Effects of fertilization and crown release on white oak (Quercus alba) masting and acorn quality

Abstract

Forest management practices that influence mast production in oaks (Quercus spp.) are ecologically and economically important for regeneration of future oak forests, timber products, and wildlife that consume acorns. We conducted a 10-year experiment in upland oak-hickory forests of eastern Tennessee to determine the influence of canopy release, fertilization (addition of nitrogen, phosphorus, and potassium), and their combined influence on white oak (Quercus alba) acorn production, acorn size and quality, and acorn depredation. We used a robust before-after-control-impact design where we collected pre-treatment acorn production (acorns/m2 of crown) data from 120 white oaks for 5 years, applied canopy release and fertilizer treatments and then monitored post-treatment acorn production on the same trees for an additional 5 years. Acorn production was temporally variable with 6 of 10 years being near complete mast failures (≤3.67 ± 8.52 acorns/m2 of crown). Also, production varied greatly among individual trees with 11% of trees classified as excellent producers accounting for 31% of all acorns produced, and 41% of trees classified as poor producers accounting for only 17% of all acorns produced. Canopy-released and canopy-released-and-fertilized trees increased acorn production 65% and 47%, respectively, following treatment relative to control trees, with effects greatest in trees classified as poor producers. Fertilization did not influence acorn production or size and did not consistently influence acorn quality. Furthermore, acorn depredation rates did not differ among treatments. Our results indicate crown release is an important management practice when management objectives include increasing white oak acorn production in closed-canopy conditions, whereas fertilization does not influence acorn production.