Classification Distribution Vegetation Accuracy

Tree canopy cover is less than 10% (or absent). Total shrub cover is 25% to 100%, and willow greater than 20 centimeters tall comprises greater than 75% of the total shrub cover. The class is comparable to the Viereck et al. (1992) hierarchical levels closed tall willow (IIB1a), open tall willow (IIB2a), closed low willow (IIC1b), and open low scrub (11C2).

The willow class occurs on a variety of sites throughout the park. Willow dominated by low stature (20 centimeters to 1.5 meters in height) willow is common at mid elevations (range of 191 to 1,116 meters based on field data; Table 3) mixed with other low shrub classes on flat river drainages and the rolling foothills bordering the north side of the Alaska Range. When tall willow (>1.5 meters) dominates the class, it occurs primarily in small patches on new alluvial stream/river deposits, alluvial fans, colluvial sideslopes and bordering small mountain streams. Both tall and low willows occur on upper slope positions mixed in with or above the alder class in the Alaska Range and Kantishna Hills.The class does not dominate any ecoregion, but is concentrated in the Alaska Range-Kantishna Hills ecoregion and the Alaska Range-south-central mountains and valleys ecoregion of the park (Tables 4a and 4b; Clark 1998). It covers 1.6% (95,590 acres) of Denali National Park and Preserve (Table 5). On the landcover map, this class is underrepresented on the south side of the Alaska Range due to its partial inclusion in the herbaceous-shrub class.

This class includes all sites dominated by willows greater than 20 centimeters tall. Willow cover ranges from 25% to 95%, and its height ranges from 20 centimeters to 4.5 meters. Sites dominated by open tall willow and closed low willow are common in the park, whereas closed tall willow is uncommon. The dominant overstory species include Salix alaxensis, S. barclayi, S. bebbiana, S. glauca, S. lanata, and S. planifolia. Other overstory and understory shrubs include Shepherdia canadensis, Vaccinium uliginosum, Betula nana, and Spirea beauverdiana. Tall alder (Alnus species) may also be found in isolated locations within the landcover class. Grasses, sedges, and mosses are an important component in some sites and include Heracleum lanatum, Calamagrostis canadensis, C. inexpansa, Epilobium angustifolium, Streptopus species and Veratrum viride. The willow class is most commonly found next to low shrub classes on gentle toeslopes, fans, floodplains and wide valleys. It is found near needleleaf classes in narrow drainages and also in wide valleys. The dry-mesic herbaceous class occurs adjacent to the willow class on sideslopes and saturated toeslopes.

The producer’s accuracy for the willow class is 55.1%, with a user’s accuracy of 50.0%. Most of the errors of commission are with the broadleaf and alder classes. Most of the omission error is with alder.