LB 9-73 - Evaluating the Use of Leaf Area Index for Estimating Mangrove Ecosystem Aboveground Biomass and Tracking Forest Responses to Hurricane Ian

Ecosystem structure and function influence one another. As a result, relationships have been developed using forest structure to predict ecosystem function for some forest systems. The goal of this project was to determine if mangrove leaf area index (LAI) could be used to measure aboveground biomass (AGB) at the ecosystem level using the LAI-2200c canopy gap fraction technique. The same technique was also used to track the forest response to hurricane Ian. Data was collected at 6 different sites comprising a total of 26 plots throughout Estero Bay, Florida. Diameter at breast height (DBH) was measured on trees with diameters >4 cm. Species within this study include: Rhizophora mangle, Avicennia germinans, Laguncularia racemosa, and Schinus terebinthifolius. Measurements using the LAI-2200c were made during diffuse light conditions (sunrise and/or sunset) to better differentiate leaves from sky. LAI was measured monthly in a 1-ha site in Estero Bay both before and after hurricane Ian. LAI from the LAI-2200c collected prior to Hurricane Ian was compared against leaf area predicted from DBH at the plot-level. LAI from DBH was computed using allometric relationships within the literature. We compared instrument-based LAI to DBH based LAI and to plot-level AGB using regression analyses to determine how closely they were related. There was a statistically significant relationship between LAI derived from the instrument and LAI calculated from DBH (p=0.0022) with the regression analysis predicting 33% of the variation (r2= 0.33). The instrument LAI versus plot biomass also exhibited a statistically significant relationship that could predict 37% of the variation (p=0.0009), (r2=0.37). A portion of the unexplained variation within the data is believed to stem from new growth from Hurricane Irma (2017) resulting in DBHs to be too small to incorporate into the study but contribute to higher LAI measurements. There was a delayed reduction (~80%) in LAI following Hurricane Ian and this reduction was spatially variable indicating changes to other ecosystem functions. The role the canopy plays as a proxy is important to understanding the response of mangrove forest systems to climate change including the implications on our global carbon cycle.