Greenhouse gas fluxes before and after Hurricane Maria

We used several methods to estimate forest damage in the neighborhood of each focal tree in order to test whether there may be a relationship between GHG fluxes and local damage severity. First, we assigned each damage category a numeric value of damage based on % canopy damage (Light = 0%-25%, Medium = 25%-75%%, and Heavy > 75%). We then calculated three mean neighborhood damage estimates for each gas sampling location by taking 1) the mean damage for all trees > 10 cm DBH in the same 20 x 20 m quadrat as our gas measurements; 2) the mean damage for all trees within a 10 m radius of our gas measurements; and 3) the mean damage for all trees within a 20 m radius of our gas measurements. We then fit simple linear models in R to test for significant relationships between CO2, CH4, and N2O and our neighborhood damage estimates. Approximately every five yearssince 1990, stems are re-measured and their statusis assessed, and new stems are added. The lastcensus of the LFDP prior to Hurricane Marı´a wascompleted in 2016, representing pre-hurricaneconditions in this study.Beginning in January 2018, all trees at least10 cm dbh in the LFDP were surveyed to assessdamage and immediate mortality from H. Marı´a(Uriarte and others 2019). The survey recordedseveral qualitative and quantitative observations oftree damage resulting from the hurricane, such asuprooting or stem break, and type of damage tostems, tree crowns and branches. Using this information,we classified each stem at least 10 cm indbh into three damage classes: (1) no or lightdamage ( £ 25% of crown volume removed by thestorm), (2) medium damage (25–75% of crownvolume lost through a combination of branchdamage and crown break), or (3) heavy or complete(> 75% of the crown lost, stem snapped, rootbreak or tip-up) Support for this work was provided by grants BSR-8811902, DEB-9411973, DEB-9705814 , DEB-0080538, DEB-0218039 , DEB-0620910 , DEB-1239764, DEB-1546686, and DEB-1831952 from the National Science Foundation to the University of Puerto Rico as part of the Luquillo Long-Term Ecological Research Program. Additional support provided by the University of Puerto Rico and the International Institute of Tropical Forestry, USDA Forest Service.