Temporal variation in photosynthetically active radiation (par) in mesic southern Appalachian hardwood forests with and without Rhododendron understories

Abstract

Understanding spatial and temporal variation in the understory light regime of southern Appalachian forests is central to understanding regeneration patterns of overstory species. One of the important contributors to this variability is the distribution of evergreen shrub species, primarily Rhododendron maximum L. We measured photosynthetically active radiation (PAR) in the understory of closed forest canopies in areas with and without R. maximum. Measurements were taken from March through November 1993 with a frequency of approximately 3 weeks. In 1994 measurements resumed from March through May. PAR under sub-canopies of R. maximum averaged 77% (e.g., 14 vs. 65 μmol m^-2s^-1) lower than in areas without R. maximum during the growing season, and 70% (e.g., 179 vs. 641 μmol m^-2s^-1) lower in the dormant season. Variation in PAR during the growing season ranged from 73% to 86% lower in R. maximum versus non-R. maximum understories. During the growing the season, light levels beneath Rhododendron were observed to be < 2% of full sun. low-light environments associated with R. maximum understories are extremely limiting with respect to regeneration of important hardwood species.

Parent Publication

• Proceedings, 10th Central Hardwood Forest Conference

Citation

Clinton, Barton D. 1995. Temporal variation in photosynthetically active radiation (par) in mesic southern Appalachian hardwood forests with and without Rhododendron understories. In: Gottschalk, Kurt W.; Fosbroke, Sandra L. C., ed. Proceedings, 10th Central Hardwood Forest Conference; 1995 March 5-8; Morgantown, WV.: Gen. Tech. Rep. NE-197. Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 534-540