Bur Oak Two-Part Inventions: Growth and Reproduction in Two Quercus macrocarpa Cohorts

Abstract

Bur oak (Quercus macrocarpa) was once a primary constituent of savannas throughout the Great Plains. Today, however, oak woodlands occupy only a small percentage of their former extent, and so efforts are underway to restore them. This study examined growth of young trees, frequency of acorn production (an index of recruitment potential), and seedling recruitment in two bur oak cohorts, planted in 2007 and 2009, in a mostly unmanaged setting undergoing old field succession. Documenting the variation in growth response is important for predicting rates of establishment and recruitment in woodland restorations where bur oaks are planted with little to no subsequent intervention. Trees grew an average 40.59 cm/year in the 2007 cohort, and 30.49 cm/year in the 2009 cohort. For both cohorts, height was a function of age (2007 cohort: r2 = 0.793; 2009 cohort: r2 = 0.616). In 2022, diameter at breast height (DBH) was a strong predictor of tree height (2007 cohort: r2 = 0.776; 2009 cohort: r2 = 0.927). There was great variation in fruit production among individual trees: annual acorn production varied from ∼1 to ∼45 % of trees in the 2007 cohort and from ∼4 to ∼24 % of trees in the 2009 cohort. In 2022, 81.25 % of randomized 4 m x 4 m quadrats contained bur oak seedlings. It is encouraging that acorn production commenced just a few years after planting and that substantial recruitment from seed began within ten years, suggesting that bur oak stands so established can become self-sustaining. These results can inform restoration ecologists who wish to reestablish native oak stands but may lack the time and resources to provide much follow-up.