ABSTRACT

Forest canopy can reduce precipitation reaching the ground by up to 50% through interception, storage, and evaporation of droplets from leaf and bark surfaces. This process, called "interception loss," impacts run-off, recharge, flood flashiness, erosion, etc., and cost of stormwater management. It is not well understood how canopy structure affects interception loss, particularly in urban forests. This research addresses this by monitoring interception loss variables for a common SE US tree species (the loblolly pine) across a natural-to-urban gradient in forest structure. Interception loss variables monitored include rainwater stored in and evaporated from the canopy, passing through the canopy (throughfall), and draining down the stem (stemflow) as well as air temperature, humidity, wind speed/direction, pressure, and incoming solar radiation during and after rainfall. These measurements will be related to new, high-resolution, non-destructive laser-scanning (LiDAR) techniques to address 2 questions: 1) how do stand structural changes ranging from natural conditions to common urban conditions affect interception loss processes; and 2) Will LiDAR-measured canopy structures and interception loss processes improve estimation and prediction of hydrologic processes and, thereby, improve water management and planning? The hypothesis is that, because tree stand conditions affect branching and leaf structures, interception loss and its underlying variables will vary in response to storm conditions. Inclusion of these responses in common models will have predictive value for water management concerning shifts in storm conditions . This is an RUI (Research at Undergraduate Institutions) project that will train undergraduate students in cutting-edge hydrologic science and be incorporated into educational outreach efforts reaching thousands of K-12 students, undergraduate students, high school teachers, and community members. Georgia Southern University (GSU) has a substantial African American student population (25.7% and 26.4% of undergraduates in 2012 and 2013), so the project will provide research experiences to underrepresented groups. Project data will be used to develop management practices on the GSU campus.

Forest canopy rainfall interception loss (I) is documented to exert significant influence on run-off, recharge, flood flashiness, erosion and the cost of stormwater management infrastructure. However, it is not well understood how the forest canopy structure controls the components of I (storage, S, and evaporation, E), particularly in urban forests. No existing study has: 1) compared S and E behavior along a natural-urban forest continuum of differing canopy architecture or 2) incorporated terrestrial LiDAR (TLiDAR) measured canopy structures and the interaction of these structures with S and E dynamics into common I models. This study will do this along a natural-to-urban forest structure gradient on the Georgia Southern University (GSU) campus using a regionally dominant species (Pinus taeda, loblolly pine). The study will couple existing biometeorological monitoring methods (meteorological, stemflow, and throughfall measurements) with novel terrestrial LiDAR techniques (LaserBark and L-Architect) to compare S and E in urban forests with directly, non-destructively measured canopy structural metrics. This addresses two questions: 1) how do across- and within-storm dynamics of S and E vary for 2 urban forest structures, and how does this compare to natural tree stands, and 2) to what extent can inclusion of directly-measured canopy structures in urban stands alter I outputs, parameters, and even parameterizations for the most commonly used models (i.e., the Gash- and Rutter-type)? These findings will advance nearly all hydrologic models that simulate or include forest interception processes. Six undergraduates supported by this proposal will receive substantial research experiences spanning the breadth of research activities (including field instrument training, installation, and maintenance; data collection and processing; modeling and model evaluation; manuscript preparation; and presentation at national meetings) in a timely and critical subfield of water resource management. Data will also be used to improve: 1) the L-Architect model, which is being incorporated into Computree, a tool used by the Office National des Forêts (France) for national improvement of forest inventories; and 2) the sustainable irrigation practices currently employed on the GSU campus.

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