Mapping plant functional types (PFTs) and tree species population dynamics is critical to understanding how natural disturbances drive ecological transformations. However, creating accurate, broad-scale historical maps of PFTs, tree species, and die-offs is challenging without integrating fine-scale data from unoccupied aerial systems (UAS) or airplanes. Here, we present an open-access, Landsat-adjusted spectral library of PFTs, tree species, and dead stands, designed to enhance spectral mixture analysis and historical ecological monitoring. We also introduce a flexible open-source tool that upscales UAS and aerial spectral data to improve and deepen moderate-resolution satellite-based models. Our tool performs topographic and Bidirectional Reflectance Distribution Function (BRDF) normalizations on both UAS-based multispectral and aerial hyperspectral data (1), resamples and cross-calibrates various sensors' data (e.g., UAS MicaSense to Landsat TM, ETM+, and OLI) (2), and compiles Nadir BRDF-Adjusted Reflectance (NBAR) spectra with varying spectral resolutions using target polygons provided by the user (3). We used UAS-based MicaSense RedEdge-MX Dual-System multispectral imagery, aerial NEON-AOP hyperspectral imagery, and field samples collected at four Western US forest sites in the Pacific Northwest, Northern Rockies, and Southern Rockies domains to create the open-source library and demonstrate our tool. We expect users to be able to use our spectral library to advance the knowledge of ecological transformation in Western US forests, as well as adjust our workflow to other historical observations, such as those from the Sentinel-2 constellation, and recent and upcoming hyperspectral missions, including DESIS, EnMap, EMIT, SBG, and CHIME. Beyond ecological transformations, our open-source tool can potentially be used to advance agriculture and urban remote sensing applications.