Patterns of Growth, Plasticity, and Canopy Structure of Acer Saccharum and Quercus Rubra in Differing Light Conditions

Indianapolis, IN

Tree species vary in their growth habits and canopy architecture according to differing levels of shade tolerance and light availability. We examined Acer saccharum (shade tolerant) and Quercus rubra (shade intolerant) in both closed canopy and open conditions in order to compare characteristics of shade tolerance as well as plasticity of growth and branching patterns. We measured branch length, space between branches, apical dominance, canopy spread, and annual growth in an old growth forest with a closed canopy and an open grown tree plantation in eastern Indiana. We found low growth rates and monolayer canopy structure in shade grown A. saccharum and high growth rates and a multilayer canopy in Q. rubra grown in high light conditions. Both species mimicked the growth strategy of the other in the opposite conditions. Our results suggest that Q. rubra displays shade-acclimated characteristics when grown under a closed canopy such as reduced growth rate and decreased apical dominance. Meanwhile, A. saccharum displayed increased growth rate, decreased spacing between branches, and narrower canopy spread when grown in high light conditions. Our results demonstrate plasticity in growth form among individuals of each species as well as specialized growth habits based on the species' shade tolerance and successional patterns. We hypothesize that the high growth rate of Q. rubra might allow it to dominate in early stages of forest succession, while the shade tolerant characteristic and relatively greater plasticity of A. saccharum may allow it to survive competitive environments in the forest interior.