively. Of those surviving seedlings, stem height did not differ significantly among light levels (p=0.26) but basal stem diameter, leaf area, root and shoot mass responded positively to increased light levels (p<0.001). Comparisons among light levels indicated that no significant growth differences between the two lowest light levels (6% and 18% full sun) or between the two highest light levels (25% and 100%). Root mass of seedlings grown in 25% full sun was 38% greater than those grown in 6% full sun. Total chlorophyll content was 20% higher in seedlings grown in 6% full sun compared with those grown in either 18% or 25% full sun. No significant growth effects were attributed to the native soil mixes, despite a 17-fold higher level of Nitrate-N in the WV soil compared with the OH soil. The observed positive responses in stem diameter growth and root mass associated with higher light levels were expected since oaks display root-centered growth.