A comparison of growth efficiency of plants on the east and west sides of a forest canopy gap

BARDEN, L. S. (Department of Biology, University of North Carolina at Charlotte, Charlotte, NC 28223). A comparison of growth efficiency of plants on the east and west sides of a forest canopy gap. Bull. Torrey Bot. Club 123:240-242. 1996.-The theoretical distribution of light in a circular forest canopy gap is symmetrically equal on the east and west sides of the gap. However, small plants on the west side of the gap receive maximum light in the morning when air temperature and vapor pressure deficit are relatively low, while plants on the east side receive maximum light in the afternoon when temperature and VPD are high. To test the hypothesis that plants on the west side of a gap are able to use light more efficiently, Microstegium vimineum, a shade-adapted annual grass, was grown in pots in a forest canopy gap, both in the actual open gap and in the extended gap. In the actual gap there was no difference in growth efficiency. However, in the extended gap growth efficiency was 39% greater on the west side than on the east side under equal light (integrated photon flux density). Thus, asymmetry of microclimate on the east and west sides of a canopy gap causes an east-west asymmetry in plant growth efficiency and may induce asymmetry in species composition of understory vegetation.