Tongass National Forest – Prince of Wales Island – Vegetation Mapping – Reference Data Young Growth Lidar

The Prince of Wales Existing Vegetation mapping project encompasses over 4.2 million acres of Southeastern Alaska—2.3 million of which are terrestrial. This map was designed to be consistent with the standards established in the Existing Vegetation Classification and Technical Guide (Nelson et al. 2015), and to provide baseline information to support project planning and inform land management of the Prince of Wales and surrounding islands. The final map comprises seven distinct, integrated feature layers: 1) vegetation type; 2) tree canopy cover; 3) trees per acre (TPA) for trees ≥ 1’ tall; 4) trees per acre for trees ≥ 6” diameter at breast height (dbh); 5) quadratic mean diameter (QMD) for trees ≥ 2” dbh; 6) quadratic mean diameter for trees ≥ 9” dbh; and 7) thematic tree size. The dominance type map consists of 18 classes, including 15 vegetation classes and 3 other land cover types. Continuous tree canopy cover, TPA, QMD, and thematic tree size was developed for areas classified as forest on the final vegetation type map layer. Geospatial data, including remotely sensed imagery, topographic data, and climate information, were assembled to classify vegetation and produce the maps. A semi-automated image segmentation process was used to develop the modeling units (mapping polygons), which delineate homogeneous areas of land cover. Field plots containing thematic vegetation type and tree size information were used as reference for random forest prediction models. Important model drivers included 30 cm orthoimagery collected during the height of the 2019 growing season, in addition to Sentinel 2 and Landsat 8 satellite imagery, for vegetation type prediction. Additionally, detailed tree inventory data were collected at precise field locations to develop forest metrics for Quality Level 1 (QL1) Light Detection and Ranging (LiDAR) data. LiDAR information was acquired across approximately 80% of the project’s land area. Continuous tree canopy cover and 2<sup>nd</sup> order forest metrics (TPA and QMD) were modeled across the LiDAR coverage area, and subsequently, extrapolated to the full project extent using Interferometric Synthetic Aperture Radar (IfSAR) as the primary topographic data source. <o:p></o:p> The Tongass National Forest recently completed a Young Growth inventory. There were two primary goals of the inventory. The first determined the actual stand attributes such as tree species, height and diameter of the trees, and trees per acre. The second was to determine which acres previously harvested are no longer considered feasible for harvest. Plots (6,475) were intersected with the mapping segments, which serve as the fundamental modeling units for the project. Each plot was reviewed within the context of the corresponding segment to ensure homogeneity and representativeness with respect to vegetation type. LiDAR calibration plot data (249) were collected by The Nature Conservancy and State of Alaska young growth inventory crews during the summer of 2018. The purpose of these data were to develop forest inventory metrics on Prince of Wales Island and secondarily to help inform the vegetation type models. Forest grid metrics were generated and summarized to the mapping segments to model tree size and stand density. Additionally, each plot was reviewed within the context of the corresponding segment to ensure homogeneity and representativeness with respect to vegetation type.