# Comparison of EPIC-Simulated and MODIS-Derived Leaf Area Index (LAI) across Multiple Spatial Scales
## Methods
### LAI Data (In Situ LAI and Upscaling, MODIS LAI, EPIC LAI)
#### 2.2.3 Epic Lai  
In concept, the EPIC model is run to estimate LAI across multiple, competing species. This model uses information regarding species, species age, and species density to simulate a multi-age, multi-species \"stand\" which is then assumed to exist on all forested land in a study area [31]. For large area studies, the modeled stand characteristics usually derive from sampled stand characteristics. As such, it is unlikely that the modelled stand will equate exactly to any real world stand within the study area, but from a statistical perspective, it should be representative of the population of stands within the forestlands and could serve to constrain the range of possible stand-level LAI estimates. Stand characteristics were estimated for use in EPIC across the four EPA LAI research sites within nine cells of a \(3\times 3\) grid, consisting of nine 12.0 km grid cells (Figure 4). We used the US Forest Service Forest Inventory and Analysis (FIA) Evalidator Tool ([[http://apps.fs.fed.us/Evalidator/evalidator.jsp](http://apps.fs.fed.us/Evalidator/evalidator.jsp)]([http://apps.fs.fed.us/Evalidator/evalidator.jsp](http://apps.fs.fed.us/Evalidator/evalidator.jsp))) to provide a consistent and reproducible estimate of species density and area information for an 88.3 km\({}^{2}\) area (5.3 km radius circle) surrounding the validation areas of interest. The FIA program samples forest land on public and private lands on average one plot for every 2428 hectares of forest land. In theory, this averages approximately 5.9 plots for every 12.0 km grid cell provided 100 percent is forested land. Stand age and diameter distribution by species were extracted for each of the nine 12.0 km grid cells per site. FIA data typically are aggregated into species groupings [31] that determine model growth parameters. In our prior study, EPIC LAI was calibrated thorough modification of distributed plant parameter values. Modified and/or added tree species plant parameter values (i.e., shade tolerance, maximum canopy height, species geographic distribution, temperature sensitivity, and seasonal growth pattern) were initially derived from the USDA Silvics manual [45]. These initial values were then calibrated using in situ observations of stand-level LAI and maximum canopy height while preserving reasonable physical and process driven relationships. Within EPIC, tree species are assessed for species maturity, then cross-checked with diameter and age class distributions extracted from the FIA database. FIA Evalidator results typically return species groupings, i.e., sycamore/pecan/elm, sugarberry/hackberry/elm/green ash, etc. If more than one species shows comparable maturity dates, then multiple simulations (i.e., cohorts) are run with each species in that grouping contributing LAI in an additive manner. Stem densities are then partitioned between these species' groupings, initiated (i.e., stems planted) at the year that brings maturity at year 2002, the year of our evaluation. All simulations were run from a simulated weather generator for the nearest National Oceanographic Atmospheric Administration's (NOAA) National Centers for EnvironmentalInformation (NCEI) Cooperative Observer Program (COOP) locations (Table 3). Parameters extracted from these weather simulations include, maximum temperature (\({}^{\circ}\)C), minimum temperature (\({}^{\circ}\)C), and precipitation (mm). EPIC can be set to run both with climate generated variables or observed meteorological data, or both within a simulation. EPIC requires stand establishment as a primary input to initiate stand development over the lifespan of the particular species. Other operational variables can be added including disturbance (i.e., 'thinning'), harvest, or prescribed burn. Detailed multilayer soil profiles, commonly used simulation inputs for biogeochemical models, were not available for any of the four research sites. Instead we used a representative soil profile at all locations, the Cecil soil profile.