Its authors propose creating a distinct tussock-tundra group, refining wet willow communities by the source of water and nutrients, and placing inland dunes and early-successional river vegetation together. The work is a regional classification exercise, not an assessment of climate effects or ecosystem function, and its recommendations remain subject to further sampling and review. The dataset came from the Ecological Land Survey Legacy Database, which contains standardized field observations collected by ABR, Inc.–Environmental Research and Services between 1992 and 2019.

The researchers initially selected 2,255 plots with complete plant-composition data from the Seward Peninsula, Chukchi Sea coast, western Brooks Range and areas north of the range. They then excluded 129 forested plots, defined as plots with at least 10% tree cover, because the study focused on non-forested Arctic tundra. The final analytical set comprised 1,825 plots assigned to the Arctic ecoregion and 262 assigned to the Boreal ecoregion.

The study area encompassed Circumpolar Arctic Bioclimate Subzones C, D and E, including the northern Seward Peninsula, western Brooks Range, and northwestern foothills and coastal plain. At each circular plot, typically about 10 metres in radius, field teams recorded vascular plants, bryophytes and lichens, foliar cover, vegetation structure, geomorphology, soil stratigraphy, hydrology, pH, electrical conductivity and thaw depth. Transects were generally 1.5–2.0 kilometres long and stratified across major geomorphic units, vegetation types, moisture and salinity gradients.

Because some projects estimated cover visually while others used line-point intercept, the researchers standardized the records to foliar cover. The final classification considered 138 peer-reviewed associations, including 50 provisional Arctic associations supported by at least 10 plots and 75 preliminary Arctic associations supported by four to nine plots. Classes containing fewer than four plots were treated as plant community types rather than formal associations.

The statistical workflow combined Partitioning Around Medoids clustering, Bray–Curtis dissimilarity, non-metric multidimensional scaling, silhouette analysis, indicator-species analysis and Generalized Additive Models. Taxonomic names were harmonized, vascular subspecies and varieties were combined at species level, and nonvascular plants were generally aggregated to genus for the ordination. Sparse taxa were omitted from that analysis, while a less transformed dataset retained characteristic species for constancy and cover summaries.

Draft classifications, environmental summaries and field keys were reviewed by local and regional experts and revised before the final ordinations were performed. The approach allowed the researchers to test whether proposed groups were compositionally distinct and whether those differences corresponded to measurable environmental gradients. At the broadest level, the Arctic plots occupied four U.S.

National Vegetation Classification divisions: Arctic Coastal Scrub & Herb Vegetation, Arctic Coastal Salt Marsh, Arctic & Boreal Freshwater Marsh, Wet Meadow & Shrubland, and Arctic Tundra & Barrens. Their plant composition differed significantly, with p less than 0.001 in the ordination analysis. A fitted model showed that water-table depth tracked the broad moisture gradient, while electrical conductivity corresponded with saline coastal conditions.

Within Arctic Tundra & Barrens, two macrogroups were distinctly separated: Arctic Dry-Moist Tundra and Arctic Scree, Rock & Cliff Barrens. Surface organic-layer thickness, active-layer thickness and soil pH explained 38%, 51% and 65% of the deviance in plot distribution, respectively, associating the vegetation differences with drainage, thaw depth and soil reaction. Low and tall willow vegetation was organized into three macrogroups and several groups and alliances.

Within Arctic Low Shrub Tundra, three existing alliances separated clearly: Arctic Acidic Low Willow Tundra, Arctic Nonacidic Low Willow Tundra and Arctic Dwarf Birch Low Shrub Tundra. Soil pH explained 69% of the deviance in the ordination for this group. Mean pH was 5.8 ± 0.5 in the acidic alliance, 5.8 ± 0.6 in the dwarf-birch alliance and 7.2 ± 0.7 in the nonacidic alliance.

The acidic alliance was dominated by Salix pulchra, whereas S. glauca or S. richardsonii characterized the nonacidic alliance; the dwarf-birch alliance was distinguished by the codominance of Betula nana and willow. The wet-shrubland analysis distinguished two kinds of wetland. The proposed Arctic Ombrotrophic Wet Low Shrublands Alliance, associated mainly with lowland settings and precipitation-fed wetlands, had acidic to circumacidic soils and mean electrical conductivity of 227 ± 272 µS/cm.

