North Cascades National Park Complex vegetation classification and mapping project report

Nielsen, Eric; Copass, Catharine; Brunner, Rachel; Wise, Lindsey

doi:10.36967/nrr-2286418

The Vegetation Mapping Inventory (VMI) is an effort by the National Park Service (NPS) to classify, describe, and map vegetation communities present on NPS units across the United States. The Institute for Natural Resources, working in cooperation with the NPS North Coast and Cascades Network (NCCN), has completed a VMI project for the vegetation communities of North Cascades National Park Complex (NOCA), including Ross Lake and Lake Chelan National Recreation Areas (NRA). The map is based on a vegetation classification developed during the project and was created using a inductive modeling approach. Data used to construct the classification were collected between 2005 and 2015, and included plots from Mount Rainier National Park and Olympic National Park. These plots were used to develop and refine the association-level National Vegetation Classification (NVC). The associations were combined into map classes based roughly on the NVC alliance-level classification, but updated to allow improved map detail and accuracy. Model training data relied only on plots from NOCA, also collected during the same years. Independent field accuracy assessment data were collected in 2016 and applied to the final map generated later. The map development process was organized around the random forests machine learning algorithm. The modeling used 2,980 plots representing 151 vegetation associations and 46 map classes. Imagery from the National Agriculture Imagery Program and the Sentinel-2 and Landsat 8 satellites, airborne lidar bare earth and canopy height data, elevation data from the U.S. Geological Survey 3D Elevation Program, and climate normals from the PRISM Climate Group were used to develop a variety of predictor metrics. The predictors and the map class calls at each plot were input to a process in which each map class was modeled against every other map class in a factorial random forests scheme. We used plot-level modeling outcomes and species composition data to adjust the crosswalk between association and map class so that floristic consistency and model accuracy were jointly optimized across all classes. The map was produced by predicting the factorial models and selecting the overall best-performing class at each 3-meter pixel. The final vegetation map, including a buffer surrounding the park complex, contains 41 natural vegetated classes, five mostly unvegetated natural classes, and five classes representing burned areas or anthropogenic disturbance. Conifers, some recently burned, cover about half of the complex. Upper montane forests dominated by mountain hemlock (Tsuga mertensiana) and silver fir (Abies amabilis) are most abundant in the National Park units. Forests at Ross Lake NRA are characterized by Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla), and Lake Chelan NRA is notable for large expanses of burned forests and Douglas-fir and ponderosa pine (Pinus ponderosa) woodlands. Broadleaf and mixed forests occupy only three percent of the complex. Riparian broadleaf forests are the most widespread, but mixed paper birch (Betula papyrifera) forests are common around Ross Lake, and mixed bigleaf maple (Acer macrophyllum) forests are very abundant on debris aprons near the Stehekin River. Shrublands cover fifteen percent of the complex and are especially concentrated in the Park units, where they are dominated by Sitka alder (Alnus viridis) and mountain-heathers (Phyllodoce empetriformis, Cassiope mertensiana). Snowbrush (Ceanothus velutinus) shrublands, associated with past fire, are common in Lake Chelan NRA. Herbaceous vegetation occupies only five percent of the overall landscape, with sparse alpine vegetation most common in the Park units, bedrock balds frequent in both NRAs, and green fescue (Festuca viridis) mostly associated with Lake Chelan NRA. Sparsely vegetated and entirely bare rock cover nearly one-fifth of the complex; bedrock barrens are most common and occupy fully sixteen percent

North Cascades National Park Complex vegetation classification and mapping project report

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