PARENT SESSION
Contributed Oral Session 83: Human Impacts on Coastal Areas
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal

Spatial/temporal variations in LAI and light environment in Myrica cerifera shrub thickets: A comparative approach.

Brantley, Steven^*,1, Young, Donald¹, ¹ Department of Biology, Richmond, VA, USA

ABSTRACT- Leaf area index (LAI) and understory light levels of Myrica cerifera shrub thickets were assessed on Hog Island, Virginia to quantify spatial and seasonal variations in leaf area and light attenuation among four thickets representing a successional chronosequence. LAI was determined by destructive sampling and development of allometric relationships, by using integrated PPFD values and the Beer-Lambert equation, and with a portable integrating radiometer (Li-Cor). The oldest and senescing thicket consistently had the lowest LAI while the younger thickets did not differ significantly (p > 0.05) during the growing season. During the winter however, the developing thicket, located just behind the primary dune, experienced the greatest reduction in LAI indicating an interaction between season and location. Peak LAI varied from 6.35 ± 0.13 for the oldest site to 12.46 ± 0.53 for a mature thicket according to the allometric models. Using the Beer-Lambert equation and an extinction coefficient of -0.52, LAI was estimated at 4.63 and 8.37 for the same thickets, respectively. Peak LAI estimates using the integrating radiometer were 2.02 ± 0.17 and 3.57 ± 0.24 for these sites which appears to be a substantial underestimate. These low diversity shrub thickets have much higher LAI than previously suggested but LAI declines in aging thickets. The high light attenuation by the shrub canopy may also contribute to the inhibition of other species and the relative lack of diversity within the thickets.

Key words: Leaf area index, Barrier island, Chronosequence, Shrub