Ecological Insights from Transferable Plant Biomass Mapping across the Arctic using Highresolution Structure-from-Motion and LiDAR Data

Warmer temperatures, permafrost thaw, and increased wildfire activity are driving rapid ecological change across the Arctic, significantly altering plant productivity and aboveground biomass (AGB).These rapid changes highlight the urgent need to improve monitoring of vegetation dynamics in the Earth's northern ecosystems, where high spatiotemporal heterogeneity occurs at scales finer than those captured by traditional satellite observations.The growing use of Unoccupied Aerial Systems (UASs) presents an opportunity to overcome this limitation.Yet, the diversity of UAS platforms, sensors, and data collection and processing workflows presents challenges for developing standardized, generalizable approaches.To address this challenge, we compiled 672 AGB plots co-located with 183 UAS-based Structure-from-Motion (SfM) or Light Detection and Ranging (LiDAR) surveys collected across the Arctic.Here, we: (1) evaluated the generalizability of UAS-derived canopy structure derived from high-resolution SfM and LiDAR for estimating AGB, (2) assessed scaling errors and their sources in two recent satellitebased AGB products derived from Landsat and MODIS, and (3) demonstrated the use of high-resolution AGB maps to quantify biomass variation across tundra plant functional types (PFTs) and to monitor postfire recovery.Our results show that both SfM and LiDAR accurately captured AGB and its variability across tundra PFTs using a Random Forest (RF) model (overall RMSE: 0.336 kg/m 2 ), with mapping performance varying slightly by region and data source.Using UAS-derived AGB maps as a benchmark, we identified systematic biases in satellite-derived AGB products, largely attributable to the magnitude of AGB and structural heterogeneity within coarse-resolution pixels.Applying our model to repeat UAS surveys following a tundra fire on Seward Peninsula, we observed rapid AGB recovery in non-shrub patches, with biomass recovering to pre-fire levels within 2 years.In contrast, shrub patches recovered more slowly, with AGB gains continuing over 2-4 years through both in-patch growth and lateral expansion (via dispersal) into remaining burned areas.Overall, these findings demonstrate the generalizability of UASbased SfM and LiDAR data for estimating tundra AGB and highlight the potential of our approach to be broadly applied to generate high-quality AGB data for ecological monitoring and model benchmarking across the Arctic.