Document: MIC-3-29-7

The effect of overstory structure and sky condition on light transmittance in a Longleaf Pine (Pinus palustris) forest.

BATTAGLIA, M.A.* ^1,2, R.J.MITCHELL ² and M.PU ¹

Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA ¹
J.W. Jones Ecological Research Center, Newton, GA 31770 USA ²

Abstract:
Sun elevation and sky condition interact with canopy structure resulting in a heterogeneous understory light environment. A study was initiated to investigate the relationship between forest canopy structure on light patterns in the understory of a longleaf pine (Pinus palustris) forest. Four tree harvest treatments were applied to create a gradient of gap sizes resulting in overstory heterogeneity. Light quantity was measured continuously with photo-diodes to assess understory irradiance through a range of climatic conditions from August 1998 to June 1999. Our objective was to determine if light transmittance was affected by: (1) direct- versus diffuse- dominated sky conditions; and (2) heterogeneity of the forest overstory structure. We found an interaction between (1) and (2). On clear days, light was more variable in the understory light environment of the small gap treatment than in the large gap treatment. On overcast days, variations in the understory light environment were not as pronounced. Total transmittance was greater in large than in small gap stands on direct light dominated days but the difference on diffuse light dominated days was not as great.

Keywords: light, canopy structure, sky conditions, longleaf pine

This abstract is being presented at: 4:15 PM in session:
Oral Session #10: Light Relations in Plants.