Landscape variations in understory PAR for a mixed deciduous forest in New England, USA

Information from horizontal quantum sensor arrays and data on forest structure was used to measure photosynthetically active radiation (PAR). Forest sites with stands of similar age and land-use history were blocked into three valley, three mid-slope, and three ridge topographic positions. Analysis of forest structure and light measurements demonstrate: (1) canopy height and leaf area index decreased on progressing from valley to ridge; (2) total understory radiation increases on progressing from the valley to ridge; (3) sunflecks contribute a disproportionate amount of photosynthetic photon flux (PPF) on sunny days (40–80%) with number and duration of sunfleck periods increasing from valley to ridge.