The Role of the Dappled Canopy: Diurnal Patterns in Surface Fuel Micrometeorology

Sub-canopy meteorological conditions are often assumed to be horizontally homogenous, having little temporal variation, except for that which is tied to the diurnal cycling of the atmospheric boundary layer. This assumption ignores the role that solar radiation plays when a naturally fractured or open canopy allows for sun exposure of the surface vegetation. In these scenarios, areas of the understory are exposed to direct solar radiation on a much smaller time scale than the above-canopy daily cycling. How these very localized changes impact wildland fire behavior is not understood. Our team uses field-based experimental techniques to quantify below-canopy solar radiation effects on the scale of centimeters. Development of open-source and inexpensive monitoring systems increase the feasibility of micro-meteorological measurements at high spatial and temporal resolutions. We present field data collected in a 50-year experimental landscape with varying fire return intervals of 1, 2, 4 years as well as unburned controls. Resulting changes to understory structure on these surface conditions are presented. Initial results indicate unique diurnal micrometeorology behavior, including atmospheric inversions, important to fuel drying and fire dynamics. We discuss the implications of these micrometeorological variations in the presence of a prescribed fire.