The proposed Arctic Minerotrophic Wet Low Shrublands Alliance occurred primarily in riverine and lacustrine settings and had circumalkaline to alkaline soils, with mean electrical conductivity of 480 ± 438 µS/cm. Salix pulchra, sometimes accompanied by Betula nana, dominated the ombrotrophic alliance, while S. richardsonii dominated the minerotrophic alliance. Both contained sedges including Carex aquatilis and Eriophorum angustifolium, but their landscapes and water chemistries differed.

The authors propose renaming the existing Betula nana–Ericaceous Arctic Wet Shrubland and Arctic Willow Wet Shrubland alliances to reflect this hydrological division. The tussock-tundra results supported removing tussock communities from the broader Arctic Herbaceous Tundra Group and creating a separate Arctic Herbaceous Tussock Tundra group. Tussock plots had the shallowest active layers, the greatest tussock cover and a distinct plant composition compared with nontussock herbaceous tundra.

Four proposed alliances combined vegetation structure with soil chemistry: Arctic Acidic Shrub Tussock Tundra, Arctic Nonacidic Shrub Tussock Tundra, Arctic Acidic Tussock Tundra and Arctic Nonacidic Tussock Tundra. Soil pH explained 42% of the deviance across these alliances. The shrub tussock alliances had greater dwarf and low-shrub cover and greater overall live cover, largely because of shrub cover, than the herbaceous tussock alliances.

The proportion of total shrub cover represented by ericaceous shrubs had a strong fit of 0.61 and an inverse relationship with predicted soil pH. Separate proposals address river bars and inland dunes. The existing Chamerion latifolium–Salix alaxensis Arctic Floodplain Alliance was retained, while three proposed alliances were added for Salix alaxensis river bars, Salix glauca river bars and dunes, and Salix alaxensis–Salix niphoclada river bars and dunes.

The researchers recommend broadening the Arctic Gravel Floodplain Vegetation group to include inland dunes and renaming it Arctic River Bar & Inland Dune Vegetation. Unlike coastal dunes, inland dunes are not influenced by saltwater and commonly support willows such as S. alaxensis and S. niphoclada, which were not found in the coastal dune data. The proposed units nevertheless have unresolved boundaries, especially where associations with the same dominant species occur in neighboring alliances.

One acidic tussock association was more similar to an association in the shrub tussock alliance, indicating that the threshold used to separate shrub and herbaceous tussock vegetation may need adjustment. The Salix alaxensis–Tanacetum bipinnatum association was also closer to communities in the Salix alaxensis River Bar alliance than to another association assigned to the S. alaxensis–S. niphoclada alliance. The study therefore calls for additional relevés from existing archives, including the Alaska Arctic Vegetation Archive and Alaska Vegetation Plots Database, as well as new fieldwork.

Its field guide provides dichotomous keys, descriptions, constancy and cover tables, photographs, distribution maps and environmental summaries, but the proposed groups and alliances are recommendations for continued refinement rather than final resolutions.

Subject of Research: EcoVeg classification of tussock tundra and low and tall willow vegetation in northwestern Arctic Alaska

Article Title: Vegetation classification for northwestern Arctic Alaska using an EcoVeg approach: tussock tundra and low and tall willow groups and alliances

Article References: Wells, A. F., Swingley, C. S., Ives, S. L., McNown, R. W., & Dissing, D. (2022). Vegetation classification for northwestern Arctic Alaska using an EcoVeg approach: tussock tundra and low and tall willow groups and alliances. Vegetation Classification and Survey, 3, 87-117. https://doi.org/10.3897/vcs.65469

Image Credits: AI Generated

DOI: 10.3897/VCS.65469

Keywords: Arctic Alaska, EcoVeg, vegetation classification, tussock tundra, low willow, tall willow, soil pH, wetland hydrology, river bars, inland dunes, US National Vegetation Classification, Vegetation