Growth, survival and sunfleck response of underplanted red oaks (Quercus spp, section Erythrobalanus) along a topographic gradient in southern New England

by

Brent R. Frey, and Mark S. Ashton

Assistant Professor (BRF), Department of Forestry, 775 Stone Blvd, Mississippi State University, Mississippi State, MS 39762; Professor (MSA), School of Forestry and Environmental Studies, 195 Prospect Street, Yale University, New Haven, CT 06511. BRF is corresponding author. To contact, call 662-325-2775 or email brent.frey@msstate.edu.

Abstract – Few studies have directly tested performance and habitat association among related species ranging across different site conditions, particularly for the purpose of refining silvicultural approaches in complex mixed species stand types. We established a common garden experiment with five red oak (Quercus, section Erythrobalanus) species under planted across a topographic gradient (ridge, midslope and valley positions) in mixed hardwood stands in southern New England. Represented were three red oak species common to intermediate site conditions of southern New England (Q. rubra, Q. velutina, and Q. coccinea), and two species commonly associated with more extremes site conditions - Q. ilicifolia (xeric, skeletal ridge tops) and Q. palustris (floodplains). Seedlings were caged to prevent deer browse, and growth, survival, dieback, and leaf number were recorded for all seedlings over an eight-year period. Response to sunflecks, the primary source of light for understory seedlings, was measured using a LiCor 6400 photosynthesis system. Overall, survival was highest for Q. rubra, followed by Q. velutina, Q. coccinea, Q. ilicifolia and finally Q. palustris. The pattern among species held for all topographic positions, with survival rates higher on ridges and lower in valleys. These patterns were positively correlated with light availability, and negatively correlated with site fertility. Net photosynthetic rates indicated Q. rubra, Q. velutina, and Q. coccinea were more responsive to sunflecks than Q. ilicifolia and Q. palustris. These results indicate strong differences in shade-tolerance and understory performance among these common red oak species, which should be considered when applying regeneration approaches.